Geochronology, stable isotopes and pyrite chemistry of the Cangzhuyu gold deposit in the North China Craton: Implications for gold metallogeny of Xiaoqinling

Abstract

The ore genesis of gold deposits in Xiaoqinling, located in the south margin of the North China Craton (NCC), remains highly debated. Either a magmatic source or a metamorphic origin has been advocated for the ore-forming fluids. In this paper, we report new 40Ar/39Ar dating, in-situ pyrite trace elements and C-H-O isotopic data for the Cangzhuyu deposit, hosted in quartz veins within the Archaean metamorphic rocks to constrain the ore-forming processes. Four stages of mineralization and alteration can be recognized in the deposit, including Stage I: quartz-pyrite veins; Stage II: pyrite-quartz-ankerite veins; Stage III: polymetallic sulfides-ankerite-quartz veins; Stage IV: quartz-carbonate veins. Sericite from stage III gold-bearing veins has a 40Ar/39Ar plateau age of 130.7 ± 1.3 Ma, which is synchronous with the regional gold mineralization event in the Xiaoqinling district. Laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS) trace element analysis shows that Stage I and Stage IV pyrite show similar compositions and rarely contain lattice gold. In contrast, gold mostly occur as native gold or Au-Te-Bi mineral inclusions within Stage III pyrite, which are consistent with their high Ni, Te, Bi contents. The ore-forming fluids equilibrated with ankerite have C-O isotopes of −6.6 to −4.1‰ and 8.8 to 10.8 ‰, respectively. They are consistent with H and O isotopes of sericite that δDfluid ranges from −61.1 to −60‰ and δ18Ofluid ranges from 8.2 to 7.2 ‰, implying a magmatic source. We hence suggest that the Cangzhuyu gold deposit was formed from mantle-derived magmas in a setting of the destruction of NCC and lithospheric thinning.