LA-ICPMS trace elements of pyrite from the super-large Dulong Sn-Zn polymetallic deposit, southeastern Yunnan, China

The Dulong Sn-Zn polymetallic deposit, located in the southeastern Yunnan Province, is a super-large Sn-Zn polymetallic deposit with by-products of In, Cu, Pb, W, Fe, Ag, etc. Many studies on mineralogy, ore deposit geochemistry and chronology have been carried out on this deposit, confirming a genetical relationship of its Sn-Zn mineralization to the Late Yanshanian magmatic activity. However, whether the deposit underwent exhalative sedimentary Sn-Zn mineralization is still controversial. Based on detailed petrographic observation, the LA-ICPMS trace element compositions of pyrite that widely occur in the Dulong deposit are investigated systematically in this paper. Field and microscopic observations show that four types of pyrite have been identified in Dulong, including the oolitic pyrite (Py1), fine vein pyrite (Py2) crosscutting and/or replacing Py1, euhedral pyrite (Py3) coexisting with sphalerite and other sulfides, anhedral pyrite (Py4) enclosing early generated pyrite and sphalerite. LA-ICPMS analysis results suggest that pyrite is enriched in Co, Ni, As and Ge, which are mainly incorporated into the pyrite lattice in the form of isomorphism. Other elements occur mostly as mineral micro-inclusions in pyrite. The trace element compositions of the four types' pyrite exhibit significant difference from each other: Py1 is enriched in Zn and As but depleted in Co, Ni and Cu with low Co/Ni ratios (< 1.0), which share similar features with typical sedimentary pyrite; Py2 is similar in its trace element compositions and Co/Ni ratios to those in Py1; while Py3 and Py4 have elevated Zn, As, Mn, Co, Ni, Cu, Sb, Pb and Bi contents with high Co/Ni ratios (mostly >1.0), which is consistent with that of euhedral pyrite formed by magmatic-hydrothermal activity rather than sedimentary pyrite. Comparing with the trace element compositions of pyrite in different types, we consider that Py1 is of sedimentary origin, Py2 that inherits the trace element features of Py1 is formed by metamorphic reworking of Py1, while Py3 and Py4 are formed by late magmatic-hydrothermal activity. Ag and Bi in pyrite display potential probobilities as a geochemical indicator to distinguish pyrite of different genetic types. Oolitic pyrite formed in the depositional diagenesis stage may provide some sulfur and a small amount of Zn for the later Sn-Zn mineralization. The regional metamorphic reworking in the Hercynian to Indosinian displays a limited effect on the Sn-Zn mineralization, while Late Yanshanian magmatic-hydrothermal activity is the controlling factor for the formation of the super-large scale Dulong Sn-Zn polymetallic deposit.

Automated summary

The Dulong Sn-Zn polymetallic deposit in southeastern Yunnan Province is a super-large deposit with high production of tin and zinc along with various by-products. Studies indicate a genetic relationship between the deposit's mineralization and the Late Yanshanian magmatic activity, but the exhalative sedimentary origin of the deposit is still debated. LA-ICPMS analysis of pyrite in the deposit shows significant differences in trace element compositions among different types.