Geological mapping of a planned extraction area for hard-rock aggregates, Seljestokken, Flora, Sogn og Fjordane

Abstract

Geological mapping of a planned extraction area for hard-rock aggregates has been carried out at Seljestokken, Flora municipality, for Hertig Natursteine AG. A number of hand-specimens of the bedrock were collected and thin-sections were subsequently examined under the microscope. The bedrock of the area consists of fine-granied, Devonian sandstone with a few, thin beds of siltstone. The thin-sections show that the grain size usually ranges between 0.4 and 0.05 for most of the rocks. The sandstone beds strike between 10o and 25o west of north (i.e., c. NNW-SSE) and dip at 20o towards ENE. The most conspicuous joint sets are transecting the rocks along approximately N-S and ENE-WSW trends. Field investigations, microscopic examination and mechanical testing indicate that the sandstone is well suited for aggregate production. The homogeneous appearance of the rocks leads us to conclude that it should not be neccessary to conduct a drilling programme in the planned exctraction area. NGU, however, recommends that the area should be further sampled for mechanical testing according to the plan described in our 2nd preliminary report that is enclosed together with this report.