Study On The Coal Lithology And Coal Quality Features And Its Forming Environment Of The Mid-Lower Jurassic Coal Seam In Korjay Sunken,Turpan-Hami Basin

This paper takes Korjay Sunken coal seam of Turpan-Hami Basin as the research object,based on the data analysis of coal petrography identification,industrial analysis and ash composition index of main coal seam samples.On the basis of a systematic study of geological conditions such as the distribution of stratum and the characteristics of coal measures,methods such as coal geology,coal petrology and geochemistry were adopted.This paper comprehensively summarizes the coal seam occurrence and coal petrography and quality in each mining area,reveals its horizontal and vertical variation rules,and discusses the constraint of coal forming environment on coal petrography and quality.From west to east,there are 6 coal mining areas,such as Bostan,Burjay,Panjitage,Runtian-Runbei,Bosheng,Zhaohequan and so on.The coal seam is mainly developed in the strata of the Badaowan Formation(J₁b)and the Xishanyao Formation(J₂x)of the middle Jurassic,with ten main coal seams occurring from bottom to top.The coal petrography is characterized by the rich vitrinite and poor inertinite,low ash,low sulfur and high volatile.The coal ash is mainly composed of SiO₂and Al₂O_3.The coal metamorphism stage is low,and the coal is all belong to long-flame coal(CY).Sulfur and ash content decrease gradually from east to west in the Xishanyao Formation,but increased gradually from the edge to the center in the Badaowan Formation.The vertical evolution of coal seams present the various trends from deep to shallow described as:the V/I ratio change from small to big,the ash content change from high to low,the volatile change from low to high,the sulfur content increase initially to decrease second and increase afterwards,and the the reducibility increases gradually.In conclusion,the main coal seams of the Mid-lower Jurassic in this study area were formed in the sedimentary environments of alluvial fan,fan delta,shore-shallow lake and semi-deep lake.It has the characteristics of continental coal formation.The coal-forming environment is warm and humid.And there is a good correlation between coal petrography and quality parameters and coal forming environment.