Metallogenic Regularity And Prospecting Direction Of Fe-Mn Ore In The Carboniferous Volcanic-sedimentary Basin In Western Tianshan

The Awulale iron metallogenic belt which is developed in the Carboniferous volcanic-sedimentary basin in the western Tianshan Mountains, is an important iron ore belt discovered in recent years. Numerous large-medium scale Fe deposits are found in this area, including Chagangnuoer, Zhibo, Dunde, Nixintage-Akesayi, Songhu and Shikebutai. Additionally, Motuosala Fe-Mn ore and Jiamantai-Akesu Mn ore have been explored in the southern margin of the basin.1. This basin was formed based on the Muyunkum-Kyzylkum-Ili micro-plate (continental crust) during Devonian-Carboniferous. Both of Mountain Awulale in the north and Mountain Yishijilike in the centre are volcanic belts generated in the Carboniferous rift environment, whereas the central Tianshan magmatic belt in the south is a stable continental margin.Ore-forming materials and volcanic matters have the same source, derived from sodic-rich basalt magma created from the partial melting of oceanic crust involving terrigenous materials in upper mantle. Volcanic apparatus and volcanism control the spatial distribution and metallogenic mechanism of Fe-Mn deposits. Four types of significant Fe-Mn mineralization have been recognized, including ore magma emplacement, volcanic sedimentation, chemical sedimentation and hydrothermal overprint. 2. Fe-Mn deposits can be divided into three categories, including marine (sub-) volcanic type, marine volcanic-sedimentary type and marine chemical-sedimentary type. Furthermore, six mineralizing sub-types can subdivided, which are ore magma intruded-hydrothermal metasomatic filled sub-type (?), ore magma injected-hydrothermal metasomatic filled sub-type (e.g., Chagangnuoer, Beizhan), ore magma effused-hydrothermal metasomatic filled sub-type (e.g., Zhibo, Dunde, and Kuolasayi), volcanic eruptive-sedimentary-hydrothermal metasomatic sub-type (e.g., Nixintage-Akesayi, Songhu), volcanic-exhalative sedimentary sub-type (e.g., Shikebutai, Motuosala), and chemical colloidal deposition sub-type (e.g., Motuosala, Jiamantai-Akesu Mn), respectively.3. It is under the influence of simple shear model and block detachment mechanism that this basin results in volcanic passive continental margins, and stable continental margins as well as the diversity of volcanic-sedimentary mineralization. The former controls the formation of marine (sub-) volcanic Fe deposits, whereas the later determinates the generation of marine chemical-sedimentary Fe-Mn deposits.4..The volcanic-sedimentary mineralization model, together with 3-D systems of "metallogenic epoch-metallogenic mechanism-metallogenic model", indicates that volcanic mineralization dominated the first place, and integrated with sedimentary mineralization as a whole during the ore-forming history. From late Early Carboniferous to early Late Carboniferous, the strength of iron mineralization gradually decayed as time, whereas the dominant mineralizing types transferred ore magma intrusion, injection and effusion into volcanic eruption, and exhalation. Mineralization of Fe-Mn deposits experienced five tectonic-volcanic-metallogenic evolving stages, respectively, the formation of basin base, construction of basin volcanic apparatus, ore magma emplacement, volcanic sedimentation, and land-forming.5. This basin developed the metallogenic series of Fe-Mn-Cu-Pb-Zn-Au-Ag deposits which are related to marine volcanic-sedimentary mineralization. Special strata and rock formation and ore-host space around volcanic crater should be the major prospecting targets for exploring Fe-Mn deposits, whereas the "vacancies" of mineral species and mineralizing types are significantly supplementary for ore exploration.