The Study On Metallogeny And Metallogenic Regularity Of Iron Deposits From Abagong To Mengku Area In Altaid, Xinjiang

The metallogenetic belt of Altay is an important metallogenetic province in our country. In this belt, the main iron deposits are located in the Kelan and Mazy volcanic-sedimentary basin from Abagong to Mengku area in the southern margin of Altay. The prevenient investigation mostly focused on the mineral deposits of copper, lead, zinc and rare metal etc. in despite of a lot of works and prominent achievement on metal deposits in the area. The less special and systematical research resulted in much dispute on metallogenesis and genetic type of several iron deposits such Mengku deposit as the first. In this study, the geological features of several tipical iron deposits were surveyed detailedly on the base of the in-depth investigation in the field and the petrology, the geochemistry, the isotopic geology, the inclusion fluid and trace elements, REE were systematically studied on producting-ore stratum, granites, typical deposits and altered hostrocks. In the mean time, the key problems about tectonic setting, origin of metal, ore-forming fluid and geochronology were mainly discussed. On these basic works, we summarized the metallogenesis of the iron deposits and its regulation and primarily constructed the metallogenesis model of the area.The Abagong iron deposit is attributed to the intrusion and filling of late ore magma by magmatic differentiation and the Mengku, Serblak and Jerbast iron deposits are shared by skarn iron deposits related to the silicic plutons. The shape of ore bodies are controlled by the northwest sub-fault belts near the large regional faults. They are mainly characterized by simple mineral assemblage and skarn alteration for hostrocks.The study on petrology, geochemistry and isotope geology indicates that there are the common resource and tectonic setting for the Kangbutiebao formation with metamorphic volcanic rocks and the granite plutons related to the main iron deposits.They are different facies from magma evolvement in late Silurian-early Devonian. The protolyte for the Kangbutiebao formation with volcanic-sedimentary rocks resides in the formation with quartz ceratophyre, ceratophyre and protolyte formed at about 413Ma. They attribute to the calc-alkalic unit from basic to intermediate to silicic volcanic rocks resulted from the melting and differentiation evolvement of oceanic crust with assimilating crustal material in the continent-arc setting due to oceanic plate subduction. The granite plutons related to metallogenesis of iron mostly formed from 410Ma to 400Ma, resulted from the melt and differentiation of oceanic crust in a arc-continent setting because of subduction of plate. Only did few plutons related to iron deposits form at about early Permian(287Ma), showing post-orogenic setting.We have studied the geochemical characteristics of several typical iron deposits.The feature of oxygen isotope for magnetite from Abagong iron deposit reflects that the water in the fluid of mineralization resides in the initial magma, implying the magma genesis of mineralization. The similaritary features of REE and trace elements for coexisting apatite with magnetite in the Abagong, the Kiruna type and the Ninwu porphyrite iron deposit show their common genesis, indicating that Abagong iron deposit resulted from the intrusion of late ore magma due to the magma differentiation. The characteristic of sulfur isotope composition implies that the Abagong iron deposit resides in basaltic magma from mantle resource. The bimodal feature of sulfur isotope composition for the pyrite from ore and hostrocks indicates that sulfur in the Mengku iron deposit partly originates from stratum, partly from granitics, implying that the deposit attributes to skarn type resulted from the reaction between silicic pluton and volcanic stratum. The Kangbutiebao formation volcanics, the Mengku pluton and the Serblak granite related directly to the formation of iron deposit all take on mantle resource, indicating that iron resides in the subducted oceanic crust. Above all geochemical characteristics of typical iron deposits, we think that the Kangbutiebao formation volcanic rocks and granites-related provided the main origin of metal. The ore-forming fluids derived from more complex resources that some were mainly derived from magmatic water with some contributions from meteoric water, some prominently resulted from meteoric water and some were partly influenced by metamorphic water. The formation of magnetite arised mainly in the late stage of skarn period in which the fluid appeared in the middle-low temperature, low salt and density.The study on geochronology indicates that the age of Mengku iron deposit is defined at about 400Ma, Abagong iron deposit at later than 413Ma somewhat, Saerblak iron deposit at about 410Ma and Jerbast iron deposit at about 287Ma. The above all illustrate that the iron deposits in Abagong-Mengku area were mainly formed in the period of late Silurian-early Devonian, few in the period of early Permian.Based on the above study, the metallogenesis model of iron in this area was suggested as follow: The subduction of the Paleo-Asia ocean north-ward beneath the Siberian plate beginned in the early Paleozoic provides the resource of power driving metallogenesis in the southern margin of Altay. Because of the subduction, a series of stretched and fault-through basins formed in late Silurian to early Devonian, volcanic emission and magmatic intrusion directly urged metallogenesis. The late bearing-ore magma (ore-magma) formed by the differentiation and immiseibility of magma may form the intrusive iron body, but more iron deposits attribute to skarn type resulted from the metasomatic reaction between intrusive magma and stratum. The intrusion of magma mainly controlled the iron mineralization.