YANG Song-ping¹, BAO Guang-ping^{2,3 *}, LAN An-ping¹, LU Mao-da¹, XU Lei¹, HUANG Lin¹, AN Qi¹

(1. No. 104 Geological Team, Bureau of Geology and Mineral Exploration and Development of Guizhou Province, Duyun 558000, China;
2. School of Resource Environment and Earth Science, Yunnan University, Kunming 650504, China;
3. Stake Key Laboratory of Ore Deposit Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550081, China)

Abstract: The Shanshulin Pb-Zn deposit is a representative medium-sized deposit in NW Guizhou province. Due to the relatively low degree of relevant geological and geochemical researches on this deposit, there is still a wide divergence in understanding of its genesis. In this paper, inductively coupled plasma-mass spectrometry (ICP-MS) was used to analyze concentrations of trace elements and rare earth elements in sulfides (sphalerite and galena) of the main ore-stage, in order to reveal the genetic mechanism of the deposit from the perspective of elemental geochemistry. The results show that Cu, As, Cd, Sb, Tl, and Bi of sulfides were significantly enriched, while other trace elements were relatively depleted or not obviously enriched. The enrichment of these elements implies that the deposit contains a combination of both medium temperature elements and low temperature elements, indicating the complexity of ore genesis of the Shanshulin deposit. In addition, Cu and Cd are much more concentrated in sphalerite, while Sb, Tl, and Bi are more abundant in galena, suggesting the affinity of these trace elements to relevant host minerals. Sphalerite of the deposit is mainly in color of dark brown. The sphalerite and galena have the Ga/In ratios and their mean values of over 1, and the Zn/Cd ratios of around 500, suggesting that the deposit was formed in medium temperature (>250 ℃), which is similar to temperatures (135－292 ℃) calculated on the basis of the assumed S isotopic equilibrium between sphalerite and galena. The sulfides have very low total REE contents (ΣREE<1×10-6), with obvious positive Eu anomalies (δEu =1.6－2.5), but obvious negative Ce anomalies (δCe = 0.2－0.6). The calcite has relatively high total REE contents (ΣREE = 12.71×10-6), with obvious negative Eu anomalies (δEu = 0.7) and Ce negative anomalies (δCe = 0.25). Therefore, the authors have speculated that the ore-forming fluids of the Shanshulin Pb-Zn deposit were evolved from reduction to oxidation states. The REE of the Shanshulin Pb-Zn deposit could be originated from multiple potential source rocks. With the integration of previous geological and geochemical researches, it is believed that the Shanshulin Pb-Zn deposit could be produced by the mixing of higher temperature fluids with lower temperature fluids, with the ore-forming process experienced the transformation from reduced to oxidized environments. It belongs to the epigenetic hydrothermal deposit, and is certainly different to the typical brine originated MVT deposits in the low temperature basin.

Keywords: trace elements; rare earth elements; sulfide minerals; ore-forming environment; ore genesis; the Shanshulin Pb-Zn deposit