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Moraine as a source of gold in stream sediments and the relationship to a Shear Zone in the Rombak-Skjomen area of Norway
2010 (English)Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
Abstract [en]

The Rombak-Skjomen area of northern Norway consists of a c.2.3-1.78 Ga Proterozoic basement window overlain by Phanerozoic metamorphosed sedimentary rocks from the Caledonian Orogeny. The window consists of volcanic arc and sedimentary rocks deformed during the Svecokarelian Orogeny when the area was situated on the margin of the Norrbotten craton. The area is geologically similar to other important mining areas of northern Fennoscandia such as the Skellefte District and the Gold Line of northern Sweden. Exploration for gold and base metal deposits during the 1980s produced a lot of geological, geophysical and geochemical data. Stream sediment survey data has been used together with new moraine sampling data to see if there is any relation between a recently identified shear zone and unexplained gold anomalies in nearby stream sediments (Larsen et al., 2010). Different statistical methods have been used to identify anomalous metal concentrations in stream sediment surveys to produce anomaly maps that can be used alongside the new data to identify areas of mineralisation. The area has the potential to host orogenic gold style mineralisation as has been found in other areas of northern Fennoscandia. Moraine samples have been taken in profiles across the shear zone and analysed to see if the moraine is a possible source of gold in these stream sediment anomalies and if the shear zone is gold bearing. Analysis of the moraine showed that the concentration of gold is very low and it is possible that the moraine is an indirect source of gold in stream sediment anomalies. Gold can enter moraine by weathering of gold bearing mineralisations in the surrounding bedrock, but because of its fine grained nature, it is quickly washed out of the moraine to be re-deposited in stream sediments several kilometres away from its parent rock. The area probably contains more than one type of gold mineralisation that are small, widely dispersed and have different mineralogy making them hard to locate using stream sediment sampling alone. The sampling results show that the moraine contains very low gold and arsenic concentrations. However, one sample collected close to a known mineralisation shows anomalous concentrations in several base metals. This means that moraine sampling can be used to locate base metal mineralisations by identifying metal anomalies down ice of the mineralisation. Higher concentrations of zinc where also found in samples collected close to the inferred shear zone and moraine sampling may be able to identify large scale structures such as shear zones if they contain higher concentrations of certain metals such as zinc or arsenic. There is the potential to find new mineralisation in the Rombak basement window especially at depth which has only been drilled at a small number of locations. A gold bearing quartz-ankerite boulder was found in the moraine may be similar to a new gold mineralisation found in the Mauken basement window further to the north. It is important to understand the relationships between these two basement windows and how they fit in to the tectonics at the margins of the Norrbotten craton during the Proterozoic.

Place, publisher, year, edition, pages
Keyword [en]
Life Earth Science, Orogenic gold, moraine sampling, Rombak basement window, svecokarelian orogeny, Fennoscandian shield
Keyword [sv]
Bio- och geovetenskaper
URN: urn:nbn:se:ltu:diva-42062ISRN: LTU-PB-EX--10/057--SELocal ID: 01eea6ba-9175-4ccd-bf35-297fb5dd5e96OAI: diva2:1015278
Subject / course
Student thesis, at least 30 credits
Educational program
Geosciences, master's level
Validerat; 20101217 (root)Available from: 2016-10-04 Created: 2016-10-04Bibliographically approved

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