N2-Ar-He systematics and source of ore-forming fluid in Changkeng Au-Ag deposit, central Guangdong, China* |
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Authors: | Xiaoming Sun David I Norman Kai Sun Binghui Chen Jingde Chen |
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Institution: | (1) Department of Earth Sciences, Zhongshan University, 510275 Guangzhou, China;(2) State Key Laboratory of Metallogenesis, Nanjing University, 210093 Nanjing, China;(3) Department of Earth & Environmental Sciences, New Mexico Institute of Mining and Technology (NMT), NM87801 Socorro, USA |
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Abstract: | Changkeng Au-Ag deposit is a newly-discovered new type precious metal deposit. N2-Ar-He systematics studies and3He/4He and δD- δ18O composition analyses show that the ore-forming fluid of the deposit is composed mainly of formation water (sedimentary brine)
but not of meteoric water, which was thought to be source of the ore-forming fluid by most previous researchers. The content
of mantle-derived magmatic water in the ore-forming fluid is quite low, usually lower than 10%. According to the source of
the ore-forming fluid, the Changkeng Au-Ag deposit should belong to sedimentary brine transformed deposits. From the Late
Jurassic to the Early Cretaceous Period, with deposition and accumulation of thick sediments in Sanzhou Basin, the formation
water in the sedimentary layers was expelled from the basin because of overburden pressure and increasing temperature. The
expelled fluid moved laterally along sedimentary layers to the margin of the basin, and finally moved upward along a gently-dipping
interlayer fault. Because of a decline in pressure and temperature, ore minerals were deposited in the fault.
Project supported by the National Natural Science Foundation of China (Grant No. 495020291, the Natural Science Foundation
of Zhongshan University, the Research Foundation of National Key Laboratory of Metallogenesis in Nanjing University (Grant
No. 039704) and the Lingnan Foundation. |
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Keywords: | oreforming fluid N2-Ar-He systematics 3He/4He and δ D-δ 18O composition formation water (sedimentary brine) Changkeng Au-Ag deposit |
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