Jonnagiri gold deposit is a lone example of granitoid-hosted orogenic gold deposit in India. Gold mineralization is concentrated within silicified alteration zones along shear zones within the Pagadarayi granodiorite. Geochemical characteristics of unaltered Pagadarayi granodiorite show that, (i) these are granodiorite-tonalite suite of rocks, (ii) contain lower and variable amount of silica (63-72%), (iii) high Fe(Tot), (iv) varying alkali concentrations, (v) large variations in LILE and LREE, particularly K2O, Sr, Ba, Th, La, Ce. Further, in the Harker-type variation diagrams these granitoids show (i) decreasing agpaitic index (molecular Al2O3/Na2O + K2O) with increasing SiO2, (ii) characteristically low Sr/Sr* values, and (iii) no significant correlation of (Ce/Y)N. Hence, these rocks were possibly derived from partial melting of a mafic source with contribution from the LILE-enriched felsic crust. Harker-type variation diagrams plotted against SiO2 show decreasing trend for Fe2O3, MgO, CaO and TiO2 while Na2O increases with increasing silica content. These features are consistent with the initial stage fractional crystallization of plagioclase, pyroxene ? magnetite, followed by hornblende and biotite at a later stage. The higher Na2O, CaO, Sr and lower Cr, Ni, concentrations are similar to the continental arc magmas and therefore, these are grouped under the I-type granitoids which is in agreement with their crystallization from more oxidized melts in relation to major granitoid-hosted gold deposits elsewhere in the world.
Geochemistry of Gold-Hosting Granitoids from Jonnagiri Greenstone Belt, Eastern Dharwar Craton: Implications on Petrogenesis and Gold Mineralization
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Jonnagiri gold deposit is a lone example of granitoid-hosted orogenic gold deposit in India. Gold mineralization is concentrated within silicified alteration zones along shear zones within the Pagadarayi granodiorite. Geochemical characteristics of unaltered Pagadarayi granodiorite show that, (i) these are granodiorite-tonalite suite of rocks, (ii) contain lower and variable amount of silica (63-72%), (iii) high Fe(Tot), (iv) varying alkali concentrations, (v) large variations in LILE and LREE, particularly K2O, Sr, Ba, Th, La, Ce. Further, in the Harker-type variation diagrams these granitoids show (i) decreasing agpaitic index (molecular Al2O3/Na2O + K2O) with increasing SiO2, (ii) characteristically low Sr/Sr* values, and (iii) no significant correlation of (Ce/Y)N. Hence, these rocks were possibly derived from partial melting of a mafic source with contribution from the LILE-enriched felsic crust. Harker-type variation diagrams plotted against SiO2 show decreasing trend for Fe2O3, MgO, CaO and TiO2 while Na2O increases with increasing silica content. These features are consistent with the initial stage fractional crystallization of plagioclase, pyroxene ? magnetite, followed by hornblende and biotite at a later stage. The higher Na2O, CaO, Sr and lower Cr, Ni, concentrations are similar to the continental arc magmas and therefore, these are grouped under the I-type granitoids which is in agreement with their crystallization from more oxidized melts in relation to major granitoid-hosted gold deposits elsewhere in the world.
Publication Mode |
Online |
---|---|
Publication Author |
Sakthi Saravanan Chinnasamy |
Publication Language |
English |
Publication Type |
Conference Paper |
Publication Year |
2021 |
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