Abstract
The Xiejiagou deposit is a representative medium-sized gold deposit in Jiaodong the Peninsula, which contains gold reserves of 37.5 t. The orebodies are hosted in the Linglong biotite granite with a zircon LA-ICP-MS U–Pb age of 160.5±1.3 Ma (N=15, MSWD=1.2) and are characterized by disseminated- or stockwork-style ores. Mineralization and alteration are structurally controlled by the NE-striking fault. Three stages of mineralization were identified with the early stage being represented by (K-feldspar) sericite quartz pyrite, the middle stage by quartz gold polymetallic sulfide, and the late stage by quartz carbonate. Ore minerals and gold mainly occurred in the middle stage. Three types of primary fluid inclusions were distinguished in the Xiejiagou deposit, including carbonic-aqueous, pure carbonic, and aqueous inclusions. The primary fluid inclusions of the three stages were mainly homogenized at temperatures of 262–386°C, 192–347°C, and 137–231°C, with salinities of 2.22–8.82, 1.02–11.60, and 1.22–7.72 wt% NaCl equivalent, respectively. These data indicate that the initial ore-forming fluids were a medium temperature, CO2-rich, and low-salinity H2O–CO2–NaCl homogeneous system, and the ore-forming system evolved from a CO2-rich mesothermal fluid into a CO2-poor fluid. Considering the fluid inclusion characteristics, H–O–S–Pb isotopes, and regional geological events, the ore-forming fluid reservoir was likely metamorphic in origin. Trapping pressures of the first two hydrothermal stages estimated from the carbonic aqueous inclusion assemblages were ~224–302 MPa and ~191–258 MPa, respectively. This suggests that the gold mineralization of the Xiejiagou gold deposit occurred at a lithostatic depth of ~7.2–9.7 km. Au(HS)2− was the most probable gold-transporting complex at the Xiejiagou deposit. Precipitation of gold was caused by a CO2 effervescence of initial auriferous fluids.
Highlights
The Jiaodong Peninsula (Figure 1) is an important gold metallogenic belt in China hosting about 4000 t of gold reserves and considered as one of the most famous gold mineralization belts in the world [1,2,3,4,5,6,7,8,9,10,11]
The majority of gold deposits in the region are temporally and spatially related to Mesozoic NE-trending faults, and the deposits have been classified as Jiaojia-type and Linglong-type mineralization, where the former refers to a combination of disseminated and stockwork/veinlet gold mineralization and the latter to auriferous quartz veins [1, 12,13,14,15]
These geochronological data indicate that the age of Xiejiagou gold mineralization occurred at ~123.6–115.2 Ma, which is identical to 120 ± 5 Ma, the generally considered main mineralizing period of the major gold deposits within the Jiaodong Peninsula [46]
Summary
The Jiaodong Peninsula (Figure 1) is an important gold metallogenic belt in China hosting about 4000 t of gold reserves and considered as one of the most famous gold mineralization belts in the world [1,2,3,4,5,6,7,8,9,10,11]. Gold deposits are generally related to tectonic, geological, and geochemical processes, in which the nature of the hydrothermal fluids is of fundamental importance [24,25,26]. Based upon ore geological characteristics and mineralization style, the Jiaodong gold mineralization has been treated as an “orogenic type” and it has been proposed that the ore-forming fluids were derived from metamorphic water [21]. The Xiejiagou deposit is a representative mediumsized Jiaojia-type gold deposit, which contains gold reserves of >35 t Given that this deposit is an important producer of gold, some geochemical studies have been undertaken with the aim of characterizing the nature of the Au mineralization (e.g., [29,30,31,32,33,34]).
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