Baimazhai, Yunnan Province, China: A Hydrothermally Modified Magmatic Nickel-Copper-PGE Sulfide Deposit

Abstract

The Baimazhai Ni-Cu-PGE (platinum-group-elements) sulfide deposit, southeast Yunnan Province, is hosted in mafic-ultramafic intrusions of the Permian Emeishan large igneous province, with which it is temporally and genetically related. The typical orthomagmatic sulfide ores of the Baimazhai deposit locally exhibit peculiar textural features, and are intimately associated with hydrothermal minerals such as biotite, amphibole, and chlorite. This suggests that magmatic sulfide ores were subjected to hydrothermal alteration and subsequent redistribution, resulting in enrichment in Cu, Pd, and Au. Whole-rock 40 Ar-39 Ar age data yielded plateau ages of about 160-170 Ma, at odds with the established Permian age of the host intrusions and the Emeishan large igneous province. We interpret these younger ages as due to thermal resetting during post-Permian tectonothermal events such as the Jurassic Cretaceous Yanshanian orogeny, and propose a model in which tectonic movements and hydrothermal fluids modified the pre-existing magmatic sulfides. Given the high degree of overprinting, we suggest two possible scenarios: (1) sulfide disseminations that surround the massive magmatic ores are the result of deformation and hydrothermal alteration; and (2) both magmatic massive and disseminated sulfides were produced initially, in which case the scale and metasomatic remobilization would have been smaller, but still detectable.

Mangrove Soil-Borne Trace Elements in Qi’ao Island: Implications for Understanding Terrestrial Input of Trace Elements into Part of the Pearl River Estuary

“…The close relationship between Ni and Cu (Table 6) could be attributed to their concurrent presence in nickel-copper sulfide ores [30]. The sources of nickel include nickel plating, non-Ni ore mining, burning of coal and oil, nickel-cadmium batteries, sewage, phosphate fertilizers, and pesticides, which also involve other trace elements [31].…”

40Ar-39Ar dating of lamprophyre dykes in the Baimazhai nickel deposit, Yunnan Province, China, and its geological significance

“…Geological, petrological, mineralogical and geochemical characteristics of lamprophyres in the Baimazhai nickel deposit are described by Guan Tao et al (2003), and Zhang et al (2006). Phlogopite as one of the essential minerals of lamprophyres in the orefield occurs as phenocrysts and matrix.…”

“…The ore-hosted rock body in the Baimazhai nickel deposit is a basic-ultrabasic complex which is composed of peridotite, pyroxenite, and gabbro (Guan Zhang et al, 2006). The ore-hosted complex body in the orefield intruded into the Ordovician rammell and is considered as the product of Variscan magmatic activity (Zhang Qi et al, 1992;Deng Jiafan, 1999).…”