The genesis of the Xujiagou copper deposit, Mian‐Lue‐Ning area of Shaanxi Province, NW China: Constraints from mineral chemistry and in situ Pb isotope composition

The Mian‐Lue‐Ning area, bounded by the Hanjiang fault zone in the south and the Mian‐Lue suture in the north, is one of the most important polymetallic mineralization concentration regions in the Qinling orogenic belt. The Xujiagou copper deposit is representative in this area with chalcopyrite and pyrrhotite as the main ore minerals, subordinate sphalerite, and pyrite. However, the source of the ore‐forming materials and the genesis of the Xujiagou copper deposit are still in a controversy due to the lack of detailed study on the mineral composition. In this study, the electron probe micro‐analyzer (EPMA) analysis shows that the pyrrhotite in the Xujiagou copper deposit is mostly monoclinic pyrrhotite of low‐temperature phase, indicating that the metallogenic temperature should be below 304 °C. The percent of FeS molecules in sphalerite is 8.16–12.1%, indicating that the metallogenic temperature is 230–258 °C, which is mesothermal mineralization. The in situ Pb isotope composition of chalcopyrite (206Pb/204Pb = 19.087–20.861; 207Pb/204Pb = 15.533–16.062; 208Pb/204Pb = 38.121–39.391) and pyrrhotite (206Pb/204Pb = 20.241–20.664; 207Pb/204Pb = 15.7–15.996; 208Pb/204Pb = 38.659–39.372) in the Xujiagou copper deposit was analysed by fLA‐MC‐ICPMS, and it indicates that the ore‐forming materials were mainly sourced from the upper crust. Moreover, the contents and ratios of Co and Ni in pyrrhotite (Ni: 500–1600 ppm, Co