Resource Calculations

The quantity, or tonnage, of mineralized material in a deposit can be calculated if the volume of the deposit is known. The volume can be measured by the widths and depths of the drill holes, and the distance between them — it is now usual to make such calculations using sophisticated computer software that also allows a three-dimentional view of the deposit on.

Multiplying the volume by the average density of the mineralization gives the number of tonnes in the deposit. Although this sounds simple, orebodies can be quite complex; densities change, grades are often discontinuous and the shape of an ore- body is often highly irregular.

The grades determined by sampling the drill cores are plotted, and a weighted average of the grades is calculated, giving a resource figure. This estimate gives the grade and tonnage of the deposit, so far as it is known by drilling. More tonnage can be added by drilling areas that have not yet been drilled, but extend along the strike and down the dip of the mineralized zones.

Resource estimates are classified as “measured” if the drill holes are closely spaced and the geologist is satisfied that the tonnage is reasonably certain; “indicated” if a significant amount of drilling has been done, but some presumed mineralized zones are not fully tested; and “inferred” if the estimate is based on information from widely-spaced drill holes.