Abstract:

The Luoshan gold deposit, one of the biggest gold deposits in the Linglong goldfield, develops both altered-rock type and auriferous quartz vein type mineralization. Based on detailed field and microscopic work, this study measures the trace elements and rare earth elements of the auriferous pyrite with the method of ICP-MS. The characteristics of REE and trace elements in pyrites from the two ore types are compared, and the nature and source of the ore-forming fluids are discussed. The total content of rare earth elements is low, and the REE distribution reveals an obvious light REE enrichment pattern, with negative Eu anomalies and absence of Ce anomalies. The Hf/Sm, Nb/La and Th/La ratios are less than 1, indicating the ore-forming fluids in the Luo-shan gold deposit might be Cl-rich reduced fluids. The Co/Ni ratios of auriferous pyrite range from 0.08 to 3.77, with an average value of 1.09. The Co/Ni ratios and contents of Co, Ni, Bi, Cu and Zn of the pyrite are close to average values of those from metamorphic-hydrothermal type gold deposit. The Y/Ho ratios generally range from 21 to 32, coincident with the continental crust of East China. Combined with weak positive Eu anomalies in few samples, and previous studies, the ore-forming fluids are presumed to be similar to the metamorphic fluid which mainly derived from the dehydration and decarbonization of the subducting paleo-Pacific plate, and may be mixed with felsic magmatic fluid and crustal fluid. There are no obvious differences of REE and trace element composition in the auriferous pyrite from both altered-rock type and auriferous quartz vein type ores, with small Y/Ho, Nb/Ta, and Zr/Hf ranges, which indicate the pyrite from both types of ores was formed in the same hydrothermal activity.

Key words: auriferous pyrite, REE and trace element, source of ore-forming fluid, altered-rock type and auri-ferous quartz vein type ores, Luoshan gold deposit, Jiaodong