Anatomy of a world-class epizonal orogenic-gold system: A holistic thermochronological analysis of the Xincheng gold deposit,Jiaodong Peninsula,eastern China |
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| Institution: | 1. State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Beijing 100083, China;2. School of Earth, Atmosphere and Environment, Monash University, Vic 3800, Australia;3. Key Laboratory of Gold Mineralization Processes and Resource Utilization Subordinated to the Ministry of Natural Resources, Shandong Institute of Geological Sciences, Jinan 250013, China;4. Orebusters Pty Ltd, Gwelup 6018, Western Australia, Australia;5. School of Earth Sciences, University of Melbourne, Vic 3010, Australia;6. Shandong Gold Mining Stock Co., Ltd., Laizhou 261400, China;1. Orsu Metals Corporation, London, United Kingdom;2. AIRIE, Dept. of Geosciences, Colorado State University, Fort Collins, USA;3. Paladin Energy, Hay Street, Subiaco, Perth, Western Australia, Australia;1. Center for Mineral Resources Science, Department of Geology and Geological Engineering, Colorado School of Mines, 1516 Illinois Street, Golden, CO 80401, USA;2. State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Beijing 100083, China;3. Department of Geology, The University of Kansas, 1475 Jayhawk Boulevard, Lawrence, KS 66045, USA |
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| Abstract: | Xincheng is a world-class orogenic-gold deposit hosted by the Early Cretaceous Guojialing granitoid in the Jiaodong Peninsula, eastern China. A zircon U–Pb age of 126 ± 1.4 Ma, together with previous data, constrain the emplacement of the Guojialing intrusion to 132–123 Ma. The granitoid underwent subsolidus ductile deformation at >500 °C following its intrusion. The small difference in age between the youngest zircon U–Pb age of unaltered granitoid (~123 Ma) and the ca. 120 Ma 40Ar/39Ar ages of sericite, associated with breccias and gold mineralization within it indicate initial rapid cooling from magmatic temperatures to those prevalent during brittle deformation and associated gold mineralization at ~220–300 °C. Evidence of a direct association between granitic magmatism and gold mineralization, such as at least localized near-magmatic depositional temperatures and metal zoning evident in undoubted intrusion-related gold deposits, is absent. The 40Ar/39Ar age of ~120 Ma coincides with the mineralization age of many other orogenic-gold deposits along the Jiaojia Fault. Sixteen zircon fission-track (ZFT) ages across the ore and alteration zones range from 112.9 ± 3.4 to 99.1 ± 2.7 Ma. The long period of cooling to the ~100 Ma ZFT closure temperatures recorded here suggests that ambient temperatures for hydrothermal alteration systems lasted to ~100 Ma, possibly because of their focus at Xincheng within the young Guojialing granitoid as it cooled more slowly below approximately 300 °C to 220 °C. However, the restricted number of auriferous ore stages, combined with the presence of cross-cutting gold-free quartz-carbonate veins, indicate that gold itself was only deposited over a restricted time interval at ~120 Ma, consistent with studies of orogenic gold deposits elsewhere. This highlights the complex interplay between magmatism, deformation and the longevity of hydrothermal systems that cause genetic controversies. Based on apatite fission-track (AFT) ages, the Xincheng gold deposit was then uplifted and exhumed to near the surface of the crust at 15 Ma, probably due to movement on the crustal-scale Tan-Lu Fault. Recognition of such exhumation histories along gold belts has conceptual exploration significance in terms of the probability of discovery of additional exposed or sub-surface gold ore bodies as discovery is as much a function of preservation as formation of the deposits. |
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