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北大巴山城口地区广泛发育富集V、Ag、Se等多种元素的下寒武统黑色岩系,但是否存在铂族元素矿化以及来源一直存在争议。本文利用ICP-MS方法测定了城口地区孙家坝剖面下寒武统鲁家坪组(对应牛蹄塘组)黑色岩系多金属富集层的铂族元素(PGE)、Au和Ag含量,在判断铂族元素异常的基础上,利用铂族元素地球化学特征探讨其来源。结果表明,该剖面黑色岩系样品具有较高的PGE含量(32.2~142.5 ng/g),平均88.9 ng/g,与上地壳平均值对比具有明显的PGE富集特征;同时金、银也具有较高的含量,平均值分别为40.2 ng/g和31.7μg/g。铂族元素配分模式表现为相对富集Pd、Pt、Os、Ru,亏损Ir、Rh,依据Ir含量以及与球粒陨石的对比分析,认为鲁家坪组黑色岩系PGE不具备地外物质来源。铂族元素球粒陨石标准化配分模式、PGE含量顺序及铂族元素相关图解显示其来源可能与海底热水作用关系密切。有机碳和PGE含量之间没有明显相关性,表明有机质可能是通过改变氧化还原条件导致PGE进一步富集。城口地区埃迪卡拉纪-寒武纪过渡阶段海底热水作用和PGE异常的识别不仅对于理解黑色岩系型矿床的成因,而且对全球重大事件如寒武纪生命大爆发的认识都具有重要意义。
The Lower Cambrian black rock series enriched with V, Ag, Se and other elements are widely developed in the Chengkou area of the North Dabashan Mountain. However, the existence of platinum group element mineralization and its origin have been controversial. In this paper, ICP-MS method was used to determine the content of PGE, Au and Ag in the polymetallic rich layers of the Black Cambrian Lujiaping Formation (corresponding to the Niutitang Formation) in the Lower Cambrian of the Sunjiaba section Based on the analysis of the anomalies of PGs, the origin of PGs is discussed based on their geochemical characteristics. The results show that the samples of the black rock series have high PGE content (32.2-142.5 ng / g) with an average of 88.9 ng / g, which shows obvious PGE enrichment characteristics compared with the average value of the upper crust. At the same time, gold and silver also have The higher content, with an average of 40.2 ng / g and 31.7 μg / g, respectively. The distribution pattern of platinum group elements is relatively enriched in Pd, Pt, Os, Ru and depleted in Ir and Rh. Based on the Ir content and the correlation with chondrule meteorites, it is concluded that the PGEs in the Lujiaping black rock series do not possess extraterrestrial material . Platinum group chondrule meteorites normalized distribution patterns, PGE content sequence and platinum group element diagram shows that the source may be closely related to the role of sea water. There was no significant correlation between organic carbon and PGE content, suggesting that organic matter may cause further PGE enrichment by changing the redox conditions. Seabed hot water effect and PGE anomaly identification in the Edicarcao-Cambrian transitional stage of the Chengkou area are not only important for understanding the genesis of the black shale deposits but also for the understanding of major global events such as the Cambrian explosion significance.