Abstract:
In this article, we present the textural, mineralogical, and geochemical studies of a suite of volcanic rocks and their economic mineral potential from the Kadiri Volcanic Province (KVP) - a greenstone belt in the Eastern Dharwar Craton (EDC) of southern peninsular India. The volcanic rocks are represented by primary pyroclastic deposits dominated by tuff breccia, minor lapilli tuff, and pyroclastic flows together with lava flows, namely, metabasalts, andesites, dacites, and rhyolites. Metabasalts and high-Mg andesites in the KVP are associated with sporadic occurrences of disseminated-type gold. The ancient works on gold are confined to the ductile-brittle shear zones in en-echelon pattern. The source of gold is likely to be from deep fractures (greater than 200 km) at mantle depths that paved the magma to move upper crustal levels due to partial melting of peridotites which tapped the siderophile elements (Au-Ag) from deeper source. Some andesites and dacites contain atomic minerals [uranium, thorium, and rare earth element (REE)], which requires attention in future studies. Monazite occurring in such dacites is a major source of REE such as cerium (Ce), lanthanum (La), neodymium (Nd), and Yttrium (Y), contributing 50-60 percent of REEs. Presence of thorite (ThSiO sub(4)) in dacite, a metamict mineral, strongly radioactive containing upto 10 percent uranium (U). This study confirms multi-metal mineralization in KVP, for example, gold, silver, atomic (U and Th), rare-earths along with base metals. Emplacements of rhyolite and alkali granite appears to be synchronous with the major thermal event at 2.51 Ga of the Dharwar Craton. The diverse volcanic associations are formed in a subduction-accretion orogeny at approx. 2.7 Ga, coeval with the global accretion event and gold mineralization. Au-U-Th-REE abundances in the composite arc-back arc system of Kolar-Hutti-Kadiri-Jonnagiri greenstone belts of EDC are primarily attributed to devolatilization and melting of subducted oceanic slab, fluid-fluxed metasomatism of mantle wedge and elemental cycling associated with different stages of subduction.
