ZHU Zheng-jie1,2, ZHANG Bin-chen3, TANG Qing-min1, MAO Ling-ling1, SHUANG Yan1, ZHANG Xiong1
(1. Chongqing Key Laboratory of Exogenic Mineralization and Mine Environment, Chongqing Institute of Geology and Mineral Resources, Chongqing 400042, China;
2. Chongqing Research Center of State Key Laboratory of Coal Resources and Safe Mining, Chongqing 400042, China;
3. Chongqing Institute of Geological Survey, Chongqing 400042, China)
Abstract: Black rock series in the Lower Cambrian are well developed in Chengkou district, northern Dabashan, southwestern China, and are enriched in numerous elements, such as silver, vanadium and selenium, while the mineralization of platinum group element (PGE) remains to be debated. In this study, ICP-MS technique was used to analyze concentrations of PGE, gold and silver in the Lower Cambrian Lujiaping Formation (equivalent Niutitang Formation) black rock series, meanwhile the mineralization and origin for this extreme polymetallic enrichment was discussed on the basis of PGE geochemistry. Results indicate that black rock series of the Lower Cambrian yield with higher PGE and Au contents, with average values of 88.9 ng/g and 40.2 ng/g, respectively, showing obvious potential of mineralization. All samples have higher Ag concentrations (17.1－51.7 μg/g), with the average value of 31.7 μg/g. Distribution patterns of platinum group elements display the enrichment of Pt, Pd, Os and Ru, and depletion of Ir and Rh. Based on Ir content and comparison with the chondrite, it is suggested that PGEs in the Lujiaping Formation black rock series in Chengkou district are not extraterrestrial origin. Chondrite-normalized patterns of platinum group element and diagrams of PGE indicate that PGE in black rock series sequence in Chengkou district likely has a hydrothermal origin. No correlation between organic matter and PGE contents demonstrates that the enrichment of PGE is due to the change of environment, and anoxic environment may enhance extreme metal enrichments. The recognition of hydrothermal activity and the extreme enrichment of PGE during Ediacaran-Cambrian transition in Chengkou district are of particular significance, not only concerning with the genesis of those type ore deposits, but also shedding light on global events, such as Cambrian Explosion.
Keywords: Platinum group elements; Black rock series; Hydrothermal origin; Chengkou district
E-mail：zhuzhjie@163.com
ACTA MINERALOGICA SINICA Vol. 37, No. 4, 2017, Page 495
