EKLOGITT

Rapporten presenterer de foreløpige resultatene fra en detaljert kartlegging av et lite område (0,5 x 2 km) med diamantførende gneiser på den nordøstlige delen av Fjørtoft (Nordøyane i Haram kommune, Møre og Romsdal). Området er delt inn i 3 ulike tektoniske blokker: Knurrevika- og Vågholmen-blokkene lengst i nord og Hellvika-blokken som tolkes som underlaget. Knurrevika-blokken inne- holder ulike granat-amfibol-biotitt-gneiser (med og uten klinopyroksen), granat biotit-gneiss og mange små og store eklogittlinser. Vågholmen-blokken domineres av en granat-kyanitt-biotitt-gneiss og inneholder mindre eklogittlinser (opptil 100 x 20 m). Hellvika-blokken består av varierende plagioklas-rike gneiser, migmatittiske gneiser, øyegneiser, granodiorittiske gneiser og eklogitter. Bergartene er intenst deformerte med betydelig skjærbevegelse, strekning og injeksjon av granittiske årer og linser. Knurrevika- og Vågholmen-blokkene ser ut til å være karakterisert av henholdsvis subhorisontale og subvertikale line- asjoner. Høsten 1992 ble det ekstrahert mikrodiamanter fra en prøve av granat-kyanitt- biotitt-gneis og en prøve av granat-amfibol-pyroksen-biotitt-gneis ca. 700 m øst for Hellvika. Til nå har vi ekstrahert og bekreftet 2 diamantkorn i en prøve av granat-kyanitt-biotitt-gneis fra steinbruddet på Vågholmen.

NGU har i flere år foretatt undersøkelser av rutilførende eklogittbergarter i det aktuelle området, men uten å gå noe særlig inn på de detaljerte geologiske relasjoner. Geologien er kompleks med en serie proterozoic felsiske og mafiske bergarter som har gjennomgått en omfattende kaledonsk deformasjon og metamorfose. Karakteristiske bergarter er granitoide gneiser og amfibolitter i forskjellige varianter, metagabbroer, kloritt-harzburgitter pyroksenitter og eklogitter. Formålet med den utførte kartleggingen har vært å få bedre kontroll på felt- relasjonene i Gjørlangeområdet med særlig henblikk på proterozoic gabbroer, som tildels er Ti-rike, og deres eklogittiserte ekvivalenter.

As a part of a collaborative project with DuPont, NGU has made gravity measure- ments across the eastern part of the Engebøfjellet rutile-bearing eclogite deposit in Fjaler commune, Sogn and Fjordane county. The main objective of the investigations was to delineate the morphology and subsurface extension of the eclogite body through gravity modelling. Gravity measurements were made at 39 stations along one 775 m long profile. Two alternative models are proposed in the interpretation of the gravity data. The first model (model 1) has one eclogite body with a density of 3400 kg/m3 and a dip 70-75° towards north-north-west. The length along the dip is on the order of 350-400 m. The average width (horizontal cross section) of the body is c.90 m, and it seems to become thicker towards the surface. The length of the modelled eclogite in the strike direction is set to 1200 m (although the eclogite is longer and wider towards west, but this has little or no effect on the calculated model response). With the dimensions given above, the total volume of the modelled body is c.40.10/6 m3 equivalent to a mass of c. 136 Mt. Model 2 was constructed to get a better match between the calculated model response and the observed Bouguer anomaly values for some stations. An additional body had to be added to the south and in the close vicinity of the main eclogite body to get a better match. However, it was found that the stations in question suffered from erroneous or insufficient terrain corrections due to severe topography, and that these stations should be taken into little or no account in the modelling. The introduction of the additional body in model 2 thus seemed unlikely.

Based on an agreement between Fjord Blokk and Conoco/DuPont a series of drill- holes have been done on the Engebøfjellet rutile-bearing eclogite on the northern side of Førdefjord. The purpose of the project is to investigate and evaluate the rutile resource at Engebøfjellet. The project has been supported by Prospekteringsfondet. This report, which summariezes the results of the first 1000 m of drilling, is preliminary, primarily for Prospekterings- fondet. When the drilling program is finished, at approx. 2200m, all drilling results will be reported together in a comprehensive report. The eclogite is a 2 km long and up to 500 m wide lens-formed eclogite body surrounded by Proterozoic granitoid gneisses. Three major rock types have been distinguished within the deposit. The margins of the eclogite body are dominated by an amphibolitic unit containing amphibolite, amphibolitic eclogite and numerous gneiss bands and interactions. The central parts of the deposit contains a leucogabbroic eclogite unit and a massive Ti-rich eclogite which is the target rock for the rutile investigations. To date (May 1996) 8 drill-holes have been drilled; of these Dh1,2,3,4 and 5 are included in this report.

The report is a guidebook for a four day excursion in connection to the COPENA meeting held at NGU 18.-22.Aug.1997. The first day of the excursion will visit localities in the Caledonian Nappes at Oppdal, and then continue over Sogne- fjell to Sogndal with stops along the contacts to the Jotun Nappe and in the nappe itself. The second day the excursion will continue through the Western Gneiss Region to Måløy with several stops in the Proterozoic gneisses. Many of the classic eclogite localities will be visited, eg. in Almklovdalen, at Selje and Verpeneset, and there will also be some stops in the Devonoan sedi- ments. The third day will also consentrate on the Western Gneiss Region with stops at the Fiskå anorthosite, the Ulsteinvik eclogite and then continue over to Nordøyana and visit the Haram gabbro and examine the structures in the gneisses. The last day will go from Lepsøy to Trondheim via Molde. Here the same nappe sequence as was seen at Oppdal will be visited at several locali- ties, but the nappe sequences are in places only a few meters thick.

Fortrolig til 31.12.2003 Gravity measurements have been carried out along four profiles to the east and west of the Engebøfjellet rutile-bearing eclogite deposit. The main objective of the gravity measurements was to delineate possible heavy (ore-type eclogite) bodies at depth to the west and the east of the known, exposed eclogite deposit.

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.

The Hellevik-Flekke area comprises Precambrian crystalline rocks that have experienced a complex history of deformational and metamorphic events through both Precambrian and Caledonian times. The area can be divided into four different lithological units. The Basal Gneisses, the Flekke Unit, the Gjøl- anger Unit and the Vardeheia Unit. During the Caledonian Orogeny all units were deformed and metamorphosed under eclogite facies conditions, but relicts of undeformed and unmetamorphosed protholiths from the units can be identified. To the south, granodioritic and monzonitic gneisses occur together with granites, pegmatites, and minor amphibolitic and eclogitic bands and lenses. This assembly of lithologies is similar to those of the Western Gneiss Complex in the middle part of the Sognefjord transect. The Flekke Unit is interpreted to represent an allocthonous nappe containing a layered mafic-ultramafic complex. The gabbroic rocks of th complex are dated to 1522+-55 Ma (Sm-Nd age). The Gjølanger Unit consists of grey and green orthogneisses of dioritic to granitic composition, with geochemical character- istics of rocks formed at an active continental margin. Rb-Sr isotopic data indicate a minimum age for the gneisses of 155 Ma, with subsequent Sr-isotope disturbance. This unit is also interpreted to be an allochthonous nappe. The Vardeheia Unit in the north experienced the strongest Caledonian deformation and is dominated by heterogeneous banded gneisses and mylonites with small lenses of amphibolites and eclogites.

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.