Intracontinental Eocene-Oligocene Porphyry Cu Mineral Systems of Yunnan, Western Yangtze Craton, China: Compositional Characteristics, Sources, and Implications for Continental Collision Metallogeny

Yongjun Lu, Robert Kerrich, Anthony Kemp, Campbell Mccuaig, Z.-Q. Hou, C.J.R. Hart, Z.-X. Li, Peter Cawood, Leon Bagas, Z.-M. Yang, John Cliff, E.A. Belousova, F. Jourdan, N.J. Evans

Research output: Contribution to journalArticlepeer-review

122 Citations (Scopus)

Abstract

The Yao'an porphyry Au system, Machangqing porphyry Cu-Mo system, and Beiya porphyry-skarn Au system, are spatially and temporally associated with potassic felsic intrusions emplaced during the Eocene to Oligocene epochs at 37 to 33 Ma in a postcollisional intracontinental setting in western Yunnan, western Yangtze craton, China. The Yao'an monzonite and quartz monzonite porphyry intrusions are alkaline and potassic with high K2O/ Na2O ratios (1.1-1.5). They have Sr-Nd-Pb isotopes similar to coeval lamprophyres and are characterized by uniform zircon εHf (-6.4 to -8.7) and δ18O values (6.6-7.0‰). They are interpreted as products of fractional crystallization of lamprophyre-like potassic mafic magma derived from ancient metasomatized lithospheric mantle, a scenario similar to the mid-Cretaceous postcollisonal Scheelite Dome gold system in Yukon, Canada. The Machangqing granitic intrusions are high K calc-alkaline and show high Sr, Sr/Y, and La/Yb, but low Y and Yb geochemical signatures. They have Sr-Nd-Pb isotope compositions similar to amphibolite xenoliths hosted by potassic felsic intrusions in western Yunnan. The zircon εHf values of the Machangqing granitic intrusions are positive (0.3-4.7), and the zircon-depleted Hf mantle model ages are 1.1 to 0.8 Ga. They also have mantle-like zircon δ18O values (5.5-6.4‰). The Machangqing granites were most likely derived from partial melting of Neoproterozoic lower crust. The Beiya granitic intrusions are alkaline, with high K2O/Na2O (1.9-2.7), Sr/Y and La/Yb ratios, high Sr contents, and low Y and Yb contents. They contain abundant zircon inheritance and have variable magmatic zircon εHf (-4 to +4) and the highest magmatic zircon δ18O values (6.6-7.8‰). The Beiya felsic intrusions are interpreted to be derived from partial melting of a K-rich mafic source mixed with a metasedimentary component. The Eocene-Oligocene intracontinental potassic intrusions and associated mineralization in western Yunnan are located proximal to the Mesozoic Jinsha suture, suggesting that this Mesozoic lithospheric boundary may have provided a first-order control on localization of Cenozoic mineral systems. These potassic felsic intrusions are coeval with regional potassic mafic magmatism in western Yunnan and were emplaced between 37 to 33 Ma, after the collision between India and Asia at ca. 60 to 55 Ma. It is therefore postulated that continental collision may have preferentially thickened the continental lithospheric mantle (CLM) adjacent to the Jinsha suture, in which overthickened lower continental lithospheric mantle was subsequently removed during 37 to 33 Ma, inducing melting of residual metasomatized lithospheric mantle as well as lower crust. The gold-rich Yao'an and Beiya intrusions are alkaline and potassic, characterized by high zircon δ18O values (>6.5‰), which is consistent with supracrustal contributions. In contrast, the Cu-Mo-rich Machangqing intrusions are high K calc-alkaline with mantle-like zircon δ18O values (
Original languageEnglish
Pages (from-to)1541-1576
JournalEconomic Geology
Volume108
Issue number7
DOIs
Publication statusPublished - 2013

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