In this study, U-Pb-Hf isotope composition and trace element chemistry of zircon from basement gneisses and quartzites of the Bihar Mica Belt (BMB), a belt of supracrustal rocks within the Central Indian Tectonic Zone, is used to constrain crustal growth and reworking. The protoliths of BMB gneisses were emplaced at 1651 +/- 5 Ma. The magmas were derived from juvenile and 1747 +/- 7 Ma I-type long-lived felsic precursors that survive as xenocrystic cores. Zircon grains from quartzites display two distinct morphologies. Grains with little rounding of edges have internal structures comprising 1750 +/- 5 Ma inherited cores mantled by 1657 +/- 4 Ma igneous zones that are identical to those from the granite gneisses. The epsilon Hf (t) and trace element composition of both the xenocrystic cores and the igneous mantles in these detrital grains are identical to those of zircon in the gneisses. They constitute molasse-like sediments derived from the nearby basement. More rounded grains furnish age clusters between 1857 and 2848 Ma, suggestive of long-distance transport and derivation from multiple sources. In -situ formed metamorphic rims around zircons in gneisses and quartzites furnish 1476-1466 Ma ages, dating the earliest metamorphic overprint. The age of sedimentation is bracketed between 1657 Ma and 1466 Ma. The 1651 +/- 5 Ma gneisses and its 1747 +/- 7 Ma felsic precursor were I-type, and emplaced in an arc setting. They constitute part of the expansive suite of Paleoproterozoic gneisses of the Chhota Nagpur Gneiss Complex emplaced during protracted period of arc-magmatism between 1.75 Ga and 1.65 Ga. Strongly positive epsilon Hf (t) of 2.0-2.85 Ga detrital zircons conforms to the global trend of positive epsilon Hf (t) excursions and high dT/dP gradients, and may correspond to passive margin juvenile magmatism associated with the break-up of Archean supercratons prior to Columbia assembly. The 1.86 Ga and 1.75 Ga detrital and xenocrystic zircons from the BMB have enriched epsilon Hf (t), in accordance with negative excursions seen in global zircon between 2.0 Ga and 1.70 Ga, reflecting progressive assembly of Columbia through collisional orogenesis. An excursion to strongly positive epsilon Hf (t), coinciding with low dT/dP gradients at ca. 1.65 Ga, reflects wide-spread formation of arcs linked to accretionary growth of Columbia.

Hydrothermal Iron-oxide-Cu-Au (IOCG) deposits are important exploration targets for a number of metals of economic importance. Voluminous sodium metasomatism is ubiquitous in most IOCG provinces. The origin of the metasomatic fluid responsible for the formation of albite-rich rocks in such terranes is contentious; both evaporite-derived fluid and magmatic fluid have been advocated. The Singhbhum IOCG province in India is known for hosting several polymetallic deposits from which U, Cu, and apatite-magnetite are mined as principal commodities together with Ni, Au, Ag, Se, Te, Mo, and low-Ti magnetite as by-products. Voluminous albite-rich rocks occur at several sites along the mineralized belt. Metasomatic albite schist comprising predominantly albite and quartz at Pathargora contains tourmaline intricately associated with albite. Based on textures and miner-alogical associations, tourmaline is classified as: tur1: coarse nodular tourmaline +/- albite +/- magnetite aggregate; tur2: disseminated fine-grained tourmaline in a schistose matrix; and tur3: tourmaline + biotite + magnetite + apatite clots. All tourmaline belongs to the alkali group and most to the dravite sub-group. Very low concen-trations of Li (avg 3.8 ppm), Zn (avg 6 ppm) and Mn (avg 21 ppm) but high V (avg 2130 ppm) and Ni (avg 306.5 ppm) in tur1 core (tur1c) co-genetic with albite contrast with what is reported in magmatic/magmatic-hydrothermal tourmaline of granitic affinity. The 811B values of tourmaline are mostly positive, ranging be-tween -4.0 and 9.2 %o (avg 4.0 +/- 3.0; n = 79); values of tur1 cores are 4.9-9.2 %o. Previous fluid inclusion studies described the presence of halite and barite daughter crystals in primary fluid inclusions and demonstrated the involvement of a high-temperature (>= 450 degrees C) and high-salinity (>= 50 wt% NaCl equivalent) brine in the for-mation of cores of tur1. Calculated 811B values of the hydrothermal fluid in equilibrium with tur1c range from 7.3 to 11.5 %o (for a crystallization temperature of 450 degrees C). Based on the textural setting of the tur1c-albite assem-blage, geochemical and boron isotope composition of tur1c, and evidence of a high saline brine, we propose that the albite schist is the product of Na-metasomatism by brines that derived major constituents from the disso-lution of marine evaporite. The inferred paleo-latitude and geological environment of sedimentation related to the host lithologies are consistent with the evaporitic model. We further suggest that a similar mechanism might have played an important role in the formation of albite-rich rocks in other IOCG provinces where the involvement of evaporite-derived fluids in mineralization/alteration have been demonstrated. Similar major element, trace element and positive boron isotope (1.5-6.3 %o) composition of tur3 suggest similar source of fluid as that of tur1c, and tur3 formed either during the same alteration event or during a separate fluid pulse. On the other hand, the mode of occurrence, very low trace element concentration and weakly negative to positive 811B (-4 to 2.3 %o) value of tur2 suggest their metamorphic origin.

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.

Tourmaline is the principal repository of boron in crustal rocks and therefore useful for tracing B-cycling during prograde dehydration and retrogression of supracrustal rocks. Here, we use the major-trace element, and B isotope composition of tourmaline from schists, quartzites, and tourmaline-quartz veins of the Gangpur Schist Belt in eastern India to constrain the source of boron and the physicochemical evolution of B-rich fluids during prograde dehydration metamorphism. Tourmaline growth and re-equilibration in rocks of the Gangpur Schist Belt was a multi-stage process involving several fluid sources. The 811B varies between -6%o and -18%o, indi-cating a dominantly continental source for boron. Tourmaline in schists, quartzites, and tourmaline-quartz veins grew over a wide range of P-T conditions and record multiple episodes of metamorphic dehydration between ca. 1.6 Ga and ca. 0.95Ga. The tourmaline in tourmaline-quartz veins and quartzites has lighter B-isotope compo-sition, typical of continental detritus, while those in the schists and quartzites record pelite-dehydration signa-ture with values decreasing gradually from ca. -12%o in the cores to ca. -17%o in the rims. Heavier isotopic compositions (811B of ca. -6%o) measured in some grains in the pelites and quartzites indicate boron contri-bution from meta-carbonate sources. The mixing of a heavier B-rich metacarbonate-derived fluid with pelite-derived metamorphic fluids could explain the lower B-isotope values in such tourmaline. The study also at-tempts to constrain the controls on the intake of trace elements in tourmaline. The results suggest that the partitioning of Mn, Y, V, Co and Ti in tourmaline is affected by the growth of porphyroblast phases such as garnet, staurolite, and biotite, while Li, Sr, Zn and Sn reflect the signature of the metamorphic fluid.

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.

The source of the mineralizing fluid in Archean greenstone-hosted orogenic gold deposits is widely debated, with the available geochemical and isotope data interpreted as reflecting the involvement of metamorphogenic fluid produced by devolatilization of greenstone belt metaigneous/metasedimentary rocks or granite-derived magmatic-hydrothermal fluids or both. Orogenic gold deposits form in complex geologic environment involving multiple fluid sources, reflected in the large variation in the B-isotope composition of tourmaline (delta(11) B = -24.8 parts per thousand to +19.8 parts per thousand). The delta B-11 distribution of tourmaline from world-wide orogenic gold deposits define two peaks, one at ca. -15 parts per thousand, and the other between -5 and 0 parts per thousand. In this study, we modelled the release of boron and associated B-isotope fractionation during prograde metamorphic dehydration of representative mafic and pelitic greenstone rocks using a mass balance approach and compared the results with the B-isotope composition of tourmalines measured globally from orogenic gold deposits. The results indicate that the boron content of greenstone belt metabasalts decreases from similar to 26 ppm to similar to 2.7 ppm by 530 degrees C while those in metapelites decrease from similar to 60 ppm at 300 degrees C to similar to 40 ppm by the terminal chlorite breakdown temperature of about 570 degrees C. In both mafic and pelitic assemblages, terminal chlorite breakdown reactions occurring during the greenschist to amphibolite facies transition (530-570 degrees C) release large amounts of 10B-rich fluids, which rapidly lower the delta B-11 of the metamorphic fluid. The delta B-11 of the fluids released from metabasalts and metapelites at these conditions are estimated to be about similar to 14.2 to similar to 10.8 parts per thousand and similar to 5.7 to 0.0 parts per thousand, respectively. Tourmalines precipitating from such metabasalt-derived fluid are expected to have delta B-11 between similar to 18.0 parts per thousand and similar to 12.4 parts per thousand while those crystallizing from metapelite-derived fluid will have delta B-11 between similar to 9.5 parts per thousand and similar to 1.6 parts per thousand for the temperature range of ore formation (300-550 degrees C) in orogenic gold deposits. Our calculated range of delta B-11 for the metabasalt- and metapelite-derived metamorphic fluids matches closely with the two peaks in the delta B-11 distribution of tourmaline from orogenic gold deposits. The delta B-11 of metabasalt-derived fluid is highly variable (+2 parts per thousand to similar to 15 parts per thousand between 450 degrees C and 610 degrees C) and strongly dependent on the metamorphic grade attained by the greenstone belt lithologies. The majority of measured tourmaline delta B-11 values from orogenic gold deposits of all ages can potentially be explained by different peak metamorphic temperatures with a single fluid source from metabasalts, or by mixing between basalt-derived and pelitederived metamorphic fluids, or both. Prior characterization of the metamorphic grade of the rocks and the temperature of mineralization are desirable before using the B-isotope composition of tourmaline for evaluating fluid source. The delta B-11 (similar to 14.0 parts per thousand to similar to 3.3 parts per thousand) of tourmalines measured by us from the Hutti and Kolar gold deposits as a case study can be explained by our modelled results with the isotopic variations attributed to mixing between metapelite- and metabasalt-derived fluids. Low Li concentrations in the tourmalines of Hutti and Kolar (avg. 21.7 and 28.0 ppm in Hutti and Kolar, respectively) further support a metamorphic origin for the hydrothermal fluid. The relatively higher V contents of the Hutti tourmalines (avg. 962 ppm) vis-a-vis the Kolar tourmalines (avg. 615 ppm) is suggestive of greater pelitic input in Hutti. (C) 2021 Elsevier Ltd. All rights reserved.

The Western Dharwar Craton in southern India is underlain by Paleoarchean to Neoarchean granitoids. Here, we use major-trace element chemistry and zircon U-Pb-Hf isotopic composition to identify major components of the crust, constrain the timing of juvenile crust extr action, and discuss the implications for Archean tectonic processes. The granitoids are metaluminous to weakly peraluminous, magnesian, and calcic. They were derived from basaltic protoliths with minor components sourced from pre-existing felsic crust. Low La/Yb and Sr/Y indicate shallow garnet-free plagioclase-bearing amphibolitic sources. The granitoids display large variations in concentration of trace elements, attributed to plagioclase accumulation or fluid-assisted mobilization of REEs during metamorphism. Zircon ages help to constrain four major episodes of granitoid crust formation at 3.43-3.41 Ga, 3.36-3.34 Ga, 3.29-3.25 Ga, and 2.66-2.65 Ga. The 3.43-3.41 Ga, 3.36-3.34 Ga, and 3.29-3.25 Ga granitoid suites have positive epsilon(Hfi) (2.7-4.5) and plot on a common cm; vs. time trend consistent with repeated granitoid extraction at 3.43-3.41 Ga, 3.36-3.34 Ga, and 3.29-3.25 Ga from mafic sources that separated from model depleted mantle between 3.55 Ga and 3.35 Ga. The epsilon(Hfi) (0.4-0.69) of the 2.66-2.65 Ga Neoarchean granitoids can be explained by melting of similar 3.35 Ga mafic crust or by mixing between juvenile magmas and preexisting granitoids. Uranium-Pb ages from metamorphic zircons indicate polyphase metamorphism of the granitoids at 3353-3329 Ma, 3264-3256 Ma, 3187-3141 Ma, 3083-3062 Ma, and 2574-2526 Ma. Hf-isotopic data from zircons in granitoids from several cratons indicate that prior to c. 3.5 Ga most granitoids have chondritic or crust-like epsilon(Hfi) explained by repeated granitoid extraction from long-lived mafic crusts with limited interaction with juvenile magmas. Juvenile eta and short protolith residence times of the Western Dharwar Craton Paleoarchean granitoids is suggestive of a tectonic setting with rapid recycling of basalts as in subduction zones. In contrast, greater protolith residence times and crust-like signature of granitoids older than 3.5 Ga in the crustal record indicate a tectonic setting where basalts persisted for prolonged periods of times such as in an oceanic plateau.

Gold mineralization in the newly discovered Bhukia deposit in northwestern India is hosted in Proterozoic metamorphosed volcano-sedimentary rocks of the Aravalli-Delhi Belt. Three generations of tourmaline occurring in different textural settings are recognized in the host rocks of the deposit. Fine-grained texturally early tourmalines (Tur-I) precipitated during the gold-sulfide mineralization stage. They are dravitic in composition and occur parallel to the Si tectonic foliation as fine-grained crystals in tourmaline-albite layers within quartz-albite rock and as scattered grains in calc-silicate rocks. Coarse-grained texturally later schorls (Tur-II) are also restricted to calc-silicate and quartz-albite rocks and characterized by sector zoning. Late-stage type III tourmaline (Tur-III), also of schorl composition, replaces Tur-II along fractures and margins. They are interpreted to have formed during a phase of ore remobilization. All tourmalines, especially the schorls, are strongly enriched in Li, Ga, Mn and Zn with Ga concentrations being the highest ever reported in natural tourmalines (up to 1380 ppm). The boron isotope composition is similar in all three tourmaline types with the consistently light delta B-11 (-10.4 parts per thousand to -7.2 parts per thousand) indicative of a continental source for B. The chemical and B-isotopic composition of tourmaline is suggestive of the involvement of two fluids, a granitic-derived hydrothermal fluid and metapelite-derived metamorphic fluid. The delta B-11 variations in the tourmalines can be explained by mixing between B-11-poor granitic-derived hydrothermal fluid and B-11-rich metamorphic-hydrothermal fluid. While high V (2110-4247, avg. 3339 ppm) in the early dravitic tourmalines indicate mixing of granitic-derived hydrothermal fluid with pelite-derived metamorphic hydrothermal fluids during gold sulfide mineralization, the enrichment of Li, Mn, Zn and Ta, and depletion of V in the later schorlitic tourmalines suggest increasing influence of granitic-derived hydrothermal fluids during ore remobilization. (C) 2019 Elsevier B.V. All rights reserved.

Linear chains of Deformed Alkaline Rocks and Carbonatites (DARCs) mark sutures where continents had rifted apart and later amalgamated. Since DARCs are products of two well-defined components of Wilson cycle, i.e., continental rifting and subsequent collision, geochronological constraints from DARCs along the Singhbhum/Bastar Craton-Eastern Ghats Belt contact in eastern India is used to unravel the history of continental breakup and amalgamation in the Indo-Antarctic Enderbia continent. Proto India and East Antarctica were involved in several episodes of collision and breakup during the assembly of past supercontinents. The Napier Complex of East Antarctica collided with the Dharwar Craton and Ongole Domain at 1.60 Ga forming the central-eastern Indian shield. Zircon U-Pb ages from DARCs at the craton-Eastern Ghats Belt margin show that the alkaline complexes (Kamakhyanagar: 1350 +/- 14 Ma; Rairakhol: 1379 +/- 6 Ma; Koraput: 1387 +/- 34 Ma; Kunavaram: 1360 +/- 5 Ma; Jojuru: 1352 +/- 6 Ma) were emplaced between 1320 Ma and 1370 Ma. The alkaline magmatism marks an episode of rifting in the Indo-Antarctic continental fragment, correlatable with the breakup of the Columbia supercontinent. The Khariar alkaline complex was emplaced at 1478 +/- 5 Ma during an earlier phase of crustal extension coeval with the formation of the Mesoproterozoic Chattisgarh rift basin. Metamorphic zircons from the alkaline rocks furnish age populations at 953-930 Ma, 808-795 Ma, and 661-563 Ma. The 953-930 Ma ages are correlated with oceanic closure between Ruker Terrane of East Antarctica and India during Rodinia assembly. The resultant collision of the Ruker Terrane with India-Napier Complex composite produced the Grenville-age Eastern Ghats Province-Rayner Complex orogen. The 808-795 Ma ages record disintegration of Rodinia when India broke away from East Antarctica. In the early Paleozoic, India redocked with East Antarctica and Australia during Gondwanaland assembly. The 661-563 Ma zircon ages date the resulting collisions during Pan-African orogenesis. The assembly of the Eastern Ghats Province and the Rayner Complex with the Bastar-Singhbhum Craton occurred in the early Neoproterozoic during the final stages of Rodinia assembly, supporting the existence of Enderbia continent comprising crustal units from India and East Antarctica.

Deformed Alkaline Rocks and Carbonatites (DARCs) are markers of suture zones where continents have rifted apart and later amalgamated [1]. Petrological and geochronological data indicates that parts of India and East Antarctica may have been involved in several episodes of collision and breakup during the assembly of past supercontinents [2]. DARCs at the eastern margin of the Eastern Ghats Province (EGP) in India preserve the record of these amalgamation and breakup events. It is thought that the Napier Complex of East Antarctica collided with the Dharwar Craton of India at ca. 1.60 Ga forming the central and eastern Indian shield [3]. New zircon U-Pb ages from DARCs at the EGP margin show that the alkaline complexes (Kamakhyanagar: 1350±14 Ma; Rairakhol: 1379±6 Ma; Khariar: 1478±5 Ma; Koraput: 1387±34 Ma; Kunavaram: 1360±5 Ma; Jojuru: 1352±6 Ma) were emplaced in a narrow time interval. The alkaline magmatism marks an episode of rifting in the Indo-Antarctic continental fragment, correlatable with breakup of the Columbia supercontinent. Metamorphic zircon from the alkaline rocks furnish age populations at 917-950 Ma, 792806 Ma and 562-569 Ma. The 917-950 Ma ages are correlated with the closure of an oceanic basin between the Ruker Terrane of East Antarctica and the Indian Shield during the assembly of the Rodinia supercontinent. This led to the collision of the Ruker Terrane with the combined India-Napier Complex producing the Grenville-age EGPRayner Complex orogen [2, 3]. The 792-806 Ma ages record the disintegration of Rodinia when Greater India started to break away from East Antarctica [4]. In the early Paleozoic, India reconverged towards Antarctica and Australia during Gondwanaland assembly. The 562-569 Ma zircon ages date the resulting collisions during Pan-African orogenesis.