Seafloor hydrothermal chimneys from back-arc basins are important hosts for metals such as Cu, Zn, Pb, Ag, and Au. Although the general growth history of chimneys has been well documented, recent studies have revealed that the fine-scale mineralogy can be highly complex and reflects variable physicochemical conditions of formation. This study utilized a novel combination of scanning electron microscopy (SEM)-based electron backscattered diffraction (EBSD) and synchrotron X-ray fluorescence microscopy (SXFM) to uncover the detailed growth processes of multiple chalcopyrite-lined conduits within a modern chalcopyrite-sphalerite chimney from Manus Basin and to assess the controls on native gold precipitation. On the basis of previous studies, the chimney conduit was thought to develop from an initial sulfate-dominated wall, which was subsequently dissolved and replaced by sphalerite and chalcopyrite during gradual mixing of hydrothermal fluids and seawater. During this process, sphalerite was epitaxially overgrown by chalcopyrite. Accretionary growth of chalcopyrite onto this early formed substrate thickened the chimney walls by bi-directional growth inward and outward from the original tube wall, also enclosing the outgrown pyrite cluster. A group of similar conduits with slightly different mineral assemblages continued to form in the vicinity of the main conduit during the further fluid mixing process. Four types of distinct native gold-sulfide/sulfosalt associations were developed during the varying mixing of hydrothermal fluids and seawater. Previously unobserved chains of gold nanoparticles occur at the boundary of early sphalerite and chalcopyrite, distinct from gold observed in massive sphalerite as identified in other studies. These observations provide baseline data in a well-preserved modern system for studies of enrichment mechanisms of native gold in hydrothermal chimneys. Furthermore, native gold is relatively rarely observed in chalcopyrite-lined conduit walls. Our observations imply that: (1) native gold is closely associated with various sulfides/sulfosalts in chalcopyrite-lined conduit walls rather than limited to the association with tennantite, Bi-rich minerals, and bornite as reported previously; and (2) the broad spectrum of gold occurrence in chalcopyrite-line conduits is likely to be determined by the various mixing process between hot hydrothermal fluids with surrounding fluids or seawater. Quantitative modeling of fluid mixing processes is recommended in the future to probe the precise gold deposition stages to efficiently locate gold in modern hydrothermal chimneys.

中文翻译：

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现代热液烟囱（马努斯盆地，PNG）内黄铜矿衬里管道生长过程中的原生金富集过程

来自弧后盆地的海底热液烟囱是铜、锌、铅、银和金等金属的重要宿主。尽管烟囱的一般生长历史已被充分记录，但最近的研究表明，精细矿物学可能非常复杂，并反映了可变的物理化学形成条件。本研究利用基于扫描电子显微镜 (SEM) 的电子背散射衍射 (EBSD) 和同步辐射 X 射线荧光显微镜 (SXFM) 的新组合来揭示现代黄铜矿-闪锌矿烟囱内多个黄铜矿衬里管道的详细生长过程来自马努斯盆地并评估对原生金沉淀的控制。根据先前的研究，烟囱管道被认为是从最初的硫酸盐为主的墙壁发展而来的，随后在热液和海水的逐渐混合过程中溶解并被闪锌矿和黄铜矿取代。在此过程中，闪锌矿被黄铜矿外延生长。黄铜矿在这个早期形成的基底上的增生生长通过从原始管壁向内和向外双向生长使烟囱壁增厚，同时也包围了长大的黄铁矿簇。在进一步的流体混合过程中，在主管道附近继续形成一组具有略微不同矿物组合的类似管道。在热液流体和海水的不同混合过程中，形成了四种不同的天然金硫化物/硫盐组合。以前未观察到的金纳米粒子链出现在早期闪锌矿和黄铜矿的边界，不同于其他研究中发现的在块状闪锌矿中观察到的金。这些观察结果为保存完好的现代系统提供了基线数据，用于研究热液烟囱中天然金的富集机制。此外，在黄铜矿衬里的管道壁中相对很少观察到天然金。我们的观察表明：（1）天然金与黄铜矿衬里管道壁中的各种硫化物/硫盐密切相关，而不是如先前报道的那样仅限于与钙钛矿、富铋矿物和斑铜矿相关；(2) 黄铜矿线管道中金的广泛分布可能是由热液流体与周围流体或海水之间的各种混合过程决定的。