Monazite chemistry and timing of mineralization at Paramanahalli, Chitradurga Greenstone Belt, Dharwar Craton, India: Implications for gold exploration

Abstract

Paramanahalli gold deposit, Chitradurga greenstone belt in the Western Dharwar Craton, is a shear zone-hosted/ structurally controlled, mineralization confined to carbonated metabasalt and Banded Iron Formation. Chlorite (Fe-rich) + quartz + ankerite + rutile + monazite ± pyrite ± gold is the mineral association found in the mineralized zone. Monazite from carbonated metabasalt (intensely altered rocks; proximal alteration zone) is interpreted as hydrothermal in origin, based on its mode of occurrence, texture, and chemical composition, particularly its low ThO₂ content, whereas monazite grains from schistose metabasalt (least altered rocks; distal alteration zone), found to be metamorphic. Hydrothermal monazite from the mineralized zone is enriched in light rare earth elements LREEs (La₂O₃ + Ce₂O₃ > 51 wt%) and exhibits low ThO₂ concentrations (<1.5 wt%) classified as anomalous values, in contrast to metamorphic monazite, contain lower LREEs (La₂O₃ + Ce₂O₃ < 45 wt%) and higher ThO₂ (> 1.5 wt%) identified as background values. The ratios such as Ce/Pr, La/Nd, La/Pr, along with REE trends, serve as diagnostic tools to target and exploration of orogenic gold deposits. This study highlights the utility of monazite as a geochemical tool to unravel mineralized zones, thereby enhancing exploration strategies for orogenic-type gold mineralization in the Dharwar Craton and similar terranes. Notably, we are the first to report the timing of a hydrothermal event related to gold mineralization at Paramanahalli by estimating the chemical ages (CHIME) of monazites through Electron Probe Micro Analysis. The study reveals two distinct ages: 2622 ± 08 Ma (older) and 2510 ± 12 Ma (younger), corresponding to metamorphism and syn-ore hydrothermal alteration/mineralization events, respectively. The Neoarchean mineralization event at Paramanahalli (2510 ± 12 Ma) aligns closely with ages estimated for gold mineralization in Ajjanahalli (2520 ± 9 Ma) and Gadag (2522 ± 6 Ma) within the Western Dharwar Craton. Our findings indicate that gold mineralization across the WDC is attributed to a regional tectono-thermal event around 2520 Ma, characterized by extensive fluid flux into the crust.