Problem 1: A retreat long wall coal mining system utilizes twin accesses on both the intake and return sides of a panel whose face width is 300m. If the access drives are 5m wide and chain pillars are 20m wide between the accesses determine the extraction ratio for the following cases:
a) Panel under development
b) Panel under production
It may be assumed that rib pillars 40 m wide are left for support between panels. It can also be assumed that a barrier pillar of 40 m width is left to protect the main mine entries and that the panel length is 3km.
Problem 2: A company changes stopping methods and discovers that the new method gives a substantially higher dilution rate and yet the profit margin is higher. Show by simple calculation how this can come about.
Problem 3: An ore body dips at 90° and has a vertical depth of 140m. The top of the ore body is 180m from the surface and surface mining operations have been discarded in favour of underground operations. The strike length of the deposit is 350m. The ore body varies from 8m to 20m and averages 15m.
Grades are as follows:
Lead =10%(90% recovery)
Zinc =15%(85% recovery)
Silver =120 g/t(60% recovery)
Gold =2 g/t(50% recovery)
What is the total ore resource in tonnes, assume an SG of 3.6, and what is it worth at today's metal prices in A$?
Note: to calculate the worth of an ore body recovery must be considered. Recovery as quoted in the above figures means mill recovery.
Problem 4: The diagram below illustrates the amount of coal that is left intact after mining in pillars and the amount of coal that is extracted in the rooms. If al = 20m, a2 = 22.5 m, b1 = 5m and b2 = 4.5m determine the recovery ratio in a 2.5 m coal seam.
Attachment:- Coal extraction.rar