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Precambrian Geology

Precambrian rocks are older than 540 million years (Ma) and carry most of the mineral products mined in Sweden, which has the largest mining sector in the EU. These crystalline bedrocks have often been through orogenic mountain-building processes which recrystallised them due to high temperatures and pressures and change their mineral composition in a process called metamorphism.

Our research in Precambrian Geology focusses on the origin of the earths crust and the mineral deposits which it holds. In the Baltic Shield we are investigating the age and history of the different continental blocks or terranes which have been put together by plate-tectonic processes over three thousand Ma.

We do fieldwork based on Geological Survey maps, take samples, analyse them geochemically and in thin section with optical and electron microscopes, date them using microbeam mass spectrometers and work out how and when they formed and what they did after that. Yes, rocks have a life of their own, just a lot slower than ours! For example, in a paper by Hegardt et al, (2005) we showed that rocks which crop out like sausages at Viared in a cutting along the national road from Gothenburg to Borås had a long history. They formed as igneous rocks at 1700 Ma ago and were folded and partially melted during the Hallandian orogeny 1420 Ma ago. Later they were involved in the Sveconorwegian orogeny, during which they were subducted beneath the crust to a depth of at least 50km, recrystallised to beautiful red and green garnet-pyroxene eclogites, before popping back up to the surface by 974 Ma, nearly melting again, producing small amounts of silver molybdenite and largely turning back into black and white amphibolites.

The barren rocks of the Namib desert in Namibia shown here contain mineral deposits such as copper and gold and yield information about the origin of the earths crust in southern Africa, part of our project on the Paleoproterozoic Evolution of south-western Africa.

In southern Africa we are doing a lot of precise zircon uranium-lead dating on rocks and ore districts in regions where the crustal development history is not well known. For example, the huge lead-copper-zinc mines of the Bushmanland Ore District were thought to be 1600 Ma old and to have formed as chemical sediments on a 2000 Ma granitic basement. We have now shown in a paper by Cornell et al (2009) that the giant ore bodies are actually younger than 1200 Ma old and the '2000 Ma basement' rocks are only 1166 ±13 Ma old, but formed by melting of much older Archean >2500 Ma rocks. With this research we are contributing to the understanding of how crustal rocks and ore deposits form, essential knowledge for future mineral prospecting.

Precambrian Geology Group


Prof David Cornell
Prof Jimmy Stigh
Prof emeritus Sven-Åke Larson

Research Students

Eric Austin Hegardt

Page Manager: Robert Karlsson|Last update: 10/7/2010

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