Gold mineralization without quartz veins in a ductile-brittle shear zone, Macraes Mine, Otago Schist, New Zealand
Gold mineralization without quartz veins in a ductile-brittle shear zone, Macraes Mine, Otago Schist, New Zealand
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DOI：
10.1007/s001260050211
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发表时间：
1999-05
影响因子：
4.8
通讯作者：
D. Craw;S. Windle;P. Angus
中科院分区：
文献类型：
--
作者：
D. Craw;S. Windle;P. Angus
新西兰东奥塔哥Macraes矿的绿片岩相片岩已被垂直于片理的120米厚的后变质（下绿片岩相）流体普遍蚀变。变质钛矿被金红石代替，绿帘石被菱铁矿、绿泥石、白云母、方解石等多种变质矿物代替。这种蚀变的早期阶段发生在与千米规模的平卧褶皱相关的延性解理发育过程中。解理被一组近平行的间隔（毫米尺度）微剪广泛覆盖，这些微剪局部富含金红石和热液石墨。然后，应变集中在狭窄的（m尺度）区域，在该区域中，岩石的更强烈变形部分被紧密间隔的（100 μm尺度）微剪交叉并高度破坏。高应变岩石表现出糜棱岩和碎裂岩相结合的微观结构，包括晶塑性晶粒缩小和云母再结晶形成新的片理。在糜棱质碎裂岩中，白云母以钠长石为代价生长。热液蚀变伴生有黄铁矿、毒砂和金，未见石英脉发育。在水热石墨还原流体过程中，金与硫化物一起沉淀。整个蚀变岩层序后来被含金、白钨矿、金红石、黄铁矿和毒砂的中温石英脉零星切割。该矿床在片岩带隆升过程中表现出连续的后变质作用和热液流动。
Greenschist facies schist which hosts the Macraes Mine in East Otago, New Zealand has been pervasively altered by post-metamorphic (lower greenschist facies) fluids over a 120 m thick section perpendicular to foliation. Metamorphic titanite has been replaced by rutile, and epidote has been replaced by a variety of metamorphic minerals including siderite, chlorite, muscovite and calcite. The early stages of this alteration occurred during development of a ductile cleavage associated with kilometre scale recumbent folding. The cleavage was widely overprinted by a subparallel set of spaced (mm scale) microshears which are locally enriched in rutile and hydrothermal graphite. Strain was then concentrated into narrow (m scale) zones where more intensely deformed portions of the rock are crossed and highly disrupted by closely spaced (100 μm scale) microshears. The highly strained rocks show a combination of mylonitic and cataclastic microstructures, including crystal-plastic grain size reduction and recrystallization of micas to form a new foliation. Muscovite has grown at the expense of albite in the mylonitic cataclasites. Hydrothermal alteration was accompanied by addition of pyrite, arsenopyrite and gold without development of quartz veins. Gold precipitated with sulphides during reduction of the fluid by hydrothermal graphite. The whole altered rock sequence was later cut sporadically by mesothermal quartz veins which contain gold, scheelite, rutile, pyrite and arsenopyrite. This deposit displays a continuum of post-metamorphic processes and hydrothermal fluid flow which occurred during uplift of the schist belt.