Ore-fluid geochemistry of the Hehuashan Pb-Zn deposit in the Tongling ore district, Anhui province, China: evidence from REE and C–H–O isotopes of calcite

Abstract

Calcite is the main gangue mineral of the Hehuashan lead-zinc deposit, which is located in the Tongling ore district, Anhui Province, East China. The ore bodies of the Hehuashan deposit are hosted by dissolution breccia of the Lower Triassic carbonate sediments. We report petrography, rare earth elements (REE), and C-H-O isotope data of four generations of calcite recognized in the Hehuashan deposit, namely the pre-ore stage calcite (Cal-1), early ore-forming stage calcite (Cal-2), late ore-forming stage calcite (Cal-3) and post-ore stage calcite (Cal-4). In addition, we also report C-H-O isotopes data of dolostone from the Lower Triassic carbonate sediments. All four calcite generations show a low ∑REE content (13-50 ppm on average), indicating that the related ore-forming fluids may not have been derived a magmatic fluid but rather be derived from the carbonate sediments or basinal brines. Low LREE/HREE ratio (1.1-6.1 on average) of all four calcite generations implies that no significant REE fractionation happened during the mineralizing processes. The wide distribution of Y/Ho ratios (17-70) of calcite indicates a result of fluids mixing. The δ13C values of calcite (1.4‰ to 4.2‰) are comparable to marine carbonates, but the δ18O values are lower, indicating possibly a result of carbonates dissolution. Calculated δ18O of the fluid in equilibrium with calcite vary from -3.1‰ to -0.1‰, combining the δDV-SMOW (-100‰ to -81‰), implying a fluid mixing of a brine fluid and meteoric water or diagenetic pore water for the mineralization of the Hehuashan deposit