Recognition of late Paleoproterozoic gold mineralization in the North China craton: Evidence from multi-mineral U-Pb geochronology and stable isotopes of the Shanggong deposit

Abstract

Abstract The North China craton was stabilized in the late Paleoproterozoic but experienced significant removal of ancient lithospheric keel in the late Mesozoic that resulted in the formation of numerous world-class gold deposits with combined reserves of more than 7000 t of gold. However, it remains uncertain whether the North China craton contains older gold deposits formed during generation and final stabilization of the craton. Here, we show that the Shanggong gold deposit (105 t Au at 5.31 g/t) on the southern margin of the North China craton formed in the late Paleoproterozoic during the collision between the Eastern and Western blocks that led to formation of the Trans–North China orogen and final stabilization of the craton. The Shanggong deposit is hosted in amphibolite-facies rocks of the Neoarchean to early Paleoproterozoic Taihua Group and overlying volcanic rocks of the late Paleoproterozoic Xiong’er Group. Gold mineralization is structurally controlled by NE-striking faults and occurs in four segments: the Liuxiugou, Hugou, Shanggong, and Qiliping segments. The ores consist mainly of quartz-ankeritesulfide stockworks and sulfide disseminations in hydrothermally altered wall rocks. Gold is mostly contained in arsenian pyrite that is variably associated with minor sphalerite, galena, and chalcopyrite. Ore-related alteration assemblages comprise mainly quartz, ankerite, K-feldspar, sericite, and tourmaline. Both the stockworks and mineralized alteration assemblages contain hydrothermal accessory minerals, including monazite, apatite, and rutile. Paragenetic relations and textural data show that these accessory phases precipitated synchronously with gold-bearing sulfides. Laser ablation–inductively coupled plasma–mass spectrometry spot analyses of monazite and apatite from the Shanggong segment yielded reproducible U-Pb dates of 1747 ± 20 Ma (2σ, mean square of weighted deviates [MSWD] 0.46) and 1788 ± 200 Ma (2σ, MSWD = 11.3), respectively. These dates are indistinguishable within errors from an apatite U-Pb date of 1743 ± 79 Ma (2σ, MSWD = 1.6) at the Liuxiugou segment and a rutile U-Pb date of 1804 ± 52 Ma (2σ, MSWD = 0.77) at the Hugou segment. These new dates suggest that the Shanggong deposit formed at ca. 1.80–1.74 Ga, coeval with or immediately after formation of the Trans–North China orogen and final stabilization of the North China craton. Sulfides from the Shanggong gold deposit have δ34S values ranging from −18.5‰ to −6.9‰, whereas the coexisting ankerite has δ13CPDB of −6.81‰ to −1.61‰ and δ18OSMOW of 15.70‰–17.62‰. The stable isotope data are distinctively different from values of the Early Cretaceous gold deposits in the southern North China craton, indicating contrasting hydrothermal systems responsible for these two categories of gold deposits. The results presented here, combined with independent geologic evidence, allow Shanggong to be the first confirmed Paleoproterozoic orogenic gold deposit in the North China craton. Recognition of Paleoproterozoic orogenic gold mineralization provides significant new insights into the gold metallogeny of the well-endowed North China craton and has implications for future gold exploration along the three Paleoproterozoic orogenic belts in this craton.