Abstract: Located in eastern Gejiu area, the Gejiu tin ore deposit is a superlarge polymetallic deposit dominated by tin and copper mineralization and featured by characteristics of the volcanosedimentary ore deposits. Reworked by granites of the Yanshanian epoch, the basalts of the Gejiu Formation underwent intense metamorphism. The authors deal with the geological and geochemical features of the basalt and related mineralization in the area. The results of the research are: The contents of Sn, Cu, Pb, Zn, Ag and Au in the Indosinian basalt in the area are higher than those in average basalt of the world;The sulfur isotopes of sulfides in the deposits are between -1.5‰ and 4.0‰, similar to those of the mantle; Model ages of lead isotopes of the ores can be divided into two groups: The first group ranges from 180 Ma to 240 Ma, which represents basic volcanosedimentary mineralization of the Indosinian epoch, while the second group ranges from 80 Ma to 140 Ma representing the superimposed mineralization of the Yanshanian granite. It’s believed that the Indosinian basalt provided the oreforming materials for the ore deposit and was directly related to the mineralization in the area.

Key words: mineralization in the Indosinian basalt, superimposition of the Yanshanian granite, tin deposit, Gejiu, Yunnan Province