Metamorphic fluid produced by devolatilization of greenstone belt metavolcanic and metasedimentary rocks plays a critical role in the formation of Archean lode gold-only deposits. In this study, mass balance and phase equilibria modelling were combined with trace element analyses and 87Sr/86Sr composition of hydrothermal scheelite and apatite from gold-mineralized reefs of the Neoarchean Hutti gold deposit in southern India. These approaches were integrated to constrain the nature of fluid and to quantify the relative contributions of metabasalt- and metapelite-derived fractions involved in mineralization. Variable REE patterns, Eu anomalies, and trace elements concentrations enabled classification of scheelite into four types and apatite into three, reflecting fluid composition. Low Mo concentrations and high Sr/Mo ratios in scheelite indicate a reduced, metamorphic fluid, with little magmatic input. The bulk of the measured 87Sr/86Sr ratios of apatite from Hutti range from 0.70140 to 0.70860 (mean: 0.70343 ± 0.00193, 2σ) while those in scheelite span 0.70156 to 0.70818 (mean: 0.70327 ± 0.00181, 2σ). We modelled the stepwise release of Sr and the 87Sr/86Sr ratios of fluids expunged during prograde metamorphism of metabasalt and metapelite using a mass balance approach. The model estimates the isotopic compositions of fluids resulting from mixing varying proportions of metabasaltic (0.70109 ± 0.00185) and metapelitic (0.71186 ± 0.00453) inputs across different metamorphic grades. Mixing calculations indicate that 70–95% metabasalt-derived fluid mixed with 30–5% metapelite-derived fluid can explain the 87Sr/86Sr ratios of most scheelite and apatite. The metapelitic component was crucial for explaining the gold and sulphur budget, although the bulk of the fluid itself was derived from metabasalt.

Calcite is one of the primary host for rare earth elements (REE) in carbonatites. The Kamthai carbonatite complex contains the largest REE budget among Indian carbonatite complexes. This study reports new 87Sr/86Sr isotope ratios of six textural types of calcite in carbonatite and calcite-quartz veins in phonolite of Kamthai along with their major and trace element composition to constrain the magmatic and hydrothermal evolution of carbonatite. Four textural types of calcite (magmatic: CalM and CalPR; and secondary: CalSK and CalS) in carbonatite show consistent mantle-like 87Sr/86Sr ratios. The CalM has restricted 87Sr/86Sr (0.70437±0.00005) and contains high concentrations of ƩREE, Sr, Ba, and Mn without any Ce anomaly. It probably crystallized from the late-stage brine-melt with primary carbocernaite. The CalM is partially re-equilibrated into CalPR (0.70425±0.00024) during interaction with syn-magmatic fluid, resulting in the loss of a significant amount of REE and Sr. The two secondary varieties of calcite show overlapping and marginally higher 87Sr/86Sr (CalSK: 0.70469±0.00041; CalS: 0.70478±0.00025; δCe*:

This article reviews all the contributions made on genetic aspects of various Indian metallic ore deposits between the period 2020 and 2023. We cover ores of chromite, platinum group elements, gold, uranium-copper ores of Iron Oxide Copper Gold (IOCG) affiliation, rare earth metals (+ niobium + tantalum + yttrium), and lithium-tungsten, the last two being fresh additions compared to the earlier reviews. Inferences are mainly derived by in-situ trace element analysis of important common ore minerals such as pyrite, chalcopyrite, sphalerite, magnetite and apatite, along with the hydrothermally precipitated gangue phases such as biotite and tourmaline. Studies on conventional stable isotope (of oxygen, carbon and sulfur) analysis continues to be a widely used tool for constraining ore genetic models. In addition, in-situ isotopic measurement of boron and lithium, respectively in tourmaline and micas, along with U–Pb dating of hydrothermal monazite, provided a quantum jump in our understanding of ore-forming processes.

The major-trace element and C-O-Sr isotopic composition of calcite constitute important proxies for reconstructing the magmatic and hydrothermal evolution of carbonatites. This study reports new 87Sr/86Sr isotope data measured in-situ from six textural types of calcite in carbonatite and fenitized phonolites of the Kamthai carbonatite complex in western India. Textural relations, along with major-trace element chemistry, and Sr isotope composition helps to discriminate four types of calcite in carbonatites-magmatic (CalM), partially reequilibrated magmatic (CalPR), and two varieties of secondary (CalSK and CalS). CalM has high concentrations of FREE + Y, Sr, Ba and Mn, restricted 87Sr/86Sr (0.70437 +/- 0.00005), and lacks Ce or Y anomaly. It crystallized from late-stage brine-melt together with primary carbocernaite after prolonged fractional crystallization of the carbonatite magma. CalPR has identical 87Sr/86Sr (0.70425 +/- 0.00024) as CalM, and formed by its partial reequilibration, accompanied by significant loss of REE, and Sr during interaction with synmagmatic fluid. The two secondary varieties of calcite in the carbonatites have overlapping but marginally higher 87Sr/86Sr (CalSK = 0.70469 +/- 0.00041; CalS = 0.70478 +/- 0.00025) compared to CalM, which indicates that they were altered by syn- to para- magmatic fluids with minor contribution from post-magmatic fluid (e.g., external crust-derived fluid). Both types are highly porous and have low-Z contrast in back scattered electron images, which is the result of expulsion of most of its original Sr and REE budget during fluid-induced reequilibration. Two types of secondary calcite (CalS1 and CalS2) are identified in three veins within fenitized phonolite. These contain the lowest abundance of THREE + Y, Sr, Ba and Mn. One type (CalS2) occurs in calcite-quartz-pyrite veins and is characterized by LREE-depleted REE patterns and igneous-calcite-like 87Sr/86Sr (0.70434 +/- 0.00073). It possibly crystallized from evolved late-stage para-magmatic fluids from the carbonatite magma after the brine-melt stage of primary LREE mineralization. The other type of vein calcite (CalS1) is characterized by strong negative Ce (delta Ce*: << 0.034) anomalies, which indicates that it crystallized from oxidized fluids from which Ce was removed as Ce (IV). The 87Sr/86Sr of some of these calcites are significantly more radiogenic (0.70768 +/- 0.00011) than magmatic calcite. This indicates that post-magmatic fluid played a significant role in their formation. Two component mixing calculations show that up to 40-70 % post-magmatic fluid mixed with syn-magmatic fluid can account for their Sr isotope composition. Magmatic calcite and carbocernaite were the major sources of REE and Sr during secondary redistribution.

Quartz is one of the most abundant mineral in the continental crust, occurring in a wide variety of igneous, metamorphic, and sedimentary rocks. It incorporates several trace elements such as Ti, Al, Li, Ge, B, and P in its structure during crystallization/precipitation from magma/fluid, which can potentially be used as petrogenetic indicators. Being physically and chemically resilient during sedimentary recycling, detrital quartz can retain the signatures of the physicochemical environment of their formation. Earlier studies have mostly attempted to discriminate quartz from magmatic and magmatic-hydrothermal systems using bivariate or ternary discrimination diagrams. In this study, we developed three robust machine learning (ML) methods (XGBoost, LightGBM, and CatBoost models) to discriminate quartz from a wide variety of magmatic/magmatic-hydrothermal host rocks based on their trace element chemistry. For this purpose, we compiled published 11,267 trace element analyses of quartz grains considering 50 trace elements from 14 different host rocks, namely A-, S-, I- type granitoids and pegmatites, A-, I- type volcanic rocks, A-, S- type- granite greisen, hydrothermal veins associated with A-, S-, I- type intrusions, and metamorphic rocks. The three ML classifiers can successfully discriminate quartz from the aforementioned groups with an average accuracy of ∼95%. Quartz hosted in each system can be correctly predicted with >75% classification accuracy, except for I-type pegmatite. The Shapley Additive exPlanations (SHAP) algorithm, which measures the contribution of each element to the output predicted by the ML models, indicates that Ti, Li, Ge, Al, B, and P exert the highest control on the ML classifiers. We propose our ML models as a new tool for constraining sedimentary provenance and demonstrate the usefulness of our approach using the trace element data of detrital quartz from sediments in the catchment area of the Bega River in the Lachlan Fold Belt, Australia.

The composition of the fluid phase is often a poorly constrained variable in many ore deposits. In this study, we used calcite-fluid partition coefficients extrapolated to the P-T conditions of mineralization using the lattice strain model to reconstruct the composition of the hydrothermal fluids associated with different stages of the hydrothermal alteration and secondary rare earth element (REE) mineralization in the Kamthai carbonatite complex of western India. We identified three generations of calcite including magmatic, two generations of secondary/hydrothermal, as well as partially reequilibrated magmatic grains. The magmatic and partially reequilibrated calcite are unusually enriched in the REE, particularly the LREE, and Sr, which were incorporated via coupled cationic substitutions from highly differentiated brine- and incompatible element-enriched carbonatitic melts. Calcite and carbocernaite were the important primary phases that sequestered the REE from the carbonatite magma. Textural and geochemical evidence suggest that magmatic calcite and carbocernaite underwent extensive partial to complete reequilibration through dissolution and reprecipitation during hydrothermal alteration. The prominent chemical changes during the alteration of calcite involved loss of substantial REE, Sr, Fe, and Mn, and transition from LREE-dominated to LREE-poor compositions. The REE released during hydrothermal alteration were incorporated in secondary REE minerals such as REE-(fluor)carbonates, REE-(hydroxyl)carbonates, ancylite, and cerianite. The reconstructed chemistry of the carbonatite melt and the hydrothermal fluid, together with the trace element chemistry of secondary calcite, point towards progressive decrease in the REE contents. However, the HREE were conserved and ƒO2 increased from the most primitive to the most evolved fluid. The REE were redistributed as alkali‑carbonate-hydroxyl complexes, which can explain the LREE/HREE fractionation observed between the early and the late-stage hydrothermal fluid. Precipitation of the LREE-bearing secondary minerals is attributed to a decrease in temperature of the hydrothermal fluid as a consequence of mixing of the carbonatite-derived fluid with a relatively cooler and oxidized fluid. Such mixing explains the observed negative Ce-anomaly in hydrothermal calcite.

In this study, textural relations coupled with mineral chemistry of hydrothermal magnetite, fluorapatite, monazite and allanite from the Mohuldih uranium deposit in the Singhbhum Shear Zone (SSZ) is used to characterize the nature of the fluid during various events of alteration and uranium precipitation. These minerals have two distinct textural types, the earlier of which are coeval with the uraninite mineralization. The later type formed during subsequent hydrothermal overprint as a result of coupled dissolution‐reprecipitation of earlier fluorapatite and mobilization of light rare earth elements. Uranium‐lead dating of texturally‐constrained hydrothermal monazite grains yields two major concordant age clusters at 1855 ± 7 Ma and 963 ± 10 Ma and several discordant analyses. Two spot analyses furnish concordant ages of 1656 ± 33 Ma and 1438 ± 35 Ma that are identical within error of the 207Pb/206Pb ages (1628–1643 Ma and ca. 1392 Ma) of several discordant data points. Similar ages have been reported by other studies from the rocks of the SSZ and are therefore considered to be geologically meaningful. The oldest age of ca. 1855 Ma obtained from the texturally early core regions of monazite corresponds to the earliest stage of uraninite mineralization. The two main alteration types can be interpreted based on the known metamorphic events in the SSZ. A combination of high‐temperature calcic iron ± sodic and high‐temperature potassic iron alteration accompanied the M1 metamorphic event and the low‐temperature silicification/K‐Al alteration during the M2 metamorphic event. A comparative study between our data on magnetite and fluorapatite compositions with those from global iron oxide‐Cu‐gold (IOCG) and iron oxide‐apatite deposits classifies Mohuldih as an IOCG‐type deposit.

Calcite carbonatites from the Kamthai alkaline complex in western India are highly enriched in Sr and the rare earth elements (REE) owing to their formation from highly differentiated carbonatitic magma. Pegmatitic calcite carbonatites preserve rare magmatic intergrowth of rod/pod-like carbocernaite [(Ca, Na)(Sr, REE, Ba)(CO3)2] and REE + Sr-rich calcite. This intergrowth is interpreted to be the result of rapid simultaneous crystallization of the phases from a brine-rich carbonatitic magma. Primary carbocernaite, calcite, and britholite [(LREE, Ca)5(SiO4, PO4)3(OH, F)] sequestered Sr and REE from the brine-rich melt and constitute the major sources of these elements during hydrothermal redistribution. Replacement textures suggest fluid-assisted, post-magmatic hydrothermal REE redistribution through dissolution-reprecipitation process that concentrated the REE into secondary REE-(fluor/hydroxyl)carbonates, cerianite (ideally Ce4+O2), ancylite [(Sr, Ca)LREE(CO3)2(OH)& BULL; (H2O)], and monazite. Hydrothermal alteration of magmatic calcite leached out the LREE, whereas in case of carbocernaite and britholite, an increase in their REE contents is noticed, followed by pseudomorphic replace-ment by REE-(fluor/hydroxyl)carbonate minerals. The carbonatite-derived hydrothermal fluids initially transported the REE as sulfate and later as hydrox-yl-carbonate complexes. The ligand transition was a consequence of the precipitation of baryte, celestine, and pyrite, which led to a reduction in fluid sulfur content and increase in its pH due to interaction with carbonates. Precipitation of secondary REE minerals was triggered by decrease in ore fluid temperature due to interaction with relatively cooler, oxidized fluid and interaction with carbonates. Carbocernaite, ancylite, cerianite, and Ce-bearing REE-(fluor)carbonates constitute early precipitated secondary REE minerals along with baryte, celestine, and pyrite as by-product phases, whereas both Ce-and La-rich, hydroxyl-dominated members of bastna & BULL;site, parisite, and synchysite, along with monazite were the dominant REE minerals which precipitated during the advanced hydrothermal stage, with siderite as a by-product.

In this study, we review changes in Archean granitoid chemistry using stacked probability density estimation and statistical change-point analyses. A significant change in Archean sodic granitoid composition occurs in the 3.9-3.75 Ga period, marked by a shift of SiO2, Al2O3, Na2O, V, Cr, Sr, Sr/Y to higher, and TiO2, FeOT, MnO, P2O5, A/NK, A/CNK, Sc, Ba, Ta, Nb, Hf, Y, and rare earth elements to lower values, which reflects different formation P-T regime and petrogenetic processes. Using phase equilibria and trace element modelling, we demonstrate that the pre-3.9 Ga Acasta Tonalite Gneiss (ATG)-like granitoids formed at shallow depths (similar to 3 km) but are chemically distinct from impactites of all known large impact craters with basaltic/mixed target rocks. Impact melting produces MgO-rich melts at relatively greater "apparent" depths, reflecting target rock chemistry and contribution from the upwelling mantle, and is unlikely to have produced the shallow-seated ATG rocks. The ATG trace element chemistry is similar to many modern-day non-arc settings felsic rocks, which suggests that the melting regime in these extensional settings also existed before 3.9 Ga and ATG formed in a mantle plume-driven extensional tectonic regime involving melting of long-lived mafic proto-crust at shallow crustal depths above mantle upwelling. In contrast, the 3.9-3.75 Ga transitional and post-3.75 Ga TTGs formed by deep-seated (25-50 km) melting in equilibrium with garnet-bearing amphibolite. When considered together with Ti isotopic evidence of shift from tholeiitic to calc-alkaline magmatism in the 4.0-3.75 Ga period, the evidence for a transition from a regime dominated by crustal reworking to one of significant juvenile input at 3.60-3.85 Ga, noted in trace element/Hf-isotope composition of detrital zircon from several cratons and the reported ultra-high pressure metamorphism/interleaving arc-plume sequence, require a greater depth of melting. We interpret this transition to mark a gradual shift from stagnant-lid to intermittent mobile-lid-type plate tectonics involving deeper subduction of oceanic lithosphere. However, from the single occurrence of pre-3.9 Ga ATG rocks and their similarity with some Archean Fe-rich silica-saturated rocks chemistry, it is unknown whether plume magmatism was the only active mechanism or operated in conjunction with mobile-lid tectonics on early Earth, like in Archean.

Fluids play an important role in many geological/ore genetic processes. The composition of the hydrothermal fluid is a critical but often unknown parameter that controls the mobilization of elements and their concentration into mineralized zones. In-situ analyses of fluid inclusions trapped in minerals using laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS) is a powerful tool to constrain the composition of the mineralizing fluid. The LA-analysis of fluid inclusions is analytically challenging due to potential mismatch of matrix between fluid inclusions and solid NIST reference glasses commonly used as calibrating standards. We conducted experiments to evaluate the effects of using solid and liquid as calibrating standard on data quality during ablation of liquid/mineral fluid inclusions, as well as the effects of variable energy fluence and repetition rate on the time-dependent elemental fractionation. The LA-analyses of liquids (with NaCl matrix) when standardized against another solution has lower precision and accuracy compared to standardization with NIST reference glasses. The 193 nm laser has little matrix effect and causes negligible elemental fractionation. The trace element concentrations of liquids retrieved by external standardization with NIST reference glass has better accuracy and precision. Higher laser fluence (8.5 J/cm2) produces better sensitivity, lesser time-dependent elemental fractionation, lower detection limits, and better accuracy/precision and is recommended for ablation of natural fluid inclusions or liquids. We tested our preferred analytical protocol by analyzing the composition of quartzhosted fluid inclusions from the Malanjkhand copper deposit in central India. The LA-ICPMS measurements of the fluid inclusions help to establish that the mineralizing fluid had high concentrations of K, Rb, and Cs. Fluid inclusions from the Malanjkhand copper deposit are trapped from fluids that are dominantly of magmatic origin, sourced from highly differentiated granitic magmas. The NIST glasses are appropriate calibrating standards for ablation of synthetic liquids as well as natural fluid inclusions. (c) 2023 Elsevier B.V. All rights reserved.

Zinnwaldite, a Li, Rb-mica is a common magmatic or hydrothermal mineral in many tungsten deposits. In this study, we use the trace element and Li-isotope composition of zinnwaldite from Degana, the largest tungsten deposit of India, to constrain the source and evolution of the ore fluid, the precipitation mechanism of W and the roles of fractional crystallization, fluid exsolution and fluid-rock interaction in the mineralization process. Textural evidence suggests that the mineralization in the Degana rocks involved at least two stages of fluid infiltration. The earlier of the two was multi-pulsed and responsible for the primary tungsten and zinnwaldite mineralization. The second hydrothermal stage caused partial dissolution and reprecipitation of both wolframite as well as zinnwaldite, reflected in the patchy zones that replace both minerals. The ore fluid had high con-centration of Li, Rb, Cs, Nb, and Ta as evident from zinnwaldite chemistry. The delta 7Li of the ore fluid (+14 to +19 %o), estimated from the Li-isotope composition of zinnwaldite in mineralized veins (delta 7Li = +12 to +17%o), is significantly heavier compared to upper/middle continental crust, ruling out the possibility of a metamorphic fluid source. The high concentration of incompatible elements including Cs, extremely low K/Rb (10-15), is best explained by its growth from fluids exsolved from an enriched, late-fractionated granitic melt. Alteration of the host granite, formation of greisen, large-scale albitization and muscovitization are indicative of fluid-rock interaction, which might have increased the fluid pH, destabilizing fluoride complexes of W, resulting in the precipitation of wolframite. The shift in the chemical and Li-isotope composition from the early mica to late altered ones in the greisen indicates interaction of the hydrothermal fluid with the host rocks. A U-Pb Concordia age of 838 +/- 9 Ma retrieved from magmatic domains of zircon from the Degana granite dates it emplacement and represents the maximum age of the W-mineralization.

The Amba Dongar carbonatite complex in western India comprises an inner ring of carbonatite breccia surrounded by a sövite ring dike. The various carbonatite units in the body include calcite carbonatite, alvikite, dolomite carbonatite, and ankerite carbonatite. The carbonate phases (calcite and ankerite) occur as phenocrysts, groundmass phases, fresh primary grains, and partially altered grains and/or pseudomorphs when hydrothermally overprinted. Rare earth element (REE) enrichment in the groundmass/altered calcite grains compared to the magmatic ones is ascribed to the presence of micron-sized REE phases. Fluorapatite and pyrochlore constitute important accessory phases that are altered to variable extents. Higher concentrations of Sr, Si, and REEs in fluorapatite are suggestive of a magmatic origin. Fresh pyrochlore preserves its magmatic composition, characterized by low A-site vacancy and high F in the Y-site, which on alteration becomes poorer in Na, Ca, and F and displays an increase in vacancy. The C-O isotope compositions of the carbonates also corroborate the extensive low-temperature hydrothermal alteration of the carbonatites. The REE mineralization is the result of interaction of the carbonatite with a sulfur-bearing, F-rich hydrothermal fluid that exsolved from late-stage carbonatitic magmas. The hydrothermal fluids caused dissolution of the primary carbonates and simultaneous precipitation of REEs and other high field strength element (HFSE)-bearing minerals. Complex spatial associations of the magmatic minerals with the REE fluorocarbonates, [synchysite-(Ce), parisite-(Ce), bastnäsite-(Ce)] and florencite-(Ce) point to the formation of these REE phases as a consequence of postmagmatic hydrothermal dissolution of the REEs from fluorapatite, pyrochlore, and carbonates. Ubiquitous association of fluorite and barite with REE minerals indicates transport of REEs as sulfate complexes in F-rich fluids. Precipitation of REE fluorocarbonates/florencite resulted from fluid-carbonate interaction, concomitant increase in pH, and decrease in temperature. Additionally, REE precipitation was aided and abetted by the removal of sulfur from the fluid by the precipitation of barite, which destabilized the REE sulfate complexes.

Recent experimental works suggest that complexation with alkalis, carbonate, and hydroxyl groups enhances rare earth element (REE) transport and HREE/LREE fractionation, seen in carbonatite-hosted REE deposits. The Amba Dongar carbonatite complex in western India hosts fluorite and REE-fluorcarbonate mineralization occurring as vug/vein fillings or as disseminated ores associated with calcite, dolomite, apatite, baryte, and quartz. In this study, we analyzed the major and trace element composition of fluorite-hosted fluid inclusions, and the trace element chemistry of calcite and fluorite, using laser ablation inductively coupled plasma mass spectrometer (LA-ICP-MS) to characterize the nature of the hydrothermal fluid and the processes of mineral-fluid interaction. Fluorite contains aqueous bi-phase (liquid + vapor) fluid inclusions of variable size that furnish low salinities (0.4-2.2 wt% NaCl equivalent) and liquid-vapor homogenization temperatures (130 degrees C-155 degrees C). The fluid inclusions have high concentrations of alkalis (Na, K), Si, Al, Mg, and Mn, and their chemistry resembles orthomagmatic fluid derived from evolved carbonatite melts. They also have elevated MREE and HREE con-centrations relative to the LREE, that is significantly higher than in many other hydrothermal settings. Such fluids with fractionated LREE/HREE were likely derived from residual brines post the LREE-mineralization stage, when the HREE still remained in solution. This report of hydrothermal fluids with elevated MREE and HREE solubility from natural carbonatites supports experimental findings that alkali-carbonate-hydroxyl complexation helps to mobilize REE and fractionate the LREE from MREE and HREE. Magmatic calcite has LREE-enriched REE patterns while those of hydrothermally-altered calcite is nearly flat. The secondary calcite also has elevated concentrations of Na and K, which suggests that the alkali-rich fluids scavenged the REE from magmatic calcite and redistributed them into more insoluble REE-fluorcarbonates. The REE patterns of fluorite mimic those of its fluid inclusions, with the inclusions containing higher and more variable REE concentrations, suggesting that the REE signals of fluorite are coming from the ablation of fluid inclusions, and not from fluorite themselves.

Quartz is a ubiquitous mineral found in a wide range of igneous, metamorphic, and sedimentary rocks.As the mineral survives sedimentary recycling, detrital grains can retain the signatures of the P-T-X conditions during their crystallization/precipitation from magma/fluid.The trace element composition of quartz can, therefore, potentially reflect the genetic information of its host rock.Previous studies on using quartz chemistry for petrogenetic discrimination have either used bivariate or ternary discrimination diagrams (e.g., Ti-Al; Ti-Al/10-10*Ge), considering a limited number of elements [1, 2] or have used machine learning-based approaches to classify specific ore-genetic environments [3].Here, we have compiled published 11,567 trace element analyses of quartz grains from 14 different types of host rocks: granitoids (A-, S-, I-types), volcanic rocks (A-, S-, I-types), granitic pegmatites (A-, S-, I-types), greisen (altered A-, S-type granitoids), hydrothermal veins (associated with A-, S-, I-type magma), and metamorphic rocks.A rigorous machine learning tool has been applied to discriminate the large and high dimensional database of quartz hosted in different rock types, taking into account 50 trace elements.Our result shows that two supervised machine learning classifiers, i.e., XGBoost and LightGBM models, are able to discriminate quartz trace element data with an average accuracy of 95.5% and 95.8%, respectively.For both models, the normalized confusion matrix shows that each class (host rock) can be correctly predicted with more than 82% accuracy, except for metamorphic (~74%) and Itype pegmatite (33%).Additionally, the Shapley Additive exPlanations (SHAP) algorithm shows that Ti, Li, Ge, Al, Si, B, and P contents in quartz exert significant control in discriminating host rock types.These classifier tools can be used to identify the provenance of detrital quartz grains using their trace element chemistry.

in The nature of the geodynamic regime of crust formation in the Headean and early Archean remains poorly understood. There is also considerable debate on whether modern-day-like plate tectonic processes operated on the early Earth, as the thermal and mechanical structure of the lithosphere and mantle may have been different [1]. The bulk of the Archean continental crust is composed of tonalite-trodhjhemite-granodiorites (TTGs) produced by partial melting of hydrated basaltic rocks [2]. Secular changes in TTGs composition through the Archean may therefore reflects changing conditions of melting of metabasalts due to change in the geodynamic regime of crust formation. In this study, we applied stacked probability density estimates and statistical change-point analysis (Bai-Perron multiple breakpoints test and Bayesian change-point algorithm) on published dataset of TTG rocks [3] with ages spanning from 4.0 to 2.5 Ga to identify the timings of statistically significant changes in TTG chemistry. A systematic shift towards higher value in SiO 2 , Al 2 O 3 , MgO, Na 2 O, V, Sr, Rb contents, Sr/Y, La N /Yb N , Gd N /Yb N ratios, and towards lower value in the TiO 2 , FeO t , MnO, Sc, Cu, Zn, HFSEs, Y, Sm, Eu, and HREEs concentrations of TTG rocks is observed since ca. 3.7-3.8 Ga. The results are suggestive of a significant change in the process/conditions of continental crust formation in the Eoarchean and may be related to transition in tectonic mode, possibly from a stagnant-lid to intermittent

In the Proterozoic tungsten belts of Balda and Motiya in western India, tungsten mineralization is hosted in tourmaline-bearing quartz veins intrusive into pelitic schists and granites. Tourmaline is a ubiquitous phase in all rock types, and in this study, we use its major, trace element and B-isotope composition to constrain the nature of the tungsten (W)-bearing hydrothermal fluid and the processes involved in the precipitation of wolframite. We have also reconstructed the compositions of the W-precipitating fluids from mineral-fluid trace element partition coefficients that were extrapolated using the Lattice Strain Model. The tourmalines from both belts are of schorl composition and have high alkali, low Ca content, and moderate X-site vacancies. High Li, Mn, Zn, and Sn in the fluid in Motiya is suggestive of relatively saline fluid possibly derived from a granitic source. The high V/Sc ratios of tourmalines in the mineralized veins and wall-rock tourmalinites indicate an important role of biotite dissolution and fluid-rock interaction that contributed Fe-Mn for the precipitation of tourmaline and wolframite. The tourmalines in the mineralized veins at Balda (delta B-11(tur) = -10.9 +/- 0.7 parts per thousand, 2 sigma; n = 10) and those in the associated granites (delta B-11(tur) = -11.5 +/- 0.7 parts per thousand, 2 sigma; n = 6) have similar B-isotope composition, while those of the associated topaz granites and pegmatites (-13.9 +/- 0.7 parts per thousand, 2 sigma; n = 19) are isotopically lighter than the granites. The B-isotopic variation in the granite-pegmatite-vein system can be explained by fluid exsolution with the mineralized vein forming from exsolved fluid and the topaz-bearing granites and the pegmatites crystallizing from the residual melts. The delta B-11 of the mineralizing fluid is estimated to be ca. -7.4 parts per thousand at Balda and ca. -7.6 parts per thousand at Motiya, and were possibly derived from granites, consistent with extensive tourmalinization and muscovitization of the adjacent wall rocks, and high concentration of elements such as F, Li, B, Sn, Mn in the tourmalines and the reconstructed fluid. The chemistry and B-isotope composition of tourmalines in both the belts support the hypothesis that W-bearing hydrothermal fluid was primarily derived from a fractionated granitic source, and that precipitation of wolframite and tourmaline involved interaction of the granitic fluid with surrounding pelitic rocks.

In this study, the chemical and B-isotope composition of tourmalines that coprecipitated with uraninite in schistose rocks of the Mohuldih and Bagjata uranium deposits along the Singhbhum Shear Zone are used to constrain the sources and the nature of the mineralizing fluids, along with the mechanism of primary uraninite precipitation. Three generations of tourmaline are identified, which can be correlated with three generations of uraninite in the host rocks. These correspond to three major episodes of hydrothermal alteration of the shear zone rocks at 1.8-1.9 Ga, 1.66-1.56 Ga, and ca. 1.0 Ga, synchronous with metamorphism/granitoid activity. The texturally earliest tourmaline with δ11B of 8.8 ± 0.3 ‰ precipitated together with primary uraninite from externally-sourced high saline fluids derived from subducting slab during the 1.8–1.9 Ga hydrothermal alteration event. The precipitation of uraninite can be linked to the decreasing salinity of the hydrothermal fluid as a consequence of fluid-rock interaction. Dissolution of chlorite/biotite and the precipitation of more Mg-rich tourmalines resulted in decrease of fluid salinity, which destabilized Fe-chloride and U-chloride complexes leading to the precipitation of Fe-rich tourmaline together with primary uraninite. The texturally later second and third generation tourmalines (δ11B = 2.5 to 6.3 ‰) and uraninites formed from mixed fluids derived from the slab and dehydration of pelitic assemblages during renewed episodes of hydrothermal alteration synchronous with metamorphism at 1.66-1.56 Ga and ca. 1.0 Ga. The δ11B of the tourmalines from the schists of the Singhbhum Shear Zone correspond to the range of values (–10.4 ‰ to +6.0 ‰) reported for IOCG-type deposits associated with metamorphic slab-derived fluid sources.