Ann: Porphyry Copper Prospects , page-32

Had no idea what Porphyry meant. Sorry, yes I googled again and copied and pasted


Porphyry deposits are the most important source of copper and molybdenum, and major sources of silver, gold, and tin. Porphyry deposits may also host valuable by-products, including platinum, palladium, and tungsten.

Approximately 50-60 percent of the world’s copper, and 95 percent of molybdenum comes from porphyry deposits. In the past, porphyry deposits were often overlooked with conventional drilling and assaying exploration methods due to their low grade. The discovery of many large porphyry deposits has prompted exploration companies to look more critically at their drilling and assaying results. Junior miners report their drilling results showing that drill cores “started and ended in mineralization” and that drill cores provided an “extension of mineralization.” These are important facts to consider when trying to determine the overall extent of mineralization in an area.

Although the grade may be low, porphyry copper deposits typically contain hundreds of millions of tonnes of ore. Grades for the different metals vary considerably, but generally average less than 1%. In porphyry Cu deposits, for example, copper grades range from 0.2% to more than 1% copper. The metal content of porphyry deposits is diverse. For deposits with sub-economic grades and tonnages, subtypes are based on probable co-product and by-product metals, assuming that the deposits were economic. In porphyry deposits, ore minerals are dominantly structurally controlled, which means that the bulk of mineralization in these deposits is hosted in stockworks, veins, vein sets, fractures and breccias.

Types

In porphyry copper deposits, copper grades range from 0.2% to more than 1%, molybdenum grades range from approximately 0.005 to about 0.03%; and silver contents range from 0.004 to 0.35 g/t, gold content ranges from 0.2 to 5 g/t. Copper grades in porphyry copper-gold deposits are comparable to those of the copper-porphyry, however, the gold content tends to be considerably higher. There are a limited amount of copper-porphyry deposits in the world, however, one prime example is Freeport McMoRan’s (NYSE:FCX) Grasberg in Indonesia, with a resource greater than 2.5 billion tonnes grading 1.1% copper and 1.04 g/t gold.

The future

Exploration companies are always in search of the next great copper porphyry deposit. Not only are these deposits an excellent source for copper, extra money can be made from the significant co- and by-products. Examples of porphyry copper deposits include El Salvador, the Bingham, Utah, and the giant Chuquicamata deposit in Chile, which originally comprised over 9000 million tonnes of mined ore and reserves. Porphyry deposits are amenable to open-pit mining, offering a low cost way to extract the resource.