Research On Geology And Geochemical Characteristics Of HuangYouTan Polymetallic Ore Deposit In Zhejiang Province

The Huangyoutang copper polymetallic deposit in Shao Xing, Zhejiang province is a typical skarn type deposit. This ore deposit located in northeast part of the Qin-Hang suture zone in the collision belt of the Yangzi district and Huaxia district, which is also called the Jiangshao-Chenzhou-Qinfang jointing strip district. It is also close to the Jiangshan-Shaoxing suture zone, which is the transition belt between two different tectonic units in northwest and southeast Zhejiang province. Previous work on this ore deposit was rare, and the geological characteristics and metallogenic mechanism are still clearing debated. In this study, based on the geological characters, a systematic work of fluid inclusions, isotopic geochemistry and geochronology was finished. The genesis of ore deposit and its mineralization process are also proposed, which provide the scientific basement for the further prospecting.The field investigation and mineralogical studies showed that the Huangyoutang ore deposit was hosted by argillaceous dolomite, dolomitic limestone, limy dolomite and skarn. The main ore minerals involve chalcopyrite, pyrite, magnetite, magnetic pyrite, galena, sphalerite, etc. The secondary minerals are malachite, chalcocite, limonite, azurite, sericite, etc. Wall rock alterations are dominated mainly by skarn, silicification and sericitization etc., which are mainly distributed in both sides of fractures and contact zones of intrusion and surrounding rock. The ore-forming process can be divided into two metallogenic periods, i.e., skarn stage and quartz sulfide stage.The Huangyoutang fluid inclusion can be divided into two types:the gas-liquid two phase inclusions (V+L) and daughter mineral-bearing two phases inclusions (S+V+L). The ore-forming fluid has moderate to high temperature and medium to low salinity. The 8Dv-smow values for garnets range from-91.7‰ to-83.9‰, and δ18Ov-SMOW values are 3.4‰～6.6‰,δ18OH2O values are 5.3‰～7.9‰. The δDV-SMOW values for quartz samples are-76.5‰～-66.2‰; δ18OV-SMOW values are 9.3‰-9.8‰; δ18OH2O values are 3.6%o-4.1%o. The measured 813CPDB values range from-2.4%o to-5.7%oand δ18OSMOW values are-0.2‰～2.6‰. The C-H-O isotope data indicate that the fluid is mainly derived from magma with less amounts of meteoric water. The measured δ34S values for sulfide are 3.8‰～6.1‰, with a mean value of 4.9%o. The relatively narrow range of the data shows the uniform sulfur isotopic composition, which also indicates a magmatic source for sulfur.Based on the geochemical characteristics of magmatic rocks in the Huangyoutang copper polymetallic deposit, the local Shanxi granodiorite was identified as the ore related geologic body. The intrusion shows I-type granite features, with a U-Pb age of 152Ma-150Ma, which was related to the early Yanshanian magmatism.Based on the above studies, we preliminary discuss the mineralization process of the deposit. After Indosinian orogeny, due to the subduction of ancient Pacific plate to Asia continental margin, intense intracontinental extension and rift activities occurred in southeast part of the Huanan, triggering partial melting of the crust. It produced a large amount of magmas including the Shanxi intrusion. With the re-activation of a series of north-east trending faults and pressure decreasing, the magmatic-hydrothermal fluids emplaced along the fractures. These fluids containing copper, sulfur and other minerals intruded and reacted with the carbonate rocks to form skarn minerals. A large number of metal components dissolved in the hydrothermal fluids could combine with H2S to form abundant sulfides in the quartz-sulfide stage, i.e., pyrite, chalcopyrite, galena, sphalerite, etc.