The Origin of Hydrothermal Dolomite in the Huize Giant Pb-Zn Ore-field in the Yunnan Province and its Geological Implications

Hydrothermal dolomitization was pervasively developed in the Lower Carboniferous Baizuo Formation, which is the major ore-bearing strata of the Huize giant lead-zinc ore deposit in the Sichuan-Yunnan-Guizhou lead-zinc ore province. Based on detailed petrographic observation and major and trace element analyses, the paragenetic sequence is delineated and the origin and evolution of hydrothermal dolomitizing fluid and ore-forming fluid as well are discussed. There are two types of hydrothermal dolomite, including fine- to medium-grained dolomite and coarsely crystalline dolomite. Fine- to medium-grained dolomite shows dull to dark red luminescent zones and core-rim structures under cathodoluminescence and has total rare earth element (REE) contents and patterns similar to those of the micritic and fine crystalline dolomite formed in the early burial stage, which suggests the fine- to medium-grained dolomite inherited the REE signatures of the parent rock. The coarsely crystalline dolomite occurs in massive and crumby shapes. It has total REE contents lower than that of the limestone and shows light REE depletion, which indicates the limestone was leached by the hydrothermal dolomitizing fluid (basin brine), and the REEs in the dolomite were likely derived from the limestone. The coarsely crystalline dolomite near the ore shows bright red luminescence under cathodoluminescence and has higher Fe and Mn contents, indicating the interaction between ore-forming fluid and the coarsely crystalline dolomite might have promoted the precipitation of the sulfides. Gangue calcite is enriched in Fe, Mn, REE, and Y and shows light and middle REE enrichment without Ce anomaly, implying ore-forming fluid was deep-derived acid brine that extracted the REEs and ore metals in the basement rocks. The hydrothermal coarsely crystalline dolomite near the ore and gangue calcite have similar Y/Ho values, suggestive of precipitation from a common hydrothermal fluid system albeit during different stages. This study emphasizes that the hydrothermal dolomitization occurs before and during the lead-zinc mineralization, both processes occur in the common tectonic-fluid system and are associated with successive basinal fluid and deep-circulated metal-rich hydrothermal fluid flow driven by tectonic activity. Given the close temporal, spatial, and genetic relationship between hydrothermal dolomite and lead-zinc ore deposit, hydrothermal dolomite can be a useful indicator for ore prospecting. © 2023 Science Press. All rights reserved.