21.
In a cut-and-fill stope, the main purpose of back filling is to

26.
The sale value of chromite ore from an open pit mine is Rs. 6500 per tonne. Cost of mining, excluding stripping cost, is Rs. 2450 per tonne. If the cost of stripping is Rs. 1150 per m3, the breakeven stripping ratio in m3/tonne is

27.
From a hard rock open pit mine, the following data available
Burden : 3 m
Spacing : 4 m
Bench height : 12 m
Sub-drilling : 1 m
Collar stemming : 4 m
Diameter of hole : 150 mm
Density of rock : 2500 kg/m3
Density of explosive : 800 kg/m3
The powder factor in kg/t is

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