Quarriable limit

Quarriable limit

The cost of removing overburden to extract mineral lying below it goes up as the quarrying operations extend to the dip side of the property and the thickness of overburden increases. The stripping ratio, thickness of overburden: thickness of mineral deposit therefore decides the economic working limit of quarrying, i.e. the quarriable limit. The softer the rock, the less is the expense of overburden removal and higher is the stripping ratio. The wages of labour, the selling price of mineral and the margin of profit are the major considerations in deciding the limiting ratio which is as follows in coal mines;

i. Manual quarrying 1.5 : 1

ii. Semi-mechanised quarrying 2 : 1

iii. Mechanised quarrying:

a. With dipper-shovel, dumper combination; 4 to 5 : 1

b. With draglines: 8 to 10 : 1

c. With bucket wheel excavators: 3 to 4 : 1

The maximum depth from the surface in existing mines in our country is 120 m but future mines are planned to reach a depth of nearly 480 m.