Fineness features of placer gold in the middle part of the Bangonghu lake to Nujiang River mineralization belt,Tibet

The fineness of placer gold in this district is apparently featured by inhomogeneity,inheritance and afterdeformation.The range of fineness is wide(531 48～1 000).The bigger the grain size is,the higher the fineness will be.The placer gold deposits in the western district with coefficient of solution1 03 belong to proxial primary placer gold,those in the eastern district with coefficient of solution 1 03～1 10 belong to midium proximal primary placer gold,and the Bengnazangbu belong to distant primary placer gold because its coefficicent of solution is1 10. Study of the chemical composition of native gold indicates that the primary gold deposits belong to mesothermal epithermal gold deposits,its possiable to find primary gold deposits in granite of later Yanshan orogenic period in the Nalanggou area.