The time has now come to combine the economics introduced in Chapter 2 with the mineral inventory developed in Chapter 3 under the geometric constraints discussed in Chapter 4 to define the mineable portion of the overall inventory. The process involves the development and superposition of a geometric surface called a pit onto the mineral inventory. The mineable material becomes that lying within the pit boundaries. A vertical section taken through such a pit is shown in Figure 5.1. The size and shape of the pit depends upon economic factors and design/production constraints. With an increase in price the pit would expand in size assuming all other factors remained constant. The inverse is obviously also true. The pit existing at the end of mining is called the ‘final’ or the ‘ultimate’ pit. In between the birth and the death of an open-pit mine, there are a series of ‘intermediate’ pits. This chapter will present a series of procedures based upon:
(1) hand methods, (2) computer methods, and (3) computer assisted hand methods
Figure 5.1. Superposition of a pit onto a mineral inventory.