Genesis of the Boka vein-type Au deposit, Dongchuan, southwestern China: Insights from rutile U–Pb dating and pyrite chemistry

Abstract

The Boka gold deposit, located in the Kangdian metallogenic province of southwestern China, is a newly explored vein-type gold deposit that is distinct from the typical iron oxide-copper–gold (IOCG) deposits in the region. Gold mineralization is primarily hosted in quartz-sulfide veins within alteration zones surrounding diabase, with an estimated reserve of 20 tons and an average grade of 1.6  g/t. Given that gold predominantly occurs as native gold in quartz-pyrite veins, the timing and source of ore-forming materials remain widely debated. To better understand the genesis of the Boka deposit and its relationship to regional tectonic events, this study conducted in situ rutile U–Pb dating and geochemical analysis on hydrothermal rutile and pyrite associated with native gold. The U–Pb dating of rutile yields a lower intercept age of 783 ± 32  Ma, consistent with previously reported pyrite Re-Os ages, thereby providing a precise formation age for the Boka gold deposit. The δ³⁴S values of gold-stage pyrite (4.54 ‰-6.03 ‰), combined with its low Co/Ni ratios (<1), indicate that hydrothermal fluids are primarily derived from magmatic fluids associated with coeval diabase. Gold-enriched strata in the region are interpreted to have formed in a continental-rift setting during the Paleoproterozoic to Mesoproterozoic, providing the primary source of gold. Magmatism of diabase, emplaced in an extensional tectonic setting, acts as a key driver for hydrothermal-fluid circulation and gold remobilization. Based on these findings, we propose that the Boka deposit is a product of subduction-related magmatism during Neoproterozoic, representing a new magmatic–hydrothermal deposit type in the Kangdian region. These insights are expected to advance our understanding of regional metallogenesis and offer valuable guidance for future exploration.