云南金顶铅锌矿床的生物标志物特征及意义

CHARACTERISTICS AND SIGNIFICANCE OF BIOMARKERS OF THE JINDING LEAD-ZINC DEPOSIT,YUNNAN,CHINA

采用GC-MS分析方法对金顶铅锌矿床进行研究,结果表明:该矿床正构烷烃呈前高后低的单峰型分布,nC16或nC22为主峰碳,轻烃组分占有绝对优势,OEP值0.837～0.976,接近平衡值1.00,Pr/Ph为0.1～0.88,显示植烷优势;萜烷丰度顺序为五环三萜烷>三环萜烷>四环萜烷;规则甾烷呈不对称的“V”字形分布,表现为C29>C27>C28的分布特征。这些特征显示,金顶铅锌矿床有机质(生物)来源物质以菌藻类生物为主,可能有部分高等植物的贡献;矿床形成于缺氧的高盐度环境。结合金顶铅锌矿床下含矿层(原地沉积岩系)沉积于水深较浅的蒸发盐湖环境(即氧化环境),可以推断该矿床成矿流体中丰富的有机质形成的还原条件以及外来推覆岩系形成的封闭条件是金顶铅锌矿床形成的必要条件,矿床属于后期充填作用为主的矿床。

With the methods and the measures of GC-MS analysis,this paper studies the characteristics of biomarkers of the Jinding lead-zinc deposit,and discusses the correlation between organic matters and Pb and Zn. Abundant biomarkers, including n-alkanes, isoprenoid, steranes and terpanes,are detected by GC-MS from this ore. The n-alkanes of mineral samples show a low carbon molecular components with highest peaks of nC16 or nC22. OEP values of the n-alkanes show no odd-even carbon dominance. Pr/Ph ratios indicate that mineral samples possess phytane dominance. The terpanes distribution patterns of mineral samples are pentacyclic terpanes〉tricyclic terpanes〉tetracyclic terpanes. The steranes consist mainly of C27-steranes,C28-steranes and C29- steranes. According to abundance, C29-steranes〉C27-steranes〉C28-steranes, pregn-steranes and 4- methyl-steranes are also identified. All these characteristics indicate mixed contributions from bacterial and algae and higher plant wax sources with a possible dominance of bacterial and algae origin organic matter. The Jinding lead-zine ore was probably deposited in a reduction environment and high saline condition. Considering the sedimentary environment of the mineral-bearing strata, we conclude that reducing environment and sealing condition play an important role in the formation of the Jinding lead-zinc ore.