Paleozoic porphyry-style hydrothermal alteration and mineralization has previously been recognized within the Delamerian orogen, South Australia, where porphyry prospects include Anabama Hill, Netley Hill, and Bendigo. However, limited exploration due in part to thick postmineralization cover hinders the understanding of the temporal context, metallogenic setting, and mineral potential of the porphyry systems along the Proterozoic continental margin of Australia. In this study, we have characterized the hydrothermal alteration and mineralization of these porphyry occurrences. Zircon U-Pb, molybdenite Re-Os, and white mica Rb-Sr ages have been determined to constrain the timing for emplacement of magmatic intrusions, precipitation of metal-bearing sulfides, and duration of hydrothermal alteration in the Delamerian orogenic belt. Zircon U-Pb laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) analyses of nine granitoids reveal that the intrusive rocks were emplaced mostly between 485 and 465 Ma, whereas three intrusions at Bendigo have zircon U-Pb ages of 490 to 480 Ma. Molybdenite isotope dilution-negative thermal ion mass spectrometry (ID-NTIMS) Re-Os dating of the four prospects identifies two porphyry Cu-Mo mineralization events at 480 and 470 to 460 Ma, respectively. Nineteen white mica Rb-Sr LA-ICP-MS/MS (tandem mass spectrometers) analyses return an age range between 455 and 435 Ma for phyllic alteration at the Anabama Hill and Netley Hill prospects, whereas intense white mica-quartz-pyrite alteration at Bendigo prospect appears to have developed between 470 and 460 Ma. These geochronologic results indicate that the Delamerian porphyry systems postdated subduction-related magmatism in the region (514–490 Ma) but instead formed within an inverted back-arc regime, where mineralized magmas and fluids ascended along favorable lithospheric-scale structures, probably due to asthenospheric upwelling triggered by mafic delamination. Porphyritic stocks, dikes, and aplites with ages of 470 to 460 Ma are the most likely hosts to porphyry-style mineralization in the Delamerian orogen that appears to have formed simultaneously with the oldest known porphyry systems in the intraoceanic Macquarie arc (e.g., Marsden, E43, and Milly Milly; 467–455 Ma). These results emphasize the significance and potential of Early-Middle Ordovician intrusive systems to host such a type of magmatic-hydrothermal mineralization in the Delamerian orogen.

中文翻译：

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南澳大利亚德拉莫里亚造山带斑岩铜钼矿化和蚀变的成矿环境和时间演化：来自锆石 U-Pb、辉钼矿 Re-Os 和原位白云母 Rb-Sr 地质年代学的见解

古生代斑岩式热液蚀变和矿化此前已在南澳大利亚德拉梅里亚造山带内得到确认，该地区的斑岩前景包括阿纳巴马山、内特利山和本迪戈。然而，部分由于厚厚的矿化后覆盖层导致的勘探有限，阻碍了对澳大利亚元古代大陆边缘斑岩系统的时间背景、成矿背景和矿产潜力的了解。在这项研究中，我们描述了这些斑岩矿点的热液蚀变和矿化作用。锆石 U-Pb、辉钼矿 Re-Os 和白云母 Rb-Sr 年龄已被确定，以限制德拉默里亚造山带岩浆侵入的侵位时间、含金属硫化物的沉淀以及热液蚀变的持续时间。对 9 块花岗岩的锆石 U-Pb 激光烧蚀-电感耦合等离子体质谱 (LA-ICP-MS) 分析表明，侵入岩大多在 485 至 465 Ma 之间就位，而本迪戈的 3 块侵入岩的锆石 U-Pb 年龄为490 至 480 Ma。辉钼矿同位素稀释-负热离子质谱 (ID-NTIMS) 对四个远景的 Re-Os 测年确定了两个斑岩铜钼矿化事件，分别发生在 480 和 470 至 460 Ma。对 19 个白云母 Rb-Sr LA-ICP-MS/MS（串联质谱仪）进行分析，得出 Anabama Hill 和 Netley Hill 矿区的页岩蚀变年龄范围为 455 至 435 Ma，而在本迪戈矿区似乎是在 470 至 460 Ma 之间开发的。这些地质年代学结果表明，德拉莫里亚斑岩系统晚于该地区与俯冲有关的岩浆作用（514-490 Ma），而是在倒弧后区域内形成，其中矿化岩浆和流体沿着有利的岩石圈尺度结构上升，可能是由于由镁铁质分层引发的软流圈上升流。年龄为 470 至 460 Ma 的斑岩岩群、岩脉和细岩最有可能是德拉莫里亚造山带斑岩型矿化的宿主，该矿化似乎与洋内麦格理岛弧中已知最古老的斑岩系统同时形成（例如，马斯登， E43，和米莉·米莉；467-455 Ma）。这些结果强调了早中奥陶世侵入系统在德拉莫造山带中形成这种类型的岩浆热液矿化的重要性和潜力。