Abstract
The Jinchang gold deposit has been extensively studied, but precise dates for its formation are debated. Native gold mainly occurs as inclusions within pyrite and quartz. In this study, we analysed quartz crystals coeval with gold precipitation from two different types of mineralization using the ArgusVI multi-collector noble gas mass spectrometer by the stepwise crushing technique to resolve the timing and genesis of gold mineralization. 40Ar/39Ar dating of quartz samples (J12Q) from breccia ore yields a plateau age of 109.87 ± 0.86 Ma, and an inverse isochron age of 109.87 ± 0.88 Ma. Quartz samples (J18Q) from vein ore yields a slightly younger plateau age of 107.76 ± 0.85 Ma, with an inverse isochron age of 107.76 ± 0.92 Ma. These dates place the ore-forming age of the Jinchang gold deposit at 107~110 Ma, much younger than previously published radiometric ages, suggesting the gold mineralization is spatio-temporally associated with the granite porphyry. The formation of the Jinchang gold deposit is consistent with the regional late Mesozoic porphyry-epithermal gold mineralization event in the Yanbian-Dongning area. Finally, our study shows that 40Ar/39Ar of quartz can be used as a powerful tool to date the formation ages of hydrothermal ore deposits.
Highlights
The Jinchang gold deposit has been extensively studied, but precise dates for its formation are debated
Quartz was chosen for determining the metallogenic age in the Jinchang deposit by 40Ar/39Ar stepwise crushing technique because of the following reasons: (1) previous studies indicated that native gold mainly occurs as inclusions within quartz and pyrite[21], and the presence of sulfide daughter minerals-bearing FIs in the quartz further suggests the mineralization and quartz are contemporaneous (Fig. 3a); (2) quartz itself has low radioactivity after irradiation[29]; (3) it has an abundance of K-rich minerals-bearing FIs (Fig. 3a,b) and has high chemical purity in its lattice[30], neutron induced noble gas isotopes released during analysis are predominantly from the fluid inclusions and not the lattice
Quartz crystals, and gold grains are syngenetic, the Ar-Ar dates reported in this study can be taken as the age of ore formation in the Jinchang gold deposit
Summary
The Jinchang gold deposit has been extensively studied, but precise dates for its formation are debated. With the development of analytical techniques and a new generation of mass spectrometers, more attention has been focused on the 40Ar/39Ar stepwise crushing technique, which has been applied to successfully date the time of ore formation of lead-zinc and tungsten deposits recently[3,4,5] These cases show the potential of this method for determining the ore-forming time of hydrothermal mineral deposits. The Jinchang gold deposit, located in the northeastern part of the Yanbian-Dongning area (Fig. 1b), differs from other gold deposits in this region by its distinctive types of mineralization, which include cryptoexplosive breccia pipe type, veinlet disseminated type, and fault-controlled veins from early to late estimated by the occurrences of ore bodies as well as decreasing compositional complexity and homogenization temperature of fluid inclusions[16].
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