2012-01-27_REPORT - M1973021 - Laserfiche WebLink

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5.2 Central Quarry The observed condition of the slopes within the Central Quarry appears to be stable. Observations of the Central Quarry include: • No large scale failures in the past year. • Minor accumulations of small rocks (up to 1'/2 feet diameter) on bench surfaces. • Nearly all material was contained on the adjacent bench surfaces with very little evidence of the material proceeding down slope to subsequent benches or into the water storage reservoir. • The stabilized slope in the northeast section of the Quarry did not exhibit any instability or large erosional features. • The highwall face adjacent to the haul road did not exhibit any instability or large erosional features. 5.3 South Quarry Mining in the South Quarry in 2011 appeared to adhere to the mine plan and did not extend the quarry depth below approximate elevation of 6700. Rock observed in the highwalls consisted primarily of biotite and granitic gneiss with localized areas of pegmatitic intrusions. Rock exposed at elevation 7350 and 7250 and portions of the rock exposed at elevation 6700 appeared fresh to moderately weathered. Portions of rock exposed at elevation 6760, and 6700 and associated with the fault zone appeared weak (poor), highly weathered, and altered by shear. Highwall orientations are primarily north to south (east facing) with a localized east to west (north and south facing) highwall on bench 6700. Foliation and joint orientations are favorable with respect to this highwall development plan. Tetra Tech is currently evaluating future highwall development options for the South Quarry. Recommendations will be provided in a forthcoming technical revision to the mine permit. Rock observed in the highwalls was predominantly competent with the following exceptions: • Bench 6700 stations 8 +60 to 13 +80 consisted of altered sillimanitic gneiss that is very poor in quality and appears to be related to the fault zone. Local instability due to overtopping has occurred. The instability is roughly parallel to the zone of weak rock associated with the fault. Extra caution should be taken when developing highwalls in areas shear this rock is present. If, during mining, this rock is encountered in areas not mentioned in this report, Tetra Tech should be contacted and the areas evaluated. • Throughout the South Quarry, there are localized zones of more highly fractured and weathered material that will tend to ravel. Raveling will tend to be caught on the underlying benches. Extra care should be taken in these areas. These areas are outlined in the field data section of this report. • The movement was on the order of 4 to 6 feet northeast and appeared to be the result of overtopping. Immediately to the south the rock is strong. • Highwalls near the fault zone will be monitored and observed for movement. Care should be taken when removing the weak rock because the strong rock - 11 - Morrison Quarry Annual Report 2011 P.\23514 \133- 23514 -1 2002 \ Deliverables \Deliv -01- Annual Report \Annual_Report_20I 1_Geotech doc January 2012