This paper is the result of mineral exploration engineering.
[Objective]As one of the most important porphyry metallogenic systems in Gangdese metallogenic belt in Tibet, Jiama has a four in one orebody structure of porphyry, skarn, hornfels, and vein gold ore-body, forming riched minerals and diverse metal mineralization. Pyrrhotite is one of the important metal minerals, and its mineral geochemistry and relationship with gold mineralization are still obscure.
[Methods]The mineralogy and geochemistry of pyrrhotite in different occurrences of the Jiama porphyry system are the main objects for this paper according to detailed field geological survey, petrography, and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) analysis.
[Results]The results show that pyrrhotite is obviously enriched in Co, Ni, Cu, Zn, Ge, and Se, and weakly enriched in Pb, Bi, Sb, Te, Ag, and As, and low content of Mo, Cd, In, Sn, Ba, W, Au, Tl, Th, U, relatively. Moreover, the pyrrhotite from skarn has a high ratio of Co/Ni, represent the its magmatic-hydrothermal genesis, while the pyrrhotite hosted in hornfels shows sedimentary characteristics.
[Conclusions]The variation of contents of Cu, Zn, and Pb in pyrrhotite are related to the spatial mineralization in the Jiama deposit. The massive pyrrhotite in skarn is closely related to gold mineralization and the gold is mainly anhedral or irregular free gold occurring in the cavity and boundary of pyrrhotite grains. The enrichment and precipitation of gold could be related to bismuth-rich melts in the ore-fluids.
Highlights: Pyrrhotite is one of the important metal mineral in the Jiama deposit. The LA-ICP-MS analysis of pyrrhotite shows its geochemistry and genesis. The high-grade Au in pyrrhotite hosted in skarn could be related to the bismuth-rich melts in the orerelated fluids.