A Nanoscale Investigation of Carlin-Type Gold Deposits: An Atom-Scale Elemental and Isotopic Perspective
A Nanoscale Investigation of Carlin-Type Gold Deposits: An Atom-Scale Elemental and Isotopic Perspective
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DOI：
10.5382/econgeo.4676
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发表时间：
2019-09-01
期刊：
影响因子：
5.8
通讯作者：
Moody, Michael P.
中科院分区：
文献类型：
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作者：
Gopon, Phillip;Douglas, James O.;Moody, Michael P.
卡林型金矿是世界上最重要的金矿化类型之一。尽管它们在经济上的重要性和大量的工作已经出版，仍然有关于它们的成矿作用的关键问题。这种不确定性很大程度上是由于金矿床的神秘性质，金作为分散的纳米级夹杂物存在于早期形成的贫瘠黄铁矿核心上形成的宿主黄铁矿边缘内。小尺寸的金包裹体确定其性质内的主机硫化物和机制，他们沉淀的矿石fluids.This研究结合高分辨率电子探针显微分析（EPMA）与原子探针层析成像（APT），以限制金是否发生纳米球或分散在卡林黄铁矿。APT提供了以近原子空间分辨率获得主要、次要、痕量和同位素化学信息的独特能力。我们利用这种能力来调查的微量元素的原子尺度分布在卡林型黄铁矿轮辋，以及硫同位素的相对差异的边缘和核心的金托管septyre.We表明，金内的样品从绿松石岭存款（内华达州）发生在砷黄铁矿过度生长（轮辋），形成的黄铁矿核心。此外，该富As边缘不包含金的纳米块，而是在黄铁矿晶体结构内包含分散的晶格结合的Au。我们的样品中金和砷的空间相关性与局部砷浓度的增加一致，局部砷浓度的增加增强了含砷黄铁矿容纳分散金的能力（Kusebauch等人，2019年）。我们推测，在晶格中的点缺陷诱导砷的黄铁矿结构促进金的传播。在我们的研究中缺乏金纳米球与以前的工作是一致的，表明分散在砷黄铁矿中的金可以以高达1：200（金/砷）的浓度出现。我们还报告了一种方法来确定硫同位素比值的黄铁矿（+/- As），说明了黄铁矿核心和它的Au和砷黄铁矿边缘之间的相对变化的原子探针数据集。这种空间变化证实，所观察到的黄铁矿核-环结构是由于两个阶段的增长，涉及沉积或岩浆热液核和热液环，而不是从不断变化的热液流体沉淀。
Carlin-type gold deposits are one of the most important gold mineralization styles in the world. Despite their economic importance and the large volume of work that has been published, there remain crucial questions regarding their metallogenesis. Much of this uncertainty is due to the cryptic nature of the gold occurrence, with gold occurring as dispersed nanoscale inclusions within host pyrite rims that formed on earlier formed barren pyrite cores. The small size of the gold inclusions has made determining their nature within the host sulfides and the mechanisms by which they precipitated from the ore fluids particularly problematic.This study combines high-resolution electron probe microanalysis (EPMA) with atom probe tomography (APT) to constrain whether the gold occurs as nanospheres or is dispersed within the Carlin pyrites. APT offers the unique capability of obtaining major, minor, trace, and isotopic chemical information at near-atomic spatial resolution. We use this capability to investigate the atomic-scale distribution of trace elements within Carlin-type pyrite rims, as well as the relative differences of sulfur isotopes within the rim and core of gold-hosting pyrite.We show that gold within a sample from the Turquoise Ridge deposit (Nevada) occurs within arsenian pyrite overgrowth (rims) that formed on a pyrite core. Furthermore, this As-rich rim does not contain nanonuggets of gold and instead contains dispersed lattice-bound Au within the pyrite crystal structure. The spatial correlation of gold and arsenic within our samples is consistent with increased local arsenic concentrations that enhanced the ability of arsenian pyrite to host dispersed gold (Kusebauch et al., 2019). We hypothesize that point defects in the lattice induced by the addition of arsenic to the pyrite structure facilitate the dissemination of gold. The lack of gold nanospheres in our study is consistent with previous work showing that dispersed gold in arsenian pyrite can occur in concentrations up to similar to 1:200 (gold/arsenic). We also report a method for determining the sulfur isotope ratios from atom probe data sets of pyrite (+/- As) that illustrates a relative change between the pyrite core and its Au and arsenian pyrite rim. This spatial variation confirms that the observed pyrite core-rim structure is due to two-stage growth involving a sedimentary or magmatic-hydrothermal core and hydrothermal rim, as opposed to precipitation from an evolving hydrothermal fluid.