The Maluntou Au deposit: A transitional mineralization type between low- and intermediate-sulfidation epithermal styles

Abstract

The Maluntou Au deposit is located in Southeast Coastal Volcanic Belt in South China. Its orebodies are hosted by the Cretaceous intermediate to silicic volcanic rocks and controlled by tensional NW-trending faults. The types of ore-related wall rock alterations consist of silicification, argillization, pyritization, and weak chloritization. Based on detailed field and microscopic petrography observation, three mineral paragenetic stages can be divided, i.e. PbZn stage, AuAg stage and post-ore stage.Electron microprobe analysis reveals slightly different composition of metal sulfides between PbZn stage and AuAg stage. The Fe content of Maluntou sphalerite is generally <2 %, indicating a typical Fe-poor sphalerite. Fluid inclusions microthermometric analysis of the early PbZn mineralization stage and late AuAg stage yielded homogenization temperatures (Th, 205–260 °C, 138–234 °C) and salinities (1.0–4.0 wt% NaCl equiv., 0.3–3.4 wt% NaCl equiv.), respectively. The low-moderate Th and low salinity ranges indicate an epithermal mineralization environment. From early stage to late stage, δDV-SMOW values show similar ranges from −69.4 ‰ ~ −64.3 ‰ to −68.2 ‰ ~ −64.9 ‰, with δ18OH2O‰ values ranges from −4.6 ‰ ~ −2.6 ‰ to −5.6 ‰ ~ −4.3 ‰, indicating ore-forming fluids derived from a magmatic and meteoric mixed source. The microthermometric data and H − O isotopic compositions of ore fluids suggest fluid mixing contributed to metal precipitation. The δ34SV–CDT values of sulfide minerals (i.e. pyrite, sphalerite, galena, chalcopyrite; −3.1 to 3.4 ‰) indicate a magmatic sulfur source. The relatively homogeneous lead isotopic compositions of the ore minerals (206Pb/204Pb = 18.4203–18.4814, 207Pb/204Pb = 15.6712–15.6853, and 208Pb/204Pb = 38.7730–38.8636) suggest a crustal origin.All the above results imply that the Maluntou Au deposit is a transitional type epithermal deposit between low- and intermediate-sulfidation styles which occurred distal to the magmatic hydrothermal system. Considering the close time and space relationship of this type deposit with other epithermal type and porphyry type mineralization, our results also suggest a possible exploration potential for the epithermal-porphyry type mineralization in the surrounding altered volcanic rocks in Zhenghe–Jian'ou area.