2014-06-26_PERMIT FILE - M2014027 (2)

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JOHN F. ABEL, JR. • MINING ENGINEER 310 LOOKOUT%NEW COURT GQI. EN CO&AO, TILEPROME 301 m•]100 J l z»-.wl April 18, 1985 Mr. George A. Holcomb R`C VEt Draco Mines 1144 Miracle Mile AUG 1 6 1985 Tucson, Arizona 85705 MINED LAND Dear George: RECLAMATION DIVISION I have three major recommendations for action with respect to ultimate pit slope design at the Crystal Hill Mining Co. pit: (1) Three detail line joint samples consisting of approximately 100 joints each should be taken in the pit. One each in the quartz latite, the sedimentary ash-fall tuff and the agglomerate. This can be accomplished by LaRon Taylor, geologist at the site. (2) Each of the rock units should be physically tested to determine the angles of surface and internal friction and to determine rock-on-rock and intact rock cohesion. I recommend that two uniaxial and six triaxial specimens be tested for each rock unit, and that three sets of specimens be tested in direct shear. A price list is conveniently attached. (3) The existing pit and haul road bench faces should be described by direction, slope angle, hieyht and rock unit involved. These bench faces are in effect test benches, against which the ultimate pit wall can be compared. Dan King, the mining engineer at the site, can probably develop this data. This is in effect bootstrapping, we will use the existing stability to demonstrate future stability. I have reached several tentative conclusions as the result of my visit. First, the already existing 60-ft high bench in the quartz latite indicates considerable stability. The face of this bench is iron stained along the two joints which control the approximately 72° bench face angle. The iron staining should decrease with depth. There is, however, no visual evidence as yet for such a decrease in weathering with depth, and, thereby, an increase in stability. The planned 10-ft wide bench width/40-ft bench height should providea stable overall pit wall angle of 600 on the northeast side of the pit. There was not sufficient exposure of northwest and southeast pit wall benches to do more than determine that the potentially adverse N48°E striking, 44° SE dipping joint set detected by R. D. Call is present in the agglomerate. The potentially adverse N48°E striking, 63°NW dipping joint set was not observed.