The lithocap at Mankayan is a contiguous zone of alunite + quartz + pyrite that occur as pervasive alteration of the metavolcanic basement and dacitic pyroclastic rocks. Alunite + quartz + pyrite assemblage also occurs within hydrothermal gold-bearing veins and breccias. Several high-sulfidation epithermal gold orebodies have been previously delineated in the Lepanto Main Enargite orebody, and in the Northwest, Carmen, Florence West and Florence East quartz-pyrite-gold (QPG) veins. This study presents new data of mineral composition and sulfur isotopic ratios of alunites from different zones of the lithocap at Mankayan. Elemental composition maps and point analysis of alunites indicate compositional heterogeneity within a single alunite crystal. Common substituents to the K⁺ site are Na⁺ and H₃O⁺, with few Ca²⁺ substitution in some sites. Limited occurrences of PO₄^3- substitution to SO₄^2- were also documented. Sulfur isotopic ratios (δ³⁴S_CDT) of alunite range from + 13 ‰ to + 24 ‰, which are typical of hypogene alunite. Sulfur isotopic ratios of coexisting pyrite are mostly negative, ranging from −5.4 to −1.0 ‰. Few samples of alunite from the Northwest and Florence West quartz-pyrite-gold veins have sulfur isotopic ratios similar to the values of its coexisting pyrite. The estimated temperature of formation using sulfur isotope geothermometry of alunite-pyrite pairs ranges from 197 °C to 364 °C, with most of the samples varying within 220 to 270 °C. The calculated bulk δ³⁴S of the hydrothermal fluid was found to be + 5 to + 6 ‰ for the different mineralization events in Mankayan.

The alunite crystals are heterogeneous even in the microscopic scale. Compositional maps show that K and Na concentration vary within single crystals, as well as among different crystals of a sample. The variations of K and Na content mostly follow the crystal growth structure, however, some alunite crystals with irregular variations are also present. Some samples contain aluminum-phosphate-sulfate (APS) minerals intergrown with alunite. Electron probe microanalysis of the alunite crystals showed a generally wide range of composition between the alunite – natroalunite solid solution.

Using thermodynamic functions, a relationship between temperature and K⁺/Na⁺ of the hydrothermal fluids was determined across the range of alunite-natroalunite solid solution system. The model curves suggest that at temperatures less than ∼ 250 °C a slight change in fluid composition and/or temperature can vary the number of Na atoms per formula unit by 0.3 units. At higher temperatures, a more significant change in the physicochemical conditions is required for a substitution to occur. This explains the wide range of Na content in the alunites from the different parts of the lithocap.

The characteristics compiled in this study reflect the fluctuations in temperature and fluid compositions that occurred during the multiple hydrothermal events in the Mankayan District.

Mankayan 的岩石盖层是一个由明矾石 + 石英 + 黄铁矿组成的连续带，作为变质火山基底和英安岩火山碎屑岩的普遍蚀变而出现。明矾石 + 石英 + 黄铁矿组合也出现在热液含金矿脉和角砾岩中。先前已在 Lepanto Main Enargite 矿体以及西北的 Carmen、Florence West 和 Florence East 石英-黄铁矿-金 (QPG) 矿脉中圈定了几个高硫化超热液金矿体。本研究提供了来自 Mankayan 岩石盖层不同区域的明矾石矿物成分和硫同位素比的新数据。明矾石的元素组成图和点分析表明单个明矾石晶体内的成分异质性。^{K +}位点的常见取代基是 Na ⁺和H ₃ O ⁺，在某些位点几乎没有Ca ²⁺取代。还记录了有限发生的 PO ₄ ^3-替代 SO ₄ ^2-。硫同位素比（δ ³⁴ S _CDT) 的明矾石的范围从 + 13 ‰ 到 + 24 ‰ ，这是典型的低质明矾石。共存黄铁矿的硫同位素比值多为负值，范围为-5.4～-1.0‰。来自西北和佛罗伦萨西石英-黄铁矿-金矿脉的明矾石样品很少有硫同位素比率与其共存的黄铁矿的值相似。使用硫同位素地热法对明矾石-黄铁矿对的估计形成温度范围为 197 °C 至 364 °C，大多数样品在 220 至 270 °C 之间变化。对于 Mankayan 的不同矿化事件，计算出的热液流体体积 δ ³⁴ S 为 + 5 至 + 6 ‰。

即使在微观尺度上，明矾石晶体也是异质的。成分图显示 K 和 Na 浓度在单晶内以及样品的不同晶体之间变化。K和Na含量的变化大多遵循晶体生长结构，但也存在一些不规则变化的明矾石晶体。一些样品含有与明矾石共生的磷酸铝硫酸盐 (APS) 矿物质。明矾石晶体的电子探针显微分析显示明矾石 - 钠矾固溶体之间的成分范围广泛。

利用热力学函数，在明矾石-钠矾石固溶体系范围内确定了温度与热液K ⁺ /Na ^{+的关系。}模型曲线表明，在低于~ 250 °C 的温度下，流体成分和/或温度的轻微变化可以使每个分子式单元的钠原子数改变 0.3 个单元。在更高的温度下，发生取代需要物理化学条件发生更显着的变化。这解释了来自岩石盖层不同部分的明矾石中钠含量范围广泛的原因。

本研究中汇编的特征反映了曼卡延地区多次热液事件期间发生的温度和流体成分的波动。