Ann: Development Progress - Lindi Jumbo Mine, page-120

The point is that waste rock without any graphite content is easily visually distinguishable from 10 percent or 20 percent ore. The ore stands out because the graphite is a different colour (darker) than the host schist rock. When it comes to distinguishing between 10 percent low grade and 17.9 percent high grade they look very similar because low grade is hosted within 90 percent barren schist and high grade hosted within 82.1 percent barren sschist. It's hard to tell the difference especially when it has been blasted and you can't see under the top of the muckpile.