摘要
在所研究的某些碳酸盐交代型锡矿床中,生成矽卡岩的流体以Ca/Na之比值高为特征。当不知道流体的热力学参数(p,t,V,X)时,其捕获压力不能用流体包裹体压力计求得。作者根据热力学计算,推导出一种用于估算多盐体系中流体包裹体捕获压力的经验公式。以氯化钠当量为单位的含盐度可以根据各盐分的重量百分比计算,且由于流体压力是水的摩尔分数的函数,故含盐度和温度可以用公式估算,其误差大体上不超过3％。对大厂、个旧矿田和新路锡矿床进行研究的结果表明,矽卡岩的生成温度为550～600℃,压力为80～90kPa。这一结果与前人用其他方法获得的实验结果吻合。
Fluids forming the skarns in some carbonate replacement tin deposits studied here are characterized by high Ca/Na ratios, and trapping pressuresof these fluids could not be determined by fluid inclusion geobarometry astheir p-V-X-t properties are unknown. However, the experimental results show that at high temperatures (>450℃) the water activity, which is closeto 1, has nothing to do with the salinity of the fluid (Sourirajan and Ken-nedy, 1962). At low temperatures(150～350℃) different sorts of ions (K^+ orNa^+) with the same activity have almost the same effect on the water acti-vity (Zerembo et al, 1980). Based on thermodynamic calculation, an empi-rical equation is proposed to estimate the trapping pressures of fluid inclu-ions in a multi-salts system. The salinity in terms of NaCl equivalent canbe calculated according to the weight percentage of individual salts Salinity=C_(NaCl)+0.78C_(KCl)+0.50C_(CaCl_2)+0.46C_(FeCl_2)+0.43C_(ZnCl_2)and the fluid pressure being a function of water mole fracon, salinity and temperature can be estimaied by the equation P_A=X_A(0.9892-0.0039S+1.866·10^(-4)S^2-3.515·10^(-8)S^3)× (-649.14+1.5938t+1.8810·10^(-3)t^2)with an error mostly less than 3%. Skarns in the Gejiu ore field, the Da-chang ore field and the Xinlu tin deposit were estimated to be formed atthe pressures between 80 and 90 kPa at the temperatures from 550 to 600℃.These predictions are in agreement with previous experimental results.
关键词
盐
溶液
流体
包裹体
压力
锡矿
fluid inclusion
tin ore deposit
skarn
empirical method/trapping pressure
