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

对不列颠哥伦比亚省布鲁斯杰克浅成热液矿床金矿化成因的控制

• 批准号: 543413-2019
• 负责人: WilliamsJones, AnthonyAE
• 金额: $ 4.07万
• 依托单位: McGill University
• 依托单位国家: 加拿大
• 项目类别: Collaborative Research and Development Grants
• 财政年份: 2022
• 资助国家: 加拿大
• 起止时间: 2022-01-01 至 2023-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=751004
• 关键词: Controls; genesis; gold; mineralisation; Brucejack

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.

一些浅成热液矿床的特点是金和银的金属浓度极高，但尽管它们具有明显的吸引力，但由于超富集区（富矿区）通常与贫瘠区相邻，因此它们很难勘探和开发。 Pretium Resources Inc. 于 2017 年开始开采不列颠哥伦比亚省北部的 Brucejack 矿床，就是此类矿床的一个例子。在那里，含有公斤金/吨的矿脉与不含金（金金矿）的同一代矿脉相伴。该矿床和其他一些矿床含有这些局部超富集的金银矿脉的原因尚未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能够通过简单的沉淀将金填充几厘米宽的裂缝（布鲁斯杰克的情况），因为这些液体的浓度已显示为 10 ppb 左右。 Brucejack 样品中金银纳米颗粒（直径 3-7 nm）的初步高分辨率透射电子显微镜 (HRTEM) 图像表明，另一种假设是，金/银作为金金纳米颗粒过饱和。颗粒随后絮凝、积聚，然后被机械输送到选定的裂缝中，可能是主要流体管道的附属部分。我们将通过进一步的 HRTEM 成像、EDS 辅助 TEM 分析以及旨在产生胶体并确定其絮凝控制的实验来检验这一假设。 Brucejack 的富矿金矿化先于含金砷黄铁矿，该黄铁矿局部发育在 5 公里长的金矿蚀变走廊内，可能反映了深部的斑岩系统，对资源贡献很大，并与金金矿密切相关。拟议的研究将为 Brucejack 矿床的成因开发一个综合模型，该模型将解释页岩蚀变、砷黄铁矿和富矿型金金矿（以及它们之间的联系），考虑望远镜浅成热液-斑岩系统的可能性，并帮助指导正在进行的勘探和矿山开发。