Chemical evolution and mineral deposition in boiling hydrothermal systems
Chemical evolution and mineral deposition in boiling hydrothermal systems
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DOI：
10.2113/gsecongeo.80.1.126
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发表时间：
1985-02
期刊：
影响因子：
5.8
通讯作者：
S. E. Drummond;H. Ohmoto
中科院分区：
文献类型：
--
作者：
S. E. Drummond;H. Ohmoto
建立了一个热液沸腾的热力学模型，并在广泛的物理和化学条件下得到应用。在自然沸腾热液系统中观察到的条件范围内，液-气分配过程及其对矿物溶解度的影响是高度变化和复杂的。与氯化物络合的金属在很大程度上是由于沸腾过程中与CO2出溶相关的质子浓度降低而沉积的。当质子浓度的降低相对于H2S的损失缓慢时，金属二硫化物络合物最不稳定。当CO 2/H（super+）和CO 2/Sigma SO 4浓度比最初很高时，仅几个百分比的溶液的蒸发可以使质子浓度降低几个数量级。沸腾前的质子浓度、CO2浓度和SO 4浓度与沸腾后的质子浓度之间的关系可以用几个简单的方程来明确定义。这些方程沿着与方解石和硬石膏的溶解度构成了显着的矿物沉积沸腾的化学边界条件。典型的热液流体在沸腾进行到汽相和液相体积相等的点时，将其大部分挥发性组分损失到汽相，并将其大部分金属损失到矿物相。在决定沸腾热液的化学演化过程中，当挥发性组分以类似于完全分馏（瑞利）蒸馏的方式从溶液分配到气相时，矿物沉积最剧烈。随着温度降低，用于从溶液中沉积金属的沸腾效率增加，并且溶液中的金属量通常降低，使得沸腾的净效应在约300摄氏度的温度下最有利于矿石形成。矿物和金属络合物的化学计量与CO2和H2S的相对挥发度相结合，决定了沸腾过程中矿物沉积的一般顺序。这些主要的变量，许多其他的小变量，以及它们的多重相互作用被严格地考虑。提出了许多假设的热液系统中沸腾沉积的矿石和脉石矿物的数量和共生。对这些结果的分析表明，在许多沸腾热液系统中，沸腾可能是最普遍有效的矿床沉积机制。
A thermodynamic model of boiling hydrothermal solutions is developed and applied over a wide range of physical and chemical conditions. Within the range of conditions observed in natural boiling hydrothermal systems the processes of liquid-vapor partitioning and the resultant effects on mineral solubilities are highly varied and complex. Metals that are complexed by chloride are deposited largely as a result of the decreasing proton concentration associated with CO 2 exsolution during boiling. Metal bisulfide complexes are destabilized most when the decrease in proton concentration is sluggish relative to the loss of H 2 S.Vaporization of only a few percent of a solution can decrease the proton concentration by several orders of magnitude when the CO 2 /H (super +) and CO 2 /Sigma SO 4 concentration ratios are initially high. The relationship between the proton, CO 2 , and Sigma SO 4 concentrations prior to boiling to the proton concentration after boiling is defined explicitly by a few simple equations. These equations along with the solubilities of calcite and anhydrite constitute the chemical boundary conditions for significant mineral deposition by boiling. Typical hydrothermal fluids lose most of their volatile components to the vapor phase and most of their metals to mineral phases by the time boiling has proceeded to the point where the volumes of the vapor and liquid phases are equal.Physical variables such as the heat budget and the restrictions on the partitioning of mass between liquid and vapor, although significant, are subordinate to the compositional variables in determining the chemical evolution of a boiling hydrothermal solution. Mineral deposition is most vigorous when the volatile components partition from the solution to the vapor phase in a manner resembling perfect fractional (Rayleigh) distillation. As temperature decreases, the efficiency of boiling for depositing metals from solution increases, and the amount of metals in solution typically decreases such that the net effect of boiling is most favorable for ore formation at temperatures around 300 degrees C. Mineral and metal complex stoichiometries in combination with the relative volatilities of CO 2 and H 2 S determine the general sequence of mineral deposition during boiling. These major variables, many other minor variables, and the multiple interactions thereof are accounted for rigorously. The amount and paragenesis of ore and gangue minerals deposited by boiling are presented for numerous hypothetical hydrothermal systems. Analysis of these results suggests that boiling is perhaps the most generally effective ore depositional mechanism at the conditions operative in many boiling hydrothermal systems.