PETROLOGI

Nikkel-mineraliseringen ved Bruvannsfeltet i Råna-massivet i Ofoten ligger nesten utelukkende som disseminasjon av sulfid i peridotitt. Forekomsten er beregnet til 43.6 mill. tonn med 0,33% sulfid-Ni, 0,08% Cu og 0,015% Co. Forekomsten er delt i to av en NØ-SV strøkende hengselsforkastning. Vest for forkastningen har man en øvre og en nedre malm og derunder en sekvens (nedover) av steril peridotitt, pyroksenitt og noritt. Øst for forkastningen har man ekvivalenten til den nedre malmen mens de underliggende lag er blottet NØ for Bruvannsfeltet. Rapporten beskriver forekomstens geologi, malmgeologi og strukturgeologi og gir bl.a. en tolkning av 12 N-S profiler, 12 Ø-V profiler og 13 horisontale snitt gjennom forekomsten med kommentar på styrkene og svakhetene i tolkningen av de enkelte profiler.

The project has documented the existence of several previously unknown platinum group element (PGE) mineralizations in Norwegian ophiolites, of a type previously not well-documented anywhere, i.e. stratiform platinum- palladium-gold mineralization in ultramafic cumulates in ophiolites. PGE- bearing podiform chromitite and high level Ni-Cu sulphide mineralizations have also been studied. It has been documented that PGE-enrichment in the ultramafic bodies hosting the podiform chromitites is confined to the chromitite bodies. Both the podiform chromitite and Ni-Cu sulphide miner- alizations are of such limited tonnage that they have no economic interest. The stratiform PGE mineralizations found so far, in the Leka and Lyngen ophiolites are submarginal but are sufficiently rich and of sufficient dimensions that they are considered to indicate a possible potential for mineralizations of economic interest in these complexes and in all others with well developed, laterally extensive sequences of olivine-rich ...........

Denne rapport er baseret på feltarbejde udført i sommeren 1995 indenfor "Samtolkning af geodata i Grongfeltet" under NGU og Nord-Trøndelag Fylkeskommune. Rapporten beskæftiger sig med feltforhold, petrografi af gabbroiske intrusioner og gangbjergarter i Grøndalsfjellområdet i Grong- feltet. Undersøgelserne har bestået af en kombination af kortlægning/ prøvetagning og mikroskopering af tyndslib fremstillet på basis af prøve- tagning i 1994. Hovedmålet for disse undersøgelser er, at belyse den magmatiske udvikling af Grongeltets intrusive bjergarter for derigennem at opnå en bedre forståelse af de magmatiske og hydrotermale processer, der har været aktive under dannelsen af Grongfeltets vulkanogene massive sulfider. På baggrund af feltarbejde i Grongfeltet i 1994 er Grøndalsfjellområdet udvalgt som hoved- område for studierne, idet visse af områdets bjergarter viser teksturelle og geokemiske paralleller til dele af den vulkanske stratigrafi i Grongfeltet. Samtidig er området velblottet og tilgængeligt og, sammenlignet med øvrige dele af Grongfeltet, det område der rummer de bedste betingelser for studier af de primære magmatiske processer og kontaktrelationerne mellem forskellige intrusiver. Rapporten fokuserer på relationerne mellem et kompleks bestående aflagdelte og ikke lagdelte gabbroer og et kompleks bestående af hornblenderige gabbroiske bjergarter. Samtidig lægges der vækt på beskrivelsen af mafiske og ultramafiske gange og disses relationer til hhv. lagdelt gabbro og hornblende- rig gabbro.

IGCP project 371 COPENA (Structure and Correlation of the Precambrium in NE Europe and the North Atlantic Realm) is a major current research and corre- elation venture in the North Atlantic Region and the European Precambrian craton. In 1997 the annual meeting of COPENA was arranged at the Geological Survey of Norway in Trondheim, Norway. The meeting focussed on recent advances in understanding the evolution the Proterozoic orogenic belt. This report contains the abstracts submitted to the meeting, and also includes the conference proceedings and a list of participants. Two field excursions were arranged in connection with the meeting. The field guides were published as NGU-Reports 97.132 (Proterozoic geology and Scandian high-pressure overprinting in the Western Gneiss Region) and 97.133 (Protero- zoic basement and Scandian geology of the outer Trondheims fjord).

This report is a guidebook for a five day excursion in connection with the Alice Wain Memorial West Norway Eclogite Field Symposium held in Selje from June 21st-28th, 2003. The Western Gneiss Region provides some of the largest, most comprehensive, and accessible exposures of eclogites and eclogite-facies rocks and garnet peridotites in the world. Perhaps more important for some, it lies in ther heart of a great Paleozoic thrust orogen, the late Silurian - early Devonian Scandian orogen, where there is opportunity for using the sciences of tectono-stratigraphy and geochronology as keys to determine the evolutionary history of how these rocks attained their special petrology at great depth and then were preserved and exhumed to the locations of their present exposure. Much of the tectono-stratigraphic framework is preserved in fartraveled thrust sheets in the foreland of the orogen in western Sweden and southern Norway, and these regions need to be visited to gain a full appreciation of the scale and diversity of tectonically assembled units. On the first day of the excursion, the entire group will travel together from Selje to Lepsøya or Midsund, stopping to investigate eclogites and related rocks of the Ulstein Region. Thereafter, excursion participants, divided into two groups, will visit localities at Nordøyane, teh Brattvåg Peninsula, Fjørtoft, and Midsund

Geological mapping and interpretation has shown that the rocks in Berakvam operating quarry can be subdivided in four NW-trending zones, which continue at depth down to the northeast. The southwestern and northeastern zones consist almost exclusively of prophyritic granodiorite while the two central zones consist of prophyritic granodiorite with bodies of gneissic granite and fine-grained grey gneisses with subordinate sheets of pegmatite, respectively.
Since Norsk Stein A/S wish to extract rocks down to a level of -50 m in the present quarry, four boreholes supplemented geological mapping of the quarry. The interpretation concludes that the rock volume between the quarry's present level and the -50 m level in the southwestern 3/5 of the quarry predominantly consists of porphyritic granodiorite of known good mechanical quality. In the remaining northeastern 2/5 of the quarry, the rock volume down to the -50 m level consists of porphyritic granodiorite intercalated with c. 20% fine-grained grey gneisses. The later will possibly raise the average mechanical properties, as argued from the petrological analysis. The fine-grained grey gneisses contain scattered 5 m wide sheet-like bodies of pegmatite a 100 m wide zone in the southwest, which locally could reduce the homogeneity and quality.
The geological investigation of the Berakvam reserve area shows that the rockshere must have similar or better mechanical properties than in the present quarry. The mapping showed that the northern and eastern parts of the reserve area predominantly consist of uniform porphyritic granodiorite with plenty of lenses of fine-grained grey gneisses, and some of small-porphyritic diorite. Particularly interesting is a large irregular body of fine-grained grey gneisses that dominates the southern half of this part of the reserve area. As for the quarry, the petrological analysis of rocks from the area indicate that the fine-grained grey gneisses may show better mechanical properties than those obtained for the porphyritic granodiorites.
At the moment, virtually no data exist to document the assumed better mechanical property of the fine-grained grey gneisses. Because they are so important in volume in the western part of the reserve area, close to the present quarry, mechanical testing of these gneisses is recommended.

To områder er kartlagt i Kristansand området med hensyn på etablering av pukkuttak.
Området ved Kjevik domineres av en rødlig granitt med antatt god til middels kvalitet. Pga. den homogene berggrunnsgeologien ansees området som tilfredsstillende kartlagt mht. omfang av antall materialtekniske prøver.
Geologien innenfor Krogevann området er mer varierende, men domineres av ulike gneis varianter. K valiteten innenfor det arealmessig største området innenfor den kartlagte forekomsten består av bergarter med en antatt god kvalitet. I og med at det kun er tatt en prøve per bergartstype i området, anbefales det å ta noen flere prøver slik at en kan få avklart om det opptrer kvalitetsvariasjoner innenfor et aktuelt uttaksområde.

The Kordalsnuten-Grøneviksåsen prospect is a 2.8 km2 target area with the potential to become a major international hard rock deposit. Located to the north-east of the operating Berakvam quarry owned by Norsk Stein AS, the prospect has been investigated by NGU to assess its significance.
In the target area, NGU has identified and analysed two rocks of interest for aggregate production. The dominant rock is a uniform granodiorite which covers nearly ninety percent of the prospect. While showing variations in foliation intensity, the granodiorite is exceptionally homogeneous and devoid of any significant structural features. The granodiorite samples have returned good and generally similar Los Angeles, Nordic Abrasion and micro-Deval values. Some variations are nevertheless reported, mostly affecting the Los Angeles coefficient. Those variations correlate to the flakiness index measured on the same samples, although it is unclear why they occur. Despite of those variations in mechanical properties, the granodiorite is considered as a very suitable material for aggregate production.