Characterization of the Dibang kyanite Minerals from the Southern Domain of the Central Fold Belt in Cameroon: Geological Environment, Liberation Mechanism and Industrial Properties

Characterization of the Dibang kyanite Minerals from the Southern Domain of the Central Fold Belt in Cameroon: Geological Environment, Liberation Mechanism and Industrial Properties | 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 Characterization of the Dibang kyanite Minerals from the Southern Domain of the Central Fold Belt in Cameroon: Geological Environment, Liberation Mechanism and Industrial Properties Thérèse Valérie Ngonlep Miyemeck, Joel Fabrice Nyemb Bayamack, and 6 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-6649891/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 18 You are reading this latest preprint version Abstract The Central Africa Fold Belt (CAFB) in Cameroon, is made up of high-grade metamorphic rocks endowed with kyanite alluvial minerals that are poorly characterized for industrial purposes. To resolve this constraint, field occurrence, optical microscopic observations and morphoscopic study of Dibang kyanite alluvial minerals were carried out. X-Ray Diffraction, X-ray Fluorescence, thermal and sintering analyses were conducted to elucidate their geological environment, liberalization mechanism and industrial properties. In Dibang, kyanite minerals generally occur in kyanite-garnet micaschists, weathering mantles and in alluvial deposits. They are mostly elongated and prismatic with angular rounded or sub-rounded borders. They are of deep dark blue colour associated with garnet and quartz. Their quasi-smooth or smooth morphology is ascribed to the combined action of transportation (torrential and fluvial) and water erosion after withdrawal and release by residual drainage. Microscopic observations of fresh kyanite-garnet micaschists display a grano-nemato-lepidoblastic and oriented microstructure made up of garnet, quartz, kyanite, muscovite, plagioclase, pyroxene and opaques minerals. X-Ray Diffractogram portrays kyanite, with impurities, including micas, muscovite, K-feldspars, quartz, and pyrite mineral phases. The naturally composed mineral composition of the kyanite deposit is pseudo-perfect for the formation of mullitized elements, impeccable for refractory applications. X-ray fluorescence of major elements shows the predominance of alumina and silica, and a quite low percentage of iron oxide. The alkaline and the alkali earth metal oxides occur in traces. The thermal and sintering analysis demonstrates mutillization and recrystallization processes at quite low temperatures (1100ºC to 1300 ºC), with the complete transformation of kyanite to mullite. Kyanite Petrological Analysis Geological Environment Liberalization Mechanism Industrial Properties Central Africa Fold Belt 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 1. Introduction Kyanite is exclusively a metamorphic mineral belonging to the alumino-silicate group and also one of the polymorphs indicating precise pressure and temperature of metamorphism. Kyanite minerals, the exploitation of which dates back to early 1930’s [ 1 ] was primarily used as raw materials in ceramic industries, for refractory elements such as for metallurgical and glass-manufacturing furnaces as well as for kilns [ 2 ]. However, later during the Second World War, kyanite minerals were applied to solve high temperature issues in aircraft industries [ 3 , 4 ], due to their special ability to resist decomposition by heat, pressure or chemical attacks at high temperatures and their capacity to return strength and form [ 2 , 5 ]. They were thus considered as a super refractories or super duties and thereafter, studies on the mineral applicability were developed to resolve high temperature issues in other domains such as steel, cement, energy and chemicals, non-ferrous metals and other end-user industries [ 5 , 6 ]. Owing to its several uses in multiple domains, advancements were recorded in materials science, especially the particles size analysis at the mineral scale, even at granulometry < 1 mm. Indeed, the development of economic activities of the Asian industries [ 6 , 7 ], most prominently in the steel domain [ 6 , 8 ], the economic value of kyanite significantly increased worldwide, particularly from the last decade of the twenteeth century. In Cameroon, kyanite minerals were reported from granulites and amphibolites facies characterized by high grade metamorphism in Adamawa-Yade [ 9 , 10 ] and Southern domain (e.g Yaounde group) [ 11 , 12 , 13 ] of the Central Africa Fold Belt (Fig. 1 , CAFB). In addition, the prospection works of four rivers and their tributaries (river Nyiba, river Nyong, river Nyamakouba and river Evie) [ 14 , 15 , 16 , 17 , 18 ] evidenced some kyanite minerals deposits in Akonolinga and Dibang [ 19 ] in the Southern domain of the CAFB. In the Yaounde Group, the reserve of kyanite minerals was estimated at about two million tons of which only about 50 tons were extracted and exported to France in 1963 [ 17 ]. Other than these prospection works, little or no information is known to our knowledge about the characteristics of these mineral deposits. However, undocumented artisanal exploits of these minerals is focused on local application such as aggregates of mud bricks productions for constructions. In addition, recent studies had shown that kyanite can be used to reinforce intrinsic mullite strength of natural porous refractory materials. They can also be used to obtain high strength mullite composites characterized by low sintering shrinkage at elevated temperatures with suitable shock resistance and excellent mechanical properties [ 21 , 22 , 23 , 24 ] reducing high cost of technological processes and energy consumption [ 25 , 26 ].This line of research was motivated from the growing demand for locally available raw materials for the production of most needed refractory elements in refractory sectors in developing countries at the verge of industrialization. This work presents the combination of field characterization, mineralogical, geochemical, thermal and sintering data of the Dibang kyanite minerals to assess their potential uses in industries. 2. Geological setting 2.1. Regional geology The result of the collision of Sahara meta-craton, Adamawa-Yade Domain (AYD) and the Congo Archean craton between 620 and 600 Ma, following 750–650 Ma subduction was formed the Central African Fold Belt (CAFB, Fig. 1 ) [ 27 ]. The CAFB in Cameroon is subdivided into three geodynamic Domains [ 28 ]: (i) the Northern Domain, regarded as an early Neoproterozoic Domain [ 27 , 29 ]. This Domain which extends to the southern Chad [ 29 ], is delineated to the south by the Tcholliré Shear Zone [ 30 ]. It is predominantly made of a mosaic of magmatic arcs that includes tectonic collage of the Domains of Adamawa-Yade, Mayo Kebbi, and West Cameroon [ 31 , 32 ]. Its evolution is characterized by an early crustal thickening as a result of the subduction and collision events [ 27 ] associated to the emplacement of calco-alkaline magmatic rocks. This stage is followed by a post collisional stage magmatism (Source from the lower continental crust or metasomatized lithospheric mantle uncompleted melts down) induced by crustal delamination and controlled by lithospheric scale Shear Zone, which also controlled mineralization in the Poli area [ 33 ]. The high-grade metamorphic rocks of this area recrystallized in granulites and amphibolites. Their protoliths might have been deposited in a back arc basin [ 34 ] or magmatic arc [ 35 ]. (ii) The Adamawa-Yade Domain (AYD), which is considered either as Archean Domain overprinted by subsequent Paleo-proterozoic and Neoproterozoic events [ 36 ], is made up of 2.1 Ga crustal mantle derived from gneisses associated to 2.5–2.9 Ga archean nucleus reported in the Bafia area [ 36 ]. These Formations are imbedded with Neoproterozoic metasedimentary rocks (e.g) Kékem meta-sediments [ 37 ], Kombé area [ 38 ], Bafia meta-sediments [ 39 ], the protoliths of which is represented by pelites and greywackes [ 39 ]. These protoliths were recrystallized under amphibolites to granulites facies metamorphism during crustal thickening as a result of the collision between the Adamawa-Yade Domain and the meta-craton [ 37 ]. The above mentioned lithology is intruded by variably deformed granitoids emplaced in 638–554 Ma from the early stage to the last stage of the deformation, originated from the partial melting of a heterogeneous lower continental crust, lithospheric mantle and or as a result of the mixing between crustal and lithospheric mantle original melts [ 40 ]. This Domain is affected by lithospheric scale Shear Zone [ 41 ], some of which controls the gold mineralization in the Lom region (e.g Betaré Oyashear area ([ 42 ]) that resulted from transpressive or strike slip tectonics [ 43 ]) developed during amphibolite and green schist facies metamorphism [ 44 ]. The lithology is cross cut by 500 Ma Cambrian tholeiitic gabbro in the Kékem area, which marked the early stage of fragmentation related to the opening of the South Atlantic Ocean [ 45 ]. (iii) The Southern Domain, which thrusts on to the Congo Craton [ 46 ], is made up of meta-sedimentary units of the Yaounde Group. This Group consists of the Yaounde and Bafia series [ 47 ], the protoliths of which are represented by pelites and grey wackes [ 34 ] of Paleoproterozoic and Archean crust [ 39 ] deposited in passive [ 48 ] or active [ 19 ] margins, recrystallized under granulites and amphibolites facies metamorphism during crustal thickening as a result of the collision between the Adamawa-Yade Domain and the Archean Congo Craton [ 49 ]. These high-grade metamorphic rocks, associated to basic and intermediate rocks were formed as a result of subduction and collision between the Congo Craton and the AYD [ 9 ]. The rocks are represented by 660Ma granitoids [ 50 ], the evolution of which is characterized by polyphase deformation that includes an EW to NW–SE (D1) first deformation phase shortening and crustal thickening by stacked nappe and a second deformation phase (D2), that led to generalized N–S and E–W extension with orogenic collapse and exhumation of the Yaoundé series [ 12 , 13 ]. 1.2. Local geology The Dibang area (Fig. 2 ) is located at the Western margin of the Southern Domain. It belongs to the Yaounde series, which is one of the three series that constitutes the Yaounde Group [ 38 ]. This series is made up of rocks recrystallized under high-pressure conditions with increasing gradient from south to north [ 11 , 13 ], such as quartzites, talcschists, garnet-micaschists, garnet-chlorite-micaschists, garnet-kyanite- micaschists, gneiss, garnet-kyanite-migmatites with minor calc-silicates associated to mafic to ultramafics (gabbros, hornblendite, amphibolites and pyroxenites (Fig. 2 )). Dibang and its nearest environs are mostly comprised of gneiss and micaschists, with associated rocks, where the micaschists formation thrusts on to the TTG of the Nyong complex [ 51 ]. Their composition ranges from semi-pelites to aluminous shales and their protoliths have been interpreted as the erosion products of both crustal rocks and Neoproterozoic magmatic arcs [ 19 , 51 ].On hard and fresh rocks, these micaschists are quartz-rich at the base (100–150 m) and kyanite-bearing upwards (≤ 300 m) with a NNE-SSW syncline orientation [ 52 ]. On weathering mantles, kyanite occurs mainly in recent residual and alluvial deposits. 3. MATERIALS AND METHODS 3.1. Materials Characterization was done on kyanite crystals collected from alluvial deposits. The alluvial deposits were sampled for analyses based on the fact that the latter are receptacle of residual environments, favoured by the combined action of transportation (torrential and fluvial) and water erosion. Also, in streams, light particles and some chemical elements are sure to be optimally eliminated. Samples were collected through panning technic and the elongated dark grains of kyanite were sorted from the mixture. The kyanite grains were dried in an oven at 105 ± 5°C for 24 hours, then crushed, ball milled and sieved through 75 µm sieve. The obtained powder was used for geochemical, mineralogical and thermal analysis. Part of the powder was used for microstructural analysis. A portion of a rock sample of micaschists encircling kyanite-garnet-quartz grains was used for the preparation of thin sections. 3.2. Characterization methods 3.2.1. Morphoscopy analysis Morphoscopy analyses were carried out on one detrital sample kyanite alluvial minerals over a total granulometric detrital fraction of which a semi-quantitative evaluation of this latter was done on the relative percentage distribution of 100 kyanite grains compared to their morphologies. 3.2.2. Mineralogical analysis The mineralogical composition of the powdered kyanite samples was determined by means of an X-ray diffraction (XRD). Here, XRD data were collected using a 2θ diffractometer (Panalytical, CuαK), with multiple strip detector for fast data acquisition. A soller slit of 0.04 radiation and a divergence and anti-scattering blade of 5 mm made the pathway incident beam. The face scan was performed at a degree 2θ range of 5–70. The mineral phase identification was performed using XRD.EXL.xlsx and XRD.PPT.pptx. 3.2.3. Chemical analysis Major element concentrations were obtained by X-Ray Fluorescence after heating and diluting of milled kyanite alluvial minerals samples. They were later melted with a lithium tetraborate flux using a Rigaku RIX-3000 wavelength-dispersive spectrometer, BIR-1-1242 and BIR-1-1243 international references, house standards MRB-29-8539, NPD-1-0964 and NPD-1-0965 [ 57 ] and relative error 0.2 to 5%. Ferrous concentrations were obtained a result of a fusion with potassium dichromate. International standard SY-4-0397 and laboratory internal standards MRB-29-8536, MRB-29-8537 and MRB-32-1411were used to identify mineral phases. 3.2.4. Differential and gravimetrical thermal analysis Standard thermal instrument (model DTA 409, NETZSCH) was used for differential and gravimetrical analysis. Measurement was done from ambient to 1400°C at a heating rate of 10°C min − 1 . Sintering was performed using an electric furnace (laboratory scale) 1750°C limit. Four different temperatures 1000°, 1100°, 1200° and 1300°C were fixed for 5 h and maintained for extra 1 h at maximum temperatures. Mineral phases were obtained using DTA.TXT and TG.TXT 3.2.5. Scanning electron microscope analysis The microstructure (elemental, mineralogical and morphological data) of kyanite alluvial minerals was studied by the using a scanning electron microscope (SEM) (Quanta-200 model) combine with an EDS (X_EDS INCA model). Polished specimens were mounted on aluminium stubs and sputter-coated with 10 nm of Au/Pd. Mineral phase identification was done with foto.bmp and edxs.docx. 4. RESULTS 4.1. Field occurrence and macroscopic features of kyanite minerals The Kyanite minerals in Dibang area founded mainly as grains of various sizes in parent rocks (micashists, gneiss), weathering mantle along outcrop, and alluvial deposits in stream. 4.1.1. Kyanite minerals derived from parent rocks Rocks bearing kyanite were found in the village of Mbanda, more precisely on the upstream and downstream of Tanbale and Nsaï streams, with their respective geographic coordonates being: latitudes N04°00’55.2’’ - N04°00’59.3’’ and longitudes E010°45’54.3’’ - E010°45’59.5’’. These rocks are isolated massive blocks in the beds of the water courses and in slabs in alteration zones (Fig. 3 ). They are dark greenish and white sparkling with mica flakes. They visibly contain rounded to sub-rounded grains of garnets, ortho-rhombic platelets of kyanite, quartz granules and disintegrated flakes of micas (muscovite and biotite) of variable sizes, ranging from millimeters to centimeters. Their structure is heterogranular. These rocks are kyanite-garnet micaschists with kyanite having a dominant and scintillating matted luster. Macroscopic observation of these kyanite-garnet micaschists highlights the mineralogical details that are very distinct to the naked eye. 4.1.2. Kyanite minerals derived from weathered Micaschist outcrops The Kyanite minerals are observed in the thick eroded micaschists mantles filled with moderately corroded to completely corroded nodules (garnet, kyanite and quartz) where soil indurations (micaschists) are observed (Figs. 4 a, b). This weathering allows the release of sub-rounded to rounded garnets grains. The elongated- prismatic kyanite sheets by physical and chemical alterations are also identified in the study area. The soils are generally ferrallitic (reddish or yellowish), rich in kyanite, garnet and quartz crystals, wrapped or not in semi-pisolithic indurations. The reddish ferrallitic soils are developed on garnet kyanite micaschists, rich in hematite, while the yellow soils are derived to the amphibolites, gneiss or migmatites n rich in geothite. Both types of soils contain sandy clayey matrix, rich in gibbsite [ 58 ] and relatively in kaolinite. Indurations folding these crystals are characterized by yellowish (goethitic) filling cells and reddish ochre (hematitic) cortex. 4.1.2.1. Kyanites derived to the roadcuts and weathering profiles Roadcuts outcrops generally appear on hill slopes of Tamalong village. They are mostly consisted of micaschists, which imprison kyanite, garnet and quartz crystals (Fig. 5 ) The base layers are very dark green altered micaschists which traps kyanite, garnet and quartz grains (Fig. 5 b). These layers appear in forms of thick (2–14 cm) and tiny (< 2 cm) ribbons. The thicker ribbons are mainly consisted of kyanite and garnet, while the finer ones are made up of quartz. Garnet minerals are subhedral, porphyroblasts and poikiloblasts of 4 x 1.5 mm to 2 x 0.5 mm. Kyanite grains are elongated-prismatic in-shape of about 8 x 4 mm and 4 x 2 mm. Quartz are mostly comprised of small granulated blocks and micas are generally in form of disintegrated flakes of variable sizes (dm-cm). The breakdown of these micaschists permits the liberation of minerals in the form of grains that are widely spread on the soils of the region. Three (03) pits of 1.8, 2.5 and 3.8 m were dug for better observations. The pit of 3.8 m deep (Fig. 6 ) being the most representative of the three, was chosen to be described. Munsell colour chart [ 59 ] was used for colour identification. From top to base, the different structures are as follow: Layer 1: (0–60 cm). Very dark brown colour that tends to black (5YR3/6). There is an abundance of roots, dead leaves, termites and ants. This level is topped by plants. Its limit with the next level is distinct. Layer 2: (60–210 cm). Garnet, kyanite and quartz grains are of centimetric to decimetric sizes. The clay matrix is less abundant than the crystals and it is of dark brown colour (5YR4/8). Its limit with the lower layer is progressive. Layer 3: (210–330 cm). Clay matrix is of brown colour (5YR5/8) with sufficient amount of centimetric to decimetric sizes, as compared to the grains (garnet, kyanite and quartz). Two levels of tiny ferruginization can be observed. Its limit with the next layer is gradual. Layer 4: (330–380cm). Of moderate brown colour (5YR6/8), the matrix is veryclayey filled with quartz, garnet and kyanite grains of millimetric and centimetric sizes. 4.1.2.2. Kyanite minerals derived from alluvial deposits The alluvial deposits were mainly located in the Lipahe and Pougoue streams (Fig. 7 a, b). Smooth kyanite, garnet and quartz grains of decimetric sizes lie near large eroded miscaschists blocks where they were being imprisoned along the borders of streams. These imprisoned grains were/are released by the help of the action of stream water, that penetrates these masses and thereby accelerates their weathering by dissolution and lixiviation of chemical elements. In the middle of streams, these grains are usually absent. They can only be found under large rocks that succeeded to roll-up to that area. A morphoscopic analysis of kyanite minerals collected from the upstream and downstream floors Lipahe and Pougoue (Fig. 7 c d, e et f) allows us to distinguish that kyanite minerals are generally elongated, smooth while garnet pebbles are rounded and smooth. Mica flakes are leached but not completely. They are of tiny corroded whitish-pink colour on the surfaces of the minerals (Fig. 7 e, f). 4.3. Microsopic observations of garnet-kyanite-micaschists Fresh samples of garnet-kyanite micaschists under the microscope light (Fig. 8 ) displays a grano-nemato-lepidoblastic and oriented microstructure made up of garnet (20–25%), kyanite (15–20%), quartz (10–15%), muscovite (5–8%), plagioclase (5%), pyroxene (< 2%) and opaques minerals (< 5%). Garnet crystals generally occur as subhedral poeciloblasts with quartz and oxides inclusions (which defines an internal schistosity) of 6 x 3.5 mm to 2 x 0.5 mm sizes (Fig. 8 a,b,c). Kyanite crystals are usually longitudinal sections, parallelly oriented by the schistosity defined by the other minerals (Fig. 8 d,e). Their sizes range between 8 x 4 and 4 x 2 mm and they contain opaques minerals inclusions. Quartz appears as sub-euhedral crystals or platy crystals displaying ondular extinction, with average size of 1.5 x 0.7 mm. Their orientation is parallel to the schistosity. Muscovite occurs as long lamellae of 2 x 1 mm. They are at the origin of the observed schistosity. Plagioclase (Fig. 8 d,e) occurs as euhedral to subhedral porphyroblast crystals, with very scarce ondular extinction sections, with some inclusion such as oxide, zircon and apatite, and frequently engrained with quartz minerals. Pyroxene (Fig. 8 f) is frequently the clinopyroxene with euhedral to subhedral crystals, and oxide and quartz inclusions and size ranging from 3 x 1.5 mm to 1.5 to 0.5 mm. Opaques minerals (Fig. 8 a,d,e,f) show an average size of 0.2 x 0.1 mm and are appear as either subhedral or euhedral minerals frequently in inclusion. 4.4. Mineralogical properties of kyanite alluvial minerals The X-ray Diffraction pattern (Fig. 9 ) shows four ranges of peak intensities. The first range is the predominant peak at about 26.86°2θ, attributed to quartz and kyanite with a density of 3.34. The second range is of medium intensities with peaks at 35.83º and 46.35º 2θ associated to mica (muscovite), kyanite, titane oxides (ilmenite, rutile, magnetite and pyrite). The third range is the most abundant in terms of peaks characterized by weak intensities, linked to muscovite, kyanite, quartz, alkaline-feldspars (orthose and microcline), plagioclase (anorthite) and iron, titane and iron minerals (hematite, rutile, ilmenite, magnetite and pyrite). The fourth range is of very weak peak intensities and it’s composed of all the referential minerals as in the third range. The diffractogram of the typical alluvial kyanite deposits a highly crystallised mineral phase, which is characteristic feature of weathered fragments subjected to prolonged washing by water current along the river. It indicates that the alluvial kyanite has undergone a complete natural lixiviation and surface refinement. 4.5. Chemical properties of Kyanite alluvial minerals Table 1 presents the weight percentages of major oxides normalized with PAAS. Samples were collected at the upstream (D1) and dowun-stream floors (D2). Al 2 O 3 (41.1–57.8%) and SiO 2 (38.6–47.1%) are in high concentrations while Fe2O3 is quite low (0.99–3.67%) and the other oxides are in trace concentrations. Apart from Al 2 O 3 and TiO 2 with values superior to PAAS, [PAAS Al2O3 (18.9%) and PAAS TiO2 (1%)]), the percentage contents of all the other oxides are lower than that of PAAS values (Table 1 ). {SiO 2 (38.6–47.1%)-PAAS SiO2 (62.8%); Fe 2 O 3 (0.99–3.67%)-PAAS Fe2O3 (6.5%); CaO (0.04–0.19%)-PAAS CaO (1.3%);MgO (0.05–0.15%)-PAAS MgO (2.2%); Na 2 O (0.03–0.09%)-PAAS Na2O (1.2%); K 2 O (0.14–0.29%)-PAAS K2O (3.7%);MnO (< 0.01–0.01%)- PAAS MnO (0.11%); P 2 O 5 (0.03–0.05%)-PAAS P2O5 (0.16%)} (Table 1 and Fig. 10 ). The relatively high content of alumina and iron oxides can be attributed to the depletion of primary minerals through leaching processes. Silica in lesser amounts as compared to alumina can be associated to their loss due to heavy drenching, linked to the humid climate. Titanium in trace amounts as well as the other oxides are completely leached. Blue coloration of kyanite has been studied by different authors. White and White [ 60 ] attributed the coloration to the presence of Ti 3+ traces, Wenk and Bulakh [ 61 ]; Robbins and Strens [ 62 ] credited it to the charge-transfer of Fe 2+ ↔ Ti 4+ [ 61 ] which is inconsistent to Pearson and Shaw [ 63 ]; Albee and Chodos [ 64 ] To Wildner [ 65 ] the blue coloration is exclusively due to Cr 3+ . To Yonta Ngoune et al. [ 66 ], the deep dark blue colour of the Dibang kyanite is linked to the presence of graphite infiltrated in kyanite grains though cracks. Based on the chemical composition (Table 1 ) and the spectrum of major elements (Fig. 10 ), the deep dark blue coloration of Dibang kyanite crystals may come from alkaline and alkali earth metal that penetrated the cracks found on the crystals surfaces. Table 1 Chemical composition of major oxides of kyanite powders compared with the PAAS values Oxydes SiO 2 Al 2 O 3 Fe 2 O 3 CaO MgO Na 2 O K 2 O Cr 2 O 3 TiO 2 MnO P 2 O 5 SrO BaO LOI Total D1 47.1 47.1 3.67 0.19 0.15 0.09 0.29 0.03 1.09 < 0.01 0.03 < 0.01 0.01 1.84 101.6 D2 38.6 57.8 0.99 0.04 0.05 0.03 0.14 0.03 1.09 < 0.01 0.05 < 0.01 0.01 1.96 100.79 PAAS 62.8 18.9 6.5 1.3 2.2 1.2 3.7 1 0.11 0.16 6 4.6. Thermal and sintering properties The behaviour of the powdered alluvial grains submitted to thermal and sintering conditions are presented in Fig. 11 . The thermo-gravimetric and differential thermal graphs reveal four tendencies with variation of mass in terms of temperature. As temperature increases in the interval 200ºCto 300 ºC, a mass loss of about 0.33wt% is recorded, which can be attributed to the evaporation of interlocked water molecules [ 67 ]. Between 450 ºC and 620 ºC, a thermal phenomenon is observed, with a mass loss of approximately 0.16wt%. This is link to the thermal decomposition of muscovite [ 68 ]. The mass loss extends at a gentle pace, up to about 800,depicting the transformation of pyrite (FeS 2 ) to more stable form (FeS) [ 69 ], and feldspars, in the presence of alkaline metals [ 70 ]. From 800ºC to about 1050ºC, the most significant mass loss of about 0.70 wt% is observed. This major loss can be associated to the thermal decomposition phases of kyanite into mullite and cristobalite, the co-presence of Fe 2 O 3 , TiO 2 and alkaline metal oxides [ 69 ]. The epitactic rearrangement of mullite and cristobalite sets in at about 1200 ± 50 o C, leading to the complete transformation of the kyanite mineral at temperature of 1300 o C. The quite low mullitilization temperature observed in the Dibang alluvial kyanite, below the conventional 1400ºC, can be justified by the co-presence of Fe 2 O 3 , TiO 2 and alkaline metal oxides, acting as fusing agents [ 71 ]. 4.7. Microstructural properties Figure 12 displays the SEM-EDS information of kyanite powder prepared from typical alluvial grains. The texture at both higher (Fig. 12 a) and lower (Fig. 12 b) magnifications reveals a loose matrix with homogenous display of powdered and small elongated (sizes ≈ 10 µ m) particles. The elemental weight percent values, by EDS show the predominance of aluminium, superior to 35 wt.% (Fig. 12 d) and silicon, up to 40 wt.% (Fig. 12 c). Oxygen values are moderate, between 14 and 20 wt% (Fig. 12 d) and that of iron is represented in quite small amounts, inferior to 3 wt.% (Fig. 12 c,d). This is in accordance with the chemical (Table 1 ) and mineralogical compositions (Fig. 8 ), which confirms the abundance of alumina, linked to the nature of the bedrock embedding the kyanite minerals. The homogenous spread out of the matrix is associated to the different minerals (mica, quartz, garnet, etc…) that succeeded to infiltrate the many cracks found on the surfaces of kyanite minerals before they were being crushed. The surface exposure of these minerals as indicated on the microstructure predicts their easy amorphization and thermal transformation into phases such as mullite and silica glass. 5. DISCUSSIONS 5.1. Liberation processes of kyanite minerals in weathering mantles In the intertropical area, the presence of minerals/crystals in abundance, lesser or trace amounts are closely linked to the landscape, the vegetation and the climate [ 58 , 72 , 73 ]. In humid climate characterized by profuse rainfalls, abound water facilitates the chemical dissolution and precipitation of primary elements to secondary elements and their transportation from the hill slopes to their settlement on the basements, generally in valleys where streams usually flow. Likewise, vegetation through its roots as well, aids in the penetration of water in rocks and thus, accelerates alteration processes due to an excellent internal drainage by dismantling and transportation of materials to depression levels. Similar observations are highlighted in the characterization of lateritic weathering in intertropical humid zones in Africa [ 72 , 73 ]. These characteristics are specifically observed in the South Cameroon plateau landscapes [ 58 , 73 , 74 , 75 ]. In the study area, intense weathering favours hydrolysis processes of primary silicates permitting the formation of secondary minerals such as kaolinite (monosiallitization), gibbsite (allitization), iron oxides and the individualization of coarse minerals (kyanite, garnet and quartz) observed along the pedologic profile. Also, at the level of the different pedologic profiles, kaolinite amount diminishes the more the layer is deeper into the soil. Its alteration leads to the formation of gibbsite due to the iron-rich environment in which it is found [ 58 , 73 , 74 , 75 , 76 ]. Pyrite and pyrhotite are imprisoned in compact porphyloblastic garnet phases in granitic michaschists [ 76 ]. Micaschists erosion permit the liberation of mica (biotite, muscovite), iron hydroxide (goethite), iron oxide (hematite) and the embedded iron sulphide (pyrite and pyrhotite) [ 58 , 73 , 74 , 75 , 76 ]. Mica corrosion also results in the genesis of gibbsite. Geothite is the dominant iron form observed along the different horizons, confirming the humid climate of the studied area in which the rocks are exposed. Its depletion equally gives birth to gibbsite by aluminium accumulation during allitization process. Alkaline feldspars and plagioclases are leached but not completely. Their erosion as primary minerals lead to the formation of kaolinite during monosiallitization process. All titanium oxides are completely leached during intense weathering. Contrary to what is usually seen in South Cameroon plateau where kaolinite is the main mineral, which accompanies iron oxides in altitude ≤ 800 m [ 58 , 73 , 74 , 75 , 76 ]. In Dibang, gibbsite is the main mineral which accompanies iron oxides (goethite). 5.2. Thermal and sintering properties Mullitization and recrystallization processes during the decomposition of kyanite by heating are closely linked to the particles size and the oxides composition of kyanite itself. In relation to particles size, [ 7 ] demonstrated that crushed kyanite minerals decomposition begin at lower temperatures than that of uncrushed ones, thereby accelerating the appearance of mullite and silica glass. Also, Kashcheev et al. [77] detailly described the effect of RO, R 2 O 3 , and RO 2 oxides and impurity materials on decomposition during heating of kyanite in oxidizing and reducing atmosphere. He highlighted that these oxides not only increase or diminish the quantity of mullite and cristobalite to be formed but also influence the temperature and rates at which they are produced. In the Dibang area, case of the study, kyanite minerals were crushed and sieved under < 75 µm and the obtained powder was used for geochemical, thermal and sintering analyses. Geochemical result of major oxides portrayed the predominance of alumina ( 41.1–57.8%) followed by silica (38.6–47.1%) and a quite low percentage of iron (0.99–3.67%). The other oxides (CaO, MgO, Na 2 O, K 2 O, Cr 2 O 3 , TiO 2 , MnO, P 2 O 5 , SrO, BaO) being in trace concentrations. Exposed to heating conditions, the powder completely transformed into mullite and cristobalite at < 1300 ºC. This can be explained by the role of some oxides during heating such as Cr 2 O 3 which tended to uplift temperature rates of decomposition by about 20–30ºC thereby delaying the occurrence of mullite and silica glass phases. On the other hand, CaO, TiO 2 and MgO, has the tendency of reducing mullitization temperature and slowing down the mullitization process, while Fe 2 O 3 inclined to increase the quantity of mullite and cristobalite. It should be noted that, the alkaline oxides of trace concentrations have negligible threat on the refractory properties of the final product (mullite and cristobalite). However, their presence in the raw kyanite may contribute to low temperature transformation of kyanite to mullite and cristobalite. Furthermore, the Dibang kyanite totally transforms to mullite and silica glass (cristobalite) at < 1300 ºC which is advantageous on the part of energy consumption most especially in refractory industries. 5.3. Industrial applications Based on the chemical, thermal and sintering results combined with the microstructural observations of the Dibang kyanite minerals, it is observed that alumina is the predominant oxide (41.1–57.8%) followed by silica (38.6–47.1%) and iron (0.99–3.67%). The other alkalins are in trace concentrations (0.19–0.01%). Also, the milled kyanite began its decomposition at about 800°C to completely transform to mullite and cristobalite at about 1300°C. Whereas, it has been proven that kyanite utilization is very wide in the industrial area. Its demand is linked to the production of high alumina refractories after firing process [78]. Seven sectors are identified worldwide as concerned the consumption of all types of refractory materials according to their rate of consumption. The first rang is occupied by the (i) “metallurgical industries” which essentially dials with the production of steel and iron with a total consumption of 70% worldwide, followed by the (ii) “cement industries” with a total consumption of 7%, (iii) “energy and chemical industries” with 6%, (iv)“non-ferrous industries” with 3–4%, (v) “ceramic industries” with 4%, (vi) “glass industries” with 2–3% and (vii) “other-end users industries” with 3% [79]. In all these different industries, kyanite is mainly used as pre-fired grog mixed with other components before being applied in different ways depending on the final usage. Also, chemically spoken, these seven refractory sectors have the same specifications which is “high alumina content, low iron and alkalies content”. Meanwhile, the technical specifications vary from one sector to the other. In the metallurgical, glass, non-ferrous, energy and chemical sectors, the technical specifications are low thermal conductivity, excellent heat insulation, excellent thermal shock resistance, significant energy-saving effects, semi-light weight to light weight in furnace bodies, insulators and the like, very slow corrosion and strong penetration resistance to acidic and alkaline slag, high refractoriness under load - temperatures of ≥ 1000–1700°C [78, 80]. Those of ceramic sectors are semi-light and light weight refractory coatings in low and medium temperatures (≥ 400–1200°C), good bonding strength at medium to high temperatures, good abrasive thermal shock, peeling and good wear resistance, high refractoriness under load [80]. While those of cement sectors are poor porosity, high density and strength, good volume stability, excellent thermal and erosion shock resistance [80]. And those of other end-users are high refractoriness under load, high strength and good heat insulation and energy-saving effects during service, temperature of ≥ 400–1200°C [80]. This clearly demonstrates that chemically spoken, Dibang kyanite minerals responds to the chemical specifications demanded in all the seven refractory sectors and based on its technical specifications. Dibang Kyanite minerals are suitable for the elaboration of refractory for low energy consumption as kyanite minerals are transformed into mullite at temperature below 1300°C. However, further investigations are needed to study the thermal behaviour of the low-temperature pre-calcinated product, to qualify the specific industrial applications and the suited modifier additives. 6. CONCLUSION In the light of this study, the following remarks can be drawn. The Dibang kyanite minerals are general dominantly found in weathering mantles and alluvial deposits although they are also found in kyanite-garnet micaschists. They are of ≤ 6.5 cm elongated and prismatic with angular (residual deposits) or rounded and sub-rounded borders. They are of deep dark blue colour generally associated with garnet and quartz. Their rough or smooth morphology is ascribed to the combine action of transportation (torrential and fluvial) and water erosion after their withdrawal and release by residual drainage. Microscopic observations on fresh garnet-kyanite micaschists displays an hetero-granular granoblastic texture made up of garnet (20–25%), biotite, quartz (10–15%), kyanite (15–20%), muscovite (< 10%), biotite (5–8%), K-feldspars and accessory minerals such as zircon, apatite and opaques minerals. The occurrence of free kyanite minerals in various levels of weathering mantles could be ascribed to various weathering processes, including physical alteration and chemical alteration. Kaolinite results from monosiallitization processes while gibbsite is of allitization processes. Geothite is the dominant iron type observed in all the weathering mantles. Hematite appears either as an early stage of ferruginization in some layers of weathering profiles or as a result of the corrosion of garnet crystals. X-ray diffraction depicts a highly crystallised mineral phase, which is characteristic feature of weathered fragments subjected to prolonged washing by water current along the river a prove that the kyanite alluvial minerals has undergone a complete natural lixiviation and surface refinement. X-ray fluorescence of major elements illustrates the different oxides of rich (alumina, silica) and poor (iron, alkaline and alkali metals) quantities justified by the chemical alteration in which they are exposed. Thermal and sintering behaviour portrays a complete transformation of kyanite to mullite and silica glass at about at 1300ºCwhich is advantageous characteristic of low energy consumption. Declarations Acknowledgments The authors would like to thank the editor of the journal “Discover Geoscience” for suggesting the publication of this paper. The authors would also thank all the anonymous reviewers who assisted greatly to improve the quality of this paper. Author contribution TVNM, JFNB and MST conceptualized the current study. TVNM and JFNB wrote the first draft manuscript. MST, SPN, EK, ECB and JE edited and reviewed the manuscript. All authors have read and agreed to the published version of the manuscript. Funding Statement Not applicable Data Availability All data used in this manuscript were results of the field and laboratory investigations carried out on the application of propecting of kyanite alluvial minerals. The procedures to achieving these results have been extensively described under the methodology. No data were sourced online or replicated from previous studies. All information is primary and, on this note, no available link to any data. In addition, appropriates references have been duly cited in the work to corroborate the indings of previous work done. Ethics approval, consent to participate and consent for publication Not applicable Clinical trial number Not applicable Competing Interests policy The authors declare that there are no competing interests regarding the publication of this paper. References Jonas AI. Geology of kyanite belt of Virginia. Virginia Geol Surv Bull. 1932; pp 1–38. Johnson SS. Virginia Mineral. 1967:13(22903). Cooper J. 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Cite Share Download PDF Status: Under Review Version 1 posted Editorial decision: Revision requested 02 Sep, 2025 Reviews received at journal 11 Aug, 2025 Reviews received at journal 06 Aug, 2025 Reviews received at journal 04 Aug, 2025 Reviews received at journal 04 Aug, 2025 Reviewers agreed at journal 01 Aug, 2025 Reviewers agreed at journal 30 Jul, 2025 Reviewers agreed at journal 29 Jul, 2025 Reviewers agreed at journal 27 Jul, 2025 Reviews received at journal 16 Jul, 2025 Reviewers agreed at journal 08 Jul, 2025 Reviewers agreed at journal 29 Jun, 2025 Reviewers agreed at journal 26 Jun, 2025 Reviewers invited by journal 23 Jun, 2025 Editor assigned by journal 23 Jun, 2025 Editor invited by journal 20 Jun, 2025 Submission checks completed at journal 10 Jun, 2025 First submitted to journal 10 Jun, 2025 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. 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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-6649891","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":475426861,"identity":"b6006f19-13a6-4000-968e-b901a1b70714","order_by":0,"name":"Thérèse Valérie Ngonlep Miyemeck","email":"","orcid":"","institution":"University of Douala","correspondingAuthor":false,"prefix":"","firstName":"Thérèse","middleName":"Valérie Ngonlep","lastName":"Miyemeck","suffix":""},{"id":475426862,"identity":"16da370d-828f-4edd-848e-6d9e7208fe6b","order_by":1,"name":"Joel Fabrice Nyemb Bayamack","email":"","orcid":"","institution":"University of Douala","correspondingAuthor":false,"prefix":"","firstName":"Joel","middleName":"Fabrice Nyemb","lastName":"Bayamack","suffix":""},{"id":475426863,"identity":"784d29cc-56e2-467f-b73e-08eef94b2ded","order_by":2,"name":"Paul Venyite","email":"","orcid":"","institution":"University of Yaoundé I","correspondingAuthor":false,"prefix":"","firstName":"Paul","middleName":"","lastName":"Venyite","suffix":""},{"id":475426864,"identity":"59cd3e35-c33c-46c2-b4d3-2e907dcff9ab","order_by":3,"name":"Milan Stafford Tchouatcha","email":"","orcid":"","institution":"University of Dschang","correspondingAuthor":false,"prefix":"","firstName":"Milan","middleName":"Stafford","lastName":"Tchouatcha","suffix":""},{"id":475426865,"identity":"532c685e-46d3-470d-a9b2-a5d33a5e22b1","order_by":4,"name":"Sayom Pemha Nyemb","email":"","orcid":"","institution":"University of Douala","correspondingAuthor":false,"prefix":"","firstName":"Sayom","middleName":"Pemha","lastName":"Nyemb","suffix":""},{"id":475426866,"identity":"3d4ddb11-3488-4ba2-96a8-046b42eef733","order_by":5,"name":"Elie Kamseu","email":"","orcid":"","institution":"University of Yaoundé I","correspondingAuthor":false,"prefix":"","firstName":"Elie","middleName":"","lastName":"Kamseu","suffix":""},{"id":475426867,"identity":"e55fd48d-ee09-4d8c-83c7-b0f186235361","order_by":6,"name":"Elie Constantin Bayiga","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA9UlEQVRIiWNgGAWjYDACCSBOYGCQY2NmbHzAwHAAyGV8QJQWY3725sMGEC3MBoS1AEHizJ5jaRJEaeGXbn4m8eCXHeOGGzlm1Tw1d+T4GZjZPuDTIjnnmJlEYl8yswFQy22eY8+MJRuYmWfg02JwIwGopYeZDaKF7XDihgP8h/E6zP5G+jeglnoekJZinn8gLczMeLUYSOSYSST8OCwhCfQ+M28bEVok7pwptkhsOG4ACmTJuX2HjSWbCWjhn92+8eaPP9X1bcCo/PDm22E5oF78WoCARYKxDcJi4gGRBDUAlXxg+ANhMf4grHoUjIJRMApGIAAAsONOGO0n7JsAAAAASUVORK5CYII=","orcid":"","institution":"University of Douala","correspondingAuthor":true,"prefix":"","firstName":"Elie","middleName":"Constantin","lastName":"Bayiga","suffix":""},{"id":475426868,"identity":"b0bd9e72-1581-49aa-a9c7-5f0aadb9c65f","order_by":7,"name":"Jacques Etame","email":"","orcid":"","institution":"University of Douala","correspondingAuthor":false,"prefix":"","firstName":"Jacques","middleName":"","lastName":"Etame","suffix":""}],"badges":[],"createdAt":"2025-05-12 22:38:19","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-6649891/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-6649891/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":85509283,"identity":"07e50ba1-8408-47ca-9562-0d4b095e4bbc","added_by":"auto","created_at":"2025-06-26 16:09:07","extension":"jpg","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":112147,"visible":true,"origin":"","legend":"\u003cp\u003eCentral Africa Fold Belt in Cameroon [52], modified\u003c/p\u003e","description":"","filename":"Picture1.jpg","url":"https://assets-eu.researchsquare.com/files/rs-6649891/v1/e84ecebd3fe23fb44cef42b6.jpg"},{"id":85509620,"identity":"dbca55b8-5b68-429c-8c2e-a6552aa8ff1b","added_by":"auto","created_at":"2025-06-26 16:17:07","extension":"jpg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":414594,"visible":true,"origin":"","legend":"\u003cp\u003eGeological map of Dibang area [19, 50], modified\u003c/p\u003e","description":"","filename":"Picture2.jpg","url":"https://assets-eu.researchsquare.com/files/rs-6649891/v1/fc4c46788d16db4b4fa06ced.jpg"},{"id":85509280,"identity":"d178916f-702a-4056-8438-f2f4fa47fc24","added_by":"auto","created_at":"2025-06-26 16:09:07","extension":"jpg","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":83172,"visible":true,"origin":"","legend":"\u003cp\u003eImages of kyanite minerals derived from the kyanite-garnet micaschists\u003c/p\u003e","description":"","filename":"Picture3.jpg","url":"https://assets-eu.researchsquare.com/files/rs-6649891/v1/eca40eb4e63e6e75981346cb.jpg"},{"id":85509621,"identity":"fe540081-59c4-4ed2-be06-832ccbaaedcf","added_by":"auto","created_at":"2025-06-26 16:17:07","extension":"jpg","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":594333,"visible":true,"origin":"","legend":"\u003cp\u003e(a) Slab of altered micaschist trapping kyanite grains; (b) Enlargement of a portion of the kyanite slab\u003c/p\u003e","description":"","filename":"Picture4.jpg","url":"https://assets-eu.researchsquare.com/files/rs-6649891/v1/ca8cd5b240f37fec3628e38c.jpg"},{"id":85509286,"identity":"a3503448-4136-40fa-b061-b6e4660f699a","added_by":"auto","created_at":"2025-06-26 16:09:07","extension":"jpg","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":54013,"visible":true,"origin":"","legend":"\u003cp\u003eGarnet and kyanite grains released from ferruginous nodules in a weathering profile\u003c/p\u003e","description":"","filename":"Picture5.jpg","url":"https://assets-eu.researchsquare.com/files/rs-6649891/v1/bf45dc13e82e1e10a87c90f7.jpg"},{"id":85510716,"identity":"56dae671-806a-45cf-b08d-e28a0da6858a","added_by":"auto","created_at":"2025-06-26 16:33:07","extension":"jpg","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":91419,"visible":true,"origin":"","legend":"\u003cp\u003ePedologic profile of loose matrix of Dibang\u003c/p\u003e","description":"","filename":"Picture6.jpg","url":"https://assets-eu.researchsquare.com/files/rs-6649891/v1/6f4c1e98e3965b692dc9b389.jpg"},{"id":85509292,"identity":"0490ffb3-893c-4e8d-8e3a-5307f42d3970","added_by":"auto","created_at":"2025-06-26 16:09:07","extension":"jpg","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":609031,"visible":true,"origin":"","legend":"\u003cp\u003eImages: (a, b) Blocks of kyanite-garnet micaschists of Lipahe and Pougoue streams; (c) A pan showing kyanites, garnets and quartz grains of Lipahe and Pougoue streams; (d, e et f) Morphoscopic analysis of kyanite minerals\u003c/p\u003e","description":"","filename":"Picture7.jpg","url":"https://assets-eu.researchsquare.com/files/rs-6649891/v1/714013224dfaead8388fad52.jpg"},{"id":85509302,"identity":"51bf9eb1-7bc6-44ee-997f-d123452b12ab","added_by":"auto","created_at":"2025-06-26 16:09:07","extension":"jpg","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":150817,"visible":true,"origin":"","legend":"\u003cp\u003eMicroscopic observations ofkyanite-garnet micaschist from Dibang. a: Lepido-granoblastic microstructure (PL= Polarized light); b: Same picture in PPL = plan polarized light); c: Detail showing Poecilitic garnet (with quartz and oxides inclusions), PL; d: Granoblastic and oriented microstructure, PL; e: Grano-nemato-lepidoblastic microstructure, PL; f: Grano-nematoblastic and oriented microstructure, Pl.\u003c/p\u003e","description":"","filename":"Picture8.jpg","url":"https://assets-eu.researchsquare.com/files/rs-6649891/v1/10002e7d45ecf166cdcf9970.jpg"},{"id":85509287,"identity":"8a2e2c73-4076-4135-bce7-20b01e1abd22","added_by":"auto","created_at":"2025-06-26 16:09:07","extension":"jpg","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":32748,"visible":true,"origin":"","legend":"\u003cp\u003eDiffractogram of kyanite mineral observed in the studies materials\u003c/p\u003e","description":"","filename":"Picture9.jpg","url":"https://assets-eu.researchsquare.com/files/rs-6649891/v1/ddd820d7a8249bdd2a577b1c.jpg"},{"id":85509291,"identity":"b96604fd-bd81-43ac-ab7c-779bda2d3be6","added_by":"auto","created_at":"2025-06-26 16:09:07","extension":"jpg","order_by":10,"title":"Figure 10","display":"","copyAsset":false,"role":"figure","size":40829,"visible":true,"origin":"","legend":"\u003cp\u003eMajor elements spectrum normalized with PAAS\u003c/p\u003e","description":"","filename":"Picture10.jpg","url":"https://assets-eu.researchsquare.com/files/rs-6649891/v1/c36fbfaed1ee9c36b031ece1.jpg"},{"id":85509298,"identity":"194478bd-6318-42f4-9f5d-2a62ed8d5016","added_by":"auto","created_at":"2025-06-26 16:09:07","extension":"jpg","order_by":11,"title":"Figure 11","display":"","copyAsset":false,"role":"figure","size":44483,"visible":true,"origin":"","legend":"\u003cp\u003eThermal and sintering behaviour of the Dibang kyanite powder\u003c/p\u003e","description":"","filename":"Picture11.jpg","url":"https://assets-eu.researchsquare.com/files/rs-6649891/v1/6a482a95214e707fc4e517e3.jpg"},{"id":85510419,"identity":"001a3be3-5eb1-4186-a320-4addb4b8a211","added_by":"auto","created_at":"2025-06-26 16:25:08","extension":"jpg","order_by":12,"title":"Figure 12","display":"","copyAsset":false,"role":"figure","size":69165,"visible":true,"origin":"","legend":"\u003cp\u003eSEM images (a and b) and their respective EDS spectra (c and d) of powder prepared from typical alluvial deposit grains, at ×2000 and ×1000 magnifications\u003c/p\u003e","description":"","filename":"Picture12.jpg","url":"https://assets-eu.researchsquare.com/files/rs-6649891/v1/32376ed32a5d207b17cedb52.jpg"},{"id":85511521,"identity":"98f70989-51fb-4d5e-ad28-4badee68e87f","added_by":"auto","created_at":"2025-06-26 16:41:09","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":3459840,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-6649891/v1/1f06004a-2224-46c9-91ef-e7e3403e6eba.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Characterization of the Dibang kyanite Minerals from the Southern Domain of the Central Fold Belt in Cameroon: Geological Environment, Liberation Mechanism and Industrial Properties","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eKyanite is exclusively a metamorphic mineral belonging to the alumino-silicate group and also one of the polymorphs indicating precise pressure and temperature of metamorphism. Kyanite minerals, the exploitation of which dates back to early 1930\u0026rsquo;s [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e] was primarily used as raw materials in ceramic industries, for refractory elements such as for metallurgical and glass-manufacturing furnaces as well as for kilns [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]. However, later during the Second World War, kyanite minerals were applied to solve high temperature issues in aircraft industries [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e, \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e], due to their special ability to resist decomposition by heat, pressure or chemical attacks at high temperatures and their capacity to return strength and form [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e, \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e]. They were thus considered as a super refractories or super duties and thereafter, studies on the mineral applicability were developed to resolve high temperature issues in other domains such as steel, cement, energy and chemicals, non-ferrous metals and other end-user industries [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e, \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e]. Owing to its several uses in multiple domains, advancements were recorded in materials science, especially the particles size analysis at the mineral scale, even at granulometry\u0026thinsp;\u0026lt;\u0026thinsp;1 mm. Indeed, the development of economic activities of the Asian industries [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e, \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e], most prominently in the steel domain [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e, \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e], the economic value of kyanite significantly increased worldwide, particularly from the last decade of the twenteeth century. In Cameroon, kyanite minerals were reported from granulites and amphibolites facies characterized by high grade metamorphism in Adamawa-Yade [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e, \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e] and Southern domain (e.g Yaounde group) [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e, \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e, \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e] of the Central Africa Fold Belt (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e, CAFB). In addition, the prospection works of four rivers and their tributaries (river Nyiba, river Nyong, river Nyamakouba and river Evie) [\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e, \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e, \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e, \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e, \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e] evidenced some kyanite minerals deposits in Akonolinga and Dibang [\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e] in the Southern domain of the CAFB. In the Yaounde Group, the reserve of kyanite minerals was estimated at about two million tons of which only about 50 tons were extracted and exported to France in 1963 [\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e]. Other than these prospection works, little or no information is known to our knowledge about the characteristics of these mineral deposits. However, undocumented artisanal exploits of these minerals is focused on local application such as aggregates of mud bricks productions for constructions. In addition, recent studies had shown that kyanite can be used to reinforce intrinsic mullite strength of natural porous refractory materials. They can also be used to obtain high strength mullite composites characterized by low sintering shrinkage at elevated temperatures with suitable shock resistance and excellent mechanical properties [\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e, \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e, \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e, \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e] reducing high cost of technological processes and energy consumption [\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e, \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e].This line of research was motivated from the growing demand for locally available raw materials for the production of most needed refractory elements in refractory sectors in developing countries at the verge of industrialization. This work presents the combination of field characterization, mineralogical, geochemical, thermal and sintering data of the Dibang kyanite minerals to assess their potential uses in industries.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e"},{"header":"2. Geological setting","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e2.1. Regional geology\u003c/h2\u003e \u003cp\u003eThe result of the collision of Sahara meta-craton, Adamawa-Yade Domain (AYD) and the Congo Archean craton between 620 and 600 Ma, following 750\u0026ndash;650 Ma subduction was formed the Central African Fold Belt (CAFB, Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e) [\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e]. The CAFB in Cameroon is subdivided into three geodynamic Domains [\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e]: (i) the Northern Domain, regarded as an early Neoproterozoic Domain [\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e, \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e]. This Domain which extends to the southern Chad [\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e], is delineated to the south by the Tchollir\u0026eacute; Shear Zone [\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e]. It is predominantly made of a mosaic of magmatic arcs that includes tectonic collage of the Domains of Adamawa-Yade, Mayo Kebbi, and West Cameroon [\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e, \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e]. Its evolution is characterized by an early crustal thickening as a result of the subduction and collision events [\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e] associated to the emplacement of calco-alkaline magmatic rocks. This stage is followed by a post collisional stage magmatism (Source from the lower continental crust or metasomatized lithospheric mantle uncompleted melts down) induced by crustal delamination and controlled by lithospheric scale Shear Zone, which also controlled mineralization in the Poli area [\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e]. The high-grade metamorphic rocks of this area recrystallized in granulites and amphibolites. Their protoliths might have been deposited in a back arc basin [\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e] or magmatic arc [\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e]. (ii) The Adamawa-Yade Domain (AYD), which is considered either as Archean Domain overprinted by subsequent Paleo-proterozoic and Neoproterozoic events [\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e], is made up of 2.1 Ga crustal mantle derived from gneisses associated to 2.5\u0026ndash;2.9 Ga archean nucleus reported in the Bafia area [\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e]. These Formations are imbedded with Neoproterozoic metasedimentary rocks (e.g) K\u0026eacute;kem meta-sediments [\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e], Komb\u0026eacute; area [\u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e], Bafia meta-sediments [\u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e], the protoliths of which is represented by pelites and greywackes [\u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e]. These protoliths were recrystallized under amphibolites to granulites facies metamorphism during crustal thickening as a result of the collision between the Adamawa-Yade Domain and the meta-craton [\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e]. The above mentioned lithology is intruded by variably deformed granitoids emplaced in 638\u0026ndash;554 Ma from the early stage to the last stage of the deformation, originated from the partial melting of a heterogeneous lower continental crust, lithospheric mantle and or as a result of the mixing between crustal and lithospheric mantle original melts [\u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e40\u003c/span\u003e]. This Domain is affected by lithospheric scale Shear Zone [\u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e41\u003c/span\u003e], some of which controls the gold mineralization in the Lom region (e.g Betar\u0026eacute; Oyashear area ([\u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e42\u003c/span\u003e]) that resulted from transpressive or strike slip tectonics [\u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e43\u003c/span\u003e]) developed during amphibolite and green schist facies metamorphism [\u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e44\u003c/span\u003e]. The lithology is cross cut by 500 Ma Cambrian tholeiitic gabbro in the K\u0026eacute;kem area, which marked the early stage of fragmentation related to the opening of the South Atlantic Ocean [\u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e45\u003c/span\u003e]. (iii) The Southern Domain, which thrusts on to the Congo Craton [\u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e46\u003c/span\u003e], is made up of meta-sedimentary units of the Yaounde Group. This Group consists of the Yaounde and Bafia series [\u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e47\u003c/span\u003e], the protoliths of which are represented by pelites and grey wackes [\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e] of Paleoproterozoic and Archean crust [\u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e] deposited in passive [\u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e48\u003c/span\u003e] or active [\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e] margins, recrystallized under granulites and amphibolites facies metamorphism during crustal thickening as a result of the collision between the Adamawa-Yade Domain and the Archean Congo Craton [\u003cspan citationid=\"CR49\" class=\"CitationRef\"\u003e49\u003c/span\u003e]. These high-grade metamorphic rocks, associated to basic and intermediate rocks were formed as a result of subduction and collision between the Congo Craton and the AYD [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e]. The rocks are represented by 660Ma granitoids [\u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e50\u003c/span\u003e], the evolution of which is characterized by polyphase deformation that includes an EW to NW\u0026ndash;SE (D1) first deformation phase shortening and crustal thickening by stacked nappe and a second deformation phase (D2), that led to generalized N\u0026ndash;S and E\u0026ndash;W extension with orogenic collapse and exhumation of the Yaound\u0026eacute; series [\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e, \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e].\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e1.2. Local geology\u003c/h2\u003e \u003cp\u003eThe Dibang area (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e) is located at the Western margin of the Southern Domain. It belongs to the Yaounde series, which is one of the three series that constitutes the Yaounde Group [\u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e]. This series is made up of rocks recrystallized under high-pressure conditions with increasing gradient from south to north [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e, \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e], such as quartzites, talcschists, garnet-micaschists, garnet-chlorite-micaschists, garnet-kyanite- micaschists, gneiss, garnet-kyanite-migmatites with minor calc-silicates associated to mafic to ultramafics (gabbros, hornblendite, amphibolites and pyroxenites (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e)). Dibang and its nearest environs are mostly comprised of gneiss and micaschists, with associated rocks, where the micaschists formation thrusts on to the TTG of the Nyong complex [\u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e51\u003c/span\u003e]. Their composition ranges from semi-pelites to aluminous shales and their protoliths have been interpreted as the erosion products of both crustal rocks and Neoproterozoic magmatic arcs [\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e, \u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e51\u003c/span\u003e].On hard and fresh rocks, these micaschists are quartz-rich at the base (100\u0026ndash;150 m) and kyanite-bearing upwards (\u0026le;\u0026thinsp;300 m) with a NNE-SSW syncline orientation [\u003cspan citationid=\"CR52\" class=\"CitationRef\"\u003e52\u003c/span\u003e]. On weathering mantles, kyanite occurs mainly in recent residual and alluvial deposits.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e"},{"header":"3. MATERIALS AND METHODS","content":"\u003cdiv id=\"Sec6\" class=\"Section2\"\u003e \u003ch2\u003e3.1. Materials\u003c/h2\u003e \u003cp\u003eCharacterization was done on kyanite crystals collected from alluvial deposits. The alluvial deposits were sampled for analyses based on the fact that the latter are receptacle of residual environments, favoured by the combined action of transportation (torrential and fluvial) and water erosion. Also, in streams, light particles and some chemical elements are sure to be optimally eliminated. Samples were collected through panning technic and the elongated dark grains of kyanite were sorted from the mixture. The kyanite grains were dried in an oven at 105\u0026thinsp;\u0026plusmn;\u0026thinsp;5\u0026deg;C for 24 hours, then crushed, ball milled and sieved through 75 \u0026micro;m sieve. The obtained powder was used for geochemical, mineralogical and thermal analysis. Part of the powder was used for microstructural analysis. A portion of a rock sample of micaschists encircling kyanite-garnet-quartz grains was used for the preparation of thin sections.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec7\" class=\"Section2\"\u003e \u003ch2\u003e3.2. Characterization methods\u003c/h2\u003e \u003cdiv id=\"Sec8\" class=\"Section3\"\u003e \u003ch2\u003e3.2.1. Morphoscopy analysis\u003c/h2\u003e \u003cp\u003eMorphoscopy analyses were carried out on one detrital sample kyanite alluvial minerals over a total granulometric detrital fraction of which a semi-quantitative evaluation of this latter was done on the relative percentage distribution of 100 kyanite grains compared to their morphologies.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec9\" class=\"Section3\"\u003e \u003ch2\u003e3.2.2. Mineralogical analysis\u003c/h2\u003e \u003cp\u003eThe mineralogical composition of the powdered kyanite samples was determined by means of an X-ray diffraction (XRD). Here, XRD data were collected using a 2θ diffractometer (Panalytical, CuαK), with multiple strip detector for fast data acquisition. A soller slit of 0.04 radiation and a divergence and anti-scattering blade of 5 mm made the pathway incident beam. The face scan was performed at a degree 2θ range of 5\u0026ndash;70. The mineral phase identification was performed using XRD.EXL.xlsx and XRD.PPT.pptx.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec10\" class=\"Section3\"\u003e \u003ch2\u003e3.2.3. Chemical analysis\u003c/h2\u003e \u003cp\u003eMajor element concentrations were obtained by X-Ray Fluorescence after heating and diluting of milled kyanite alluvial minerals samples. They were later melted with a lithium tetraborate flux using a Rigaku RIX-3000 wavelength-dispersive spectrometer, BIR-1-1242 and BIR-1-1243 international references, house standards MRB-29-8539, NPD-1-0964 and NPD-1-0965 [\u003cspan citationid=\"CR57\" class=\"CitationRef\"\u003e57\u003c/span\u003e] and relative error 0.2 to 5%. Ferrous concentrations were obtained a result of a fusion with potassium dichromate. International standard SY-4-0397 and laboratory internal standards MRB-29-8536, MRB-29-8537 and MRB-32-1411were used to identify mineral phases.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec11\" class=\"Section3\"\u003e \u003ch2\u003e3.2.4. Differential and gravimetrical thermal analysis\u003c/h2\u003e \u003cp\u003eStandard thermal instrument (model DTA 409, NETZSCH) was used for differential and gravimetrical analysis. Measurement was done from ambient to 1400\u0026deg;C at a heating rate of 10\u0026deg;C min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. Sintering was performed using an electric furnace (laboratory scale) 1750\u0026deg;C limit. Four different temperatures 1000\u0026deg;, 1100\u0026deg;, 1200\u0026deg; and 1300\u0026deg;C were fixed for 5 h and maintained for extra 1 h at maximum temperatures. Mineral phases were obtained using DTA.TXT and TG.TXT\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec12\" class=\"Section3\"\u003e \u003ch2\u003e3.2.5. Scanning electron microscope analysis\u003c/h2\u003e \u003cp\u003eThe microstructure (elemental, mineralogical and morphological data) of kyanite alluvial minerals was studied by the using a scanning electron microscope (SEM) (Quanta-200 model) combine with an EDS (X_EDS INCA model). Polished specimens were mounted on aluminium stubs and sputter-coated with 10 nm of Au/Pd. Mineral phase identification was done with foto.bmp and edxs.docx.\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e"},{"header":"4. RESULTS","content":"\u003cdiv id=\"Sec14\" class=\"Section2\"\u003e \u003ch2\u003e4.1. Field occurrence and macroscopic features of kyanite minerals\u003c/h2\u003e \u003cp\u003eThe Kyanite minerals in Dibang area founded mainly as grains of various sizes in parent rocks (micashists, gneiss), weathering mantle along outcrop, and alluvial deposits in stream.\u003c/p\u003e \u003cdiv id=\"Sec15\" class=\"Section3\"\u003e \u003ch2\u003e4.1.1. Kyanite minerals derived from parent rocks\u003c/h2\u003e \u003cp\u003eRocks bearing kyanite were found in the village of Mbanda, more precisely on the upstream and downstream of Tanbale and Nsa\u0026iuml; streams, with their respective geographic coordonates being: latitudes N04\u0026deg;00\u0026rsquo;55.2\u0026rsquo;\u0026rsquo; - N04\u0026deg;00\u0026rsquo;59.3\u0026rsquo;\u0026rsquo; and longitudes E010\u0026deg;45\u0026rsquo;54.3\u0026rsquo;\u0026rsquo; - E010\u0026deg;45\u0026rsquo;59.5\u0026rsquo;\u0026rsquo;. These rocks are isolated massive blocks in the beds of the water courses and in slabs in alteration zones (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e). They are dark greenish and white sparkling with mica flakes. They visibly contain rounded to sub-rounded grains of garnets, ortho-rhombic platelets of kyanite, quartz granules and disintegrated flakes of micas (muscovite and biotite) of variable sizes, ranging from millimeters to centimeters. Their structure is heterogranular. These rocks are kyanite-garnet micaschists with kyanite having a dominant and scintillating matted luster. Macroscopic observation of these kyanite-garnet micaschists highlights the mineralogical details that are very distinct to the naked eye.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec16\" class=\"Section3\"\u003e \u003ch2\u003e4.1.2. Kyanite minerals derived from weathered Micaschist outcrops\u003c/h2\u003e \u003cp\u003eThe Kyanite minerals are observed in the thick eroded micaschists mantles filled with moderately corroded to completely corroded nodules (garnet, kyanite and quartz) where soil indurations (micaschists) are observed (Figs.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ea, b). This weathering allows the release of sub-rounded to rounded garnets grains. The elongated- prismatic kyanite sheets by physical and chemical alterations are also identified in the study area. The soils are generally ferrallitic (reddish or yellowish), rich in kyanite, garnet and quartz crystals, wrapped or not in semi-pisolithic indurations. The reddish ferrallitic soils are developed on garnet kyanite micaschists, rich in hematite, while the yellow soils are derived to the amphibolites, gneiss or migmatites n rich in geothite. Both types of soils contain sandy clayey matrix, rich in gibbsite [\u003cspan citationid=\"CR58\" class=\"CitationRef\"\u003e58\u003c/span\u003e] and relatively in kaolinite. Indurations folding these crystals are characterized by yellowish (goethitic) filling cells and reddish ochre (hematitic) cortex.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cdiv id=\"Sec17\" class=\"Section4\"\u003e \u003ch2\u003e4.1.2.1. Kyanites derived to the roadcuts and weathering profiles\u003c/h2\u003e \u003cp\u003eRoadcuts outcrops generally appear on hill slopes of Tamalong village. They are mostly consisted of micaschists, which imprison kyanite, garnet and quartz crystals (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e) The base layers are very dark green altered micaschists which traps kyanite, garnet and quartz grains (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eb). These layers appear in forms of thick (2\u0026ndash;14 cm) and tiny (\u0026lt;\u0026thinsp;2 cm) ribbons. The thicker ribbons are mainly consisted of kyanite and garnet, while the finer ones are made up of quartz. Garnet minerals are subhedral, porphyroblasts and poikiloblasts of 4 x 1.5 mm to 2 x 0.5 mm. Kyanite grains are elongated-prismatic in-shape of about 8 x 4 mm and 4 x 2 mm. Quartz are mostly comprised of small granulated blocks and micas are generally in form of disintegrated flakes of variable sizes (dm-cm). The breakdown of these micaschists permits the liberation of minerals in the form of grains that are widely spread on the soils of the region.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThree (03) pits of 1.8, 2.5 and 3.8 m were dug for better observations. The pit of 3.8 m deep (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e) being the most representative of the three, was chosen to be described. Munsell colour chart [\u003cspan citationid=\"CR59\" class=\"CitationRef\"\u003e59\u003c/span\u003e] was used for colour identification. From top to base, the different structures are as follow:\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eLayer 1: (0\u0026ndash;60 cm). Very dark brown colour that tends to black (5YR3/6). There is an abundance of roots, dead leaves, termites and ants. This level is topped by plants. Its limit with the next level is distinct.\u003c/p\u003e \u003cp\u003eLayer 2: (60\u0026ndash;210 cm). Garnet, kyanite and quartz grains are of centimetric to decimetric sizes. The clay matrix is less abundant than the crystals and it is of dark brown colour (5YR4/8). Its limit with the lower layer is progressive.\u003c/p\u003e \u003cp\u003eLayer 3: (210\u0026ndash;330 cm). Clay matrix is of brown colour (5YR5/8) with sufficient amount of centimetric to decimetric sizes, as compared to the grains (garnet, kyanite and quartz). Two levels of tiny ferruginization can be observed. Its limit with the next layer is gradual.\u003c/p\u003e \u003cp\u003eLayer 4: (330\u0026ndash;380cm). Of moderate brown colour (5YR6/8), the matrix is veryclayey filled with quartz, garnet and kyanite grains of millimetric and centimetric sizes.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec18\" class=\"Section4\"\u003e \u003ch2\u003e4.1.2.2. Kyanite minerals derived from alluvial deposits\u003c/h2\u003e \u003cp\u003eThe alluvial deposits were mainly located in the Lipahe and Pougoue streams (Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003ea, b). Smooth kyanite, garnet and quartz grains of decimetric sizes lie near large eroded miscaschists blocks where they were being imprisoned along the borders of streams. These imprisoned grains were/are released by the help of the action of stream water, that penetrates these masses and thereby accelerates their weathering by dissolution and lixiviation of chemical elements. In the middle of streams, these grains are usually absent. They can only be found under large rocks that succeeded to roll-up to that area. A morphoscopic analysis of kyanite minerals collected from the upstream and downstream floors Lipahe and Pougoue (Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003ec d, e et f) allows us to distinguish that kyanite minerals are generally elongated, smooth while garnet pebbles are rounded and smooth. Mica flakes are leached but not completely. They are of tiny corroded whitish-pink colour on the surfaces of the minerals (Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003ee, f).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv id=\"Sec19\" class=\"Section2\"\u003e \u003ch2\u003e4.3. Microsopic observations of garnet-kyanite-micaschists\u003c/h2\u003e \u003cp\u003eFresh samples of garnet-kyanite micaschists under the microscope light (Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e) displays a grano-nemato-lepidoblastic and oriented microstructure made up of garnet (20\u0026ndash;25%), kyanite (15\u0026ndash;20%), quartz (10\u0026ndash;15%), muscovite (5\u0026ndash;8%), plagioclase (5%), pyroxene (\u0026lt;\u0026thinsp;2%) and opaques minerals (\u0026lt;\u0026thinsp;5%). Garnet crystals generally occur as subhedral poeciloblasts with quartz and oxides inclusions (which defines an internal schistosity) of 6 x 3.5 mm to 2 x 0.5 mm sizes (Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003ea,b,c). Kyanite crystals are usually longitudinal sections, parallelly oriented by the schistosity defined by the other minerals (Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003ed,e). Their sizes range between 8 x 4 and 4 x 2 mm and they contain opaques minerals inclusions. Quartz appears as sub-euhedral crystals or platy crystals displaying ondular extinction, with average size of 1.5 x 0.7 mm. Their orientation is parallel to the schistosity. Muscovite occurs as long lamellae of 2 x 1 mm. They are at the origin of the observed schistosity. Plagioclase (Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003ed,e) occurs as euhedral to subhedral porphyroblast crystals, with very scarce ondular extinction sections, with some inclusion such as oxide, zircon and apatite, and frequently engrained with quartz minerals. Pyroxene (Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003ef) is frequently the clinopyroxene with euhedral to subhedral crystals, and oxide and quartz inclusions and size ranging from 3 x 1.5 mm to 1.5 to 0.5 mm. Opaques minerals (Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003ea,d,e,f) show an average size of 0.2 x 0.1 mm and are appear as either subhedral or euhedral minerals frequently in inclusion.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec20\" class=\"Section2\"\u003e \u003ch2\u003e4.4. Mineralogical properties of kyanite alluvial minerals\u003c/h2\u003e \u003cp\u003eThe X-ray Diffraction pattern (Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003e) shows four ranges of peak intensities. The first range is the predominant peak at about 26.86\u0026deg;2θ, attributed to quartz and kyanite with a density of 3.34. The second range is of medium intensities with peaks at 35.83\u0026ordm; and 46.35\u0026ordm; 2θ associated to mica (muscovite), kyanite, titane oxides (ilmenite, rutile, magnetite and pyrite). The third range is the most abundant in terms of peaks characterized by weak intensities, linked to muscovite, kyanite, quartz, alkaline-feldspars (orthose and microcline), plagioclase (anorthite) and iron, titane and iron minerals (hematite, rutile, ilmenite, magnetite and pyrite). The fourth range is of very weak peak intensities and it\u0026rsquo;s composed of all the referential minerals as in the third range. The diffractogram of the typical alluvial kyanite deposits a highly crystallised mineral phase, which is characteristic feature of weathered fragments subjected to prolonged washing by water current along the river. It indicates that the alluvial kyanite has undergone a complete natural lixiviation and surface refinement.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec21\" class=\"Section2\"\u003e \u003ch2\u003e4.5. Chemical properties of Kyanite alluvial minerals\u003c/h2\u003e \u003cp\u003eTable\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e presents the weight percentages of major oxides normalized with PAAS. Samples were collected at the upstream (D1) and dowun-stream floors (D2). Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e (41.1\u0026ndash;57.8%) and SiO\u003csub\u003e2\u003c/sub\u003e (38.6\u0026ndash;47.1%) are in high concentrations while Fe2O3 is quite low (0.99\u0026ndash;3.67%) and the other oxides are in trace concentrations. Apart from Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e and TiO\u003csub\u003e2\u003c/sub\u003e with values superior to PAAS, [PAAS\u003csub\u003eAl2O3\u003c/sub\u003e (18.9%) and PAAS\u003csub\u003eTiO2\u003c/sub\u003e (1%)]), the percentage contents of all the other oxides are lower than that of PAAS values (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). {SiO\u003csub\u003e2\u003c/sub\u003e (38.6\u0026ndash;47.1%)-PAAS\u003csub\u003eSiO2\u003c/sub\u003e (62.8%); Fe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e(0.99\u0026ndash;3.67%)-PAAS\u003csub\u003eFe2O3\u003c/sub\u003e(6.5%); CaO (0.04\u0026ndash;0.19%)-PAAS\u003csub\u003eCaO\u003c/sub\u003e (1.3%);MgO (0.05\u0026ndash;0.15%)-PAAS\u003csub\u003eMgO\u003c/sub\u003e (2.2%); Na\u003csub\u003e2\u003c/sub\u003eO (0.03\u0026ndash;0.09%)-PAAS\u003csub\u003eNa2O\u003c/sub\u003e (1.2%); K\u003csub\u003e2\u003c/sub\u003eO (0.14\u0026ndash;0.29%)-PAAS\u003csub\u003eK2O\u003c/sub\u003e (3.7%);MnO (\u0026lt;\u0026thinsp;0.01\u0026ndash;0.01%)- PAAS\u003csub\u003eMnO\u003c/sub\u003e (0.11%); P\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e(0.03\u0026ndash;0.05%)-PAAS\u003csub\u003eP2O5\u003c/sub\u003e (0.16%)} (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e and Fig.\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003e). The relatively high content of alumina and iron oxides can be attributed to the depletion of primary minerals through leaching processes. Silica in lesser amounts as compared to alumina can be associated to their loss due to heavy drenching, linked to the humid climate. Titanium in trace amounts as well as the other oxides are completely leached. Blue coloration of kyanite has been studied by different authors. White and White [\u003cspan citationid=\"CR60\" class=\"CitationRef\"\u003e60\u003c/span\u003e] attributed the coloration to the presence of Ti\u003csup\u003e3+\u003c/sup\u003e traces, Wenk and Bulakh [\u003cspan citationid=\"CR61\" class=\"CitationRef\"\u003e61\u003c/span\u003e]; Robbins and Strens [\u003cspan citationid=\"CR62\" class=\"CitationRef\"\u003e62\u003c/span\u003e] credited it to the charge-transfer of Fe\u003csup\u003e2+\u003c/sup\u003e \u0026harr; Ti\u003csup\u003e4+\u003c/sup\u003e [\u003cspan citationid=\"CR61\" class=\"CitationRef\"\u003e61\u003c/span\u003e] which is inconsistent to Pearson and Shaw [\u003cspan citationid=\"CR63\" class=\"CitationRef\"\u003e63\u003c/span\u003e]; Albee and Chodos [\u003cspan citationid=\"CR64\" class=\"CitationRef\"\u003e64\u003c/span\u003e] To Wildner [\u003cspan citationid=\"CR65\" class=\"CitationRef\"\u003e65\u003c/span\u003e] the blue coloration is exclusively due to Cr\u003csup\u003e3+\u003c/sup\u003e. To Yonta Ngoune \u003csup\u003eet\u003c/sup\u003e al. [\u003cspan citationid=\"CR66\" class=\"CitationRef\"\u003e66\u003c/span\u003e], the deep dark blue colour of the Dibang kyanite is linked to the presence of graphite infiltrated in kyanite grains though cracks. Based on the chemical composition (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e) and the spectrum of major elements (Fig.\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003e), the deep dark blue coloration of Dibang kyanite crystals may come from alkaline and alkali earth metal that penetrated the cracks found on the crystals surfaces.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eChemical composition of major oxides of kyanite powders compared with the PAAS values\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"16\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c8\" colnum=\"8\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c9\" colnum=\"9\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c10\" colnum=\"10\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c11\" colnum=\"11\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c12\" colnum=\"12\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c13\" colnum=\"13\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c14\" colnum=\"14\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c15\" colnum=\"15\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c16\" colnum=\"16\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eOxydes\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eSiO\u003csub\u003e2\u003c/sub\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eAl\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eCaO\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eMgO\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c7\"\u003e \u003cp\u003eNa\u003csub\u003e2\u003c/sub\u003eO\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c8\"\u003e \u003cp\u003eK\u003csub\u003e2\u003c/sub\u003eO\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c9\"\u003e \u003cp\u003eCr\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c10\"\u003e \u003cp\u003eTiO\u003csub\u003e2\u003c/sub\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c11\"\u003e \u003cp\u003eMnO\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c12\"\u003e \u003cp\u003eP\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c13\"\u003e \u003cp\u003eSrO\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c14\"\u003e \u003cp\u003eBaO\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c15\"\u003e \u003cp\u003eLOI\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c16\"\u003e \u003cp\u003eTotal\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eD1\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e47.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e47.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e3.67\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.19\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.15\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e0.09\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e0.29\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e0.03\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003e1.09\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c11\"\u003e \u003cp\u003e\u0026lt;\u0026thinsp;0.01\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c12\"\u003e \u003cp\u003e0.03\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c13\"\u003e \u003cp\u003e\u0026lt;\u0026thinsp;0.01\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c14\"\u003e \u003cp\u003e0.01\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c15\"\u003e \u003cp\u003e1.84\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c16\"\u003e \u003cp\u003e101.6\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eD2\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e38.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e57.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.99\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.04\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.05\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e0.03\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e0.14\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e0.03\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003e1.09\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c11\"\u003e \u003cp\u003e\u0026lt;\u0026thinsp;0.01\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c12\"\u003e \u003cp\u003e0.05\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c13\"\u003e \u003cp\u003e\u0026lt;\u0026thinsp;0.01\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c14\"\u003e \u003cp\u003e0.01\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c15\"\u003e \u003cp\u003e1.96\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c16\"\u003e \u003cp\u003e100.79\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003ePAAS\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e62.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e18.9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e6.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e1.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e2.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e1.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e3.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c11\"\u003e \u003cp\u003e0.11\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c12\"\u003e \u003cp\u003e0.16\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c13\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c14\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c15\"\u003e \u003cp\u003e6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c16\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec22\" class=\"Section2\"\u003e \u003ch2\u003e4.6. Thermal and sintering properties\u003c/h2\u003e \u003cp\u003eThe behaviour of the powdered alluvial grains submitted to thermal and sintering conditions are presented in Fig.\u0026nbsp;\u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e11\u003c/span\u003e. The thermo-gravimetric and differential thermal graphs reveal four tendencies with variation of mass in terms of temperature. As temperature increases in the interval 200\u0026ordm;Cto 300 \u0026ordm;C, a mass loss of about 0.33wt% is recorded, which can be attributed to the evaporation of interlocked water molecules [\u003cspan citationid=\"CR67\" class=\"CitationRef\"\u003e67\u003c/span\u003e]. Between 450 \u0026ordm;C and 620 \u0026ordm;C, a thermal phenomenon is observed, with a mass loss of approximately 0.16wt%. This is link to the thermal decomposition of muscovite [\u003cspan citationid=\"CR68\" class=\"CitationRef\"\u003e68\u003c/span\u003e]. The mass loss extends at a gentle pace, up to about 800,depicting the transformation of pyrite (FeS\u003csub\u003e2\u003c/sub\u003e) to more stable form (FeS) [\u003cspan citationid=\"CR69\" class=\"CitationRef\"\u003e69\u003c/span\u003e], and feldspars, in the presence of alkaline metals [\u003cspan citationid=\"CR70\" class=\"CitationRef\"\u003e70\u003c/span\u003e]. From 800\u0026ordm;C to about 1050\u0026ordm;C, the most significant mass loss of about 0.70 wt% is observed. This major loss can be associated to the thermal decomposition phases of kyanite into mullite and cristobalite, the co-presence of Fe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e, TiO\u003csub\u003e2\u003c/sub\u003eand alkaline metal oxides [\u003cspan citationid=\"CR69\" class=\"CitationRef\"\u003e69\u003c/span\u003e]. The epitactic rearrangement of mullite and cristobalite sets in at about 1200\u0026thinsp;\u0026plusmn;\u0026thinsp;50\u003csup\u003eo\u003c/sup\u003eC, leading to the complete transformation of the kyanite mineral at temperature of 1300\u003csup\u003eo\u003c/sup\u003eC. The quite low mullitilization temperature observed in the Dibang alluvial kyanite, below the conventional 1400\u0026ordm;C, can be justified by the co-presence of Fe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e, TiO\u003csub\u003e2\u003c/sub\u003e and alkaline metal oxides, acting as fusing agents [\u003cspan citationid=\"CR71\" class=\"CitationRef\"\u003e71\u003c/span\u003e].\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec23\" class=\"Section2\"\u003e \u003ch2\u003e4.7. Microstructural properties\u003c/h2\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig12\" class=\"InternalRef\"\u003e12\u003c/span\u003e displays the SEM-EDS information of kyanite powder prepared from typical alluvial grains. The texture at both higher (Fig.\u0026nbsp;\u003cspan refid=\"Fig12\" class=\"InternalRef\"\u003e12\u003c/span\u003ea) and lower (Fig.\u0026nbsp;\u003cspan refid=\"Fig12\" class=\"InternalRef\"\u003e12\u003c/span\u003eb) magnifications reveals a loose matrix with homogenous display of powdered and small elongated (sizes\u0026thinsp;\u0026asymp;\u0026thinsp;10\u003cem\u003e\u0026micro;\u003c/em\u003em) particles. The elemental weight percent values, by EDS show the predominance of aluminium, superior to 35 wt.% (Fig.\u0026nbsp;\u003cspan refid=\"Fig12\" class=\"InternalRef\"\u003e12\u003c/span\u003ed) and silicon, up to 40 wt.% (Fig.\u0026nbsp;\u003cspan refid=\"Fig12\" class=\"InternalRef\"\u003e12\u003c/span\u003ec). Oxygen values are moderate, between 14 and 20 wt% (Fig.\u0026nbsp;\u003cspan refid=\"Fig12\" class=\"InternalRef\"\u003e12\u003c/span\u003ed) and that of iron is represented in quite small amounts, inferior to 3 wt.% (Fig.\u0026nbsp;\u003cspan refid=\"Fig12\" class=\"InternalRef\"\u003e12\u003c/span\u003ec,d). This is in accordance with the chemical (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e) and mineralogical compositions (Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e), which confirms the abundance of alumina, linked to the nature of the bedrock embedding the kyanite minerals.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe homogenous spread out of the matrix is associated to the different minerals (mica, quartz, garnet, etc\u0026hellip;) that succeeded to infiltrate the many cracks found on the surfaces of kyanite minerals before they were being crushed. The surface exposure of these minerals as indicated on the microstructure predicts their easy amorphization and thermal transformation into phases such as mullite and silica glass.\u003c/p\u003e \u003c/div\u003e"},{"header":"5. DISCUSSIONS","content":"\u003cdiv id=\"Sec25\" class=\"Section2\"\u003e \u003ch2\u003e5.1. Liberation processes of kyanite minerals in weathering mantles\u003c/h2\u003e \u003cp\u003eIn the intertropical area, the presence of minerals/crystals in abundance, lesser or trace amounts are closely linked to the landscape, the vegetation and the climate [\u003cspan citationid=\"CR58\" class=\"CitationRef\"\u003e58\u003c/span\u003e, \u003cspan citationid=\"CR72\" class=\"CitationRef\"\u003e72\u003c/span\u003e, \u003cspan citationid=\"CR73\" class=\"CitationRef\"\u003e73\u003c/span\u003e]. In humid climate characterized by profuse rainfalls, abound water facilitates the chemical dissolution and precipitation of primary elements to secondary elements and their transportation from the hill slopes to their settlement on the basements, generally in valleys where streams usually flow. Likewise, vegetation through its roots as well, aids in the penetration of water in rocks and thus, accelerates alteration processes due to an excellent internal drainage by dismantling and transportation of materials to depression levels. Similar observations are highlighted in the characterization of lateritic weathering in intertropical humid zones in Africa [\u003cspan citationid=\"CR72\" class=\"CitationRef\"\u003e72\u003c/span\u003e, \u003cspan citationid=\"CR73\" class=\"CitationRef\"\u003e73\u003c/span\u003e]. These characteristics are specifically observed in the South Cameroon plateau landscapes [\u003cspan citationid=\"CR58\" class=\"CitationRef\"\u003e58\u003c/span\u003e, \u003cspan citationid=\"CR73\" class=\"CitationRef\"\u003e73\u003c/span\u003e, \u003cspan citationid=\"CR74\" class=\"CitationRef\"\u003e74\u003c/span\u003e, \u003cspan citationid=\"CR75\" class=\"CitationRef\"\u003e75\u003c/span\u003e]. In the study area, intense weathering favours hydrolysis processes of primary silicates permitting the formation of secondary minerals such as kaolinite (monosiallitization), gibbsite (allitization), iron oxides and the individualization of coarse minerals (kyanite, garnet and quartz) observed along the pedologic profile. Also, at the level of the different pedologic profiles, kaolinite amount diminishes the more the layer is deeper into the soil. Its alteration leads to the formation of gibbsite due to the iron-rich environment in which it is found [\u003cspan citationid=\"CR58\" class=\"CitationRef\"\u003e58\u003c/span\u003e, \u003cspan citationid=\"CR73\" class=\"CitationRef\"\u003e73\u003c/span\u003e, \u003cspan citationid=\"CR74\" class=\"CitationRef\"\u003e74\u003c/span\u003e, \u003cspan citationid=\"CR75\" class=\"CitationRef\"\u003e75\u003c/span\u003e, \u003cspan citationid=\"CR76\" class=\"CitationRef\"\u003e76\u003c/span\u003e]. Pyrite and pyrhotite are imprisoned in compact porphyloblastic garnet phases in granitic michaschists [\u003cspan citationid=\"CR76\" class=\"CitationRef\"\u003e76\u003c/span\u003e]. Micaschists erosion permit the liberation of mica (biotite, muscovite), iron hydroxide (goethite), iron oxide (hematite) and the embedded iron sulphide (pyrite and pyrhotite) [\u003cspan citationid=\"CR58\" class=\"CitationRef\"\u003e58\u003c/span\u003e, \u003cspan citationid=\"CR73\" class=\"CitationRef\"\u003e73\u003c/span\u003e, \u003cspan citationid=\"CR74\" class=\"CitationRef\"\u003e74\u003c/span\u003e, \u003cspan citationid=\"CR75\" class=\"CitationRef\"\u003e75\u003c/span\u003e, \u003cspan citationid=\"CR76\" class=\"CitationRef\"\u003e76\u003c/span\u003e]. Mica corrosion also results in the genesis of gibbsite. Geothite is the dominant iron form observed along the different horizons, confirming the humid climate of the studied area in which the rocks are exposed. Its depletion equally gives birth to gibbsite by aluminium accumulation during allitization process. Alkaline feldspars and plagioclases are leached but not completely. Their erosion as primary minerals lead to the formation of kaolinite during monosiallitization process. All titanium oxides are completely leached during intense weathering. Contrary to what is usually seen in South Cameroon plateau where kaolinite is the main mineral, which accompanies iron oxides in altitude\u0026thinsp;\u0026le;\u0026thinsp;800 m [\u003cspan citationid=\"CR58\" class=\"CitationRef\"\u003e58\u003c/span\u003e, \u003cspan citationid=\"CR73\" class=\"CitationRef\"\u003e73\u003c/span\u003e, \u003cspan citationid=\"CR74\" class=\"CitationRef\"\u003e74\u003c/span\u003e, \u003cspan citationid=\"CR75\" class=\"CitationRef\"\u003e75\u003c/span\u003e, \u003cspan citationid=\"CR76\" class=\"CitationRef\"\u003e76\u003c/span\u003e]. In Dibang, gibbsite is the main mineral which accompanies iron oxides (goethite).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec26\" class=\"Section2\"\u003e \u003ch2\u003e5.2. Thermal and sintering properties\u003c/h2\u003e \u003cp\u003eMullitization and recrystallization processes during the decomposition of kyanite by heating are closely linked to the particles size and the oxides composition of kyanite itself. In relation to particles size, [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e] demonstrated that crushed kyanite minerals decomposition begin at lower temperatures than that of uncrushed ones, thereby accelerating the appearance of mullite and silica glass. Also, Kashcheev et al. [77] detailly described the effect of RO, R\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e, and RO\u003csub\u003e2\u003c/sub\u003e oxides and impurity materials on decomposition during heating of kyanite in oxidizing and reducing atmosphere. He highlighted that these oxides not only increase or diminish the quantity of mullite and cristobalite to be formed but also influence the temperature and rates at which they are produced. In the Dibang area, case of the study, kyanite minerals were crushed and sieved under \u0026lt;\u0026thinsp;75 \u0026micro;m and the obtained powder was used for geochemical, thermal and sintering analyses. Geochemical result of major oxides portrayed the predominance of alumina \u003cb\u003e(\u003c/b\u003e41.1\u0026ndash;57.8%) followed by silica (38.6\u0026ndash;47.1%) and a quite low percentage of iron (0.99\u0026ndash;3.67%). The other oxides (CaO, MgO, Na\u003csub\u003e2\u003c/sub\u003eO, K\u003csub\u003e2\u003c/sub\u003eO, Cr\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e, TiO\u003csub\u003e2\u003c/sub\u003e, MnO, P\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e, SrO, BaO) being in trace concentrations. Exposed to heating conditions, the powder completely transformed into mullite and cristobalite at \u0026lt;\u0026thinsp;1300 \u0026ordm;C. This can be explained by the role of some oxides during heating such as Cr\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e which tended to uplift temperature rates of decomposition by about 20\u0026ndash;30\u0026ordm;C thereby delaying the occurrence of mullite and silica glass phases. On the other hand, CaO, TiO\u003csub\u003e2\u003c/sub\u003e and MgO, has the tendency of reducing mullitization temperature and slowing down the mullitization process, while Fe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e inclined to increase the quantity of mullite and cristobalite. It should be noted that, the alkaline oxides of trace concentrations have negligible threat on the refractory properties of the final product (mullite and cristobalite). However, their presence in the raw kyanite may contribute to low temperature transformation of kyanite to mullite and cristobalite. Furthermore, the Dibang kyanite totally transforms to mullite and silica glass (cristobalite) at \u0026lt;\u0026thinsp;1300 \u0026ordm;C which is advantageous on the part of energy consumption most especially in refractory industries.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec27\" class=\"Section2\"\u003e \u003ch2\u003e5.3. Industrial applications\u003c/h2\u003e \u003cp\u003eBased on the chemical, thermal and sintering results combined with the microstructural observations of the Dibang kyanite minerals, it is observed that alumina is the predominant oxide (41.1\u0026ndash;57.8%) followed by silica (38.6\u0026ndash;47.1%) and iron (0.99\u0026ndash;3.67%). The other alkalins are in trace concentrations (0.19\u0026ndash;0.01%). Also, the milled kyanite began its decomposition at about 800\u0026deg;C to completely transform to mullite and cristobalite at about 1300\u0026deg;C. Whereas, it has been proven that kyanite utilization is very wide in the industrial area. Its demand is linked to the production of high alumina refractories after firing process [78]. Seven sectors are identified worldwide as concerned the consumption of all types of refractory materials according to their rate of consumption. The first rang is occupied by the (i) \u0026ldquo;metallurgical industries\u0026rdquo; which essentially dials with the production of steel and iron with a total consumption of 70% worldwide, followed by the (ii) \u0026ldquo;cement industries\u0026rdquo; with a total consumption of 7%, (iii) \u0026ldquo;energy and chemical industries\u0026rdquo; with 6%, (iv)\u0026ldquo;non-ferrous industries\u0026rdquo; with 3\u0026ndash;4%, (v) \u0026ldquo;ceramic industries\u0026rdquo; with 4%, (vi) \u0026ldquo;glass industries\u0026rdquo; with 2\u0026ndash;3% and (vii) \u0026ldquo;other-end users industries\u0026rdquo; with 3% [79]. In all these different industries, kyanite is mainly used as pre-fired grog mixed with other components before being applied in different ways depending on the final usage. Also, chemically spoken, these seven refractory sectors have the same specifications which is \u0026ldquo;high alumina content, low iron and alkalies content\u0026rdquo;. Meanwhile, the technical specifications vary from one sector to the other. In the metallurgical, glass, non-ferrous, energy and chemical sectors, the technical specifications are low thermal conductivity, excellent heat insulation, excellent thermal shock resistance, significant energy-saving effects, semi-light weight to light weight in furnace bodies, insulators and the like, very slow corrosion and strong penetration resistance to acidic and alkaline slag, high refractoriness under load - temperatures of \u0026ge;\u0026thinsp;1000\u0026ndash;1700\u0026deg;C [78, 80]. Those of ceramic sectors are semi-light and light weight refractory coatings in low and medium temperatures (\u0026ge;\u0026thinsp;400\u0026ndash;1200\u0026deg;C), good bonding strength at medium to high temperatures, good abrasive thermal shock, peeling and good wear resistance, high refractoriness under load [80]. While those of cement sectors are poor porosity, high density and strength, good volume stability, excellent thermal and erosion shock resistance [80]. And those of other end-users are high refractoriness under load, high strength and good heat insulation and energy-saving effects during service, temperature of \u0026ge;\u0026thinsp;400\u0026ndash;1200\u0026deg;C [80]. This clearly demonstrates that chemically spoken, Dibang kyanite minerals responds to the chemical specifications demanded in all the seven refractory sectors and based on its technical specifications. Dibang Kyanite minerals are suitable for the elaboration of refractory for low energy consumption as kyanite minerals are transformed into mullite at temperature below 1300\u0026deg;C. However, further investigations are needed to study the thermal behaviour of the low-temperature pre-calcinated product, to qualify the specific industrial applications and the suited modifier additives.\u003c/p\u003e \u003c/div\u003e"},{"header":"6. CONCLUSION","content":"\u003cp\u003eIn the light of this study, the following remarks can be drawn. The Dibang kyanite minerals are general dominantly found in weathering mantles and alluvial deposits although they are also found in kyanite-garnet micaschists. They are of \u0026le;\u0026thinsp;6.5 cm elongated and prismatic with angular (residual deposits) or rounded and sub-rounded borders. They are of deep dark blue colour generally associated with garnet and quartz. Their rough or smooth morphology is ascribed to the combine action of transportation (torrential and fluvial) and water erosion after their withdrawal and release by residual drainage. Microscopic observations on fresh garnet-kyanite micaschists displays an hetero-granular granoblastic texture made up of garnet (20\u0026ndash;25%), biotite, quartz (10\u0026ndash;15%), kyanite (15\u0026ndash;20%), muscovite (\u0026lt;\u0026thinsp;10%), biotite (5\u0026ndash;8%), K-feldspars and accessory minerals such as zircon, apatite and opaques minerals. The occurrence of free kyanite minerals in various levels of weathering mantles could be ascribed to various weathering processes, including physical alteration and chemical alteration. Kaolinite results from monosiallitization processes while gibbsite is of allitization processes. Geothite is the dominant iron type observed in all the weathering mantles. Hematite appears either as an early stage of ferruginization in some layers of weathering profiles or as a result of the corrosion of garnet crystals. X-ray diffraction depicts a highly crystallised mineral phase, which is characteristic feature of weathered fragments subjected to prolonged washing by water current along the river a prove that the kyanite alluvial minerals has undergone a complete natural lixiviation and surface refinement. X-ray fluorescence of major elements illustrates the different oxides of rich (alumina, silica) and poor (iron, alkaline and alkali metals) quantities justified by the chemical alteration in which they are exposed. Thermal and sintering behaviour portrays a complete transformation of kyanite to mullite and silica glass at about at 1300\u0026ordm;Cwhich is advantageous characteristic of low energy consumption.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAcknowledgments\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors would like to thank the editor of the journal \u0026ldquo;Discover Geoscience\u0026rdquo; for suggesting the publication of this paper. The authors would also thank all the anonymous reviewers who assisted greatly to improve the quality of this paper.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthor contribution\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eTVNM, JFNB and MST conceptualized the current study. TVNM and JFNB wrote the first draft manuscript. MST, SPN, EK, ECB and JE edited and reviewed the manuscript. All authors have read and agreed to the published version of the manuscript.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding Statement\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNot applicable\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eData Availability\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eAll data used in this manuscript were results of the field and laboratory investigations carried out on the application of propecting of kyanite alluvial minerals. The procedures to achieving these results have been extensively described under the methodology. No data were sourced online or replicated from previous studies. All information is primary and, on this note, no available link to any data. In addition, appropriates references have been duly cited in the work to corroborate the indings of previous work done.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eEthics approval, consent to participate and consent for publication\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNot applicable\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eClinical trial number\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNot applicable\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCompeting Interests policy\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare that there are no competing interests regarding the publication of this paper.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eJonas AI. Geology of kyanite belt of Virginia. Virginia Geol Surv Bull. 1932; pp 1\u0026ndash;38.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eJohnson SS. 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All rights Reserv.\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"discover-geoscience","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"","sideBox":"Learn more about [Discover Geoscience](https://www.springer.com/journal/44288)","snPcode":"44288","submissionUrl":"https://submission.nature.com/new-submission/44288","title":"Discover Geoscience","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Discover Series","inReviewEnabled":true,"inReviewRevisionsEnabled":true},"keywords":"Kyanite, Petrological Analysis, Geological Environment, Liberalization Mechanism, Industrial Properties, Central Africa Fold Belt","lastPublishedDoi":"10.21203/rs.3.rs-6649891/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-6649891/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThe Central Africa Fold Belt (CAFB) in Cameroon, is made up of high-grade metamorphic rocks endowed with kyanite alluvial minerals that are poorly characterized for industrial purposes. To resolve this constraint, field occurrence, optical microscopic observations and morphoscopic study of Dibang kyanite alluvial minerals were carried out. X-Ray Diffraction, X-ray Fluorescence, thermal and sintering analyses were conducted to elucidate their geological environment, liberalization mechanism and industrial properties. In Dibang, kyanite minerals generally occur in kyanite-garnet micaschists, weathering mantles and in alluvial deposits. They are mostly elongated and prismatic with angular rounded or sub-rounded borders. They are of deep dark blue colour associated with garnet and quartz. Their quasi-smooth or smooth morphology is ascribed to the combined action of transportation (torrential and fluvial) and water erosion after withdrawal and release by residual drainage. Microscopic observations of fresh kyanite-garnet micaschists display a grano-nemato-lepidoblastic and oriented microstructure made up of garnet, quartz, kyanite, muscovite, plagioclase, pyroxene and opaques minerals. X-Ray Diffractogram portrays kyanite, with impurities, including micas, muscovite, K-feldspars, quartz, and pyrite mineral phases. The naturally composed mineral composition of the kyanite deposit is pseudo-perfect for the formation of mullitized elements, impeccable for refractory applications. X-ray fluorescence of major elements shows the predominance of alumina and silica, and a quite low percentage of iron oxide. The alkaline and the alkali earth metal oxides occur in traces. The thermal and sintering analysis demonstrates mutillization and recrystallization processes at quite low temperatures (1100\u0026ordm;C to 1300 \u0026ordm;C), with the complete transformation of kyanite to mullite.\u003c/p\u003e","manuscriptTitle":"Characterization of the Dibang kyanite Minerals from the Southern Domain of the Central Fold Belt in Cameroon: Geological Environment, Liberation Mechanism and Industrial Properties","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-06-26 16:09:02","doi":"10.21203/rs.3.rs-6649891/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2025-09-02T11:36:49+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-08-11T17:31:07+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-08-06T07:13:45+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-08-05T00:25:34+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-08-04T07:20:14+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"48954317984602839478205817413849967490","date":"2025-08-01T23:35:07+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"295108836090187685342084152957549812462","date":"2025-07-31T02:51:28+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"18093513736429955169963651372735018702","date":"2025-07-29T21:06:34+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"1625017883493518087853365669564976247","date":"2025-07-28T00:03:32+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-07-16T11:41:42+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"62654060806004451181147685771066962062","date":"2025-07-08T10:48:39+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"160669653770034590251891419412771022411","date":"2025-06-29T18:10:56+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"314808935459476171142847541647840488352","date":"2025-06-26T17:36:08+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2025-06-23T23:47:24+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2025-06-23T23:40:02+00:00","index":"","fulltext":""},{"type":"editorInvited","content":"","date":"2025-06-20T18:44:51+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2025-06-10T20:22:20+00:00","index":"","fulltext":""},{"type":"submitted","content":"Discover Geoscience","date":"2025-06-10T20:17:22+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"discover-geoscience","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"","sideBox":"Learn more about [Discover Geoscience](https://www.springer.com/journal/44288)","snPcode":"44288","submissionUrl":"https://submission.nature.com/new-submission/44288","title":"Discover Geoscience","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Discover Series","inReviewEnabled":true,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"eabeaf6c-7ac2-4d70-bea5-10768353e65a","owner":[],"postedDate":"June 26th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[],"tags":[],"updatedAt":"2025-12-17T09:24:37+00:00","versionOfRecord":[],"versionCreatedAt":"2025-06-26 16:09:02","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-6649891","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-6649891","identity":"rs-6649891","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}