铅锌在热液中的迁移形式与富集机理

我国南方某些铅锌硫化物矿床与岩浆活动无直接联系,明显受“层、相、位”的控制。据矿体形态、产状、矿物共生组合和围岩蚀变等特征,以及包体测温和包体成分资料可以认为:该类矿床系经历了沉积-成岩作用初步富集成矿源层和部分矿体,以及后期地下热卤水型成矿热液强烈改造,叠加富集成矿所形成的典型层控矿床。欲研究这类矿床的成矿机制,首先要了解地下热卤水如何萃取成矿物质并演化为成矿热液,以及成矿物质以何种形式搬运迁移,何种因素促使其再次富集成矿等重要问题。围绕上述问题有的学者进行了一些实验和论述,但尚不能阐明铅锌活化迁移的条件、形式与定位机制。针对上述问题笔者进行了有关实验研究,并根据溶液中各组分同时平衡的热力学原理,引进函数(?)和(?),对实验数据进行处理,得出几点认识供研讨。

THE MIGRATION FORM AND CONCENTRATION MECHANISM OF LEAD-ZINC IN HYDROTHEMAL SOLUTION OF LOW-TEMPERATURE

Features of the mode and occurrence of ore bodies, the mineral assemblages and the texture and structure of ores in bed-bound Pb-Zn sulphide deposits are characterized by the syngenetic deposition diagenetic miner-algenesis and obvious remoulding of double thermal solution. In order to examine the possible migration forms and the concentration mechanism of lead and zinc during hydrothemal mineralization, we have made studies on the composition of mineral inclusion. of spholerite and calcite the sulful isotope of galena and sphalerite and the thermodynamic-condition analysis of mineralization. On this basis, the solubility of galena and sphalerite are determined in the NaCl-solution containing organic matters ( for example, α-Lam, H₃Cit, etc.) or NH₄OH, at 90℃. The phalerite solublity in NaCl-solution containing organic matters or NH₄OH has come up to the minimum metal concentration of mineralization (about n×10-5M), and it increases with the rise of concentration and temperature of ligand in the solution. A maximun solubility ( about 25× 10-5M) is found in α-Lam H₃C-it solution at 90℃. In addition, on the basis of the simultaneous equilibrium theory of hydrothermal system,the accumulative stable constants of diffrent zinc-lead in organic and organic complexes at different temperature ( 30°, 50°, 70°, 90°) and different ionic strength ( I= 0.1, 0.5), are determined within the ranges of 1 atm and the pH 4-8 by using the electrone potential method. This paper deals with the remobilization of leadzinc sulphide in source beds, its factors controlling its limit,the migration form, stability and distribution of lead and zinc in the low-temperature hyorothemal solution, the reproduction of sphalerite, the crystalline deposit of galena and the deposit mechanism of galena and sphalerite. Our study shows that the ability of remobilization and migration is linear with the Fronaenus function φ and the Ledan function ψ. Its limit is controlled by the kind and temperature of ligand ion in solution and the thermodynamic conditions of environment, such as T, Eh, and pH. In the Me-Cl-H_2O thermal saline water of low-temperature, the migration form of zinc is mainly Zn2+ when Log Cl- is -2. With the increase of T and (Cl-), Zn2+ is replaced by ZnCl_n2-n. ZnCl₃2-. and ZnCl₃1- is preponderant in high salinewa- ter. Pb2+prevails only at T100℃ and Log(Cl-)-2 . 5 . PbCl₂4 is preferred in all other conditions. On the basis of our study and analysis, we have pointed out that the mineralization solution is mainly the Na-Ca-Cl type of thermal brine water bearing nich orgahic matters. This kind of thermal brine water extracts metallogenetic elements from the source bed, and transports them to the favorable structural locations. Thus, they turn into lead-zinc sulfide deposits under the control of geochemical impediments.