Genetic aspects of gold mineralization in the Southern Granulite Terrain,India |
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| Institution: | 1. Department of Earth Sciences, Indian Institute of Technology, Roorkee 247667, India;2. Department of Geology and Geophysics, Indian Institute of Technology, Kharagpur 721302, India;3. Geological Survey of India, DK Block, GSI Complex, Karunamoyee, Salt Lake, Kolkata 700091, India;4. PPOD Laboratory, Geological Survey of India, Bangalore 560070, India;1. CAS Key Laboratory of Crust–Mantle Materials and Environments, School of Earth and Space Sciences, University of Science and Technology of China, Hefei 230026, China;2. School of Earth and Environmental Sciences, Seoul National University, Seoul 151-742, Republic of Korea;3. No. 313 Geological Team, Bureau of Geology and Exploration of Anhui, Liu''an 236000, China;4. Key Laboratory for Mineralogy and Metallogeny, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China |
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| Abstract: | Gold mineralization in Southern Granulite Terrain (SGT) of India has close spatial relationship with the shear zones (Moyar–Bhavani) present in Cauvery Suture Zone. Gold is found to be associated with primary quartz veins, placers and laterites. The gold prospects in SGT can be broadly grouped into three provinces i) Wynad-Nilgiri, ii) Malappuram and iii) Attappadi. The auriferous quartz veins are within the deformed biotite/hornblende bearing gneisses and amphibolite. Wall rock alteration is conspicuous around the mineralized veins and gives an assemblage of muscovite–calcite–ankerite–chlorite–biotite–pyrite related to fluid–rock interaction at the time of vein formation. Fluid inclusion studies of vein quartz gives an idea of the nature of the ore forming fluids, the fluid involved in gold mineralization is of low saline and aqueous-carbonic in composition and quite similar to the orogenic lode gold deposits reported world-wide. Micro-thermometric data indicates fluid immiscibility (phase separation) during trapping of fluid inclusions and this must have played an important role in gold deposition. Geochronological studies of mineral separates from Wynad-Nilgiri province using Rb–Sr and Sm–Nd isochron methods of the auriferous quartz veins gave an age of approximately 450 Ma for the vein formation. The present studies on SGT gold mineralization indicate 1. During the Pan-African orogeny, extensive fluid influx from mantle and metamorphism extracted gold from a mafic source and were focused along major structural discontinuities of Moyar–Bhavani Shear Zone, 2. The aqueous–carbonic ore fluid interacted with rocks of the upper crust and triggered a set of metasomatic changes responsible for the dissolved components such as Ca, Si and Fe and finally precipitating in the veins and 3. The mineralizing fluid with dissolved gold in sulphide complex got destabilized due to fluid immiscibility and wall rock alteration leading to the deposition of gold with associated sulphide minerals in the vein system. |
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