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The coal reserves in protection pillar of roadways are expected to be left in the mining processin underground mines in Quangninh coal basin which is relatively large (about 16% of the total reserves).If it can be exploited, it will help to save non-renewable coal resources, reduce the cost of preparingroadway meters, extend the mine life and increase the efficiency of construction investment. In the world,in order to reduce coal loss in protection pillar of roadways, mining technology to exploit and use artificialprotection pillars are quite popular. Accordingly, in order to simultaneously exploit coal in the protectionpillar and maintain the transport roadway as a ventilation roadway for the longwall in below level, thepost-mining coal pillar will be replaced by artificial pillars formed from the stone backfill cribs, columns,metal cribs, chemical materials or low-grade concrete mortar mixes formed from fly ash, bottom ash ofthermal power plants, combined crushed waste rock and a cement additive,... This paper will evaluate thepossibility and propose a number of mining technological scheme as well as the type of constructionmaterials suitable for artificial columns.

Muong Lat granitoid complex located in Thanh Hoa province. It is composed of two mica granite, aplite and pegmatoid. Rock forming minerals include mainly K-feldspar, quartz biotite and muscovite. Crystallization age of pegmatite in Muong Lat body is determined by U-Pb zircon LA-ICP-MS method. Most of the analytical results 206Pb age / 238U ranged from 217–238 Ma, average 230 ± 7 Ma. Age results indicate, the existence magma activity in the study area. Three inherited zircon core gaves age of ~2.8Ga, ~2.4Ga, ~1.8Ga, ~400Ma and ~750 Ma, suggesting that the continental crust of the study area including material composition of the Neoarchean, Paleoproterozoic, Paleozoic and Neoproterozoic