沉淀-陈化-返溶作用和压力对热液中氟钛络合物高温水解的影响及地质意义

The effects of precipitation-aging-re-dissolution and pressure on hydrolysis of fluorine-rich titanium complexes in hydrothermal fluids and its geological implications

钛是自然界中最不活泼的金属元素之一,然而越来越多的证据显示钛可以在特定条件下能进入热液流体中发生迁移,其中氟可能在其中扮演着重要的角色。本文研究了300℃和50~400MPa压力条件下氟钛络合物（K2Ti F6）的稳定性以及沉淀-陈化-返溶作用和压力对氟钛络合物水解行为的影响。研究结果显示,氟钛络合物水解的过程中,由于Ti O2沉淀物的陈化作用,在稳定的温度和压力条件下,沉淀物的返溶很难发生;但在缓慢降温和机械性振荡过程中,沉淀物的返溶会明显发生。而且,在温度不变的情况下,压力的改变对K2Ti F6水解并没有显著的影响,显示氟钛络合物不管在高压还是低压环境下均遵循近似的水解规律。本文认为主要的原因在于压力的增高会促进水解反应沉淀物的陈化,进而抑制沉淀物的返溶,但并不破坏水解反应的平衡。最后,本文提出金属络合物的形成-水解-沉淀/返溶-陈化过程是水-岩作用或热液成矿过程中高场强元素活化、迁移和成矿的主要机制。

Titanium is one of the least active metal elements in nature. More and more evidences, however, support that titanium can be transported by hydrothermal fluids in certain conditions, where fluorine plays an important role in it. In this study, the stability of F-rich titanium complex, K2TiF6, was studies at temperature of 300℃ and pressures from 50MPa to 400MPa to investigate the effects of precipitation-aging-re-dissolution process and pressure. The results show that during the hydrolysis of the F-rich titanium complex the precipitates cannot re-dissolve into the fluids under a constant temperature and pressure condition, but it happens obviously with a slow cooling and in a vibrating process. Moreover, the pressure does not affect the hydrolysis of K2TiF6 significantly in the case of constant temperature, indicating that similar regularity is obeyed when K2TiF6 hydrolyzes regardless of various pressure conditions. The main reason is that increasing pressure indeed promotes the aging process on the precipitates, and thus refrains from the re- dissolution on the precipitates, which is not likely to upset the reaction equilibrium of the hydrolysis of K2TiF6. Finally, this study infers that for the F-rich metal complex the formation-hydrolysis-precipitation/re-dissolution-aging process is a primary mechanism on the mobilities, migrations and mineralizations of the high field strength elements during the water-rock reaction or in a hydrothermal mineralization process.