Genesis of chlorite and its constraints on rhenium enrichment in the Tieshangeng sandstone-hosted rhenium deposit, southwestern Sichuan Basin, China

Sandstone-hosted rhenium (Re) deposits are rare, and their mineralization mechanisms remain poorly constrained. The Re deposits in the Muchuan area of the southwestern Sichuan Basin provide an excellent natural laboratory for investigating Re enrichment in sandstone-hosted systems. In these deposits, chlorite is widespread and closely associated with mineralization, indicating its potential as an indicator mineral for tracing ore-forming processes. Here, EPMA, LA-ICP-MS, and TEM analyses were conducted to characterize the morphology and composition of ore-related chlorite, aiming to elucidate the genesis of chlorite and assess its significance in recording ore-forming processes. Two chlorite types were recognized. Altered chlorite formed through hydrothermal replacement of biotite at 89–290°C and evolved from Fe-rich to Mg-rich compositions during cooling, recording a fluid evolution from reducing, weakly acidic conditions to relatively oxidizing and more alkaline conditions. Authigenic chlorite occurred as grain-coating, pore-lining, and pore-filling cement and was characterized by Al-rich, Fe-poor compositions, high Re contents (average 32.70 × 10 -6 ), and formation temperatures of 37–153°C. Chlorite was identified as a host for Re. Part of the Re was incorporated into chlorite-associated jordisite through isomorphous substitution, whereas the remainder was concentrated by adsorption onto chlorite and chlorite-hosted organic matter. Hydrocarbon-bearing hydrothermal fluids derived from the Upper Triassic Xujiahe Formation migrated into oxidized Jurassic sandstones, where fluid–rock interaction induced chloritization and Re precipitation. These results establish a genetic link among hydrocarbon-related fluids, chloritization, and Re enrichment, and identify chlorite as a key indicator mineral for sandstone-hosted Re mineralization.