Deformation, metamorphism, and mobilization of Ni–Cu–PGE sulfide ores at Garson Mine, Sudbury
Deformation, metamorphism, and mobilization of Ni–Cu–PGE sulfide ores at Garson Mine, Sudbury
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DOI：
10.1007/s00126-013-0479-y
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发表时间：
2014-02
影响因子：
4.8
通讯作者：
J. Mukwakwami;B. Lafrance;C. Lesher;D. Tinkham;N. Rayner;D. Ames
中科院分区：
文献类型：
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作者：
J. Mukwakwami;B. Lafrance;C. Lesher;D. Tinkham;N. Rayner;D. Ames
Garson镍-铜-铂族元素矿床是一个变形、翻转、低镍品位接触型矿床，位于萨德伯里火成岩杂岩体（SIC）与1.85-Ga萨德伯里构造南部休伦超群的地层下伏岩石之间的接触处。矿体与陡峭的南倾、南北向 D1 剪切带重合，该剪切带在中角闪岩相变质作用期间叠瓦状覆盖了 SIC、其矿带和下伏的休伦期岩石。在D2at中绿片岩相变质作用期间，剪切带重新激活为南向北的反向剪切带。 Syn-D2 变质钛矿的年龄为 1,849±±6 Ma，表明 D1 和 D2 是在 Penokean 造山运动期间 SIC 结晶后立即发生的。矿体向南陡倾，与共线的L1和L2矿线平行，表明矿体的几何形状受D1和D2强烈控制。硫化物矿化由角砾岩矿石组成，少量浸染状硫化物存在于苏长岩中，以及 syn-D2 石英-方解石-硫化物矿脉中。延性塑性流动的流动是 D1 和 D2 期间硫化物/金属流动的主要机制，D2 期间热液还对 Cu、Fe 和 Ni 进行了少量的热液流动。在 D1 变形矿带中，变质镍黄铁矿过度生长 S1 铁辉石叶理。 D1 停止后，镍黄铁矿从再结晶的多边形磁黄铁矿晶粒中溶出，导致角砾岩矿石内沿多边形磁黄铁矿晶界随机分布的大镍黄铁矿晶粒和随机取向的镍黄铁矿环。它还在 D2 剪切区域过度生长 S2 绿泥石叶状结构。角砾岩矿石沿着狭窄的剪切带发生 D2 变形时，磁黄铁矿发生再结晶并被压扁。镍黄铁矿环沿这些扁平颗粒的晶界溶出，产生了磁黄铁矿-镍黄铁矿层状结构，这在 D1 变形矿带中未观察到。镍黄铁矿对两种叶理的叠印以及镍黄铁矿沿扁平磁黄铁矿晶粒晶界的溶出表明，Garson 矿石在 D1 期间在 550 至 600 °C 的温度范围内恢复为变质单硫化物固溶体，并在 D2 期间继续变形为单硫化物固溶体。
The Garson Ni–Cu–platinum group element deposit is a deformed, overturned, low Ni tenor contact-type deposit along the contact between the Sudbury Igneous Complex (SIC) and stratigraphically underlying rocks of the Huronian Supergroup in the South Range of the 1.85-Ga Sudbury structure. The ore bodies are coincident with steeply south-dipping, north-over-south D1shear zones, which imbricated the SIC, its ore zones, and underlying Huronian rocks during mid-amphibolite facies metamorphism. The shear zones were reactivated as south-over-north, reverse shear zones during D2at mid-greenschist facies metamorphism. Syn-D2metamorphic titanite yields an age of 1,849 ± 6 Ma, suggesting that D1and D2occurred immediately after crystallization of the SIC during the Penokean Orogeny. The ore bodies plunge steeply to the south parallel to colinear L1and L2mineral lineations, indicating that the geometry of the ore bodies are strongly controlled by D1and D2. Sulfide mineralization consists of breccia ores, with minor disseminated sulfides hosted in norite, and syn-D2quartz–calcite–sulfide veins. Mobilization by ductile plastic flow was the dominant mechanism of sulfide/metal mobilization during D1and D2, with additional minor hydrothermal mobilization of Cu, Fe, and Ni by hydrothermal fluids during D2. Metamorphic pentlandite overgrows a S1ferrotschermakite foliation in D1deformed ore zones. Pentlandite was exsolved from recrystallized polygonal pyrrhotite grains after cessation of D1, which resulted in randomly distributed large pentlandite grains and randomly oriented pentlandite loops along the grain boundaries of polygonal pyrrhotite within the breccia ore. It also overgrows a S2chlorite foliation in D2shear zones. Pyrrhotite recrystallized and was flattened during D2deformation of breccia ore along narrow shear zones. Exsolution of pentlandite loops along the grain boundaries of these flattened grains produced a pyrrhotite–pentlandite layering that is not observed in D1deformed ore zones. The overprinting of the two foliations by pentlandite and exsolution of pentlandite along the grain boundaries of flattened pyrrhotite grains suggest that the Garson ores reverted to a metamorphic monosulfide solid solution at temperatures ranging between 550 and 600 °C during D1and continued to deform as a monosulfide solid solution during D2.