| 浙江银坑山金银矿床地质特征及成因讨论 |
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| 引用本文：.1985.A discussion on geological features and genesis of the Yinkenshan gold-silver deposit，Zhejiang province[J].Mineral Deposits,4(4):47~55 |
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| A discussion on geological features and genesis of the Yinkenshan gold-silver deposit，Zhejiang province |
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| Abstract:The Yinkenshan Au-Ag deposit, located in the Ssoutheast Zhejjang, occurs in the metamorphic rocks of pre-Devonian Chencai Group overlain by Mesozoic volcanic rocks. The-host rocks are biotite-plagioclase gneiss containing garnet and graphite, and the ore-controlling structure is a NE-NEE trending tension-shearing fracture zone. The mineralization could be divided into 4 stages, i. e., (1) native gold-telluride, (2) kastelite-Ag-sulfide, (3) pyritization, (4) polymetallic sulfides. Mineralogical constituents of the ores are extremgly complicated. The main gangue minerals are quartz, rhodonite and rhodochrosite. In addition to sulfides, the common ore minerals are Au-Ag series minerals consisting of native gold, electrum, kustelite and native silver. There also exist tellurides such as hessite, petzite, altaire, telluro-bismuthite and volynskite, Ag-sulfides such as argentite, acanthite, jalpaite, and seIenargentite, and Ag-sulfosalts, such as polybasite and selenpoly-basite. The deposit occurs in the Circum-Pacific volcanic belt. Abundant evidence shows that there exists a Jurassic caldera. The geological setting, mineral associtation, obvious vertical mineral zoning, low Au-Ag ratios and the Au-Ag series minerals with low fineness(378) all suggest that the deposit is similar to some epithermal Au-Ag deposits in the Circum-Pacific metallogenic belt. The sulfur isotopic values δ34S of 49 sulfide samples from the deposit arc low positive with average value +5.47‰, maximum deviation 3.6‰, and stand ard deviation 0.8％, showing the common characteristics of magmatic hydro-thermal deposits. The δ18O of the quartz water is -1.75一+3.91‰, δD=-58.6一61.4‰. These data suggest that the ore-forming fluids are mixtures of magmatic and meteoric waters. This conclusion could also be substantiated by the fact that the deposit was emplaced in parametam orphie rocks with high value of δ18O rather than in volcanic rocks. The hydrothermal fluids could obtain a rather high value of δ18O through repeated exchange reaction with metamorphie rocks, because of the low water/rock ratio. The Pb isotopic compositions of 6 galena samples from the deposit are uniform. and theμvalues (9.47—9.65) have resemblance to those of the stratabound polymetallic sulfide deposits occurring in the metamorphic rocks of Chencai Group.The Pb isotopic composition has a single stage evolution history and is of “B” pattern, which was not influenced by the Mesozoic geothermal event. The temperature determinations of the inclusions suggest that the ore-forming process occurred at temperatures lower than 300℃.In summary, the authors of the present paper consider that the Yinken-shan AU-Ag deposit is an epithermal one related genetically to the Mesozoic volcanic activities. |
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