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Biogeochemistry as an exploration tool for gold in the Brännfors area, northern Sweden
Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering. Luleå University of Technology.
2019 (English)Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
Abstract [en]

Using plants as a sampling medium have been shown to be very successful when other exploration methods are ineffective. This is especially the case in glaciated terrains, where the overburden might be blanketing mineralised bedrock. Plants are able to take up nutrients and trace elements from the soil through different biogeochemical processes and later these concentrations can be analysed. What kind of element that is absorbed and the amount of it differ between species and even between different plant tissues. In this study, it is investigated whether biogeochemistry works as an alternative exploration method for the conditions prevailing in the Brännfors area, northern Sweden. Brännfors is an interesting area because several gold-rich boulders have been found there and an aeromagnetic survey that has been conducted in the area show positive anomalies.

A sampling plan was designed before any sampling could take place. It was chosen to sample in profiles to delineate where the possible mineralisation is located. The sampling took place in September 2018 and was completed within two weeks. The chosen sampling medium was twigs from Scots pine (Pinus sylvestris) and they were as often as possible collected from trees of about the same age and state of health. The branches were usually cut from four metres height using a pole snipping tool. Then the twigs, with needles left on them, were cut from the branches with a hand held snipping tool. All samples were stored in paper bags, with coordinates and sample ID written on them, and was sent to ALS Scandinavia AB for analysis within a week after sampling.

This exploration method is fast as one person can carry many samples before it gets too heavy, since one sample only weigh around 200 grams. No heavy equipment is needed either and therefore, it is possible for two persons to collect up to 30 samples/day. Moreover, the method is relatively cheap and because of the small sample size required, the method leaves a minimal impact on the environment.

The analysed data show elevated concentrations of many elements of interest in sampled pine twigs. Especially Ag, As, Cu, Hg and Tl exhibit similar patterns in the middle of both sampling profiles, where the strongest anomalies are located along the ice movement direction from northwest. All these elements can be used as pathfinders for Au and might very well indicate a mineralisation because no previous mining activity or any other contamination risk exist in the area. Because of this, it can be said that the exploration method is working at the Brännfors area, but to a certain limit. Patterns could be clearer but there are probably several factors that influence the metal uptake of plants. Among those factors are geological and environmental issues. The possible mineralisation may for example be buried too deep below the ground surface, so that the tree roots cannot quite reach down to the bedrock.

Several factors indicate however that the possible mineralisation is located further towards the ice movement direction instead, and that it is the ice sheet and/or the groundwater flow that have dispersed the anomalies. The gold-rich boulders found in the study area may also have been transported by the ice. The aeromagnetic anomaly can then be explained by the pyrrhotite-rich metasedimentary rock and some minor magnetite occurrences.

Place, publisher, year, edition, pages
2019. , p. 110
Keywords [en]
biogeochemical exploration, mineral exploration, northern sweden, gold, scots pine
National Category
Geosciences, Multidisciplinary
Identifiers
URN: urn:nbn:se:ltu:diva-73338OAI: oai:DiVA.org:ltu-73338DiVA, id: diva2:1299696
External cooperation
Boliden Mineral AB
Educational program
Natural Resources Engineering, master's
Supervisors
Examiners
Available from: 2019-04-25 Created: 2019-03-28 Last updated: 2019-04-25Bibliographically approved

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