QI You-qiang1, HU Rui-zhong1, LI Xiao-feng1, LENG Cheng-biao1, LIU Shen1, WU Li-yan1, LIU Rui1,2
(1. State Key Laboratory of Ore Deposit Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550002, China;
2. University of Chinese Academy of Sciences, Beijing 10049, China)

Abstract: The Lengshuikeng Ag-Pb-Zn ore deposit contains big vein ore bodies, veinlet-dissemination ore bodies and bedded ore bodies, which has attracted the attention of many many researchers. However, the relationship between two ore body types, especially the relationship between granite porphyry veins and bedded ore bodies, as well as the genetis of the iron and manganese carbonate rock formation in which the bedded ore bodies occur, and the reasons for differences in sulphide compositions between the two ore bodies remain ambiguous. This paper focuses on the Xiabao Ag-Pb-Zn ore deposit, which is the largest in the Lengshuikeng ore deposit. Samples were taken along a section that crosses the granite porphyry veins and the bedded ore body. Subsequently, the chemical characteristics of sphalerite in both ore bodies were analysed by using electron microprobe analysis. It is not the gradual feature in field contact area between granite porphyry and bedded ore body. The chemical content and ratios of various elements show obvious differences between the two ore bodies. Granite porphyry veins have higher Al, Ba, Sr, K and Na content, whereas bedded ore bodies occurring in iron and manganese carbonate have higher Ag, Fe, Mn, Zn, Pb and Mg content. The Iron and manganese carbonate rock dispays chemical characteristics indicating sedimentary origin without having undergone larger-scale hydrothermal metasomatism. These findings indicate that the cause of formation is likely a volcanic-sedimentary deep-lake-basin related to the continental facies. The microprobe analysis also examined other chemical characteristics of sphalerite samples from both ore bodies. Sulphur content of sphalerite ranges from 32.05% to 33.81% with a mean of 33.02%, while the corresponding Zn content ranges from 53.51% to 63.79% with a mean of 59.38%. Iron content showed a larger range (2.02%―12.42%), exposing significant difference between the two ore bodies. The Fe content of sphalerite in the bedded ore body ranges from 2.02% to 7.69% with a mean of 4.17%. However, sphalerite in the big vein ore deposit has a much higher Fe content, ranging from 8.02% to 12.42% with mean of 9.49%. Although the bedded ore body occurs in the iron and manganese carbonate rock, the sphalerite has a much lower Fe and Mn content than that found in the big vein ore body. The elements Fe, Mn, Pb and Zn within the magmatic system with respect to the mineralization process, may have been influenced by different physical and chemical conditions (e.g. temperature, pressure, pH, and so on) resulting in mineralization differences related to the magmatic system.

Keywords: big vein ore body; bedded ore body; iron and manganese carbonate; sphalerite; Lengshuikeng; Gan-Hang tectonic belt

Email: qiyouqiang@vip.gyig.ac.cn

ACTA MINERALOGICA SINICA Vol. 35, No. 2, 2015, Page 136-146