黄山东铜镍矿的韧性变形特征和磁黄铁矿形成机制研究

发布时间：2018-04-01 22:30

本文选题：铜镍硫化物矿床　切入点：矿石结构　出处：《高校地质学报》2017年01期

【摘要】：黄山东铜镍硫化物矿床产于东天山地区的黄山—镜儿泉韧性剪切带中,大地构造上属中亚造山带东天山觉罗塔格岛弧带。该铜镍矿所在的黄山东镁铁—超镁铁岩体呈纺锤状侵位于晚石炭世火山岩中,其边部发生了与区域剪切带总体走向一致的强烈糜棱岩化作用。矿床中的部分矿体发生强烈韧性变形,其中17号矿体完全产于韧性变形带内,岩石和矿石都发生了强烈的破碎和蚀变而形成矿石糜棱岩。在上述韧性变形带内,还发育一定规模的网脉状和细脉状富铜碳酸盐—硫化物脉。论文在野外地质和构造形迹观察的基础上,对黄山东矿床不同类型的矿石开展了细致的显微岩相和矿相学观察,识别出三种类型矿石:原生矿石、强烈变形矿石和热液叠加矿石。海绵陨铁结构的原生矿石中,脉石矿物几乎不发生蚀变和变形,矿石矿物仅发生脆性破裂;强烈变形矿石中,脉石矿物和矿石矿物均发生强烈变形,主要以纤闪石的波状消光和膝折、金云母的书斜构造、磁黄铁矿的定向拉长为特征;热液叠加矿石中的磁黄铁矿普遍发育颗粒的扁平化、重结晶,局部可见磁黄铁矿的退火平衡结构。黄山东铜镍硫化物矿床的侵位与变形时间与区域黄山-镜儿泉剪切带的韧性剪切作用时间相一致。岩体冷却过程经历的强烈韧性剪切变形作用不但造成矿石矿物的强烈韧性变形而形成矿石糜棱岩,还使伴生脉石矿物发生细粒化和热液蚀变,释放出流体和成矿元素,并叠加于变形的矿石和岩石之上,从而形成了网脉状和细脉状矿体。黄山东铜镍矿的原生硫化物固熔体铁含量较高,因而在硫化物熔体结晶过程只形成六方磁黄铁矿而无伴生单斜磁黄铁矿和黄铁矿。在热液叠加过程中,流体沿边缘和裂隙面交代早期六方磁黄铁矿,形成单斜磁黄铁矿反应边。本次研究还发现六方磁黄铁矿形成的新机制:即在高硫逸度和高氧逸度的条件下,随着体系温度的降低,单斜磁黄铁矿可从热液六方磁黄铁矿中出溶形成呈叶片状单斜—六方磁黄铁矿交生体。
[Abstract]:The Cu-Ni sulfide deposit in Huangshan, Shandong Province, is located in the Huangshan-Jingerquan ductile shear zone in the East Tianshan area. It belongs to the eastern Tianshan Jurothagg island arc belt of Central Asia orogenic belt. The Huangshan magnesium-ultramafic intrusive body is located in the late Carboniferous volcanic rock, which is located in Huangshan, Shandong Province, and is located in the late Carboniferous volcanic rocks. There is a strong mylonitization in the edge of the deposit consistent with the overall strike of the regional shear zone. Some of the ore bodies in the deposit have strong ductile deformation, of which orebody 17 is completely located in the ductile deformation zone. Ore mylonite is formed by strong breakage and alteration of rock and ore. In the ductile deformation zone mentioned above, On the basis of field geological and structural observation, detailed microlithofacies and mineralogical observation of different types of ore in Huang-Shandong deposit have been carried out. Three types of ores were identified: primary ores, strongly deformed ores and hydrothermal superimposed ores. In primary ores with spongy meteorite structure, almost no alteration and deformation occurred in gangue minerals, only brittle rupture occurred in ore minerals; in strongly deformed ores, Both gangue minerals and ore minerals are strongly deformed, characterized mainly by the wavy extinction and knee fold of amphibole, the diagonal structure of phlogopite, the directional elongation of pyrrhotite, and the flattening of pyrrhotite grains in hydrothermal superimposed ores. Recrystallization, The annealing equilibrium structure of locally visible pyrrhotite. The emplacement and deformation time of Cu-Ni sulfide deposit in Huangshan is consistent with the ductile shear time of the Huangshan-Jingerquan shear zone. Ductile shear deformation not only resulted in strong ductile deformation of ore minerals, but also formed ore mylonite. The associated gangue minerals are also fine-grained and hydrothermal altered, resulting in the release of fluids and ore-forming elements, which are superimposed on deformed ores and rocks. Therefore, the net vein and vein-like orebodies were formed. The primary sulfide solid melt iron content was higher in the Cu-Ni deposit in Shandong Province, and the iron content of the primary sulphide solid melt was relatively high. Therefore, only hexagonal pyrrhotite and pyrite are formed in the crystallization process of sulfide melts without associated monoclinic pyrrhotite and pyrite. In the process of hydrothermal superposition, the fluid metamorphoses early hexagonal pyrrhotite along the edges and fissures. A new mechanism for the formation of hexagonal pyrrhotite was also found: under the conditions of high sulfur fugacity and high oxygen fugacity, with the decrease of system temperature, Monoclinic pyrrhotite can be dissolved from hydrothermal hexagonal pyrrhotite to form a blade like monocline-hexagonal pyrrhotite.
【作者单位】：南京大学地球科学与工程学院内生金属矿床成矿机制研究国家重点实验室;长安大学地球科学与资源学院西部矿产资源与地质工程教育部重点实验室;
【基金】：国家自然科学基金(41272098;40872050) 南京大学内生金属矿床成矿机制研究国家重点实验室(ZZKT-201111)联合资助
【分类号】：P618.41;P618.63

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