PERMFILE139344

• Permit No: M1996081
• IBM Index Class Name: Permit File
• Doc Name: MEMO-REVIEW OF SLOPE STABILITY ANALYSIS REPORT-FN M-96-081
• From: DMG
• To: BERHAN KEFFELEW
• Media Type: D
• Archive: No

DIVISION OF MINERALS AND GEOLOGY
Depanmenl of Nahnal Resources
1311 Sherman SL, Ruom 215
Denver, Colorado RO203
Phone: [phone]
FAY: 1303) 832 8106

_G-r_ e ~r_'r__
III IIIIIIIIIIIII III F
999
MEMORANDUM
TO: Berhan Keffelew /~~
FROM: James Dillie ~/~/'~
RE: Review of Slope Stability Analysis Report - File No. M-96-081
~~~ l
DEPARTMENT OF
NATURAL
RESOURCES
Roy Romer
Governor
lames 5. Lochhead
Eseculrve Diredo.
Michael B. Long
Division Direnor
Per your request, I reviewed the proposed mining and reclamation plans (pages 10-12 inclusive) for the
turquoise mine near Cripple Creek. Specifically, the information regarding slope failure was analyzed
to determine whether or not the mining activity would adversely affect any man-made structure located
within 200 feet of the affected lands.
The applicant states that "experience in the district at the permit site, the Portland Pit and the
Altman/Goldstar pit has shown [hat a 50 degree overall pit slope would be adequate." Adequate,
apparently, to prevent slope failure. The operator proposes to mine the pit to a depth of 50 feet. The
bottom 35 foot bench would have a 70 degree outslope and the top 15 foot bench would be mined a[ a
1:1 (45 degree) outslope. A 50 - 55 degree overall slope could be achieved by this mining method.
The operator describes the upper layer of material (l5 feet) as a decomposed rock but did not describe
the bottom 35 foot layer. In general, rock characteristics in the Cripple Creek area are described as a
partially-mostly decomposed granite at the surface with solid to partially weathered-highly fractured
granite -granite schist underneath.
Decomposed granite can be safely mined at a 1:1 outslope since the angle of repose is about 45 degrees.
Except for minor disturbances at [he surface, slope failure is usually non-existent at the angle of repose
(assumes no seismic activity). Slope failure of the competent layer is not a concern at this site due to the
small size of the pit . if a slope failure did occur, the material could only move a short distance. This
type of slope failure would not be significant enough to adversely affect structures outside the permit
area.
As proposed, backfilling the pit is part of the reclamation plan. Slope stability will not be a concern once
the pit is reclaimed.
If you need anything else, let me know.
COLORADO
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