WU Sha1, RUAN Wei-ling2*, JIN Zhong-guo1,2, ZHENG Ming-hong2, GUN Min-can3
(1. Institute of Resources and Environmental Engineering, Guizhou University, Guiyang 550025, China;
2. Non-ferrous Metals and Nuclear Industry Geological Exploration Bureau of Guizhou, Guiyang 550005, China;
3. Institute of Geology and Mineral Resources Exploration, Non-ferrous Metals and Nuclear Industry Geological Exploration Bureau of Guizhou, Guiyang 550005, China)
Abstract: The northwestern Guizhou is an important part of the Sichuan-Yunnan-Guizhou ore deposit concentration area, in which lead-zinc deposits are distributed in clusters and zones. There are associated pyrite in most of those lead-zinc deposits. However, the relationship between pyrite and the lead-zinc mineralization has been rarely studied. It is insufficient to deeply understand the lead-zinc mineralization in this area. The Qingshan lead-zinc deposit, located in the right limb of the Weishui inverted fold anticline, is a representative medium-sized lead-zinc deposit in the northwestern Guizhou. Pyrite is one of the main ore minerals in the deposit. It is generally associated with sphalerite. In this paper, the electron probe (EPMA) and laser ablation inductively coupled plasma mass spectrometer (LA-ICP-MS) are used to have analyzed different types of pyrites in this deposit, in order to reveal compositional characteristics and occurrence states of trace elements in pyrites, and to discuss the genesis of pyrite and its relationship with the lead-zinc mineralization, and then to provide a basis for understanding the Pb-Zn mineralization of this deposit. The results show that contents of Fe and S in pyrites of the deposit are slightly lower than theoretical values of Fe and S in pyrite. Pyrites of the deposit have characteristics of generally depleted Fe and S. Their S/Fe ratios are less than 2. Thus, they belong to the sulfur deficit type sedimentary pyrite. Two stages of pyrites in the deposit have been identified. The early-stage pyrite (PyⅠ) is relatively rich in As, Mn, Zn, Ni, Ga, Se, Cd, In, Sn and Tl, with its Co/Ni ratios ranging from 0.03 to 0.67 (mean 0.14, n=30). The late-stage pyrite (PyⅡ) is relatively rich in Pb, Cu, Ag, Mo, Sb and other elements, with its Co/Ni ratios ranging from 0.03 to 2.54 (mean 0.41, n=38). Pb, Sb, As, Co, Ni, Zn, Ge and other elements occurred in the form of isomorphism for substituting Fe or S in lattice of two stages of pyrites. Field observation and microscopic identification results show that the formation of pyrites of two stages in the Qingshan deposit is about later than that of sphalerite, but earlier than that of galena. It is believed that pyrites of two stages were products of the same hydrothermal activity. The compositions of trace elements of pyrites are similar to those of the MVT type lead-zinc deposits in the Sichuan-Yunnan-Guizhou area. However, due to the pyrite of the Qingshan deposit had inherited trace element composition of pyrite formed in diagenetic period, it has the characteristics of sedimentary pyrite. Combined with the geological characteristics of the Qingshan deposit, it is considered that the Qingshan lead-zinc deposit belongs to the MVT type lead-zinc deposit.
Keywords: EPMA; LA-ICPMS; characteristics of trace elements; metallogenic information; genesis of mineral deposit; Qingshan Pb-Zn deposit
