Once a prospect has been identified, and the right to explore it acquired, assessing it involves advancing through a progressive series of definable exploration stages. Positive results in any stage will lead to advance to the next stage and an escalation of the exploration effort. Negative results mean that the prospect will be discarded, sold or joint ventured to another party, or simply put on hold until the acquisition of fresh information/ideas/technology leads to its being reactivated. Although the great variety of possible prospect types mean that there will be some differences in the exploration process for individual cases, prospect exploration will generally go through the stages listed below.
Target Generation
This includes all exploration on the prospect undertaken prior to the drilling of holes directly targeted on potential ore.The aim of the exploration is to define such targets. The procedures carried out in this stage could include some or all of the following:
- a review of all available information on the prospect, such as government geological mapping and geophysical surveys, the results of previous exploration and the known occurrence of minerals.
- preliminary geological interpretations of air photographs and remote sensed imagery.
- regional and detailed geological mapping.
- detailed rock-chip and soil sampling for geochemistry.
- regional and detailed geophysical surveys.
- shallow pattern drilling for regolith or bedrock geochemistry.
- drilling aimed at increasing geological knowledge.
Target Drilling
This stage is aimed at achieving an intersection of ore, or potential ore. The testing will usually be by means of carefully targeted diamond or rotary-percussion drill holes, but more rarely trenching, pitting, sinking a shaft or driving an adit may be employed. This is probably the most critical stage of exploration since, depending on its results, decisions involving high costs and potential costs have to be made. If a decision is made that a potential ore body has been located, the costs of exploration will then dramatically escalate, often at the expense of other prospects. If it is decided to write a prospect off after this stage, there is always the possibility that an ore body has been missed.
Resource Evaluation Drilling
This stage provides answers to economic questions relating to the grade, tonnes and mining/metallurgical characteristics of the potential ore body. A good understanding of the nature of the mineralization should already have been achieved that understanding was probably a big factor in the confidence needed to move to this stage. Providing the data to answer the economic questions requires detailed pattern drilling and sampling. Because this can be such an expensive and time-consuming process, this drilling will often be carried out in two sub-stages with a minor decision point in between: an initial evaluation drilling and a later definition drilling stage. Evaluation and definition drilling provide the detail and confidence levels required to proceed to the final feasibility study.
Feasibility Study
This, the final stage in the process, is a desk-top due-diligence study that assesses all factors: geological, mining, environmental, political, economic relevant to the decision to mine. With very large projects, the costs involved in evaluation are such that a preliminary feasibility study is often carried out during the preceding resource evaluation stage. The preliminary feasibility study will identify whether the costs involved in exploration are appropriate to the returns that can be expected, as well as identify the nature of the data that must be acquired in order to bring the project to the final feasibility stage.