1. Genesis of hydrous-oxidized parental magmas for porphyry Cu (Mo, Au) deposits in a postcollisional setting: examples from the Sanjiang region, SW China.
- Author
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Xu, Lei-Luo, Zhu, Jing-Jing, Huang, Ming-Liang, Pan, Li-Chuan, Hu, Ruizhong, and Bi, Xian-Wu
- Subjects
PORPHYRY ,MAGMAS ,GOLD ores ,AMPHIBOLES ,SUBDUCTION ,METALLOGENY ,ZIRCON ,PLATINUM group - Abstract
Magmatic sources of porphyry deposits in postcollisional settings remain controversial. We have used new and published petrological and geochemical data for the Eocene–Oligocene porphyry Cu ± Mo ± Au deposits in the Sanjiang region, SW China, to address this outstanding issue. New data for three deposits (Machangqing, Tongchang, and Beiya) in the Ailaoshan–Red River porphyry Au-Cu-Mo belt (southern part of the Sanjiang region) suggest that ore-forming porphyries were emplaced at ~ 35 Ma, have high (
87 Sr/86 Sr)i (0.7068–0.7071) and negative εNd (t) (− 6.9 to − 5.0), low zircon εHf (t) (− 5.3 to 4.5), and relatively high δ18 O (5.9–9.0‰). Magmatic amphibole phenocryst compositions indicate that the parental magmas are all relatively oxidized (ΔFMQ = 1.7 ± 0.6), and H2 O-rich (3.8 ± 0.3 wt% H2 O). These results are consistent with those estimated from zircon compositions (ΔFMQ = 1.8 ± 0.8) and high whole-rock Sr/Y ratios (75 ± 31), respectively. Based on the new and published data, we suggest that the parental magmas for the Ailaoshan–Red River porphyry Au-Cu-Mo belt were derived from a preserved juvenile arc lower-crust and the underlying metasomatized subcontinental lithospheric mantle (SCLM) attributed to a Neoproterozoic subduction event, whereas the parental magmas for the Yulong porphyry Cu-Mo belt (northern part of the Sanjiang region) originated from the Permian–Triassic juvenile arc lower-crust and metasomatized SCLM. Additionally, parental magmas for these porphyry deposits are all oxidized and H2 O-rich, and we attribute such characteristics to inheritance from mixed mantle-crust sources that were modified by previous oceanic slab subduction. [ABSTRACT FROM AUTHOR]- Published
- 2023
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