The Early Permian Lizzie Creek Volcanic Group of the northern Bowen Basin, NE Queensland, Australia, has compositions that range from basalt through andesite to rhyolite with geochemical signatures (e.g., enrichment in Cs, Rb, Ba, U, Th, and Pb, depletion in Nb and Ta) that are typical of arc lavas. In the Mount Carlton district the Lizzie Creek Volcanic Group is host to high-sulfidation epithermal Cu-Au-Ag mineralization, whereas farther to the south near Collinsville (~50 km from Mount Carlton) these volcanic sequences are barren of magmatic-related mineralization. Here, we assess whether geochemical indicators of magma fertility (e.g., Sr/Y, La/Yb, V/Sc) can be applied to volcanic rocks through study of coeval volcanic sequences from these two locations.The two volcanic suites share similar petrographic and major element geochemical characteristics, and both have undergone appreciable hydrothermal alteration during, or after, emplacement. Nevertheless, the two suites have distinct differences in alteration-immobile trace element (V, Sc, Zr, Ti, REE, Y) concentrations. The unmineralized suite has relatively low V/Sc and La/Yb, particularly in the high SiO₂ rocks, which is related to magma evolution dominated by fractionation of clinopyroxene, plagioclase, and magnetite. By contrast, the mineralized suite has relatively high V/Sc but includes high SiO₂ rocks with depleted HREE and Y contents, and hence high La/Yb. These trends are interpreted to reflect magma evolution under high magmatic H₂O conditions leading to enhanced amphibole crystallization and suppressed plagioclase and magnetite crystallization. These rocks have somewhat elevated Sr/Y compared to the unmineralized suite, but as Sr is likely affected by hydrothermal mobility, Sr/Y is not considered to be a reliable indicator of magmatic conditions.Our data show that geochemical proxies such as V/Sc and La/Yb that are used to assess Cu-Au fertility of porphyry intrusions can also be applied to cogenetic volcanic sequences, provided elemental trends with fractionation can be assessed for a volcanic suite. These geochemical tools may aid regional-scale exploration for Cu-Au mineralization in convergent margin terranes, especially in areas that have undergone limited exhumation or where epithermal and porphyry mineralization may be buried beneath cogenetic volcanic successions.

中文翻译：

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弧形火山岩的铜金肥力：来自澳大利亚昆士兰东北部的早二叠世 Lizzie Creek 火山群的案例研究

澳大利亚昆士兰东北部博文盆地北部的早二叠世 Lizzie Creek 火山群的成分范围从玄武岩到安山岩再到具有地球化学特征的流纹岩（例如，富集 Cs、Rb、Ba、U、Th 和 Pb，耗尽在Nb和Ta中），这是弧形熔岩的典型特征。在卡尔顿山地区，Lizzie Creek 火山群拥有高硫化度的低温热液 Cu-Au-Ag 矿化，而在南柯林斯维尔附近（距离卡尔顿山约 50 公里），这些火山序列缺乏与岩浆相关的矿化。在这里，我们通过研究这两个位置的同期火山序列来评估岩浆肥力的地球化学指标（例如 Sr/Y、La/Yb、V/Sc）是否可以应用于火山岩。这两个火山岩层具有相似的岩相学和主要元素地球化学特征，并且都在置入过程中或置入后经历了明显的热液蚀变。尽管如此，这两个套件在蚀变固定的微量元素（V、Sc、Zr、Ti、REE、Y）浓度方面存在明显差异。未矿化套件具有相对较低的 V/Sc 和 La/Yb，特别是在高 SiO₂岩石，与以单斜辉石、斜长石和磁铁矿分馏为主的岩浆演化有关。相比之下，矿化套件具有相对较高的 V/Sc，但包括具有耗尽 HREE 和 Y 含量的高 SiO ₂岩石，因此具有高 La/Yb。这些趋势被解释为反映了高岩浆 H ₂下的岩浆演化O 条件导致角闪石结晶增强并抑制斜长石和磁铁矿结晶。与未矿化的岩层相比，这些岩石的 Sr/Y 有所升高，但由于 Sr 可能受热液流动性的影响，因此 Sr/Y 不被认为是岩浆条件的可靠指标。我们的数据显示，V/Sc 等地球化学指标用于评估斑岩侵入体的 Cu-Au 富集性的 La/Yb 和 La/Yb 也可以应用于共生火山序列，前提是可以评估火山套件的分馏的元素趋势。这些地球化学工具可能有助于区域尺度勘探收敛边缘地体中的 Cu-Au 矿化，特别是在经历有限折返的地区，或者在这些地区，浅成热液和斑岩矿化可能被埋在共生火山序列之下。