Browsing by Author "Rajagopal Krishnamurthi"

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Abundance of Carbonic Fluid Inclusions in Hira-Buddini Gold Deposit, Hutti-Maski Greenstone Belt, India: Inferences from Petrography and Volume Ratio Estimation of Fluid Components
(China University of Geosciences, 2020) Rajagopal Krishnamurthi; Ajit Kumar Sahoo; Rajesh Sharma; Prabhakar Sangurmath
Low saline aqueous carbonic fluids are considered to be the ore forming solutions for orogenic lode gold deposits. Phase separation/fluid immiscibility of the ore fluid is quite common and is one of the major reasons for deposition of gold in these deposits. Abundant carbonic fluid inclusions have been observed in quartz grains of Hira-Buddnini Gold Deposit. Theoretical estimation indicates that more volume of H2O compared to CO2 is likely to be trapped in inclusions at different P-T conditions. Preferential loss of H2O from fluid inclusions during ductile deformation of quartz grains have been attributed as the suitable reason for abundance of carbonic fluid inclusions. © 2020, China University of Geosciences (Wuhan) and Springer-Verlag GmbH Germany, Part of Springer Nature.
Gold Mineralization at Paramanahalli Prospect, Chitradurga Greenstone Belt, Western Dharwar Craton, Karnataka, India
(Geological Society of India, 2025) Manju Sati; Rajagopal Krishnamurthi; Sakthi Saravanan Saravanan Chinnasamy; Ajit Kumar Sahoo; Prabhakar Sangurmath
Paramanahalli gold prospect is hosted by deformed metamorphosed volcano-sedimentary rocks of the Chitradurga Group. Mineralization is confined to altered host rocks and quartz veins, and structurally controlled by NNW-SSE trending ductile to brittle-ductile shear zones. Surface indication of mineralization is found in the form of sulfide-rich quartz-ankerite veins with pyrite disseminated in host rocks. Detailed petrographic studies indicate a mineral assemblage of chlorite-1 ± biotite ± albite ± quartz in metabasalt formed by low-grade metamorphism. Microstructures such as brecciation, microfractures, micro folds, and strain fringes indicate that the metamorphosed volcano-metasedimentary rocks (metabasalt, phyllite, greywacke) experienced brittle-ductile deformation. Carbonatization and sulfidation are common hydrothermal alterations in the areas of oxide facies of the Banded Iron Formation (BIF), where gold is enriched. Altered metabasalt and BIF contain a significant amount of sulfides with native gold. The above studies indicate that mineralization at Paramanahalli was associated with deformation and alteration processes. Hence, an attempt has been made to understand the genetic aspects of gold mineralization at the Paramanahalli gold prospect based on petrography and mineralogy of altered host rocks. © 2025 Geological Society of India, Bengaluru, India.
Gold-Sulfide Mineralization in Banded Iron Formation at Girar, Bundelkhand Craton, India: Inferences from Field Observations and Petrography
(Springer, 2023) Ajit Kumar Sahoo; Rajagopal Krishnamurthi; Gautam Kumar Dinkar; N. V. Chalapathi Rao; Arun Kumar Ojha; Sneha Raghuvanshi; Sudipa Bhunia
Gold mineralization associated with quartz veins and sulfide minerals has been reported in Banded Iron Formation (BIF) at Girar, Bundelkhand Craton, India. The BIF is deformed with the development of tight- isoclinal folds in high strain zones and hosts four types of quartz veins viz., (i) folded veins, (ii) band parallel veins, (iii) low angle cross-cutting veins, and (iv) high angle cross-cutting veins. Folded and band parallel veins are continuous with each other and spatially restricted to zones of tight-isoclinal folds in BIF. Shape of quartz aggregates in the folded and band parallel veins is interlobate, and these veins contain pyrite and chalcopyrite as dominant sulfide minerals along with gold. Microstructure of quartz grains and presence of fragments of BIF in sulfide mineralgold bearing folded and band parallel veins indicate that the formations of these veins were related to a single deformation episode. Spatial association of folded and band parallel veins to intensely folded zones in BIF is attributed to epigenetic nature of sulfide and gold mineralization. © 2023, Geological Society of India, Bengaluru, India.
Mineralogy and Hydrothermal Alteration of Rocks Associated With Gold Mineralization in Akobo Greenstone Belt, Southwestern Ethiopia
(John Wiley and Sons Inc, 2025) Solomon Rebso Abebe; Rajagopal Krishnamurthi; Ajit Kumar Sahoo
The Akobo Greenstone Belt gold mineralization in the Western Ethiopian Greenstone Terrain is hosted by the Surma shear zone. Talc-chlorite schist, chlorite schist, actinolite bearing rocks, granite, meta ultramafic rocks, felsic metavolcanic rocks, and Banded Iron Formation are the dominant rock types found in the Gindibab-Wolleta and Chamo-Segele areas. This study describes the geology, mineralogy, and mineral chemistry/alteration of host rocks associated to the gold mineralization. We conducted outcrop and hand specemen, petrography, and mineral chemistry analyses. The host rocks of the auriferous quartz vein in the Gindibab-Wolleta area is felsic metavolcanics and banded iron formation. The metamorphosed felsic-mafic igneous rocks of greenschist facies hosts the mineralization. Chloritization, carbonatization, sericitization, and biotitization are the common hydrothermal alteration associated with the host rocks. The hydrothermal alteration is characterized by the chlorite + plagioclase + ankerite + biotite + calcite + sericite assemblages. The chlorite geothermometery suggests that the temperatures of hydrothermal fluids associated to the gold mineralization in the Chamo-Segele and Gindibab-Wolleta areas ranges from 180°C to 350°C. © 2025 Society of Resource Geology.
Mineralogy, hydrothermal alteration and paragenesis of gold mineralization at Paramanahalli prospect, Chitradurga Greenstone Belt, Western Dharwar Craton, India
(Elsevier B.V., 2025) Manju Sati; Rajagopal Krishnamurthi; Sakthi Saravanan Saravanan Chinnasamy; Ajit Kumar Sahoo
The gold mineralization at Paramanahalli (Chitradurga, Karnataka) in the Archean Greenstone Belt of Western Dharwar Craton, India, is structurally controlled and similar to many greenstone-hosted orogenic gold deposits across the world. The volcano-sedimentary rock sequences of the Hiriyur Formation of the Chitradurga Group are the host rocks related to gold mineralization. These litho-units were subjected to greenschist facies metamorphism, later deformed and altered by hydrothermal fluids. Detailed petrographic studies indicate that the rocks experienced chloritization, carbonatization, silicification, and sulfidation due to wall rock-fluid alterations. The prominent wall rock alteration assemblage is characterized by the presence of chlorite (Mg-rich), ilmenite, albite, and quartz-1 in the distal zone and quartz-2, chlorite (Fe-rich), biotite, ankerite in the proximal zone with a significant amount of sulfide minerals and gold. Three major stages of mineral formation have been identified: albite-1, Mg-rich chlorite, quartz-1, magnetite, and ilmenite formed during the regional metamorphism and deformation stage (pre-ore stage). Fe-rich chlorite, annite, quartz-2, pistomesite, ankerite, rutile, pyrite, chalcopyrite, pyrrhotite, and gold during the mineralization stage (syn-ore stage) and albite-2, calcite and goethite formed during the post mineralization stage (post-ore stage). The development of different types of twinning in calcite indicates the deformation temperature, around 150–300 °C. The temperature range of approximately 306–326 °C is the temperature of hydrothermal fluids involved in gold mineralization based on chlorite thermometry. Kink folds and strain fringes in altered wall rocks indicate ductile deformation followed by brittle deformation in the area. © 2024
Nature of ore forming fluids, wallrock alteration and P-T conditions of gold mineralization at Hira-Buddini, Hutti-Maski Greenstone Belt, Dharwar Craton, India
(Elsevier B.V., 2018) Ajit Kumar Sahoo; Rajagopal Krishnamurthi; Prabhakar Sangurmath
Gold mineralization at Hira-Buddini deposit in Hutti-Maski Greenstone Belt of Dharwar Craton, India is associated with quartz veins and hydrothermal alteration formed during a brittle-ductile deformation episode. The vein minerals (quartz and plagioclase) exhibit microstructures of dynamic recrystallization/intracrystalline deformation. Estimated temperature and pressure condition during mineralization is around 500 °C and 2.05–4.36 kbar, respectively. Carbonic inclusions are the most abundant type of fluid inclusions found in quartz grains of mineralized veins. Such abundance of carbonic inclusions must be due to preferential loss of water from original fluid inclusions during intracrystalline deformation of quartz. Rock-fluid interaction led to enrichment of SiO2 (in the form of quartz veins), K, Pb, S and LOI in the auriferous lode. It is inferred that the hydrothermal fluids involved in gold mineralization were of both metamorphic and magmatic origin. Deposition of gold has been attributed to phase separation as well as wall rock sulfidation. © 2018 Elsevier B.V.
The nature and composition of hydrothermal fluids related to gold mineralization in parts of Akobo greenstone belt, southwestern Ethiopia
(Elsevier Ltd, 2023) Solomon Rebso Abebe; Rajagopal Krishnamurthi; Ajit Kumar Sahoo
Gold mineralization in the Akobo greenstone belt of Southwestern Ethiopia is confined to metamorphosed volcano-sedimentary rocks of greenschist-amphibolite facies and is closely associated with shear/fault zones. Gold is found in quartz veins of the Gindibab-Wolleta area, while altered mafic-ultramafic rocks are the hosts for Chamo-Segele prospects. Microstructures found in vein quartz indicate intra-crystalline ductile deformation followed by fracturing during later brittle deformation episode. The assemblage of fluid inclusions in mineralized quartz veins in Gindibab-Wolleta area has been grouped into three types and inferred to be compositionally and texturally modified during the formation-deformation of quartz veins. Aqueous biphase inclusions are the only fluid inclusions found in the vein quartz of the Chamo-Segele area and retain the primary nature of fluid entrapment. Microthermometric analyses of inclusions indicate a striking difference in the composition of hydrothermal fluids responsible for the quartz vein formation in Gindibab-Wolleta and Chamo-Segele areas. The ore-forming fluids related to vein formation and gold mineralization in the Gindibab-Wolleta area were low saline aqueous carbonic. In contrast, in the case of the Chamo-Segele area, the quartz veins were formed by low to moderate saline aqueous fluid. The results of the fluid inclusion in the Akobo Greenstone Belt indicate an orogenic type of lode gold mineralization in the Gindibab-Wolleta area of the Gambella region, Ethiopia. © 2022
Uranium enrichment in altered metasedimentary rocks of Jahaz uranium deposit, North Delhi fold belt, Rajasthan, India: Inferences from whole-rock geochemical studies
(Elsevier Ltd, 2025) Priyanka Mishra; Rajagopal Krishnamurthi; Ajit Kumar Sahoo; Shailendra Kumar Sharma
Jahaz deposit is one of the promising Na-metasomatic uranium deposits along the “albitite line” and is hosted in the Meso-Proterozoic metamorphic rocks of the North Delhi Fold Belt, Rajasthan, India. This article presents whole-rock geochemical analyses of major, trace, and rare-earth elements of less to moderately altered and albitized rocks, which are used to quantify the exchange of chemical components during fluid-rock interaction. The alteration box plot indicates the intensity of alterations (albitization, chloritization, calcitization, sericitization, pyritization), and it is inferred that Na-Ca-Mg-K metasomatism was responsible for the formation of albite, chlorite, calcite, and sericite in the altered rocks. Isocon diagrams have been constructed using major and selected trace element concentrations of less to moderately altered and albitized garnetiferous quartz biotite schist/amphibolite to determine the net loss and gain of elements during rock-fluid interaction. The correlation coefficients indicated that elements such as Zr, Nb, Hf, and Ti were less mobile during fluid-rock interaction. Isocon analyses show that the albitized garnetiferous quartz biotite schist is significantly enriched in U, Na, Mg, Fe, Ca, Mo, Cu, Rb, and depleted in K, Pb, Ba, Ni, Zn. Albitized amphibolites are enriched in Na, Cu, Mg, Cu, Y, Cr, Se, Ni, K, LOI and depleted in Ba, Co, Pb, Zn, Ca, P, Mn, Fe. The low Th/U ratio of albitized garnetiferous quartz biotite schist indicates that the albitized rocks are significantly enriched in uranium. Hence, uranium enrichment is positively correlated with Na, Mo, Cu, Th, Zr, LOI, and light rare-earth elements of albitized garnetiferous quartz biotite schist/amphibolite in the Jahaz uranium deposit. These results are similar to Kirovograd and Novoukrainka (Ukraine), Lagoa Real (Brazil), Valhalla (Australia), Longshoushan (China), Aricheng (Guyana) and Coles Hill (USA) Na-metasomatic uranium-deposits. © 2025 Elsevier Ltd