Formerly with Atomic Minerals Directorate for Exploration and Research, India
*Corresponding author: Yamuna Singh, Centre for Earth, Ocean and Atmospheric Sciences, University of Hyderabad, Gachibowli, P.O. Central University, Hyderabad, India
Submission: July 02, 2017; Published: October 04, 2018
ISSN: 2577-1949Volume3 Issue2
FThe granite-pegmatite systems of the Bastar craton, central India host polymetallic Nb,Ta,Sn,Be,Li ore deposits, which are genetically related to various granitic bodies locally called the Paliam-, Darba-, Metapal- and Kawadgaon-granites. In addition, limited occurrences of Rare Earth Elements (REE) are also known. Generally, the granites and associated pegmatite aureoles locally show physical continuity, suggesting that the pegmatites are late magmatic injections. Field observation shows that unzoned pegmatites occur as veins and fracture fillings within biotite granite. The granites comprise chiefly of quartz, microcline, perthite, albite-oligoclase, with muscovite, biotite and (secondary) hydrated muscovite, sericite, and chlorite as accessories. In addition, zircon, rutile, xenotime, sphene, ilmenite, magnetite, zoisite, and clinozoisite are also present. Occasionally, the granites host pale yellow euhedral monazite crystals displaying a brown dotted pigmentation. The dominance of primary muscovite over biotite in the granites suggests that they are peraluminous.
Chemically, the bulk of granites fall in the compositional field for granite. The granites are highly peraluminous (A/CNK ratio>1; 1.05-1.25), and distinctly enriched in Rb, Y, Nb, Pb and depleted in Sr and Ba. In terms of the molar A/CNK vs. A/NK plots, the granites fall in the field for S-type granites. The available geochemical data indicates that the peraluminous pluton was appreciably influenced by feldspar fractionation. The available high initial 87Sr/86Sr isotopic ratios, including mol. CaO/(MgO+FeOt) vs. mol. Al2O3/(MgO+FeOt) plots, of the granites also indicate that the granitic bodies were derived from the reworking of the older crustal rocks involving metapelite and metagreywacke sources in the generation of the magmas.
Keywords:Geochemistry; Ore-bearing granites and pegmatites; Bastar craton; Central India