Abstract

Nb-rich trachytes from Virginia, shoshonite from Colorado and high-K dacite from the Bolivian Andes contain diverse suites of native metals and alloys. Virginia trachytes are differentiates of mafic within-plate magmas derived from oceanic island basalt (OIB)-type mantle sources in the post-orogenic extensional regime of the Appalachian mobile belt. Colorado shoshonite and Bolivian dacite were produced via crystal fractionation of Fe–Mg silicates from trachybasalt and basalt magma, respectively, derived from subduction-related mantle modified by either crustal contamination (both regions are underlain by thick, mature continental-type crust) or recycling of marine sediment. Metal assemblages include refractory metals (Pt with minor Fe and Cr, native W, Co–W and Fe–W alloys), Cu–Ag–Au alloys, chalcophile metals (Cu–Sn alloy, native Cu and Zn) and associated sulfides (galena). Textural evidence (metals occur as inclusions in phenocrysts, high temperatures of their formation, etc.) and compositional features of metallic phases suggest their magmatic origin. Metal-rich magmas (both mafic and differentiated) transport metals in convergent and within-plate tectonic settings and deliver ore metals to the oxidized porphyry and epithermal environments in the upper crust.

中文翻译：

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美国大陆的粗面岩和肖松岩以及玻利维亚安第斯山脉的高钾英安岩中的原生金属和合金：会聚和板内构造环境中矿石金属的岩浆成因

摘要

来自弗吉尼亚的富含 Nb 的粗面岩、来自科罗拉多的钙磷灰石和来自玻利维亚安第斯山脉的高 K 英安岩含有多种原生金属和合金。弗吉尼亚粗面岩是在阿巴拉契亚移动带的造山后伸展体系中源自大洋岛玄武岩（OIB）型地幔源的镁铁质板内岩浆的区别。科罗拉多玄武岩和玻利维亚英安岩分别是通过从粗面玄武岩和玄武岩岩浆中的 Fe-Mg 硅酸盐的晶体分馏产生的，这些硅酸盐来自与俯冲相关的地幔，受到地壳污染（两个区域都位于厚厚的成熟大陆型地壳之下）或再循环的影响海洋沉积物。金属组合包括难熔金属（含少量 Fe 和 Cr、天然 W、Co-W 和 Fe-W 合金）、Cu-Ag-Au 合金、嗜热金属（Cu-Sn 合金、天然铜和锌）和相关的硫化物（方铅矿）。纹理证据（金属作为斑晶中的夹杂物出现，它们形成的高温等）和金属相的组成特征表明它们的岩浆起源。富含金属的岩浆（镁铁质和分化的）在会聚和板块内构造环境中输送金属，并将矿石金属输送到上地壳的氧化斑岩和超热液环境中。