豫西熊耳山地区北岭金矿Pb、S同位素特征及其地质意义

Geochemical Characteristics of Sulfur and Lead Isotope Composition in the Beiling Gold Deposit,Xiong ershan Area,Henan Province and Their Geological Significance

位于豫西熊耳山地区的北岭金矿是一构造蚀变岩型金矿床,其金矿化严格受断裂构造控制。本文在详细的矿床地质特征研究基础上,采集主成矿阶段的矿石并挑选其中的黄铁矿进行铅和硫同位素研究。结果表明,黄铁矿的208 Pb/204 Pb值为36.789~37.861,平均值为37.455;207 Pb/204 Pb值为15.383~15.505,平均值为15.444;206 Pb/204 Pb值为16.373~17.294,平均值为16.939。矿石铅μ值为9.36~9.43,平均值为9.38;Th/U值为4.04~4.17,平均值为4.09。矿石铅主要来源于地幔,有壳源物质的混染。黄铁矿的δ34 S为-9.6‰^-16.6‰,平均为-14.85‰,表明随着成矿过程的进行,硫同位素发生了较强烈的分馏,分馏原因可能是因天水加入到成矿流体中导致氧逸度升高造成的。

The Beiling gold deposit,located in the Xiong ershan area,western Henan,is of the tectonically altered rock type.Its gold mineralization is strictly controlled by fault structure.In this work,lead and sulfur isotope characteristics were studied based on detailed field investigations.The results show that 208 Pb/204 Pb,207 Pb/204 Pb,206 Pb/204 Pb ratios of pyrites in the main mineralization stage are in the ranges of 36.789~37.861,15.383~15.505 and 16.373~17.294,respectively.Theμvalues vary in 9.36~9.43,9.38 on average.The Th/U ratios range from 4.04 to 4.17,with an average value of 4.09.The lead isotope composition suggests that the ore materials might have mainly originated from mantle with crustal contamination.Theδ34 S values of pyrites vary in the range of-9.6‰^-16.6‰,with an average value of-14.85‰.The data indicates strong sulfur isotope fractionation because of the rise in oxygen fugacity of the ore-forming fluid in the mineralization process,which might be the result of the addition of atmospheric water.