Shooting Gold Grains with Lasers to Find Out Where They Came From

A recently completed study By Rob Chapman and Dave Banks facilitated by a £40k grant from Geoscience BC was the subject of a press release in Vancouver.

Shooting gold grains smaller than a pin head with lasers may have revealed a new efficient and low-impact method for discovering gold deposits in British Columbia, according to a Geoscience BC report.

Called Detrital Gold as a Deposit-Specific Indicator Mineral by LA-ICP-MS Analysis, the new report details how a new technique using Laser-Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS) can be used to identify where a gold grain has come from - and where a deposit may be located.

Researchers have known for some time that the trace elements found in gold particles from BC's gold-mineralized systems and the mineralogy of micro inclusions occurring within gold particles can be used to identify which type of deposit they came from. However, using this as a tool for mineral exploration generally requires more gold particles than are routinely collected during reconnaissance stream sediment sampling programs. For this study, researchers from the University of Leeds, UK, explored whether the trace element analysis of gold facilitated by using two types of LA-ICP-MS could provide additional information, and reduce the number of gold particles required.

Using samples from streams and bedrock sources around Kamloops, Princeton, Prince George and the Cariboo, researchers found that the compositional heterogeneity of gold at the trace level was far greater than previously recognized. This has profound implications for how the results of studies of gold grains which rely only on alloy compositions are interpreted.

Micro-inclusions within gold have previously been recognized as the most useful feature for predicting their source type, and this work has raised the importance of these features because they appear to act as 'sinks' for certain trace elements. This mix of trace elements appears to vary according to the source and style of mineralization, providing a new avenue for investigation.

Rob Chapman, project lead and Senior Lecturer in Mineral Exploration at University of Leeds and David Banks, Principal Research Fellow, said: "The funding provided by Geoscience BC has underpinned research which has showed that the trace element heterogeneity within natural gold alloy is far greater than anyone imagined."

"Whilst we can't simply use the trace element composition of a single gold grain to deduce its source, we may be able to gain such information from further study of trace element partitioning to mineral inclusions within the gold."

Geoscience BC Vice President of Minerals and Mining, Bruce Madu said: "This innovative study is helping to develop new techniques that can be used by researchers and mineral explorers to more accurately and efficiently identify potential gold deposit locations. Additional research will help understand benefits and appropriate applications of the technique."