Abstract
The Sizhuang gold deposit with a proven gold resource of >120 t, located in northwest Jiaodong Peninsula in China, lies in the southern part of the Jiaojia gold belt. Gold mineralization can be divided into altered rock type, auriferous quartz vein type, and sulfide-quartz veinlet in K-feldspar altered granite. According to mineral paragenesis and mineral crosscutting relationships, three stages of metal mineralization can be identified: early stage, main stage, and late stage. Gold mainly occurs in the main stage. The petrography and microthermometry of fluid inclusion shows three types of inclusions (type 1 H2O–CO2 inclusions, type 2 aqueous inclusions, and type 3 CO2 inclusions). Early stage quartz-hosted inclusions have a trapped temperatures range 303–390 °C. The gold-rich main stage contains a fluid-inclusion cluster with both type 1 and 2 inclusions (trapped between 279 and 298 °C), and a wide range of homogenization temperatures of CO2 occurs to the vapor phase (17.6 to 30.5 °C). The late stage calcite only contains type 1 inclusions with homogenization temperatures between 195 and 289 °C. With evidences from the H–O isotope data and the study of water–rock interaction, the metamorphic water of the Jiaodong Group is considered to be the dominating source for the ore-forming fluid. The ore-fluid belonged to a CO2–H2O–NaCl system with medium-low temperature (160–360 °C), medium-low salinity (3.00–11.83 wt% NaCl eq.), and low density (1.51–1.02 g/cm3). Fluid immiscibility caused by pressure fluctuation is the key mechanism in inducing gold mineralization in the Sizhuang gold deposit.
Highlights
The giant Jiaodong gold deposit, with more than 4500 t proven gold reserves [1], is the most important gold producer of China [2,3]
There is a phenomenon in main stage that both type 1 and type 2 fluid inclusions with similar total homogenization temperatures occur in the same inclusion cluster (Figure 9f), which suggests immiscibility during main stage
The H2 O–CO2 and aqueous inclusions hosted in pyrite-related quartz in main stage can occur in a same inclusion cluster (Figure 9f), which can be considered as evidence of a fluid immiscibility
Summary
The giant Jiaodong gold deposit, with more than 4500 t proven gold reserves [1], is the most important gold producer of China [2,3]. More than 150 deposits in Jiaodong area are generally divided into two styles, Jiaojia-style and Linglong-style [4] The mineralization of the former is the disseminated-stockwork type which occurs in the pyrite-sericite-quartz alteration belt and the latter’s is the auriferous quartz vein type which is mostly controlled by subsidiary faults [5]. Both styles invariably occur in every single deposit in Jiaodong [6,7], with similar mineral paragenesis, alteration assemblages, and gold deposition ages [1,8]. They belong to the CO2 –H2 O–NaCl ± CH4 fluid system with a medium-high temperature (158–393 ◦ C) and a Minerals 2019, 9, 190; doi:10.3390/min9030190 www.mdpi.com/journal/minerals
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