Discovery of coarse-grained bastnaesite in Dalucao rare earth element deposit,Sichuan Province,and its prospecting significance
The Dalucao deposit in Sichuan Province,China,is the only confirmed rare earth deposit associated with cryptoexplosion.It is characterized by shallow burial,high-grade ore and large tonnage.Bastnaesite,the primary rare earth industrial mineral identified in this deposit,is mainly found in the fine-to-micro cements of breccia ore and is not easy observable with the naked eye.In this study,we discovered coarse-grained to pegmatitic bastnae-site in the breccia ore of the deposit.These coarse-grained bastnaesite distribute in bastnaesite-bearing aegirine augite-fluorite-barite breccia,bastnaesite-bearing fluorite-barite-calcite breccia and bastnaesite-bearing calcite car-bonate breccia,they also appear as the bastnaesite mineral breccia.The bastnaesite grains in breccia usually ex-hibit plate columnar and granular morphology,occur as euhedral or subhedral crystals with varying size of medi-um-coarse or even pegmatitic,and mostly have cataclastic texture.The breccias are cemented by fine-to-micro-grained quartz-fluorite-cerite,and the cements also contain bastnaesites in the form of acicular crystal,tabular crystal or radiate-columnar aggregate,with grain size mostly smaller than 100um.The content of rare earth ox-ides(REO)in coarse-grained bastnaesite ranges between 65％and 71％,with a higher abundance of cerium and lanthanum(accounting for 82％～95％of the total rare earth content),and relatively lower proportions of praseo-dymium and neodymium(accounting for 4％～17％of the total rare earth content);the 206Pb/238U weighted average age obtained by LA-ICP-MS is(14.78±0.27)Ma(MSWD=1.1,n=21).The occurrence of coarse-grained bastnae-site in the Dalucao deposit makes the ore having higher grade,and also enhances its economic value(higher re-coverability).Furthermore,it suggests the possible occurrence of a certain scale of rare earth mineralization in the area prior to the formation of the cryptoexplosive brecciation,this indicates the possible presence of coarse grained or pegmatitic veins containing bastnaesite at depth in the deposit.
coarse-grained bastnaesitesbreccia REE oreU-Pb ageDalucao rare earth element depositSi-chuan Province
万方数据
维普
