Geochemical and mineralogical constraints on lithium mineralization in rare-metal pegmatites of the Amareshwar region, Eastern Dharwar Craton, India

Abstract

Around 50 percent of global lithium resources are hosted in the rare-metal pegmatites. The present study deals with whole-rock geochemistry as well as zinnwaldite mineral chemistry of rare-metal pegmatites from Amareshwar, Gurugunta schist belt, Eastern Dharwar Craton to understand the source of lithium bearing ore fluids in these pegmatites and to evaluate their mineralization potential. Detailed petrography and mineral chemistry of Amareshwar pegmatites indicate that lithium is hosted in both spodumene and zinnwaldite. The zinnwaldite mineral chemistry elucidates the incorporation of lithium in mica crystal lattice along the vector Al₂(R²⁺)_–3. The whole rock geochemical signatures suggest that these pegmatites are alkaline to calc-alkaline in nature, peraluminous and emplaced in S-type and syn-collisional tectonic setting. The chondrite normalized REE patterns are characterized by prominent negative Eu anomalies coupled with significant LREE enrichment and HREE depletion indicating fractional crystallization with plagioclase separation. Elevated concentrations of Li (Avg. = 1355 ppm), Cs (Avg. = 246 ppm), Ta (Avg. = 124 ppm), Sr (Avg. = 105 ppm) and Rb (Avg. = 2234 ppm) coupled with their geochemical characteristics classify them as LCT type of rare-metal pegmatites. The relationship between La/Ta versus Mg/Li and Zr/Hf versus Nb/Ta attest that the studied samples are lithium mineralized pegmatites of magmatic-hydrothermal origin. Extremely low ratios of Mg/Li (0.004), K/Rb (0.004), K/Cs (0.05), K/Ba (0.07), Al/Ga (0.23) fingerprint that these pegmatites have evolved from highly fractionated, fertile parental granitic magma having promising economic potential.