Textural Characteristics of Barren and Mineralized Colloform Quartz Bands at the Low-Sulfidation Epithermal Deposits of the Omu Camp in Hokkaido, Japan: Implications for Processes Resulting in Bonanza-Grade Precious Metal Enrichment
Textural Characteristics of Barren and Mineralized Colloform Quartz Bands at the Low-Sulfidation Epithermal Deposits of the Omu Camp in Hokkaido, Japan: Implications for Processes Resulting in Bonanza-Grade Precious Metal Enrichment
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日本北海道 Omu 营地低硫化浅成热液矿床中贫瘠和矿化胶体石英带的结构特征：对富矿级贵金属富集过程的影响
DOI：
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发表时间：
2021
期刊：
影响因子：
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通讯作者：
Q. Hennigh
中科院分区：
文献类型：
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作者：
Lauren R. Zeeck;T. Monecke;T. J. Reynolds;E. Tharalson;K. Pfaff;N. Kelly;Q. Hennigh
日本北海道东北部大木营中新世低硫化浅成热液矿床是贵金属的小型生产者，是高品位Au和Ag矿石的重要勘探目标。研究了矿石样品的石英结构和矿石矿物在石英脉中的分布，以确定导致富矿级贵金属在这些矿床中富集的过程。在高品位的石英脉样品中，矿石矿物仅产于胶体状石英带中，这些样品在手标本中呈十字状或角砾状。高倍率显微镜显示，含矿胶体带由细粒石英表现出遗迹微球纹理和石英具有马赛克纹理，通过微球的重结晶形成。残余微球的存在证明，微晶石英托管的矿石矿物形成通过重结晶的非结晶二氧化硅前体相。含矿胶体带由团聚微球组成，与无矿胶体石英带交替出现，无矿胶体石英带由玉髓重结晶形成的纤维状玉髓石英和镶嵌石英组成。这项研究的结果是一致的，与以前的模型链接富矿级贵金属富集和形成带的非晶二氧化硅在低硫化浅成热液脉的热液系统在近地表环境中的间歇性剧烈沸腾或闪光。
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.