RE:RE:RE:RE:Long holes but insufficient GradesCopper Porphyry copper deposits are low grade, but are important sources of copper because they can be worked at a large scale for low costs. They typically contain between 0.4 and 1 percent copper in concert with smaller amounts of other metals, such as molybdenum, silver and gold. Porphyry copper mineral deposits are usually massive, with extraction taking place by open-pit mining.