Other Precious Metals
Noble metals are metals that are resistant to corrosion and oxidation in moist air. The most generally agreed short list of chemically noble metals are : Ruthenium, Rhodium, Palladium, Silver, Osmium, Iridium, Platinum and Gold.
In contrast, Precious Metals are rare, naturally occurring metallic chemical element of high economic value. Precious metals tend to be less reactive than most elements. They are commonly ductile and have a high lustre. Precious metals have been historically important as currency and are regarded mainly as investment metals (jewellery/bullion) but also have some industrial uses.
The best known precious metals are the coinage metals, gold and silver. Other precious metals include the Platinum Group Metals: ruthenium, rhodium, palladium, silver, osmium, iridium, platinum of which platinum is the most widely traded. The demand for precious metals is driven not only by their practical use but also by their role as investments and a store of value. Historically, precious metals have commanded much higher prices than common industrial metals. Gold, silver, platinum, and palladium each have an ISO 4217 currency code.’
Osmium, Iridium, Ruthenium, Rhodium, Silver
Osmiridium is a naturally occurring alloy of iridium and osmium found in platinum-bearing river sands in the Ural Mountains and in North and South America. Trace amounts of osmium also exist in nickel-bearing ores found in the Sudbury, Ontario region along with other platinum group metals. Even though the quantity of platinum metals found in these ores is small, the large volume of nickel ores processed makes commercial recovery possible.
Metallic iridium is found with platinum and other platinum group metals in alluvial deposits. Naturally occurring iridium alloys include osmiridium and iridosmine, both of which are mixtures of iridium and osmium. It is recovered commercially as a by-product from nickel mining and processing.
Ruthenium is generally found in ores with the other platinum group metals in the Ural Mountains and in North and South America. Small but commercially important quantities are also found in pentlandite extracted from Sudbury, Ontario and in pyroxenite deposits in South Africa.
The industrial extraction of rhodium is complex, because it occurs in ores mixed with other metals such as palladium, silver, platinum, and gold. It is found in platinum ores and obtained free as a white inert metal which is very difficult to fuse. Principal sources of this element are located in river sands of the Ural Mountains, in North and South America and also in the copper-nickel sulfide mining area of the Sudbury Basin region. Although the quantity at Sudbury is very small, the large amount of nickel ore processed makes rhodium recovery cost effective. However, the annual world production in 2003 of this element is only 7 or 8 tons and there are very few rhodium minerals.
The principal sources of silver are the ores of copper, copper-nickel, lead, and lead-zinc obtained from Peru, Bolivia, Mexico, China, Australia, Chile, Poland and Serbia. In Peru, Bolivia and Mexico have silver has been mined since 1546, and they are still major world producers. Globally significant silver-producing mines are Cannington (Australia), Fresnillo (Mexico), San Cristóbal (Bolivia), Antamina (Peru), Rudna (Poland), and Penasquito (Mexico). Major near-term mine developments in south America include: Pascua Lama (Chile), Navidad (Argentina), Jaunicipio (Mexico), Malku Khota (Bolivia).
Global production of silver in 2014 was 26,800t (USGS), Mexico was the top producer of silver (5,000 tonnes), followed by China (4,060 t) and Peru (3,780 t).
Silver metal and compounds of silver have many uses outside of the traditional space of jewellery and bullion, which include coatings, electrical and medical applications.