RUTIL

Engebøfjellet is situated on the northern side of Førdefjord within an area characterized by a series of Proterozoic felsic and mafic rocks heavily affected by Caledonian deformation and metamorphism. During the Caledonian high-pressure metamorphism Proterozoic mafic rocks were transformed into eclogites. In this transformation ilmenite was replaced by rutile. The protolith to the Engebøfjell eclogite is believed to be a layered, Ti-rich, Proterozoic gabbroic complex; it now has the form of a highly irregular, east- west trending, 2.5 km long and up to 0.5 km broad lens dipping steeply to the north. It consists of two major eclogite varieties; a leucogabbroic eclogite with low Ti-and Fe-content, and a ferrogabbroic, Ti-and Fe-rich eclogite. This ferrogabbroic eclogite is the rutile ore that has been the focus of the rutile exploration work at Engebøfjellet. In the period October 1995 to June 1996 ten reconnaissance bore-holes were drilled to investigate the character of the Engebøfjell ferrogabbroic eclogite at depth; altogether 2340 meters of core were recovered. This report gives a summary of these drilling results with analytical data and mineralogical descriptions.

Confidential to 31.12 2002. Gravity measurements have been carried out along two profiles across the Engebøfjellet rutile-bearing eclogite deposit. The main objective of the investigations was to delineate the morphology and subsurface extension of the eclogite body, given results and constraints from surface mapping and drillholes. Two alternative models are proposed for both profiles. The volume and mass estimates for the models given must be mistaken for the total volume and mass of the whole eclogite deposit, which is larger. This is because the eclogite deposit extends to the east at a longer distance thean would affect the calculated reponse.

Fortrolig til 04.05.2003. The Engebøfjellet eclogite deposit is situated at the northern side of Førde- fjord near the small community Vevring in Naustdal kommune, Sogn og Fjordane county, W.Norway. Geologically the Førdefjord area belongs to the "Western Gneiss Region", between the Devonian Kvamshesten basin to the south and the Devonian Håsteinen basin to the North. Recent mapping divide the Førdefjord region into two major geologic units: the Hegreneset complex and the Helle complex. The Hegreneset complex (oldest) contains a variety of amphibolite, eclogite and gabbroic rocks, together with tonalitic to dioritic gneisses. The Helle complex comprises mainly granitic and granodioritic gneisses.

The gravity measurements in the region between Naustdal and Engebø have been supplemented with 6 profiles. The objective of the measurements was to confirm the anomalies and the size of the indicated bodies from the 1998 investigations. Two profiles east of Naustdal eclogite deposit have shown that the deposit have a limited extension to the east. In the area east of Bygdahaugen, four profiles have confirmed the anomalies from 1998, and have better mapped the extension of the eclogites bodies. All profiles in this area indicates eclogite bodies, and the result from the modelling support the conclusions from 1998. The size of the possible eclogite body seems to be in order of 400 mill. tons.

Gravity measurements have been carried out along 10 profiles in the region in between Naustdal and Engebø. The objective of the measurements was to detect new heavy bodies of eclogite and to map the extension to the depth of the known eclogite at Bygdahaugen. To confirm the ability of the gravity method, two profiles were measured across the known eclogite deposit in Naustdal. The size (depth) of this deposit should be estimated. The results show that the gravity method is well suited for such investigations and the Naustdal deposit was clearly indicated bye a strong anomaly. To the east of Bygdahaugen a new body with a possible density of around 3400 kg/m3 (eclogite) was indicated body. The depth extent is estimated to 600 m in the model. The size of the body is probably in the same range as the Engbø deposit, approximately 400 mill. tons. More detailed investigations, both geophysical and geological, have to be carried out before drilling can start. At least four gravity profiles should be measured which will confirm the anomalies and lead to an improved estimate of the size of the indicated deposits.

(Forkortet) Important rutile deposits in Norway are two of main types: eclogite rutile deposits in Western Norway and metasomatic rutile deposits in the Bamble province of southernmost Norway. Eclogite deposits formed by the metamorphic tranformation of Proterozoic mafic rocks during Caledonian high-pressure metamorphism at 400 Ma. Rutile-bearing eclogites are found in various geologicl sub-provinces from the Bergen region in the south to the Kristiansund region in the north. The metasomatic rutile deposits, such as various rutile-bearing amphibolites and albitites in the Bamble geological province in the southernmost Norway, formed by the metasomatic tranformation of ilmenite-bearing gabbroic and amphibolitic rocks at approx. 1150 Ma.

Confidential until 31.12.2004. See the text in Report 99.129, Vol.1.

See the text in Report 99.129, Vol.1.
Innhold:
App. 1: Overview geographic map of Norway with rutile localities
App. 2: Compilation of analyses of rutile deposits and rutile-bearing rocks
App. 3: Rutile provinces and localities of Norway
App. 4: Rutile grain size data
App. 5: Rutile grain-size distribution graphs
App. 6: Photocopies (A4) of thin sections
App. 7: Overview of microphotographs
(App. 8: CD-ROM with report)

Rutil/eclogitt-forekomster i Sunnfjord representerer en "ny" type rutil- forekomst som kan få stor økonomisk betydning i framtiden. Den mest kjente av forekomstene er Engebøfjellet på nordsiden av Førdefjorden i Naustdal kommune; den var gjenstand for omfattende undersøkelser i 1995-97 i regi av det amerikanske indiustriselskapet DuPont og det da DuPont-eide oljeselskapet Norske Conoco. Disse undersølelser resulterte i påvisning av en ressurs på 400 millioner tonn rutilmalm til en in situ verdi på i størrelsesorden 60 MRDkr Engebøfjell-prosjektet stoppet opp ved årsskiftet 1997/98 som en konsekvens av endringer i DuPonts overordnede strategi. Det er i fagmiljøet akseptert at Engebøfjellet og andre forekomster i regionen representerer en mineralressurs av stor nasjonal og internasjonal betydning. Formålet med denne rapporten er å oppsumere hovedtrekkene vedrørende rutil/ eklogitt-forekomstene i Sunnfjord, og derigjennom stimulere til en fornyet interesse for ressursen.

The Bamble Sector (Arendal-Bamble region) of the Fennoscandian Shield in S. Norway is affected by metasomatic processes related to large-scale fluid migration during Sveconorwegian (Grenvillian) tectonothermal events. In some areas such as at Ødegårdens verk, pervasive fluid infiltration has transformed gabbroic amphibolites into a characteristic scapolite-hornblende rock (ødegårdite). Ilmenite in the gabbroic protolith breaks down to rutile during the metasomatic processes while iron is removed from the system by the fluids. Thus, the metasomatism creates rutile ores.
The region has been regarded to have a potential for economic rutile deposits. However, a disadvantage is a relatively high content of uranium in the rutile. In order to obtain additional information on the character of rutile in various parts of the region and the U contents, rutile from stream sediment heavy fractions have been studied by SEM and analysed for U by laser-ablation ICP-MS.
Mixed mineral grains with ilmenite, rutile and titanite are common in the stream sediments indicating that rutile-forming geological processes in the respective areas have been incomplete; some stream sediment samples have "good rutile" without ilmenite or titanite intergrowths.
Based on the laser-ablation ICP-MS, analysed rutile from the Arendal-Bamble region contains 30-80 ppm U in general, although values up to 180 ppm U have been identified. Values below 10 ppm U are common in ilmenite-rutile-titanite intergrowths representing incomplete rutile transformation.
The potential for economically attractive rutile deposits in the Arendal-Bamble region is probably small due to the overall high uranium content in rutile.