Scientists from the University of Adelaide have discovered a surprising way to find platinum group metals (PGMs)—through bacteria. According to the University’s web site, investigations of platinum group elements from Brazil, Colombia and Tasmania revealed that specialized bacteria play a role in the formation and movement of platinum and related metals in surface environments.
Project leader Dr. Frank Reith explains:
“Traditionally it was thought that these platinum group metals only formed under high pressure and temperature systems deep underground, and that when they were brought to the surface through weathering and uplift, they just sat there and nothing further happened to them.
“We’ve shown that that is far from the case. We’ve linked specialised bacterial communities, found in biofilms on the grains of platinum group minerals at three separate locations around the world, with the dispersion and re-concentration of these elements in surface environments.
“We’ve shown that nuggets of platinum and related metals can be reformed at the surface through bacterial processes.”
The study is significant because mineable deposits of platinum group metals (platinum, palladium, rhodium, iridium, ruthenium, and osmium) are rare and much less productive than those containing more common metals. PGMs are valued for their numerous industrial applications including the manufacture of automotive catalytic converters. Read Analyzing Metals’ series on PGMs to learn more about their numerous uses.
The U.S. Geological Survey’s 2014 Platinum Group Elements Fact Sheet describes some of reasons why productive deposits are so elusive:
- The Earth’s upper crust contains only about 0.0005 parts per million (ppm) platinum.
- The average grade of platinum-group elements (PGEs) in ores mined for their PGE concentrations range from 5 to 15 ppm.
- In most rocks, platinum-group minerals range in size from less than a micron to a few hundred microns in diameter, so the presence of PGEs must be confirmed by laboratory analysis.
- Over 100 minerals contain PGEs as an essential component.
PGM extraction and refinement is time consuming and expensive. According to the International Platinum Group Metals Association (IPA), it can take as long as six months from initial mining activities to produce the final metal. The process from extraction to final product involves crushing and milling the ore into fine particles, concentrating the particles using froth flotation followed by drying and smelting at high temperature, removing iron and sulfur, and finally, separating out the base metals (nickel, copper, cobalt) and refining the PGMs using a variety of techniques.
Pathfinder elements can be used to locate potential zones of metals that occur in low concentrations, such as PGMs. These pathfinder elements are successful exploration tools because they have a genetic relationship with the precious metal. The type of pathfinder elements depends on the target element and deposit type. In PGM exploration, a high correlation between the target element and a given element “X” (based on laboratory assays) may show that element X can be used as a pathfinder in fieldwork using portable x-ray fluorescence (XRF). Read this study showing how it is possible to locate high concentrations of precious metals (platinum, palladium, and gold in this case) by using a portable XRF analyzer on pathfinder elements.