黔北桑木背斜铅锌成矿带S、Pb同位素特征及成矿物质来源探讨

Discussion of Sulfur-lead Isotope Characteristics and Source of Ore-forming Materials of Lead-zinc Metallogenic Belt in Sangmu Anticline of Northern Guizhou

本文以S、Pb同位素作为示踪元素研究黔北桑木背斜铅锌成矿带成矿物质来源。桑木背斜铅锌成矿带矿石矿物中硫化物的δ34 S值变化范围较大最小值为16.1‰,最大值为31.5‰,平均值为25.6‰,极值为15.4‰;矿石矿物为相对富集重硫型;据此判断其硫的来源可能为沉积岩。研究区内来自不同矿区、不同矿物的Pb同位素变化均很小。206 Pb/204 Pb介于18.2518.57之间,207 Pb/204 Pb介于15.6315.92之间,208 Pb/204 Pb介于37.8238.93之间,三者变化范围均很小,且不同硫化物样品之间的Pb同位素组成也不存在明显的差异,表明桑木背斜地区的铅锌矿床可能具有较为单一的铅金属来源。通过投图分析,笔者认为桑木铅锌矿成矿带的铅金属可能来源于下伏基底地层。

In this paper,S and Pb isotopes were used as trace elements to study the metallogenic material sources in the Pb-Zn mineralization belt of Sangmuanticline in the northern Guizhou Province.Theδ34 Svalues of sulphide or sulfate in the Pb-Zn mining areaof Sangmuanticline rangefrom16.1‰to 31.5‰,with average value of 25.6‰,and extreme value of 15.4‰,which are relatively enriched in heavy sulfurisotopes.The sulfur isotope allplot in the field of sedimentary rocks,which are similar to the sulfur isotopes of sulfate in seawater duringearth history,indicating that the sulfur may besourcedfrom sedimentary rocks.Pb isotopic variations of different minerals from different mining areas are very small in the study area.206 Pb/204 Pbvalues are between 18.25 and 18.57,207 Pb/204 Pbratios are between 15.63 and 15.92,and 208 Pb/204 Pb ratios arefrom 37.82 to 38.93.There is no obvious difference in Pb isotope composition between different sulfide samples,indicating that the Pb-Zn deposit in the Sangmuanticline area may have a single source ofthe Pb metal.Pb isotope analyses show that the Pb metal in the Pb-Zn mineralization belt of Sangmu area may be from the underlying basement strata.