Lithium Isotope Distribution in Hydrothermal Alteration from the Cochenour Extension of the Red Lake Gold Mine, Ontario

Goldcorp是世界上最大的黄金生产商之一，实际上正在开发其Cochenour矿，该矿位于安大略省红湖区的Cochenour-Willans老矿场，通过地下5公里的运输巷道与Red Lake矿相连。在Cochenour，发现了两种不同类型的矿化：(1)含/不含毒砂的交替型矿化；(2)具有可见金的石英-阳起石脉型矿化。公司特有的问题是，尽管砷的浓度可以在有毒砂存在的情况下作为金的代用品，但尚未确定有无毒砂的交代矿化或脉状矿化的地球化学代用品。这项研究的目的是验证金矿化周围热液蚀变岩石的锂同位素比值(D7Li)是否可以作为这两种矿化类型的替代。先前在柯克兰湖金矿公司的S马卡萨金矿(纳多，2017年)证明了热液蚀变岩石的d7Li与金相关，这种相关性很可能也存在于Cochenour矿床中。使用锂同位素的基本原理是，像钠和钾一样，锂是一种可移动的碱性元素，因此与热液蚀变有关。然而，由于锂以微量浓度存在于岩石/流体中，它遵循非理想的亨利安行为，因此受矿物和流体之间的分配控制。此外，Li有两个稳定的同位素，很容易通过水-岩相互作用分馏，因此热液蚀变岩石的Li浓度和7Li/6Li比值应该可以追踪热液蚀变环境中热液的来源和途径。柯克兰湖金矿公司S马卡萨金矿发现d7Li和Au的部分相关性的原因尚不清楚，本研究旨在研究单一岩性类型中较简单的系统，以揭示金矿化与锂同位素比值之间的关系。

Goldcorp is one of the largest gold producers in the world and is actually developing its Cochenour mine, located on the old Cochenour-Willans mine site within the Red Lake district, Ontario, and connected to the Red Lake mine through an underground 5 km haulage drift. At Cochenour, two different types of mineralizations are identified: (1) replacement-style mineralization with/without arsenopyrite; and (2) quartz-actinolite vein-style mineralization with visible gold. The company-specific problem is that although the concentration of arsenic can act as a proxy for gold when arsenopyrite is present, no geochemical proxy has yet been identified for replacement-style mineralization without arsenopyrite or for vein-style mineralization. The objective of this research is to verify if the lithium isotope ratio (d7Li) of hydrothermally-altered rock surrounding the gold mineralization could act as a proxy for both styles of mineralization. It was previously demonstrated that the d7Li of hydrothermally altered rocks could correlate with gold at Kirkland Lake Gold Inc.'s Macassa Gold Mine (Nadeau, 2017) and it is likely that this correlation may also be present at the Cochenour deposit. The rationale behind the use of Li isotopes is that like Na and K, Li is a mobile alkaline element and is thus involved in hydrothermal alterations. However, because Li is present in rocks/fluids in trace concentrations, it follows a non-ideal Henrian behaviour and is thus controlled by partitioning between minerals and fluids. Furthermore, Li has 2 stable isotopes which fractionate readily via water-rock interactions so the Li concentration and the 7Li/6Li ratio of hydrothermally altered rocks should allow tracing the sources and pathways of hydrothermal fluids within hydrothermally-altered environments. The reason why partial correlation of d7Li and Au was identified at Kirkland Lake Gold Inc.'s Macassa mine has remained unclear and the present research aims to study a simpler system in a single type of lithology in order to shed light on the relations that exist between gold mineralization and lithium isotopic ratios.