Genesis and compositional variation among ilmenite 
deposits in the Rogaland anorthosite province.

Henrik Schiellerup, NTNU, Norway

Work in progress

Fe-Ti rich rock accompany Proterozoic massif-type anorthosite magmatism in most anorthosite terranes around the world. The Rogaland anorthosite province in South Norway has a rich history of Fe-Ti oxide exploitation dating back more than 200 years, and oxides have been mined at more than 80 localities around the province.

The aim of the current study is to constrain the genesis of the Rogaland Fe-Ti deposits and establish the controls on ilmenite quality. New isotopic data document that the Rogaland Fe-Ti rich intrusions are compositionally restricted in terms of initial strontium, neodymium and osmium isotopes. Our isotope data along with existing data are in accordance with the Fe-Ti rich rocks being derived from melt batches of similar composition and origin. Ilmenite compositions strongly correlate with their host assemblages, and the MgO-content in ilmenite displays a strong decreasing tendency with increasing complexity of the coexisting mineral assemblage. These observations imply that all investigated deposits have a similar origin, and were, most likely, derived as cumulates from differentiating melt batches, ultimately of similar composition. Our data also show that the MgO-content in ilmenite (expressed as the modal geikielite content) under favourable conditions provide an excellent differentiation index, and that the ilmenite quality, in terms of composition, in most cases is predictable.

References:

Schiellerup, H., Robins, B., Lambert, D.D., Prestvik, T. and Nilsson, L.P. (in prep.). Genesis and compositional variation among ilmenite deposits in the Proterozoic Rogaland anorthosite province, South Norway.