Geology, fluid inclusions and isotope geochemistry of the Herenping gold deposit in the southern margin of the Yangtze Craton, China: A sediment-hosted reduced intrusion-related gold deposit?

Abstract

The Herenping gold deposit is a typical gold deposit in the Xuefengshan arcuate tectonic zone in the southern margin of the Yangtze Craton, and the major feature of the gold mineralisation in the zone is the varying degrees of tungsten and antimony mineralisation in the ore deposits. The Herenping gold deposit occurs in the reddish-purple sandy slate in the middle section of the Madiyi Formation of the Neoproterozic Banxi Group and is controlled by the fault-fold zone associated with the Liulincha anticlinorium and F8 fault zone. However, its sources of mineralisation and relationships between hydrothermal fluids and magmatic rocks are unclear, which similar to those of many gold deposits in metasedimentary terranes in the worldwide.The mineralisation can be divided into four stages: an albite-quartz stage (I), an albite-quartz-pyrite-gold stage (II), a quartz-gold-polymetallic sulphide stage (III), and a quartz-carbonate stage (IV). The gold mineralisation occurred in albite-quartz veins in stage II and in sulphide-rich quartz veins in stage III in the deposit. A study of the fluid inclusions reveals that the homogenisation temperature and salinity were slightly higher in stage II (Th., 186–348 °C; W., 5.2–17.43 wt% NaCl equiv.) than in stage III (Th., 145–249 °C; W., 2.9–15.57 wt% NaCl equiv.), indicating that the temperature and salinity of the ore-forming fluid are gradually decreasing. The H-O (δD = −62.3 to −53.0‰; δ18O = 4.2–11.8‰) isotope characteristics reveals that the ore-forming fluid is a magmatic hydrothermal source. The sulphur (δ34S, −4.8–2.0‰) isotope characteristics and the alteration mineral assemblage (sericite-chlorite-pyrite) indicates that the ore-forming fluids was reduced. The lead (206Pb/204Pb = 17.419–17.436, 207Pb/204Pb = 15.519–15.535, and 208Pb/204Pb = 37.86–37.90) isotope characteristics reflect the ore-forming materials were likely derived from a deep magmatic source. In addition, the geochemical characteristics of albitite veins show that they are silicon rich (64.02–66.26 wt%) and significantly reduced. Notably, the Herenping gold deposit is located in the western portion of the tungsten/tin metallogenic provinces in South China, is host in epimetamorphic detrital rocks and was formed at least two stages of mineralisation; typical gold-bearing albite-quartz veins developed during the primary stage. These characteristics are consistent with those of reduced intrusion-related deposits such as the Muruntau, Kumtor and Telfer deposits. Thus, the Herenping gold deposit may be a sediment-hosted intrusion-related gold deposit. Based on the phase transition pattern from sulphide-rich quartz veins to albite-quartz veins to albitite veins with increasing depth in the deposit, we propose that reduced intrusions deep in the Herenping gold deposit could be discovered in the future, which implies the possible existence of a reduced intrusion-related gold system in the Xuefengshan arcuate tectonic zone.