THE MINEROGENETIC CONDITIONS FOR THE Hg-Sb-Au DEPOSITS IN XUNYANG DISTRICT, SHAANXI PROVINCE

Xunyang district is situated at the southeast end of the South Qinling Mts., where are broadly developed Palaeozoic metamorphic microclastic rock and carbonate rock strata which contain abundant multi-metallic minerals, such as Hg, Sb, Au etc. The deposits are obviously controlled by Middle-Late Palaeozoic sedimentary basin, especially the seabed hydrothermal spurt related to the contemporaneous faults in basin fringes. The scales of the deposits was correlated to the dimensions of the sedimentary basins, that is, the larger the sedimentary basin is, the larger the deposit is. The reformation produced shoots. In Xunyang area, the multi-metallic metallogenetic series seem to undergo two stages of mineralization. The first was split extensional structure stage in Middle-Late Palaeozoic, especially Silurian-Devonian period. At that time, the Xunyang-Shangxian-Luonan northeast-trending basement strike-slip fault, together with the faults in the basin fringes, formed the structural drive and the chief hydrotheraml circulation channel for the hydrothermal spurt at the sea bottom. Amounts of anatectic minerogenetic material entered the sedimentary basin, forming of source bed for the multi-metals of Hg, Bb, Au etc. The second stage, during Indosinian-Yanshanian period, was a block mergence-compressive nappe structure mineralization stage. Along with the collision of the North China block and Yangtse block, this area developed many thrust nappings, and various scales of folds, bed-ding-slip shear structures and so on. Various fluids from the strata and rocks blended with precipitated water and circulated, forming high salinity hot brine which contained amounts of Hg, Sb, As, Pb, Zn, Au, Ag, W etc. and depositted in appropriate environment.