PERMFILE106632

• Permit No: M1988112
• IBM Index Class Name: Permit File
• Doc Date: 3/2/1989
• Doc Name: GEOTECHNICAL EVALUATION FOR THE SOUTH WALL WEST PIT SAN LUIS PROJECT
• Media Type: D
• Archive: No

i 0 INTPODUCTI
g ..r,a s= .r c
' Battle Mountain Gold Cpmpany (BMG) Is In the process Of developing the San Luls Pro)ect In
Colorado. The slope stabillty evaluation previously completed by Steffen Robertson and Klrslen
(SRK/88) had Identlfletl the south wall of the West Plt as an area which required further
' Investlgetlon.
A drill program under the direction of SRK was Implemented in December of 1988 at the request of
' BMG. The purpose of the Investigation was to assess the geotechnlcal and hydroNoglcal
characteristics pf the materials that would potentially Influence the stabillty of the Wesl PII In the
vicinity of the Rlto Seco.
'
2.0 PROJECT DESCRIPTION
' The revised ultimate pit limits employing SAK slope design recommendations (SRK/88) are shown
In Figure 1. The proximity of the final south wall to the Rlto Seco River varies from 600 feet along
' section 2,045,500E to 1 BD feet along section 2,046,500E. The closest approach to the south Inrall
Ilan obliquely to section 2,046,650E and Is In the order of 125 ft. as measured perpendicular to the
crest of the pit and the Rho Seco. The soli units comprising the south wall Consist of alluvium and
1 Santa Fe (fanglomerate and eollan) materials and are underlain by a competent bl~othe gneiss rock
unit. The "Green Clay" fault forms the contact between the sot! and rock unh. Prior studies
' (SRK/88) had shown that the south wall could be designed at an angle of 38 degrees assuming
that dry condltlons could be achieved. The ImpllCatlons of the Alto Seco on the stabillty of the
south wall and the potential for pit recharge Is assessed in this study.
' Th
l
y consisted of
e proposed geotechnlcal program Is described in detail In Appendix I and Initial
drllling three to six vertical coreholea located along the perimeter of the south wall ~t the West Pit.
' Due to dlftlcult drilling condltlons encountered In the allWlum and weather constraVnts only the
2,046,500E section of drllling was completed. This section has the ultimate ph cress being
' approximately 180 feat from the Rho Seco. This section was employed for purposes of testing and
design. Further deilneatlon of the south wall w111 ba corducted by trenching along the perimeter
during the production phase of mining. This report summarizes the drill program artd testing that
' have been conducted to date and the implications on stability.
2.1 Method of Investigation

The geotechnlcal program consisted of:
' a) Drllting three vertical holes along section 2,046,500E as shown In Figure 1. Holes G1 and
G3 were cored to 155 and a3 test respectively as shown in Figure 2. This euiabltid a
' stratlgraphlc section to be developed through the alluvium artd Sente Fe materlal6. Hde
G2 was rotary drilled In the vicinity of 01(10 feet east) to a depth Of 43 fee'.
1