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<br />4.1.2 Facts of Coal CleanlnQ on Qualify of Product Early in the planning stages Tor the <br />• Deserado Mine, it was recognized that a coal preparation plant would be necessary to provide a <br />' Gean coal product for the Bonanza Station because oT the high projected ash content of the raw B <br />and D Seam coals. The Deserado preparation plant is designed to produce a consistent, relatively <br />low ash product from the raw coal feed. Inherent ash in the coal (ash which cannot be removed by <br />' cleaning) generally runs in the range of about 6.2 wt 9o to 11 wt %. <br />' Ash contributors include inseam non-coal partings and out of seam roof and floor rock referred to <br />as dilution. Dilution is added to the mined coal by inadvertent bumping of the floor and roof while <br />mining rock-to-rock with the continuous miners. Dilution may also be added to the run-of-mine <br />' coal by purposely mining poor roof to remove unstable rock and mining broken floor to provide good <br />footing for men and equipment. The lithology of both roof and floor rock determines to a large extent <br />just how much out of seam material must be mined with the coal. <br />t 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 <br />or out of seam dilution which will be rejected by the preparation plant. Experience at Deserado <br />indicates that while mining development entries, dilution from roof and floor material can result in <br />' greater than 389'o preparation plant reject. However, roof and floor dilution at the longwall face Is <br />minimal. Typically, about 759'0 of the daily coal production comes from the longwall face while the <br />other 25% comes from development mining of entries. The higher tonnage from the longwall face <br />with lower percentage dilution material reduces the effect of high dilution rates from development <br />mining. While dilution from roof and floor is minimal at the longwall face, the occurrence of major <br />' partings and splits will result in high in-seam dilution and high preparation plant reject rates. The <br />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. During 1995, a raw coal bypass system <br />' utilizing an online ash analyzer was installed at Deserado to allow bypassing the preparation plant <br />with clean coal from the longwall panels. This system is successful but washing of coal primarily <br />' from the continuous miner sections is still anticipated. <br />4.2 Mlning Methods <br />' The Deserado Mine is an underground multiple seam mine from which coal is extracted by <br />continuous and longwall mining methods. The mine plan is based upon mining two separate coal <br />seams, the D Seam and the B Seam complex (hereafter called the B Seam). The D Seam, which <br />overlies the B Seam, averages about 7.5 feet thick. It is mineable throughout the southern and <br />' eastern part of the lease area, but thins and becomes unmineable toward the northwest. Exploration <br />drilling located east of and adjacent to Lease C-44693 defines a major parting in the D Seam which <br />limits the recoverable coal potential of the D Seam in that area. The B Seam reaches maximum <br />' thickness in leases C-8424 and C-8425 and is mineable throughout these areas. <br />'• 17 <br />