赋存于云南前寒武系中的宝石伟晶岩

GEM—BEARING PEGMATITE IN PRE—CAMBRIAN SERIES OF YUNNAN

云南的宝石90％以上来源于前寒武纪地层中,主要是赋存于其中的含宝石伟晶岩。哀牢山构造-岩浆-变质带和高黎贡山构造-岩浆-变质带是两大产宝石伟晶岩的岩带。宝石伟晶岩与高温低变质带直接有关,变质矿物相为矽线石+红柱石+黑云母±堇青石。宝石伟晶岩可分两个亚类:有核晶洞型伟晶岩和无核晶洞型伟晶岩。前者是原地生成的,宝石产于石英核之晶洞中,以海蓝宝石、工艺水晶→海蓝宝石、天河石、墨晶,以及F型黄玉、水晶→红绿宝石或OH型粉红色黄玉组合为主;后者是异地生成的,无石英核,晶洞可以出现在任何相带中,以绿色-多色碧玺→黄玉组合为主。宝石伟晶岩的围岩年龄,哀牢山岩带中的大于1958.Ma,高黎贡山岩带中的大于806Ma。宝石伟晶岩形成年龄,产于哀牢山的为25.2—28.7Ma,产于高黎贡山的为16.2Ma。

More than 90 percent of gem deposits in Yunnan are mined out from Pre-Cambrian strata as the pattern of gem-bearing pegmatite. The Ailao Moun-tain and the Gaoligong Mountain tectonic-magmatic-metamorphic belts are two large gem-bearing pegmatite zones. Occurrences of gem-bearing pegmati-tes are directly related to metamorphic zones of high-temperature and low-pressure with their metamorphic mineral facies composed of sillimanite+an-dalusite+biotite±cordierite. The gem-bearing pegmatite can be divided into two subtypes. Miarolitic pegmatite subtype with core was autochthonous. Gem is found in miarolitic cavities of quartz core. Crystal assemblage was mainly composed of aquama-rine, rock crystal of technical use→aquamarine, amazoriite, morion, F-type topaz, rock crystal→morganite or OH-type pink topaz. Pegmatite of non-core miarolitic subtype was allochthonous without quartz core in it. Miaro-litic cavities could be found in every facies zone. Mineral assemblage was mai-nly of verdelite-pleochromatic turmaline→topaz. Ages of wallrocks of gem-bearing pegmatite are older than 1958.3 Ma in the Ailao Mountain and older than 806 Ma in the Gaoligong Mountain. Ages of the gem-bearing pegmtite are 25.2-28.7 Ma in the Ailao Mountain and 16.2 Ma in the Gaoligong Mountain.