云南腾冲地热区I/M混层矿物的研究

A STUDY ON THE I/M MIXED-LAYER MINERALS FROM THE GEOTHERMAL ALTERATION AREA OF TENGCHONG,YUNNAN PROVINCE

云南腾冲地热区水热活动强烈,各种岩石明显蚀变,形成了硅化带、明矾石化带、高岭土化带、泥化带和规则混层带。I/M不规则混层主要产于高岭土化带和泥化带。I/M规则混层矿物出现在规则混层带,空间分布上与热泉出露区的方向一致,主要是高温地热蒸气与围岩发生交代作用的产物。I/M混层矿物是蚀变过程中由蒙脱石向高岭石转化的中间产物。

Tengchong, one of the largest geothermal alteration areas in China, coversan area of about 6000km^2 and embraces a great number of hot springs. Rocksof different origins have altered intensely because of evident geothermal activi-ty. Five alteration zones can be distinguished in terms of characteristic alter-ation mineral assemblages: (1)silicified zone; (2)alunized zone; (3)kaolinizedzone; (4)argillized zone; and(5)regular mixed-layer mineral zone. RegularI/M mixed-layer minerals were formed in the No.5 Zone and their distribu-tion is consistent with that of hot springs in the geothermal area and controlledby N-S extending faults. Calculation based on Weaver's curves indicates thatthe amount of expandable interstratification in irregular I/M mixed-layer min-erals comes up to 13-28%. IR study shows that the absorption features of the mixed-layer minerals areintermediate between those of illite and montmorillonite, The IR absorption, spectra of regular mixed-layer mierals are close to that of rectolite. The I/Mmixed-layer minerals tend to be transformed into kaolinite through the evolutionof montmorillonite→I/M mixed layer→illite during desilicification.