藏南扎西康铅锌多金属矿床成因——硫化物原位硫同位素证据

藏南扎西康铅锌多金属矿床是特提斯喜马拉雅构造带（TH）东段发现的首个大型铅锌矿床，但其成因备受争议。本文在详细研究矿床地质特征的基础上，对矿硐内具有"同心环带"或"热水蛋"构造的铅锌矿石中的黄铁矿、方铅矿和闪锌矿进行了原位微区硫同位素分析。结果显示：铅锌矿石硫同位素组成变化范围在8.88‰~11.83‰之间，平均为10.50‰，总硫同位素组成（δ³⁴S_∑S）约为10.07‰。其中：7个黄铁矿（Py）测点的δ³⁴S_Py值为10.29‰~11.14‰，平均为10.70‰；6个闪锌矿（Sp）测点的δ³⁴S_Sp值为10.78‰~11.83‰，平均为11.49‰；5个方铅矿（Gn）测点的δ³⁴S_Gn值为8.88‰~9.18‰，平均为9.04‰。总体表现为δ³⁴S_Sp > δ³⁴S_Py > δ³⁴S_Gn，指示硫同位素未达到分馏平衡。利用方铅矿与闪锌矿矿物对硫同位素温度计计算可得，铅锌成矿温度介于224~280℃之间，平均值为259℃。结合前人研究成果，进一步得出扎西康铅锌多金属矿床主成矿期硫源主要来自日当组（J₁r）围岩地层，并可能有少量岩浆硫的混入，属受控于地层-构造-岩浆热液作用的中温热液矿床。

Genesis of Zhaxikang Pb-Zn Polymetallic Deposit in Southern Tibet: Evidence from in Situ S Isotopes of Sulfides

Zhaxikang Pb-Zn polymetallic deposit is the first large-scale Pb-Zn deposit discovered in the eastern Tethys Himalaya (TH), but its genesis is still controversial. Based on the detailed study of the geological characteristics, the authors analyzed the in situ S isotope of pyrite, galena, and sphalerite in the Pb-Zn ore with "concentric ring zone" or "hot water egg" structure in the mine chamber. The results of in situ S isotopic analysis show that the isotopic composition of Pb-Zn ore varies from 8.88‰ -11.83‰, with an average of 10.50‰, and the total sulfur isotopic composition (δ³⁴S_∑S) is about 10.07‰. Among them, the δ³⁴S_Py of seven pyrite measuring points is 10.29‰-11.14‰, with an average of 10.70‰;the δ³⁴S_Sp of six sphalerite measuring points is 10.78‰-11.83‰, with an average of 11.49‰;and the δ³⁴S_Gn of five galena measuring points is 8.88‰-9.18‰, with an average of 9.04‰. It shows a trend of δ³⁴S_Sp > δ³⁴S_Py > δ³⁴S_Gn, indicating a status of fractionation disequilibrium. Using S isotope thermometer between galena and sphalerite, the Pb-Zn mineralization temperature is constrained between 224 ℃ and 280 ℃ with an average of 259 ℃. Combined with the results of previous studies, it is concluded that the sulfur source of Zhaxikang Pb-Zn polymetallic deposit is mainly from the surrounding strata of Ridang Formation (J₁r) with minor magma sulfur, and Zhaxikang Pb-Zn polymetallic deposit belongs to the filling metasomatic mesothermal deposit controlled by the stratigraphic, tectonic and magmatic hydrothermal processes.