Objective As an important part of the Qin−Hang Metallogenic Belt, the Dayaoshan district develops abundant gold deposits. However, due to the lack of effective constraints on the ore−forming process ore source the genesis of these deposits has always been controversial. The aim of this study is to provide constraints on the deposit genesis of regional gold deposits by taking the Jinzhuzhou gold deposit in the Dayaoshan district as the study object.

Methods Pyrite is a common mineral in hydrothermal deposits, and its trace element geochemistry can play an important role in constraints on physicochemical conditions, ore−forming process and origin of deposits. In this paper, the internal structure and in situ trace element studies of Jinzhuzhou pyrite are carried out through field geological investigations, on the basis of fine dissection of the metallogenic process, and with the help of SEM, EPMA, LA−ICP−MS and other testing techniques.

Results The Jinzhuzhou gold deposit is one of the typical gold deposits in this district, and characterized by the NS−trending ore−bearing quartz veins. Its mineralization can be divided into three stages: (Ⅰ) Quartz−sericite−pyrite−arsenopyrite stage; (Ⅱ) Quartz−native gold−polymetallic sulfide stage; (Ⅲ) Quartz−calcite−chlorite stage. Systematic back−scattering imaging observations revealed that the Stage Ⅰ pyrite (Py1) has developed a distinct core−mantle−rim texture, while the porous Stage Ⅱ pyrite (Py2) trapping some sulfide inclusions commonly replaces the mantle zone (Py1b) of Py1. In−situ LA−ICP−MS trace element analysis showed that the core zone (Py1c) of Py1 is enriched in Co, Ni, Se, and Bi. Py1b is commonly enriched in As and Au, while the rim zone of (Py1c) of Py1 is commonly depleted in trace elements. Generally, Py2 is characterized by the depletion of Au−As. Notably, the Co−Ni concentrations declines from Py1a, through Py1b, to Py1c, suggesting a gradual decreasing temperature, which may have been responsible for the core−mantle−rim texture of Py1. Moreover, the sharp and irregular contact boundary between Py2 and Py1b, abundant porosities and mineral inclusion of Py2, and the lower Au−As concentrations of Py2 than Py1b, indicate that Py2 may have been formed via dissolution and precipitation of Py1b. This process results in the remobilization of gold solid solution within Py1b and the further precipitation of visible gold in Stage Ⅱ.

Conclusions Generally, the Jinzhuzhou pyrite is obviously enriched in Se (3.76 ~ 73.3×10⁻⁶, with an average of 16.5×10⁻⁶). Combining with the widespread development of magmatic−hydrothermal gold deposits, and the possible concealed magmatic pluton in the Dayaoshan district, it is inferred that the Jinzhuzhou gold deposit may have been magmatic hydrothermal origin.