Mineralogy, Petrogenesis and SIMS SHRIMP U-Pb Age PGE-Cu-Ni Deposit of the “Ore Horizon 330” of the Sopcha Intrusion in the Paleoproterosoic Monchegorsk Pluton, Kola Region, Russia

Mineralogy, Petrogenesis and SIMS SHRIMP U-Pb Age PGE-Cu-Ni Deposit of the “Ore Horizon 330” of the Sopcha Intrusion in the Paleoproterosoic Monchegorsk Pluton, Kola Region, Russia | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Mineralogy, Petrogenesis and SIMS SHRIMP U-Pb Age PGE-Cu-Ni Deposit of the “Ore Horizon 330” of the Sopcha Intrusion in the Paleoproterosoic Monchegorsk Pluton, Kola Region, Russia Victor V. Chashchin, Yevgeny E. Savchenko, Sergey A. Sergeev This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-4678396/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract The “Ore Horizon 330” deposit (or OH330) is located among the orthopyroxenite of the Sopcha intrusion of the Paleoproterozoic layered Monchegorsk pluton (or Monchepluton) in the Kola Region. It is a sill-like body with a length of 3300 m, width of 1200 m, and thickness of 4‒6 m. OH330 was studied in two sections of its north-western part with a thickness of 5.2 and 5.5 m. There, it consists of regularly alternating interlayers (from bottom to top) of dunite, harzburgite, and orthopyroxenite. Olivine (Fo 87–84 ) and orthopyroxene (En 84–83 ) in the OH330 rocks were depleted in Ni compared to the Monchepluton rocks and were similar in Mn content. The total rare earth element (REE tot ) content did not exceed 1 ppm in dunite and harzburgite, with an average value of 3.15 ppm in orthopyroxenite. LREE fractioning is typical of all OH330 rocks, with the (Ce/Sm) N values of 1.21 ppm in dunite, 1.69 ppm in harzburgite, and 1.81 ppm in orthopyroxenite on average. The trace element distribution in dunite and harzburgite is characterized by U, Ta, and Sr positive anomalies, whereas orthopyroxenite exhibits Nb and Ta negative anomalies, in addition to positive U anomalies. The geochemical features of the OH330 rocks were determined by fractional crystallization and crustal contamination of the parental magma. The liquidus temperatures of dunite and harzburgite magmatic crystallization were determined using the olivine-melt thermometer, with values of 1600‒1470°C. This is due to the genetic link between the OH330 parental melt and the mantle diapir. The orthopyroxene-melt equilibrium temperatures the OH330 rocks were 1290‒1120°C. The calculated pressure values for the OH330 rocks varried from 1 to 6 kbar, with an average value of 3.5 ± 1.5 kbar. The SIMS SHRIMP U-Pb magmatic zircon age of the OH330 orthopyroxenite is 2492.5 ± 4.1 Ma, indicating that the OH330 is younger than the age of the marginal zone of the Monchepluton ultramafic subchamber. A concordant U-Pb age of 2818.0 ± 3.1 Ma was obtained from the xenocryst zircon population, which corresponds to the age of the Archean granitoid basement rocks. OH330 Mineralogy Geochemistry SIMS SHRIMP U-Pb age Sopcha intrusion Monchepluton Kola Region Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 Figure 11 Figure 12 Introduction A total of more than 20 Paleoproterozoic layered intrusions, comprising two age groups, have been identified within the Archean Kola and Karelia provinces of the north-eastern Fennoscandian Shield (Chashchin and Ivanchenko 2023). The more ancient intrusions (ca. 2.50 Ga) are found exclusively in the Kola Province, whereas the younger intrusions (ca. 2.45 Ga) are predominantly located in the Karelia Province, with a smaller presence in the Kola Province. Many layered intrusions were associated with chromium, sulfide PGE-Cu-Ni, low-sulfide Pt-Pd, and Fe-Ti-V ores. Among all the ore-bearing layered Fennoscandian intrusions, the Monchepluton exhibits the greatest industrial potential. It is associated with chromium and low-sulfide Pt-Pd deposit, and two PGE-Cu-Ni deposits and six manifestations. Its total Pt + Pd reserves and resources are estimated to be more than 800 tons (Chashchin and Ivanchenko, 2022 ). Monchepluton, along with the ore-bearing intrusions Volchya Tundra (Chashchin and Petrov 2013 ) and Monchetundra (Kazanov et al. 2016 ; Chashchin et al. 2018 ), as well as the Fedorovo-Pana layered complexes (Groshev et al. 2019), constitutes part of the extensive Kola platinum-metal province (Mitrofanov et al. 1999 ). The Monchepluton formation is characterized by a regular vertical change in rock composition from ultramafic to mafic. This led to the formation being considered the result of a one-act magmatic event (Kozlov 1973 ). However, in some cases, this regular change is disturbed. For instance, the middle part of the orthopyroxenite series of the Sopcha intrusion orthopyroxenite contains the finely layered OH330, and the Nyud intrusion displays disrupted cumulus stratigraphy due to the presence of an olivine horizon (Smolkin et al. 2004 ). These characteristics be attributed to the injection of distinct magma pulses. With regard to the olivine horizon, this hypothesis was corroborated by data from SIMS SHRIMP U-Pb zircon dating, which indicated that the olivine horizon was formed at a time of 2484.3 ± 5.6 Ma (Chashchin and Sergeev 2023 ). This age is slightly younger than the U-Pb age of the Nyud intrusion gabbronorite, which is 2493 ± 7 Ma (Balashov et al. 1993 ). OH330 is a finely layered body bearing a commercially valuable Cu-Ni mineralization. Initially, it was considered to be the main ore base for the Severonickel Mining Plant. However, the discovery of rich sulfide vein ores made the development of this deposit unprofitable. In the late 1990s, the possibility of commercial exploitation of the horizon was re-evaluated when an increased Pt content was revealed in the ore. From a scientific perspective, the OH330 has long been a matter of interest (Eliseev 1953 ; Kozlov 1973 ; Sharkov 2006 ; Konnikov and Orsoev 1991 ; Orsoev et al. 1994 ; Neradovsky et al. 2002 ; Smolkin et al. 2004 ; Sharkov and Chistyakov 2014 ; Karykowski et al. 2018 ; Chashchin and Petrov 2023 ). The deposit is of interest due to its relatively small size and layered structure, which contains PGE-enriched sulfide ore. The composition of the platinum-group minerals and the genesis of OH330 PGE-Cu-Ni deposit have recently been studied (Chashchin and Petrov 2023 ), which has been assigned to a sulfide reef type (Chashchin and Ivanchenko 2022 ). Despite the extensive research conducted on the OH330, questions remain regarding the origin of this finely layered ore horizon and its age, which require further investigation. The principal objective of our research was to conduct a comprehensive investigation of the OH330 rocks, including their mineral composition, PT conditions, geochemical attributes, and age. This paper presents the findings of the OH330 study. The results include data on the chemical compositions of olivine, orthopyroxene, and whole-rocks, as well as SIMS SHRIMP U-Pb dating. The obtained data enabled us to determine the formation conditions of OH330 and its age. It is assumed that an understanding of the OH330 genesis is important for the comprehension of the processes that form the fine layering observed in reef-type thin ore horizons. Geology of Layered Monchepluton The Paleoproterozoic layered ore-bearing Monchepluton, with an age of ca. 2.50 Ga and an area of approximately 50 km², is located in the central part of the Kola Region (Fig. 1 a). The site lies in the Archean granitoidal basement and is associated with the north-western closure of the Paleoproterozoic Imandra-Varzuga greenstone belt (Fig. 1 b). At the present erosional truncation, the Monchepluton exhibits an arched shape, comprising two branches: a north-eastern branch and a sub-latitudinal branch (Gorbunov et al. 1985 ). The north-eastern branch is more than 7 km long and 2 km wide in its central part and is represented by the Nittis-Kumuzhya-Travyanaya (or NKT) intrusion. The sub-latitudinal branch is approximately 11 km long and 3 km wide and encompasses the Sopcha, Nyud, Poaz, and Vuruchuayvench intrusions (Fig. 1 b). According to its specific internal structure, the Monchepluton can be divided into two parts or subchambers (Chashchin and Ivanchenko 2022 ). The first subchamber (ultramafic) encompasses the NKT and Sopcha intrusions, which exhibit vertical thicknesses of up to 1000 and 1200 m, respectively. These intrusions consist of ultrabasic cumulates and exhibit similar internal structure. These intrusions section comprise the following rocks (from the bottom to the top): norite and orthopyroxenite in the marginal zone, dunite developed exclusively in the NKT (Dunite Block), harzburgite, an alternation of harzburgite and orthopyroxenite, and orthopyroxenite. The U-Pb zircon ages of the norite and quartz norite of the marginal zone of the NKT intrusion are 2505.5 ± 7.0 Ma and 2506 ± 10 Ma, respectively (Bayanova et al. 2004 ; Semenov et al. 2022 ). The U-Pb ages of the dunite and chromium ore in the Dunite Block were determined from single zircon and are 2500 ± 10 Ma and 2500 ± 2 Ma, respectively (Chashchin and Bayanova 2021 ). The middle part of the Sopcha intrusion orthopyroxenite includes OH330 (Fig. 1 c), which is described in detail below. The second subchamber (mafic) comprises the Nyud, Poaz, and Vuruchuayvench intrusions, which exhibit vertical thicknesses of up to 800, 400, and 900 m, respectively. The sections of the Nyud and Poaz intrusions exhibit similar cumulus stratigraphy, divided into upper and lower zones that differ in thickness. The lower zone was formed by melanonorite and plagioorthopyroxenite with thickness of 300 m (Nyud) and 70‒120 m (Poaz). These rocks are formed by orthopyroxene cumulus and plagioclase intercumulus, with rare clinopyroxene poikilitic porphyroblast, and are essential orthocumulates. The upper zone of these intrusions is represented by a leuco-mesocratic norite with interlayers of gabbronorite with thickness of up to 250 m (Poaz) and 350 m (Nyud). These rocks are mesocumulates composed of cumulus orthopyroxene and plagioclase, sometimes with high clinopyroxene contents. All of the above intrusions exhibit symmetrical trough-like forms with limbs dipping at angles of 20–45° toward the axes. The similarity of the cumulus stratigraphy of the Nyud and Poaz intrusions is underlined by the similar ages of their upper zone rocks. For example, the U-Pb zircon age of the mesocratic gabbronorite of the Nyud intrusion is 2493 ± 7 Ma (Balashov et al. 1993 ), whereas the age of the Poaz intrusion gabbronorite is 2493 ± 5 Ma (Chashchin and Bayanova 2023 ). In the western, northern, and southern parts of the Nyud intrusion, there is a crescent-shaped olivine horizon with a length of 6 km and a thickness of approximately 100 m (Fig. 1 b). It occurs subhorizontally between the melanocratic and mesocratic norite. The olivine horizon comprises orthopyroxenite, plagioorthopyroxenite, and melanonorite with various olivine contents (up to 30 vol%, rarely more) connected with each other by gradual transitions. The SHRIMP U-Pb zircon age of the Nyud olivine horizon is 2484.3 ± 5.6 Ma (Chashchin and Sergeev 2023 ). The Vuruchuayvench intrusion is situated to the south and southeast of the Nyud and Poaz intrusions, at contact with the Paleoproterozoic Imandra-Varzuga greenstone belt (Fig. 1 a). At the base of this belt lies a horizon of conglomerates, the debris of which are represented by rocks from the Vuruchuaivench intrusion. This intrusion displays a monocline structure and a gently trending orientation, dipping to the south-east. This shape differs from the general trough-like shape of the Monchepluton. The Vuruchuayvench intrusion comprises metagabbronorite with layers of metaplagioclasite in its upper part and is the only intrusion within the Monchepluton that has undergone intense amphibolization. The SIMS SHRIMP U-Pb zircon ages of metagabbronorite and metaplagioclasite from the Vuruchuayvench intrusion are 2504.2 ± 8.4 Ma and 2507.5 ± 6.6 Ma, respectively (Rundkvist et al. 2014 ). The ID-TIMS U-Pb zircon ages are 2494 ± 4 Ma and 2495.3 ± 2.2 Ma, respectively (Chashchin et al. 2016 ). Analytical Methods The objects of our study were outcrops 422 and 423 in the north-western part of OH330 (Fig. 1 c), where bedrock exposures present the OH330 with the most comprehensive sections. Sixteen samples of the OH330 rocks and the host orthopyroxenite were selected from these outcrops. The OH330 and host rocks were subjected to petrographic study in thin sections using polarized light microscopy with transmitted light. All polished sections were examined using a LEO-1450 scanning electron microscope (Carl Zeiss, Germany) with an energy-dispersive X-ray analytical device (EDS) to create images of the studied minerals in back-scattered electrons (BSE) and perform a preliminary chemical analysis. Chemical Composition of Minerals Olivine and orthopyroxene were analyzed by wavelength dispersion spectrometry (WDS) using a Cameca MS-46 electron probe microanalyzer (EPMA) (27 spot analyses of 27 mineral grains from 16 polished sections). The probe diameter, accelerating voltage, and probe current were 3–5 µm, 22 kV, and 3–40 nA, respectively. Elemental peaks were measured in 4–5 10 s cycles and then averaged. Background measurements were performed in two 10-s cycles at each side of a peak for further averaging. The minor elements were measured in the same manner, but the measurements lasted for 20 s. The X-ray line of Kα was analyzed for all elements. The following artificial and natural compounds were used as standards: wollastonite (Si, Ca), lorenzenite (Ti), forsterite (Mg), hematite (Fe), Y 3 Al 5 O 12 (Al), MnCO 3 (Mn), chromite (Cr), and metals (Ni). The detection limits of electron microprobe analyses were as follows (wt%): 0.01 (Fe, Mn, Ni), 0.02 (Ti, Cr), 0.03 (Ca), 0.05 (Si, Al), and 0.1 (Mg). To avoid the influence of secondary effects, all measurements were performed at a distance of no less than 10 µm between the minerals and the contacting mineral phases. Whole-rock Chemical Composition The whole-rock chemical composition was determined by wet chemistry. In order to define the major elements, the following methods were employed: atomic absorption flame (Si, Al, Cr, Fe, Mg, Ca, Mn), emission flame (Na, K), photocolorimetric (Ti), weight (LOI, H 2 O), and volumetric (FeO) analysis. The REE and trace element contents were determined using an ICP-MS method with a NexION 300S quadruple mass spectrometer (Perkin Elmer, USA). The microwave sample dissolution was conducted using a mixture of acids (HCl + HNO 3 + HF) via a Berghof Speedwave MWS 3 + system. The precision of element detection was maintained using certified samples of basalt (BCR-2) and andesite (AGV-2) (USGS). The obtained concentrations of REE and trace elements were in acceptable agreement with the attested values; the permissible variations were within 15%. The detection limits for these elements were within the range of 0.005‒0.1 ppm. The average uncertainty in the determination of trace elements was in the range of 2–10% with dependent on elements and their concentration levels. SIMS SHRIMP U-Pb Dating A geochronological sample (76 kg) was collected from orthopyroxenite in the 422/3 outcrop. Eighteen zircon grains were extracted from the sample using heavy liquids. Geochronological studies of the zircons were conducted using a SIMS SHRIMP-II (Secondary Ion Mass Spectrometry on a Sensitive High-Resolution Ion Micro Probe instrument) method. The selected zircons were mounted in an epoxy disk (2.5 cm in diameter) with international zircon standards (TEMORA and 91500) using a microscope. They were then abraded to approximately half their original thickness and polished. Before analysis, all samples were coated with a conductive gold layer in a cathodic vacuum nebulizer (duration of one minute, current of 20 mA). Subsequently, the zircon grains were documented using a CamScan МХ2500 scanning electron microscope (CamScan Electron Optics, Ltd, Great Britain) with a CLI/QUA2 system for cathodoluminescence (CL) and back-scattered electron (BSE) imaging. This property was used to study the internal zircon structure. The working distance was 25‒28 mm, the accelerating voltage was 20 kV, and the current of the focused beam on the Faraday cylinder was 4‒6 nA. Measurements of the U-Pb ratios were carried out according to the method (Schuth et al. 2012 ) described in (Williams 1998 ). The intensity of the primary O 2− ion beam was 4 nA, with a spot diameter of approximately 30 µm and a pit depth of 2 µm. The U-Pb ratios were normalized to that in Temora standard zircon (0.0668), which corresponds to the 206 Pb/ 238 U age of 416.75 ± 0.24 Ma (Black et al. 2003 ). The 91500 standard zircon with an average U content of 81.2 ppm, a 206 Pb/ 238 U age of 1062.4 ± 0.4 Ma (Wiedenbeck et al. 1995 ), was employed as the standard for uranium and radiogenic lead concentrations. The obtained data were processed using SQUID software (Ludwig 2001 ). Individual analyses (ratios and ages) are presented with uncertainties at a 1σ level, whereas uncertainties in calculated ages, including concordant ones, are provided at a 2σ level. Concordia diagrams were plotted using the ISOPLOT/EX software (Ludwig 2003 ). A correction was made to non-radiogenic Pb based on the measured 204 Pb and modern Pb isotope compositions in the Stacey-Kramers model (Stacey and Kramers 1975 ). Geology of Ore Horizon 330 General Description OH330 was discovered in the 1930s because of exploration work on the western slope of Mt. Sopcha (Monchepluton). It is a gently dipping sill-like bed-shaped body with a thickness of 4–6 m (up to 13 m in some bulges). The drilling data indicate that the body extends along the entire perimeter of the Sopcha intrusion at a distance of 3300 m and a width of 1200 m. The thickest and most comprehensive section of the OH330 has been revealed within its northwest outcrops. In general, the section is represented (from bottom to top) by dunite, harzburgite, and inequigranular orthopyroxenite. In the east, the OH330 section is typically diminished by the notable absence or near-absence of dunite and harzburgite, resulting in a representation of orthopyroxenite on the eastern flank. The OH330 rocks exhibit disseminated sulfide chalcopyrite-pentlandite-pyrrhotine mineralization in amounts ranging from rare grains to 2–3 wt% in coarse-grained orthopyroxenite and in the upper part of a harzburgite interlayer (Chashchin and Petrov 2023 ). The average Ni content around the deposit is 0.46 wt%, Cu 0.23 wt%, Pt 0.24 ppm, Pd 0.93 ppm, and Pt + Pd = 1.17 ppm, with a Pd/Pt ratio of 3.9 (Chashchin and Ivanchenko 2022 ). The age of OH330 was previously determined by the Sm-Nd method from rock-forming minerals, sulfides, and the whole-rock of harzburgite as 2451 ± 64 Ma with ε Nd = -6.0 ± 0.6 (Chashchin et al. 2016 ). This suggests that OH330 was formed later than the rocks in the Sopcha intrusion. Its formation is associated with a mantle source that was subjected to more intense crustal contamination than the Sopcha orthopyroxenite with ε Nd values ​​from + 1.2 to -2.3 (Bayanova et al. 2004 ). Geological Structure The results of the OH330 sections study are presented in Fig. 2 . The obtained data indicate that the thickness of OH330 in section 422 is 5.5 m, while that in section 423 it is 5.2 m (Fig. 2 ). A 1-meter thick dunite with an adcumulate texture is present in the basement of section 422 (Fig. 2 e). It comprises idiomorphic olivine grains with a size of 1–3 mm and features fine chromite dissemination (olivine-chromite cumulus) (Fig. 3 a). Harzburgite (orthopyroxene-olivine cumulus) occurs above the dunite in section 422 and in the basement of section 423, with thicknesses of 2.3 and 2.2 m, respectively (Fig. 2 ). In the lower part of the interlayer, this rock is monotonous (Fig. 2 d), while in the upper part, it usually has a finely banded structure due to alternating interlayers with varying olivine contents (Fig. 2 c). It is sometimes observed to form complex bends and small folds, which are considered evidence of a viscous melt flow (Eliseev 1953 ; Sharkov 2006 ). Harzburgite comprises composed of idiomorphic (rarely xenomorphic) olivine grains (0.5–1 mm) and subordinated orthopyroxene grains (ca. 1 mm), with secondary minerals (tremolite, talc) partially developed after these grains (Fig. 3 b). The OH330 section is completed by orthopyroxenite (orthopyroxene cumulus), which is 2.2 m (section 422) and 3.0 m (section 423; Fig. 2 ). These units exhibit various structural forms and comprise two to three interlayers, each characterized by a distinct grain-size distribution. An interlayer of medium- to coarse-grained orthopyroxenite with thicknesses of 0.9 m (section 422) and 1.5 m (section 423) formed in the basement of the orthopyroxenite when in contact with harzburgite (Fig. 2 b). The rocks in question were composed of partially amphibolized prismatic orthopyroxene crystals ranging in size from 2 to 5–6 mm (Fig. 3 c). At a higher level in the section, this rock is replaced by an interlayer of fine- and medium-grained slightly amphibolized orthopyroxenite, which sometimes contains olivine, with thickness of 0.4 m (section 422) and 1.5 m (section 423) (Fig. 2 a). This orthopyroxenite displays an inequigranular composition comprising individual tabular grains of orthopyroxene with a size of 2–2.5 mm, set against a background of a fine-grained matrix, measuring ca.1 mm (Fig. 3 d). In section 422, the upper part of the orthopyroxenite contains an interlayer of equigranular fine-grained orthopyroxenite with a thickness of 0.9 m (Fig. 2 ). It was composed of idiomorphic and sub-idiomorphic orthopyroxene grains with a size of approximately 0.5–1 mm with rare grains of intercumulus plagioclase (Fig. 3 e). Olivine orthopyroxenite (orthopyroxene cumulates) of the host rocks of the OH330 formation have a visible thickness of 0.5 m and occur in the hanging and footwalls (Fig. 2 ). Furthermore, these rocks are developed at elevations of 12 and 38 m above the OH330 section, and 65 and 90 m below the section (Fig. 1 d). The rock is predominantly composed of tabular grains of orthopyroxene with a size of 1–2 mm and sub-idiomorphic grains of olivine with an amount of 5–10 vol% and a size of 0.5–2 mm (Fig. 3 f-g). The OH330 hanging wall contained eruptive auto-breccia represented by debris from dunite (section 422; Fig. 2 f) and harzburgite (section 423) in the olivine orthopyroxenite (Eliseev 1953 ; Konnikov and Orsoev 1991 ; Orsoev et al. 1994 ; Karykowski et al. 2018 ; Chashchin and Petrov 2023 ). The debris exhibited a polygonal and rounded shape with a size of 2–5 cm. They are characterized by sharp irregular contacts with the olivine orthopyroxenite cementing them (Fig. 3 h). The presence of eruptive breccia indicates a later injection of olivine orthopyroxenite compared with OH330. Mineralogy Olivine and orthopyroxene are the main rock-forming minerals of OH330. All rocks of OH330 contain accessory chromite in amount ranging from rare grains to 1–2 vol% in dunite, which is present as both homogeneous cumulate grains and zoned grains (Chashchin and Savchenko 2021 ). The secondary minerals included chlorite, talc, and amphiboles of two types, tremolite and Mg-hornblendite (Chashchin and Savchenko 2021 ). A noteworthy aspect of OH330 is the presence of sulfide mineralization in the form of intercumulus dissemination within the interstices of olivine and orthopyroxene in harzburgite and orthopyroxenite, with an estimated concentration ranging from rare grains to 2–5 vol%. This mineralization is associated with PGE minerals, which include Pt-Fe alloys, sulfides, arsenides, sulfoarsenides, bismuth-tellurides, tellurium-bismuthides and tellurides (Chashchin and Petrov 2023 ). Olivine Olivine is predominantly represented by polygonal grains with size of 1–2 mm. Olivine from the OH330 dunite exhibited the most magnesian composition (Fo 86.7 ). The olivine composition in the harzburgite and orthopyroxenite of OH330 lie in the Fo 86.2–83.8 range. Olivine from the host olivine orthopyroxenite had a similar composition and was within the range Fo 86.0–83.4 (Table S1 ). In terms of the NiO (wt%) and MnO (wt%) ratios with Fo (mol%), olivines from all the rocks OH330 and host olivine orthopyroxenites are similar, while the content of NiO and MnO in them does not depend on changes in Fo (Figs. 4 a-b). Olivines from OH330 and the host rocks were distinguished by their lower NiO contents compared to those of the NKT intrusion rocks and a lower Fo value compared to olivines from dunite in the Dunite Block (Fig. 4 a), yet they exhibited similarities to those of the NKT intrusion in terms of their MnO content (Fig. 4 b). Orthopyroxene Orthopyroxenes in harzburgite and orthopyroxenite are represented by prismatic crystals of size 2–3 mm and, in rare cases, by isometric grains with of size 0.5–0.3 mm. The orthopyroxenes exhibited a narrow range of enstatite molecule contents (En 83.9–82.5 ) and slight variations in the Al 2 O 3 (1.9–1.5 wt%), CaO (2.0–1.6 wt%), and Cr 2 O 3 (0.8–0.6 wt%) contents (Table S2 ; Figs. 5 a-c). The orthopyroxenes from the host orthopyroxenite exhibit similar values of the enstatite molecule content (En 83.1–82.2 ) and are mainly similar to the OH330 rocks in terms of chemical composition, with the exception of some specific cases with lower contents of CaO and Cr 2 O 3 (Table S2 ; Figs. 5 b-c). The orthopyroxenes from the OH330 and host rocks most closely correspond to those from the harzburgite and orthopyroxenite of the NKT intrusion in terms of chemical composition. They were located in the fields of their compositions (Figs. 5 a-d). The exceptions were the lower NiO contents in the OH330 and host orthopyroxenes rocks compared to the NKT intrusion rocks (Fig. 5 e). There was no correlation between the En content in OH330 orthopyroxenes and the Fo content in coexisting olivines. All samples exhibited above the 1:1 linear correlation between Fo content in olivines and En in orthopyroxenes due to the higher Fo content in the former (Fig. 5 d). Figure 6 illustrates the variations in the chemical composition of rock-forming minerals along the OH330 sections. The results obtained indicate a consistent increase in the En and Cr 2 O 3 content of the orthopyroxenes from harzburgite to coarse-grained orthopyroxenite (Fig. 6 ). PT Crystallization Conditions for OH330 and Host Rocks In order to calculate the temperature and pressure of the crystallization of the OH330 and host rocks, we used the chemical compositions of coexisting olivines and orthopyroxenes presented in Tables S1 and S2. The olivine-melt and orthopyroxene-melt thermometers, and an orthopyroxene barometer (Putirka 2008 ), were employed. The resulting calculation outcomes are presented in Table S3 . The data indicate that the temperature of the olivine-melt for water-free conditions for the OH330 rocks is 1800–1780°C. The temperature was slightly higher for the host olivine orthopyroxenite, within the 1810–1790°C range (Table S3 ). In the presence of water, the temperature of the olivine-melt equilibrium for the OH330 rocks decreased to 1600–1470°C, whereas that for the host olivine orthopyroxenite was 1670–1620°C (Table S3 ). The temperature of orthopyroxene crystallization of the OH330 rocks in the absence of water was determined using two equations (Putirka 2008 ). According to the first equation, the temperature of the orthopyroxene-melt equilibrium in the OH330 rocks is 1240–1100°C, while according to the second equation, it has a wider range of 1290–1120°C. With regard to the host rocks, their temperature was more stable, falling within the 1240–1220°C range, in accordance with the first equation. In contrast, the temperature was considerably higher according to the second equation, reaching 1310–1270°C (Table S3 ). The pressure calculations indicated that the OH330 rocks exhibited a pressure range of 1–6 kbar, with an average value of 3.5 ± 1.5 kbar. In contrast, the host rocks exhibited a more stable pressure range of 6–8 kbar, with an average value of 6.1 ± 0.7 kbar (Table S3 ). Whole-rock Chemical Composition The contents of major and trace elements are given in Table S4 and Figs. 6 – 9 . Major Elements The maximum MgO concentration in dunite OH330 was determined as 42.3 wt%. In harzburgite, the MgO content is in the range of 36.2–39.6 wt% (on average 37.95 ± 1.03 wt%), in orthopyroxenite – 28.2–31.4 wt% (on average 30.10 ± 1.06 wt%), and in host olivine orthopyroxenite – 28.9–30.7 wt% (on average 29.98 ± 0.46 wt%; Table S4 ). At the same time, the Mg# values of all studied rocks is in a narrow range (0.77–0.72; Table S4 ). The SiO 2 contents exhibit a gradual increase from 38.7 wt% in harzburgite to 53.4 wt% in orthopyroxenite (Fig. 7 a). The Al₂O₃ content is 0.32 wt% in dunite, varying from 0.00 to 0.52 wt% in harzburgite and from 1.6 to 2.3 wt% in orthopyroxenite (Table S4 , Fig. 7 b). The CaO contents were 0.14–0.46 wt% in harzburgite and 1.6–1.4 wt% in orthopyroxenite (Fig. 7 c). It is noteworthy that the iron contents exhibit a consistent decline from 13.0 wt% of FeO tot in dunite to 12.5–11.8 wt% in harzburgite and 11.0–9.4 wt% in orthopyroxenite (Table S4 , Fig. 7 d). It should be noted that there is a positive correlation between the contents of MgO and FeO tot , whereas negative correlations are determined between the contents of MgO and SiO 2 , Al 2 O 3 , CaO, and Cr 2 O 3 , which are described by regression equations (Figs. 7 a-e). In general, the distribution of major elements is primarily influenced by variations in the modal quantities of olivine and orthopyroxene (Fig. 7 ). A regular decrease in the contents of MgO and, to a lesser extent, FeO tot is observed with an increase in SiO 2 contents in the OH330 sections from the bottom to the top (from dunite and harzburgite to orthopyroxenite) (Fig. 6 ). Furthermore, the OH330 dunite differs from the Monchepluton dunite in its higher contents of FeO tot and lower contents of MgO and Al 2 O 3 . The OH330 harzburgite and orthopyroxenite differed from the corresponding rocks of the NKT and Sopcha intrusions in lower contents of Al 2 O 3 and CaO (Fig. 7 ). It is worth noting that the harzburgite and orthopyroxenite of the OH330 described by Karykowski et al. ( 2018 ) have a less magnesian composition than the corresponding rocks in our data (Fig. 7 ). The host olivine orthopyroxenite displayed higher contents of Al₂O₃ (3.2–2.0 wt%) and CaO (2.4–1.5 wt%) but lower Ni concentrations than the OH330 orthopyroxenite, while the other major elements were present in comparable amounts (Fig. 7 ). Trace elements The OH330 dunite and harzburgite exhibited low REE and trace elements contents in the 0.04–0.7 range in relation to the primitive mantle (Fig. 8 a). The REE tot contents did not exceed 1 ppm in these rocks (Table S4 ). Normalized to the primitive mantle, the REE plots form gentle U-like curves with negative slopes in the LREE field and positive slopes in the range of Gd-Lu elements (Fig. 8 a). This peculiarity of the REE spectra in dunite and harzburgite of OH330 is reflected in positive values of (Ce/Sm) N varying from 1.21 to 1.86 and low values of (Gd/Yb) N , which are in the 0.87–0.37 range (Table S4 ). U, Ta, and Sr form positive anomalies (Fig. 8 a), and a positive Eu anomaly is observed for dunite (Eu/Eu*) N = 1.56, while mostly negative Eu anomalies are observed for harzburgite (Eu/Eu*) N = 0.59–1.04 (Fig. 8 a, Table S4 ). The obtained trace-element distribution features are comparable to those observed in harzburgite OH330 according to Karykowski et al. ( 2018 ), with the exception of higher concentrations and positive Th anomalies (Fig. 8 a). The OH330 orthopyroxenite exhibited elevated concentrations of REE and trace elements, with values of 0.2–1.7 in relation to the primitive mantle (Fig. 8 b). The REE tot contents of orthopyroxenite ranged from 2.0 to 4.5 ppm (with an average of 3.16 ppm). The REE tot highest concentrations are observed in the medium-to-coarse-grained orthopyroxenite of section 422 and the fine-to-medium-grained orthopyroxenite of section 423 (Table S4 ). The REE distribution in the OH330 orthopyroxenite was characterized by greater fractionation in the LREE area than in harzburgite and lack of fractionation in the Gd-Lu range (Fig. 8 b). This is indicated by the positive of (Ce/Sm) N values varying from 1.82 to 2.22 and the low (Gd/Yb) N values, which are in the range of 1.02–0.69 (Table S4 ). Slightly pronounced negative Eu anomalies (or their absence) are detected in the orthopyroxenites, with (Eu/Eu*) N values ranging from 0.83 to 0.97 (Fig. 8 b, Table S4 ). The OH330 orthopyroxenite typically exhibits negative Nb-Ta anomalies and positive U anomalies (Fig. 8 b). It is important to note that the OH330 orthopyroxenite analyzed by Karykowski et al. ( 2018 ) differs from the aforementioned samples in that it exhibits positive Th, Sr, Zr, and Hf anomalies while exhibiting similar negative Nb-Ta anomalies (Fig. 8 b). The host olivine orthopyroxenite exhibited REE and trace element concentrations of 1.1–1.0 in relation to the primitive mantle (Fig. 8 c). REE tot contents in these orthopyroxenite were in the 4.4–1.3 ppm range, with the highest REE tot concentrations detected in the olivine orthopyroxenite from the hanging wall and footwall in comparison with the olivine orthopyroxenite on removed from the contact. The maximum REE content was determined in the olivine orthopyroxenite of the footwall of section 422 (Table S4 ). The REE tot distribution in the olivine orthopyroxenite was less fractionated in the LREE area than in the OH330 orthopyroxenite, and a slight positive inclination was observed in the HREE area (Fig. 8 c). The (Ce/Sm) N values varied from 1.41 to 2.69, whereas the (Gd/Yb) N value varied from 0.52 to 1.27 (Table S4 ). These rocks exhibit negative Nb and variable Eu anomalies with (Eu/Eu*) N values ​​varying from 0.80 to 1.51 (Fig. 8 a, Table S4 ). Olivine orthopyroxenite according to Karykowski et al. ( 2018 ) differs markedly from the samples we studied because of lower LREE distribution and positive anomalies of Th, Zr and Hf (Fig. 8 b). The distributions of REE tot , La, and trace elements in the OH330 sections exhibit low values in dunite and harzburgite and increased values in orthopyroxenite (Fig. 9 ). The content of these elements in the host olivine orthopyroxenite is highly variable. In section 423, the concentrations of these elements were lower than those of the OH330 orthopyroxenite. Conversely, the olivine orthopyroxenite from the hanging wall of section 422 exhibits comparable concentrations to the OH330 orthopyroxenite, while those from the footwall of the section 422 display abnormally high concentrations of these elements (Fig. 9 ). SIMS SHRIMP U-Pb Age of Zircon In total, 18 local U-Pb isotope analyses were conducted on 15 zircon grains. The results are presented in Table S5 and illustrated in Fig. 10 . The studied zircons were divided into two populations based on isotopic parameters. The first population included eight zircon grains of different morphologies. Five of the zircon grains exhibit a short prismatic shape and crystal fragments ranging in size from 90 × 60 to 230 × 140 µm, with length-to-width ratio varying from 1.5:1 to 2.1:1 (Fig. 10 a). The two zircon grains exhibit oval and rounded shapes with dimensions of 90 × 45 µm and 90 × 90 µm, respectively. One zircon grain exhibited an elongated and resorbed shape with dimensions of 80 × 20 µm and a length-to-width ratio of 4:1 (Fig. 10 a). According to CL characteristics, most of zircon grains in this population exhibit a heterogeneous internal structure comprising two to three domains that differ in brightness within the CL image. In some instances, the internal domains exhibit a combination of small dark and light areas, as observed in grain 17 (Fig. 10 a). Additionally, in one zircon grain with a homogeneous CL-dark image, small irregularly shaped areas with a CL-gray image can be observed (19.1 and 20.1, Fig. 10 a). One zircon from this population exhibits oscillatory zoning, which is defined as fine, periodic variations in the mineral composition, in the absence of a visible core and with a thin, discontinuous rim (grain 13, Fig. 10 a). Zircons from this population exhibit considerable variability in U and Th contents, ranging from 138 to 1303 ppm U and 8 to 4610 ppm Th. The average contents of these elements are (n = 9): U = 537 ± 352 ppm, Th = 1234 ± 1331 ppm, and Th/U = 1.91 ± 1.68 (Table S5 ). The variations in U and Th contents observed in different magmatic zircon domains were not correlated with changes in the brightness of their CL images. For instance, the U content in the seven CL-dark grey domains variesd from 158 to 1303 ppm, whereas the Th content varied from 8 to 1609 ppm. In contrast, in the two CL-light grey domains, the U content was 226 and 289 ppm, and the Th content was 64 and 282 ppm (Table S5 , Fig. 10 a). There was no correlation between U and Th contents in zircons from this population (Fig. 10 b). All zircons from the first population exhibited similar U and Pb isotopic ratios (Table S5 ), indicating the absence of a significant impact of secondary processes and contamination by a substance of a different composition on the U-Pb isotope system. All obtained age values were concordant or subconcordant. A concordant U-Pb age was obtained for this zircon population, equal to 2492.5 ± 4.1 Ma and, MSWD = 0.68 (n = 9, 2σ) (Fig. 10 c). Age is considered concordant when the ellipses of analytical errors intersect the concordia. This result is corroborated by the low degree of discordance, which ranges from − 0.16 to 3.62 (Table S5 ). The concordant age is equivalent to the weighted average 207 Pb/ 206 Pb age of zircons from this population, which is 2492.6 ± 4.2 Ma, MSWD = 0.66 (n = 9, 2σ) (Fig. 10 d). The resulting concordant age can be interpreted as the time zircon magmatic crystallization and accordingly the age of the OH330 rocks. The second zircon population comprises seven zircon grains represented by long-prismatic crystals and their fragments. These grains are sometimes well-preserved with crystallographic shapes ranging in size from 90 × 45 to 200 × 80 µm and a length-to-width ratios ranging from 2:1 to 4:1 (Fig. 10 a). The majority of zircons in this population exhibit oscillatory zoning in CL images (grains 7, 9, 10, and 14–15, Fig. 10 a). In some cases, they contain a core in the absence of rims. The remaining zircons display a more homogeneous internal structure, typically comprising two to three domains that differ in brightness in the CL image. The U and Th contents of this zircon population, as well as those of the zircons of the first population, exhibit significant variability. They range from 212 to 1829 ppm U and from 78 to 1090 ppm Th, with Th/U ratios ranging from 0.17 to 0.62 (Table S5 ). The average values of these components were as follows (n = 9): 674 ± 458 ppm U, 314 ± 269 ppm Th, and Th/U = 0.43 ± 0.10. Furthermore, there is a strong positive correlation between the U and Th contents (Fig. 10 b). The concordant U-Pb age of this zircon population is 2818.0 ± 3.1 Ma, with a MSWD = 1.8 (n = 9, 2σ) (Fig. 10 c). A weighted average 207 Pb/ 206 Pb age of 2818 ± 3.2 Ma was determined with an MSWD = 1.7 (n = 9, 2σ) (Fig. 10 d). This concordant age provides a rationale for considering the zircon of the second population xenocryst, as extracted from the rocks of the Archean granitoid basement. This is because it falls within the age range of the Archean granitoid of the Kola Block, which is estimated to be between 2835 and 2736 Ma (Chen et al. 1998 ; Pripachkin et al. 2020 ). It is important to note that the CL-light grey domain 4.1 of xenocryst zircon differs from other zircons of this population in terms of its lowest contents of U = 212 ppm and 206 Pb* = 89 ppm, as well as its lower values of Pb-U isotopic parameters: 207 Pb*/ 235 U = 13.55 ± 0.16 and 206 Pb*/ 238 U = 0.4894 ± 0.0054 (Table S5 ). In addition, this domain exhibits a high degree of discordance ( D = 10.32, Table S5 ). These results suggest that this zicron was subjected to later metamorphic-metasomatic processes. Discussion Th/U Ratio in Magmatic Zircon and Geochronology The studied magmatic zircon consists of by individual grains with partially preserved facets and partially resorbed grains (Fig. 10 a). It is evident that such forms reflect the complex evolution of their formation. In terms of morphology, it is similar to zircon from rocks of the olivine horizon of the Nyud intrusion (Chashchin and Sergeev 2023 ), although it is smaller. However, it differs significantly from metagabbronorite zircons from the Vuruchuayvench intrusion from Monchepluton, represented by fragments of prismatic grains (Rundkvist et al. 2015 ). This magmatic zircon displays a wide range of U and Th concentrations, with values ranging from 138 to 1303 ppm and 8 to 4610 ppm, respectively, and an average Th/U ratio is 1.91 ± 1.68 (Table S5 ). In terms of this value, it is most similar to zircon from the Nyud olivine horizon (1.80; Chashchin and Sergeev 2023 ). At the same time, it should be noted that in mafic-ultramafic rocks, especially in layered intrusions, the Th/U value in zircons varies significantly. In particular, the Th/U values in zircon from the rocks of the lower Platreef, Bushveld is 0.6 ± 0.2, and of the upper Platreef is 0.77 ± 0.4 (Yudovskaya et al. 2013 ). A comparable Th/U ratio was identified in zircon from the Great Dyke websterite in Zimbabwe (0.61; Armstrong and Wilson 2000 ). A higher Th/U ratio was determined in zircon from the Merensky Reef in Bushveld (2.5 ± 0.8; Yudovskaya et al. 2013 ), as well as from the metagabbro of the Vuruchuayvench intrusion (2.86; Rundkvist et al. 2015 ). The data presented demonstrate that Th/U value in zircon is influenced by both the composition of the parental magma and fractionation processes in the intermediate hearth and magma chamber. The U content of sample 422/3 of orthopyroxenite was 0.014 ppm, the Th content was 0.05 ppm, and the Th/U ratio was 3.57 (Table S4 ). Consequently, the distribution coefficient K D Th/U (zircon/rock) was 0.54, which was approximately 3–4 times higher than that defined for zircons from gabbro (0.14; Kirkland et al. 2015 ) and anorthosite (0.19; Bindeman et al. 2006 ). This may indicate that the U and Th contents in zircon OH330 are not controlled by the K D Th/U (zircon/rock) value and that its formation occurs under conditions of nonequilibrium crystallization (Wang et al., 2011). This is also evidenced by oscillatory zoning in individual zircon, which results from a process in which the growth of zircon crystals alters the adjacent melt, thereby affecting its composition (Fowler et al. 2002 ). The presence of unusually high U and Th contents (> 1000 ppm) in some magmatic zircons may be attributed to the crystallization of zircon from residual intercumulus liquid enriched in U and Th (Wang et al. 2011). Moreover, because these zircons exhibit a considerable range of U and Th contents, it is feasible if the focus of residual liquid were separated from each other during the solidification process and behaved as isolated systems. Currently, there is limited geochronological data on the rocks of the NKT and Sopcha intrusions that are part of the Monchepluton ultramafic chamber. Previously, the U-Pb method by zircon determined the age of quartz norite from the bottom of the Travyanaya intrusion, which was 2507 ± 9 Ma (Bayanova et al. 2004 ). Subsequently, the same method was employed to determine the age of norite in the marginal zone of the Nittis intrusion, which was found to be 2505.5 ± 7.0 Ma (Semenov et al. 2022 ). The similar U-Pb ages were derived from single zircons from dunite and chromium ore in the Dunite Block which make up 2500 ± 10 and 2500 ± 2 Ma, respectively (Chashchin and Bayanova 2021 ). Therefore, the obtained age of orthopyroxenite OH330 (2492.5 ± 4.1 Ma) within the uncertainty was younger than the ages of the lower zone rocks of the Monchepluton ultramafic subchamber. At the same time, it is close to the age of the rocks from the upper zone of the Nyud (2493 ± 7 Ma; Balashov et al. 1993 ) and Poaz (2493 ± 5 Ma; Chashchin and Bayanova 2023 ) intrusions of the Monchepluton mafic subchamber. This indicates that the injection of OH330 magma occurred in synchrony with the crystallization of rocks in the Monchepluton mafic subchamber. Sequence of OH330 formation The geological structure, mineral, and geochemical composition of the OH330 rocks allow reconstruction of the sequence of formation. This process started with the formation of the parental melt, which resulted from the rise of the mantle diapir and its partial melting. The extent of partial melting of the mantle substrate, which is probably spinel peridotite of the fertile mantle MORB (FMM)-type, was quantified using the V-Yb ratio, as shown in Fig. 11 . This diagram compares the compositions of OH330 rocks with the theoretical melting trends of spinel peridotites as a function of oxygen fugacity, as presented in (Pearce et al. 2000 ). The compositions of the OH330 rocks ranged from 10 to 20% melting degrees (on average ca. 15%) and was between QFM and QFM + 1 oxygen fugacity (on average ca. QFM + 0.5) (Fig. 11 ). It is notable that the oxygen fugacity determined for the olivine-chromite cumulus association using an oxybarometer (Ballhaus et al. 1991 ) was Δlog(fO 2 ) QFM = 0.6 (Chashchin and Savchenko 2021 ), which is comparable to the obtained data. Noted that the composition of the host olivine orthopyroxenite lies around 13% partial melting and QFM-0.5 oxygen fugacity (Fig. 11 ). It is likely that the liquidus temperature of the parental magma corresponded to that obtained for olivine-liquid equilibrium in aqueous conditions, which comprised 1600–1470°C (Table S3 ). Noted that this temperature significantly exceeds the potential temperature of the convecting mantle (1350°C), according to McKenzie and Bickle ( 1988 ). The apparent contradiction can be explained by the genetic connection between the parental melt of OH330 and the rise of the mantle diapir, which occurred as a result of the activation of a long-lived Paleoproterozoic mantle plume associated with the formation of numerous layered intrusions of the Fennoscandian Shield (Sharkov et al. 2000 ; Smolkin et al. 2009 ). It is important to note that the equilibrium temperature of olivine-melt for anhydrous conditions in OH330 rocks corresponds to 1800–1780°C (Table S3 ), which raises reasonable doubts becaus it exceeds the formation temperatures of the highest-temperature komatiite and meimechite magmas (1670–1600°C), as shown (Sobolev et al. 2009 ; Nisbet et al. 1993 ; Sossi and O'Neill 2016; Wilson 2019 ). Subsequently, the parental melt ascended through the crust through a vertical channel and entered the chamber of the Sopcha intrusion (Fig. 12 a). During the uplift, the magma was contaminated with crustal material, as evidenced by the Sm-Nd isotopic data of the OH330 harzburgite with a value of ε Nd = -6.0 ± 0.6 (Chashchin et al. 2016 ), as well as the presence of xenocryst zircons with an age of 2818 Ma extracted from the host Archean granitoid. This process was accompanied by an enrichment of the melt in U, Sr, and LREE, accompanied by a slight increase in the Ta and Nb contents. This result is expressed by the appearance of negative anomalies of Nb and Ta in the orthopyroxenites (Fig. 8 b). Furthermore, the parental magma was saturated with S and chalcophilic elements, ultimately lead to the formation of sulfide PGE-Cu-Ni mineralization (Chashchin and Petrov 2023 ). After reaching the middle part of the orthopyroxenite section of the Sopcha intrusion, the OH330 parental magma spread along the subhorizontal surface in the form of a sill-like thin body (Fig. 12 a). The dunite-to-orthopyroxenite phase observed in the OH330 sections can be explained by the fractional crystallization of magma from bottom to the top as the temperature decreases. Furthermore, the change in olivine-rich rocks in the west of OH330 to olivine-free rocks in the east is attributed to hydrodynamic fractionation (Barnes et al. 2016 ) during the laminar flow of magma from west to east (Fig. 12 b). The crystallization process did not occur simultaneously along the entire length of OH330. It started on its western flank with more primitive rocks, after which the crystallization front of a more fractionated melt proceeded from west to east. This occurred under conditions of a decrease in flow pressure and velocity in the westerly direction, which contributed to the deposition of the previously highlighted solid olivine particles. It is noteworthy that in the OH330 section, above the harzburgite layer, there is always a layer of coarse-grained orthopyroxenites, which are usually affected by amphibolization. This can be explained by the influence of the accumulated aqueous fluids in the middle of OH330. The OH330 crystallization occurred at a temperature of 1290–1100°C, in accordance with the orthopyroxene-melt equilibrium and an average pressure of 3.5 kbar (Table S3 ), which corresponds to a depth of approximately 10 km. At the same stage of evolution, at a temperature of ca. 1170°C, cumulus olivine and chromite crystallized (Chashchin and Savchenko 2021 ). Further cooling of the OH330 rocks, starting at 1000°C, separated an immiscible sulfide liquid that accumulated chalcophile and platinum group elements. This process was accompanied by the crystallization of sulfides of basic metals and platinum group minerals, which proceeded to 600–400°C (Chashchin and Petrov 2023 ). The presence of olivine orthopyroxenite in the lower and upper parts of OH330, which contains dunite and harzburgite autoliths, indicates that olivine orthopyroxenite formed later than 2492 Ma as a result of one additional pulse of the mantle diapir. Conclusions The following conclusions can be drawn from the results of the conducted studies. OH330 is located within the orthopyroxenites of the Sopcha intrusion and is a sill-like body with a thickness of 4–6 m, length of 3300 m, and width of 1200 m. The complete OH330 section was studed in the outcrops of its western part. Here, it is represented (from bottom to top) by dunite, harzburgite, and orthopyroxenite with various grain sizes. In the eastern direction, the proportions of dunite and harzburgite in the OH330 section are significantly reduced until they are completely lost. Accordingly, only orthopyroxenites are present on the eastern flank of the OH330 section. The geochemical features of the OH330 rocks were characterized by a decrease in Mg and Fe contents during the transition from dunite to orthopyroxenite, positive U anomaly in dunite and harzburgite, enrichment of LREE and negative Nb and Ta anomalies in orthopyroxenite. This result is due to both fractional crystallization and crustal contamination of the parental melt. According to the olivine-melt thermometer, the liquidus temperature was determined to be 1600–1470°C under water conditions, which is explained by a genetic link between the OH330 parental melt and the mantle diapir formed as a result of activation of the long-term Paleoproterozoic mantle plume. The orthopyroxene-melt equilibrium temperature is 1290–1100°C. The OH330 parental melt was formed as a result of partial (15%) melting of the FFM spinel peridotite under buffer QFM + 0.5 control. Two zircon populations were isolated from coarse-grained orthopyroxenite sample. Based on the magmatic zircon population, a concordant SIMS SHRIMP U-Pb age of 2492.5 ± 4.1 Ma was obtained, which is interpreted as the time of magmatic crystallization and therefore the age of the OH330 rocks. A concordant U-Pb age of 2818.0 ± 3.1 Ma was obtained from the xenocryst zircon population, which corresponds to the age of the Archean granitoid basement rocks. The obtained age of the OH330 orthopyroxenite (2492.5 ± 4.1 Ma) was younger than the age of the norite in the marginal zone of the NKT intrusion (ca. 2507 Ma), and therefore the Sopcha intrusion, which is part of the ultramafic subchamber of Monchepluton, was obtained. This provides compelling evidence that the OH330 formed as a result of additional magma injection. Declarations Conflict of Interest The authors declare no conflict of interest. Funding The studies have been performed in accordance with the following topics of scientific research of the Geological Institute KSC RAS: FMEZ–2024–0004 (Ch.V.V.) and FMEZ–2024–0008 (S.Ye.E.). Author Contribution The authors contributions the following:V.Ch. processed all the materials obtained, calculated of PT conditions, prepared all the figures and tables, and wrote the main text of the manuscript.Ye.S. studied the chemical composition of minerals.S.S. determined the U-PB age of zircon and provided data for Table S5 and Fig. 10.All authors have reviewed the manuscript. Acknowledgments The authors are grateful to L. Koval (Geological Institute KSC RAS, Apatity) for the crushing of rocks and the separation of zircons and to V. Anatsky translated the manuscript into English. References Armstrong R, Wilson AH (2000) A SHRIMP U-Pb study of zircons from the layered sequence of the Great Dyke, Zimbabwe, and a granitoid anatectic dyke. 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(In Russian) Chistyakova S, Latypov R, Zaccarini F (2016) Chromitite dykes in the Monchegorsk layered intrusion, Russia: in situ crystallization from chromite-saturated magma flowing in conduits. J Petrol 56:2395-2424. https://doi.org/10.1093/petrology/egv079 Eliseev EN (1953) Disseminated sulfide mineralization of the Sopcha ore layer. In: Eliseev NA (ed) Ultrabasic and basic intrusions and sulfide copper-nickel deposits of the Moncha. USSR Academy of Sciences, Leningrad, pp. 112-143 (In Russian) Fowler A, Prokoph A, Stern R, Dupuis C (2002) Organization of oscillatory zoning in zircon: analysis, scaling, geochemistry, and model of a zircon from Kipawa, Quebec, Canada. Geochem Cosmochim Acta 66:311-328. https://doi.org/10.1016/s0016-7037(01)00774-8 Gorbunov GI, Yakovlev YuN, Goncharov YuV, Gorelov VA, Telnov VA (1985) Kola Peninsula nickel-bearing regions. In: Gorbunov GI, Papunen H (eds) Baltic shield copper-nickel deposits. 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Chem Geol 120:223-253 McKenzie D, Bickle MJ (1988) The volume and composition of melt generated by extension of the lithosphere. J Petrol 29 (3):625-679. https://doi.org/10.1093/petrology/29.3.625 Mitrofanov FP, Balabonin NL, Bayanova TB, Korchagin AU, Latypov RM, Osokin AS, Subbotin VV, Karpov SM, Neradovsky YuN (1999) Kola platinum metal province: new data. In: Orlov VP (ed). Platinum of Russia. Vol. 3. Problems of development of the mineral resource base of platinum metals in the 21st century. Moscow. JSC "Geoinformmark" pp. 43–52. (In Russian) Neradovsky YuN, Rundkvist TV, Galkin AS, Klimentev VN (2002) To the problem of the Sopcha “Horizon-330” PGE bearing and its industrial use (Monchegorsk Pluton). Vestnik Murmansk Tekhn Univers 5:85-90. (In Russian) Nisbet EG, Cheadle MJ, Arndt NT, Bickle MJ (1993) Constraining the potential temperature of the Archaean mantle: A review of the evidence from komatiites. Lithos 30:291–307. https://doi.org/10.1016/0024-4937(93)90042-b Orsoev DA, Konnikov EG, Zaguzin GN (1994) Mineralization of the Mt. Sopcha peridotite layer in Monchegorsk area. Zap Vsesoyuznogo Mineral Obs 123 (3):26-40 (In Russian) Pearce JA, Barker PF, Edwards SJ, Parkinson IJ, Leat PT (2000) Geochemistry and tectonic significance of peridotites from the South Sandwich arc-basin system, South Atlantic. Contrib Mineral Petrol 139:36-53. https://doi.org/10.1007/s004100050572 Pripachkin P, Rundkwist T, Croshev N, Bazai A, Serov P (2020) Archean rocks of the diorite windows block in the southern framing of the Monchegorsk (2.5 Ga) layered mafic-ultramafic complex (Kola Peninsula, Russia). Minerals 10 (10). https://doi.org/10.3390/min10100848 Putirka K (2008) Thermometers and barometers for volcanic systems. Rev Miner Geochem 69:61-120. https://doi.org/10.2138/rmg.2008.69.3 Rundkvist TV, Bayanova TB, Sergeev SA, Pripachkin PV, Grebnev RA (2014) The Paleoproterozoic Vurechuaivench layered Pt-bearing pluton, Kola Peninsula: new results of the U-Pb (ID-TIMS, SHRIMP) dating of baddeleytte and zircon. Dokl Earth Sci454 (1):1-6. https://doi.org/10.1134/s1028334x14010048 Rundkvist TV, Balashov YuA, Skublov SG, Pripachkin PV, Grebnev RA (2015) Geochemistry and U-Pb age of zircon from the platinum-bearing Vurechuaivench massif, Monchegorsk complex, Kola region. Notes the Russ Mineral Soc 144 (3):14–30. (In Russian) Schuth S, Gornyy VI, Berndt J, Shevchenko SS, Sergeev SA, Karpuzov AF, Mansfeldt T (2012) Early Proterozoic U-Pb zircon ages from basement gneiss at the Solovetsky Archipelago, White Sea, Russia. Inter J Geosci 3:289-296. https://doi.org/10.4236/ijg.2012.32030 Semenov VS, Kazanov OV, Korneev SI, Salnikova EB, Semenov SV (2022) Conditions of formation of layered intrusions of the Monchegorsk magmatic cluster. Petrol 30 (4):369–391. https://doi.org/10.1134/S0869591122030079 Sharkov EV (2006) Formation of layered intrusions and their ore mineralization. Scientific World, Moskow, 368 pp (In Russian) Sharkov EV, Chistyakov AV (2014) Geological and petrological aspects of Ni-Cu-PGE mineralization in the early Paleoproterozoic Monchegorsk layered mafic-ultramafic complex, Kola Peninsula. Geol Ore Deposits 56:147-168. https://doi.org/10.1134/s1075701514030040 Sharkov EV, Bogatikov OA, Krasivskaya IS (2000) The role of mantle plumes in the tectonics of the Early pcambrian of the eastern part of the Baltic Shield. Geotectonics (2):3-25. (In Russian) Smolkin VF, Fedotov ZhA, Orsoev DA, Ohnenstetter D (2004) Ore-bearing layered Monchepluton. In: Mitrofanov FP, Smolkin VF (eds). Layered intrusions of the Monchegorsk ore region: petrology, mineralization, isotopy, and deep structutre. Part 1. Apatity. Kola Science Center RAS. pp. 36-74 (In Russian) Smolkin VF, Kremenetsky AA, Vetrin VR (2009) Geological and genetic model of the formation of Paleoproterozoic ore-magmatic systems of the Baltic Shield. Otech Geol (2):54–62. (In Russian) Sobolev AV, Sobolev SV, Kuzmin DV, Malitch KN, Petrunin AG (2009) Siberian meimechites: origin and relation to flood basalts and kimberlites. Russ Geol Geoph 50:999–1033. https://doi.org/10.1016/j.rgg.2009.11.02 Sossi PA, O’Neill HStC (2016) Liquidus temperatures of komatiites and the effect of cooling rate on element partioning between olivine and komatiitic melt. Contrib Mineral Petrol 171. https://doi.org/10.1003/s00410-016-1260-x Stacey JS, Kramers JD (1975) Approximation of terrestrial lead isotope evolution by a two-stage model. Earth Planet Sci Lett 26:207-221. https://doi.org/10.1016/0012-821x(75)90088-6 Tkachenko KN, Yudin BA (1982) Chemical analysis of rocks from the mafic-ultrabasic complexes of the pcambrian Kola Peninsula. Apatity. Kola Branch of the USSR Academy of Sciences. 216 p. (In Russian) Wang Xiang, Griffin WL, Chen Li, Huang Pinyun, Li Xiang (2011) U and Th contents and Th/U ratios of zircon in felsic and mafic magmatic rocks: improved xircon-melt distribution coefficients. Acta Geol Sin 85 (1):164-174. https://doi.org/10.1111/j.1755-6724.2011.00387.x Warr LN (2021) IMA-CNMNC approved mineral symbols. Mineral Mag 85:291-320. https://doi.org/10.1180/mgm.2021.43 Wiedenbeck M, Alle P, Corfu F, Griffin WL, Meier M, Oberli F, Von Quadt A, Roddick JC, Spiegel W (1995) Three natural zircon standards for U-Th-Pb, Lu-Hf trace element and REE analyses. Geostandard Newslett 19:1-23. https://doi.org/10.1111/j.1751-908x.1995.tb00147.x Williams IS (1998) U-Th-Pb geochronology by ion microprobe. In: McKibben MA, Shanks WC, Ridley WI (eds.) Applications of microanalytical techniques to understanding mineralizing processes. Socorro, New Mexico. Rev Econ Geol 7:1-35 Wilson AH (2019) The Late-Paleoarchean ultra-depleted Сommondale komatiites: Earth’s hottest lavas and consequences for eruption. J Petrol 60 (8):1575–1620. https://doi.org/10.1093/petrology/egz040 Yudovskaya M, Kinnaird J, Naldrett AJ, Rodionov N, Antonov A, Simakin S, Kuzmin D (2013) Trace-element study and age dating of zircon from chromitites of the Bushveld Complex (South Africa). Miner Petrol 109:915–942. https://doi.org/10.1007/s00710-013-0269-3 Additional Declarations No competing interests reported. Supplementary Files TableS1.xlsx TableS2.xlsx TableS3.xlsx TableS4.xlsx TableS5.xlsx Cite Share Download PDF Status: Posted Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-4678396","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":326700797,"identity":"397e5955-5830-471f-af10-c3a5a0e5e60f","order_by":0,"name":"Victor V. Chashchin","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAAw0lEQVRIiWNgGAWjYHACNiA+wGDAzMD4sIFULcyGJGoBMiSJ0mJwgPnZgx9/7sibs/Meq5zxx47BfEYCIS1s5oa9bc8Mdzbzpd3c2JbMIHODgBbJBh42Cd6GwwkGh3nMbj5sOMAgIUGEFsk/fyBaCh/8IUILPwMPmzQPG0QL4wY2YrQws5lJy7YdNtxwmMdYcmZbMo8EzwP8WtjYm59JvvlzWN7g/BnDjz1/7OQk2AnYwsCMxuchoH4UjIJRMApGATEAAEZMPXWqSnJOAAAAAElFTkSuQmCC","orcid":"","institution":"Geological Institute of the Kola Science Center, RAS","correspondingAuthor":true,"prefix":"","firstName":"Victor","middleName":"V.","lastName":"Chashchin","suffix":""},{"id":326700798,"identity":"1b1d794b-9226-4b0d-aa7d-cdc668e12a9b","order_by":1,"name":"Yevgeny E. Savchenko","email":"","orcid":"","institution":"Geological Institute of the Kola Science Center, RAS","correspondingAuthor":false,"prefix":"","firstName":"Yevgeny","middleName":"E.","lastName":"Savchenko","suffix":""},{"id":326700799,"identity":"4b06f46b-074a-4e25-89e4-d80a0deb51fd","order_by":2,"name":"Sergey A. Sergeev","email":"","orcid":"","institution":"Karpinsky Russian Research Geological Institute","correspondingAuthor":false,"prefix":"","firstName":"Sergey","middleName":"A.","lastName":"Sergeev","suffix":""}],"badges":[],"createdAt":"2024-07-03 07:25:23","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-4678396/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-4678396/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":61268134,"identity":"28d885d1-c6e4-4843-b0e2-00d4c93aa4ae","added_by":"auto","created_at":"2024-07-29 01:06:42","extension":"jpg","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":1064044,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003ea\u003c/strong\u003e Kola Region geological scheme. \u003cstrong\u003eb\u003c/strong\u003eMonchepluton geological map. \u003cstrong\u003ec\u003c/strong\u003eSopcha intrusion geological map and section along line A-B line, \u003cstrong\u003ed\u003c/strong\u003e Detailing of outcrops in the zones of the OH330 upper and lower contact modified from Chashchin and Petrov (2023)\u003c/p\u003e","description":"","filename":"Fig1.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4678396/v1/47bcccf55a0de2b4b9889991.jpg"},{"id":61268556,"identity":"86c50fc8-b3f2-431a-bfe0-6928e0f9cb84","added_by":"auto","created_at":"2024-07-29 01:14:42","extension":"jpg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":879904,"visible":true,"origin":"","legend":"\u003cp\u003eSections 422 and 423 of the OH330 with field photos of some rock outcrops: \u003cstrong\u003ea\u003c/strong\u003e fine-to-medium-grained orthopyroxenite (outcrop 423/1), \u003cstrong\u003eb\u003c/strong\u003e medium-to-large-grained orthopyroxenite (outcrop 422/3), \u003cstrong\u003ec\u003c/strong\u003e banded harzburgite (outcrop 423/3), \u003cstrong\u003ed\u003c/strong\u003e lower part of the harzburgite interlayer (outcrop 422/5), \u003cstrong\u003ee\u003c/strong\u003e dunite (outcrop 422/6), \u003cstrong\u003ef\u003c/strong\u003edunite autoliths in host olivine orthopyroxenite (outcrop 422/8)\u003c/p\u003e","description":"","filename":"Fig2.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4678396/v1/77514586db726a69e8d0d961.jpg"},{"id":61268136,"identity":"7b3a95c0-066a-4949-a795-f40fade9269b","added_by":"auto","created_at":"2024-07-29 01:06:42","extension":"jpg","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":2360036,"visible":true,"origin":"","legend":"\u003cp\u003eCross-polarised transmitted photomicrographs of thin sections of the typical OH330 rocks: \u003cstrong\u003ea\u003c/strong\u003e dunite (sample 422/6), \u003cstrong\u003eb\u003c/strong\u003e harzburgite (sample 422/4), \u003cstrong\u003ec\u003c/strong\u003e medium-to-large-grained orthopyroxenite (sample 422/3), \u003cstrong\u003ed\u003c/strong\u003efine-to-medium-grained orthopyroxenite (sample 422/2), \u003cstrong\u003ee\u003c/strong\u003e fine-grained orthopyroxenite (sample 422/1), \u003cstrong\u003ef\u003c/strong\u003e host olivine orthopyroxenite of the handing wall (sample 422), \u003cstrong\u003eg\u003c/strong\u003e host olivine orthopyroxenite of the footwall (sample 423/6), \u003cstrong\u003eh\u003c/strong\u003e contact of dunite autolite with host olivine orthopyroxenite at the bottom of ОН330 (sample 422/8). Mineral symbols after Warr (2021)\u003c/p\u003e","description":"","filename":"Fig3.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4678396/v1/c47bbb42ed07667860ea3085.jpg"},{"id":61268127,"identity":"060c88d8-4433-46bf-998a-9179a99250dc","added_by":"auto","created_at":"2024-07-29 01:06:42","extension":"jpg","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":204673,"visible":true,"origin":"","legend":"\u003cp\u003eOlivine chemical compositions from OH330 rocks and the host olivine orthopyroxenite in comparison with the olivine compositions from the Monchepluton rocks: harzburgite, olivine orthopyroxenite, and orthopyroxenite of the NKT intrusion (Karykowski et al. 2018) and dunite of the Dunite Block (Chistyakova et al. 2016): \u003cstrong\u003ea\u003c/strong\u003e NiO (wt%) versus Fo (mol%), \u003cstrong\u003eb\u003c/strong\u003e MnO (wt%) versus Fo (mol%)\u003c/p\u003e","description":"","filename":"Fig4.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4678396/v1/c4174e484d89cb398cc43e28.jpg"},{"id":61268131,"identity":"52a30f0e-5cf0-4741-bafe-9d2f8be0acb9","added_by":"auto","created_at":"2024-07-29 01:06:42","extension":"jpg","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":347305,"visible":true,"origin":"","legend":"\u003cp\u003eOrthopyroxene chemical compositions from OH330 rocks and the host olivine orthopyroxenite in the plots: \u003cstrong\u003ea-e\u003c/strong\u003e Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e, CaO, Cr\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e, MnO, and NiO (wt% ) versus En (mol%), respectively, \u003cstrong\u003ed\u003c/strong\u003e Fo (mol%) in olivine versus En (mol%) in orthopyroxene. Same symbols as in \u003cstrong\u003eFig. 4\u003c/strong\u003e. The orthopyroxene field from harzburgite, olivine orthopyroxenite, and orthopyroxenite of the NKT intrusion after Karykovski et al. (2018)\u003c/p\u003e","description":"","filename":"Fig5.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4678396/v1/c9098fb02dee62ea76bf6fbc.jpg"},{"id":61268129,"identity":"db094d20-97e4-4f63-a96c-5adb148a25e7","added_by":"auto","created_at":"2024-07-29 01:06:42","extension":"jpg","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":459923,"visible":true,"origin":"","legend":"\u003cp\u003eThe distribution of the Fo (mol%) in olivine, En (mol%), Cr\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e (wt%), and CaO (wt%) in orthopyroxene, SiO\u003csub\u003e2\u003c/sub\u003e (wt%), MgO (wt%), and FeO\u003csub\u003etot \u003c/sub\u003e(wt%) concentrations in the OH330 rocks at the sections 422 and 423. Legend as in \u003cstrong\u003eFig. 2\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"Fig6.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4678396/v1/5dbeb65b9fa4989023efedf9.jpg"},{"id":61268557,"identity":"3fde6dbd-87ea-4315-8682-d93a8dea4170","added_by":"auto","created_at":"2024-07-29 01:14:42","extension":"jpg","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":649384,"visible":true,"origin":"","legend":"\u003cp\u003eVariations of the major elements and Ni compositions in OH330 rocks and the host olivine orthopyroxenite, converted to 100 % anhydrous composition in comparison with the OH330 harzburgite and orthopyroxenite and rocks of the NKT and Sopcha intrusions of the Monchepluton after Tkachenko and Yudin (1982)\u003c/p\u003e","description":"","filename":"Fig7.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4678396/v1/4b5906315ba14ec33b3b6a4e.jpg"},{"id":61268559,"identity":"1cab6467-f3a8-4bfa-b648-4ac6495505a3","added_by":"auto","created_at":"2024-07-29 01:14:42","extension":"jpg","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":522999,"visible":true,"origin":"","legend":"\u003cp\u003ePrimitive mantle normalized after McDonough and Sun (1995) trace element compositions for OH330 rocks: \u003cstrong\u003ea\u003c/strong\u003e dunite and harzburgite, \u003cstrong\u003eb\u003c/strong\u003e orthopyroxenite, and \u003cstrong\u003ec\u003c/strong\u003e host olivine orthopyroxenite\u003c/p\u003e","description":"","filename":"Fig8.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4678396/v1/50d0a229d33977179a2a298c.jpg"},{"id":61268140,"identity":"3f23dd8a-2dfe-4643-9847-bb69f397bb23","added_by":"auto","created_at":"2024-07-29 01:06:42","extension":"jpg","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":438316,"visible":true,"origin":"","legend":"\u003cp\u003eThe distribution of the REE\u003csub\u003etot\u003c/sub\u003e, La, Ba, Nb, Sr, Zr, and Y (ppm) chemical compositions in the OH330 rocks and host olivine orthopyroxenite at sections 422 and 423. Legend as in \u003cstrong\u003eFig. 2\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"Fig9.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4678396/v1/d8adfb6bcaf33dd710d55a6e.jpg"},{"id":61268558,"identity":"497e0b70-8c21-4460-b53a-99f4d2935bec","added_by":"auto","created_at":"2024-07-29 01:14:42","extension":"jpg","order_by":10,"title":"Figure 10","display":"","copyAsset":false,"role":"figure","size":550809,"visible":true,"origin":"","legend":"\u003cp\u003eU-Pb dating results for zircon from sample 422/3 of the OH330 orthopyroxenite: \u003cstrong\u003ea\u003c/strong\u003e CL image of magmatic and xenocryst zircon with location and analytical craters (diameter 30 mm), and \u003csup\u003e207\u003c/sup\u003ePb/\u003csup\u003e206\u003c/sup\u003ePb ages, \u003cstrong\u003eb\u003c/strong\u003e Th (ppm) versus U (ppm) plot for magmatic and xenocryst zircon with regression lines, \u003cstrong\u003ec \u003c/strong\u003econcordia plot for magmatic and xenocryst zircon. The points coordinates are centers of error ellipses (2σ), \u003csup\u003e207\u003c/sup\u003ePb/\u003csup\u003e206\u003c/sup\u003ePb weighted average ages for\u003cstrong\u003e d\u003c/strong\u003e magmatic and \u003cstrong\u003ee\u003c/strong\u003e xenocryst zircon\u003c/p\u003e","description":"","filename":"Fig10.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4678396/v1/4792b39e759c61144aef34ee.jpg"},{"id":61268143,"identity":"110d7fca-a368-4ad3-ba76-d2b455069773","added_by":"auto","created_at":"2024-07-29 01:06:42","extension":"jpg","order_by":11,"title":"Figure 11","display":"","copyAsset":false,"role":"figure","size":107823,"visible":true,"origin":"","legend":"\u003cp\u003eThe diagram of V versus Yb for rocks OH330 and the host olivine orthopyroxenite with trends in partial melting of spinel lherzolites of the fertile MORB mantle (FMM) and oxygen fugacity conditions according to (Pearce et al. 2000)\u003c/p\u003e","description":"","filename":"Fig11.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4678396/v1/d8658e3aab5aa135e1e8b45f.jpg"},{"id":61268141,"identity":"ff6a473a-f2cb-4671-bf21-f467764a4849","added_by":"auto","created_at":"2024-07-29 01:06:42","extension":"jpg","order_by":12,"title":"Figure 12","display":"","copyAsset":false,"role":"figure","size":270320,"visible":true,"origin":"","legend":"\u003cp\u003eA schematic model of the OH330 formation: \u003cstrong\u003ea\u003c/strong\u003e the uplift of the mantle diapir, introduction of the parental melt into the Sopcha intrusion chamber, flowing along the horizontal plane, and crystallization during 2493 Ma, \u003cstrong\u003eb\u003c/strong\u003e the OH330 rocks formation by sequential crystallization of olivine and orthopyroxene in a sill-like body from a flowing magma flow, modified after Barnes et al. (2016)\u003c/p\u003e","description":"","filename":"Fig12.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4678396/v1/75d7dacc97d4be08bdf04a17.jpg"},{"id":61269283,"identity":"e8ac423d-bdbb-4b8e-ba65-303049dfedea","added_by":"auto","created_at":"2024-07-29 01:30:44","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":8544188,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-4678396/v1/21d27234-0f6b-4ace-ae03-66ae24c072be.pdf"},{"id":61268142,"identity":"69e2cbde-36af-4f52-8fa3-a732c85e4dc2","added_by":"auto","created_at":"2024-07-29 01:06:42","extension":"xlsx","order_by":14,"title":"","display":"","copyAsset":false,"role":"supplement","size":13971,"visible":true,"origin":"","legend":"","description":"","filename":"TableS1.xlsx","url":"https://assets-eu.researchsquare.com/files/rs-4678396/v1/bdf008e901756a5d9365d34c.xlsx"},{"id":61268132,"identity":"a93c5405-4269-44b3-ab62-f38fc915fd16","added_by":"auto","created_at":"2024-07-29 01:06:42","extension":"xlsx","order_by":15,"title":"","display":"","copyAsset":false,"role":"supplement","size":14076,"visible":true,"origin":"","legend":"","description":"","filename":"TableS2.xlsx","url":"https://assets-eu.researchsquare.com/files/rs-4678396/v1/3c05f83324ccac7d0e4e804f.xlsx"},{"id":61268144,"identity":"5769dacb-4fcf-4464-ab26-a66492aff334","added_by":"auto","created_at":"2024-07-29 01:06:43","extension":"xlsx","order_by":16,"title":"","display":"","copyAsset":false,"role":"supplement","size":23804,"visible":true,"origin":"","legend":"","description":"","filename":"TableS3.xlsx","url":"https://assets-eu.researchsquare.com/files/rs-4678396/v1/53bfd1900fe84874cfaa2b6e.xlsx"},{"id":61268138,"identity":"9b2797a1-248a-4638-85f5-fe6de0e2f51b","added_by":"auto","created_at":"2024-07-29 01:06:42","extension":"xlsx","order_by":17,"title":"","display":"","copyAsset":false,"role":"supplement","size":19238,"visible":true,"origin":"","legend":"","description":"","filename":"TableS4.xlsx","url":"https://assets-eu.researchsquare.com/files/rs-4678396/v1/3285d895c7515d01efc8fc04.xlsx"},{"id":61268139,"identity":"2653d53a-92f4-49fb-aa3e-404ed9005eff","added_by":"auto","created_at":"2024-07-29 01:06:42","extension":"xlsx","order_by":18,"title":"","display":"","copyAsset":false,"role":"supplement","size":14761,"visible":true,"origin":"","legend":"","description":"","filename":"TableS5.xlsx","url":"https://assets-eu.researchsquare.com/files/rs-4678396/v1/1991a21b36910aebece049be.xlsx"}],"financialInterests":"No competing interests reported.","formattedTitle":"Mineralogy, Petrogenesis and SIMS SHRIMP U-Pb Age PGE-Cu-Ni Deposit of the “Ore Horizon 330” of the Sopcha Intrusion in the Paleoproterosoic Monchegorsk Pluton, Kola Region, Russia","fulltext":[{"header":"Introduction","content":"\u003cp\u003eA total of more than 20 Paleoproterozoic layered intrusions, comprising two age groups, have been identified within the Archean Kola and Karelia provinces of the north-eastern Fennoscandian Shield (Chashchin and Ivanchenko 2023). The more ancient intrusions (ca. 2.50 Ga) are found exclusively in the Kola Province, whereas the younger intrusions (ca. 2.45 Ga) are predominantly located in the Karelia Province, with a smaller presence in the Kola Province. Many layered intrusions were associated with chromium, sulfide PGE-Cu-Ni, low-sulfide Pt-Pd, and Fe-Ti-V ores. Among all the ore-bearing layered Fennoscandian intrusions, the Monchepluton exhibits the greatest industrial potential. It is associated with chromium and low-sulfide Pt-Pd deposit, and two PGE-Cu-Ni deposits and six manifestations. Its total Pt\u0026thinsp;+\u0026thinsp;Pd reserves and resources are estimated to be more than 800 tons (Chashchin and Ivanchenko, \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). Monchepluton, along with the ore-bearing intrusions Volchya Tundra (Chashchin and Petrov \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2013\u003c/span\u003e) and Monchetundra (Kazanov et al. \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e2016\u003c/span\u003e; Chashchin et al. \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2018\u003c/span\u003e), as well as the Fedorovo-Pana layered complexes (Groshev et al. 2019), constitutes part of the extensive Kola platinum-metal province (Mitrofanov et al. \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e1999\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eThe Monchepluton formation is characterized by a regular vertical change in rock composition from ultramafic to mafic. This led to the formation being considered the result of a one-act magmatic event (Kozlov \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e1973\u003c/span\u003e). However, in some cases, this regular change is disturbed. For instance, the middle part of the orthopyroxenite series of the Sopcha intrusion orthopyroxenite contains the finely layered OH330, and the Nyud intrusion displays disrupted cumulus stratigraphy due to the presence of an olivine horizon (Smolkin et al. \u003cspan citationid=\"CR49\" class=\"CitationRef\"\u003e2004\u003c/span\u003e). These characteristics be attributed to the injection of distinct magma pulses. With regard to the olivine horizon, this hypothesis was corroborated by data from SIMS SHRIMP U-Pb zircon dating, which indicated that the olivine horizon was formed at a time of 2484.3\u0026thinsp;\u0026plusmn;\u0026thinsp;5.6 Ma (Chashchin and Sergeev \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). This age is slightly younger than the U-Pb age of the Nyud intrusion gabbronorite, which is 2493\u0026thinsp;\u0026plusmn;\u0026thinsp;7 Ma (Balashov et al. \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e1993\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eOH330 is a finely layered body bearing a commercially valuable Cu-Ni mineralization. Initially, it was considered to be the main ore base for the Severonickel Mining Plant. However, the discovery of rich sulfide vein ores made the development of this deposit unprofitable. In the late 1990s, the possibility of commercial exploitation of the horizon was re-evaluated when an increased Pt content was revealed in the ore. From a scientific perspective, the OH330 has long been a matter of interest (Eliseev \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e1953\u003c/span\u003e; Kozlov \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e1973\u003c/span\u003e; Sharkov \u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e2006\u003c/span\u003e; Konnikov and Orsoev \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e1991\u003c/span\u003e; Orsoev et al. \u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e1994\u003c/span\u003e; Neradovsky et al. \u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e2002\u003c/span\u003e; Smolkin et al. \u003cspan citationid=\"CR49\" class=\"CitationRef\"\u003e2004\u003c/span\u003e; Sharkov and Chistyakov \u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e2014\u003c/span\u003e; Karykowski et al. \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e2018\u003c/span\u003e; Chashchin and Petrov \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). The deposit is of interest due to its relatively small size and layered structure, which contains PGE-enriched sulfide ore. The composition of the platinum-group minerals and the genesis of OH330 PGE-Cu-Ni deposit have recently been studied (Chashchin and Petrov \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2023\u003c/span\u003e), which has been assigned to a sulfide reef type (Chashchin and Ivanchenko \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). Despite the extensive research conducted on the OH330, questions remain regarding the origin of this finely layered ore horizon and its age, which require further investigation.\u003c/p\u003e \u003cp\u003eThe principal objective of our research was to conduct a comprehensive investigation of the OH330 rocks, including their mineral composition, PT conditions, geochemical attributes, and age. This paper presents the findings of the OH330 study. The results include data on the chemical compositions of olivine, orthopyroxene, and whole-rocks, as well as SIMS SHRIMP U-Pb dating. The obtained data enabled us to determine the formation conditions of OH330 and its age. It is assumed that an understanding of the OH330 genesis is important for the comprehension of the processes that form the fine layering observed in reef-type thin ore horizons.\u003c/p\u003e"},{"header":"Geology of Layered Monchepluton","content":"\u003cp\u003eThe Paleoproterozoic layered ore-bearing Monchepluton, with an age of ca. 2.50 Ga and an area of approximately 50 km\u0026sup2;, is located in the central part of the Kola Region (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ea). The site lies in the Archean granitoidal basement and is associated with the north-western closure of the Paleoproterozoic Imandra-Varzuga greenstone belt (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eb). At the present erosional truncation, the Monchepluton exhibits an arched shape, comprising two branches: a north-eastern branch and a sub-latitudinal branch (Gorbunov et al. \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e1985\u003c/span\u003e). The north-eastern branch is more than 7 km long and 2 km wide in its central part and is represented by the Nittis-Kumuzhya-Travyanaya (or NKT) intrusion. The sub-latitudinal branch is approximately 11 km long and 3 km wide and encompasses the Sopcha, Nyud, Poaz, and Vuruchuayvench intrusions (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eb). According to its specific internal structure, the Monchepluton can be divided into two parts or subchambers (Chashchin and Ivanchenko \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). The first subchamber (ultramafic) encompasses the NKT and Sopcha intrusions, which exhibit vertical thicknesses of up to 1000 and 1200 m, respectively. These intrusions consist of ultrabasic cumulates and exhibit similar internal structure. These intrusions section comprise the following rocks (from the bottom to the top): norite and orthopyroxenite in the marginal zone, dunite developed exclusively in the NKT (Dunite Block), harzburgite, an alternation of harzburgite and orthopyroxenite, and orthopyroxenite. The U-Pb zircon ages of the norite and quartz norite of the marginal zone of the NKT intrusion are 2505.5\u0026thinsp;\u0026plusmn;\u0026thinsp;7.0 Ma and 2506\u0026thinsp;\u0026plusmn;\u0026thinsp;10 Ma, respectively (Bayanova et al. \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2004\u003c/span\u003e; Semenov et al. \u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). The U-Pb ages of the dunite and chromium ore in the Dunite Block were determined from single zircon and are 2500\u0026thinsp;\u0026plusmn;\u0026thinsp;10 Ma and 2500\u0026thinsp;\u0026plusmn;\u0026thinsp;2 Ma, respectively (Chashchin and Bayanova \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). The middle part of the Sopcha intrusion orthopyroxenite includes OH330 (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ec), which is described in detail below.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe second subchamber (mafic) comprises the Nyud, Poaz, and Vuruchuayvench intrusions, which exhibit vertical thicknesses of up to 800, 400, and 900 m, respectively. The sections of the Nyud and Poaz intrusions exhibit similar cumulus stratigraphy, divided into upper and lower zones that differ in thickness. The lower zone was formed by melanonorite and plagioorthopyroxenite with thickness of 300 m (Nyud) and 70‒120 m (Poaz). These rocks are formed by orthopyroxene cumulus and plagioclase intercumulus, with rare clinopyroxene poikilitic porphyroblast, and are essential orthocumulates. The upper zone of these intrusions is represented by a leuco-mesocratic norite with interlayers of gabbronorite with thickness of up to 250 m (Poaz) and 350 m (Nyud). These rocks are mesocumulates composed of cumulus orthopyroxene and plagioclase, sometimes with high clinopyroxene contents. All of the above intrusions exhibit symmetrical trough-like forms with limbs dipping at angles of 20\u0026ndash;45\u0026deg; toward the axes. The similarity of the cumulus stratigraphy of the Nyud and Poaz intrusions is underlined by the similar ages of their upper zone rocks. For example, the U-Pb zircon age of the mesocratic gabbronorite of the Nyud intrusion is 2493\u0026thinsp;\u0026plusmn;\u0026thinsp;7 Ma (Balashov et al. \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e1993\u003c/span\u003e), whereas the age of the Poaz intrusion gabbronorite is 2493\u0026thinsp;\u0026plusmn;\u0026thinsp;5 Ma (Chashchin and Bayanova \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2023\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eIn the western, northern, and southern parts of the Nyud intrusion, there is a crescent-shaped olivine horizon with a length of 6 km and a thickness of approximately 100 m (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eb). It occurs subhorizontally between the melanocratic and mesocratic norite. The olivine horizon comprises orthopyroxenite, plagioorthopyroxenite, and melanonorite with various olivine contents (up to 30 vol%, rarely more) connected with each other by gradual transitions. The SHRIMP U-Pb zircon age of the Nyud olivine horizon is 2484.3\u0026thinsp;\u0026plusmn;\u0026thinsp;5.6 Ma (Chashchin and Sergeev \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2023\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eThe Vuruchuayvench intrusion is situated to the south and southeast of the Nyud and Poaz intrusions, at contact with the Paleoproterozoic Imandra-Varzuga greenstone belt (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ea). At the base of this belt lies a horizon of conglomerates, the debris of which are represented by rocks from the Vuruchuaivench intrusion. This intrusion displays a monocline structure and a gently trending orientation, dipping to the south-east. This shape differs from the general trough-like shape of the Monchepluton. The Vuruchuayvench intrusion comprises metagabbronorite with layers of metaplagioclasite in its upper part and is the only intrusion within the Monchepluton that has undergone intense amphibolization. The SIMS SHRIMP U-Pb zircon ages of metagabbronorite and metaplagioclasite from the Vuruchuayvench intrusion are 2504.2\u0026thinsp;\u0026plusmn;\u0026thinsp;8.4 Ma and 2507.5\u0026thinsp;\u0026plusmn;\u0026thinsp;6.6 Ma, respectively (Rundkvist et al. \u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e2014\u003c/span\u003e). The ID-TIMS U-Pb zircon ages are 2494\u0026thinsp;\u0026plusmn;\u0026thinsp;4 Ma and 2495.3\u0026thinsp;\u0026plusmn;\u0026thinsp;2.2 Ma, respectively (Chashchin et al. \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e2016\u003c/span\u003e).\u003c/p\u003e"},{"header":"Analytical Methods","content":"\u003cp\u003eThe objects of our study were outcrops 422 and 423 in the north-western part of OH330 (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ec), where bedrock exposures present the OH330 with the most comprehensive sections. Sixteen samples of the OH330 rocks and the host orthopyroxenite were selected from these outcrops. The OH330 and host rocks were subjected to petrographic study in thin sections using polarized light microscopy with transmitted light. All polished sections were examined using a LEO-1450 scanning electron microscope (Carl Zeiss, Germany) with an energy-dispersive X-ray analytical device (EDS) to create images of the studied minerals in back-scattered electrons (BSE) and perform a preliminary chemical analysis.\u003c/p\u003e\n\u003ch3\u003eChemical Composition of Minerals\u003c/h3\u003e\n\u003cp\u003eOlivine and orthopyroxene were analyzed by wavelength dispersion spectrometry (WDS) using a Cameca MS-46 electron probe microanalyzer (EPMA) (27 spot analyses of 27 mineral grains from 16 polished sections). The probe diameter, accelerating voltage, and probe current were 3\u0026ndash;5 \u0026micro;m, 22 kV, and 3\u0026ndash;40 nA, respectively. Elemental peaks were measured in 4\u0026ndash;5 10 s cycles and then averaged. Background measurements were performed in two 10-s cycles at each side of a peak for further averaging. The minor elements were measured in the same manner, but the measurements lasted for 20 s. The X-ray line of Kα was analyzed for all elements. The following artificial and natural compounds were used as standards: wollastonite (Si, Ca), lorenzenite (Ti), forsterite (Mg), hematite (Fe), Y\u003csub\u003e3\u003c/sub\u003eAl\u003csub\u003e5\u003c/sub\u003eO\u003csub\u003e12\u003c/sub\u003e (Al), MnCO\u003csub\u003e3\u003c/sub\u003e (Mn), chromite (Cr), and metals (Ni). The detection limits of electron microprobe analyses were as follows (wt%): 0.01 (Fe, Mn, Ni), 0.02 (Ti, Cr), 0.03 (Ca), 0.05 (Si, Al), and 0.1 (Mg). To avoid the influence of secondary effects, all measurements were performed at a distance of no less than 10 \u0026micro;m between the minerals and the contacting mineral phases.\u003c/p\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003eWhole-rock Chemical Composition\u003c/h2\u003e \u003cp\u003eThe whole-rock chemical composition was determined by wet chemistry. In order to define the major elements, the following methods were employed: atomic absorption flame (Si, Al, Cr, Fe, Mg, Ca, Mn), emission flame (Na, K), photocolorimetric (Ti), weight (LOI, H\u003csub\u003e2\u003c/sub\u003eO), and volumetric (FeO) analysis.\u003c/p\u003e \u003cp\u003eThe REE and trace element contents were determined using an ICP-MS method with a NexION 300S quadruple mass spectrometer (Perkin Elmer, USA). The microwave sample dissolution was conducted using a mixture of acids (HCl\u0026thinsp;+\u0026thinsp;HNO\u003csub\u003e3\u003c/sub\u003e\u0026thinsp;+\u0026thinsp;HF) via a Berghof Speedwave MWS 3\u0026thinsp;+\u0026thinsp;system. The precision of element detection was maintained using certified samples of basalt (BCR-2) and andesite (AGV-2) (USGS). The obtained concentrations of REE and trace elements were in acceptable agreement with the attested values; the permissible variations were within 15%. The detection limits for these elements were within the range of 0.005‒0.1 ppm. The average uncertainty in the determination of trace elements was in the range of 2\u0026ndash;10% with dependent on elements and their concentration levels.\u003c/p\u003e \u003c/div\u003e"},{"header":"SIMS SHRIMP U-Pb Dating","content":"\u003cp\u003eA geochronological sample (76 kg) was collected from orthopyroxenite in the 422/3 outcrop. Eighteen zircon grains were extracted from the sample using heavy liquids. Geochronological studies of the zircons were conducted using a SIMS SHRIMP-II (Secondary Ion Mass Spectrometry on a Sensitive High-Resolution Ion Micro Probe instrument) method.\u003c/p\u003e \u003cp\u003eThe selected zircons were mounted in an epoxy disk (2.5 cm in diameter) with international zircon standards (TEMORA and 91500) using a microscope. They were then abraded to approximately half their original thickness and polished. Before analysis, all samples were coated with a conductive gold layer in a cathodic vacuum nebulizer (duration of one minute, current of 20 mA). Subsequently, the zircon grains were documented using a CamScan МХ2500 scanning electron microscope (CamScan Electron Optics, Ltd, Great Britain) with a CLI/QUA2 system for cathodoluminescence (CL) and back-scattered electron (BSE) imaging. This property was used to study the internal zircon structure. The working distance was 25‒28 mm, the accelerating voltage was 20 kV, and the current of the focused beam on the Faraday cylinder was 4‒6 nA.\u003c/p\u003e \u003cp\u003eMeasurements of the U-Pb ratios were carried out according to the method (Schuth et al. \u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e2012\u003c/span\u003e) described in (Williams \u003cspan citationid=\"CR58\" class=\"CitationRef\"\u003e1998\u003c/span\u003e). The intensity of the primary O\u003csup\u003e2\u0026minus;\u003c/sup\u003e ion beam was 4 nA, with a spot diameter of approximately 30 \u0026micro;m and a pit depth of 2 \u0026micro;m. The U-Pb ratios were normalized to that in Temora standard zircon (0.0668), which corresponds to the \u003csup\u003e206\u003c/sup\u003ePb/\u003csup\u003e238\u003c/sup\u003eU age of 416.75\u0026thinsp;\u0026plusmn;\u0026thinsp;0.24 Ma (Black et al. \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2003\u003c/span\u003e). The 91500 standard zircon with an average U content of 81.2 ppm, a \u003csup\u003e206\u003c/sup\u003ePb/\u003csup\u003e238\u003c/sup\u003eU age of 1062.4\u0026thinsp;\u0026plusmn;\u0026thinsp;0.4 Ma (Wiedenbeck et al. \u003cspan citationid=\"CR57\" class=\"CitationRef\"\u003e1995\u003c/span\u003e), was employed as the standard for uranium and radiogenic lead concentrations. The obtained data were processed using SQUID software (Ludwig \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e2001\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eIndividual analyses (ratios and ages) are presented with uncertainties at a 1σ level, whereas uncertainties in calculated ages, including concordant ones, are provided at a 2σ level. Concordia diagrams were plotted using the ISOPLOT/EX software (Ludwig \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e2003\u003c/span\u003e). A correction was made to non-radiogenic Pb based on the measured \u003csup\u003e204\u003c/sup\u003ePb and modern Pb isotope compositions in the Stacey-Kramers model (Stacey and Kramers \u003cspan citationid=\"CR53\" class=\"CitationRef\"\u003e1975\u003c/span\u003e).\u003c/p\u003e "},{"header":"Geology of Ore Horizon 330","content":"\u003cdiv id=\"Sec8\" class=\"Section3\"\u003e \u003ch2\u003eGeneral Description\u003c/h2\u003e \u003cp\u003eOH330 was discovered in the 1930s because of exploration work on the western slope of Mt. Sopcha (Monchepluton). It is a gently dipping sill-like bed-shaped body with a thickness of 4\u0026ndash;6 m (up to 13 m in some bulges). The drilling data indicate that the body extends along the entire perimeter of the Sopcha intrusion at a distance of 3300 m and a width of 1200 m. The thickest and most comprehensive section of the OH330 has been revealed within its northwest outcrops. In general, the section is represented (from bottom to top) by dunite, harzburgite, and inequigranular orthopyroxenite. In the east, the OH330 section is typically diminished by the notable absence or near-absence of dunite and harzburgite, resulting in a representation of orthopyroxenite on the eastern flank. The OH330 rocks exhibit disseminated sulfide chalcopyrite-pentlandite-pyrrhotine mineralization in amounts ranging from rare grains to 2\u0026ndash;3 wt% in coarse-grained orthopyroxenite and in the upper part of a harzburgite interlayer (Chashchin and Petrov \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). The average Ni content around the deposit is 0.46 wt%, Cu 0.23 wt%, Pt 0.24 ppm, Pd 0.93 ppm, and Pt\u0026thinsp;+\u0026thinsp;Pd\u0026thinsp;=\u0026thinsp;1.17 ppm, with a Pd/Pt ratio of 3.9 (Chashchin and Ivanchenko \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e2022\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eThe age of OH330 was previously determined by the Sm-Nd method from rock-forming minerals, sulfides, and the whole-rock of harzburgite as 2451\u0026thinsp;\u0026plusmn;\u0026thinsp;64 Ma with ε\u003csub\u003eNd\u003c/sub\u003e = -6.0\u0026thinsp;\u0026plusmn;\u0026thinsp;0.6 (Chashchin et al. \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e2016\u003c/span\u003e). This suggests that OH330 was formed later than the rocks in the Sopcha intrusion. Its formation is associated with a mantle source that was subjected to more intense crustal contamination than the Sopcha orthopyroxenite with ε\u003csub\u003eNd\u003c/sub\u003e values ​​from +\u0026thinsp;1.2 to -2.3 (Bayanova et al. \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2004\u003c/span\u003e).\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv id=\"Sec9\" class=\"Section2\"\u003e \u003ch2\u003eGeological Structure\u003c/h2\u003e \u003cp\u003eThe results of the OH330 sections study are presented in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e. The obtained data indicate that the thickness of OH330 in section 422 is 5.5 m, while that in section 423 it is 5.2 m (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). A 1-meter thick dunite with an adcumulate texture is present in the basement of section 422 (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ee). It comprises idiomorphic olivine grains with a size of 1\u0026ndash;3 mm and features fine chromite dissemination (olivine-chromite cumulus) (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ea). Harzburgite (orthopyroxene-olivine cumulus) occurs above the dunite in section 422 and in the basement of section 423, with thicknesses of 2.3 and 2.2 m, respectively (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). In the lower part of the interlayer, this rock is monotonous (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ed), while in the upper part, it usually has a finely banded structure due to alternating interlayers with varying olivine contents (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ec). It is sometimes observed to form complex bends and small folds, which are considered evidence of a viscous melt flow (Eliseev \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e1953\u003c/span\u003e; Sharkov \u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e2006\u003c/span\u003e). Harzburgite comprises composed of idiomorphic (rarely xenomorphic) olivine grains (0.5\u0026ndash;1 mm) and subordinated orthopyroxene grains (ca. 1 mm), with secondary minerals (tremolite, talc) partially developed after these grains (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eb).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe OH330 section is completed by orthopyroxenite (orthopyroxene cumulus), which is 2.2 m (section 422) and 3.0 m (section 423; Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). These units exhibit various structural forms and comprise two to three interlayers, each characterized by a distinct grain-size distribution. An interlayer of medium- to coarse-grained orthopyroxenite with thicknesses of 0.9 m (section 422) and 1.5 m (section 423) formed in the basement of the orthopyroxenite when in contact with harzburgite (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eb). The rocks in question were composed of partially amphibolized prismatic orthopyroxene crystals ranging in size from 2 to 5\u0026ndash;6 mm (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ec). At a higher level in the section, this rock is replaced by an interlayer of fine- and medium-grained slightly amphibolized orthopyroxenite, which sometimes contains olivine, with thickness of 0.4 m (section 422) and 1.5 m (section 423) (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ea). This orthopyroxenite displays an inequigranular composition comprising individual tabular grains of orthopyroxene with a size of 2\u0026ndash;2.5 mm, set against a background of a fine-grained matrix, measuring ca.1 mm (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ed). In section 422, the upper part of the orthopyroxenite contains an interlayer of equigranular fine-grained orthopyroxenite with a thickness of 0.9 m (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). It was composed of idiomorphic and sub-idiomorphic orthopyroxene grains with a size of approximately 0.5\u0026ndash;1 mm with rare grains of intercumulus plagioclase (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ee).\u003c/p\u003e \u003cp\u003eOlivine orthopyroxenite (orthopyroxene cumulates) of the host rocks of the OH330 formation have a visible thickness of 0.5 m and occur in the hanging and footwalls (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). Furthermore, these rocks are developed at elevations of 12 and 38 m above the OH330 section, and 65 and 90 m below the section (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ed). The rock is predominantly composed of tabular grains of orthopyroxene with a size of 1\u0026ndash;2 mm and sub-idiomorphic grains of olivine with an amount of 5\u0026ndash;10 vol% and a size of 0.5\u0026ndash;2 mm (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ef-g). The OH330 hanging wall contained eruptive auto-breccia represented by debris from dunite (section 422; Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ef) and harzburgite (section 423) in the olivine orthopyroxenite (Eliseev \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e1953\u003c/span\u003e; Konnikov and Orsoev \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e1991\u003c/span\u003e; Orsoev et al. \u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e1994\u003c/span\u003e; Karykowski et al. \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e2018\u003c/span\u003e; Chashchin and Petrov \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). The debris exhibited a polygonal and rounded shape with a size of 2\u0026ndash;5 cm. They are characterized by sharp irregular contacts with the olivine orthopyroxenite cementing them (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eh). The presence of eruptive breccia indicates a later injection of olivine orthopyroxenite compared with OH330.\u003c/p\u003e \u003c/div\u003e "},{"header":"Mineralogy","content":"\u003cp\u003eOlivine and orthopyroxene are the main rock-forming minerals of OH330. All rocks of OH330 contain accessory chromite in amount ranging from rare grains to 1\u0026ndash;2 vol% in dunite, which is present as both homogeneous cumulate grains and zoned grains (Chashchin and Savchenko \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). The secondary minerals included chlorite, talc, and amphiboles of two types, tremolite and Mg-hornblendite (Chashchin and Savchenko \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). A noteworthy aspect of OH330 is the presence of sulfide mineralization in the form of intercumulus dissemination within the interstices of olivine and orthopyroxene in harzburgite and orthopyroxenite, with an estimated concentration ranging from rare grains to 2\u0026ndash;5 vol%. This mineralization is associated with PGE minerals, which include Pt-Fe alloys, sulfides, arsenides, sulfoarsenides, bismuth-tellurides, tellurium-bismuthides and tellurides (Chashchin and Petrov \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2023\u003c/span\u003e).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec11\" class=\"Section2\"\u003e \u003ch2\u003eOlivine\u003c/h2\u003e \u003cp\u003eOlivine is predominantly represented by polygonal grains with size of 1\u0026ndash;2 mm. Olivine from the OH330 dunite exhibited the most magnesian composition (Fo\u003csub\u003e86.7\u003c/sub\u003e). The olivine composition in the harzburgite and orthopyroxenite of OH330 lie in the Fo\u003csub\u003e86.2\u0026ndash;83.8\u003c/sub\u003e range. Olivine from the host olivine orthopyroxenite had a similar composition and was within the range Fo\u003csub\u003e86.0\u0026ndash;83.4\u003c/sub\u003e (Table \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e). In terms of the NiO (wt%) and MnO (wt%) ratios with Fo (mol%), olivines from all the rocks OH330 and host olivine orthopyroxenites are similar, while the content of NiO and MnO in them does not depend on changes in Fo (Figs.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ea-b). Olivines from OH330 and the host rocks were distinguished by their lower NiO contents compared to those of the NKT intrusion rocks and a lower Fo value compared to olivines from dunite in the Dunite Block (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ea), yet they exhibited similarities to those of the NKT intrusion in terms of their MnO content (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eb).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec12\" class=\"Section2\"\u003e \u003ch2\u003eOrthopyroxene\u003c/h2\u003e \u003cp\u003eOrthopyroxenes in harzburgite and orthopyroxenite are represented by prismatic crystals of size 2\u0026ndash;3 mm and, in rare cases, by isometric grains with of size 0.5\u0026ndash;0.3 mm. The orthopyroxenes exhibited a narrow range of enstatite molecule contents (En\u003csub\u003e83.9\u0026ndash;82.5\u003c/sub\u003e) and slight variations in the Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e (1.9\u0026ndash;1.5 wt%), CaO (2.0\u0026ndash;1.6 wt%), and Cr\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e (0.8\u0026ndash;0.6 wt%) contents (Table \u003cspan refid=\"MOESM2\" class=\"InternalRef\"\u003eS2\u003c/span\u003e; Figs.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ea-c). The orthopyroxenes from the host orthopyroxenite exhibit similar values of the enstatite molecule content (En\u003csub\u003e83.1\u0026ndash;82.2\u003c/sub\u003e) and are mainly similar to the OH330 rocks in terms of chemical composition, with the exception of some specific cases with lower contents of CaO and Cr\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e (Table \u003cspan refid=\"MOESM2\" class=\"InternalRef\"\u003eS2\u003c/span\u003e; Figs.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eb-c). The orthopyroxenes from the OH330 and host rocks most closely correspond to those from the harzburgite and orthopyroxenite of the NKT intrusion in terms of chemical composition. They were located in the fields of their compositions (Figs.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ea-d). The exceptions were the lower NiO contents in the OH330 and host orthopyroxenes rocks compared to the NKT intrusion rocks (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ee). There was no correlation between the En content in OH330 orthopyroxenes and the Fo content in coexisting olivines. All samples exhibited above the 1:1 linear correlation between Fo content in olivines and En in orthopyroxenes due to the higher Fo content in the former (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ed).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e illustrates the variations in the chemical composition of rock-forming minerals along the OH330 sections. The results obtained indicate a consistent increase in the En and Cr\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e content of the orthopyroxenes from harzburgite to coarse-grained orthopyroxenite (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e "},{"header":"PT Crystallization Conditions for OH330 and Host Rocks","content":"\u003cp\u003eIn order to calculate the temperature and pressure of the crystallization of the OH330 and host rocks, we used the chemical compositions of coexisting olivines and orthopyroxenes presented in Tables S1 and S2. The olivine-melt and orthopyroxene-melt thermometers, and an orthopyroxene barometer (Putirka \u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e2008\u003c/span\u003e), were employed. The resulting calculation outcomes are presented in Table \u003cspan refid=\"MOESM3\" class=\"InternalRef\"\u003eS3\u003c/span\u003e. The data indicate that the temperature of the olivine-melt for water-free conditions for the OH330 rocks is 1800\u0026ndash;1780\u0026deg;C. The temperature was slightly higher for the host olivine orthopyroxenite, within the 1810\u0026ndash;1790\u0026deg;C range (Table \u003cspan refid=\"MOESM3\" class=\"InternalRef\"\u003eS3\u003c/span\u003e). In the presence of water, the temperature of the olivine-melt equilibrium for the OH330 rocks decreased to 1600\u0026ndash;1470\u0026deg;C, whereas that for the host olivine orthopyroxenite was 1670\u0026ndash;1620\u0026deg;C (Table \u003cspan refid=\"MOESM3\" class=\"InternalRef\"\u003eS3\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eThe temperature of orthopyroxene crystallization of the OH330 rocks in the absence of water was determined using two equations (Putirka \u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e2008\u003c/span\u003e). According to the first equation, the temperature of the orthopyroxene-melt equilibrium in the OH330 rocks is 1240\u0026ndash;1100\u0026deg;C, while according to the second equation, it has a wider range of 1290\u0026ndash;1120\u0026deg;C. With regard to the host rocks, their temperature was more stable, falling within the 1240\u0026ndash;1220\u0026deg;C range, in accordance with the first equation. In contrast, the temperature was considerably higher according to the second equation, reaching 1310\u0026ndash;1270\u0026deg;C (Table \u003cspan refid=\"MOESM3\" class=\"InternalRef\"\u003eS3\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eThe pressure calculations indicated that the OH330 rocks exhibited a pressure range of 1\u0026ndash;6 kbar, with an average value of 3.5\u0026thinsp;\u0026plusmn;\u0026thinsp;1.5 kbar. In contrast, the host rocks exhibited a more stable pressure range of 6\u0026ndash;8 kbar, with an average value of 6.1\u0026thinsp;\u0026plusmn;\u0026thinsp;0.7 kbar (Table \u003cspan refid=\"MOESM3\" class=\"InternalRef\"\u003eS3\u003c/span\u003e).\u003c/p\u003e \u003c/div\u003e "},{"header":"Whole-rock Chemical Composition","content":"\u003cp\u003eThe contents of major and trace elements are given in Table \u003cspan refid=\"MOESM4\" class=\"InternalRef\"\u003eS4\u003c/span\u003e and Figs.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e\u0026ndash;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e9\u003c/span\u003e.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec15\" class=\"Section2\"\u003e \u003ch2\u003eMajor Elements\u003c/h2\u003e \u003cp\u003eThe maximum MgO concentration in dunite OH330 was determined as 42.3 wt%. In harzburgite, the MgO content is in the range of 36.2\u0026ndash;39.6 wt% (on average 37.95\u0026thinsp;\u0026plusmn;\u0026thinsp;1.03 wt%), in orthopyroxenite \u0026ndash; 28.2\u0026ndash;31.4 wt% (on average 30.10\u0026thinsp;\u0026plusmn;\u0026thinsp;1.06 wt%), and in host olivine orthopyroxenite \u0026ndash; 28.9\u0026ndash;30.7 wt% (on average 29.98\u0026thinsp;\u0026plusmn;\u0026thinsp;0.46 wt%; Table \u003cspan refid=\"MOESM4\" class=\"InternalRef\"\u003eS4\u003c/span\u003e). At the same time, the Mg# values of all studied rocks is in a narrow range (0.77\u0026ndash;0.72; Table \u003cspan refid=\"MOESM4\" class=\"InternalRef\"\u003eS4\u003c/span\u003e). The SiO\u003csub\u003e2\u003c/sub\u003e contents exhibit a gradual increase from 38.7 wt% in harzburgite to 53.4 wt% in orthopyroxenite (Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e7\u003c/span\u003ea). The Al₂O₃ content is 0.32 wt% in dunite, varying from 0.00 to 0.52 wt% in harzburgite and from 1.6 to 2.3 wt% in orthopyroxenite (Table \u003cspan refid=\"MOESM4\" class=\"InternalRef\"\u003eS4\u003c/span\u003e, Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e7\u003c/span\u003eb). The CaO contents were 0.14\u0026ndash;0.46 wt% in harzburgite and 1.6\u0026ndash;1.4 wt% in orthopyroxenite (Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e7\u003c/span\u003ec). It is noteworthy that the iron contents exhibit a consistent decline from 13.0 wt% of FeO\u003csub\u003etot\u003c/sub\u003e in dunite to 12.5\u0026ndash;11.8 wt% in harzburgite and 11.0\u0026ndash;9.4 wt% in orthopyroxenite (Table \u003cspan refid=\"MOESM4\" class=\"InternalRef\"\u003eS4\u003c/span\u003e, Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e7\u003c/span\u003ed). It should be noted that there is a positive correlation between the contents of MgO and FeO\u003csub\u003etot\u003c/sub\u003e, whereas negative correlations are determined between the contents of MgO and SiO\u003csub\u003e2\u003c/sub\u003e, Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e, CaO, and Cr\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e, which are described by regression equations (Figs.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e7\u003c/span\u003ea-e). In general, the distribution of major elements is primarily influenced by variations in the modal quantities of olivine and orthopyroxene (Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e7\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eA regular decrease in the contents of MgO and, to a lesser extent, FeO\u003csub\u003etot\u003c/sub\u003e is observed with an increase in SiO\u003csub\u003e2\u003c/sub\u003e contents in the OH330 sections from the bottom to the top (from dunite and harzburgite to orthopyroxenite) (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e). Furthermore, the OH330 dunite differs from the Monchepluton dunite in its higher contents of FeO\u003csub\u003etot\u003c/sub\u003e and lower contents of MgO and Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e. The OH330 harzburgite and orthopyroxenite differed from the corresponding rocks of the NKT and Sopcha intrusions in lower contents of Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e and CaO (Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e7\u003c/span\u003e). It is worth noting that the harzburgite and orthopyroxenite of the OH330 described by Karykowski et al. (\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e2018\u003c/span\u003e) have a less magnesian composition than the corresponding rocks in our data (Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e7\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eThe host olivine orthopyroxenite displayed higher contents of Al₂O₃ (3.2\u0026ndash;2.0 wt%) and CaO (2.4\u0026ndash;1.5 wt%) but lower Ni concentrations than the OH330 orthopyroxenite, while the other major elements were present in comparable amounts (Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e7\u003c/span\u003e).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec16\" class=\"Section2\"\u003e \u003ch2\u003eTrace elements\u003c/h2\u003e \u003cp\u003eThe OH330 dunite and harzburgite exhibited low REE and trace elements contents in the 0.04\u0026ndash;0.7 range in relation to the primitive mantle (Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e8\u003c/span\u003ea). The REE\u003csub\u003etot\u003c/sub\u003e contents did not exceed 1 ppm in these rocks (Table \u003cspan refid=\"MOESM4\" class=\"InternalRef\"\u003eS4\u003c/span\u003e). Normalized to the primitive mantle, the REE plots form gentle U-like curves with negative slopes in the LREE field and positive slopes in the range of Gd-Lu elements (Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e8\u003c/span\u003ea). This peculiarity of the REE spectra in dunite and harzburgite of OH330 is reflected in positive values of (Ce/Sm)\u003csub\u003eN\u003c/sub\u003e varying from 1.21 to 1.86 and low values of (Gd/Yb)\u003csub\u003eN\u003c/sub\u003e, which are in the 0.87\u0026ndash;0.37 range (Table \u003cspan refid=\"MOESM4\" class=\"InternalRef\"\u003eS4\u003c/span\u003e). U, Ta, and Sr form positive anomalies (Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e8\u003c/span\u003ea), and a positive Eu anomaly is observed for dunite (Eu/Eu*)\u003csub\u003eN\u003c/sub\u003e = 1.56, while mostly negative Eu anomalies are observed for harzburgite (Eu/Eu*)\u003csub\u003eN\u003c/sub\u003e = 0.59\u0026ndash;1.04 (Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e8\u003c/span\u003ea, Table \u003cspan refid=\"MOESM4\" class=\"InternalRef\"\u003eS4\u003c/span\u003e). The obtained trace-element distribution features are comparable to those observed in harzburgite OH330 according to Karykowski et al. (\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e2018\u003c/span\u003e), with the exception of higher concentrations and positive Th anomalies (Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e8\u003c/span\u003ea).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe OH330 orthopyroxenite exhibited elevated concentrations of REE and trace elements, with values of 0.2\u0026ndash;1.7 in relation to the primitive mantle (Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e8\u003c/span\u003eb). The REE\u003csub\u003etot\u003c/sub\u003e contents of orthopyroxenite ranged from 2.0 to 4.5 ppm (with an average of 3.16 ppm). The REE\u003csub\u003etot\u003c/sub\u003e highest concentrations are observed in the medium-to-coarse-grained orthopyroxenite of section 422 and the fine-to-medium-grained orthopyroxenite of section 423 (Table \u003cspan refid=\"MOESM4\" class=\"InternalRef\"\u003eS4\u003c/span\u003e). The REE distribution in the OH330 orthopyroxenite was characterized by greater fractionation in the LREE area than in harzburgite and lack of fractionation in the Gd-Lu range (Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e8\u003c/span\u003eb). This is indicated by the positive of (Ce/Sm)\u003csub\u003eN\u003c/sub\u003e values varying from 1.82 to 2.22 and the low (Gd/Yb)\u003csub\u003eN\u003c/sub\u003e values, which are in the range of 1.02\u0026ndash;0.69 (Table \u003cspan refid=\"MOESM4\" class=\"InternalRef\"\u003eS4\u003c/span\u003e). Slightly pronounced negative Eu anomalies (or their absence) are detected in the orthopyroxenites, with (Eu/Eu*)\u003csub\u003eN\u003c/sub\u003e values ranging from 0.83 to 0.97 (Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e8\u003c/span\u003eb, Table \u003cspan refid=\"MOESM4\" class=\"InternalRef\"\u003eS4\u003c/span\u003e). The OH330 orthopyroxenite typically exhibits negative Nb-Ta anomalies and positive U anomalies (Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e8\u003c/span\u003eb). It is important to note that the OH330 orthopyroxenite analyzed by Karykowski et al. (\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e2018\u003c/span\u003e) differs from the aforementioned samples in that it exhibits positive Th, Sr, Zr, and Hf anomalies while exhibiting similar negative Nb-Ta anomalies (Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e8\u003c/span\u003eb).\u003c/p\u003e \u003cp\u003eThe host olivine orthopyroxenite exhibited REE and trace element concentrations of 1.1\u0026ndash;1.0 in relation to the primitive mantle (Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e8\u003c/span\u003ec). REE\u003csub\u003etot\u003c/sub\u003e contents in these orthopyroxenite were in the 4.4\u0026ndash;1.3 ppm range, with the highest REE\u003csub\u003etot\u003c/sub\u003e concentrations detected in the olivine orthopyroxenite from the hanging wall and footwall in comparison with the olivine orthopyroxenite on removed from the contact. The maximum REE content was determined in the olivine orthopyroxenite of the footwall of section 422 (Table \u003cspan refid=\"MOESM4\" class=\"InternalRef\"\u003eS4\u003c/span\u003e). The REE\u003csub\u003etot\u003c/sub\u003e distribution in the olivine orthopyroxenite was less fractionated in the LREE area than in the OH330 orthopyroxenite, and a slight positive inclination was observed in the HREE area (Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e8\u003c/span\u003ec). The (Ce/Sm)\u003csub\u003eN\u003c/sub\u003e values varied from 1.41 to 2.69, whereas the (Gd/Yb)\u003csub\u003eN\u003c/sub\u003e value varied from 0.52 to 1.27 (Table \u003cspan refid=\"MOESM4\" class=\"InternalRef\"\u003eS4\u003c/span\u003e). These rocks exhibit negative Nb and variable Eu anomalies with (Eu/Eu*)\u003csub\u003eN\u003c/sub\u003e values ​​varying from 0.80 to 1.51 (Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e8\u003c/span\u003ea, Table \u003cspan refid=\"MOESM4\" class=\"InternalRef\"\u003eS4\u003c/span\u003e). Olivine orthopyroxenite according to Karykowski et al. (\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e2018\u003c/span\u003e) differs markedly from the samples we studied because of lower LREE distribution and positive anomalies of Th, Zr and Hf (Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e8\u003c/span\u003eb).\u003c/p\u003e \u003cp\u003eThe distributions of REE\u003csub\u003etot\u003c/sub\u003e, La, and trace elements in the OH330 sections exhibit low values in dunite and harzburgite and increased values in orthopyroxenite (Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e9\u003c/span\u003e). The content of these elements in the host olivine orthopyroxenite is highly variable. In section 423, the concentrations of these elements were lower than those of the OH330 orthopyroxenite. Conversely, the olivine orthopyroxenite from the hanging wall of section 422 exhibits comparable concentrations to the OH330 orthopyroxenite, while those from the footwall of the section 422 display abnormally high concentrations of these elements (Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e9\u003c/span\u003e).\u003c/p\u003e \u003c/div\u003e "},{"header":"SIMS SHRIMP U-Pb Age of Zircon","content":"\u003cp\u003eIn total, 18 local U-Pb isotope analyses were conducted on 15 zircon grains. The results are presented in Table \u003cspan refid=\"MOESM5\" class=\"InternalRef\"\u003eS5\u003c/span\u003e and illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003e. The studied zircons were divided into two populations based on isotopic parameters.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe first population included eight zircon grains of different morphologies. Five of the zircon grains exhibit a short prismatic shape and crystal fragments ranging in size from 90 \u0026times; 60 to 230 \u0026times; 140 \u0026micro;m, with length-to-width ratio varying from 1.5:1 to 2.1:1 (Fig.\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003ea). The two zircon grains exhibit oval and rounded shapes with dimensions of 90 \u0026times; 45 \u0026micro;m and 90 \u0026times; 90 \u0026micro;m, respectively. One zircon grain exhibited an elongated and resorbed shape with dimensions of 80 \u0026times; 20 \u0026micro;m and a length-to-width ratio of 4:1 (Fig.\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003ea). According to CL characteristics, most of zircon grains in this population exhibit a heterogeneous internal structure comprising two to three domains that differ in brightness within the CL image. In some instances, the internal domains exhibit a combination of small dark and light areas, as observed in grain 17 (Fig.\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003ea). Additionally, in one zircon grain with a homogeneous CL-dark image, small irregularly shaped areas with a CL-gray image can be observed (19.1 and 20.1, Fig.\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003ea). One zircon from this population exhibits oscillatory zoning, which is defined as fine, periodic variations in the mineral composition, in the absence of a visible core and with a thin, discontinuous rim (grain 13, Fig.\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003ea).\u003c/p\u003e \u003cp\u003eZircons from this population exhibit considerable variability in U and Th contents, ranging from 138 to 1303 ppm U and 8 to 4610 ppm Th. The average contents of these elements are (n\u0026thinsp;=\u0026thinsp;9): U\u0026thinsp;=\u0026thinsp;537\u0026thinsp;\u0026plusmn;\u0026thinsp;352 ppm, Th\u0026thinsp;=\u0026thinsp;1234\u0026thinsp;\u0026plusmn;\u0026thinsp;1331 ppm, and Th/U\u0026thinsp;=\u0026thinsp;1.91\u0026thinsp;\u0026plusmn;\u0026thinsp;1.68 (Table \u003cspan refid=\"MOESM5\" class=\"InternalRef\"\u003eS5\u003c/span\u003e). The variations in U and Th contents observed in different magmatic zircon domains were not correlated with changes in the brightness of their CL images. For instance, the U content in the seven CL-dark grey domains variesd from 158 to 1303 ppm, whereas the Th content varied from 8 to 1609 ppm. In contrast, in the two CL-light grey domains, the U content was 226 and 289 ppm, and the Th content was 64 and 282 ppm (Table \u003cspan refid=\"MOESM5\" class=\"InternalRef\"\u003eS5\u003c/span\u003e, Fig.\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003ea). There was no correlation between U and Th contents in zircons from this population (Fig.\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003eb). All zircons from the first population exhibited similar U and Pb isotopic ratios (Table \u003cspan refid=\"MOESM5\" class=\"InternalRef\"\u003eS5\u003c/span\u003e), indicating the absence of a significant impact of secondary processes and contamination by a substance of a different composition on the U-Pb isotope system. All obtained age values were concordant or subconcordant.\u003c/p\u003e \u003cp\u003eA concordant U-Pb age was obtained for this zircon population, equal to 2492.5\u0026thinsp;\u0026plusmn;\u0026thinsp;4.1 Ma and, MSWD\u0026thinsp;=\u0026thinsp;0.68 (n\u0026thinsp;=\u0026thinsp;9, 2σ) (Fig.\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003ec). Age is considered concordant when the ellipses of analytical errors intersect the concordia. This result is corroborated by the low degree of discordance, which ranges from \u0026minus;\u0026thinsp;0.16 to 3.62 (Table \u003cspan refid=\"MOESM5\" class=\"InternalRef\"\u003eS5\u003c/span\u003e). The concordant age is equivalent to the weighted average \u003csup\u003e207\u003c/sup\u003ePb/\u003csup\u003e206\u003c/sup\u003ePb age of zircons from this population, which is 2492.6\u0026thinsp;\u0026plusmn;\u0026thinsp;4.2 Ma, MSWD\u0026thinsp;=\u0026thinsp;0.66 (n\u0026thinsp;=\u0026thinsp;9, 2σ) (Fig.\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003ed). The resulting concordant age can be interpreted as the time zircon magmatic crystallization and accordingly the age of the OH330 rocks.\u003c/p\u003e \u003cp\u003eThe second zircon population comprises seven zircon grains represented by long-prismatic crystals and their fragments. These grains are sometimes well-preserved with crystallographic shapes ranging in size from 90 \u0026times; 45 to 200 \u0026times; 80 \u0026micro;m and a length-to-width ratios ranging from 2:1 to 4:1 (Fig.\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003ea). The majority of zircons in this population exhibit oscillatory zoning in CL images (grains 7, 9, 10, and 14\u0026ndash;15, Fig.\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003ea). In some cases, they contain a core in the absence of rims. The remaining zircons display a more homogeneous internal structure, typically comprising two to three domains that differ in brightness in the CL image. The U and Th contents of this zircon population, as well as those of the zircons of the first population, exhibit significant variability. They range from 212 to 1829 ppm U and from 78 to 1090 ppm Th, with Th/U ratios ranging from 0.17 to 0.62 (Table \u003cspan refid=\"MOESM5\" class=\"InternalRef\"\u003eS5\u003c/span\u003e). The average values of these components were as follows (n\u0026thinsp;=\u0026thinsp;9): 674\u0026thinsp;\u0026plusmn;\u0026thinsp;458 ppm U, 314\u0026thinsp;\u0026plusmn;\u0026thinsp;269 ppm Th, and Th/U\u0026thinsp;=\u0026thinsp;0.43\u0026thinsp;\u0026plusmn;\u0026thinsp;0.10. Furthermore, there is a strong positive correlation between the U and Th contents (Fig.\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003eb).\u003c/p\u003e \u003cp\u003eThe concordant U-Pb age of this zircon population is 2818.0\u0026thinsp;\u0026plusmn;\u0026thinsp;3.1 Ma, with a MSWD\u0026thinsp;=\u0026thinsp;1.8 (n\u0026thinsp;=\u0026thinsp;9, 2σ) (Fig.\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003ec). A weighted average \u003csup\u003e207\u003c/sup\u003ePb/\u003csup\u003e206\u003c/sup\u003ePb age of 2818\u0026thinsp;\u0026plusmn;\u0026thinsp;3.2 Ma was determined with an MSWD\u0026thinsp;=\u0026thinsp;1.7 (n\u0026thinsp;=\u0026thinsp;9, 2σ) (Fig.\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003ed). This concordant age provides a rationale for considering the zircon of the second population xenocryst, as extracted from the rocks of the Archean granitoid basement. This is because it falls within the age range of the Archean granitoid of the Kola Block, which is estimated to be between 2835 and 2736 Ma (Chen et al. \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e1998\u003c/span\u003e; Pripachkin et al. \u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e2020\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eIt is important to note that the CL-light grey domain 4.1 of xenocryst zircon differs from other zircons of this population in terms of its lowest contents of U\u0026thinsp;=\u0026thinsp;212 ppm and \u003csup\u003e206\u003c/sup\u003ePb* = 89 ppm, as well as its lower values of Pb-U isotopic parameters: \u003csup\u003e207\u003c/sup\u003ePb*/\u003csup\u003e235\u003c/sup\u003eU = 13.55\u0026thinsp;\u0026plusmn;\u0026thinsp;0.16 and \u003csup\u003e206\u003c/sup\u003ePb*/\u003csup\u003e238\u003c/sup\u003eU = 0.4894\u0026thinsp;\u0026plusmn;\u0026thinsp;0.0054 (Table \u003cspan refid=\"MOESM5\" class=\"InternalRef\"\u003eS5\u003c/span\u003e). In addition, this domain exhibits a high degree of discordance (\u003cem\u003eD\u003c/em\u003e\u0026thinsp;=\u0026thinsp;10.32, Table \u003cspan refid=\"MOESM5\" class=\"InternalRef\"\u003eS5\u003c/span\u003e). These results suggest that this zicron was subjected to later metamorphic-metasomatic processes.\u003c/p\u003e \u003c/div\u003e"},{"header":"Discussion","content":"\u003cdiv id=\"Sec19\" class=\"Section2\"\u003e \u003ch2\u003eTh/U Ratio in Magmatic Zircon and Geochronology\u003c/h2\u003e \u003cp\u003eThe studied magmatic zircon consists of by individual grains with partially preserved facets and partially resorbed grains (Fig.\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003ea). It is evident that such forms reflect the complex evolution of their formation. In terms of morphology, it is similar to zircon from rocks of the olivine horizon of the Nyud intrusion (Chashchin and Sergeev \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2023\u003c/span\u003e), although it is smaller. However, it differs significantly from metagabbronorite zircons from the Vuruchuayvench intrusion from Monchepluton, represented by fragments of prismatic grains (Rundkvist et al. \u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e2015\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eThis magmatic zircon displays a wide range of U and Th concentrations, with values ranging from 138 to 1303 ppm and 8 to 4610 ppm, respectively, and an average Th/U ratio is 1.91\u0026thinsp;\u0026plusmn;\u0026thinsp;1.68 (Table \u003cspan refid=\"MOESM5\" class=\"InternalRef\"\u003eS5\u003c/span\u003e). In terms of this value, it is most similar to zircon from the Nyud olivine horizon (1.80; Chashchin and Sergeev \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). At the same time, it should be noted that in mafic-ultramafic rocks, especially in layered intrusions, the Th/U value in zircons varies significantly. In particular, the Th/U values in zircon from the rocks of the lower Platreef, Bushveld is 0.6\u0026thinsp;\u0026plusmn;\u0026thinsp;0.2, and of the upper Platreef is 0.77\u0026thinsp;\u0026plusmn;\u0026thinsp;0.4 (Yudovskaya et al. \u003cspan citationid=\"CR60\" class=\"CitationRef\"\u003e2013\u003c/span\u003e). A comparable Th/U ratio was identified in zircon from the Great Dyke websterite in Zimbabwe (0.61; Armstrong and Wilson \u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e2000\u003c/span\u003e). A higher Th/U ratio was determined in zircon from the Merensky Reef in Bushveld (2.5\u0026thinsp;\u0026plusmn;\u0026thinsp;0.8; Yudovskaya et al. \u003cspan citationid=\"CR60\" class=\"CitationRef\"\u003e2013\u003c/span\u003e), as well as from the metagabbro of the Vuruchuayvench intrusion (2.86; Rundkvist et al. \u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e2015\u003c/span\u003e). The data presented demonstrate that Th/U value in zircon is influenced by both the composition of the parental magma and fractionation processes in the intermediate hearth and magma chamber.\u003c/p\u003e \u003cp\u003eThe U content of sample 422/3 of orthopyroxenite was 0.014 ppm, the Th content was 0.05 ppm, and the Th/U ratio was 3.57 (Table \u003cspan refid=\"MOESM4\" class=\"InternalRef\"\u003eS4\u003c/span\u003e). Consequently, the distribution coefficient K\u003csub\u003eD\u003c/sub\u003eTh/U\u003csub\u003e(zircon/rock)\u003c/sub\u003e was 0.54, which was approximately 3\u0026ndash;4 times higher than that defined for zircons from gabbro (0.14; Kirkland et al. \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e2015\u003c/span\u003e) and anorthosite (0.19; Bindeman et al. \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2006\u003c/span\u003e). This may indicate that the U and Th contents in zircon OH330 are not controlled by the K\u003csub\u003eD\u003c/sub\u003eTh/U\u003csub\u003e(zircon/rock)\u003c/sub\u003e value and that its formation occurs under conditions of nonequilibrium crystallization (Wang et al., 2011). This is also evidenced by oscillatory zoning in individual zircon, which results from a process in which the growth of zircon crystals alters the adjacent melt, thereby affecting its composition (Fowler et al. \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2002\u003c/span\u003e). The presence of unusually high U and Th contents (\u0026gt;\u0026thinsp;1000 ppm) in some magmatic zircons may be attributed to the crystallization of zircon from residual intercumulus liquid enriched in U and Th (Wang et al. 2011). Moreover, because these zircons exhibit a considerable range of U and Th contents, it is feasible if the focus of residual liquid were separated from each other during the solidification process and behaved as isolated systems.\u003c/p\u003e \u003cp\u003eCurrently, there is limited geochronological data on the rocks of the NKT and Sopcha intrusions that are part of the Monchepluton ultramafic chamber. Previously, the U-Pb method by zircon determined the age of quartz norite from the bottom of the Travyanaya intrusion, which was 2507\u0026thinsp;\u0026plusmn;\u0026thinsp;9 Ma (Bayanova et al. \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2004\u003c/span\u003e). Subsequently, the same method was employed to determine the age of norite in the marginal zone of the Nittis intrusion, which was found to be 2505.5\u0026thinsp;\u0026plusmn;\u0026thinsp;7.0 Ma (Semenov et al. \u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). The similar U-Pb ages were derived from single zircons from dunite and chromium ore in the Dunite Block which make up 2500\u0026thinsp;\u0026plusmn;\u0026thinsp;10 and 2500\u0026thinsp;\u0026plusmn;\u0026thinsp;2 Ma, respectively (Chashchin and Bayanova \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). Therefore, the obtained age of orthopyroxenite OH330 (2492.5\u0026thinsp;\u0026plusmn;\u0026thinsp;4.1 Ma) within the uncertainty was younger than the ages of the lower zone rocks of the Monchepluton ultramafic subchamber. At the same time, it is close to the age of the rocks from the upper zone of the Nyud (2493\u0026thinsp;\u0026plusmn;\u0026thinsp;7 Ma; Balashov et al. \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e1993\u003c/span\u003e) and Poaz (2493\u0026thinsp;\u0026plusmn;\u0026thinsp;5 Ma; Chashchin and Bayanova \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2023\u003c/span\u003e) intrusions of the Monchepluton mafic subchamber. This indicates that the injection of OH330 magma occurred in synchrony with the crystallization of rocks in the Monchepluton mafic subchamber.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec20\" class=\"Section2\"\u003e \u003ch2\u003eSequence of OH330 formation\u003c/h2\u003e \u003cp\u003eThe geological structure, mineral, and geochemical composition of the OH330 rocks allow reconstruction of the sequence of formation. This process started with the formation of the parental melt, which resulted from the rise of the mantle diapir and its partial melting. The extent of partial melting of the mantle substrate, which is probably spinel peridotite of the fertile mantle MORB (FMM)-type, was quantified using the V-Yb ratio, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e11\u003c/span\u003e. This diagram compares the compositions of OH330 rocks with the theoretical melting trends of spinel peridotites as a function of oxygen fugacity, as presented in (Pearce et al. \u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e2000\u003c/span\u003e). The compositions of the OH330 rocks ranged from 10 to 20% melting degrees (on average ca. 15%) and was between QFM and QFM\u0026thinsp;+\u0026thinsp;1 oxygen fugacity (on average ca. QFM\u0026thinsp;+\u0026thinsp;0.5) (Fig.\u0026nbsp;\u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e11\u003c/span\u003e). It is notable that the oxygen fugacity determined for the olivine-chromite cumulus association using an oxybarometer (Ballhaus et al. \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e1991\u003c/span\u003e) was Δlog(fO\u003csub\u003e2\u003c/sub\u003e)\u003csup\u003eQFM\u003c/sup\u003e = 0.6 (Chashchin and Savchenko \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e2021\u003c/span\u003e), which is comparable to the obtained data. Noted that the composition of the host olivine orthopyroxenite lies around 13% partial melting and QFM-0.5 oxygen fugacity (Fig.\u0026nbsp;\u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e11\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eIt is likely that the liquidus temperature of the parental magma corresponded to that obtained for olivine-liquid equilibrium in aqueous conditions, which comprised 1600\u0026ndash;1470\u0026deg;C (Table \u003cspan refid=\"MOESM3\" class=\"InternalRef\"\u003eS3\u003c/span\u003e). Noted that this temperature significantly exceeds the potential temperature of the convecting mantle (1350\u0026deg;C), according to McKenzie and Bickle (\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e1988\u003c/span\u003e). The apparent contradiction can be explained by the genetic connection between the parental melt of OH330 and the rise of the mantle diapir, which occurred as a result of the activation of a long-lived Paleoproterozoic mantle plume associated with the formation of numerous layered intrusions of the Fennoscandian Shield (Sharkov et al. \u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e2000\u003c/span\u003e; Smolkin et al. \u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e2009\u003c/span\u003e). It is important to note that the equilibrium temperature of olivine-melt for anhydrous conditions in OH330 rocks corresponds to 1800\u0026ndash;1780\u0026deg;C (Table \u003cspan refid=\"MOESM3\" class=\"InternalRef\"\u003eS3\u003c/span\u003e), which raises reasonable doubts becaus it exceeds the formation temperatures of the highest-temperature komatiite and meimechite magmas (1670\u0026ndash;1600\u0026deg;C), as shown (Sobolev et al. \u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e2009\u003c/span\u003e; Nisbet et al. \u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e1993\u003c/span\u003e; Sossi and O'Neill 2016; Wilson \u003cspan citationid=\"CR59\" class=\"CitationRef\"\u003e2019\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eSubsequently, the parental melt ascended through the crust through a vertical channel and entered the chamber of the Sopcha intrusion (Fig.\u0026nbsp;\u003cspan refid=\"Fig12\" class=\"InternalRef\"\u003e12\u003c/span\u003ea). During the uplift, the magma was contaminated with crustal material, as evidenced by the Sm-Nd isotopic data of the OH330 harzburgite with a value of ε\u003csub\u003eNd\u003c/sub\u003e = -6.0\u0026thinsp;\u0026plusmn;\u0026thinsp;0.6 (Chashchin et al. \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e2016\u003c/span\u003e), as well as the presence of xenocryst zircons with an age of 2818 Ma extracted from the host Archean granitoid. This process was accompanied by an enrichment of the melt in U, Sr, and LREE, accompanied by a slight increase in the Ta and Nb contents. This result is expressed by the appearance of negative anomalies of Nb and Ta in the orthopyroxenites (Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e8\u003c/span\u003eb). Furthermore, the parental magma was saturated with S and chalcophilic elements, ultimately lead to the formation of sulfide PGE-Cu-Ni mineralization (Chashchin and Petrov \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2023\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eAfter reaching the middle part of the orthopyroxenite section of the Sopcha intrusion, the OH330 parental magma spread along the subhorizontal surface in the form of a sill-like thin body (Fig.\u0026nbsp;\u003cspan refid=\"Fig12\" class=\"InternalRef\"\u003e12\u003c/span\u003ea). The dunite-to-orthopyroxenite phase observed in the OH330 sections can be explained by the fractional crystallization of magma from bottom to the top as the temperature decreases. Furthermore, the change in olivine-rich rocks in the west of OH330 to olivine-free rocks in the east is attributed to hydrodynamic fractionation (Barnes et al. \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e2016\u003c/span\u003e) during the laminar flow of magma from west to east (Fig.\u0026nbsp;\u003cspan refid=\"Fig12\" class=\"InternalRef\"\u003e12\u003c/span\u003eb). The crystallization process did not occur simultaneously along the entire length of OH330. It started on its western flank with more primitive rocks, after which the crystallization front of a more fractionated melt proceeded from west to east. This occurred under conditions of a decrease in flow pressure and velocity in the westerly direction, which contributed to the deposition of the previously highlighted solid olivine particles. It is noteworthy that in the OH330 section, above the harzburgite layer, there is always a layer of coarse-grained orthopyroxenites, which are usually affected by amphibolization. This can be explained by the influence of the accumulated aqueous fluids in the middle of OH330.\u003c/p\u003e \u003cp\u003eThe OH330 crystallization occurred at a temperature of 1290\u0026ndash;1100\u0026deg;C, in accordance with the orthopyroxene-melt equilibrium and an average pressure of 3.5 kbar (Table \u003cspan refid=\"MOESM3\" class=\"InternalRef\"\u003eS3\u003c/span\u003e), which corresponds to a depth of approximately 10 km. At the same stage of evolution, at a temperature of ca. 1170\u0026deg;C, cumulus olivine and chromite crystallized (Chashchin and Savchenko \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). Further cooling of the OH330 rocks, starting at 1000\u0026deg;C, separated an immiscible sulfide liquid that accumulated chalcophile and platinum group elements. This process was accompanied by the crystallization of sulfides of basic metals and platinum group minerals, which proceeded to 600\u0026ndash;400\u0026deg;C (Chashchin and Petrov \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2023\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eThe presence of olivine orthopyroxenite in the lower and upper parts of OH330, which contains dunite and harzburgite autoliths, indicates that olivine orthopyroxenite formed later than 2492 Ma as a result of one additional pulse of the mantle diapir.\u003c/p\u003e \u003c/div\u003e"},{"header":"Conclusions","content":"\u003cp\u003eThe following conclusions can be drawn from the results of the conducted studies.\u003c/p\u003e\n\u003cul\u003e\n\u003cli\u003e\n\u003cp\u003eOH330 is located within the orthopyroxenites of the Sopcha intrusion and is a sill-like body with a thickness of 4\u0026ndash;6 m, length of 3300 m, and width of 1200 m. The complete OH330 section was studed in the outcrops of its western part. Here, it is represented (from bottom to top) by dunite, harzburgite, and orthopyroxenite with various grain sizes. In the eastern direction, the proportions of dunite and harzburgite in the OH330 section are significantly reduced until they are completely lost. Accordingly, only orthopyroxenites are present on the eastern flank of the OH330 section.\u003c/p\u003e\n\u003c/li\u003e\n\u003cli\u003e\n\u003cp\u003eThe geochemical features of the OH330 rocks were characterized by a decrease in Mg and Fe contents during the transition from dunite to orthopyroxenite, positive U anomaly in dunite and harzburgite, enrichment of LREE and negative Nb and Ta anomalies in orthopyroxenite. This result is due to both fractional crystallization and crustal contamination of the parental melt.\u003c/p\u003e\n\u003c/li\u003e\n\u003cli\u003e\n\u003cp\u003eAccording to the olivine-melt thermometer, the liquidus temperature was determined to be 1600\u0026ndash;1470\u0026deg;C under water conditions, which is explained by a genetic link between the OH330 parental melt and the mantle diapir formed as a result of activation of the long-term Paleoproterozoic mantle plume. The orthopyroxene-melt equilibrium temperature is 1290\u0026ndash;1100\u0026deg;C. The OH330 parental melt was formed as a result of partial (15%) melting of the FFM spinel peridotite under buffer QFM\u0026thinsp;+\u0026thinsp;0.5 control.\u003c/p\u003e\n\u003c/li\u003e\n\u003cli\u003e\n\u003cp\u003eTwo zircon populations were isolated from coarse-grained orthopyroxenite sample. Based on the magmatic zircon population, a concordant SIMS SHRIMP U-Pb age of 2492.5 \u0026plusmn; 4.1 Ma was obtained, which is interpreted as the time of magmatic crystallization and therefore the age of the OH330 rocks. A concordant U-Pb age of 2818.0 \u0026plusmn; 3.1 Ma was obtained from the xenocryst zircon population, which corresponds to the age of the Archean granitoid basement rocks.\u003c/p\u003e\n\u003c/li\u003e\n\u003cli\u003e\n\u003cp\u003eThe obtained age of the OH330 orthopyroxenite (2492.5\u0026thinsp;\u0026plusmn;\u0026thinsp;4.1 Ma) was younger than the age of the norite in the marginal zone of the NKT intrusion (ca. 2507 Ma), and therefore the Sopcha intrusion, which is part of the ultramafic subchamber of Monchepluton, was obtained. This provides compelling evidence that the OH330 formed as a result of additional magma injection.\u003c/p\u003e\n\u003c/li\u003e\n\u003c/ul\u003e"},{"header":"Declarations","content":"\u003cp\u003e \u003ch2\u003eConflict of Interest\u003c/h2\u003e \u003cp\u003eThe authors declare no conflict of interest.\u003c/p\u003e \u003c/p\u003e\u003ch2\u003eFunding\u003c/h2\u003e \u003cp\u003eThe studies have been performed in accordance with the following topics of scientific research of the Geological Institute KSC RAS: FMEZ\u0026ndash;2024\u0026ndash;0004 (Ch.V.V.) and FMEZ\u0026ndash;2024\u0026ndash;0008 (S.Ye.E.).\u003c/p\u003e\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eThe authors contributions the following:V.Ch. processed all the materials obtained, calculated of PT conditions, prepared all the figures and tables, and wrote the main text of the manuscript.Ye.S. studied the chemical composition of minerals.S.S. determined the U-PB age of zircon and provided data for Table S5 and Fig. 10.All authors have reviewed the manuscript.\u003c/p\u003e\u003ch2\u003eAcknowledgments\u003c/h2\u003e \u003cp\u003eThe authors are grateful to L. Koval (Geological Institute KSC RAS, Apatity) for the crushing of rocks and the separation of zircons and to V. Anatsky translated the manuscript into English.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n \u003cli\u003eArmstrong R, Wilson AH (2000) A SHRIMP U-Pb study of zircons from the layered sequence of the Great Dyke, Zimbabwe, and a granitoid anatectic dyke. Earth Planet Sci Lett 180:1-12. https://doi.org/10.1016/s0012-821x(00)00162-x\u003c/li\u003e\n \u003cli\u003eBalashov YuA, Bayanova TB, Mitrofanov FP (1993) Isotope data on the age and genesis of layered basic-ultrabasic intrusions in the Kola Peninsula and northern Karelia, northeastern Baltic Shield. pcambrian Res 64:197-205. https://doi.org/10.1016/0301-9268(93)90076-E\u003c/li\u003e\n \u003cli\u003eBallhaus C, Berry RF, Green DH (1991) High pssure experimental calibration of the olivine-orthopyroxene-spinel oxygen geobarometer: implications for the oxidation state of the upper mantle. Contrib Miner Petrol 107:27-40. https://doi.org/10.1007/bf00310615\u003c/li\u003e\n \u003cli\u003eBarnes SJ, Mole DR, Le Vaillant M, Campbell MJ, Verrall MR, Roberts MP, Evans NJ (2016)\u003cem\u003e\u0026nbsp;\u003c/em\u003ePoikilitic textures, heteradcumulates and zoned orthopyroxenes in the Ntaka ultramafic complex, Tanzania: implications foe crystallization mechanisms of oikocrysts. J \u0026nbsp;Petrol 57:1171-1198.\u0026nbsp;\u003ca href=\"https://doi.org/10.1093/petrology/egw036\"\u003ehttps://doi.org/10.1093/petrology/egw036\u003c/a\u003e\u003c/li\u003e\n \u003cli\u003eBayanova TB, Smolkin VF, Fedotov ZhF, Delenitsyn AA (2004) U-Pb and Sm-Nd isotope investigations of intrusive and dike rocks.\u0026nbsp;In: Mitrofanov FP, Smolkin VF (eds). Layered intrusions of the Monchegorsk ore region: petrology, mineralization, isotopy, and deep structutre. Part 2. Apatity. Kola Science Center RAS. pp. 5-45. 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Moscow. \u0026quot;Technoneftegaz\u0026quot;. pp. 59\u0026ndash;70. (In Russian)\u003c/li\u003e\n \u003cli\u003eChistyakova S, Latypov R, Zaccarini F (2016) Chromitite dykes in the Monchegorsk layered intrusion, Russia: in situ crystallization from chromite-saturated magma flowing in conduits. J Petrol 56:2395-2424. https://doi.org/10.1093/petrology/egv079\u003c/li\u003e\n \u003cli\u003eEliseev EN (1953) Disseminated sulfide mineralization of the Sopcha ore layer. In: Eliseev NA (ed) Ultrabasic and basic intrusions and sulfide copper-nickel deposits of the Moncha. USSR Academy of Sciences, Leningrad, pp. 112-143 (In Russian)\u003c/li\u003e\n \u003cli\u003eFowler A, Prokoph A, Stern R, Dupuis C (2002) Organization of oscillatory zoning in zircon: analysis, scaling, geochemistry, and model of a zircon from Kipawa, Quebec, Canada. 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Mineral Mag 85:291-320. https://doi.org/10.1180/mgm.2021.43\u003c/li\u003e\n \u003cli\u003eWiedenbeck M, Alle P, Corfu F, Griffin WL, Meier M, Oberli F, Von Quadt A, Roddick JC, Spiegel W (1995) Three natural zircon standards for U-Th-Pb, Lu-Hf trace element and REE analyses. Geostandard Newslett 19:1-23. https://doi.org/10.1111/j.1751-908x.1995.tb00147.x\u003c/li\u003e\n \u003cli\u003eWilliams IS (1998) U-Th-Pb geochronology by ion microprobe. In: McKibben MA, Shanks WC, Ridley WI (eds.) Applications of microanalytical techniques to understanding mineralizing processes. Socorro, New Mexico. Rev Econ Geol 7:1-35\u003c/li\u003e\n \u003cli\u003eWilson AH (2019) The Late-Paleoarchean ultra-depleted Сommondale komatiites: Earth\u0026rsquo;s hottest lavas and consequences for eruption. J Petrol 60 (8):1575\u0026ndash;1620. https://doi.org/10.1093/petrology/egz040\u003c/li\u003e\n \u003cli\u003eYudovskaya M, Kinnaird J, Naldrett AJ, Rodionov N, Antonov A, Simakin S, Kuzmin D (2013) Trace-element study and age dating of zircon from chromitites of the Bushveld Complex (South Africa). Miner Petrol 109:915\u0026ndash;942. https://doi.org/10.1007/s00710-013-0269-3\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":true,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"OH330, Mineralogy, Geochemistry, SIMS SHRIMP U-Pb age, Sopcha intrusion, Monchepluton, Kola Region","lastPublishedDoi":"10.21203/rs.3.rs-4678396/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-4678396/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThe \u0026ldquo;Ore Horizon 330\u0026rdquo; deposit (or OH330) is located among the orthopyroxenite of the Sopcha intrusion of the Paleoproterozoic layered Monchegorsk pluton (or Monchepluton) in the Kola Region. It is a sill-like body with a length of 3300 m, width of 1200 m, and thickness of 4‒6 m. OH330 was studied in two sections of its north-western part with a thickness of 5.2 and 5.5 m. There, it consists of regularly alternating interlayers (from bottom to top) of dunite, harzburgite, and orthopyroxenite. Olivine (Fo\u003csub\u003e87\u0026ndash;84\u003c/sub\u003e) and orthopyroxene (En\u003csub\u003e84\u0026ndash;83\u003c/sub\u003e) in the OH330 rocks were depleted in Ni compared to the Monchepluton rocks and were similar in Mn content. The total rare earth element (REE\u003csub\u003etot\u003c/sub\u003e) content did not exceed 1 ppm in dunite and harzburgite, with an average value of 3.15 ppm in orthopyroxenite. LREE fractioning is typical of all OH330 rocks, with the (Ce/Sm)\u003csub\u003eN\u003c/sub\u003e values of 1.21 ppm in dunite, 1.69 ppm in harzburgite, and 1.81 ppm in orthopyroxenite on average. The trace element distribution in dunite and harzburgite is characterized by U, Ta, and Sr positive anomalies, whereas orthopyroxenite exhibits Nb and Ta negative anomalies, in addition to positive U anomalies. The geochemical features of the OH330 rocks were determined by fractional crystallization and crustal contamination of the parental magma. The liquidus temperatures of dunite and harzburgite magmatic crystallization were determined using the olivine-melt thermometer, with values of 1600‒1470\u0026deg;C. This is due to the genetic link between the OH330 parental melt and the mantle diapir. The orthopyroxene-melt equilibrium temperatures the OH330 rocks were 1290‒1120\u0026deg;C. The calculated pressure values for the OH330 rocks varried from 1 to 6 kbar, with an average value of 3.5\u0026thinsp;\u0026plusmn;\u0026thinsp;1.5 kbar. The SIMS SHRIMP U-Pb magmatic zircon age of the OH330 orthopyroxenite is 2492.5\u0026thinsp;\u0026plusmn;\u0026thinsp;4.1 Ma, indicating that the OH330 is younger than the age of the marginal zone of the Monchepluton ultramafic subchamber. A concordant U-Pb age of 2818.0 \u0026plusmn; 3.1 Ma was obtained from the xenocryst zircon population, which corresponds to the age of the Archean granitoid basement rocks.\u003c/p\u003e","manuscriptTitle":"Mineralogy, Petrogenesis and SIMS SHRIMP U-Pb Age PGE-Cu-Ni Deposit of the “Ore Horizon 330” of the Sopcha Intrusion in the Paleoproterosoic Monchegorsk Pluton, Kola Region, Russia","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-07-29 01:06:36","doi":"10.21203/rs.3.rs-4678396/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"482c4057-2955-4667-b18c-9650ca44a4d8","owner":[],"postedDate":"July 29th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2024-07-29T01:06:39+00:00","versionOfRecord":[],"versionCreatedAt":"2024-07-29 01:06:36","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-4678396","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-4678396","identity":"rs-4678396","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}