Contact metamorphism of Palaeozoic shale in southern Sweden: influences on clay mineralogy and implications for railway construction material properties

Abstract

Abundant shale fragments were observed in dolerite material used for railway construction in western Skåne, due to quarrying of Permo-Carboniferous dolerite in contact with Silurian shale (the Colonus Shale) in the Rönnarp Quarry, western Skåne. Shale fragments were particularly enriched in the finest fractions of the crushed rock material. We analysed the clay mineralogy of shale from the railway material and at different distances from the dolerite in the quarry, in order to better understand the properties of the delivered rock material. The illite and chlorite dominated Colonus Shale in Skåne typically shows background illite crystallinity in the uppermost diagenetic realm. In the Rönnarp Quarry, fissile shale a few meters away from the dolerite intrusion shows illite crystallinity in the anchimetamorphic stage. In massive shale less than 1 m from the shale-dolerite contact, swelling clay minerals have formed at the expense of illite. Therefore, despite the massive appearance of the contact metamorphosed shale, it is suggested that such rocks should be avoided during construction material production. A tentative model for post-intrusion hydrothermal clay mineral transformation is suggested.

Keywords:

• dolerite
• Colonus Shale
• clay minerals
• contact metamorphism