Geology, Geochemistry, and Fluid Inclusions of the Gejiu Tin-Polymetallic Field, People's Republic of China

The Gejiu tin field in southern China consists of six major deposits and many minor ones containing more than 120 million tons (pre-mining resource) at 1% Sn and significant amounts of Cu, Ag, Zn, and Pb. It is one of the largest tin fields of primary deposits in the world. Mineralization is the result of the intrusion of granitic plutons into Permian and Triassic sedimentary rocks, which are dominantly limestone, dolomitic limestone, and dolomite. Five (mostly peraluminous) granitic intrusives (64-115 Ma) are present in the area. The largest orebodies are spatially and temporally related to the Laoka (principally), Beipaotai, and Marsong granites. Tin mineralization is mainly within greisens developed at the outermost zone of a skarn zonal sequence and are mineralogically dominated by fluorite, quartz, and micas. The deposits are the result of volatile-rich ore solutions that evolved late in the plutonic crystallization history. The solutions produced metamorphic skarns as well as ore skarns, both of which later became "greisenized" skarns. Gejiu is the largest example of what has been, up to now, a style of mineralization reported only in minor amounts.