Terahertz spectroscopic characteristics of the geological diagenetic and metallogenic evolution

Abstract

The study of fluid inclusion is an important tool and method in mineral evolution research. The shape, number and size of fluid inclusions in halite crystals grown at different temperatures are different and can directly show the composition, temperature and pressure of the ore-forming fluids. Terahertz time-domain spectroscopy (THz-TDS) has been used to probe the inclusion of individual of the halite rock, exhibiting different spectral signals in the terahertz band. The relationship between absorption coefficient and temperature exhibited the nonlinear features at different frequencies, a fitted regression curve can present accordingly and the evolutionary regime of halite rock (early diagenetic phase, late diagenetic phase and approximate metamorphic phase) can be indicated by the absorption coefficient in the THz region. Furthermore, XRD and optical microscope as supplementary methods provide more information for us to understand the evolutionary regime of halite rock. The results show that under low temperature, the inclusion of individual is less but relatively large, arranged in relatively loose; at higher temperatures, the inclusion of individual were more, substantially along or parallel to the crystal surface, but individual size is relatively small. The present study of identification based on THz-TDS was in good agreement with X-ray diffraction (XRD) and optical microscopes, and the evolution is validated by theoretical simulations suggesting that the terahertz technology can act as a non-destructive, contact-free tool for the evolution of the geological diagenetic and metallogenic research. THz-TDS can be used as a complementary method for composition and characteristic analysis of ore-forming fluids in geological diagenetic research, realizing a lead in evolution of rock reservoir diagenetic systems study.