The genesis of the Hehuashan Pb-Zn deposit and implications for the Pb-Zn prospectivity of the Tongling district, Middle-Lower Yangtze River Metallogenic Belt, Anhui Province, China

Abstract

The Hehuashan lead-zinc deposit is located in the central Tongling Cu-Au-Mo mining district of eastern China and consists of stratabound ore bodies that are generally hosted by dolostone and limestone units of the Lower Triassic Lower Nanlinghu Formation. The deposit contains two types of sphalerite, namely tan to brown fine-grained (∼40 μm) type I sphalerite that is hosted by a dolomite, calcite, quartz and sericite gangue assemblage and colorless to brown coarse-grained (∼2 mm) type II sphalerite hosted within clasts in calcite-cemented breccias or within dolostone-hosted veins. Plotting these sphalerites in a Fe vs. Cd diagram indicates they have a similar composition as those within typical Mississippi Valley-type (MVT) deposits, suggesting that the Hehuashan deposit may have an MVT affinity. In addition, in-situ sulfur stable isotopic analysis of fine-grained (−7.8‰ to +3.0‰) and coarse-grained (+3.4‰ to +9.7‰) sphalerite indicates that the sulfur in the hydrothermal fluids that formed the deposit was derived from the country rocks within the Hehuashan area. Fluid inclusions within calcite and fluorite from the Hehuashan deposit have low homogenization temperatures (mean of 126 °C) and moderate salinities (mean of 7.1 wt% NaCl equivalent) that demonstrate the deposit formed from low temperature and moderate salinity hydrothermal fluids. This suggests that the Hehuashan deposit was almost certainly not formed from magmatic-hydrothermal fluids but instead was formed as a result of the mixing of basinal brines and meteoric water, again consistent with an MVT origin for this deposit. In summary, the Hehuashan lead–zinc deposit is an MVT deposit, suggesting that the Tongling district of Anhui Province, China is prospective for MVT mineralization and that the Triassic dolostones and limestones in this area represent high priority exploration targets for this style of mineralization