Open Pit Mine Planning and Design, Two Volume Set & CD-ROM Pack, Third Edition, 3rd Edition

CHAPTER 6

Production planning

6.1 INTRODUCTION

In this chapter some of the production planning activities involved in an open pit mine will

be discussed. Specifically, attention will be devoted to mine life – production rate deter-

minations, push back design and sequencing, as well as providing some general guidance

regarding both long and short range planning activities.

The basic objectives or goals of extraction planning have been well stated by Mathieson

(1982):

– To mine the orebody in such a way that for each year the cost to produce a kilogram of

metal is a minimum, i.e., a philosophy of mining the ‘next best’ ore in sequence.

– To maintain operation viability within the plan through the incorporation of adequate

equipment operating room, haulage access to each active bench, etc.

– To incorporate sufficient exposed ore ‘insurance’ so as to counter the possibility of

mis-estimation of ore tonnages and grades in the reserve model. This is particularly true in

the early years which are so critical to economic success.

– To defer waste stripping requirements, as much as possible, and yet provide a relatively

smooth equipment and manpower build-up.

– To develop a logical and easily achievable start-up schedule with due recognition to

manpower training, pioneering activities, equipment deployment, infrastructure and logis-

tical support, thus minimizing the risk of delaying the initiation of positive cash flow from

the venture.

–To maximize design pit slope angles in response to adequate geotechnical investigations,

and yet through careful planning minimize the adverse impacts of any slope instability,

should it occur.

– To properly examine the economic merits of alternative ore production rate and cutoff

grade scenarios.

– To thoroughly subject the proposed mining strategy, equipment selection, and mine

development plan to ‘what if’ contingency planning, before a commitment to proceed is

made.

Planning is obviously an ongoing activity throughout the life of the mine. Plans are made

which apply to different time spans.

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There are two kinds of production planning which correspond to different time spans

(Couzens, 1979):

– Operational or short-range production planning is necessary for the function of an

operating mine.

– Long-range production planning is usually done for feasibility or budget studies. It

supplements pit design and reserve estimation work and is an important element in the

decision making process.

Couzens (1979) has provided some very useful advice which should be firmly kept in

mind by those involved in the longer term planning activities:

How would I plan this if I had to be the mine superintendent and actually make it work?

In guiding the planner, Couzens (1979) has proposed the following five planning

‘commandments’ or rules:

1. We must keep our objectives clearly defined while realizing that we are dealing with

estimates of grade, projections of geology, and guesses about economics. We must be open

to change.

2. We must communicate. If planning is not clear to those who must make decisions and

to those who must execute plans, then the planning will be either misunderstood or ignored.

3. We must remember that we are dealing with volumes of earth that must be moved in

sequence. Geometry is as important to a planner as is arithmetic.

4. We must remember that we are dealing with time. Volumes must be moved in time to

realize our production goals. The productive use of time will determine efficiency and cost

effectiveness.

5. We must seek acceptance of our plans such that they become the company’s goals and

not just the planner’s ideas.

This chapter will focus on the longer term planning aspects both during feasibility studies

and later production.

6.2 SOME BASIC MINE LIFE – PLANT SIZE CONCEPTS

To introduce this very important topic, an example problem will be considered. Assume

that a copper orebody has been thoroughly drilled out and a grade block model constructed.

Table 6.1 presents an initial estimate for the costs and recoveries.

Since they will be refined later, this step will be called Assumption 1.

The best estimate price (in this case $1/lb) is also selected (Assumption 2). From these

values an economic block model is constructed. The break-even grade for final pit limit

Table 6.1. Costs used to generate the

economic block model.

Mining cost (ore) =$1.00/ton

Mining cost (waste) =$1.00/ton

Milling cost =$2.80/ton

G&A cost (mining) =$0.17/ton

G&A cost (milling) =$0.40/ton ore

Smelting, refining and sales =$0.30/lb Cu

Overall metal recovery =$78%