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Minerals 2017, 7(12), 251; doi:10.3390/min7120251

LA-ICP-MS U-Th-Pb Dating and Trace Element Geochemistry of Allanite: Implications on the Different Skarn Metallogenesis between the Giant Beiya Au and Machangqing Cu-Mo-(Au) Deposits in Yunnan, SW China

1,2
,
1,2,3,* , 1,2
,
2,3
and
4,5
1
School of Marine Sciences, Sun Yat-sen University, Guangzhou 510006, China
2
Guangdong Provincial Key Laboratory of Marine Resources and Coastal Engineering, Guangzhou 510275, China
3
School of Earth Science and Engineering, Sun Yat-sen University, Guangzhou 510275, China
4
Faculty of Science, University of Brunei Darussalam, Gadong BE1410, Brunei Darussalam
5
ARC Centre for Excellence in Ore Deposits (CODES), University of Tasmania, Hobart 7001, Australia
*
Author to whom correspondence should be addressed.
Received: 30 October 2017 / Revised: 13 December 2017 / Accepted: 15 December 2017 / Published: 19 December 2017
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Abstract

The giant Beiya Au skarn deposit and Machangqing porphyry Cu-Mo-(Au) deposit are located in the middle part of the Jinshajiang–Ailaoshan alkaline porphyry metallogenic belt. The Beiya deposit is the largest Au skarn deposit in China, whilst the Machangqing deposit comprises a well-developed porphyry-skarn-epithermal Cu-Mo-(Au) mineral system. In this paper, we present new allanite U-Th-Pb ages and trace element geochemical data from the two deposits and discuss their respective skarn metallogenesis. Based on the mineral assemblage, texture and Th/U ratio, the allanite from the Beiya and Machangqing deposits are likely hydrothermal rather than magmatic. Laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) allanite U-Th-Pb dating has yielded Th-Pb isochron ages of 33.4 ± 4.6 Ma (MSWD = 0.22) (Beiya) and 35.4 ± 9.8 Ma (MSWD = 0.26) (Machangqing), representing the retrograde alteration and magnetite skarn mineralization age of the two deposits. The Beiya and Machangqing alkali porphyry-related mineralization are synchronous and genetically linked to the magmatic hydrothermal activities of the Himalayan orogenic event. Major and trace element compositions reveal that the Beiya allanite has higher Fe3+/(Fe3+ + Fe2+) ratios, U content and Th content than the Machangqing allanite, which indicate a higher oxygen fugacity and F content for the ore-forming fluids at Beiya. Such differences in the ore-forming fluids may have contributed to the different metallogenic scales and metal types in the Beiya and Machangqing deposit. View Full-Text
Keywords: allanite; U-Th-Pb dating; trace elements; giant Beiya Au skarn deposit; Machangqing porphyry Cu-Mo deposit; Sanjiang region (SW China) allanite; U-Th-Pb dating; trace elements; giant Beiya Au skarn deposit; Machangqing porphyry Cu-Mo deposit; Sanjiang region (SW China)
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Fu, Y.; Sun, X.; Li, D.; Lin, H.; Lai, C. LA-ICP-MS U-Th-Pb Dating and Trace Element Geochemistry of Allanite: Implications on the Different Skarn Metallogenesis between the Giant Beiya Au and Machangqing Cu-Mo-(Au) Deposits in Yunnan, SW China. Minerals 2017, 7, 251.

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