ALUNSKIFER

Undersøkelsene hadde utgangspunkt i en mulig totalutnyttelse av kontaktmetamorf alunskifer med Zn-mineraliserte skarnlinser for å utvinne U-, Mo-, V- og Zn-innholdet. Det er påvist store tykkelser av oppdomet aktiv alunskifer i den vestlige delen av Elsjøfeltet; f.eks. 56 m mektighet med 140 ppm U, 191 ppm Mo og 895 ppm V. Sinkmineraliseringene opptrer for spredt til å utgjøre noe økonomisk tilskudd til malmverdien. Sporelementinnholdet er for lavt til at en drift med utluting av bergartene kan være økonomisk idag. Det er utført 404 m kjerneboring, en omfattende prøvetaking, radiometriske målinger, radonmålinger, jordprøvetaking og geologisk kartlegging.

As part of understanding the lithological variations of the exotic alum shales outcropping in the Oslo Rift (Fig.1), and how these represent different mineralogical, geochemical, and geomechanical properties, it is helpful to know their geographic distribution within the Oslo Rift in map view (2-D) and especially how they vary stratigraphically in vertical (1-D)sections at certain key localities.
In this report we have reviewed the chemical composition of the Cambrian and lower Ordovician sediments of the Rift based on work published 25-50 years ago, mainly the chemical analyses presented in Nyland & Teigland (1984). The lower Cambrian rocks consist of sandstones and shales desposited in an oxic environment, followed by a gradual transition in to an anoxic environment and sediments of Upper Cambrian and Lower Ordovician age, with the composition of black shales (Alum shales). Several elements including U, Mo, V, as well as radioactivity show a positive correlation with the carbon content (TOC) in the rocks.
It is our intention that this compilation of geochemical data, can be used as a database for those who need an overview of the chemical composition of the Cambrian and Lower Ordovician sedimentary rocks of the Oslo Rift.