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黑尖山铁矿床是新疆东天山阿齐山—雅满苏成矿带中典型的海相火山岩型铁矿床。黑尖山矿床围岩安山质熔岩中发育大量不规则的富铁团块,可分为钠长石磁铁矿型、钠长石钾长石磁铁矿型、钾长石磁铁矿型、绿帘石磁铁矿型和石英磁铁矿型5种类型,可能代表了在岩浆-热液成矿过程中不同演化阶段的产物,对黑尖山铁矿床成矿过程及形成环境有指示意义。本文对上述5类富铁团块中的磁铁矿进行了主量元素分析,为了精确地测出磁铁矿中铁的总量,采用差分法加入不确定的O含量,并加以ZAF矩阵校正。对比5类富铁团块中磁铁矿Ti含量,钠长石磁铁矿型最高、钠长石钾长石磁铁矿型和钾长石磁铁矿型较高、绿帘石磁铁矿型和石英磁铁矿型最低,且Ti含量与Fe含量为正相关关系;绿帘石磁铁矿型和石英磁铁矿型富铁团块Fe含量特征与矿石中磁铁矿Fe含量相近。上述特征表明钠长石磁铁矿类型是残余富铁熔体中最早的结晶产物,钠长石钾长石磁铁矿和钾长石磁铁矿类型具有岩浆热液转变的特征,而绿帘石磁铁矿和石英-磁铁矿类型则是受热液完全交代的产物,说明矿床形成于岩浆-热液成矿作用。各类富铁团块内磁铁矿的Fe含量均大于相对应蚀变环边磁铁矿的Fe含量,表明富铁岩浆结晶与热液活动分异同期发生。 相似文献
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Long-standing controversy persists over the presence and role of iron–rich melts in the formation of volcanic rock-hosted iron deposits. Conjugate iron–rich and silica–rich melt inclusions observed in thin-sections are considered as direct evidence for the presence of iron-rich melt, yet unequivocal outcrop-scale evidence of iron-rich melts are still lacking in volcanic rock-hosted iron deposits. Submarine volcanic rock-hosted iron deposits, which are mainly distributed in the western and eastern Tianshan Mountains in Xinjiang, are important resources of iron ores in China, but it remains unclear whether iron-rich melts have played a role in the mineralization of such iron ores. In this study, we observed abundant iron-rich agglomerates in the brecciated andesite lava of the Heijianshan submarine volcanic rock–hosted iron deposit, Eastern Tianshan, China. The iron-rich agglomerates occur as irregular and angular masses filling fractures of the host brecciated andesite lava. They show concentric potassic alteration with silicification or epidotization rims, indicative of their formation after the wall rocks. The iron-rich agglomerates have porphyritic and hyalopilitic textures, and locally display chilled margins in the contact zone with the host rocks. These features cannot be explained by hydrothermal replacement of wall rocks(brecciated andesite lava) which is free of vesicle and amygdale, rather they indicate direct crystallization of the iron-rich agglomerates from iron-rich melts. We propose that the iron-rich agglomerates were formed by open-space filling of volatile-rich iron-rich melt in fractures of the brecciated andesite lava. The iron-rich agglomerates are compositionally similar to the wall-rock brecciated andesite lava, but have much larger variation. Based on mineral assemblages, the iron-rich agglomerates are subdivided into five types, i.e., albite-magnetite type, albite-K-feldsparmagnetite type, K-feldspar–magnetite type, epidote-magnetite type and quartz-magnetite type, representing that products formed at different stages during the evolution of a magmatic-hydrothermal system. The albite-magnetite type represents the earliest crystallization product from a residual ironrich melt; the albite-K-feldspar-magnetite and K-feldspar-magnetite types show features of magmatichydrothermal transition, whereas the epidote-magnetite and quartz-magnetite types represent products of hydrothermal alteration. The occurrence of iron-rich agglomerates provides macroscopic evidence for the presence of iron-rich melts in the mineralization of the Heijianshan iron deposit. It also indicates that iron mineralization of submarine volcanic rock-hosted iron deposits is genetically related to hydrothermal fluids derived from iron-rich melts. 相似文献
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