Genesis of the Hongtuling Au-Mo deposit in the southern North China Craton revealed from pyrite trace element compositions and S-Pb isotopes

Abstract

The Hongtuling Au-Mo deposit on the southern margin of the North China Craton consists of Au veins and minor Mo veins that formed at ~130 Ma and ~204 Ma, respectively. Mo mineralization is dominated by molybdenite that is associated with K-feldspar, quartz and calcite, whereas Au mineralization occurs mostly as auriferous quartz-sulfides veins associated with alteration assemblages consisting of pyrite ± sericite ± quartz. Laser ablation inductively coupled plasma mass spectrometry trace element analysis shows that pyrite from Mo veins (Py-Mo) is relatively enriched in Mo and Pb, whereas pyrite from Au veins (Py-Au) contains much higher Au, Ag, Te, Cu, Pb, and Ni. Sulfide minerals and celestine from Mo veins range in δ34S values from −13.4 to −8.89‰ (n = 24) and 5.26 to 7.76‰ (n = 8), respectively. Extrapolation of sulfur isotopes of coexisting sulfides and celestine to zero sulfide-celestine fractionation on Δ34SClt-Py versus δ34S diagram shows that the hydrothermal fluid from which molybdenite precipitated has δ34S of 2.49 ± 3.93‰. In comparison, Py-Au yields δ34S values of −6.23 ~ 0.16‰, with a mean of −2.60‰ (n = 20). The Py-Mo and Py-Au have significantly different lead isotopic compositions, which form two distinct groups on the 207Pb/204Pb versus 206Pb/204Pb diagram, with Py-Au plotting close to the lead growth curve of the subcontinental lithospheric mantle of the North China Craton at ~130 Ma.Combined with previous studies, our new trace element and S-Pb isotope data suggest that Mo mineralization at Hongtuling is most likely related to magmas derived from partial melting of Late Archean to Paleoproterozoic metamorphic basement rocks under a post-collisional setting related to the collision between the North China Craton and Yangtze Craton, whereas Au mineralization is genetically associated with mantle-derived magmas generated in an extensional setting due to thinning and destruction of subcontinental lithospheric mantle keel beneath the North China Craton. As such, the Triassic Mo and Early Cretaceous Au veins can both be classified as magmatic-hydrothermal mineralization but are affiliated with two distinct systems. This study highlights the utilization of pyrite trace element and isotopic compositions in distinguishing multiple mineralization events in a single deposit.