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RUG. 1. 2600 12~S~PM DIViMINERAL c f•{0.317 P.lib <br /> • iII IIIIIIIIIIIII III • <br /> - ST A TE O F CO LO N <br />1373 <br />phone: <br />FAX: (3 <br />J OP MINERALS AND GEOLOGY <br />t of Namnl Resources - <br />nan Sc., Room 2i5 <br />dorada 80203 <br />3) 866-3567 <br />832.8106 <br />DAT 7uly 31, 2000 <br />TO: Bob Oswald <br />Poat•It• Fax NDte 7871 D~ -/-~ po8ey- <br />Te ~ 3 Fnm <br />Ce.IDept - ~~ AM Co. ~ r /~DivsV.~~ <br />PnonO Y Phone fr <br />Pex a - 7©~ z 7- to <br />Allen Sorenson <br />RE: <br />The p: <br />slope <br />inform <br />unwer <br />Green <br />in the <br />highw <br />point <br />stable <br />The D <br />weath <br />steep ', <br />geology <br />highw <br />create <br />I3ighwall Stability, Gunnison Gravel, <br />qo~ cF~G <br />~~~,, oy FO <br />UO <br />ketson Permit No. M•78.305 <br />I~ouV°k~0.1~ G/-off <br />D I~ISION OF <br />MIN RALS <br />GEO~OGY <br />0.EC LA ATION <br />MINING SAFGTY <br />nai oven, <br />Govamd <br />Creg E. w: <br />r~•eel~ve 1 <br />Mkhxl A. <br />Dlvlllon D <br />posed mine plan for the DiclcersoA Pit would leave a 200 foot high quarry face with an overall <br />f 1:1 by creating five 40 foot r/i l highwalls and 20 foot wide catch benches, Geologic <br />ttion provided aze statements from Celia Greenman of the Colorado Geological Survey that the <br />tiered granite end 'GVest Ells Breccia exposed in the pit are 'very resistant, hard rock." Ms. <br />lam did not evaluate the weathered and decomposed granite or the quartzite that aze also present <br />uatry, Tlu Rules of the Mined Land Reclamation Board require that "If not eliminated, all <br />lls shall be stabilized," (Rule 3.1.5(3)). The information provided by Gunnison Gravel to this <br />insufficient to make a deterutinatioa that the proposed final highwall configuration will be <br />This atemorandum outlines the type of information that will be required. <br />ision of Minerals and Geology must make a finding that the geologic conditions in the <br />;d and unweathered granite and the West Elk Breccia of the Dickerson Pit aze favorable for <br />slopes in order to approve the final configuration groposedby the Operator. Favorable <br />conditions relate not only to the nature of the intact rock, but also to the aspect of the final <br />~, the orientation and condition of the geologic structure,.and to the excavation practices used to <br />c final highwaU, To facilitate a finding by the Division that conditions aze favorable and to <br />the highwall proposal, certain geologic iavestigatlons aze required. <br />:lure mapping is required to evaluate the influence of natural fracture weakness in relation to the <br />K rock. Natural fractures, joints, faults, and foliation normally control slope failure in track <br />es. Adverse orientation of these structures occurs when down dipping fractures or fracture <br />ges daylight in a highwall. This condition is illustrated in the attached figure 1. The Operator <br />t measure the strike and dip of fractures and foliation exposed in the current pit to determine if <br />adverse orientations exist. A person experienced in measuring fracture orientations must be <br />cloyed to conduct the mapping. Typically the results of the measurements aze depicted on a <br />midt equal-azea net to evaluate the dominant fracture orientations. <br />2. T strength of the rock exposed in the pit wall must be evaluated. The attached table 1 provides a <br />us ful rock classification system. Any azeas of rock that fall below the R2 strength classification <br />ar not suitable for reclamation as a beached or terraced highwall, and should be reclaimed like an <br />