云南腾冲地热区主要蚀变矿物含量与蚀变母岩的关系

The Relationship between the Contents of Principal Altered Minerals and the Original Rocks in Tengchong Geothermal Area, Yunnan Province

腾冲地热区出露有众多热泉泉群,地热活动频繁,岩石发生强烈蚀变,形成的主要蚀变矿物包括高岭石、绢云母、蒙脱石、I/M间层矿物、石英和蛋白石。主要蚀变矿物的种类和含量受蚀变母岩性质的控制,花岗质砂砾岩和花岗岩形成高岭石,玄武岩形成伊利石和蒙托石,安山岩中发育硅化作用。泥化作用增强的趋势是安山岩→花岗岩→玄武岩→花岗质砂砾岩。由于花岗质砂砾岩在热区内广泛分布,通过蚀变作用形成了有经济价值的高岭土矿床。

Tengchong, one of the largest geothermal areasin China, covers an area of 6000 km^2 and is noted for a great number of hot springs. As a result of frequent geothermal activities, all the rocks, mainly late Tertiary arkose and arkosic conglomerate composed of granitic gravels, granites basalts and andesites, have been altered intensely. The hydrothermal altered, mineral assemblages include (1) siliceous minerals, dominantly quartz and opal; (2) sulfates, mainly alunite; (3) kaolin minerals, chiefly kaolinite with small amounts of halloysite and dickite; (4) montmorillonite and chlorite; (5) interstratified minerals of illite/montmorillonite (I/M); (6) phosphates such as goyazite and woodhouseite.The species and contents of the principal altered minerals are controlled by properties of the original rocks. Generally speaking, arkose and arkosic conglomerate and granites have been altered into kaolinite, and basalts into illite and smectite together with a little interstratified minerals of I/M. Silicified minerals are often developed in andesites. There occurs the sequence of argillization from andesite-granites-basalts-arkose and arkosic conglomerates in which kaolinization is developed widely.Different altered minerals are distributed selectively in different grain diameters. Studies show that kaolinites are enriched in the grain size of<2μm, interstratified minerals of I/M in the grain size of<1μm, and sericites, quartz and opal gathered together in the coarse grains.Studies show that arkose and arkosic conglomerates are responsible for the formation of kaolin minerals in the process of alteration. The kaolin deposit is formed through geothermal alteration of these rocks because they are extensively distributed in the geothermal area.