Controls on the genesis of gold mineralisation in the Brucejack epithermal deposit, British Columbia

一些浅成热液矿床的特点是金银的金属浓度极高，但尽管它们具有明显的吸引力，但它们很难勘探和开发，因为超级富集区(富集区)通常毗邻贫瘠的地带。不列颠哥伦比亚省北部的Brucejack矿藏就是这样一个矿藏。Pretium Resources Inc.于2017年在那里开始开采。在那里，含有千克Au/吨的矿脉与不含金(银)的同代矿脉伴生。这个矿床和其他一些矿床为什么含有这些局部超富集金-银脉的原因还没有得到令人满意的解释。事实上，很难理解被认为是形成浅成热液矿床的流体如何通过简单的沉淀(Brucejack)用金填充几米远的厘米宽的裂隙(Brucejack的情况)，因为这些流体的含金量已被证明约为10‘S ppb。Brucejack样品中的金银纳米颗粒(直径3-7 nm)的初步高分辨率透射电子显微镜(HRTEM)图像提出了另一种假说，即金银以银纳米颗粒的形式过饱和，这些纳米颗粒随后凝聚、聚集，然后被机械输送到选定的裂缝中，可能是主要流体管道的辅助。我们将通过进一步的HRTEM成像、EDS辅助的透射电子显微镜分析和旨在产生胶体并确定对其絮凝的控制的实验来验证这一假设。Brucejack金矿成矿先于含金砷黄铁矿，该黄铁矿在五公里长的叶状蚀变走廊内局部发育，可能反映了深部的斑岩系统，对资源有重大贡献，并与银矿密切相关。拟议的研究将为Brucejack矿床的成因开发一个全面的模型，该模型将解释叶状蚀变、砷黄铁矿和富矿型银矿(以及它们之间的联系)，考虑到伸展的浅成热液-斑岩系统的可能性，并有助于指导正在进行的勘探和矿产开发。

Some epithermal deposits are characterised by extraordinarily high metal concentrations of gold and silver, but despite their obvious attraction, they are difficult to explore and develop because zones of hyper-enrichment (bonanza zones) are commonly adjacent to barren zones. The Brucejack deposit in northern British Columbia, where Pretium Resources Inc. initiated mining in 2017, is an example of such a deposit. There, veins containing kilograms of Au/ton are accompanied by veins of the same generation that are devoid of gold (electrum). The reason why this and some other deposits contain these locally hyper-enriched gold-silver veins has not been satisfactorily explained. Indeed, it is difficult to understand how the fluids considered to be responsible for the formation of epithermal ore deposits could fill cm-wide fractures with gold for distances of several metres (the case at Brucejack) by simple precipitation, given that the gold content of these fluids has been shown to be on the order of 10's of ppb. An alternative hypothesis, which is suggested by preliminary high resolution transmitted electron microscope (HRTEM) images of gold-silver nano-particles (3-7 nm diameter) in samples from Brucejack, is that the gold/silver super-saturates as electrum nano-particles which subsequently flocculate, accumulate and then are mechanically transported into selected fractures, perhaps subsidiary to the major fluid conduits. We will test this hypothesis with further HRTEM imaging, EDS-assisted TEM analyses, and experiments designed to produce colloids and determine the controls on their flocculation. The bonanza gold mineralisation at Brucejack was preceded by auriferous arsenian pyrite that is developed locally within a five km-long corridor of phyllic alteration, possibly reflecting a porphyry system at depth, and contributes significantly to the resource and is closely associated with the electrum. The proposed research will develop a comprehensive model for the genesis of the Brucejack deposit that will explain the phyllic alteration, arsenian pyrite and bonanza-type electrum (and the links between them), consider the possibility of a telescoped epithermal-porphyry system, and help guide the ongoing exploration and mine development.