喀麦隆北部Bougma金矿流体包裹体研究

Studies on fluid inclusions of Bougma gold deposit in north Cameroon

喀麦隆北部Bougma金矿位于中非褶皱带和刚果克拉通。Bougma金矿可以划分为两个成矿期：岩浆热液期和表生期。岩浆热液期形成含金石英脉型的金矿,表生期形成古红土型金矿和砂金矿。古红土型金矿是受热带气候控制的残坡积型矿床,砂金矿是受流水等外动力地质作用控制的冲积型矿床。根据含金石英脉样品的流体包裹体实验,主成矿期有两类流体包裹体：CO2-H2O-Na Cl包裹体（Ⅰ类）和H2ONa Cl包裹体（Ⅱ类）。I类包裹体的均一温度为197～312℃,平均为255℃,平均盐度w（Na Cleq）为6.89%;Ⅱ类包裹体的均一温度为159～285℃,平均为217℃,平均盐度w（Na Cleq）为4.56%。总体看,包裹体的均一温度集中在200～300℃,盐度w（Na Cleq）集中在3.0%～9.0%,成矿流体为中低温、低盐度流体。Bougma石英脉型金矿床属浅成中温热液型矿床,成矿流体因温度、压力变化产生强烈的不混溶作用和水岩反应是金元素沉淀的主要原因。

Bougma gold deposit in north Cameroon, located in Central African Fold Belt and Congo Craton, can be divided into two ore-forming stages：magmatic hydrothermal stage and supergene stage.Lode gold deposit was formed at magmatic hydrothermal stage, and lateritic gold and placer gold deposit formed at supergene stage.Ancient lateritic gold deposit is eluvial type deposit controlled by tropical climate, and placer gold deposit is alluvial type deposit affected by extrinsic geological process of running water.According to fluid inclusion ex-periments on gold-bearing quartz veins, two types of fluid inclusions are identified： CO2 -H2O-NaCl inclu-sions（ typeⅠ） and H2O-NaCl inclusions（ typeⅡ） .Homogenization temperature of type Ⅰ ranges from 197 ℃to 312 ℃, with the average of 255 ℃ and the average salinity（w（NaCleq）） of 6.89%.Homogenization tem-perature of typeⅡranges from 159 ℃to 285 ℃, with the average temperature of 217 ℃and the average salin-ity of 4.56%.In general, the homogenization temperature is about 200-300℃, and the average salinity 3.0%-9.0%.In conclusion, the ore-forming fluid related in gold mineralization is low-intermediate temperature and low salinity.It is an epithermal deposit.Strong fluid immiscibility caused by temperature and pressure changes and water-rock reaction is the major mechanism for gold precipitation in Bougma lode deposit.