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Paleoproterozoic Bhukia gold deposit is located within the Debari Group of Aravalli Supergroup, Rajasthan, northwestern India. The major lithounits that are associated with gold–graphite (±Cu ± U) mineralization exposed in Bhukia are albitite, carbonates, and quartzite which have undergone upper greenschist to amphibolite facies metamorphism. Ore mineralization viz. pyrrhotite, arsenopyrite, chalcopyrite, pyrite, graphite, magnetite, and goethite in the study area are associated with NNW–SSE trending shear zone. Nuggets of gold are identified in the thick gossan zones that occurs parallel to the shear zone. The gold–sulfide lodes of the Bhukia deposits are largely confined either to marble or albitized marble and pure monomineralic albitite. The mineralization that is associated with the albitite, follows the boundaries of albite grains which confirms the role of these weak zones for the mobilization of mineralizing fluid and concentration of metal ions. Hence, geochemical studies of albitite would help to evaluate the petrogenesis, likely magmatic affinity, tectonic setting, controls of the mineralizing fluid, source, and their linkage to the gold (±Cu ± U) metallogeny. Bhukia albitite is characterized by Na–Al–rich and K‐poor compositions along with metaluminous nature. Geochemical analysis of various key elements suggests that albitite is the product of low‐K calc‐alkaline magma series with variation in Nb/Ta ratio indicating their fractionation during the melt–rock interaction within the shear zone. Geochemical signatures suggest the role of upper continental crust in channelizing the mineralized fluids that generated albitite with felsic to intermediate composition in and around Bhukia deciphered from their low Nb/Y ratios. Lower concentration of compatible elements (Ni and Cr) and higher concentration of incompatible elements (Th, La, and Nd) with SiO2 suggest that evolution of albitite rock is related to the fractional crystallization process. Zr/Hf ratios of 9–35 with the average of 18 suggest that albitite formed under magmatic–hydrothermal transitional environment. Rare Earth Elements (REE) patterns of albitite samples are moderately fractionated showing Light Rare Earth Elements (LREE)‐enrichment with a rather steep slope and exhibit distinct negative Eu anomalies (0.42–0.71, average 0.57). The enrichment of LREE in comparison to the Heavy Rare Earth Elements (HREE) suggests a more evolved source, i.e., process of melting at shallow environments. Tectonic setting of albitite samples suggest their origin in a volcanic arc region that underwent rifting. Detailed geochemical characterization unravelled complex evolutionary history of albitite in the Bhukia area, which attests derivation of the parental melt possibly from an enriched SCLM (Sub‐continental lithospheric mantle) source similar to most of the IOCG‐IOA deposits worldwide. [ABSTRACT FROM AUTHOR]

Numerous iron ore deposits are hostedwithin theMeso toNeo-Archean banded iron formations (BIFs) extending across the Singhbhum-Orissa Craton, eastern India. Despite the widespread distribution of BIFs, which forms part of the iron ore group (IOG), heterogeneity in their grade and mineral composition is occasionally observed even within a single ore deposit. Kiriburu-Meghahatuburu iron ore deposit (KMIOD), west Singhbhum district, Jharkhand, eastern India is characterized by a dominant hematite (often martitized) occurrence with a total resource of >150 million tonnes (MT) at 62.85 wt % Fe. Very high-grade blue dust ore (friable and powdery hematite with~67% Fe), high-grade massive, hard laminated hematitic ores (~66% Fe) and medium to low grade goethitic/lateritic ores (50%-60% Fe) are the common iron-ore lithologies in KMIOD. These ores can be distinguished in the field from their physical appearance, meso-scale texture and spatial occurrences with the host rocks along with the variation in chemical composition. The high-grade ores are characterized by high Fe (>62 wt %), low Al2O3 (1.5-2.5 wt %), low SiO2 (2.0-4.5 wt %) and low P (<0.06 wt %). Detailed field studies and laboratory investigations on the ore mineral assemblages suggest that the mineralization of high-grade iron ores at KMIOD is controlled by three major parameters, i.e., lithological, paleoclimatic and structural controls. High-grade iron ores such as blue dust seem to be formed during leaching processes through inter-bedded ferruginous shale and banded hematite jasper (BHJ) occurring within BIFs. Structural elements such as folds, joint network, fracture arrays, local faults and steeply dipping bedding planes are surmised as strong controls for the evolution of different iron ore types from the BHJ. Most of the high-grade ores are concentrated at the hinge portions of second generation folds (F2) owing to the easy access for circulation of meteoric solution along the fractures developed due to release of stresses at the hinge portions aided by supergene ore enrichment processes. The BHJ and interbedded ferruginous shale seem to have been given a significant contribution for the formation of different grades of iron ores over the area. Lithologically, the BIFs are governed by rheological features providing channel ways in the ore enrichment process. The variation in the iron ore mineralogy is caused by the variation in depositional and paleoclimatic environment, structural setting and lithological attributes. Hence, these parameters could be used for future exploration and grade recovery of iron ore resources in the region and in the adjoining areas. [ABSTRACT FROM AUTHOR]

The consumption of iron ore has increased rapidly over the past decade due to the tremendous growth of iron and steel industry. The depletion of high grade iron ore resources make it inevitable to utilize the existing low grade iron ores/fines/tailings with effective beneficiation to meet the present specification and demand. Enormous amounts of fines are produced both from the natural geological process as well during the mechanized mining operations which is hitherto in unknown resource present in the form of waste. Beneficiation and utilization of these fines/tailings still remains a challenging task. In order to find out the effective way of utilization of these fines, an in-depth characterization study is essential. A detailed insight into the different mineralogical attributes involving microscopic SEM-EDX, EPMA, XRD, FTIR, TGA, physical and chemical characterization are undertaken on the Barsua iron ores fines. These studies revealed that hematite and goethite are the major iron bearing minerals with gibbsite, kaolinite and quartz present as gangue that makes up the deleterious Al and Si content. Traces of magnetite is also observed along with martite. The liberation size of the sample is found to be below 150 μm. The bulk chemical composition shows around 57.67% Fe, 6.29% Al2O3, 3.52% SiO2 and 6.93% LOI. Based on the detailed characterization, possible routes of beneficiation of the iron ore fines are discussed. [ABSTRACT FROM AUTHOR]

Felsic volcanic rocks of rhyolite to dacite composition, hosting copper mineralization, are exposed near Mundiyawas-Khera area within the Alwar basin of Proterozoic North Delhi Fold Belt. Distinct variations in grain size, mineralogical composition, texture, sulfide mineral associations, structure, and outcrop patterns of the felsic volcanic rocks are observed in the field. In this study, litho-facies analysis of felsic volcanic rocks around Mundiyawas-Khera copper deposit has been attempted for the first time to understand their spatial distributions and bearing on copper mineralization. Signatures of five distinct facies variations in felsic volcanic rocks are recorded based on the field and laboratory studies. These facies variations recorded in the study area are (a) vitrophyric felsic volcanics; (b) fine grained felsitic fiamme bearing tuff; (c) fiamme-bearing welded ash flow tuff; (d) poorly welded ash flow tuff; and (e) volcanic ash. Presence of glass shards in the study area indicates phreatomagmatic eruptions in an aqueous to sub-aqueous environment. Occurrences of massive sulfide associated with the felsic volcanic unit can also correlate with well-known volcanic hosted massive sulfide (VHMS) deposit and is taken as an additional evidence of felsic volcanic rock occurrences at a submarine environment. [ABSTRACT FROM AUTHOR]

Copper and associated gold mineralization in the Mundiyawas-Khera area of western India is hosted by the Proterozoic felsic volcanic rocks of rhyo-dacite composition. Signatures of hydrothermal alteration represented by sericite, epidote, scapolite and carbonates are well observed around the ore mineralization zone. The felsic volcanic rocks with gently to flat sloping REE pattern, variable negative Eu anomaly, intermediate abundances of HFSE and moderate to low Zr/Y anomalies are suggested to be FII, FIIIa and FIV type rhyolite. The felsic volcanic host rock for copper mineralization has a depleted and flat HREE pattern and indicates the crustal source, which is garnet free. Negative Eu anomaly in the rock is probably because of the intracrustal partial melting formed in a rift related environment. The high temperature magmatic activities are probably evolved due to the partial melting of crust at shallow to moderate depths, suggesting an evolved continental crust. The δ13C values of the mineralized carbonate veins range between −10.4‰ and −0.9 ‰ (min = −10.6‰, n = 27), whereas the δ18O values show a range of 16.35‰ to 25.23‰ (min = 21.49‰, n = 27), ideally suggesting a mixed source for the ore bearing fluid. Geological, geochemical and stable isotope data of the Mundiyawas-Khera copper deposit suggest it to be a VMS/VHMS setup and these insights will lead to finding new deposits in the nearby areas, having same stratigraphic horizons and similar lithogeochemical assemblages. [ABSTRACT FROM AUTHOR]

In the present work, gold‐bearing carbonaceous phyllites in the Dalma volcano‐sedimentary belt (DVSB), occupying the central region of the North Singhbhum Mobile Belt in eastern India were studied to understand the nature and mode of occurrence of gold mineralization. We propose that the protolith of the carbonaceous phyllites, that is, organic‐rich black shale, was the major source of Au in the phyllite‐hosted gold mineralization reported from the DVSB. LA‐ICP‐MS analysis of pyrite in this study reveals elevated Au contents in the early‐formed sedimentary pyrite (syngenetic and diagenetic pyrite). Trace element systematics confirms the presence of invisible Au with in the sedimentary pyrite as solid solution (invisible gold). Petrographical evidences suggest a close spatial relationship of Au‐enriched pyrite and carbonaceous material. Stable carbon isotope values confirm the organic nature of the carbonaceous matter. Further, the high organic carbon content of these samples falls well within the favourable range of an auriferous carbonaceous host rock. These evidences suggest that the organic carbon played a key role in fixation of gold in the carbonaceous shales. Subsequent diagenesis resulted in the release of Au from the organic matter and its incorporation onto the coeval sedimentary pyrite. Field observations and reports by previous workers indicate that these rocks were subjected to a late‐stage metamorphic/hydrothermal event. Paragenesis of pyrite coupled with its trace element systematics reveals that this late‐stage event resulted in the formation of younger euhedral pyrite and pyrrhotite and released invisible gold from the pre‐existing sedimentary pyrite followed by its precipitation in the quartz reefs. Based on these studies, we propose a two‐stage model of gold mineralization, wherein gold was initially incorporated in black shale‐hosted sedimentary pyrite and later released and precipitated in quartz veins. [ABSTRACT FROM AUTHOR]

Cuttability of rocks is intimately related to the variation in fracture and micro-petrographic properties of the rocks. An understanding of fracture mechanism and fracture toughness (FT) of rocks is useful to evaluate production performance of rock cutting machines. A study was conducted on rock samples collected from two limestone mines located in India where surface miner (SM), a popular drum type cutting machine, was used for excavation of rock. FT in Mode I was measured by Chevron edge notched round bar (CENRB) method. A simple and accurate procedure of sample preparation of specified dimension, and experimental approach for determining the FT has been discussed in this paper. The study also covers the relation between fracture toughness and mineralogy of limestone as well as their role in estimating production performance by SM. FT was found to be strongly related to uniaxial compressive strength (σc ), point load strength index (Is) and Young's modulus (E). The study shows that the fracture toughnessof the rock is governed by the configuration of carbonate grains, grain texture and grain matrix. FT was also found to decrease with increase in marl content resulting in increase of production performance of SM. Principal component analysis (PCA) was also conducted to develop a correlation matrix for FT and its inter-relationships with other influencing parameters. Critical strain energy release rate (GIC) was also found to be related with production performance of SM. [ABSTRACT FROM AUTHOR]

Trace element abundances in three indicator minerals (corundum, chrysoberyl, and zircon grains) from the western Mamfe gem placers, as determined by LA-ICP-MS analytical techniques, are shown to be sensitive to their crystallization conditions and source rock types. Corundum is dominantly composed of Al (standardized at 529,300 ppm), Fe (2496–12,899 ppm), and Ti (46–7070 ppm). Among element ratios, Fe/Mg (73–1107), Fe/Ti (0.5–245.0), Ti/Mg (1–175), and Ga/Mg (4–90) are generally higher whereas, Cr/Ga (<0.072) is low. The Fe (≤12,899), Ga (≤398), Mg (2–62), Cr (1.1–33.0), and V (3.0–93.0) contents (in ppm) mostly typify corundum grains formed in magmatic rocks, although some are metamorphic affiliated. A very higher Ti and significantly low Ga, Ta and Nb contents in some blue grains, suggest interesting concentrations of those high-tech metals in their source rocks. Chrysoberyl is dominantly composed of Al (standardized at 425,000 ppm) and Be (62701–64371 ppm). Iron (7605–9225 ppm), Sn (502–3394 ppm), and Ti (33–2251 ppm) contents are high, whereas Ga (333–608 ppm), Ta (<456.0 ppm), and Nb (<3.0 ppm) are significantly low. The high (Be and Sn) and significantly low Ga–Rb abundances, and Ta > Nb in the western Mamfe chrysoberyls show that they were crystallized in granitic pegmatites, with some of those source rocks being enriched in Ta and Sn. Zirconium oxide (ZrO 2 : standardized at 66.1 wt.%)) is the only major oxide in analysed coarse-grained zircons. Within the minor elementary suites: Hf (4576–12,565 ppm) and Y (48–2805 ppm) contents are significantly high. The trace element suites include: Th (7–1565 ppm), U (13–687 ppm), and ∑REE (50–2161 ppm), whose values are significantly low. The (Yb/Sm) N , Ce/Ce*, and Eu/Eu* anomalies range from 1.0 to 227.0, 0 to 308, and 0.08 to 1.7 respectively. They are Hf-Y-HREE enriched and depleted zircons mainly crystallized in magmatic oxidized environments. They were mainly sorted from granitoids, syenites and kimberlites. [ABSTRACT FROM AUTHOR]

The core of detrital zircons from the southern Meiganga gold-bearing placers were analyzed by Laser Ablation Split Stream analytical techniques to determine their trace element abundances and U-Pb ages. The obtained data were used to characterize each grain, determine its formation condition, and try to trace the provenance. The Hf (5980 to 12,010 ppm), Y (27–1650 ppm), U (25–954 ppm), Th (8–674 ppm), Ti (2–256 ppm), Ta, Nb, and Sr (mainly <5 ppm), Th/U (0.06–2.35), Ti zircon temperature (617–1180 °C), ∑REE (total rare earth element) (98–1030 ppm), and Eu/Eu* (0.03 to <1.35) are predominant values for igneous crustal-derived zircons, with very few from mantle sources and of metamorphic origin. Crustal igneous zircons are mainly inherited grains crystallized in granitic magmas (with some charnockitic and tonalitic affinities) and a few from syenitic melts. Mantle zircons were crystallized in trace element depleted mantle source magmatic intrusion during crustal opening. Metamorphic zircons grown in sub-solidus solution in equilibrium with garnet "syn-metamorphic zircons" and in equilibrium with anatectic melts "anatectic zircons" during crustal tectono-metamorphic events. The U-Pb (3671 ± 23–612 ± 11 Ma) ages distinguish: Eoarchean to Neoproterozoic igneous zircons; Neoarchean to Mid Paleoproterozoic anatectic zircons; and Late Neoproterozoic syn-metamorphic grains. The Mesoarchean to Middle Paleoproterozoic igneous zircons are probably inherited from pyroxene-amphibole-bearing gneiss (TTGs composition) and amphibole-biotite gneiss, whose features are similar to those of the granites, granodiorites, TTG, and charnockites found in the Congo Craton, south Cameroon. The youngest igneous zircons could be grains eroded from Pan-African intrusion(s) found locally. Anatectic and syn-metamorphic zircons could have originated from amphibole-biotite gneiss underlying the zircon-gold bearing placers and from locally found migmatized rocks that are from the Cameroon mobile belt, which could be used as proxies for tracking gold. [ABSTRACT FROM AUTHOR]

Trace element concentrations and U–Pb ages were obtained using Laser Ablation Split Stream Method from the core of 115 zircon grains from the western Meiganga gold placer deposit. The data was used to characterize zircon, to understand the history of crystallization and to locate source rocks within the local and regional geological settings. Zircon trace element geochemistry was used to distinguish between magmatic and metamorphic affinity. The magmatic zircons have characteristics compatible with their probable origin from granitoid, syenite, tonalite, charnockite and mafic to ultramafic rocks. The metamorphic zircons composition is compatible with growth from anatectic melts and by sub-solidus crystallization in equilibrium with garnet. The zircon ages reveal Archean, Paleoproterozoic, Mesoproterozic, and Neoproterozoic events with the principal source could mainly belong to Paleoproterozoic magmatic lineage. Some of the Paleoproterozoic magmatic zircons were probably sourced from two mica granite found within the local geology, whereas the remaining zircons have features indicating source rocks within the Congo Craton. We suggest that the geologic history of these zircons is related to crustal-scale magmatic and/or tectono-metamorphic events, possibly linked to Eburnean and Pan-African orogeny. [ABSTRACT FROM AUTHOR]