广东新洲金矿床地质特征和成矿流体类型

GEOLOGY AND ORE FORMING FLUID TYPES OF THE XINZHOU GOLD DEPOSIT, GUANGDONG PROVINCE

新洲金矿带产于震旦系云母石英片岩的层间断裂带中。矿床中有金矿带１０条，第二、三矿化阶段为金的主要矿化阶段。流体包裹体和同位素研究表明，金属矿和硫来自围岩，流体主要是变质水。矿床是产于区域变质岩系中，与岩浆热动力变质作用有关。

Located at the connection between the Fengliang Fogang latitudiinal tectonic belt and the Wuchuan Sihui Neocathaysian faulted fold belt, the Xinzhou medium size gold deposit lies in the outer zone of the westward extension of the Fogang prophyritic biotite granite, and occurs in the interlayer faulted zones among Sinian two mica schist, two mica quartz schist and metamorphosed siltstone The Sinian strata contain gold 12 3×10 -9 ～29 0×10 -9 with enrichment coefficients 3 3～7 4, thus showing character of the source bed. The thermodynamic force produced by magmatic intrusion and emplacement as well as metamorphism and wall rock alteration resulted in the migration and enrichment of gold in strata to form the ore deposit. The ore deposit consists of 10 gold ore zones, with No.Ⅰ ore zone being economically most valuable. The second and the third ore forming stages are major gold mineralization stages. Native gold occurs in the forms of trapped gold, crystal crack gold and fissure gold, whose average fineness of gold is 947. The correlation coefficients of Au with Ag, As and S are 0.64, 0.87 and 0.54 respectively. Fluid inclusion and isotopic studies show that ore forming temperatures are 270 ℃～180 ℃, pressures are (150～200)×10 5 Pa, pH=5.5～6.5 , and Eh=-0.25～-0.5 eV. The fluids are enriched in H 2O, CO 2, Na +, Ca 2+ , Cl - and SO 2- 4, and have average salinity of 16 7 wt% NaCl.REE distribution patterns of wall rocks, altered rocks and ores are of similar LREE enrichment type, with the REE sources having the cognate nature. Lead isotopes show character of crustal anomalous lead. δ 34 S values are of rich 34 S type in the range of 10.00‰～12.14‰ and -46‰～-67‰ respectively. Studies show that ore forming metals and sulfur were derived from wall rocks, whereas fluids were mainly mixtures of metamorphic water and meteoric water. The thermodynamic force of magmatic activity constituted the dynamic force for mineralization. The ore deposit is a mesothermal meta hydrothermal deposit related to magmatic thermodynamic metamorphism in regional metamorphic rocks. The source bed, the metamorphic body,magmatic activity and favorable structure make up indispensable prerequisites for mineralization.