In the central Taupo Volcanic Zone, extensive zeolite (mordenite ± clinoptilolite) alteration occurs in late Quaternary rhyolitic vitric tuffs that were deposited in a lake formed by caldera collapse following the ~290 Ka Ohakuri ignimbrite eruptions. Glass shards in lacustrine vitric tuffs of the Ngakuru Formation and in the underlying Ohakuri Formation ignimbrite are replaced by mordenite ± clinoptilolite, along with hydrothermal adularia, opal-A, opal-CT, and cristobalite. This mineral assemblage is also found in the outer alteration zones of the nearby Ohakuri and Tahunaatara epithermal gold prospects. Evaluation of whole-rock chemical analyses indicates that the zeolitized vitric tuffs show a slight gain in K, and Na, Ca loss relative to unaltered Ohakuri Formation pumice, which is reflected in the presence of hydrothermal adularia in the alteration assemblage. The mordenite ± clinoptilolite alteration is associated with siliceous sinters and hydrothermal eruption breccias that were formed in recently active (39–1.5 Ka) geothermal systems. By analogy with geothermal systems elsewhere in the Taupo Volcanic Zone at Wairakei and Ohaaki, the mordenite ± clinoptilolite alteration was formed from dilute alkali-chloride aqueous liquid at 60° to 150°C. Based on the close association of the mordenite ± clinoptilolite alteration with siliceous sinters and hydrothermal eruption breccias in the central Taupo Volcanic Zone, it is classified as shallow, low-temperature, epithermal alteration. Mordenite ± clinoptilolite alteration has also been identified in Quaternary rhyolitic caldera settings in Japan and the United States, where it is termed “caldera-type zeolitization.” In exploration for epithermal Au-Ag deposits in rifted arc settings, such alteration may be overlooked, given its subtle appearance and distal location relative to veins that mark upflow areas.

中文翻译：

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与硅质烧结矿、热液喷发角砾岩和金银矿化相关的低温沸石蚀变，新西兰陶波中部火山区

在中部陶波火山带，广泛的沸石（丝光沸石 ± 斜发沸石）蚀变发生在晚第四纪流纹质玻璃凝灰岩中，这些凝灰岩沉积在约 290 Ka Ohakuri 火山灰火山喷发后由火山口坍塌形成的湖泊中。Ngakuru 组湖相玻璃凝灰岩和下伏 Ohakuri 组凝灰岩中的玻璃碎片被丝光沸石 ± 斜发沸石以及热液 adularia、蛋白石-A、蛋白石-CT 和方石英取代。在附近的Ohakuri和Tahunaatara超热金矿床的外部蚀变带中也发现了这种矿物组合。对全岩化学分析的评估表明，与未改变的Ohakuri浮石相比，沸石化的玻璃凝灰岩显示出K，Na，Ca损失略有增加，这反映在蚀变组合中热液的存在。丝光沸石±斜发沸石蚀变与近期活跃的（39-1.5 Ka）地热系统中形成的硅质烧结矿和水热喷发角砾岩有关。与怀拉基和奥哈基陶波火山区其他地方的地热系统类似，丝光沸石±斜发沸石蚀变是由稀释的碱金属氯化物水溶液在 60°C 至 150°C 下形成的。根据陶波火山带中部的丝光沸石±斜发沸石蚀变与硅质烧结矿和热液喷发角砾岩的密切关联，将其归类为浅层低温超热蚀变。在日本和美国的第四纪流纹岩火山口环境中也发现了丝光沸石±斜发沸石蚀变，它被称为“火山口型沸石化”。在裂谷弧环境中对超热液 Au-Ag 矿床进行勘探时，鉴于其微妙的外观和相对于标记上流区域的静脉的远端位置，可能会忽略这种改变。