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Richard D. Lamm <br />Governor <br />DATE <br />DEPARTMENT OF NATURAL RESOURCES <br />Davitl H. Getches, Executive Director <br />MINED LAN~DDD~_~LoML-T_~nN nivlc~nti <br />DAVID C.SHELTON,[ Z~_ Confidental?: <br />Permit #: <br />Class: Q. Type-Seq.: <br />From: t~ c-tC' To: <br />Doc. Name: i ~~,a ~`a-t ~Q-d'"~ ~' <br />March 28, 1984 Doc. Date (if no date stamp): ~- aTB~g~ <br />T0: Mark Loye <br />FROM: Jim Pendleton ~ 1~'""y~-- <br />RE: Geotechnica As s of "Pitch Mine Reclamation Plan Amendment to <br />Permit No. - HR" <br />Pursuant to your request, I have reviewed Homestake Mining Company's proposed <br />permit amendment for the Pitch Project Mine, Permit No. 77-4HR. I have <br />specifically reviewed geotechnical topics within this complex proposed permit <br />amendment. <br />The current proposal represents several significant amendments to the existing <br />approved permit. <br />(1) Post-Mining - Topographic grading is proposed to accommodate the large <br />existing landslide on the northeast wall of the existing North Pit. <br />(2) Final Reclaimed Configurations are proposed for the various overburden <br />dumps, including terracing and slope angle adjustments in some cases. <br />(3) Two lowgrade ore stockpiles/disposal structures are proposed. <br />(4) A final reclaimed drainage and erosion control system is proposed, <br />including a South Pit lake, four flow attenuation areas, and an <br />extensive surface drainage channel system. <br />(5) Reclamation costs are recalculated, based upon the proposed plan <br />amendments. <br />North Pit Landslide <br />Call and Nicholas, Inc., consultants to Homestake Mining Company, completed an <br />analysis of the existing landslide on the northeast wall of the North Pit at <br />the Pitch Project. Landsliding, which was first observed in August, 1979, has <br />reached a magnitude which has made it uneconomical to recover the remaining <br />ore within the North Pit. In August, 1979, a tension crack developed <br />approximately 500 feet upslope from the North Pit's northeast wall's crest. <br />In late 1983, the occurrence of subsequent tension crack head scarps had <br />migrated an additional 1,500 feet upslope from the northeast wall's crest. <br />Past observation suggest that upslope migration of the head scarp has greatly <br />423 Centennial Building, 1313 Sherman Street Denver, Colorado 80203 Tel. (30~) 866-3567 <br />