The Miocene low-sulfidation epithermal deposits of the Omu camp in northeastern Hokkaido, Japan, are small past-producers of precious metals and represent significant exploration targets for high-grade Au and Ag ores. The quartz textures of ore samples and the distribution of ore minerals within quartz veins were studied to identify the processes that resulted in the bonanza-grade precious metal enrichment in these deposits. In the high-grade vein samples, which are crustiform or brecciated in hand specimen, ore minerals exclusively occur within colloform quartz bands. High-magnification microscopy reveals that ore-bearing colloform bands consist of fine-grained quartz exhibiting relic microsphere textures and quartz having a mosaic texture that formed through recrystallization of the microspheres. The presence of relic microspheres is evidence that the microcrystalline quartz hosting the ore minerals formed through recrystallization of a noncrystalline silica precursor phase. The ore-hosting colloform bands composed of agglomerated microspheres alternate with barren colloform quartz bands that are composed of fibrous chalcedonic quartz and mosaic quartz formed through recrystallization of the chalcedony. The findings of this study are consistent with previous models linking bonanza-grade precious metal enrichment and the formation of bands of noncrystalline silica in low-sulfidation epithermal veins to episodic vigorous boiling or flashing of the hydrothermal system in the near-surface environment.

中文翻译：

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日本北海道Omu营地低硫化超热矿床中贫瘠和矿化的石英状石英带的结构特征：对富矿级富金属过程的影响

日本北海道东北部Omu营地的中新世低硫化超热矿床是贵金属的小规模过往生产者，代表了高品位金和银矿石的重要勘探目标。研究了矿石样品的石英质地和石英脉内矿石矿物的分布，以确定导致这些矿床中富矿级贵金属富集的过程。在手工样本中呈十字形或角砾状的高品位静脉样品中，矿石矿物仅存在于共形石英带内。高倍显微镜显示，含矿共形带由显示出微球遗迹结构的细粒石英和具有通过微球重结晶形成的镶嵌结构的石英组成。遗迹微球的存在证明了容纳矿石矿物的微晶石英是通过非晶硅石前体相的重结晶而形成的。由团聚的微球组成的主矿共晶带与贫瘠的共晶石英带交替，后者由纤维玉髓子石英和通过玉髓的重结晶形成的镶嵌石英组成。这项研究的发现与以前的模型相一致，该模型将富矿级富金属和低硫化超热矿脉中非晶硅带的形成与近地表环境中热液系统的剧烈沸腾或闪蒸联系起来。由团聚的微球组成的主矿共晶带与贫瘠的共晶石英带交替，后者由纤维玉髓子石英和通过玉髓的重结晶形成的镶嵌石英组成。这项研究的发现与以前的模型相一致，该模型将富矿级富金属和低硫化超热矿脉中非晶硅带的形成与近地表环境中热液系统的剧烈沸腾或闪蒸联系起来。由团聚的微球组成的主矿共晶带与贫瘠的共晶石英带交替，后者由纤维玉髓子石英和通过玉髓的重结晶形成的镶嵌石英组成。这项研究的发现与以前的模型相一致，该模型将富矿级富金属和低硫化超热矿脉中非晶硅带的形成与近地表环境中热液系统的剧烈沸腾或闪蒸联系起来。