Dynamics of  Late Paleozoic Pullapart Basin and Its Relationship with Mineralization of Goldpolymetallic Deposits in FengxianTaibai Counties, Shaanxi Province,China

Key words: 
• pullapart basin /
• basin dynamics /
• tectonic lithofacies /
• hydrothermal sedimentary lithofacies /
• superimposed lithofacies of tectonic hydrothermal fluids /
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Abstract: FengxianTaibai sedimentary basin could be the Paleozoic pullapart basin which might be controlled by obliquedirected subduction and collision of the Qinling and Yangtze Plates based on new research methods, i.e., reconstruction and restoration of geotectonicpaleogeographic position and tectonic lithofacies. During the initial stage of the Middle Devonian period, FengxianTaibai sedimentary basin was enclosed and separated by marginal vertical baseuplifting, and dynamics of basin was controlled by four groups of synsedimentary faults, resulted in continual migrations of subsidence and sedimentary centers in the Late Paleozoic basin. During the middle stage of the Middle Devonian period, subsidence and sedimentary centers trending northwestdirected might be located in north part of FengxianTaibai basin while subsidence and sedimentary centers trending northwestdirected shrink in the center part of FengxianTaibai pullapart basin during the Late Devonian period. However, the Carboniferous subsidence and sedimentary centers were migrated from the center to the zones of marginal synfaults of FengxianTaibai pullapart basin, and the Carboniferous to the Early Triassic wedgeshaped sedimentfilling bodies related to zone of the plate subduction and collision was located at the southern part the Shangdan suture in the northern margin of FengxianTaibai pullapart basin. Finally, formation and evolution of FengxianTaibai pullapart basin might have been controlled by the NW, NNE, NS and NWtrending synsedimentary faults in the FengxianTaibai Devonian pullapart basin. The west part of Shangdan, the middle part of LixianFengxianFengzhenShanyang, and the west part of JiujianliangZhenanBanyanzhen synsedimentary faults were of most important controls not only in the formation of the FengxianTaibai Devonian pullapart basin but also in the evolution of the Carboniferous period to the Early Triassic pullapart basin. Tectonic inversion of synsedimentary faults controlled subsidence and sedimentary centers during the evolution of the basin from the Carboniferous period to the Early Triassic period. 
 The FengxianTaibai Paleozoic pullapart basin can be divided into three different level basin based on the study of basin dynamics and tectonic lithofacies. The secondlevel, Fengxian basin is mineralization concentrated area of goldpolymetallic deposits in the west part of FengxianTaibai pullapart basin while the secondlevel, Taibai basin is mineralization concentrated area of gold deposits in the west part of FengxianTaibai pullapart basin. In the thirdlevel, BafangshanYinmushi basin, Bafangshan and Yinmushi polymetallic deposits and Baguamiao gold are the mineralization zoning at the scale of orefield and of deposits, which might be controlled by threelevel basin, synsedimentary faults, hydrothermal sedimentary lithofacies, and superimposed lithofacies of tectonic hydrothermal fluids. In the north and east part of the Paleozoic pullapart basin, formation of gold source beds and preliminary enrichment might be related to albiteite lithofacies and albitehydrothermal sedimentary lithofacies, and they may be superimposed by albitecarbonate breccia and Fedolomitealbite breccia formed by the Carboniferous tectonic hydrothermal fluids while the Triassic hydrothermal cherts and layered dacitic tuffs hosted Carlintype gold deposits in Wenjiangsi area in the south part of the Paleozoic pullapart basin. SEDEXtype leadzinc deposits may mainly related to chertic lithofacies and sideriteferrodolomitite lithofacies.