A correlation of AMS and rock quality in crystalline and sedimentary rocks in the Kiirunavaara hanging wall, Sweden

Abstract

A study of the magnetic fabric and rock quality has been performed on crystalline and sedimentary rocks from the hanging wall of the Kiirunavaara iron ore deposit, northern Sweden. The rock samples were taken from 12 outcrops and three oriented drillcores and consist of quartzite, siltstone, conglomerate, porphyritic basalts, quartz-bearing porphyry and mylonite. Anisotropy of magnetic susceptibility (AMS) was used to determine the texture of the rocks by defining the shape of the magnetic susceptibility ellipsoids, the orientation of the magnetic foliation planes and the degree of magnetic anisotropy. AMS data from the outcrops as well as data from the uppermost part of two of the drillcores was used to produce a surface contour map which indicates that both the dip of the magnetic foliation plane and the degree of magnetic anisotropy decrease towards the east. These two parameters thus generally follow the major structural features of the Kiruna region. Two classical rock mechanical parameters, RQD (Rock Quality Designation) and F/m (fractures pr. meter), were used to quantify the amount of discontinuities and fractures in the drill cores. RQD and F/m were subsequently correlated with the AMS data, and a correlation was observed, with the correlation coefficient r varying between 0.6142 and 0.7557. The correlation was limited to just one of the drillcores however it could be traced across rock type boundaries. The correlation indicates that AMS may be used as an indicator tool of the rock mechanical properties in both crystalline and sedimentary rocks.