Publisher © Czech Geological Survey, ISSN: 2336-5757 (online), 0514-8057 (print)
PGE metal-rich black shales in south China: mechanism of metal enrichment and environmental aspects
AbstractThe Zunyi region in Guizhou province (south China) is well known for the occurrences of PGE-Mo-Ni-polyelement black shales that are locally mined and processed for Mo. Preliminary results of our study covering the vicinity of the Xiao-Zhu mine, Jiepo-Ling and Tuan Shan Bao Mo-Ni prospects can be summarized as follows: (1) PGEs are bound to a sulfide fraction rather than to organic matter. (2) Massive barite originated in an anoxic basin with limited communication with the open ocean. Conversely, accessory barite of the Ni-Mo-PGE sulfide layer shows different isotope characteristics reflecting most probably later, post-sedimentary barite formation. (3) Surface soil samples from Xiao-Zhu and Tuan Shan Bao show an enrichment in Cd, Ni, Zn (Cu, Hg) when compared to the local reference subsurface soil sample, indicating addition of these metals through weathering of sulfide material and its washout downstream from mine waste dumps to agricultural sites. In contrast, surface soil from Jiepo-Ling reflects most likely only a natural enrichment from underlying metal-rich black shales. (4) Anomalous concentrations of Cd were detected in tobacco leaves and dangerous concentrations of other toxic metals in various other crop plants. The longterm regular consumption of these metal-contaminated crop plants can cause a potential health problem.