Major and trace elemental compositions and geological significance of sphalerite in the Fuxingtun Ag-Pb-Zn polymetallic deposit, Horqin Right Wing Front, Inner Mongolia

Abstract

Objective The Fuxingtun deposit is a recently discovered large Ag-Pb-Zn polymetallic deposit in Horqin Right Wing Front area, Inner Mongolia. However, the researches on the deposit are very scarce. The study investigates occurrence characteristics of ore-forming elements, precipitation mechanism and genetic type of the deposit, in order to provide theoretical basis for the genesis of the deposit. Methods This study focused on sphalerite in different stages of the Fuxingtun Ag-Pb-Zn polymetallic deposit, and obtained metallography, major and trace elemental compositions of sphalerite, in order to discuss the precipitation mechanism of ore-forming elements and the genetic types of this deposit. Results Combined with field investigation and metallography observations, the metallogenic process of the Fuxingtun deposit can be divided into three stages: Cu-Zn sulfide stage (Stage Ⅰ), Pb-Zn sulfide stage (Stage Ⅱ) and Pb-Zn sulfide stage (Stage Ⅲ). The results of electron probe microanalysis show that the content of Fe in sphalerite varies greatly, and there is an obvious negative correlation between Fe and Zn. The results of LA-ICP-MS analysis showed that, the contents of Fe, Mn and In in sphalerite decreased gradually from Stage Ⅰ to Ⅲ, whereas those of Ga, Ge and Sb increased slightly. Based on the diagrams of laser ablation signal curve and the correlation among different elements, this study constrained that Fe, Mn, Cd, Cu In, and Ag in sphalerite are present as the form of isomorphism. On the other hand, Pb exists in the form of micro-inclusions, while Bi and Sb mainly occur as galena micro-inclusions in sphalerite. The trace element compositions of sphalerite grains also show that the periodic pressure fluctuation in the ore-forming process is responsible for the formation of oscillatory zone in sphalerite. We proposed that the multiple decompression and cooling of ore-forming fluids are the main mechanism of mineral precipitation in the Fuxingtun deposit. Conclusion Combined with the geological characteristics of the deposit and the trace element characteristics of sphalerite, it is proposed that the Fuxingtun Ag-Pb-Zn polymetallic deposit is a medium-sized, epithermal sulfide deposit.

Keywords

• fuxingtun ag-pb-zn polymetallic deposit
• sphalerite
• mineral chemistry
• deposit genesis