INSPEC07603

• Permit No: M1977342
• IBM Index Class Name: Inspection
• Doc Date: 7/28/1981
• Doc Name: OBSERVATIONS ON SITE VISITATION TO HENDERSEN PROJECT AMAX CORP
• From: MLR
• To: JIM MCARDLE
• Media Type: D
• Archive: No

T
DEPARTMENT OF NATURAL RESOURCESD ~ Govrrnm III IIIIIIIIIIIII III
D. Monte Pascoe, Executive Director
MINED LAND RECLAMATION
423 Centennial Building, 1313 Sherman Street
Denver, Colorado 80203 Tel. [phone]
David C. Shelllon
Director
28 July 1981
M E M O R A N D U M
/NS~C 7/oN
T0: Jim McArdle
FROM: Jim Pendleton
RE: Observations Si Visitation to Hendersen Project, AMAX Corporation
Mina Sita:
The stope collapse pit appears to be controled by preexisting cleavage,
fracture or other plane of weakness. The upslope high wall clearly exposes
a neatly cleaned contact surface which is near vertical from bottom to about
75 feet below the scarp top and then rolls to about 75 degrees from horizontal
at the top of the scarp. The downslope wall of the collapse pit appears
controled by a high-angle fracture inclined at about 85 degrees from horizontal,
dipping into the center of the pit. The side walls do not appear cleanly
controled by any one preexisting plane of weakness.
I assume that the collapse pit will continue to enlarge along the axis
of the ore body as extraction progresses. It may also widen upslope and
downslope somewhat. The clean definition on existing shear surfaces may
tend to limit enlargement upslope and downslope. I observed no active rockfall
or collapse occurring during the five minutes which I spent in close proximity
to the collapse chimney. Only time will tell.
In general, the rock cuts at protals and other surface facilities seem
very stable throughout the mine and mill sites. The development waste pile
face does not appear particularly stable, however. The dumping of topsoil
down slopes at the angle of repose seems haphazard, at best. I beli•=_ve that
AMAX should be required to develop some workable plan for topsoiling and
revegetating the faces of the waste pile areas.
Mi11 Sita:
The only problem which I noticed during our visit to the mill site
is the lack of a definite plan involving the face of the tailings embankment.
Bench top surfaces grade in different directions with no continuous drainage
allowance. Topsoil is dumped down slope on benches with little control resulting
in extreme variation in coverage. Some bare spots exist. Thickness ranges from
0 to 18 inches of topsoil. In places a berm is left at the crest of the bench.
These berms appear to be the locus of tensional settlement cracking .snd gullying
of the topsoil. AMAX should be required to formulate a detailed plats for the
face of the tailings embankment, including final grading, topsoiling, provision
of permanent armoured dewatering facilities, and revegetating plans. Information
collected from piezometers existing and to be installed, as well as survey data
to verify the performance and stability of the embankment face, should be
submitted to the Division as a portion of annual reports.
cc: Joe Zalkind