Investigation on Longtan Coal Series of Baohetang,Middle Hunan

Longtan coal series of Baohetang, Middle Hunan, has been investigated in detail by means of sedimentalogy, coal petrology and geochemistry. It is suggested that Baohetang coal was formed in delta environment. Most of coal seam I and n was formed in water-covered swamp that developed from distributary bay. The swamp was often influenced by river and tide. Boron contents of 17 coal samples range from 10 to 500ppm, concentrated in 50- 500ppm ( 15 samples) with an average of 152ppm. Comparition Baohetang coal with those deposited in fresh-water environment shows that the former is more boron-riched and which indicates brakish to semi-brakish water environment, moreover, their rations B / Ga, V / Zr, V / Ni. V / Zn and Sr / Ba are also different obviously. Fe₂O₃ contents of the 17 coal samples fall in the range of 4.54-20.07% with an average of 9.7%. and SO₃ contents from 0.48-10. 85% ( average 5. 85% ) , ratio of ( Fe₂O₃+CaO+MgO) / (Sio₂+Al₂O₃)from 0.08-0.78 with the mean of 0.34. Baohetang coal has striking features, mainly in coal petrology and Rock- Eval. The coal is characterised by low vitrinite content (from 30% to 52% ) , high sapropel groundmass and transitional macerals content 10%-21% and 25-49%. respectively) . Sapropel groundmass and some hydrogen-rich vitrinites exhausted a great deal of exudatinite, as a result, this makes the coal series contain a little oil. The coal has a higher production of S₂, ranging from 198.40-212.40 ( mg / g) , suggests its oil forming potential. The aboundant transitional macerals must have been carried into the water-covered swamp from the oxidized zone of bank-back swamp by flood or tide. The paleocurrent analysis reveals that the sediments came mainly from the east (Shuangfeng-Guandimiao ancient land ?) and the north (Longshan uplift). but not from Xuefeng ancient land. Otherwise, three kinds of sedimental structures (bunch cross-bedding, derived ripple and washing-filling structure) have been discribed in detail, A coal-forming modle of Baohetang coal has been established.