Pyrite geochemistry has proven useful for tracking changes in the composition and physico-chemical conditions of hydrothermal fluids in ore-forming environments. Here, we investigated the microtextural features and chemical composition of pyrite, a main Au-bearing phase in the Akeshi and Kasuga deposits (Southern Kyushu, Japan), to better constrain the ore-forming processes in these high-sulfidation epithermal Au deposits. Despite the widespread distribution of Au-bearing pyrite in both deposits, no visible Au minerals coexist with pyrite. However, in situ laser ablation inductively coupled plasma mass spectrometry results show that Au concentrations in pyrite vary from below the detection limit to 41 ppm and are positively correlated with Cu (r = 0.4; up to 7400 ppm) and Bi concentrations (r = 0.44; up to 640 ppm). In both deposits, high Cu and Au concentrations occur in small (< 25 μm) anhedral grains of pyrite, which are interpreted to have rapidly crystallized from the ore-forming hydrothermal fluid. In addition, dissolution–reprecipitation textures and thin, concentric, Cu-rich overgrowths were identified in a number of larger (> 25 μm) pyrite grains and aggregates. These abrupt changes in the trace element compositions of pyrite grains likely record episodic metal-rich fluid inputs. We also propose that gold adsorption onto growing pyrite surfaces played a key role in the mineralization of these deposits.

硫铁矿地球化学已被证明可用于追踪成矿环境中热液的组成和理化条件的变化。在这里，我们研究了黄铁矿的微观结构特征和化学组成，黄铁矿是日本Akeshi和Kasuga矿床（南九州南部）的主要含金相，以更好地限制这些高硫化超热Au矿床的成矿过程。尽管在两个矿床中都广泛分布着含金的黄铁矿，但没有可见的金矿物与黄铁矿共存。然而，原位激光烧蚀电感耦合等离子体质谱分析结果表明，黄铁矿中的Au浓度从检测限以下变化到41 ppm，并与Cu（r = 0.4;最高7400 ppm）和Bi浓度（r= 0.44; 高达640 ppm）。在这两个矿床中，高浓度的铜和金都在小的（<25μm）黄铁矿晶粒中，这被解释为从成矿热液中迅速结晶出来。此外，在许多较大（> 25μm）的黄铁矿晶粒和聚集体中也发现了溶解-再沉淀的质地以及稀疏的，同心的，富含铜的过度生长。黄铁矿晶粒的微量元素组成的这些突然变化可能记录了富金属的间歇性流体输入。我们还提出，金在生长中的黄铁矿表面的吸附在这些矿床的矿化中起关键作用。