Mineralization And Metallogenic Regulartiy Of Awulale Metallogenic Belt In Western Tianshan Mountian, Northwest China

The volcangenic iron deposits has been long concerned by geologists for its large amount of mineral resource and high proporation of high grade ore. O ver decades, most of the research on the volcanogenic iron deposits were focused on the continental volcanogenic iron deposits in Luzong and N ingwu district and only a few studies about marine volcanogenic iron deposit were carried out. In recent years, a series of researches have been done in the Awulale metallogenic belt and several large-Medium sized marine volcanogenic iron deposits including Zhibo, C hagangnuoer and Songhu were found or revaluated and makes the Awulale metallogenic belt became one of the most important iron metallogenetic belts. These iron deposits provide perfect candidates for marine volcanogenic iron deposit study. Researches on these deposits can not only improve the theory about marine volcanogenic iron deposit but also guide further ore prospecting in this area. However, these iron deposits have insufficiently studied on the metallogenesis so far. Additionally, the metallogenic tectonic setting is still the subject of an intense discussion. Furthermore, the enrichment mechanism of Fe element and indicator for further prospecting should be summarized urgently. This study chosed Songhu, N ixintage and Dunde iron deposit as candidates and discuss the coupling relationship between the metallogenic tectonic setting and metallogenesis, and the genetic mechanism of iron in the fluid in the subduction zones based on systematically mineralogical, petrologic, geochemical, isotope geochemical and geochronological study. Moreover, we also propose a metallogenic model of the marine volcanogenic iron deposit.Four large size iron deposits( Beizhan, Dunde, Zhibo and Chagangnuoer) and three medium sized iron deposits( N ixintage, Songhu and Yuxukaiputai) and a series of samll sized iron deposits or mineral occurrences are exposed from esat to west along the Awulale Iron Metallogenic Belt in the eastern part of the Yili block which is an elongated wedge-shape tract tapering to a point. We exposed several calderas based on remote sensing geology interpretations and geophysic interpretations in this Belt and find that most of these iron deposits or mineral occerance are located in calderas except the yuxukaiputai ore deposit is located beside a calderas but still controlled by the volcano slope and deposition depression.The Yuxukaiputai iron deposit is hosted in the upper carboniferous Yishijilike Formation while the other 6 deposits are hosted in the Lower Carboniferous Dahalajunshan Formation. A LA-IC-MS U-Pb zircon age of 321.6±2.4Ma was gained for the andesite exposed overlying the ore bodies in Zhibo deposit while the U-Pb age of andesite overlying the Fe12 ore body in Dunde dposit is 320.6±2.4Ma and the age of basaltic andesite in Beizhan deposit is 320.6±2.2Ma. We also obtained a U-Pb age of 340.3±7Ma of the andesite overlying the ore bodies in Nixintage deposit and 343.2±2Ma for andesite lying under the ore deposit in Songhu deposit. We propose to divide the Awulale metallogenic belt into two parts by the Dushanzi-K uqa highway. Ages of the volcanic rocks and the metallogenetic epoch are mainly concentrated on 320Ma± in the eastern part and the metallogenetic epoch of hydrothermal mineralization is concentrated on 310 Ma ~ 316 Ma. However, in the western part, large-scale magnetite mineralization formed follow on the heels of volcanism at 340Ma~343Ma.The north east margin of the Yili block acted as the active continental magin of the Yili-Centure Tianshan block as the northern Tianshan ocean subduction beneath the Yili block during Carboniferous. Intense tectonic activity and magmatism provided a favorable conditons and sufficient material base for mineralization. Petrological and geochemical characteristics indicat that the ores and wall rocks are derived from the same magmatic source and the ore- forming materials came from deep source magma. The primary magma of ores in Songhu and Chagangnuoer deposit is Fe-rich andesitic magma which is formed at the root of an arc-type crust where mantle materials are enriched. O n the contrast, the ore- forming materials of Zhibo, Dunde, Beizhan and N ixintage deposit are derived from basaltic magmas formed by partial melting of the mantle wedge. As the subduction continued, the magmatic resource became more rich in Fe for enhanced metasomatism. Basaltic magmas formed by partial melting of a metamorphic mantle source has greater potential to form large scale iron deposit.The magnetites have two different characteristics: some magnetites have a high decrepitation temperature at 424℃~520℃ and indicating a magmatic origin; the others keep a similar decrepitation temperature with hydrothermal magnetite exposed in Pingchuan district. LA-ICP-MS analysis results of trace elements show that early magnetites are enriched in Ti, V, Ga and poor in Mg, Mn indicating a magmatic origin. However, the late magnetites are charactered by high Al, Mg, Mn and low Ti, V reveal a apparent transform of hydrothermal mineralization. Anyhow, the mineralization was controlled by Magmatism.These iron deposits in the Awulale metallogenic belt are all closely associated with marine volcanism and formed during magma ore-forming period and hydrothermal metallogenic period. Mineralization can be divided into four mineralization stages as: iron-rich magma eruption, ore magma immiscibility, cryptoexplosion hydrothermal mineralization and hydrothermal filling–metasomatism stage. Magmatic metallogenesis dominated during the forming of N ixintage deposit while late hydrothermal mineralization obviously transformed both the magnetites and ores in Songhu and Dunde deposit. All of the three studied iron deposits belong to marine volcanogenic olygenetic magma- hydrothermal deposit.The marine volcanogenic iron deposits in the Awulale metallogenic belt are double controlled by the basic- intermediate volcanic stratum and volcanic edifice. Ore magma or ore-rich magma formed due to the magmatic differentiation and immiscibility effect. Volcanic edifice not only provide a favorable mineralization condition but also provide storage spaces for the ores. Extensive distribution of the Carboniferous volcanic rocks and volcanic edifices indicate a large ore prospecting potential of volcanogenic iron depos it in western Tianshan area. In the future, deep and periphery prospecting work should be carried out around the volcanic edifices with comprehensive utilization of remote sensing, geophysic, geochemical and geological technology. Moreover, this district also has potential in prospecting porphyrite iron swposits and hydrothermal deposits related to the intermediate-acid intrusive rocks.