川南马边上奥陶统—下志留统黑色页岩铂族元素地球化学特征及成因分析

Geochemical characteristics and genetic analysis of PGE in the upper Ordovician-lower Silurian black shale in Southern Sichuan

关键词:  五峰-龙马溪组  铂族元素  黑色页岩  化学特征  马边地区

Key words:  Wufeng-Longmaxi Formation  PGE  Black shale  Chemical characteristics  Mabian area

摘要:

通过野外地质调查资料、X衍射、主量及铂族元素测试分析，研究川南马边地区五峰-龙马溪组页岩的矿物学、主量元素地球化学特征和铂族元素组成特征。川南马边长河碥五峰-龙马溪组页岩有机碳TOC平均含量为2.47%；矿物成分主要由石英和黏土矿物两大类构成，石英平均含量37.95%，黏土矿物平均含量为40.2%；页岩SiO₂平均含量为52.90%，Al₂O₃平均含量为11.47%；铂族元素总量在1.5～11.9 ng/g之间，平均值为5.16 ng/g。川南马边地区五峰-龙马溪组页岩铂族元素均以Pt与Pd含量高为特征，其中Pd平均含量为3.15 ng/g，Pt平均含量为1.48 ng/g。铂族元素碳质球粒陨石配分模式为Pt-Pd型，Pd含量约为Pt含量的2.12倍。剖面中富有机质页岩比贫有机质页岩更加富集铂族元素，铂族元素的富集可能与生物活动有关；黏土矿物含量与铂族元素含量呈负相关关系，铂族元素并未呈吸附态吸附在颗粒表面，黏土矿物的增加反而稀释了铂族元素含量。川南马边长河碥五峰-龙马溪组铂族元素并非来源于地外物质，可能来自地幔，且发生了明显分异，其富集程度在正常海洋沉积物范围内。

Abstract:

Through the field geological survey data, X-ray diffraction, the main component and platinum group element test analysis, the mineralogical characteristics, main geochemical characteristics and platinum group element composition characteristics of the Wufeng-Longmaxi Formation shale in the Mabian area of southern Sichuan were studied. The results show that the average content of organic carbon TOC in the Wufeng-Longmaxi shale of the Changheyan Wufeng-Longmaxi Formation in Mabian, southern Sichuan is 2.47%; the mineral composition is mainly composed of quartz minerals and clay minerals. The average content of quartz minerals is 37.95%, and the average content of clay minerals is 40.2%; the average content of shale SiO₂ is 52.90%, the average content of Al₂O₃ is 11.47%; the total amount of platinum group elements is between 1.5-11.9 ng/g, the average value is 5.16 ng/g. The platinum group elements of the Wufeng-Longmaxi shale in the Mabian area of southern Sichuan are characterized by high content of Pt and Pd. The average content of Pd is 3.15 ng/g and the average content of Pt is 1.48 ng/g. The distribution model of platinum group element carbonaceous chondrites is Pt-Pd type, with Pd content about 2.12 times of Pt content. The organic-rich shale in the profile is more enriched in platinum group elements than the lean organic shale. The enrichment of platinum group elements may be related to biological activities; the clay mineral content is negatively correlated with the platinum group element content, and the platinum group elements are not in the adsorbed state Adsorbed on the surface of the particles, the increase of clay minerals actually diluted the content of platinum group elements. The platinum group elements of the Wufeng-Longmaxi Formation in Changheying, Mabian, southern Sichuan are not derived from extraterrestrial materials, but may come from the mantle, and they are obviously differentiated, and their enrichment is within the range of normal marine sediments.