Multi-stage Cu remobilization of the Huping metamorphic-hydrothermal deposit in the southern North China Craton

The Zhongtiao region is a well-endowed Cu metallogenic province in the southern North China Craton and contains a large number of early Precambrian Cu deposits of different styles, most of which have been subjected to the ca. 1.85 Ga regional metamorphism. However, whether there was any role for the Proterozoic metamorphism on the extensive Cu mineralization is yet to be well understood. This paper presents an integrated investigation on the field geology, mineral chemistry, fluid inclusion and C-H-O-S isotopes of the Huping metamorphic-hydrothermal deposit in the Neoarchean-Paleoproterozoic Zhongtiao metamorphic terranes, and reveals multi-stage Cu remobilization that formed and upgraded the Cu deposits in the region. We identified three stages of syn- to post-metamorphic Cu remobilization/transportation in the Huping Cu deposit, including (I) early mechanical transport, (II) intermediate metamorphic-hydrothermal remobilization and (III) late meteoric fluid incursion. In stage I, sulfides were remobilized and transported internally under lower-greenschist facies metamorphism, forming the veinlet-disseminated ores and chalcopyrite (avg. delta S-34 = 2.1 parts per thousand, similar to the chlorite-amphibole schist wall rocks). In stage II, the immiscibility of metamorphic fluids (avg. delta O-18 = 4.6 parts per thousand and SD = -56.6 parts per thousand) from the metamorphic terranes triggered the precipitation of higher delta S-34 chalcopyrite (avg. 8.0 parts per thousand), led by the incorporation of extra sulfur during the fluid migration. In stage III, incursion of meteoric fluids into the waning metamorphic-hydrothermal system formed the barren quartz-calcite veins (avg. delta O-18 = 0.09 parts per thousand and delta C-13 = -0.88 parts per thousand). During these Cu remobilization processes, the earlier-formed sulfides were chemically stable during the mechanical transfer by regional metamorphism and deformation. Subsequently, the immiscibility of metamorphic fluids induced significant Cu remobilization and precipitation in the metamorphic-hydrothermal system. We thus propose a model of multi-stage mechanical and chemical Cu remobilization for the Huping Cu deposit, which highlights the crucial impacts of metamorphic-remobilization processes on the regional Cu mineralization in the Zhongtiao region.