Lignite overburden

Lignite, lignite overburden, and underclay were collected from a vertical section of a freshly exposed high wall at an actively mined pit in the Center mine. Figure 1 illustrates the lithologic sequence. 

The samples were collected from freshly exposed faces within open pit mines. The lignite, lignite overburden, and underclay were collected from two pits at the Beulah Mine where lignite is mined from the Beulah-Zap bed and from the Kinneman Creek bed in the Center mine. The sample collection procedures have been summarized by Karner ( 6) and Benson ( 7). 

Other Regions. In AustraUa, Victoria has the largest reserves, although smaller ones occur in southern AustraUa, western AustraUa, Tasmania, and Queensland (28). The main deposit consists of many thick seams in about 500 km of the Latrobe Valley. The YaHourn coal field provides most of the fuel. The top coal seam is 65 m thick and is covered with 13 m of overburden. Most of this coal is used for electric power generation. It is very moist (55—72%), but has less than 5% ash. The lignitic coal found in South AustraUa is, for the most part, too deep for economic recovery. However, some of the better deposits are mined for power generation. 

Seam thicknesses and depths vary tremendously. The most favorable deposits have shallow overburdens and thick seams that cover large areas. Acceptable stripping ratios, ie, overburden thickness to coal thickness, depend on the quaHty of the fuel. Ratios up to 10 1 have been used for bituminous coals, but lower ones are required for lignitic coals because of the lower heating value per unit weight. 

A study of the variation in the distribution of major, minor, and trace elements in lignite-bearing lithologic sequences is critical for both interpretation of deposi-tional environments and utilization of the coal. Samples of lignite of the Kinneman Creek Bed, underclay and overburden from the Center Mine were analyzed by neutron activation, x-ray fluorescence, and x-ray diffraction techniques. Major patterns of element distribution in the lignite include (1) concentration in the margins of the seam (Al, Si, S, Sc, Fe, Co, Ni, Zn, As, Zr, Ag, Ba, Ce, Sm, Eu,... 

Underclay and overburden sediments are typically clays with about 80% clay and 20% silt and muds with about 50% clay and 50% silt. The most distinct chemical variation in the overburden is the compact siderite- and dolomite-cemented concretion zone, 4.5 m above the base of the Kinneman Creek lignite. 

LRCs—for example, brown, lignite, and subbituminous coals—represent nearly one-half of the estimated coal resources in the world and are the only source of low-cost energy in many developing nations. LRCs are typically present in thicker seams with less overburden than bituminous coals, thus making them recoverable by low-cost strip mining. 

As the processes of coaliflcation (i.e., the transformation resulting from the increased temperatures and pressures) continue, there is a progressive transformation of the deposit the proportion of carbon relative to oxygen rises and volatile substances and water are driven out. Continued compaction by overburden then converts lignite into bituminous (or soft) coal and finally into anthracite (or hard) coal. 

TLS Scanner Mirror (Control Points) Overburden Lignite... 

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