The eclogites is formed by eclogitisation of a titanium-rich Proterozoic gabbroic intrusion (app. 1500 Ma) during a late stage in the Caledonian orogeny at 400 Ma, in this process titanium from Fe-Ti-oxides and silicates entered rutile.
Close-up photo of eclogite with quartz vein
The eclogite is internally folded by two eclogite facies deformation events followed by deformation under amphibolite and greenschist facies conditions. The retrograde events tend to alter rutile to ilmenite and occasionally also to titanite. Locally, retrogression has significant damaging effects on the rutile ore while in a broad scale the effects are relatively minor.
Rutile from Engebøfjellet as well as from eclogites elsewhere in W. Norway is practically free from the radioactive elements U and Th, in contrast to many rutile deposits in production elsewhere in the World.
The resource
Based on 15,000 m of core drilling a mineral resource of 400 million tons of ore-quality eclogite has been identified. The average rutile grade is c. 3.5-%, varying from less than 2 % to 6-7 % and the rutile is disseminated in the eclogite.
Additional "probable ore resources" are indicated at the continuation of the deposit at depth, and large amounts of "possible ore resources" are indicated by a gravimetric survey combined with surface geological mapping 6-10 km eastwards from Engebøfjellet.
Panorama of Engebøfjellet rutile deposit, seen from the west
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