Petrogenesis and oxidation state of granodiorite porphyry in the Jurassic Chuankeng skarn Cu deposit, South China: Implications for the Cu fertility and mineralization potential. (15th April 2020)

• Record Type: Journal Article
• Authors: Zhang, Xin; Ni, Pei; Wang, Guo-Guang; Jiang, Yao-Hui; Jiang, Ding-Sheng; Li, Su-Ning; Fan, Ming-Sen
• Is Part Of: Journal of Asian earth sciences. Volume 191(2020)
• Publication Date: 2020-04-15
• Subjects: Chuankeng copper deposit -- Neoproterozoic juvenile crust -- Adakitic rock -- Magma fertility -- South China; Earth sciences -- Asia -- Periodicals; Sciences de la terre -- Asie -- Périodiques; Earth sciences; Asia; Periodicals; 555.05
• DOI: 10.1016/j.jseaes.2019.104184
• Languages: English
• ISSNs: 1367-9120

Abstract

Graphical abstract: Highlights: The Jurassic porphyries at Chuankeng were formed at intra-plate extensional setting. Magma source are Neoproterozoic juvenile crust with minor Paleoproterozoic ancient crust. More contributions of ancient crust, lower oxygen fugacity and water contents reduce Cu fertility. Nd-Hf isotopes, zircon Ce 4+ /Ce 3+ and Tti-zr can be used together to assess the potential of Cu mineralization. Abstract: Large-scale Jurassic porphyry–skarn Cu mineralization in the Qin-Hang metallogenic belt of South China has attracted much attention, but comparative studies of porphyries in large- and small-scale deposits are lacking. In this paper, we present new zircon U–Pb ages, trace element composition and Hf isotopic composition as well as whole-rock geochemical and Sr–Nd isotopic compositions for the porphyries associated with mineralization in the small-scale Chuankeng Cu deposit. Drawing on our data for the Chuankeng deposit and existing data for the nearby giant Dexing Cu deposit, we aim to identify factors controlling the mineralization potential of both deposits. Granodiorite porphyries of Chuankeng deposit were emplaced at ca. 161–158 Ma. They have moderate SiO2 contents of 61.9–66.1 wt% and high Sr/Y (59–135) and (La/Yb)N (4–14) ratios. Their high MgO contents (0.2–2.9 wt%), lack of negative Eu anomaly, depletion in Y and Yb, relatively high initial 86 Sr/ 87 Sr ratios (0.7076–0.7078), and low εNd (t) values (−4.5 to −4.9), indicating that the Chuankeng porphyries were derived from partial melting of delaminated lower crust. The Middle–Late Jurassic Chuankeng porphyries are considered to have been formed in a localized intra-continental extension environment along the Jiangshao Fault in response to far-field stress from Paleo-Pacific Plate subduction. Although no Middle–Late Jurassic magmatic arc rocks have been found in the study area, the Chuankeng porphyries display similar characteristics to arc rocks. On the basis of their zircon εHf (t) values (−2.6 to +0.9), two-stage Hf model ages (1.4–1.1 Ga), and regional geological history, we infer that magma source of Chuankeng porphyries were mainly Neoproterozoic juvenile crust with the involvement of Paleoproterozoic ancient crust. Thus their arc-like features were inherited from the Neoproterozoic juvenile crust that formed by subduction of oceanic crust during the Jiangnan orogeny. Chuankeng porphyries have lower zircon Ce 4+ /Ce 3+ and higher Ti-in-zircon temperatures and lower whole rock εNd and zircon εHf values than the Dexing porphyries, indicating they are less oxidized and less hydrous and with more involvement of the ancient crustal material in the magma source, which could explain the relatively small-scale Cu mineralization in Chuankeng. This study highlights the values of integrated studies of whole rock Nd and zircon trace element and Hf isotopic compositions in assessing the potential for Cu mineralization.