PETROGRAPHIC EXAMINATIONS AS A TOOL IN AGGREGATE EXPLORATION
Exploring for a potential greenfield site is expensive. It requires drilling closely spaced core holes and testing to determine if rock meets specifications, which can cost hundreds of thousands of dollars. If the stone does not meet specifications then the money spent on drilling and testing is lost.
Petrographic examinations used in the initial stages of exploration provide a low-cost alternative. Petrographic samples may be obtained from outcrops or from rock chips produced by percussion drilling, which is much cheaper than core drilling. Petrography can be used to determine types and amounts of deleterious materials, identify potentially alkali-aggregate reactive components, determine if environmentally unfriendly minerals such as asbestos or asbestiforms are present, and to estimate the specific gravity and absorption of the rock. Grain boundary relationships, mineral cleavage, grain size, and alterations that form deleterious products (e.g., saussurite, epidote, etc.), may correlate to how the aggregate responds to testing. Potential savings for aggregate companies is considerable but requires a petrographer with the required experience, training, and proper equipment to conduct these examinations.