Ore genesis of the Xiyi Pb‐Zn deposit, western Yunnan province, China: Geologic, fluid inclusion, and isotopic (C‐H‐O‐S‐Pb) evidence

摘要

> The Xiyi Pb‐Zn deposit, located in the Baoshan Block of the Sanjiang region in western Yunnan, China, contains 1.2 Mt of Pb‐Zn resources. The orebodies are hosted by Devonian‐Carboniferous limestone, structurally controlled by the NE‐trending fractures, and occur in stratiform, vein, and lenticular forms. The mineral assemblage of the ores includes sphalerite, galena, pyrite, arsenopyrite, chalcopyrite, and marcasite. Calcite, barite, and quartz occur as gangue minerals. Three stages of hydrothermal mineralization are recognized based on the ore textures, crosscutting relationship, and mineral assemblages: an early stage of sphalerite?+?galena?+?calcite (Stage 1), a middle stage of galena?+?arsenopyrite?+?calcite?±?sphalerite (Stage 2), and a late stage of calcite?+?pyrite?±?barite?±?quartz (Stage 3). Two types of fluid inclusions are associated with the different ore‐forming hydrothermal stages: aqueous inclusions and hydrocarbon‐H ₂ O inclusions. The ore‐forming fluids were characterized by low temperatures (100?~?200?°C), medium salinities (8?~?20?wt% NaCl _eq ), and medium densities (1.0?~?1.1?g/cm 3 ) and contained minor amounts of CH ₄ . The δD _H2O and calculated δ 18 O _H2O values of the Stage 1 calcite range from ?89‰ to ?103‰ and from 1.5‰ to 5.5‰, respectively, indicating that the H ₂ O in the hydrothermal fluids was derived from seawater that had reacted with organic matter. The δ 13 C _PDB and δ 18 O _SMOW values of the calcite associated with Stages 1 and 3 range from ?5.2‰ to 3.2‰ and from 12.