Meng Xuyang, Kleinsasser Jackie M, Richards Jeremy P, Tapster Simon R, Jugo Pedro J, Simon Adam C, Kontak Daniel J, Robb Laurence, Bybee Grant M, Marsh Jeffrey H, Stern Richard A
Mineral Exploration Research Centre, Harquail School of Earth Sciences, Laurentian University, Sudbury, ON, Canada.
Department of Earth and Environmental Sciences, University of Michigan, Ann Arbor, MI, USA.
Nat Commun. 2021 Apr 13;12(1):2189. doi: 10.1038/s41467-021-22349-z.
Most known porphyry Cu deposits formed in the Phanerozoic and are exclusively associated with moderately oxidized, sulfur-rich, hydrous arc-related magmas derived from partial melting of the asthenospheric mantle metasomatized by slab-derived fluids. Yet, whether similar metallogenic processes also operated in the Precambrian remains obscure. Here we address the issue by investigating the origin, fO, and S contents of calc-alkaline plutonic rocks associated with the Haib porphyry Cu deposit in the Paleoproterozoic Richtersveld Magmatic Arc (southern Namibia), an interpreted mature island-arc setting. We show that the ca. 1886-1881 Ma ore-forming magmas, originated from a mantle-dominated source with minor crustal contributions, were relatively oxidized (1‒2 log units above the fayalite-magnetite-quartz redox buffer) and sulfur-rich. These results indicate that moderately oxidized, sulfur-rich arc magma associated with porphyry Cu mineralization already existed in the late Paleoproterozoic, probably as a result of recycling of sulfate-rich seawater or sediments from the subducted oceanic lithosphere at that time.
大多数已知的斑岩型铜矿床形成于显生宙，并且仅与由板块衍生流体交代的软流圈地幔部分熔融产生的中等氧化、富硫、含水的弧相关岩浆有关。然而，类似的成矿过程在前寒武纪是否也存在仍不清楚。在这里，我们通过研究与古元古代里希特斯韦尔德岩浆弧（纳米比亚南部）中与海布斑岩型铜矿床相关的钙碱性深成岩的成因、fO和硫含量来解决这个问题，该岩浆弧被解释为一个成熟的岛弧环境。我们表明，约18.86 - 18.81亿年前的成矿岩浆起源于以地幔为主的源区，有少量地壳物质贡献，相对氧化（比铁橄榄石 - 磁铁矿 - 石英氧化还原缓冲高出1 - 2个对数单位）且富硫。这些结果表明，与斑岩型铜矿化相关的中等氧化、富硫的弧岩浆在古元古代晚期就已存在，可能是当时俯冲海洋岩石圈中富含硫酸盐的海水或沉积物循环的结果。
