西天山阿吾拉勒火山岩型铁矿带东段成矿地质背景与成矿机理

备战、敦德、智博、查岗诺尔铁矿分布于阿吾拉勒火山岩型铁矿带东段的大哈拉军山组火山岩中,各个矿区基性、中性和酸性火山岩兼而有之,但所占比例不尽相同。矿区的火山岩以钾玄岩系列、高钾钙碱性系列、钙碱性系列岩石为主,也有少量拉斑系列岩石出露。岩石相对富集轻稀土元素,相对富集大离子亲石元素而亏损Nb、Ta和Ti等高场强元素。显示出岛弧或活动陆缘环境火山岩的固有特征。研究认为该地区铁矿床为矿浆-火山热液复合成因型铁矿床,其形成受岩浆-热液系统活动的制约,具体成矿作用包括氧化物熔离成矿、隐爆-贯入成矿、分离结晶+岩浆流动成矿和热液交代四种类型。矿床的控矿因素与成矿条件包括:(1)活动大陆边缘型火山岩组合与伸展构造环境;(2)基性和中性火山熔浆多次喷溢和堆积部位;(3)含矿母岩浆的强烈分异演化导致氧化物熔离,而分离结晶和岩浆流动则促使富集矿体形成;(4)岩浆热液对流循环并萃取围岩铁质,是形成热液期矿石的基本机制;(5)火山机构及其伴生裂隙是含矿岩浆活动的有利空间并为成矿物质的聚集提供物理化学条件,是铁矿体主要控矿因素和赋矿部位。铁矿床与火山作用关系极为密切,火山熔浆与火山热液反复多次活动导致了成矿作用的多期多阶段性。

Geological background and metallogenetic mechanism of the eastern Awulale volcanic-hosted iron metallogenic belt in the western Tianshan

Several iron oxide deposits are exposed along the eastern Awulale volcanic-hosted iron metallogenic belt, such as Beizhan, Dunde, Zhibo and Chagangnuoer iron deposit. These deposits are hosted in volcanic rocks of Dahalajunshan Formation. The rocks that range from basic to acid rock are widely distributed in every iron deposit, and all kinds of rocks have different proportion in very iron deposit. Rock chemical series mainly consist of shoshonite, high-K calc-alkaline and calc-alkaline series, with a small amount of tholeiite series. They are enriched in LREE and LILE with obvious depletions of Nb, Ta and Ti. It suggests that they have a blood relation with arc or volcanic-arc rocks. In this paper, we suggest that these deposits are a polygenetic magmatic deposit and volcanic hydrothermal deposit related to the magmatic-hydrothermal system. Metallization types include oxide liquation metallization, cryptoexplosive-injection mineralization, fractional crystallization mineralization with magma flow and hydrothermal metasomatic mineralization. Mineralized factors and metallogenic conditions include:(1) Active continental volcanic rock combination and borderline tectonic setting. (2) Basic and neutral volcanic magma eruption and in the part of the basic volcanic rocks. (3) The intensive differentiation evolution of primary ore magma resulted in oxide liquation metallization. It is the key mechanism for the formation of the rich ore body in central portion that fractional crystallization and magma flow. (4) Magmatic hydrothermal has been circulating in the convection. As hydrothermal fluid altered with the wall rocks, Fe is extracted into the fluid. This is the basic mechanism for the formation of hydrothermal ore. (5) Volcanic edifice and associated fractures are good space for ore magma activity, and they provided the physical and chemical conditions for mineralization and enrichment. They are main ore controlling factors and parts where ore body occurred in. Iron deposits are closely related to volcanism, the magma and hydrothermal activity repeatedly lead to multiple stages of mineralization.