Investment advisors always recommend some degree of diversification. A range of investments helps cushion downturns in individual markets and, properly allocated, still provides much of the desired upside. (Over-diversification can dilute upside potential to the point of no returns, however). One way for precious metals speculators to diversify their holdings is by investing in polymetallic deposits, ores containing multiple metals.

Such deposits come in many forms. Some South African gold mines have in the past weathered low gold prices by selling by-product uranium. Copper miners worldwide are able to work below-cutoff deposits by producing associated gold, silver, and nickel. Companies in Africa have even been able to produce copper at negative cost after revenues from by-product cobalt are taken into account.

The commonality amongst all of these deposit types is that they provide speculators a natural hedge across a variety of markets and industries – more metals, more irons in the investment fire. The following is an overview of some common polymetallic suites, and places to find them.


Base metal deposits commonly contain silver at grades ranging from a few grams to several hundred grams per ton. At locations in northeastern Mexico, central Peru, and southeastern China, lead-zinc ores with associated high-grade silver mineralization occur in dolomites and limestones (Mississippi Valley-type deposits). Sediment-hosted lead-zinc ores in eastern Australia are also silver-rich. Many of these Australian mines are overachievers in terms of silver, producing greater quantities than estimated by their reserve figures because the metal is hidden inside lead and zinc minerals, with only minor amounts occurring as primary silver.

Copper-Gold and Copper-Molybdenum Porphyries

Around the Pacific Rim, numerous low-grade, granite-hosted copper “porphyry” deposits contain either gold or molybdenum, helping offset bulk mining costs for these dilute ores. Molybdenum, a component of steel alloys, is found with copper in continental settings such as Utah, Arizona, and northern Chile at grades up to 0.05%, almost exclusively as sulfide minerals. Copper-gold deposits are found in abundance on volcanic islands and isthmuses such as Papua New Guinea and Panama, but also on portions of some continents such as southeastern Australia, with gold generally grading less than 1 g/t and occurring largely in sulfides like pyrite and chalcopyrite. British Columbia offers the best of both worlds, hosting numerous Cu-Mo and Cu-Au porphyries.

Platinum Group Metals

Major platinum deposits in South Africa, Zimbabwe, and Montana contain significant quantities of associated metals known as platinum group elements (PGEs). So too, do Siberian and eastern Canadian copper-nickel ores. Palladium is the most plentiful PGE, but rhodium – used in automobiles, thermocouples, and high-tech applications – grabbed attention when prices shot up from around $200/oz in early 1997 to reach over $2,500/oz in late 2000. These, along with less abundant PGEs like iridium, osmium, rhenium, and ruthenium, are contained within sulfide minerals, usually grading less than 1 g/t, but, in cases such as Montana’s Stillwater deposit, enriched to an impressive 20 g/t. Chromite and platinum ores in Russia’s Ural Mountains, Turkey, Albania, and Norway also contain PGEs. In addition, India and Australia may hold numerous PGE-rich platinum deposits, representing a significant future source.

Cobalt in Nickel and Copper Ores

Our planet hosts almost no primary cobalt deposits. The metal, used for jet-engine superalloys, comes mainly as a by-product of nickel and copper mining, making it a significant value-added component for these deposits. Copper ores in the Democratic Republic of Congo and Zambia are the world’s major source, generally grading less than 0.5% cobalt, as sulfides – mineralization that can be processed by relatively inexpensive hydrometallurgy. Cobalt-bearing sulfides are also mined at nickel-copper deposits in eastern Canada and Russia. A third cobalt source is laterite nickel deposits in wet, tropical nations such as Cuba, Indonesia, the Philippines, New Caledonia, and Australia, which have attracted increased attention recently, despite being lower grade than sulfide ores and more expensive to produce.

Less Can Be More

Having said the above, the presence of too many metals in a deposit can create production problems as multiple processing techniques may have to be used and calibrated with each other to reach an optimal recovery, profit-wise. Also, some metals can actually interfere with the recovery of others (some types of copper, for instance, make the production of gold more expensive). In other words, companies experienced with these deposit types can often squeeze more financial return out of the ore than could a newbie (although some complex deposits have given even savvy majors fits). The above suites, however, are some of the more commonly produced, and a good base of knowledge therefore exists on how to work these ores effectively, resulting in good shareholder value. Something to keep in mind when calculating a deposit’s potential return on your investment.