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摘要
The Ion-adsorption type rare earth (iRee) deposits in Yunnan Province are mainly distributed in the southwest where the altitude is higher than 1000m, and thus are different from the Nanling range in China. The main bedrock types are monzogranite and moyite distributed along the Sanjiang fault. Zircons from the parent rock of iRee deposits yield a concordant U-Pb age ranging from 208~240 Ma to 52~80 Ma. Based on the LREE/HREE ratio, the bedrocks are divided into two types: light rare earth (LREE: La-Eu) type and heavy rare earth (HREE: Gd-Yb+Y) type. The LREE type rocks with partially enriched HREE deserve more attention as they may become an important resource for the ion-adsorption type of HREE (iHREE) deposit. REE-bearing minerals play a decisive role towards contribution to REE in parent rocks. There are few REE in plagioclase, biotite and amphibole, whereas REE-bearing accessory minerals contribute abundant REE to REE-rich rocks. The type and intensity of metasomatism in the bedrock determines the categories of REE-rich minerals. Most of the LREE-rich minerals such as allanite, apatite, monazite, britholite, bastnaesite andcerfluorite tend to be enriched in the early stages. The HREE-rich stage builds stronger complexes with fluoride and carbonate relative to LREE at ambient temperature, thereby increasing the concentration of the HREE and crystalized minerals like xenotime, yttrocrasite, yttrofluorite and Bastnaesite-(Y). Dissolution of different minerals in the weathering crust would result in a different type of deposit. The former, previously enriched in LREE, tend to subsequently be enriched in HREE. The weathering crust can be divided into detrital, clay,and accessory minerals. REE-bearing clay is the ore. It is generally accepted that the REE were mobilized and fractionated during intense weathering of the REE-rich granite in low altitudes where the continuous and repeated weathering under warm and humid conditionsplayed an important role. ? 2020, Science Press. All right reserved.
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