芬兰马斯塔瓦纳磁铁矿-钛铁矿矿床地质特征与成因

    Geological characteristics and genetic mechanism of the Mustavaara magnetite-ilmenite deposit, Finland

    • 摘要: 马斯塔瓦纳磁铁矿-钛铁矿床位于芬兰北部,属于芬诺斯堪迪亚地盾,辉长岩是主要的含矿岩体。矿石类型主要为钛磁铁矿,含矿岩石为含钛磁铁矿、钒钛磁铁矿辉长岩。浸染状矿石金属矿物以钛磁铁矿为主,次为钛铁矿。地球化学特征研究表明,马斯塔瓦纳矿床的Zr、Hf、U、Th 在含矿辉长岩中含量非常稳定,均小于10×10-6,反映了岩浆成因的特征。由于马斯塔瓦纳矿床形成时构造环境不稳定,原始岩浆来不及长期彻底地分异,导致岩石的地球化学参数等均具有过渡特征。芬兰马斯塔瓦纳矿床的成岩成矿过程主要分为2个期次:成岩期(形成辉长岩体)和主成矿期(岩浆期形成铁矿)。初步研究表明,芬兰马斯塔瓦纳铁-钛-钒矿床与国内的“大庙式”和“攀西式”铁矿有所不同,2个国内矿床处于相对稳定的板内构造环境,而芬兰马斯塔瓦纳矿床产于特殊的造山带而非稳定的克拉通构造环境。

       

      Abstract: The Mustavaara gabbro in Finland is a small intrusion emplaced at 1881Ma into tonalitic bedrock near the boundary of the Mid Finland granitoid complex. The proposed model for ore genesis is based on stepwise or continuous flow of magma through the sill-like middle zone and the extraction of suspended materials. The abundance of ilmenite, the high ilmenite-to-magnetite ratio (3∶1) and the limited volume of apatite in the ilmenite ore hosted by the Mustavaara gabbro are different from characteristics of many other ilmenite deposits. Mustavaara represents a new type of Fe-Ti oxide deposit. To produce titanium ore, in most cases, the parent magma is likely to be at least slightly enriched in titanium. However, for titanium deposits in small mafic intrusions, such as Koivusaarenneva, an open (magma flow-through) system is an essential genetic component to produce economic deposits. The Mustavaara gabbro is an excellent example of a small mafic intrusion that may be an economically important source for titanium (ilmenite) because the intrusion is a part of a magma channelway. The difference between the two deposit types in China and Finland is probably attributed to different tectonic settings and different physicochemical conditions in the evolution process of the ore magma.

       

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