云南大平掌铜多金属矿床硫、铅、氢、氧同位素地球化学

Sulfur, lead, hydrogen and oxygen isotopic geochemistry of the Dapingzhang copper-polymetallic deposit, Yunnan Province

对云南大平掌铜多金属火山岩型块状硫化物矿床的矿石矿物和火山岩围岩的Ｓ、Ｐｂ同位素及脉石矿物、硅 化岩、硅质岩等的Ｈ、Ｏ同位素地球化学特征进行了研究，认为矿床中大多数硫来源于热液对火山岩的淋滤，或直接 来源于火山喷气作用；矿石铅与火山岩铅属同一来源，且以富放射性成因铅为特征；成矿流体可能主要来源于深循环的海水与岩浆水的混合流体，而大气降水参与的可能性很小。

The Dapingzhang copper-polymetallic deposit is a volcanic-hosted massive sulfide deposit newly found in the Sanjiang area in 1996, with current development of target exploration strategically focused on this type of deposit. Sulfur, lead isotopic compositions of the ore minerals and volcanic rocks, and hydrogen, oxygen isotopic geochemistry of quartz, silicified rocks and chert from the Dapingzhang copper deposit are discussed in this paper. There is minor change in the δ^(34) values of the sulfides selected from the disseminated ores, massive ores and veins of quartz, varying from - 1. 05‰ to + 1. 55‰, with an average of near zero, which indicates that the chemical state of the ore-forming hydrothermal fluid is kept stable. Therefore the sulfur isotopic composition of the fluid is constant during the transportation and precipitation process. It can be concluded that the sulfur in the deposit is mostly derived from magmatic sulfur, that is, most of the sulfur is leached from the volcanic rocks, such as spilite, keratophyre and quartz-keratophyre, and/or provided directly by the volcanic exhalation. The change in lead isotopic composition is usually not obvious during the leaching, transporting and precipitating process. The sources of the ore-forming materials and tectonic environment hosting the deposit can be traced effectively using the lead isotopic compositions of the ores because the lead in the ore-forming fluid can inherit the lead isotopic composition characteristics of the original area. The ores and volcanic rocks in the Dapingzhang deposit are characterized by the radiogenic lead, with ^(206)Pb/204Pb > 18. 310, ^(207)Pb/^(204)Pb > 15. 489, ^(208)/^(204)Pb > 37. 811 in the ores, and ^(206)Pb/ ^(204)Pb > 17. 653,^(207)Pb/^(204)Pb > 15. 564,^(208)Pb/^(204)Pb > 38. 016 in the volcanic rocks. These indicate that the ores and volcanic rocks are the same in the origin of lead and corresponding with the lead isotopic compositions of island-arc or continental margin hosting the Dapingzhang deposit. The variation in stable isotopic compositions of the typical minerals and rocks formed during different ore-forming stages can represent the evolution characteristics of the ore-forming fluid. The ore-forming fluid composition induced from the hydrogen and oxygen isotopic compositions of quartz, silicified rocks and chert in the deposit, ranging from + 2. 9‰ to - 2. 2‰ in 8δ^(18)O_(H_2O) value and from - 59‰ to -- 77‰ in δD value, suggest that the ore-forming fluid is most probably composed of the seawater and magmatic water, and contribution of the meteoric water is essentially nil.