Abstract The overprinting episodes of porphyry-type and epithermal-type mineralization in the Mankayan District, northern Luzon, Philippines allow an investigation on variation of geochemical signatures with different alteration assemblages. Due to the multiple hydrothermal activities in Mankayan, some older porphyry-type deposits have been overprinted by acid-sulfate alteration that is commonly associated with high-sulfidation epithermal mineralization. In this study, we analyzed metavolcanic basement rocks and dioritic rocks that host porphyry-type mineralization in the Far Southeast deposit, Honeycomb prospect and Christine prospect, which all have near-neutral pH alteration assemblage of illite/muscovite + chlorite ± quartz. We compared their geochemical data with those of the Fatima porphyry deposit, which was overprinted by quartz + alunite ± kaolinite/dickite alteration. Furthermore, we also compared the geochemical data of the metavolcanic and dioritic rocks in the Carmen and Florence prospects hosting quartz-pyrite-gold and enargite veins which overprinted earlier porphyry-type mineralization. N-MORB-normalized multi-element diagrams show that the host rocks preserve negative anomalies of high field strength elements (HFSEs) that are typical of magmas generated in a supra-subduction zone setting. The non-mineralized metavolcanic and dioritic rocks show variable signature of the large ion lithophiles (LILEs), while the altered metavolcanic and dioritic rocks show a more consistent signature. Negative anomaly of Rb is associated with acid-sulfate alteration, while positive anomaly of Rb was observed in the dioritic rocks that have been altered by near-neutral pH fluids. Furthermore, acid-sulfate alteration significantly added LREEs and depleted HREEs compared to the near-neutral pH alteration. Mass changes in altered rocks were determined using the isocon technique. Mass changes are generally more pronounced in the acid-sulfate altered rocks compared to the near-neutral pH altered rocks. The metavolcanic rocks altered to quartz + alunite in Carmen and Florence significantly gained SiO2, Al2O3 and S, and lost Na2O, CaO, MgO and Fe2O3. The dioritic and metavolcanic rocks altered to chlorite + illite in the Far Southeast, Honeycomb, Christine and Fatima porphyry deposits lost SiO2 and Al2O3, while the concentrations of other elements remain relatively unchanged. The pH-dependence of the geochemical behavior of Rb in hydrothermal conditions was utilized to construct new molar element ratios that could differentiate the rocks that underwent K-metasomatism either under near-neutral pH or acidic conditions. The recognition of this behavior could be useful in a routine lithogeochemical analysis that is being used in exploration.

中文翻译：

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菲律宾曼卡延矿区多次成矿作用的热液蚀变主岩的岩石地球化学

摘要 菲律宾吕宋岛北部曼卡延区斑岩型和超热液型矿化的叠印事件可以研究具有不同蚀变组合的地球化学特征的变化。由于 Mankayan 的多次热液活动，一些较老的斑岩型矿床被酸硫酸盐蚀变覆盖，通常与高硫化超热成矿有关。在本研究中，我们分析了远东南矿床、Honeycomb 勘探区和 Christine 勘探区中具有斑岩型矿化作用的变火山基岩和闪长岩，它们都具有接近中性的伊利石/白云母 + 绿泥石±石英的 pH 蚀变组合。我们将他们的地球化学数据与法蒂玛斑岩矿床的地球化学数据进行了比较，由石英 + 明矾石 ± 高岭石/地开石蚀变叠印而成。此外，我们还比较了 Carmen 和 Florence 勘探区中变质火山岩和闪长岩的地球化学数据，这些岩层包含石英-黄铁矿-金和磷灰岩脉，这些脉覆盖了早期的斑岩型矿化。N-MORB 归一化多元素图显示，主岩保留了高场强元素 (HFSE) 的负异常，这是超俯冲带环境中产生的岩浆的典型特征。非矿化变质火山和闪长岩显示出大离子亲石体 (LILEs) 的可变特征，而蚀变变质火山和闪长岩显示出更一致的特征。Rb 的负异常与酸-硫酸盐改变有关，而在近中性 pH 值流体改变的闪长岩中观察到 Rb 的正异常。此外，与近中性 pH 值变化相比，酸性硫酸盐变化显着增加了 LREE 和耗尽的 HREE。使用 isocon 技术确定蚀变岩石的质量变化。与近中性 pH 值蚀变岩相比，酸性硫酸盐蚀变岩中的质量变化通常更为明显。Carmen 和Florence 变质火山岩蚀变为石英+明矾石，SiO2、Al2O3 和S 显着增加，Na2O、CaO、MgO 和Fe2O3 丢失。远东南闪长岩和变质火山岩转变为绿泥石+伊利石，蜂巢、克里斯廷和法蒂玛斑岩矿床失去了SiO2和Al2O3，而其他元素的浓度保持相对不变。Rb 在热液条件下的地球化学行为的 pH 依赖性被用来构建新的摩尔元素比率，该比率可以区分在近中性 pH 或酸性条件下经历 K 交代的岩石。这种行为的识别可能有助于勘探中使用的常规岩石地球化学分析。