Source and evolution of the Luanling gold deposit in the Xiong'ershan region, western Henan Province: Constraints from pyrite trace elements, in situ sulfur isotopes, and He–Ar isotopes

Abstract

The Luanling gold deposit is a lode gold deposit in the Xiong'ershan region located on the southern margin of the North China Craton. Based on typical mineral assemblages and relative Au contents, the pyrites in the Luanling deposit can be divided into four types: Py1‐s, pyrite with abnormally high levels of Au in pyrite–quartz veins; Py1, pyrite with low levels of Au in pyrite–quartz veins; Py2‐1, pyrite intergrowth with molybdenite; and Py2‐2, pyrite with higher concentrations of Au in association with molybdenite. Inductively coupled plasma mass spectrometry analyses reveal that the gold mainly occurs as “visible gold” (either native gold or electrum) inclusions and disseminations. “Invisible gold” is only hosted in the Py2‐2 pyrite grains, and Py1 and Py2‐1 contain low levels of Au concentrations (Py1 ≤ 6.563 ppm; Py2‐1 ≤ 8.377 ppm). Interestingly, As shows a strong correlation with gold concentrations in Py2‐2. The δ34S values of Py1 from Stage I span from −7.4‰ to −5.1‰. At Stage II, the δ34S values of Py2‐1 exhibit a range of −11.0‰ to −7.5‰. Pyrite in Py2‐2 shows δ34S values from −12.6‰ to −11.0‰. In situ sulfur isotope analyses of pyrite show an obvious decreasing trend, which is a result decreasing ore‐forming temperatures during the ore‐forming process. The He–Ar isotope data indicate that the ore‐forming fluids were derived from a mantle‐fluid mixing source. The metallogenesis in the Luanling deposit is closely related to the lithospheric thinning and the destruction of the North China Craton.