Examining the planning stages in underground metal mines.

摘要

Many underground metal mining operations are facing critical challenges such as increasing depth or low commodity prices. These challenges threaten the survival of these operations and highlight the need for a systematic mine planning approach to provide management with a clear understanding of the orebody, including its mineability and potential profitability. In the past, underground hardrock mine planning has been either based solely on the quantitative reserve information or has accepted over-idealized assumptions. The misjudgment of the orebody profitability caused by such simplified treatment may result in serious errors in project evaluation and hence mislead investment and other related decisions.; This thesis develops a progressive stage-based mine planning model for underground metal mines. It solves two major problems involved in the mine planning stages, the production scale optimization problem defined in the preproduction planning stage and the development strategy definition problem specified in the production development planning stage.; Based on the orebody homogeneity assumption, the production scale optimization addresses the procedures of defining optimal production rate, production level, and planning cutoff grade by using net present value optimization and total (unit) profit maximization techniques. Unlike most of the previous attempts, this thesis considers the production level and rate as equally important indicators of the production scale. Detailed description on the interrelationship and interaction of the production rate and level is provided, and a process to optimize them together is presented.; The development strategy definition looks more into the inside features of the orebody and provides a positive approach to examine the mineability of the orebody. The mine development strategy is optimized by the total development profit maximization under the principle that only the payable material is developed and extracted. Unlike at the preproduction planning stage when the orebody mineability is judged exclusively by the cutoff grade and the orebody is treated as a mass of equally accessible material, the production development planning stage studies the mineability of each part of the orebody. A complex development layout optimization and orebody mineability examination process is introduced in detail, including dividing the orebody into mining blocks and iteratively estimating and assigning the cost and profit values to the blocks according to their location, grade and proximity to adjacent blocks.; Further to the discussion of these two fundamental optimization problems, the effects of the grade distribution and other external and internal factors on the orebody mineability and profitability are examined. It is concluded that the mineability of the orebody can not be judged by a single cutoff grade alone, and the grade variability within the orebody may change the mineability of the orebody significantly. Also, other factors such as metal price may alter the development profitability critically and thus need special attention when determining the investment strategy of the corporation.