The regional aeromagnetic features and genesis of iron deposits in Yili terrane,western Xinjiang
The newly discovered medium- to large-sized iron deposits in western Tianshan,Xinjiang are mainly distributed within the Yili Carboniferous back-arc basin.The formation of most major iron deposits were intimately linked with Early Carboniferous marine volcanic rocks(hosted by the Dahalajunshan Fm.),but some other deposits were genetically relatedto chemical deposition of iron and silica from seawater in Late Carboniferous time(hosted by the Yishijilike Fm.).The regional aeromagnetic surveys turned out a perfect response to the iron deposit distribution in the region.The iron deposits hosted within volcanic-volcaniclastic rocks ofthe Dahalajunshan Fm.were chiefly localized in the ring and radiate faults of crater structures and formed by ore-magma and/or hightemperature volcanic hydrothermal fluids,thus they are not concert with the surrounding volcanic strata in their orientations.The deposits hosted within the sedimentary rocks ofthe Yishijilike Fm.are chemically precipitated along with other sediments from the surrounding seawater,therefore they are conformable with the hosting stratigraphy and controlled by paleo-topography of the basin.However,overprinting by Sedex-type mineralization on these sedimentary iron deposit cannot be totally precluded.It is suggested that the differences between the marine volcanic rock package and sedimentary rock package might be the principal and crucial factor in controlling the generation and localization of the iron mineralization in the region.