Similarities and differences in geological characteristics and sulfur isotope composition and their controlling factors of the Dahu, Linghu and Jinqu Au(Mo) deposits in the Xiaoqinling gold province

There are a large numbers of lode Au(Mo) deposits in the Xiaoqinling gold (molybdenum) province with great economic values. In this study, we selected the Dahu, Linghu and Jinqu Au(Mo) deposits to identify their Au-Mo similarities and differences in the basic geology, sulfur isotopic compositions, and the controlling factors based on systematic structural-alteration-mineralization observations and in situ sulfur isotope studies of gold-related pyrite. The studies on structural-alteration-mineralization of the Dahu, Linghu and Jinqu deposits indicate that the Au and Mo veins are hosted in the metamorphic basement of the Archean Taihua Group, mainly controlled by the nearly EW-trending shear zones (locally NW-trending). These ore veins occur in different parts of the same shear zones, or sometimes superimposed with each other at certain area. The Mo veins are related to K-feldspar and quartz alteration, with an ore mineral assemblage mainly associated with molybdenite and pyrite. In contrast, the Au veins are commonly related to sericite quartz alteration with an ore mineral assemblage of pyrite, polymetallic sulfides and telluride. In situ S isotope studies show pyrite from the Mo veins have delta S-34 values of -3.3 parts per thousand similar to +3.3 parts per thousand, while those from the Au veins of -7.8 parts per thousand similar to +8.9 parts per thousand. Pyrites in the Dahu and Linghu Au veins hosed in EW-trending shear zones have delta S-34 values of -2.8 parts per thousand similar to +0.4 parts per thousand and -7.8 parts per thousand similar to +8.2 parts per thousand, respectively, which suggests that the sulfur isotope compositions may be controlled by differential hydrofracturing and fluid-rock interaction ratios. This is also correspondent to the phenomenon that more gentle-dip breccias in the Linghu gold vein than that in the Dahu vein. At Jinqu, pyrite in the EW- and NW-trending veins have delta S-34 values of -3.9 parts per thousand similar to -3.5 parts per thousand and 0.7 parts per thousand similar to 8.9 parts per thousand, respectively. Among them, the steeply-dipping Au veins have negative pyrite delta S-34 values of -3.9 parts per thousand similar to +3.7 parts per thousand, whereas the gently-dipping veins have positive delta S-34 values of +4.1 parts per thousand similar to +8.9 parts per thousand. These significant differences in sulfur isotopic compositions of pyrite can be attributed to the controls of different structural settings on different physicochemical conditions, such as the oxygen fugacity. Combined with previous geochronology and fluid composition, this study indicate that the ore-controlling mechanisms (hydrofracturing and fluid-rock interaction), other than source properties and mineralization routes, played an important role on the similarities and differences of Au (Mo) mineralization in Xiaoqinling.