Measuring Reserves and Resources

Resources and reserves can be further divided into different categories to quantify stock resources.

Measured reserves (sometimes called proven reserves)

These are minerals that have been identified and examined through sampling to quantify the amount of minerals available to a high level of accuracy and confidence. They are also economically, legally and technologically viable for extraction. Measured reserve is the highest level of confidence used when evaluating stock resources.

Indicated reserves (sometimes called probable reserves)

This category has much in common with measured reserves, except the level of testing is less thorough and therefore confidence in the amount of reserves is less certain. As they are still called reserves, they are economically viable to be extracted and are likely to have more testing conducted on them to determine an accurate quantity at which point they would be reclassified as measured reserves.

Inferred resources

These are minerals which are known to exist, as a result of some testing and limited knowledge of the geology in an area, however the actual quantity or quality is not known with high accuracy or confidence. For example, oil may be discovered by drilling, however further testing is required to properly understand the nature of the wider oil field and to assess the quantity, quality and extractability of the oil.

Possible resources

Possible resources are minerals which are thought to exist based on limited locational knowledge and exploration, thus the quantity and quality is known with the least confidence of any of the categories. Possible resources can sometimes be referred to as hypothetical or speculative. Hypothetical resources are those in regions where mining/drilling (or other extraction) takes place but haven't yet been discovered, but they are anticipated to exist due to particular geological conditions similar to those where they have been seen to occur before. Speculative resources are predicted resources in regions where no extraction currently takes place.