海南抱板金矿田流体包裹体地球化学研究

FLUID INCLUSION GEOCHEWCAL STUDY ON THE BAOBANGOLD FIELD, HAINAN ISLAND,SOUTH CHINA

对海南抱板金矿田的土外山、抱板和二甲等三个金矿进行的流体包裹体研究表明成矿流体为低盐度（０．１～６ｗｔ％ＮａＣｌ）、中低温（２００～２４０℃）热液，处于中低压力（６０～１６０ＭＰａ）下，其ＣＯ＿２含量较低。探针质谱分析表明流体包裹体中存在Ｈ＿２Ｓ，结合的存在，金在热液中可能是以硫氢络合物的形式迁移的。

The Baoban gold field, located in Hainan Island, South China, consists ofthree guld depeits, namely, Tuwaishan, Baoban, and Erjia. These three golddepeits are very similar in geolocrcrical characteristics and all belong to wall-rock alteration type. Three mineralization stages can be recognized: (1) quartz-pyrite-arsenopyrite stage; (2) polymetallic sulfide-gold stage; (3) quartz-calcite stage.Fluid inclusions can be divided into three composition types by theirappearance and their cooling and heating behavior: ( 1 ) aqueous fluid inclu-sions; ( 2 )H_2O-CO_2 fluid inclusions and ( 3 ) single-phase fluid inclusions. Themicrothermometric experiments were undertaken on an improved fluid inclusionstage of the U. S. Geolooerical Survey. The salinity of the fluid is about 0. 2%～6%NaCl wt eq. The homogenization temperature is about 200 to 240℃, but varieswith mineralization stages: 160～170℃ at Stage Ⅰ, 200～2400℃ at Stage Ⅱ,and 150℃ at Stage Ⅲ. The pressure of the ore-forming fluid is about (60-160 MPa.The main gas components of the fluid inclusions are CO_2, H_2O, CO, CH_4and H_2S as determined by solid-probe mass spectrometric analysis. A comparisonwith other gold deposits shows that there may exist relations between golddeposit types and content of gaseous H_2S. The content of gaseous H_2S in golddeposits of the gold-quartz vein type is lower than that in the wall-rockalteration type. Using the equation CH_4 + 2O_2 =CO_2 + 2H_2O and the gas compo-sition,it is estimated that the oxygen fugacity is about 10￣(-40).Chromatographic analysis shows that the major anions in the fluid inclu-sions are F￣-, Cl￣-, while the major cations are Na￣+, K￣+Ca￣(2+), Mg￣(2+). Wlienchemical equilibrium is considered, the coexistence of H_2S in gaseous phase andin liquid phase alld the reduction environment of the fluid(fo_2=10￣(-40))imply;that there axists HS￣- in the fluid,and that gold in this fluid can easilyform and might be transported as . It can be therefore conc-luded that the ore-forming fluid in this gold field is a low-medium salinity(0.2～6NaCl wt% eq.) , low-medium temperature(200～240℃)hydrothermal fluidwith low-medium pressure(60～160 MPa),with gold probably transported in the form of .