Large and superlarge silver deposits associated with volcanic rocks in China

<正> This paper deals with the geology and geochemistry of the Gacun and Laochang large-sized marine volcanic rock-type Ag deposits in the Sanjiang (Tri-River) area of southwestern China and of the Continental volcanic-subvolcanic rock-type Ag deposits in the Tianshan area of Xinjiang, and in the East area, China. It is considered that the marine volcanic rock-type Ag deposits occur mainly in the second-ordered volcano-sedimentary basins developed in island-arc and rift tectonic environments. The Ag deposits show an obvious zonation, with vein-network mineraliza-tion in the lower parts and hot water sedimentary rock-hosted stratified mineralization in the upper parts. From the Earth's surface downwards the ore-forming elements follows the order of As(Au)) -Ag, Pb, Zn-Cu. The whole rock Rb-Sr isotopic isochron age of layered orebodies in the Gacun deposit is 204+14 Ma, indicating that the main stage of mineralization is Late Triassic in age. The Continental volcanic-subvolcanic (porphyry) rock-type Ag deposit