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首页> 外文期刊>Earth and Planetary Science Letters: A Letter Journal Devoted to the Development in Time of the Earth and Planetary System >Modelling the role of graphite in development of a mineralised mid-crustal shear zone, Macraes mine, New Zealand
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Modelling the role of graphite in development of a mineralised mid-crustal shear zone, Macraes mine, New Zealand

机译：建模石墨在新西兰Macraes矿山矿化的中地壳剪切带中的作用

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The Hyde–Macraes Shear Zone (HMSZ) is a mineralised low-angle shear within the Otago Schist traceable for 30 km with a NW strike. It is being actively mined along 12 km of this strike, producing N6 Moz of gold. The shear zone formed under lower greenschist facies conditions as the ho st schist was uplifted through the brittle–ductile transition. Sheared rocks consist of greenschist facies schists with mineralogy only subtly different from that of the host schist. Pervasive fluid flow has occurred along grain boundaries and within microshears whose development has been enhanced by the deposition of hydrothermal graphite. We model the development of these microshears using a three-dimensional numerical code. For an inhomogeneous initial rock with lithostatic fluid pressures and a dynamic permeability deformed under dextral non-coaxial flow, deformation is distributed into weak shear bands. Graphite deposition and associated reaction-softening have a dramatic effect on the development of model shear zones. Graphite is deposited into a shear band, weakening it and further localising the deformation into that shear band, producing an anastomosing and interconnected shear zone structure such as observed in the HMSZ. The degrees of graphite precipitation and graphite-induced weakening are varied in the models. Graphite precipitation with a low degree of reaction-softening results in more diffuse shear bands. In contrast less graphite deposition but with a high degree of reaction-softening leads to the development of more focused shear bands. Graphite deposition has clearly controlled the formation of the HMSZ structure, and is an important indicator of potentially mineralised mid-crustal structures elsewhere.
机译：海德-麦克拉斯剪切带（HMSZ）是奥塔哥岩脉内的矿化低角度剪切带，西北偏走向可追踪30公里。在这次罢工的12公里处正在积极开采，生产出N6 Moz黄金。剪切带在脆性-延性转变的过程中被提升，在较低的格林斯相相条件下形成了剪切带。剪切岩由绿片岩相片岩组成，矿物学与宿主片岩的岩性略有不同。沿晶界和微切变内普遍发生了流体流动，水热石墨的沉积促进了微切变的发展。我们使用三维数字代码对这些微剪切的发展进行建模。对于具有岩石静力学压力和动态渗透率的非均质初始岩石，其在右旋非同轴流作用下变形，变形被分布到较弱的剪切带中。石墨沉积和相关的反应软化对模型剪切带的发展具有显着影响。石墨沉积在剪切带中，使其减弱并进一步将变形局部化到该剪切带中，从而产生一种吻合和相互连接的剪切区结构，例如在HMSZ中观察到的那样。在模型中，石墨沉淀的程度和石墨诱导的弱化程度是不同的。反应软化程度低的石墨沉淀导致更多的弥散剪切带。相反，较少的石墨沉积但具有高度的反应软化导致形成更集中的剪切带。石墨沉积清楚地控制了HMSZ结构的形成，并且是其他地方潜在矿化的中地壳结构的重要指示。

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