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Exploration
Minerals must group in a sufficient concentration if they are to be economically recovered. This circumstances that are likely to lead to this process must be understood, and suitable locations identified, before a deposit stands any realistic chance of being identified. Geologists will examine general structural maps (rock types and faulting patterns) before making a decision on where to drill.
Most of the world's mines are centred on the ancient 'shield' rocks of the Precambrian orogeny (comprising the Archaean period of 4.6 billion to 2.6 billion years ago, and the Proterozoic period of 2.6 billion to 570 million years ago). This is because the mountain-building activity, which helped concentrate many minerals, was intense in this early period of the planet's life.
The stages of exploration for these various orebodies might include:
Geophysical Surveys - Airborne evaluation of magnetic or density anomalies, which are good indications of areas prospective for mineral deposits.
Mapping - Consolidation of the surface expressions into a single plane for better understanding of the likely deposit configuration.
Sampling - Collection of stream sediments, surface boulders or earth (the latter usually from trenches dug across a prospective area). The material is then analysed to test for anomalous concentrations of metals to establish drilling targets.
Drilling - Recovery, for analysis, of either rock chips (at various depths) or cores (collection of the latter is by using diamond-encrusted circular drill bits and core barrels).
Modelling - Evaluation of grades and known structures (often using computer models) to determine the likely deposit configuration.
Infill Drilling - The drilling of extra holes to increasing confidence in the orebody model.
Feasibility Studies - Various scenarios tested (at different metals prices) to determine if the deposit can be extracted profitably. The last such study is called a 'bankable' feasibility study as it is used to secure funding.
There are various classifications for ore deposits, depending upon the certainty that the configuration is understood (this is usually a function of the number of drill holes):
| Inferred | Evidence suggests that there are minerals worth investigating; sometimes described as 'Potential'. |
| Resource | - Indicated Initial drilling has identified that there is mineralisation but the configuration is uncertain. - Measured Tonnage has been calculated but drilling not sufficient to be sure of the orebody's continuity. |
| Reserve | - Probable Further testing has raised the level of confidence such that initial funding can usually commence. - Proved Orebody is well understood, and the tonnages and |
For more information in this Exploration Knowledge series click the links below.
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| Metals and Minerals | Geology |
| Exploration | Mining |
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