摘要
对太古代一些金矿包裹体研究结果表明,其含金的成矿流体为低盐度<10wt%NaCl,均一温度为170～400℃,CO_2的含量为中等,并含有一定量CH_4。在这些矿床中主要见到三种类型的包裹体:CO_2包裹体。H_2O-CO_2包裹体和水溶液包裹体。这三类包裹体常产于同一裂隙中或一个晶体中、或各产于不同的裂隙中、或其中之二共存于一裂隙中,并且其均一温度相近,但盐度和CO_2含量相差甚大,这表明发生了相分离。用质谱仪对这种同一世代的包裹体进行分析,证明的确存在着相分离,即从原始的H_2O-CO_2-NaCl流体,由于压力降低而发生相分离,形成CO_2和NaCl-H_2O流体,金就是在这种相分离的过程中沉淀出来。研究也表明,对于蚀变岩型金矿来说,引起金沉淀的因素除相分离外,流体与岩石的相互作用也可能是很重要的因素。对于含金的成矿流体来说,CO_2含量高是一个很重要的特点,也许可作为找矿的一种标志。
Fluid inclusions in vein quartz and altered rocks from several Archean gold deposits indicate that gold deposition was from distinctive, low salinity (typically) less than 10 wt.% NaCl equiv.), CO_2-rich (about 10～25 mol% CO_2) ore fluids with moderate densities and a little amount of CH_4. Deposition occurred over a temperature range of 170 to 400℃, under lithostatic pressures. Phase separation in quartz vein-type deposits is characterized by variable phase ratios in CO_2 and H_2O-CO_2 inclusions, There are three types of fluid inclusion: CO_2, H_2O-CO_2 and aqueous inclusions, which occur in a same healed fracture or in a crystal (in most eases, two of them occur together), or in different fractures. Their homogenization temperatures are similar, but the salinity and concentration of CO_2 ase variable. Using solid probe mass spectrometry to analyze the gas composition of these fluid inclusions of the same generation, the spectral pattern shows extreme phase separation which is associated with pressure fluctuations. These indicate that the original fluid belongs to a H_2O-CO_2-NaCl system, which, owing to the phase separation, was separated into two fluids: CO_2 (sometimes CO_2-CH_4), and NaCl-H_2O. Gold deposition may occur during this phase separation. CO_2/H_2O ratio of fluids across the alteration zone and quartz vein may be a good exploration guide to Archean gold deposits.
出处
《矿物学报》
CAS
CSCD
北大核心
1991年第4期289-297,共9页
Acta Mineralogica Sinica
基金
国家自然科学基金
关键词
金矿
成矿
包裹体
太古代
Archean
greenstone belt
gold deposit
fluid phase separation
fluid inclusions of the same generation
Shandong
Canada
