ABSTRACT Whole rock lithogeochemical data from the andesite rocks which host low-sulfidation epithermal gold veins in the Waihi district, New Zealand have been used to interpret hydrothermal alteration processes that variably altered the andesite rocks. The andesite host rocks are interpreted to have similar primary chemical compositions throughout the Waihi area, as reflected in similar ratios of immobile elements (eg Zr, Ti and other high field strength elements). The geochemical data reveal that elevated K/Al ratios occur in rocks proximal to low-Au–Ag deposits, reflecting adularia alteration in the host rocks associated with the upflowing hydrothermal fluids. Silicification of host rocks is achieved both by the addition of SiO2, as well as the destruction of plagioclase (reflected in the loss of CaO and Na2O). The rocks have been variably altered, with calcite and pyrite abundance reflecting the addition of carbon and sulphur. Pathfinder element (eg As, Sb) concentrations are variable across the district, with high pathfinder element concentrations interpreted to reflect proximity to hydrothermal fluid flow. Together, the results provide a district-scale overview of hydrothermal alteration at Waihi, and emphasise the utility of lithogeochemistry for classifying and quantifying hydrothermal alteration that can then be used to interpret hydrothermal processes and assist mineral exploration.

中文翻译：

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新西兰怀希低温热液区热液蚀变的岩石地球化学特征

摘要 来自新西兰怀希区低硫化超热液金矿脉的安山岩的全岩岩石地球化学数据已被用于解释不同程度改变安山岩的热液蚀变过程。安山岩主岩被解释为在整个 Waihi 地区具有相似的主要化学成分，这反映在不动元素（例如 Zr、Ti 和其他高场强元素）的相似比率上。地球化学数据显示，K/Al 比率升高发生在靠近低金银矿床的岩石中，这反映了与上流热液流体相关的主岩中的灰岩蚀变。通过添加 SiO2 以及斜长石的破坏（反映在 CaO 和 Na2O 的损失上），可以实现母岩的硅化。岩石发生了不同程度的改变，方解石和黄铁矿的丰度反映了碳和硫的添加。探路者元素（例如砷、锑）浓度在整个地区是可变的，探路者元素的高浓度被解释为反映了与热液流动的接近程度。总之，这些结果提供了 Waihi 热液蚀变的区域尺度概述，并强调了岩石地球化学在分类和量化热液蚀变方面的效用，然后可用于解释热液过程并协助矿产勘探。