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4.1.2 Effects of Coal Cleaning on n Bali y of Product Early in the planning stages for the Deserado <br />Mine, it was recognized that a coal prepazation plant would be necessary to provide a clean coal product <br />for the Bonanza Station because of the high projected ash content of the raw B and D Seam coals. The <br />' Deserado preparation plant is designed to produce a consistent, relatively low ash product from the raw <br />coal feed. Inherent ash in the coal (ash which cannot be removed by cleaning) generally runs in the <br />' range of about 6.2 wt % to 11 wt %. The average "as received" clean coal quality for calendar yeaz <br />1990 was 10,646 Btu/lb., 11.51% moisture, 0.45% sulfur, and 9.62% ash. <br />' Ash contributors include inseam non-coal partings and out of seam roof and floor rock referred to as <br />dilution. Dilution is added to the mined coal by inadvertent bumping of the floor and roof while mining <br />' rock-to-rock with the continuous miners. Dilution may also be added to the run-of-mine coal by <br />purposely mining poor roof to remove unstable rock and mining broken floor to provide good footing <br />for men and equipment. The lithology of both roof and floor rock determines to a large extent just how <br />' much out of seam material must be mined with the coal. <br />The Deserado preparation plant has a designed maximum reject capacity of 38 weight percent. This <br />means that only 38 weight percent of the raw coal feed can be high ash coal or non-coal inseam or out <br />of seam dilution which will be rejected by the prepazation plant. Experience at Deserado indicates that <br />' while mining development entries, dilution from roof and floor material can result in greater than 38% <br />preparation plant reject. However, roof and floor dilution at the longwall face is minimal. Typically, <br />about 75% of the daily coal production comes from the longwall face while the other 25% comes from <br />development mining of entries. The higher tonnage from the longwall face with lower percentage <br />dilution material reduces the effect of high dilution rates from development mining. As an example, <br />the Deserado Mine preparation plant reject averaged 15.5 weight percent of total run-of-mine coal feed <br />during 1990. While dilution from roof and floor is minimal at the longwalJ face, the occurrence of <br />major partings and splits will result in high in-seam dilution and high preparation plant reject rates. <br />The location of major partings in the B and D Seams which limit longwall mining are shown on Plates <br />10 and 12; the B and D seam isopach maps, respectively. <br />' 4.2 Mining Methods <br />' The Deserado Mine is an underground multiple seam mine from which coal is extracted by continuous <br />and longwal] mining methods. The mine plan is based upon mining two separate coal seams, the D <br />' Seam and the B Seam complex (hereafter called the B Seam). The D Seam, which overlies the B Seam, <br />averages about 7.5 feet thick. It is mineable throughout the southern and eastern part of the lease area, <br />but thins and becomes unmineable toward the northwest. Exploration drilling located east of and <br />adjacent to Lease C-44693 defines a major parting in the D Seam which limits the recoverable coal <br />18 <br />t <br />