Discovery of A NeoProterozoic Pelite Bed Containing REE andNoble Metal Mineral Assemblages from the Dalian Area, China
Abstract: NeoProterozoic Sinian System of the Dalian District where is the only one outcrop area in North China, is recognized as a geonappe from South China Sinian System. The Sinian strata in the tourist scenic area of Golden Stone Beach area are composed of 7 formations (in ascending ward): the Yingchengzi(Z2y), the Shisanlitai(Z2s),the Majiatun(Z2m),the Cuijiatun(Z2c), the Zhoujiaweizi(Z2z), the Wangjiatan(Z2w),and the Xingmingchun(Z2x).REE minerals and noble metals bearing pelite is included in the Shisanlitai Formation which consists of rose colored stromatolite carbonate beds therefore the tourist scenic spot be named “Rose Garden” in the Goldstone Beach Scenic District. There are several greenish pelite beds where monazite and other REE minerals are found in the Shisanlitai Formation. Two beds among them are relative thicker than other, and more metal minerals are discovered.According to the change of ratio of FeO/Fe2O3 in strata, the main body rock of pink stromatolite limestone occurred in an oxidizing environment, however the greenish pelite in a reducing environment of a locally restrict area. Besides, a comparison of light rare earth elements (LREE) with North American Shale (NASC) shows that greenish pelite contains more LREEs but pink stromatolite limestone consists of less these elements than NASC. Further distinguished by three end-member diagram (La+Ce+Nd，Sm+Gd+Dy，and Yb+Y), the sediments deposited location of distance from marine beach shows that the greenish pelite beds should be near continent, but the pink stromatolite limestone be far away from continent.This paper issues a very rare slight metamorphosed NeoProterozoic pelite, which includes clastic and authigenicdiagenetic monazite, xenotime grains, as well as native gold, IrOs, Ir metal grains, zircon, rutile, apatite, ilmenite, hematite etc. heavy mineral associations, and some rock forming minerals. The pelite beds belong to NeoProterozoic Sinian System, the Shisanlitai Formation, which are composed of the interbedded reddish stromatolite limestone and greenish pelite intercalations. The sedimentary environmental textural facies indicators shows that there were a carbonate shore reef regions near the continent in the Shisanlitai Stage, which involves some likelagoon restrictive small basins under the reduction and oxidation alternation chemical condition and creates the favorable microenvironment for REE molecular exchanging to the authigenicdiagenetic monazite (“manshaped”, “birdshaped”) and xenotime (“catshaped”) in the syngenetic deposition and diagenetic stages. The noble metal grains are mainly clastic origin, but Au, Zn, Cu and Pb are related with oremade fluid. North China platform with the abundant REE elements and the noble metals is the original source of the NeoProterozoic REE minerals noble metals bearing pelite.