Brazilian Expedition to Collect Unusual Platinum Grains

24 January 2013

Many people imagine a typical scientist's workplace to be a sterile white laboratory littered with microscopes and specimens. While this is true some of the time, researchers at the South Australian Museum travel on adventurous expeditions to develop their expertise, even braving life-threatening situations in regional Brazil.

Our world-class minerals scientists have just returned from a field trip to the South American country, where they collected unique platinum grains. They want to study how bacteria may affect the movements of this precious metal in soils and waters. A particular creek in Brazil is the only known accessible site where platinum is found to have grown in sediments into attractive clusters up to half a millimetre in size (which is large for a platinum sample).

Fortunately, the South Australian Museum's Professor Joël Brugger and his colleagues survived the journey to tell the tale.

He says platinum is an important mineral to study because it has so many industrial uses in modern society, from car manufacturing to jewellery. It is also a key element in chemotherapy as toxic forms of platinum kill the cancer cells.

"Platinum is even rarer than gold," he says. "Its economic deposits are created in magma chambers deep within the Earth. There, platinum crystals are formed at temperatures well over 1000ºC. Once the magma solidified, erosion can bring the rocks to the Earth's surface.

"Eighty per cent of the world's platinum comes from South Africa, where there is a giant magma chamber covering more than 60,000 square kilometres. To ensure sustainable mining, we have to understand the deposits, prospecting methods and how platinum moves around in the landscape — including how bacteria affects this."

He says platinum is found in New South Wales and Western Australia but has not been developed.

"Platinum is rare. It's rather immobile in the environment, so if you want to study the interaction between bacteria and platinum then you need to find places where you have the chance to put your hands on the samples.

"Brazil offers one of these unique opportunities where we know some platinum grains actually grew in the sediments. It's even weirder than that because there is no known primary source — we don't know where this platinum comes from."

Professor Brugger travelled with a team led by the University of Adelaide to the Brazilian mining state of Minas Gerais, about 700km north of Rio. The plan was to take fresh samples of platinum from the area under field-sterile conditions, in order to preserve biofilms that may exist on the surface of the grains. The scientists also planned to collect gold grains in order to compare the biology of both precious metals. However, collecting material from the diamond and gold fields of Minas Gerais is far from easy, or safe.

"The people live on a few dollars a day and life is not that valuable," Professor Brugger says. "We needed access to mine sites so that we could get samples and compare them to other areas. But the sites were controlled by diamond and gold-hunters (garimpeiros).

"We had to find grains of platinum from the place where they were actually formed. We're interested to see if there is a biofilm of organisms living on top of those grains, so that's why we have to go there ourselves. We use gloves so as not to contaminate the samples and then use chemicals to preserve them, and bring them from Brazil to Australia where we can do high-level microscopic and genetic studies."

The team spent several days negotiating to gain access to the area they wanted to study in. "Thankfully, a local geologist agreed to guide us to the area — that got us started and gave us a good idea of how things work in the gold and diamond fields. We then discovered that local jewellery and rock shops provide an invaluable source of local knowledge to access further sampling sites. After several days of shopping, talking and sharing coffee, we found a young man who spoke English. We learned that the gold used in making jewellery was locally mined. Finally, he agreed to present us to the garimpeiros. We ended in a little car with a guy who spoke no English and we spoke no Portuguese!"

The scientists found themselves in a slum village that nobody was allowed to go into without a phone call to a ringleader.

"You absolutely do not enter without being announced, otherwise I don't want to think about what would happen to you," says Professor Brugger. "Our guide's phone was flat so he had to talk to people and find someone who would let us use their phone. The guys were nice but a bit scary!"

The team managed to negotiate with gestures that they'd like some gold samples with bacteria on them. "The miners use soap in the final step for washing out the gold; it was quite a feat to explain that we wanted the dirtiest gold possible to keep the bacteria samples on it".

The scientists not only survived working near armed and dangerous gangs, but also endured sudden and heavy rainfall, bogged cars, tropical insects and poverty-stricken regions without facilities. However, the adventure was not without its pleasures; the group admired beautiful minerals, worked in stunning landscapes, lodged in romantic Portuguese imperial cities, and enjoyed fresh food prepared in Brazilian roadhouses.

Now back in Adelaide, the researchers will use their prized samples of Brazilian platinum to see whether the bacteria in the unique sedimentary deposits actually play a role in transforming and moving the metal.

"What we're really after is seeing if something lives on those grains. If they do, then what's special about the surface of a platinum grains? What are the processes for them to interact with the platinum? Can the organisms be responsible for the formation of these unique grains?" he says.

"The only way we're ever going to prove that this is the process, is by demonstrating that we have genes in the bacteria that can actually achieve this. We will sequence the bacteria that are there, identify the genes and investigate the possible pathways of precipitation. Once we have that, we will set up some experiments with the organisms, feed them with platinum and whatever chemicals they need to do the work. Then we can prove in the lab that the process that was inspired by nature actually works, and we can actually grow platinum!"

If the scientists can conduct experiments with the bacteria and grow platinum to represent the same shape found in Brazil, they will be able to prove that the bacteria has a role in forming the mineral in a certain way.

"This is really fundamental work because we have no idea what we're going to find. How do immobile precious metals move around? We want to show that bacteria help make them soluble."

Once they understand this, the research will have many uses. Platinum from low-grade ores could be recovered using microbial methods. With the increasing use of platinum in technology and medicine, platinum waste is increasing the volume of contaminated soils.

Professor Brugger says bacteria could also be used to detoxify soils contaminated by platinum, by transforming the toxic forms of platinum into inert platinum nuggets.

The team's project is funded by an Australian Research Council Discovery Grant.