LATROBE VALLEY, VICTORIA, AUSTRALIA - A WORLD-CLASS BROWN-COAL DEPOSIT

The Latrobe Valley brown coalfields are situated some 150 km east of M elbourne in the State of Victoria, Australia. The brown coals of the L atrobe Valley were deposited within the Gippsland Basin of Victoria, A ustralia, during the Eocene to Late Miocene. The coal forms par-t of a sequence of essentially non-marine sands, clays and coals, comprising the Latrobe Valley Group. Three stratigraphic units; namely the Trara lgon, Morwell and Yallourn Formations in ascending sequence, contain t he three main coal seam groups. The seams, which form some of the thic kest continuous coal successions in the world, generally accumulated i n place, within distinct coal depocentres. The major coal depocentres largely occur to the south of the Latrobe River and west of a marine i nterface with the Gippsland Limestone. Only the Traralgon seam occurs both below the marine sediments and extends partly into the Latrobe Va lley. The depocentres are not generally spatially coincident but have shifted with time, probably due to differential compaction. Facies equ ivalents to the major coal seams comprise kaolinitic clays with sands predominating towards the marine interface. The clay sequences are int erpreted as being thick lacustrine sequences which effectively surroun ded the peat swamps and protected them from the more destructive fluvi al inputs coming from higher ground beyond the Latrobe Valley edges. A s a result, the peat swamps became stabilised for long periods of time and have produced thick brown coal seams. Nutrients were brought into the coal swamps via lateral diffusion from the lakes and by rising gr oundwater from the underlying aquifer systems of the Traralgon Formati on. Towards the central parts of the Latrobe Valley, thin brackish-mar ine silts are recognized within the terrestrial sequence of the Morwel l and Yallourn Formations and these grade laterally eastward into the marine deposits of the Seaspray Group. The marine equivalents of the T raralgon Formation lie further east beyond the Latrobe Valley limits, beneath Bass Strait. In the late Tertiary, the brown coal-bearing stra ta in the Latrobe Valley were folded, eroded and covered by a ''sheet' ' of Pliocene-Pleistocene fluvial gravels, sands and clays. The major folds are monoclines. The Latrobe Valley coals can be classified as so ft brown coal. Their high moisture content (range 48-70%) and therefor e low specific energy (net wet specific energy range 5.8-11.5 MJ/kg) m akes the coal a low-grade fuel. A wide relative change in physical and chemical properties occurs both laterally and vertically across the L atrobe Valley. The ash levels in brown coals throughout the valley are generally less than 5%, dry basis. The total brown coal resource in t he onshore Gippsland Basin is estimated as 395,000 million t. Approxim ately one third of this coal is classified as demonstrated and the rem ainder as infer-red. The latest published reserve estimates for the Gi ppsland Basin are 98,000 million tonnes (Mt), with some 33,000 Mt excl uded for town reserves, etc.. giving a balance of 65 000 Mt of availab le brown coal. Brown coal production by the State Electricity Commissi on of Victoria from all Latrobe Valley Open Cuts between 1923 and June 1989, has amounted to approximately 1000 Mt.