Paleozoic hydrothermal sedimentary basin and hydrothermal sedimentary mineralization in the Southern Qinling

Abstract：An Early Paleozoic to Middle Mesozoic sequence of carbonate rocks with finely clastic rocks occurs in the Paleozoic South Qinling sedimentary basins at the passive continental margin of the northern part of the Yangtze plate. A huge and unique lead-zinc-gold polymetallic metallogenic belt formed there. Normal sediments and hydrothermal sediments coexist in the same rift or downfaulted basins formed in an extensional regime. The hydrothermal sediments superimposed upon the normal sediments, which was a "sudden or catastrophic event", have the special material composition and mode of occurrence. Recognition and hierarchical division of the sedimentary ore-forming basins in this area show that several third-order tectono-hydrothermal sedimentary subbasins usually occur at margins of second-order sedimentary subbasins. They are controlled by contemporaneous faults and characterized by particular sedimentary facies, hydrothermal sedimentary rock associations, significant ore-forming processes and wide distribution of geophysical and geochemical anomalies. The third-order tectono-hydrothermal sedimentary subbasins are tectonic spaces for localization of ore deposits, and the fourth-order hydrothermal sedimentary subbasins are spaces accommodating orebodies (ore beds). The hydrothermal sedimentary rocks in the region are mainly barite (witherite) rock, siliceous rock, albite rock and ferro-carbonate rock. Mineral resources such as lead, zinc and barite mostly occur in the hydrothermal sedimentary rocks or in their hanging walls. The hydrothermal sedimentation generally evolved from early-stage hydrothermal eruption and replacement through main-stage hydrothermal effusion to late-stage hydrothermal exhalation. The early-stage hydrothermal eruption and replacement usually result in stockwork and brecciform mineralization along the conduits of ore fluid eruption. The main-stage hydrothermal effusion mainly gives rise to hydrothermal effusion facies and polymetallic mineralization, characterized by massive, banded and laminar ores or hydrothermal sedimentary rocks. The late-stage hydrothermal exhalation mainly produces disseminated ores and exhalative rocks.