Discovery of a new kimberlite pipe at Krishnapuram, Wajrakarur Kimberlite Field, Eastern Dharwar Craton: Constraints from Field Geology and Petrochemistry

Discovery of a new kimberlite pipe at Krishnapuram, Wajrakarur Kimberlite Field, Eastern Dharwar Craton: Constraints from Field Geology and Petrochemistry | 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 Discovery of a new kimberlite pipe at Krishnapuram, Wajrakarur Kimberlite Field, Eastern Dharwar Craton: Constraints from Field Geology and Petrochemistry V. R Abhisheka, Arijit Barik, Venkanna Banothu, S. R. Baswani, and 6 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-6345392/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 Systematic exploration by the Geological Survey of India, Hyderabad, involving geological mapping and trenching, led to the discovery of a kimberlite pipe at Krishnapuram (14° 30ʹ 22.50ʺ; 77° 36ʹ 27.20ʺ) within the Wajrakarur Kimberlite Field (WKF) of the Eastern Dharwar Craton (EDC). The identification of this pipe, designated as CC-6 in the Chigicherla (CC) cluster, was confirmed through extensive trenching, heavy mineral sampling and kimberlite indicator mineral (KIM) analysis using electron microprobe (EPMA). Petrographically, the kimberlite exhibits a typical porphyritic texture with macrocrystalline olivine grains (~1000-3000µm) embedded in a groundmass composed of phlogopite, Cr-spinel, perovskite, microcrystalline olivine, and clinopyroxene. Preliminary mineral chemistry analysis indicates that the olivine grains are rich in forsterite (Fo = 86–93), with an average MgO content of 50 wt.%. The groundmass phlogopite exhibits a high Mg# (0.88–0.91), while its Al₂O₃ vs. TiO₂ relationship suggest a kimberlitic affinity. The Cr₂O₃ vs. TiO₂ plot reveals that some spinels fall within the diamond-bearing kimberlite field. Standard major oxide plots (TiO₂ vs. Al₂O₃ and MgO vs. SiO₂) show the kimberlite fields (Group I & II), a classification further supported by trace element geochemistry plots (Y vs. Ce and La/Sm vs. La/Yb). Primitive Mg-numbers, high Ni, Cr contents, and significant enrichment in incompatible trace elements are characteristic features of CC-6. This discovery contributes to the ongoing regional mineral targeting for diamond exploration in the EDC, South India. Geochemistry Mineral Chemistry Kimberlites Chigicherla Andhra Pradesh Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 1. Introduction Kimberlite is an ultramafic, alkaline volatile-rich igneous rock of deep-seated origin that can contain significant quantities of diamond [ 1 ] and provide crucial insights into the deep mantle composition and tectonic evolution of cratonic regions [ 2 , 3 , 4 , 5 ]. The Dharwar Craton (DC), one of the oldest cratonic blocks of the Indian shield, has been a major focus for kimberlite and lamproite exploration, primarily in its eastern parts [ 6 , 7 , 8 , 9 , 10 , 11 , 12 ]. Extensive kimberlite exploration in the Eastern Dharwar Craton (EDC) of southern India, a region known as the world's largest repository of Proterozoic kimberlites, has resulted in the identification of numerous kimberlite fields. These fields, including Wajrakarur Kimberlite Field (WKF), Kalyandurg-Timmasamudram-Chigicherla Kimberlite Field (KTCF), Raichur Kimberlite Field (RKF), and Narayanpet Kimberlite Field (NKF), collectively contain over a hundred kimberlites [ 13 ]. These occurrences are typically aligned along major crustal-scale lineaments [ 14 , 15 ]. Multidisciplinary surveys conducted by Geological Survey of India recently in this region have led to the discovery of a kimberlite pipe (50 m x 30 m), concealed under alluvial soil near village Krishnapuram, Ananthapur district, Andhra Pradesh, within the granitoids of Peninsular Gneissic Complex-II. In this study, a combination of field investigations, petrographic studies, mineral chemistry and whole-rock geochemistry, has been employed to characterize the nature of this kimberlite intrusion. We studied the composition of the rocks forming the CC-6 pipe and the mantle-derived minerals contained within them. The objectives of this research are: (i) to describe the geological setting and petrographic characteristics of the newly discovered kimberlite, (ii) to determine its geochemical composition and (iii) to evaluate diamond potential, if any. 2. Geological background The Chigicherla Kimberlite Cluster (CCKC; Fig. 1 ) is confined to the southern part of the Eastern Dharwar Craton (EDC) of southern India, near the Ramagiri greenstone belt. The lithologic units exposed include: (i) Archean migmatites composed of tonalite – trondhjemite – granodiorite (TTG suites) of the Peninsular Gneissic Complex [ 16 ] (ii) greenstone rocks forming the central part of Ramagiri-Penakacherla schist belt, represented by amphibolite, metabasalt, quartz – white mica schist and banded iron formation (BIF), (iii) basic intrusive rocks including dolerite and gabbro dykes, and (iv) granitic pegmatites, quartzo-feldspathic and epidote veins and quartz reefs that form the younger felsic intrusive suite. Kimberlites are emplaced into this granite – gneiss – greenstone complex, often aligned with the E–W faults or at their intersection with the NNW–SSE faults [ 17 ]. The Wajrakarur kimberlite field in the EDC is a known for many diamond-bearing kimberlite pipes i.e. Wajrakarur, Chigicherla (CC), Timmasamudram (TK) and Kalyandurg (KL) [ 18 , 19 ]. The study area is part of the Chigicherla Kimberlite Cluster (CCKC), which includes six distinct intrusions (CC-1 to CC-6). This cluster is well-exposed within the Kalyandurg-Timmasamudram-Chigicherla Kimberlite Field (KTCF), situated along the ENE-WSW lineament [ 20 , 6 , 13 , 10 , 11 , 12 ]. The CC-6 kimberlite pipe is located 500 meters northwest of Krishnapuram village, about 15 km south of Ananthapur city in Andhra Pradesh (Fig. 2 ). 2.1. Field characteristics The CC-6 kimberlite intrudes the Peninsular Gneissic Complex (PGC), with host lithologies including tonalite-trondhjemite-granodiorite (TTG), amphibolite, and dolerite dyke. Although many field relationships are obscured by cultivation, detailed trenching (Figs. 2 & 3 a-d) allowed for the identification of distinct rock units and clarification of the field relations. Megascopically, the fresh kimberlite is pale green to greyish with globular segregation of xenoliths ( Fig. 3 a ). It is rich in mantle xenoliths, which range from rounded to elliptical and vary in size from fine to medium-grained, embedded within a fine-grained matrix ( Fig. 3 b ). Olivine crystals float in a serpentine, carbonate, and clay matrix. CC-6 exhibits a circular outcrop and is classified as a hypabyssal-facies kimberlite. The CC-6 pipe has similar morphometry with CC5 diamondiferous pipe. A detailed assessment of diamond potential of the CC1-CC5 kimberlite pipe from the WKF was provided by GSI [ 9 ], where they recovered 15 diamonds, totaling.12 carat, through processing of about 138 tons of bulk sample. 3. Methodology 3.1. Sampling and analytical techniques Detailed mapping using the tape-and-compass method, followed by heavy mineral sampling and trenching, helped the demarcation of the CC-6. Kimberlite Indicator Minerals (KIMs) such as garnet, Cr-spinel, Cr-diopside, and picroilmenite (Mg-rich ilmenite) were identified, hand-picked (extracted), and sorted from selected HM concentrate size fractions using optical binocular microscopy and scanning electron microscope (Fig. 3c) , Five representative samples from the CC-6 were chosen for petrographic, mineral chemistry and geochemistry studies. Major element analysis was determined using CAMECA SX 100 at EPMA Lab, GSI, Hyderabad, with an accelerating current of 15 kV, beam current of 15 nA, and a beam size of 1 μm. Natural olivine, clinopyroxene, and chromitite were used as standards. The accuracy of each element is 0.05%wt%. The raw electron microprobe data were processed using probe software and ZAF corrections and are listed in Tables 1. The CC-6 pipe was analyzed for bulk rock major oxide, trace element, rare-earth elements (REE) by XRF, ICP-MS and AAS. Major oxides were determined by PANalytical Magix 2424 XRF, while trace element, REE were analysed by ICPMS-ELAN-DRC methods at Chemical Division, GSI, Hyderabad. The results of the major oxide, trace element, and REE analyses are provided in Table 2. 4. Results 4.1. Petrography The petrography of the Chigicherla kimberlites has been extensively described by previous workers [ 9, 11, 12 ]. In thin section, the CC-6 samples exhibit considerable textural and mineralogical diversity. The texture of the CC-6 kimberlite is inequigranular. The mantle xenocrystic mineral populations primarily include picro ilmenite and Cr-spinel, with subordinate Cr-diopside. The olivine crystals are of two types: rounded to subrounded macrocrysts and euhedral to subhedral phenocrysts (Fig. 4a) . The olivine grains are extensively weathered and mostly pseudomorphed by antigorite/serpentine. Iddingsitization and serpentinisation are pervasive in both macrocrysts and microcrysts of olivine. The groundmass primarily comprises phlogopite (Fig. 4b) ±clinopyroxene, with additional phases such as spinel, perovskite, carbonates, serpentine, ilmenite and chlorite. Phlogopite occurs as clusters in association with carbonate in matrix as well as macrocryst (Fig. 4b) . Perovskite is the main groundmass mineral and surrounds olivine crystals (Fig. 4c) . Perovskite and other Fe-Ti oxide phases are abundant in CC-6 (Fig. 4c) . Cr-spinel exhibits a zoned texture (Fig. 4d ) , showing magmatic zoning with Cr-spinel in the core and Ti-magnetite at the margin (Fig. 4d) . Lath shaped diopside grains occur in the form of segregation. These mineral assemblages, as described by Whitney and Evans (2010) [ 21 ], were also analyzed for their major element composition using SEM and EPMA ( Figs.5a-d ). 4.2. Mineral Chemistry Olivine occurs as both phenocrysts and groundmass components, exhibiting similar compositional ranges: 6-12 wt% FeO and 0.43-0.89 wt% Al 2 O 3 . Preliminary mineral chemistry studies indicate that olivine grains are forsterite-rich (Fo = 92 for megacryst and 88 for groundmass) with an average MgO wt. % of 50.28 (Table 1) . The Mg# (magnesium number) for olivine ranges from 0.86 to 0.88. The phlogopite are relatively high in Al 2 O 3 , and depleted in TiO2 (Table 2). The phlogopite grains are similar in composition to those from typical kimberlites (Group I & II) ( Fig.6a ). TiO 2 values of phlogopites show a kimberlitic trend, falling close to or within the kimberlitic field. The Mg# of phlogopites ranges from 0.88 and 0.91, also following a kimberlitic trend. TiO 2 wt. % vs Al 2 O 3 wt % plots (Fig.6a) also confirm that the phlogopites crystallized from a melt of kimberlitic composition. The primary groundmass spinels are characteristically enriched in Mg (up to 14wt.% MgO) and Cr (up to 43 wt.% Cr2O3), and depleted in Fe (21 wt.% FeO). The spinels analysed by EPMA were plotted in Sobolev (1974) [ 22 ] plots, revealing that they are primarily kimberlitic, with MgO content ranging from 8 and 13 Wt% ( Fig.6b ). TiO 2 vs Cr 2 O 3 plots within kimberlite field ( Fig.6b ). 4.3. Bulk rock Geochemistry The CC-6 kimberlites are silica-undersaturated and exhibit variation in major oxide composition i.e. 33.01-33.97 wt% SiO 2 , MgO (25.09– 26.83 wt%), Fe 2 O 3 (8.22-8.43 wt%), CaO (8.05 – 10.84 wt%), Al 2 O 3 (2.19 – 2.67 wt%), K 2 O (0.92 – 1.25 wt%), and TiO 2 (1.22 – 1.33wt%). High loss on ignition (LOI) values, ranging from 16.51 to 17.42 wt%, indicate a significant presence of H 2 O and CO 2 . Compatible elements show relatively narrow concentration ranges: Sc (10–14 ppm); V (66-81 ppm) and Co (90–105 ppm). CC-6 is characterised by high Ni (1065–1105 ppm), moderate Cr (285–440 ppm) and notably high Ba (1903 to 2384 ppm) and Sr (1055 to 1353 ppm) concentrations. Major oxide plots confirm the kimberlitic nature (Group I & II) of CC-6, which has been characterized and compared to established kimberlites and orangeites using major oxide, trace element, and ratio data ( Figs. 7-8 ) (Table-2). 5. Discussion and Conclusions The Eastern Dharwar Craton (EDC), has been known for hosting several kimberlites and lamproite occurrences since ancient time [ 13 ]. The Chigicherla Kimberlite Field (CCKF), located within the EDC, is particularly significant for understanding kimberlite petrogenesis and its implications for diamond exploration [ 13 ]. Based on geological mapping, geophysical surveys, pitting, trenching, and preliminary petrographic and geochemical analyses, a new kimberlite pipe (CC-6) has been discovered at Krishnapuram in the Chigicherla Kimberlite Field (CCKF), Eastern Dharwar Craton, through systematic geological and geophysical surveys. The CC-6 is associated with a bipolar magnetic anomaly (-1224 to 415 nT) along a NEN-SWS lineament, suggesting structural control on kimberlite emplacement. Petrographic studies of CC-6 kimberlite reveal significant serpentinisation of olivine, as well as the presence of mantle xenoliths. The pipe contains a diverse mineral assemblage, including Cr-spinel, Cr-diopside and, picroilmenite indicating a deep mantle origin. Mineral chemistry reveals that the olivine grains are forsterite-rich (Fo = 86–93), with high Mg# values (0.88–0.91) in groundmass phlogopite, indicating a strong kimberlitic affinity. Olivine macrocrysts with higher Mg# (typically above ~ 0.84) with CaO content 0.18 wt% are considered to be crystallized from kimberlitic melt [ 23 , 24 ]. The olivine in CC-6, with Mg# values ranging from 87 to 93, suggests xenocrystic nature. Cr-spinel compositions indicate derivation from a diamond-stable field (Fig. 5 b), while spinel, perovskite, and phlogopite compositions support a primary mantle origin (Fig. 5 a ). Cr-diopside and picro-ilmenite suggest derivation from a garnet peridotite source. The high Mg# values and primitive compositions indicate minimal differentiation, preserving its original mantle characteristics. High-Mg olivine (Fo 86–93), kimberlitic phlogopite (Mg# 0.88–0.91), and Cr-rich spinels, consistent with derivation from a deep mantle source. To evaluate the kimberlitic nature of CC-6, several standard classification plots were constructed using major oxide data, trace elements, and trace element ratios, alongside well-established kimberlite and orangeite data (Figs. 6 – 8 ). The CC-6 data consistently fall within the Group I & II kimberlite fields in all classification plots [ 25 , 26 ]. The bulk rock composition of the CC-6 kimberlites is characteristic of typical kimberlites (Group I & II), with high MgO (25.09–26.83 wt%), low SiO₂ (33.01–33.97 wt%), and notable enrichment in incompatible trace elements such as Ba, Sr, and HFSEs. The whole rock major and trace element contents of CC-6 are geochemically similar to other kimberlites in the Dharwar Craton, particularly those in the Wajrakarur Kimberlite Field. This new finding, in addition to the earlier reported five kimberlite pipes (CC-1 to CC-5) in the Chigicherla cluster [ 6 , 13 , 10 , 11 , 12 ], significantly enhances diamond exploration potential in the Chigicherla cluster. Ongoing research is focused on a comprehensive characterization of CC-6, including detailed petrography, geochemistry, and in-situ mineral chemistry, as well as an evaluation of its diamond potential. The structural alignment, typical mineralogical characteristics, and geochemical signatures of this CC-6 pipe emphasize the need for continued exploration, particularly in the Ramagiri Belt and adjoining kimberlite clusters. Declarations Acknowledgements: The authors extend their sincere gratitude to Shri Janardan Prasad and Shri Ch. Venkateshwara Rao, the then ADG and HOD, GSI SR, for their unwavering support from the inception of this research project to the discovery of CC-6. Special thanks are due to Shri Asit Saha, Director General, Dr. Joyesh Bagchi, ADG & PSS-PM, S.D. Pathbaje, ADG & HOD, Dr. M. N. Praveen, DDG & RMH-II, SR GSI, for their encouragement and all essential supports in executing this project. We also acknowledge the Chemical and EPMA Laboratory of the Geological Survey of India, SR, for providing the necessary facilities to conduct this research during FS 2022-25. Author Contributions AVR and AB : Field work, collected data, data support, figure preparation, editing and reviewed manuscript; VB and SRB: field work, collected data, EPMA study, analysed data and editing MS, AS and VKT : field work, collected data, SEM study, and analysed data. SR and SS : conceived project, designed research, supervision, visualization, AB : supervision, MLD : designed research, supervision, visualization and writing original manuscript, edited and reviewed MS. All authors reviewed the manuscript. Funding The project was approved annual program of GSI, Govt of India, however, this research has not received any funding from other agencies. Data availability The data are publicly available as cited in Table 1 and 2. Detailed EPMA and bulk rock data are available on request from the first author. Ethics, Consent to Participate, and Consent to Publish declarations : not applicable. Competing interests: The authors declare no competing interests. References Mitchell RH. Kimberlites: Mineralogy, Geochemistry, and Petrology. Plenum, 1986, New York. Haggerty SE. Superkimberlites: a geodynamic diamond window to the Earth’s core. Earth Planet. Sci. Lett. 1994;122 (1): 57–69. Chalapathi Rao NV, Lehmann B. Kimberlites, flood basalts and mantle plumes: new insights from the Deccan large igneous province. Earth Sci. Rev. 2011;107 (3):315–324. Tappe S, Kjarsgaard BA, Kurszlaukis S, Nowell GM, Philips D. 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Supplementary Files Table1MneralChemisytry.docx TAblecaption.docx Table2Bulkrock.docx 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. 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Baswani","email":"","orcid":"","institution":"Geological Survey of India","correspondingAuthor":false,"prefix":"","firstName":"S.","middleName":"R.","lastName":"Baswani","suffix":""},{"id":453618451,"identity":"2db8c39c-7e87-4d55-af72-69ba168cc69b","order_by":4,"name":"Avantika Singh","email":"","orcid":"","institution":"Geological Survey of India","correspondingAuthor":false,"prefix":"","firstName":"Avantika","middleName":"","lastName":"Singh","suffix":""},{"id":453618452,"identity":"f2de54ab-3b6f-4abd-a19d-41bcb1b13c86","order_by":5,"name":"Vikash Tripathy","email":"","orcid":"","institution":"Geological Survey of India","correspondingAuthor":false,"prefix":"","firstName":"Vikash","middleName":"","lastName":"Tripathy","suffix":""},{"id":453618453,"identity":"e7d8f3b6-07ee-4575-8c63-b7620980b421","order_by":6,"name":"S Ravi","email":"","orcid":"","institution":"Geological Survey of India","correspondingAuthor":false,"prefix":"","firstName":"S","middleName":"","lastName":"Ravi","suffix":""},{"id":453618454,"identity":"07cae0f9-9876-4c7d-82b3-781808f7a912","order_by":7,"name":"S. Srinivas","email":"","orcid":"","institution":"Geological Survey of India","correspondingAuthor":false,"prefix":"","firstName":"S.","middleName":"","lastName":"Srinivas","suffix":""},{"id":453618455,"identity":"49e2d2dd-ee95-4b56-8df9-740095d94d1b","order_by":8,"name":"Apurba Banerjee","email":"","orcid":"","institution":"Geological Survey of India","correspondingAuthor":false,"prefix":"","firstName":"Apurba","middleName":"","lastName":"Banerjee","suffix":""},{"id":453618456,"identity":"e4efe198-1e47-424a-bebd-d0fec53ac5ad","order_by":9,"name":"M. L. Dora","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAAr0lEQVRIiWNgGAWjYDACdgYDIGnDDOVKEKGFGawljXQth0lwl24z88bHFTXn2c0lEhg//GCwyCOoxewwW7HhmWO3mS1nJDBL9jBIFBOhhcdMsoHtNrPBjQQGaaBfEhuI0/LvHEgL82/itTS2HQBpYSPWFqBfGvuSmQ3OPGyz7DEgRsvx5o0PG77ZJRscTz5840dFHWEtMJDMwMAIVGxArHogsCNB7SgYBaNgFIw0AACk2TV9Op4zDQAAAABJRU5ErkJggg==","orcid":"","institution":"Jawaharlal Nehru University","correspondingAuthor":true,"prefix":"","firstName":"M.","middleName":"L.","lastName":"Dora","suffix":""}],"badges":[],"createdAt":"2025-03-31 13:53:16","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-6345392/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-6345392/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":82363211,"identity":"8c5933b6-ccca-4f9e-b39b-c513f8a0cabe","added_by":"auto","created_at":"2025-05-09 12:18:18","extension":"jpg","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":3955241,"visible":true,"origin":"","legend":"\u003cp\u003e(a) Sketch map depicting the location of the kimberlite field in southern India (after Drury et al., 1984); b) Regional geological map of a portion of the Eastern Dharwar Craton, South India, highlighting the spatial distribution of various kimberlite clusters in Wajrakarur Kimberlite Field [\u003cstrong\u003e18\u003c/strong\u003e]\u003c/p\u003e","description":"","filename":"1RegionalMap.jpg","url":"https://assets-eu.researchsquare.com/files/rs-6345392/v1/4ab7807a5e2d0a9ae78717d6.jpg"},{"id":82362970,"identity":"744e3e41-05c0-4ecd-9a9b-8f2afcc4df33","added_by":"auto","created_at":"2025-05-09 12:10:18","extension":"jpg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":2697060,"visible":true,"origin":"","legend":"\u003cp\u003eDetailed geological map of CC-6 in Chigicherla cluster within the Wajrakarur Kimberlite Field (WKF) generated through tap-and-compass surveying\u003c/p\u003e","description":"","filename":"2.Fig.2.jpg","url":"https://assets-eu.researchsquare.com/files/rs-6345392/v1/15b0b217bfbbacab65507670.jpg"},{"id":82362977,"identity":"a28237b0-78ae-403d-8032-8ca3b0e71d1b","added_by":"auto","created_at":"2025-05-09 12:10:18","extension":"jpg","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":9698150,"visible":true,"origin":"","legend":"\u003cp\u003e(a) Field photograph of Kimberlite Pipe exposure (CC6) near Krishnapuram; (b) Kimberlite with abundant mantle xenoliths, ranging from rounded to elliptical, embedded in a fine-grained kimberlite matrix; (c) Kimberlite Indicator Minerals (KIMS) – from top left, clockwise: Garnet (Eclogite/Peridotite), Cr-spinel, Cr-diopside, and picroilmenite (Mg-rich ilmenite) from MH samples of CC-6; (d) Trench exposing the concealed CC-6 pipe\u003c/p\u003e","description":"","filename":"3.Fig.fieldphoto.jpg","url":"https://assets-eu.researchsquare.com/files/rs-6345392/v1/fedce67da98f4fbd8dec15db.jpg"},{"id":82362979,"identity":"e917f447-429d-4f8f-ac57-5b450786046f","added_by":"auto","created_at":"2025-05-09 12:10:18","extension":"jpg","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":9779931,"visible":true,"origin":"","legend":"\u003cp\u003e(a) Photomicrograph of kimberlite showing primary olivine macrocrysts poikilitically enclosed by olivine and phlogopite; (b) Phlogopite and carbonate enclosed within altered olivine (antigorite) and perovskite; (c) Phenocrystic perovskite along with Ti-magnetite distributed within a fine-grained groundmass; (d) Back-scattered electron (BSE) images of kimberlite pipe (CC6) showing zoned euhedral chrome spinel with a thin rim of Ti-magnetite at the margin\u003c/p\u003e","description":"","filename":"4.Petrography.jpg","url":"https://assets-eu.researchsquare.com/files/rs-6345392/v1/27e6cfa56da78585d3ab7dae.jpg"},{"id":82362986,"identity":"55e000d1-2d0f-4c7f-9204-14343321aef6","added_by":"auto","created_at":"2025-05-09 12:10:18","extension":"jpg","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":8652816,"visible":true,"origin":"","legend":"\u003cp\u003e(a-d) SEM-EDX spectrum of the altered kimberlite matrix from the CC-6 pipe, displaying dominant peaks of Si, Al, Cr, Mg, K, and Fe, confirming its mineralogical composition and characteristic features of Kimberlite Indicator Minerals (KIMS)\u003c/p\u003e","description":"","filename":"5.Fig.5EDXSEM.jpg","url":"https://assets-eu.researchsquare.com/files/rs-6345392/v1/ede0f532eea196e4ce5d99fa.jpg"},{"id":82363213,"identity":"ca3d1eec-0c61-4590-99ef-d81d70679321","added_by":"auto","created_at":"2025-05-09 12:18:18","extension":"jpg","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":3168029,"visible":true,"origin":"","legend":"\u003cp\u003eCompositional characterization of Cr-spinels by EPMA: (a) TiO\u003csub\u003e2\u003c/sub\u003e vs Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e (wt.%) plot of groundmass phlogopite from CC-6, with data from other EDC kimberlites and references to various fields for kimberlites and lamproites [\u003cstrong\u003e24\u003c/strong\u003e]; (b) TiO\u003csub\u003e2\u003c/sub\u003e vs Cr\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e discriminant plot [\u003cstrong\u003e22\u003c/strong\u003e]\u003c/p\u003e","description":"","filename":"6.Fig.MineralChemistry.jpg","url":"https://assets-eu.researchsquare.com/files/rs-6345392/v1/eeca644faa3e7055f3c21f4a.jpg"},{"id":82362985,"identity":"9b693478-7bef-41b1-bb8e-35b6a35d7212","added_by":"auto","created_at":"2025-05-09 12:10:18","extension":"jpg","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":3178763,"visible":true,"origin":"","legend":"\u003cp\u003eBulk major elemental compositional characteristics of the newly discovered CC-6 kimberlite: (a) MgO-Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e-FeO+Fe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e diagram; (b) MgO-K\u003csub\u003e2\u003c/sub\u003eO-Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e diagram [\u003cstrong\u003e25\u003c/strong\u003e].; (c-d) Discrimination plots of TiO\u003csub\u003e2\u003c/sub\u003e vs Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e and MgO vs SiO\u003csub\u003e2\u003c/sub\u003e, illustrating the compositional field of worldwide kimberlites, with data sourced from [\u003cstrong\u003e26\u003c/strong\u003e].\u003c/p\u003e","description":"","filename":"7.BulkMajorOxide.jpg","url":"https://assets-eu.researchsquare.com/files/rs-6345392/v1/c73ffdab33a7cea70496d3c4.jpg"},{"id":82362990,"identity":"eb806c6c-2390-48a5-ab55-a21ca234d882","added_by":"auto","created_at":"2025-05-09 12:10:18","extension":"jpg","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":3368403,"visible":true,"origin":"","legend":"\u003cp\u003e(a-b) Ce-Y and La/Sm-La/Yb plots for the CC-6, illustrating its kimberlitic nature. The Wajrakarur kimberlite fields are adopted [\u003cstrong\u003e24\u003c/strong\u003e].\u003c/p\u003e","description":"","filename":"8.TraceGeochem.jpg","url":"https://assets-eu.researchsquare.com/files/rs-6345392/v1/eb273441b97c97274d3fecd3.jpg"},{"id":87413961,"identity":"9167b6fc-9cfb-4fdc-a543-4c8a8e742c28","added_by":"auto","created_at":"2025-07-23 14:16:56","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":33453199,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-6345392/v1/a5b2d2b7-d836-4532-897e-1516b316ccd5.pdf"},{"id":82363209,"identity":"de276813-0962-4828-8426-e8c214f22985","added_by":"auto","created_at":"2025-05-09 12:18:18","extension":"docx","order_by":0,"title":"","display":"","copyAsset":false,"role":"supplement","size":16475,"visible":true,"origin":"","legend":"","description":"","filename":"Table1MneralChemisytry.docx","url":"https://assets-eu.researchsquare.com/files/rs-6345392/v1/2d39c97fd964353b099d08b8.docx"},{"id":82362969,"identity":"88aba2a8-6fde-4275-9229-db4242139b7a","added_by":"auto","created_at":"2025-05-09 12:10:18","extension":"docx","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":11701,"visible":true,"origin":"","legend":"","description":"","filename":"TAblecaption.docx","url":"https://assets-eu.researchsquare.com/files/rs-6345392/v1/3a2bcd7a0c520a12ce3a025a.docx"},{"id":82362976,"identity":"33d9355e-6833-4c2b-a735-92ac80ff9666","added_by":"auto","created_at":"2025-05-09 12:10:18","extension":"docx","order_by":2,"title":"","display":"","copyAsset":false,"role":"supplement","size":14857,"visible":true,"origin":"","legend":"","description":"","filename":"Table2Bulkrock.docx","url":"https://assets-eu.researchsquare.com/files/rs-6345392/v1/d029545537db6fdacea83fb5.docx"}],"financialInterests":"No competing interests reported.","formattedTitle":"Discovery of a new kimberlite pipe at Krishnapuram, Wajrakarur Kimberlite Field, Eastern Dharwar Craton: Constraints from Field Geology and Petrochemistry","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eKimberlite is an ultramafic, alkaline volatile-rich igneous rock of deep-seated origin that can contain significant quantities of diamond [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e] and provide crucial insights into the deep mantle composition and tectonic evolution of cratonic regions [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e, \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e, \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e, \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e]. The Dharwar Craton (DC), one of the oldest cratonic blocks of the Indian shield, has been a major focus for kimberlite and lamproite exploration, primarily in its eastern parts [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e, \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e, \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e, \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e, \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e, \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e, \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e]. Extensive kimberlite exploration in the Eastern Dharwar Craton (EDC) of southern India, a region known as the world's largest repository of Proterozoic kimberlites, has resulted in the identification of numerous kimberlite fields. These fields, including Wajrakarur Kimberlite Field (WKF), Kalyandurg-Timmasamudram-Chigicherla Kimberlite Field (KTCF), Raichur Kimberlite Field (RKF), and Narayanpet Kimberlite Field (NKF), collectively contain over a hundred kimberlites [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e]. These occurrences are typically aligned along major crustal-scale lineaments [\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e, \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eMultidisciplinary surveys conducted by Geological Survey of India recently in this region have led to the discovery of a kimberlite pipe (50 m x 30 m), concealed under alluvial soil near village Krishnapuram, Ananthapur district, Andhra Pradesh, within the granitoids of Peninsular Gneissic Complex-II. In this study, a combination of field investigations, petrographic studies, mineral chemistry and whole-rock geochemistry, has been employed to characterize the nature of this kimberlite intrusion. We studied the composition of the rocks forming the CC-6 pipe and the mantle-derived minerals contained within them. The objectives of this research are: (i) to describe the geological setting and petrographic characteristics of the newly discovered kimberlite, (ii) to determine its geochemical composition and (iii) to evaluate diamond potential, if any.\u003c/p\u003e"},{"header":"2. Geological background","content":"\u003cp\u003eThe Chigicherla Kimberlite Cluster (CCKC; Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e) is confined to the southern part of the Eastern Dharwar Craton (EDC) of southern India, near the Ramagiri greenstone belt. The lithologic units exposed include: (i) Archean migmatites composed of tonalite \u0026ndash; trondhjemite \u0026ndash; granodiorite (TTG suites) of the Peninsular Gneissic Complex [\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e] (ii) greenstone rocks forming the central part of Ramagiri-Penakacherla schist belt, represented by amphibolite, metabasalt, quartz \u0026ndash; white mica schist and banded iron formation (BIF), (iii) basic intrusive rocks including dolerite and gabbro dykes, and (iv) granitic pegmatites, quartzo-feldspathic and epidote veins and quartz reefs that form the younger felsic intrusive suite. Kimberlites are emplaced into this granite \u0026ndash; gneiss \u0026ndash; greenstone complex, often aligned with the E\u0026ndash;W faults or at their intersection with the NNW\u0026ndash;SSE faults [\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e]. The Wajrakarur kimberlite field in the EDC is a known for many diamond-bearing kimberlite pipes i.e. Wajrakarur, Chigicherla (CC), Timmasamudram (TK) and Kalyandurg (KL) [\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e, \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e]. The study area is part of the Chigicherla Kimberlite Cluster (CCKC), which includes six distinct intrusions (CC-1 to CC-6). This cluster is well-exposed within the Kalyandurg-Timmasamudram-Chigicherla Kimberlite Field (KTCF), situated along the ENE-WSW lineament [\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e, \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e, \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e, \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e, \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e, \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e]. The CC-6 kimberlite pipe is located 500 meters northwest of Krishnapuram village, about 15 km south of Ananthapur city in Andhra Pradesh (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e2.1. Field characteristics\u003c/h2\u003e \u003cp\u003eThe CC-6 kimberlite intrudes the Peninsular Gneissic Complex (PGC), with host lithologies including tonalite-trondhjemite-granodiorite (TTG), amphibolite, and dolerite dyke. Although many field relationships are obscured by cultivation, detailed trenching (Figs.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e \u0026amp; \u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ea-d) allowed for the identification of distinct rock units and clarification of the field relations.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eMegascopically, the fresh kimberlite is pale green to greyish with globular segregation of xenoliths \u003cb\u003e(\u003c/b\u003eFig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ea\u003cb\u003e).\u003c/b\u003e It is rich in mantle xenoliths, which range from rounded to elliptical and vary in size from fine to medium-grained, embedded within a fine-grained matrix \u003cb\u003e(\u003c/b\u003eFig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eb\u003cb\u003e).\u003c/b\u003e Olivine crystals float in a serpentine, carbonate, and clay matrix. CC-6 exhibits a circular outcrop and is classified as a hypabyssal-facies kimberlite. The CC-6 pipe has similar morphometry with CC5 diamondiferous pipe. A detailed assessment of diamond potential of the CC1-CC5 kimberlite pipe from the WKF was provided by GSI [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e], where they recovered 15 diamonds, totaling.12 carat, through processing of about 138 tons of bulk sample.\u003c/p\u003e \u003c/div\u003e"},{"header":"3. Methodology","content":"\u003cp\u003e\u003cstrong\u003e3.1. Sampling and analytical techniques\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eDetailed mapping using the tape-and-compass method, followed by heavy mineral sampling and trenching, helped the demarcation of the CC-6. Kimberlite Indicator Minerals (KIMs) such as garnet, Cr-spinel, Cr-diopside, and picroilmenite (Mg-rich ilmenite) were identified, hand-picked (extracted), and sorted from selected HM concentrate size fractions using optical binocular microscopy and scanning electron microscope \u003cstrong\u003e(Fig. 3c)\u003c/strong\u003e,\u003c/p\u003e\n\u003cp\u003eFive representative samples from the CC-6 were chosen for petrographic, mineral chemistry and geochemistry studies. Major element analysis was determined using CAMECA SX 100 at EPMA Lab, GSI, Hyderabad, with an accelerating current of 15 kV, beam current of 15 nA, and a beam size of 1 μm. Natural olivine, clinopyroxene, and chromitite were used as standards. The accuracy of each element is 0.05%wt%. The raw electron microprobe data were processed using probe software and ZAF corrections and are listed in \u003cstrong\u003eTables 1.\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe CC-6 pipe was analyzed for bulk rock major oxide, trace element, rare-earth elements (REE) by XRF, ICP-MS and AAS. Major oxides were determined by PANalytical Magix 2424 XRF, while trace element, REE were analysed by ICPMS-ELAN-DRC methods at Chemical Division, GSI, Hyderabad. The results of the major oxide, trace element, and REE analyses are provided in \u003cstrong\u003eTable 2.\u003c/strong\u003e\u003c/p\u003e"},{"header":"4. Results","content":"\u003cp\u003e\u003cstrong\u003e4.1.\u0026nbsp;\u003c/strong\u003e\u003cstrong\u003ePetrography\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe petrography of the Chigicherla kimberlites has been extensively described by previous workers [\u003cstrong\u003e9, 11, 12\u003c/strong\u003e]. In thin section, the CC-6 samples exhibit considerable textural and mineralogical diversity. The texture of the CC-6 kimberlite is inequigranular. The mantle xenocrystic mineral populations primarily include picro ilmenite and Cr-spinel, with subordinate Cr-diopside. The olivine crystals are of two types: rounded to subrounded macrocrysts and euhedral to subhedral phenocrysts \u003cstrong\u003e(Fig. 4a)\u003c/strong\u003e. The olivine grains are extensively weathered and mostly pseudomorphed by antigorite/serpentine. Iddingsitization and serpentinisation are pervasive in both macrocrysts and microcrysts of olivine. The groundmass primarily comprises phlogopite \u003cstrong\u003e(Fig. 4b)\u003c/strong\u003e \u0026plusmn;clinopyroxene, with additional phases such as spinel, perovskite, carbonates, serpentine, ilmenite and chlorite. Phlogopite occurs as clusters in association with carbonate in matrix as well as macrocryst \u003cstrong\u003e(Fig. 4b)\u003c/strong\u003e. Perovskite is the main groundmass mineral and surrounds olivine crystals\u003cstrong\u003e\u0026nbsp;(Fig. 4c)\u003c/strong\u003e. Perovskite and other Fe-Ti oxide phases are abundant in CC-6 \u003cstrong\u003e(Fig. 4c)\u003c/strong\u003e. Cr-spinel exhibits a zoned texture \u003cstrong\u003e(Fig. 4d\u003c/strong\u003e)\u003cstrong\u003e,\u0026nbsp;\u003c/strong\u003eshowing magmatic zoning with Cr-spinel in the core and Ti-magnetite at the margin \u003cstrong\u003e(Fig. 4d)\u003c/strong\u003e. Lath shaped diopside grains occur in the form of segregation. These mineral assemblages, as described by Whitney and Evans (2010) [\u003cstrong\u003e21\u003c/strong\u003e], were also analyzed for their major element composition using SEM and EPMA (\u003cstrong\u003eFigs.5a-d\u003c/strong\u003e).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e4.2. Mineral Chemistry\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eOlivine occurs as both phenocrysts and groundmass components, exhibiting similar compositional ranges: 6-12 wt% FeO and 0.43-0.89 wt% Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e. Preliminary mineral chemistry studies indicate that olivine grains are forsterite-rich (Fo = 92 for megacryst and 88 for groundmass) with an average MgO wt. % of 50.28 \u003cstrong\u003e(Table 1)\u003c/strong\u003e. The Mg# (magnesium number) for olivine ranges from 0.86 to 0.88.\u003c/p\u003e\n\u003cp\u003eThe phlogopite are relatively high in Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e, and depleted in TiO2 (Table 2). The phlogopite grains are similar in composition to those from typical kimberlites (Group I \u0026amp; II) (\u003cstrong\u003eFig.6a\u003c/strong\u003e). TiO\u003csub\u003e2\u003c/sub\u003e values of phlogopites show a kimberlitic trend, falling close to or within the kimberlitic field. The Mg# of phlogopites ranges from 0.88 and 0.91, also following a kimberlitic trend. TiO\u003csub\u003e2\u003c/sub\u003e wt. % vs Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e wt % plots (Fig.6a) also confirm that the phlogopites crystallized from a melt of kimberlitic composition.\u003c/p\u003e\n\u003cp\u003eThe primary groundmass spinels are characteristically enriched in Mg (up to 14wt.% MgO) and Cr (up to 43 wt.% Cr2O3), and depleted in Fe (21 wt.% FeO). The spinels analysed by EPMA were plotted in Sobolev (1974) [\u003cstrong\u003e22\u003c/strong\u003e] plots, revealing that they are primarily kimberlitic, with MgO content ranging from 8 and 13 Wt% (\u003cstrong\u003eFig.6b\u003c/strong\u003e). TiO\u003csub\u003e2\u003c/sub\u003e vs Cr\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e plots within kimberlite field (\u003cstrong\u003eFig.6b\u003c/strong\u003e).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e4.3. Bulk rock Geochemistry\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe CC-6 kimberlites are silica-undersaturated and exhibit variation in major oxide composition i.e. 33.01-33.97 wt% SiO\u003csub\u003e2\u003c/sub\u003e, MgO (25.09\u0026ndash; 26.83 wt%), Fe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e (8.22-8.43 wt%), CaO (8.05 \u0026ndash; 10.84 wt%), Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e (2.19 \u0026ndash; 2.67 wt%), K\u003csub\u003e2\u003c/sub\u003eO (0.92 \u0026ndash; 1.25 wt%), and TiO\u003csub\u003e2\u003c/sub\u003e (1.22 \u0026ndash; 1.33wt%). High loss on ignition (LOI) values, ranging from 16.51 to 17.42 wt%, indicate a significant presence of H\u003csub\u003e2\u003c/sub\u003eO and CO\u003csub\u003e2\u003c/sub\u003e. Compatible elements show relatively narrow concentration ranges: Sc (10\u0026ndash;14 ppm); V (66-81 ppm) and Co (90\u0026ndash;105 ppm). CC-6 is characterised by high Ni (1065\u0026ndash;1105 ppm), moderate Cr (285\u0026ndash;440 ppm) and notably high Ba (1903 to 2384 ppm) and Sr (1055 to 1353 ppm) concentrations. Major oxide plots confirm the kimberlitic nature (Group I \u0026amp; II) of CC-6, which has been characterized and compared to established kimberlites and orangeites using major oxide, trace element, and ratio data (\u003cstrong\u003eFigs.\u003c/strong\u003e\u003cstrong\u003e7-8\u003c/strong\u003e) (Table-2).\u003c/p\u003e"},{"header":"5. Discussion and Conclusions","content":"\u003cp\u003eThe Eastern Dharwar Craton (EDC), has been known for hosting several kimberlites and lamproite occurrences since ancient time [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e]. The Chigicherla Kimberlite Field (CCKF), located within the EDC, is particularly significant for understanding kimberlite petrogenesis and its implications for diamond exploration [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eBased on geological mapping, geophysical surveys, pitting, trenching, and preliminary petrographic and geochemical analyses, a new kimberlite pipe (CC-6) has been discovered at Krishnapuram in the Chigicherla Kimberlite Field (CCKF), Eastern Dharwar Craton, through systematic geological and geophysical surveys. The CC-6 is associated with a bipolar magnetic anomaly (-1224 to 415 nT) along a NEN-SWS lineament, suggesting structural control on kimberlite emplacement. Petrographic studies of CC-6 kimberlite reveal significant serpentinisation of olivine, as well as the presence of mantle xenoliths. The pipe contains a diverse mineral assemblage, including Cr-spinel, Cr-diopside and, picroilmenite indicating a deep mantle origin. Mineral chemistry reveals that the olivine grains are forsterite-rich (Fo\u0026thinsp;=\u0026thinsp;86\u0026ndash;93), with high Mg# values (0.88\u0026ndash;0.91) in groundmass phlogopite, indicating a strong kimberlitic affinity. Olivine macrocrysts with higher Mg# (typically above ~\u0026thinsp;0.84) with CaO content\u0026thinsp;\u0026lt;\u0026thinsp;0.18 wt%, are typically considered to be xenocrystic in origin, whereas those with \u0026gt;\u0026thinsp;0.18 wt% are considered to be crystallized from kimberlitic melt [\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e, \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e]. The olivine in CC-6, with Mg# values ranging from 87 to 93, suggests xenocrystic nature. Cr-spinel compositions indicate derivation from a diamond-stable field (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eb), while spinel, perovskite, and phlogopite compositions support a primary mantle origin (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ea\u003cb\u003e).\u003c/b\u003e Cr-diopside and picro-ilmenite suggest derivation from a garnet peridotite source. The high Mg# values and primitive compositions indicate minimal differentiation, preserving its original mantle characteristics. High-Mg olivine (Fo 86\u0026ndash;93), kimberlitic phlogopite (Mg# 0.88\u0026ndash;0.91), and Cr-rich spinels, consistent with derivation from a deep mantle source.\u003c/p\u003e \u003cp\u003eTo evaluate the kimberlitic nature of CC-6, several standard classification plots were constructed using major oxide data, trace elements, and trace element ratios, alongside well-established kimberlite and orangeite data (Figs.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e\u0026ndash;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e). The CC-6 data consistently fall within the Group I \u0026amp; II kimberlite fields in all classification plots [\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e, \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e]. The bulk rock composition of the CC-6 kimberlites is characteristic of typical kimberlites (Group I \u0026amp; II), with high MgO (25.09\u0026ndash;26.83 wt%), low SiO₂ (33.01\u0026ndash;33.97 wt%), and notable enrichment in incompatible trace elements such as Ba, Sr, and HFSEs. The whole rock major and trace element contents of CC-6 are geochemically similar to other kimberlites in the Dharwar Craton, particularly those in the Wajrakarur Kimberlite Field.\u003c/p\u003e \u003cp\u003eThis new finding, in addition to the earlier reported five kimberlite pipes (CC-1 to CC-5) in the Chigicherla cluster [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e, \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e, \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e, \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e, \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e], significantly enhances diamond exploration potential in the Chigicherla cluster. Ongoing research is focused on a comprehensive characterization of CC-6, including detailed petrography, geochemistry, and in-situ mineral chemistry, as well as an evaluation of its diamond potential. The structural alignment, typical mineralogical characteristics, and geochemical signatures of this CC-6 pipe emphasize the need for continued exploration, particularly in the Ramagiri Belt and adjoining kimberlite clusters.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAcknowledgements:\u0026nbsp;\u003c/strong\u003eThe authors extend their sincere gratitude to Shri Janardan Prasad and Shri Ch. Venkateshwara Rao, the then ADG and HOD, GSI SR, for their unwavering support from the inception of this research project to the discovery of CC-6. Special thanks are due to Shri Asit Saha, Director General, Dr. Joyesh Bagchi, ADG \u0026amp; PSS-PM, S.D. Pathbaje, ADG \u0026amp; HOD, Dr. M. N. Praveen, DDG \u0026amp; RMH-II, SR GSI, for their encouragement and all essential supports in executing this project. We also acknowledge the Chemical and EPMA Laboratory of the Geological Survey of India, SR, for providing the necessary facilities to conduct this research during FS 2022-25.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthor Contributions\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAVR\u0026nbsp;\u003c/strong\u003eand \u003cstrong\u003eAB\u003c/strong\u003e: Field work, collected data, data support, figure preparation, editing and reviewed manuscript; \u003cstrong\u003eVB and SRB:\u003c/strong\u003e field work, collected data, EPMA study, analysed data and editing MS, \u003cstrong\u003eAS and VKT\u003c/strong\u003e: field work, collected data, SEM study, and analysed data. \u003cstrong\u003eSR and SS\u003c/strong\u003e: conceived project, designed research, supervision, visualization, \u003cstrong\u003eAB\u003c/strong\u003e: supervision, \u003cstrong\u003eMLD\u003c/strong\u003e: designed research, supervision, visualization and writing original manuscript, edited and reviewed MS. All authors reviewed the manuscript.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe project was approved annual program of GSI, Govt of India, however, this research has not received any funding from other agencies.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eData availability\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe data are publicly available as cited in Table 1 and 2. Detailed EPMA and bulk rock data are available on request from the first author.\u003c/p\u003e\n\u003cp\u003eEthics, Consent to Participate, and Consent to Publish declarations\u003cstrong\u003e:\u0026nbsp;\u003c/strong\u003enot applicable.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCompeting interests:\u003c/strong\u003e\u0026nbsp; The authors declare no competing interests.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n \u003cli\u003eMitchell RH. Kimberlites: Mineralogy, Geochemistry, and Petrology. Plenum, 1986, New York.\u003c/li\u003e\n \u003cli\u003eHaggerty SE. Superkimberlites: a geodynamic diamond window to the Earth\u0026rsquo;s core. Earth Planet. Sci. Lett. 1994;122 (1): 57\u0026ndash;69.\u003c/li\u003e\n \u003cli\u003eChalapathi Rao NV, Lehmann B. Kimberlites, flood basalts and mantle plumes: new insights from the Deccan large igneous province. Earth Sci. Rev. 2011;107 (3):315\u0026ndash;324.\u003c/li\u003e\n \u003cli\u003eTappe S, Kjarsgaard BA, Kurszlaukis S, Nowell GM, Philips D. Petrology and Nd-Hf isotope geochemistry of the Neoproterozoic Amon kimberlite sills, Baffin Island (Canada): evidence for deep mantle magmatic activity linked to supercontinent cycles. J. Petrol., 2014; 55: 2003\u0026ndash;2042.\u003c/li\u003e\n \u003cli\u003eShaikh AM, Bussweiler Y, Viljoen F, Bolhar R, Ravi S, Hezel DC, Ueckermann H, Tappe S. Redox state of the Dharwar craton root as inferred from eclogite and peridotite sourced mantle cargo, with implications for kimberlite and lamproite magma formation. Contrib Mineral Petrol, 2023; 178:86. https://doi.org/10.1007/s00410-023-02072-2\u003c/li\u003e\n \u003cli\u003eRao KRP, Nayak SS, Reddy TAK, Dhakate MV. Chowdary VS, Ravi S, Suresh G, Rao KSB. Geology Petrology Geochemistry and Mineral chemistry of new kimberlite finds in the Wajrakarur kimberlite field, Anantapur district, Andhra Pradesh. GSI Spec. Publ. 2001; 58: 593\u0026ndash;602.\u003c/li\u003e\n \u003cli\u003eMukherjee A, Rao KS, Babu, EVSSK, Roy G. Compositional Study of Spinels from Wajrakarur Pipe-10 (Anumpalle), Ananthapur District and its Significance in Diamond Prospectivity. \u003cem\u003eJour. Geol. Soc. India,\u003c/em\u003e 1998;52 (6): 677\u0026ndash;682. doi: https://doi.org/10.17491/jgsi/1998/520606.\u003c/li\u003e\n \u003cli\u003eMukherjee A, Jha S, Babu EVSSK. et al. Discovery of a kimberlite pipe near Budikonda, Dharwar craton, south India: Field approaches, preliminary petrography and mineral chemistry. J Geol Soc India, 2014; 84: 633\u0026ndash;644. https://doi.org/10.1007/s12594-014-0174-3\u003c/li\u003e\n \u003cli\u003eRavi S, Vaideswaran T, Rao KSB. Field guide to Wajrakarur kimberlite field, Anantpur district, Andhra Pradesh. Geological Survey of India, 2009; pp 1\u0026ndash;43\u003c/li\u003e\n \u003cli\u003eRavi S, Rao KSB, Reddy RA. Diamond Fields of Southern India. Geological Survey of India, Bulletin Series A, 2018; No.68.\u003c/li\u003e\n \u003cli\u003eBabu EVSSK, Dash S, Santhosh GHNV, Mukherjee A. Origin of clinopyroxene megacrysts from the 1.1 Ga Chigicherla-4 kimberlite (CC4), Dharwar craton, southern India: implications for multi-stage metasomatism of the sub-continental lithospheric mantle. J. Asian Earth Sci. 2023; 244:105534.\u003c/li\u003e\n \u003cli\u003eKalra H, Dongre A, Viljoen F, Li Q-Li. Petrogenesis of Mesoproterozoic kimberlites in the Chigicherla region, Eastern Dharwar craton, Southern India: Insights into the origin of small-volume, enriched-mantle derived melts and link to subduction and supercontinent cycle. Journal of Asian Earth Sciences, 2025; 281: 106508. 10.1016/j.jseaes.2025.106508.\u003c/li\u003e\n \u003cli\u003eGeological Survey of India, 2011. Detailed information dossier on diamond in India, pp. 136.\u003c/li\u003e\n \u003cli\u003eSingh RVB, Babu SB, Pratap B. Gravity Anomalies and Kimberlite Exploration in the Wajrakarur Kimberlite Field of South Indian Kimberlite Province. Geological Journal, 2024; https://doi.org/10.1002/gj.5117.\u003c/li\u003e\n \u003cli\u003eMukherjee, S., Kusham, Ravi, S. et al. Characterizing Eastern Dharwar craton kimberlites in light of petrophysical, geochemical and petrological data. J Earth Syst Sci 134, 14 ,2025, doi.org/10.1007/s12040-024-02447-4.\u003c/li\u003e\n \u003cli\u003eRamakrishnan M. Vaidyanadhan R. Geology of India, 1. Geological Society of India, 2010; Bangalore.\u003c/li\u003e\n \u003cli\u003eRao KRP, Reddy TAK, Rao KVS, Rao KSB, Rao NV. Geology, petrology and geochemistry of Narayanpet kimberlite field in Andhra Pradesh and Karnataka. Jour.Geol.Soc. India, 1998; 52:663-676.\u003c/li\u003e\n \u003cli\u003eNayak SS, Kudari SAD. Discovery of diamond-bearing kimberlites in Kalyandurg area, Anantapur district Andhra Pradesh. Current Science, 1999; 76:1077-1079.\u003c/li\u003e\n \u003cli\u003eChowdary V, Rau TK, Bhaskara Rao KS, Sridhar M, Sinha KK. Timmasamudram kimberlite cluster, Wajrakarur kimberlite field, Anantapur district, Andhra Pradesh, Journal of the Geological Society of India, 2007; 69: 567-610.\u003c/li\u003e\n \u003cli\u003eMurthy DSN, Dayal AM, Natarajan R. Mineralogy and geochemistry of Chigicherla kimberlite and its xenoliths, Anantapur district, Andhra Pradesh. J. Geol. Soc. India, 1994; 443:329\u0026ndash;341.\u003c/li\u003e\n \u003cli\u003eWhitney DL, Evans BW. Abbreviations for names of rock-forming minerals. Am Miner. 2010; 95:185\u0026ndash;187. https ://doi.org/10.2138/am.2010.3371\u003c/li\u003e\n \u003cli\u003eSobolev NV. The deep seated inclusions in kimberlites and the problem of the upper mantle composition. Publishing House\u0026quot; Nauka\u0026quot; 1974.\u003c/li\u003e\n \u003cli\u003eThompson RN, Gibson SA. Transient high temperatures in mantle plume heads inferred from magnesian olivines in Phanerozoic picrites. Nature, 2000; 407: 502\u0026ndash;505.\u003c/li\u003e\n \u003cli\u003eChalapathi Rao NV, Gibson SA, Pyle DM, Dickin AP. Petrogenesis of Proterozoic lamproites and kimberlites from the Cuddapah basin and Dharwar craton, southern India. J. Petrol. 2004;45 (5):907\u0026ndash;948.\u003c/li\u003e\n \u003cli\u003eBergman, S. Lamproites and other potassium-rich igneous rocks: review of their occurrence, mineralogy and geo chemistry.in: J.G. Fitton and B.G.J. Upton (Eds.), Alkaline Igneous Rocks. Geol. Soc. Publ., 1987, v.30, pp.103-190.\u003c/li\u003e\n \u003cli\u003eLefebvre, N., Kopylova, M., Kivi, K., Archeancalc-alkaline lamprophyres of Wawa, Ontario Canada: unconventional diamondiferous volcaniclastic rocks. Precambrian Res. 2005. 138, 57\u0026ndash;87.\u003c/li\u003e\n\u003c/ol\u003e"},{"header":"Tables","content":"\u003cp\u003eTables 1 and 2 are available in the Supplementary Files section\u003c/p\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"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":"Geochemistry, Mineral Chemistry, Kimberlites, Chigicherla, Andhra Pradesh","lastPublishedDoi":"10.21203/rs.3.rs-6345392/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-6345392/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eSystematic exploration by the Geological Survey of India, Hyderabad, involving geological mapping and trenching, led to the discovery of a kimberlite pipe at Krishnapuram (14° 30ʹ 22.50ʺ; 77° 36ʹ 27.20ʺ) within the Wajrakarur Kimberlite Field (WKF) of the Eastern Dharwar Craton (EDC). The identification of this pipe, designated as CC-6 in the Chigicherla (CC) cluster, was confirmed through extensive trenching, heavy mineral sampling and kimberlite indicator mineral (KIM) analysis using electron microprobe (EPMA).\u003c/p\u003e\n\u003cp\u003ePetrographically, the kimberlite exhibits a typical porphyritic texture with macrocrystalline olivine grains (~1000-3000µm) embedded in a groundmass composed of phlogopite, Cr-spinel, perovskite, microcrystalline olivine, and clinopyroxene. Preliminary mineral chemistry analysis indicates that the olivine grains are rich in forsterite (Fo = 86–93), with an average MgO content of 50 wt.%. The groundmass phlogopite exhibits a high Mg# (0.88–0.91), while its Al₂O₃ vs. TiO₂ relationship suggest a kimberlitic affinity. The Cr₂O₃ vs. TiO₂ plot reveals that some spinels fall within the diamond-bearing kimberlite field. Standard major oxide plots (TiO₂ vs. Al₂O₃ and MgO vs. SiO₂) show the kimberlite fields (Group I \u0026amp; II), a classification further supported by trace element geochemistry plots (Y vs. Ce and La/Sm vs. La/Yb). Primitive Mg-numbers, high Ni, Cr contents, and significant enrichment in incompatible trace elements are characteristic features of CC-6. This discovery contributes to the ongoing regional mineral targeting for diamond exploration in the EDC, South India.\u003c/p\u003e","manuscriptTitle":"Discovery of a new kimberlite pipe at Krishnapuram, Wajrakarur Kimberlite Field, Eastern Dharwar Craton: Constraints from Field Geology and Petrochemistry","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-05-09 12:10:13","doi":"10.21203/rs.3.rs-6345392/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":"f0a15f62-ae5d-424d-bbc8-43f3b88e88bc","owner":[],"postedDate":"May 9th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2025-07-23T14:08:16+00:00","versionOfRecord":[],"versionCreatedAt":"2025-05-09 12:10:13","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-6345392","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-6345392","identity":"rs-6345392","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}