Structure-sedimentary facies and hydrothermal mineralization characteristics of Shiti(in Ankang)-Shenhe(in Xunyang) Early Paleozoic hydrothermal basin in South Qinling orogenic belt

The Early Paleozoic Shiti(in Ankang)-Shenhe(in Xunyang) area belongs to the South Qinling orogenic belt and has the characteristics of the so-called chert-limestone-mudstone sedimentary edifice in deep-water setting.It was a rifting basin formed in the extensive structural regime,and there coexisted the classic deep-water sedimentation,volcanic exhalative sedimentation and hydrothermal sedimentation,producing the special and unique polymetallic field composed mainly of barite and magnetite.The facies of hydrothermal sedimentary mineralization basin show distinct several-dimensional associations comprising structural deformation,petrologic composition,geochemical signature and features of sedimentary rocks.The structure-sedimentary facies of the third-grade hydrothermal sedimentary basin in South Qinling orogenic belt can be roughly divided into 3 types.The first type is the structure-sedimentary facies of volcanic hydrothermal sedimentary mineralization basin,which has the Quaternary characteristics of volcanic sedimentation,hydrothermal sedimentation,deep-water chemical sedimentation and hydrothermal sedimentary mineralization.The second is the facies of the deep-water and oxygen-absent rifting sedimentary mineralization basin,which has the trinity characteristics of hydrothermal sedimentation,deep-water chemical sedimentation and hydrothermal sedimentary mineralization.The third is the facies of the shallow-water carbonate platform,which has the trinity characteristics of normal shallow-water chemical sedimentation,hydrothermal sedimentation and hydrothermal sedimentary mineralization. The analysis and identification show that the third-grade hydrothermal sedimentary mineralization basin is controlled by the syngenetic faults and the volcanic actions,having the geographic features of the sedimentary rocks,association of hydrothermal sedimentary rock,exhalation association,obvious mineralization and distribution of geophysical and geochemical anomalies.The third-grade hydrothermal sedimentary mineralization basin is the structural space for ore deposits,and the fourth-grade hydrothermal sedimentary depression acts as the suitable space for ore body.The exhalites in the region mainly include baritite,chert,magnet-albitite and ferro-carbonate.The minerals such as barite and magnetite are mostly grown in the exhalites or the hanging wall of the volcanic sedimentary rocks.