The controls of the host basins on ore-forming elements from the sedex deposits in Xizang

The hydrothermal sedimentation, diagenesis and mineralization may occur in various tectonic settings such as spreading zones, mid-oceanic ridges, trenches, island arcs, back-arc basins, continental rifts and intracontinental fault zones, especially in pericontinental aulacogens and deep swales on carbonate platforms. The Jiama polymetallic deposit and Shalagang antimony deposit have been addressed herein as two good examples. They are all assigned to the sedex deposits and the orebodies commonly appear as stratified and stratoid forms along the stratigraphic horizons. The formation and evolution,sedimentation, diagenesis and mineralization of the basins in which these deposits are hosted tend to be controlled directly or indirectly by the tectonism in south-central Xizang. The comparative study of the two deposits shows that the Jiama polymetallic deposit is located in the inter-arc shallow-marine basin on the active continental margins, whereas the Shalagang antimony deposit lies in the low divide deep-marine basin on the passive continental margins. The differences in tectonic settings are responsible for those in host rocks, elemental components, mineral compositions, types, textures and structures of ores.