Corundum-bearing assemblages from the Proterozic Zn—Pb—Cu deposit of Saxberget, central Sweden

Abstract

Rocks bearing corundum and spinel (mostly hercynite-rich) occur in the Saxberget area, central Sweden. These rocks are quartz-free and most of them are phlogopite-chlorite schists with or without orthoamphiboles. Magnetite, garnet, cordierite or orthoamphibole are essential minerals in other corundum- and spinel-bearing rock types. The rocks have been affected by two low-pressure thermal events. The first of these reached temperatures of high-grade metamorphism, the second temperatures of medium-grade metamorphism. The latter, which was a static metamorphism, produced the non-schistose corundum-bearing assemblages. Inclusion-free corundum is found together with cordierite and spinel, but also together with magnetite. In the latter case corundum and hercynite exsolved from an aluminous magnetite. Symplectites of corundum and magnetite or corundum and pyrrhotite/chalcopyrite are found in chloritized parts of the samples. They are formed by retrograde oxidation of hercynite to corundum and magnetite. The pyrrhotite is attributed to a later sulfurization of magnetite.

Key Words:

• Corundum
• hercynite
• symplectite
• oxidation
• sulfurization
• undersaturated rocks
• metamorphism
• Leptite formation
• Svecokarelian
• Precambrian
• Saxberget
• Dalarna
• central Sweden
• N6009
• E1456

Additional information

Notes on contributors

Klint Lennart Karlsson

Klint Lennart Karlsson (1951-08-11-1983-12-09) worked with the Ore Research Group, Stockholm University. He prepared this report in August 1983. Further communications concerning the paper should be addressed to Professor David Rickard, Department of Mineral Exploitation, University College, Cardiff CF2 1TA, UK.