QUARTZ VEINS AND THEIR FEATURES OF MICRO-GRAIN TYPE DISSEMINATED GOLD DEPOSITS IN NORTH-WESTERN SICHUAN PROVINCE

The north-western Sichuan Province, one of the main micro-grain disseminated gold metallogenic zone in China, possesses about twenty important gold deposits (or occurrences) such as Ma'naoke etc. Studies show that several kinds of quartz veins are often developed in the mining districts in this region, among which pyrite-arsenopyrite-quartz, quartz-stibnite as well as quartz-realgar (orpiment) veins are intimately related with gold mineralization and their spatial distribution is mainly constrained in the gold mineralization belts. While the development degree of these three kinds of quartz veins can indicate gold mineralization intensity to some extent, so they are important macroscopic marks for exploration and evaluation of this type of gold deposits in the region. Studies on fluid inclusions show that these kinds of quartz veins formed in a hydrothermal condition with temperature range from 170 ℃ to 210 ℃ and salinity of fluids range from 4% to 11%, the w(CO₂) / w (H₂O) value of the gaseous compositions of fluid inclusions is between 0.240 and 0.491 in general, and the relatively light density values of quartz are usually lower than 8.0. All these are obviously different from other kinds of quartz veins, so these parameters of quartz form the important microscopic marks for exploration and evaluation of gold deposits in the region.