| 其他摘要 | The Gongguan-Qingtonggou Hg-Sb deposit, located in the Xianyang continent -marginal depression zone of eastern of southern Qinling in Shaanxi province, is one of typical and largest mercury and antimony deposits in Qingling - Central Asia Hg-Sb deposit zone. However, there is no consensus on the genesis of this deposit. Several models have been proposed, such as, sedimentary rework, magmatic hydrothermal and hydrothermal alteration. This study focuses on discussing the genesis of the deposit on the basis of regional geology, ore deposit geology and deposit geochemistry.
Based on the detailed field work, several modern methods such as microthermometry, stable isotopic analysis and Inductively Coupled Plasma-Mass Spectrometry (ICP-MS) have been employed to discuss geochemical features and characteristics of inclusions in different minerals in this paper. These evidences indicate that Gongguan-Qingtonggou Hg-Sb deposit is formed in a collision-orogenic setting. The other conclusions are also made as follows:
1. Gongguan-Qingtonggou Hg-Sb deposit, hosted in the Devonian dolomite, is usually associated with fault belts. The ores mainly consist of antimonite, cinnabar, quartz and calcite. According to different mineral component, two types of ores can be classified: Hg-Sb type and Hg type.
2. The analysis of fluid inclusions shows that:inclusions from quartz have the homogeneous temperature of 136～274℃ and salinity of 1.57～11.34 wt.% NaCl equivalent, while the ones from calcites have homogeneous temperature of 180～272℃ with corresponding salinity of 1.23～8.81 wt.% NaCl equivalent. Calculated density of fluid ranges from 0.38 g/cm3 to 0.58 g/cm3.Ore-forming fluid in Gongguan-Qingtonggou is reworked hydrothermal fluid characterized by lower temperature, lower salinity and lower density, compared with other Hg-Sb deposits in China (such as Xikuangshan Sb deposit, Shiliping Sb deposit, Woxi Au-Wu-Sb deposit).
3. The features of rare earth element show that: calcites have similar REE pattern with dolomite, both of which are all characterized by LREE enrichment.
4. Analysis of stable isotope shows that: the δ34S value of antimonite and cinnabar ranges from 2.03‰ to 9.37‰ and from 3.26‰ to 11.62‰, respectively. This feature is similar with the δ34S value of pyrites (ranging from -1.72‰ to 8.6‰ )from host strata, which indicates that the sulfide are mainly originated from host strata. Analytical results of D and O isotope indicate that ore-forming fluid is characterized by the reworked hydrothermal fluid which was formed by recycling of deep strata construction water. However, meteoric water played a significant role at the late stage of ore-forming process.
5. Previous studies show that the 87Sr/86Sr value of ores is higher than dolomite, but with positive correlations between Hg and Sb contents, which indicates that Hg, Sb and Sr ingredient of ores originate from the same resource. In contrast to main anomalous lead in dolomite, the Pb of antimonite is normal common lead, which indicates that lead of ores mainly originate from basic rocks.
6. Firstly, the mineralization of Hg in dolomite are formed in the first stage of mineralization in the period of increasing temperature and pressure. Sencondly, the second stage of Sb-mineralization and third stage of Hg-mineralization are formed in the period of decreasing temperature and increasing pressure , which is the main ore-forming stage. The minerals are main quartz with minor calcite. Lastly, the coarse grain calcite vein with only tiny mineralization or without were presented at the forth stage of mineralization in the period of decreasing temperature and pressure. |
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