For miners in Canada’s westernmost province, the difficulties of exploration are a perennial problem. Discovery rates have dropped in recent years, creating a pressing need for new techniques to come into play.
As it turns out, the answer to these problems may lie in the rich and diverse environment naturally bestowed upon the region.
In August, a team of researchers revealed it had developed a new set of analytical methods, in which snow, soil and trees can be used to indicate the presence of desirable mineral deposits.
The project, funded by local NGO Geoscience BC, measured the concentration of halogens – fluorine, bromine, chlorine and iodine – in samples collected from Vancouver Island’s Mount Washington gold-copper-silver prospect, and the Lara zinc-copper-lead-silver-gold showing.
Samples were collected from a diverse range of articles, including twig ends, ‘tree sweat’ and pine needles, as well as to snow and upper-layers of topsoil.
Halogens are known to be associated with the likes of copper and gold. Their elements cause the metals to be transported in a hydrothermal solution that forms in deposits, found in alteration minerals. When these minerals are exposed on the surface, they release halogens into the soil, vegetation and snow.
The idea behind this project was to discover if detectable amounts of those elements could be found directly above mineral deposits, making it easier for mining companies to determine likely locations of deposits.
Ross Davies speak to Colin Dunn, a co-author of the project, to learn more about the story.
Ross Davies: How did your involvement in the Geoscience BC project come about? And when did it start?
Colin Dunn: This is the latest in a series of projects we have completed for Geoscience BC over the last nine years. I am part of a team of three, alongside Dave Heberlein and Sarah Rice. My focus is on vegetation, while Dave and Sarah’s studies are around soils and analysis, respectively.
Together, we have many years of expertise in the collection and analysis of surface materials, and relating the patterns of elements at the surface to concealed mineralisation.
We see a need to develop environmentally friendly sampling and analytical methods with low levels of detection for the halogen elements at costs acceptable to the resource sector.
There is also the need for some field studies for proof of concept and to determine the typical levels of the halogens in common natural surface materials in British Columbia over different types of mineralisation – so, gold and base metals – and in background areas.
RD: How do the methodologies work?
CD: Many types of mineral deposit become emplaced in the near-surface layers of the earth with the assistance of the halogen elements because of their high volatilities.
As a deposit in the subsurface slowly degrades, with the help of microbial and weathering processes, elements move toward the earth’s surface – since the earth continually degases – resulting in an upward flux.
The halogen elements are among the first to be released and can be captured in surface soils, taken up by vegetation through their root systems, and volatilised into the atmosphere.
RD: What were the main take-away results from the project?
CD: We were able to trace the pathways of the halogens by measuring their contents in different layers of soils, in the different tissues of common tree species and in the liquids that transpire through the stomata of the tree foliage, through which gases and water vapour pass.
By placing plastic bags over twigs and foliage we could collect and analyse the fluids that accumulated over the course of a day.
And by burying carbon and resin sachets in the ground for several months – in a contraption that we designed specifically for this purpose – we could measure the different concentrations of halogens and other elements emitted as gases at sites, with and without known mineralisation.
Late in the winter season, we sampled snow at different levels in the snow pack to see what might have accumulated over a short period of time. By analysing the melted snow samples, we could determine that there was a steady upward flux of the halogens, particularly bromine and iodine.
RD: What kind of potential do the techniques have, as far as mitigating the environmental impact of mineral exploration?
CD: The techniques have little or no impact on the environment other than leaving a few footprints, such that the only evidence is from slight pruning of twigs collected for analysis, or a small square of surface organic-rich soil being removed.
There is no impact whatsoever from the collection of transpired fluids or snow.
RD: Are there any further trials coming up? Will you look to test the techniques at sites beyond Vancouver Island?
CD: We consider this a proof of concept study to demonstrate the levels of halogens and other elements that typically accumulate in surface materials, and how the concentrations, including commodity metals, relate to sometimes deeply buried mineral deposits.
As such, they provide first ultra-low impact methods for providing focus for more detailed and invasive procedures, such as trenching and drilling. New analytical methods have been developed with the assistance of ALS Minerals in Vancouver and the laboratories of the British Columbia Department of Environment & Climate Change Strategy on Vancouver Island.
These methods are now available to the exploration and environmental industries at a very modest cost. Further analytical experimentation will refine the methodologies and lower the analytical detection levels even more.
At this point no further trials are planned, but we feel that the methods should be tested at other sites in BC, as well as over different types of mineralisation.