There are two parameters to an intercept: grade and width. sometimes there is more value to a wider lower grade intercept than to a very narrow higher grade intercept. Assuming all of the drill holes have similar areas of influence, grade x thickness analysis allows the geologist to think in terms of the relative amount of metal represented by the intercept.

The initial result of any exploration drilling program is a tabulation of intercept widths and grades for each successful drill hole.

For vein targets, we end up with several intercepts plotted on a longitudinal section like the one that is being presented for San Miguel.

When the geologists estimate the resources represented by the drilling, they calculate the tonnage by multiplying the “area of influence” of each drill hole by the width of the intercept and the specific gravity of the ore. They then multiply the tonnage by the grade of the intercept to obtain the ounces of gold and/or silver contained by that block of ground.

To be mathematically correct, the longitudinal section should be vertical and the intercepts should be projected horizontally, at right angles to the section.

If it is assumed that the structure (vein) is drilled on a grid, which should be approximately true, the grade x thickness product gives you a sense of the gross ounces of gold and/or silver represented each the intercept.

Contouring the grade x thickness provides the geologist with a sense of the trend (plunge) of the ore shoot and the opportunity to target future drilling at the most favorable locations.