贵州云炉河坝地区铅锌矿床元素地球化学特征、碳氧同位素组成及其地质意义

Element Geochemical Characteristics and C-O Isotopic Compositions of Pb-Zn Deposit in Yunluheba Area of Guizhou and Their Geological Implications

黔西北是中国川滇黔铅锌成矿域的一个重要组成部分,以该区研究程度较低的云炉河坝地区为研究对象,采用元素地球化学和碳氧同位素地球化学分析方法,对区内典型铅锌矿床(如昊星、顺达、富强和狮子洞等)进行了研究。成矿元素和稀土元素分析结果表明,包括赋矿围岩在内的区域各时代地层中的Pb、Zn、Cu等成矿元素含量普遍低于地壳克拉克值,不可能构成铅锌矿床的主要物质来源,结合前人S、Pb同位素研究,推测该区铅锌矿床的成矿物质可能主要来自于基底岩石。碳氧同位素分析结果表明,铅锌矿石和赋矿围岩的碳氧同位素组成整体上均接近海相碳酸盐岩范围,说明相关流体主要来自于海相碳酸盐的溶解作用。然而,矿石与围岩相比却具有相对更高的δ^(18)O值,表明成矿流体并非直接源自于赋矿地层,而更可能来自于深源流体的长距离迁移。此外,个别方解石显示较低的δ^(13)C值(-10.9‰^-8.1‰,PDB),接近沉积有机物的碳同位素组成范围,表明其受到了有机物脱羟基作用的影响。

Northwestern Guizhou is an important area in Sichuan-Yunnan-Guizhou Pb-Zn metallogenic domain.Yunluheba area in the northwestern Guizhou was taken as the object of the study.The element geochemical characteristics and C-O isotopic compositions of typical Pb-Zn deposits in the area including Haoxing,Shunda,Fuqiang and Shizidong were studied.The results of metallogenic and earth rare elements show that the contents of metallogenic elements（Pb,Zn and Cu,etc.）from the strata with different ages including host rocks are generally lower than the Clark value of the continental crust;PAAS-normalized REE patterns have a wide range withweak negative Ce anomaly and no-influencing from hydrothermal fluid.It is suggested that all the strata including host rocks do not supply the material sources for Pb-Zn deposits,but the characteristics are derived from the sedimentary environment.According to the previous result of S and Pb compositions,it is inferred that the main material sources of Pb-Zn deposits may be the basement rocks.The C-O Isotopic compositions show that dolomite has relatively highδ13 C values（-1.0‰-1.1‰,PDB）and δ^（18）O values（20.4‰-23.6‰,V-SMOW）,whereas the asphalt has relatively low δ^（13）C values（-6.0‰-3.9‰）andδ^（18）O value（15.2‰）;most of the calcites have δ^（13）C values of-4.1‰--0.5‰and δ^（18）O values of 15.2‰-21.3‰,which are between those of dolomite and asphalt;C-O Isotopic values of Pb-Zn and host rocks are consistent with those of marine carbonate rocks as a whole,suggesting that they are mainly derived from the dissolution of marine carbonate.Pb-Zn rocks have higherδ^（18）O values than those of host rocks,suggesting that metallogenic fluids are not directly derived from host strata,and may be derived from the long-distance migration of deep source fluid.In addition,the individual calcite has lowerδ13 C values（-10.9‰--8.1‰）,which are consistent with C isotopic value of sedimentary organic material,so that the calcite suffers the dehydroxylation of organic material.