Bergvesenet Postboks 3021, 7002 Trondheim Rapportarkivet Bergvesenetrapportnr InternJournalnr Interntarklvnr Rapportlokalisering GraderIng BV398

Kommerfra ..arkiv Ekstemrapportnr Oversendtfra Fortroligpga Fortrollgfradato: Østlandske NGU 1750/490

Tittel Geologisk kartlegging på Romeriksåsene, Oslofeltet, Nannestad, ,

Forfatter Dato Bedrift 1979 USB

Kommune Fylke BergdIstrIkt 1:50000kartblad 1:250000 kartblad Nannestad, , østlandske Nittedal, Lunner Oppland

Fagområde Dokumenttype Forekomster Geologi

Råstofftype Emneord Malm/metall

Sammendrag UNDERSØKELSEAV STATENS BERGRETTIGHETER

1979

NGU-rapportnr. 1750/49G Geologiskkartleggingpå Romeriksåsen Oslofeltet. Nannestad/Nittedal/Lunner, Akershus og Oppland fylker. Norges geologiske undersøkelse Leiv Eiriksons vei 39Postboks 3006Postgiront. 5168232 TIL (075) 15 8607001 TrondheimBankgironr. 0633.05.70014

Rapport nr. 1750/49 G Apex/Fortrolig til 31/12 1980 Tittel:

Geologisk kartlegging på Romeriksåsen i Oslofeltet.

Oppdragsgiver: Forfatter: Industridepartementet Dr. Peter W. Scott University of Hull, England

Forekomstens navn og koordinater: Kommune: Nannestad, Nittedal og Lunner

Fylke: Kartbladnr. og -navn (1:50 000): Akershus og Oppland 1915 III, Nannestad

Utførts Sidetall: 13 Tekstbilag: Feltarbeid: 1976-79 Rapport : Sept. -79 Kartbilag: 1

Prosjektnummer og - navn: 1750 - Undersøkelse av statens bergrettigheter Prosjektleder: Førstestatsgeolog Ingvar Lindahl

Sammendrag av Svein Olerud:

Det kartlagte området utgjør den nordligste delen av kartblad Nannestad, 1:50 000.

Bergartene i området er hovedsakelig intrusive Oslofeltbergarter av monzonittisk-granittisk sammensetning, de er inndelt i til- sammen 14 enheter. Lavabergarter forekommer som mindre xeno- litter. Kambro-siluriske hornfelser og prekambriske gneiser finnes i området. Hovedtrekkene ved kartet er to sirkulære strukturer. Stryken ringstruktur ligger i vest med senter ved Harestuvatnet, i øst ligger en ufullstendig ringstruktur representert med ekeritt sentrum og syenitt rundt. Den sistnevnte kan være et ring- kompleks som er delvis ødelagt av den sentrale- (og yngste-) ekeritt intrusjonen. Det er påvist 8 områder med hydrotermal omvandling av bergartene Disse omvandlingene kan være indikator for mineraliseringer av typen porphyry molybden. Noen av disse områdene bør følges opp med detaljerte undersøkelser.

Berggrunn

Nøkkelord Hydrotermale omvandlinger

Mo Ved referanse til rapporten oppgis forfatter, tittel og rapportnr. -2-

INNHOLD

Side

INNLEDNING - KONKLUSJON (S. Olerud) 3

INSTRUCTION FOR WORK 5

DESCRIPTION OF ROCK TYPES AND DISTRIBUTION ON THE MAP 5

Syenite 6 Syenite porphyry 7 Peralkaline syenite 7 Ekerite 8 Biotite granite 8 Monzonite 9 Felsite, felsite porphyry and breccia 9

SEQUENCE OF INTRUSION 10

HYDROTHERMAL ALTERATION AND OTHER AREAS OF POTENTIAL ORE MINERAL DEPOSITION

FURTHER WORK NECESSARY

REFERENCES

TEGhING

1750/49G-01 Geological map, Romeriksåsen -3-

INNLEDNING - KONKLUSJON

Arbeidet for denne rapporten er gjort av Dr. P.W. Scott, Universitet i Hull, England. Feltsesongen 1976 og 1977 kartla Scott Stryken ringstrukturen som har sitt senter ved Harestuavatnet. Feltsesongen 1979 lyktes det å få Scott til å fortsette kartleggingen lengre østover på kartblad Nannestad, 1:50 000 med støtte fra USB. Deler av arbeidet er gjort med stud.techn. J.S. Sandstad som assistent og samarbeid med undertegnede.

Hensikten med kartleggingen var følgende:

Å sette Elsjøfeltet og dets mineraliseringer i en større strukturgeologisk sammenheng.

Feltsesongen -78 ble det gjort et par funn av molybden- glansmineraliseringer på den nordlige delen av kartblad Nannestad i områdene Mosatjern (UTM 058768) og Gåstjern (UTM 053785). ønsket om å sette disse mineraliseringene inn i en større geologisk sammenheng var derfor endel av hensikten med arbeidet. I tillegg til dette skulle kartleggingen omfatte regi- strering av hydrotermale omvandlingsfenomener som even- tuelt kan ha tilknytning til molybdenmineraliseringer av typen porphyry molybden.

Berggrunnskart for kartblad Nannestad 1:50 000 er under arbeid og materialet vil bli brukt på dette kartet.

Resultatet av kartleggingen er at en i tillegg til Stryken ringstrukturen i vest på kartet (Tegn. 1) får fram en ny struktur i det østlige området. Sannsynligvis er det restene av en ringstruktur som er delvis ødelagt av en yngre ekeritt intrusjon. Elsjøfeltet ligger som en kambro- silur rest i utkanten av denne ringstrukturen. Molybden- mineraliseringene og et nytt funn av en blymineralisering er plassert i de sentrale deler av ekeritt intrusjonen. -4-

De nye områdene med hydrotermal omvandling av bergartene som er funnet er interessante, og noen av dem bør følges opp med mer detaljerte arbeider, for å undersøke om de kan være indikatorbergarter for mineraliseringer av typen porphyxy molybden.

Området avmerket med 1. på Tegn. 1 ved Høgbrenna er av spesiell interesse da en der har et område på flere hundre meter i diameter med fullstendig omvandling til kvarts- sericitt bergart.

Trondheim, 14. november 1979

( Svein Olerud -5-

INSTRUCTION FOR WORK

Location: Northern part of Nannestad 1:50 000 sheet.

Objectives: (a) To map at 1:10 000 scale the area to the north of the Storøyungen granite and to the east of the Stryken Ring Complex.

(b) To search for and note areas of hydrothermal alteration and other signs of potential ore deposition.

DESCRIPTION OF ROCK TYPES AND DISTRIBUTION ON THE MAP

The following main igneous rock types are present: syenite (porphyritic and non-porphyritic), syenite porphyry, peral- kaline syenite, ekerite, biotite granite, monzonite, felsite (and felsite porphyry) and breccia. Pre-Cambrian gneiss with a dominant east - west foliation are present in the north-east of the area and probably underlies most of the thickly covered area to the north and north-west of Garder- moen. Hornfelsed Cambrosilurian sediments occupy the inlier of Tripperudhøgda and Engelstadkampen. Similar rocks are present as blocks within syenites adjacent to the inlier.

The major feature of the map is the two circular structures: namely, the Stryken Ring Complex in the west and the incom- plete structure represented by the syenite and ekerite in the east. Appropriately, the oldest strata are found on the outside of the circular structure (Pre-Cambrian and Cambro- silurian) and between this structure and the Stryken Ring Complex (nonzonites). The Stryken Ring Complex is inter- preted as a 'cauldron root' (cf. Segalstad 1975 p. 322) ex- posed at a deeper level of erosion than other cauldrons in the Oslo region. -6-

Solid geology boundaries have been drawn as a dashed line on the map in the extreme east of the area where there is a thick cover of Quarternary clays. It has been possible to indicate the position of boundaries here as intermittent ex- posures of solid bedrock are present in the deep valleys occupied by the rivers and Rotua.

The following description of the igneous rock types is based solely on examination of the rocks in the field and may not correspond exactly to descriptions once thin sections have been examined.

Svenite

This rock is equivalent to the Grefsen syenite of Oftedahl (1948) and the nordmarkite type 1 of Barth (1944), ie. it has a significant amount of plagioclase and the ferromagnesian minerals are biotite and hornblende. Small amounts of quartz (<10%) may or may not be present. The rock is overall orange-ish or grey-ish, but typically the plagioclase is present as medium to dark grey crystals. Porphyritic varie- ties, with medium to dark grey feldspar phenocrysts in an overall grey or more usually orange-ish or red-ish matrix, occur. An attempt has been made on the map to show areas where the porphyritic type is dominant, ie. mainly to the north of Råsjøen and surrounding the felsite north-west of Råbjørn.e.The syenite around Skotjernet is medium grained, equigranular and orange in colour, but immediately adjacent to the lake, a fine grained syenite is present.

To the north of Råsjøen the porphyritic syenite is in sharp contact with the grey syenite porphyry to the west (see p. 7), but to the south of the lake, areas of porphyritic syenite are present within the syenite porphyry without any sharp contact. -7-

To the north of Bjertnessjøen adjacent to the ekerite, the syenite sometimes contains less biotite and plagioclase be- coming more like a peralkaline syenite. This maybe an effect to the later intrusion of the ekerite; but, elsewhere the ekerite is in sharp contact and sends veins into the syenite. Xenoliths of Pre-Cambrian gneisses are common within the syenite near to the contact with the Storøyungen granite.

S enite or h r

This rock is equivalent to the Byvatn and Fjellsjøhøgda types of syenite porphyry of Saether (1962). The matrix is always grey in colour in the finer grained varieties with the feldspar phenocrysts being dark grey when fresh, but appearing cream or pink-ish on weathered or joint surfaces. The ferromagnesian minerals are biotite, hornblende and pyroxene. This porphyry forms the outermost ring dyke of the Stryken Ring Complex to the west where its outcrop is narrow and the intrusion is steep-sided. However, it is areally a more extensive intrusion in the eastern part of the ring complex, is overall more coarsely crystallised, and in places forms an even coarser rock indistinguishable from some varieties of the porphyritic syenite. This simi- larity is to be expected, where conditions favoured the coarser crystallisation, as mineral compositions in the Grefsen syenite and syenite porphyry have been shown by the author to be almost identical.

Peralkaline s enite

This is equivalent to nordmarkite type 2 of Barth (1944) and nordmarkite of Saether (1962). In the present area, apart from the major intrusion around Harestua within the Stryken Ring Complex and the Hakadal nordmarkite, it occurs only as -8-

a local quartz poor development within the major ekerite body. The rock is medium to coarse grained comprises alkali feld- spars, greenish amphibole and/or aegirine without biotite. In the field it is the absence of biotite and dark grey feld- spar which distinguishes this rock from Grefsen syenite, and the lack of quartz (<10%) which distinguishes it from eke- rite.

Ekerite

This alkali granite is dominantly a pale pink-ish or grey rock, ranging from medium to coarse grained. It comprises alkali feldspar, a variable amount of quartz (10-30%) and one of more alkali pyriboles. There is no biotite. Typi- cally one pyribole is late crystallising and forms as fib- rous crystals in cavities. Often the ferromagnesian mine- rals are almost non-existant. A fine grained variety of ekerite is present as small veins and patches throughout the main intrusion. Where this type is dominant it is shown separately on the map.

Biotite ranite

In addition to the Storøyungen granite, a small area of biotite granite is present in the north-east edge of the map. The biotite granite is coarse grained with pink and white feldspars, abundant quartz (ca. 30%) and mica. Finer grained varieties are present as small patches within the Storøyungen granite. -9-

Monzonite

Two areas are rovisionall mapped as monzonites (larvikite on the map) because of the increased amounts of ferromagnesian minerals in these rocks. One sharp contact of the monzonite south of Råsjøen with the syenite porphyry has been found showing the monzonite to be older. This monzonite is domi- nantly coarse grained; but, in places, is crammed with xenoliths. The xenoliths range from fine grained grey types to medium grained types with a similar mineralogy to the monzonites. In some fine grained types porphyroblasts of feldspar and mica indicate that the xenoliths are ln an advanced stage of assimilation.

The monzonite around Lauvtangen is coarse grained with bio- tite as the dominant ferromagnesian mineral. The extent of this body southwards is not known.

Felsite, felsite or h r and breccia

These are dealt with together because they form a single intrusive phase (probably a diatreme) and sharp contacts bet- ween these rocks are never observed. The felsite is a grey, brown or white rock, very fine grained, well jointed commonly with manganese staining on joint surfaces. When feldspar phenocrysts are developed it becomes a felsite porphyry. Flow banding is occasionally observed in both varieties. In one small area quartz phenocrysts are also present (quartz feldspar porphyry). -10-

SEQUENCE OF INTRUSION

The general order of intrusion is established as follows;

Intrusion of monzonite.

Intrusion of syenite porphyry comprising outer ring dyke of Stryken Ring Complex. Explosive event with emplacement of diatremes in outer part of syenite porphyry ring dyke.

Intrusion of syenite and porphyritic syenite.

Intrusion of nordmarkite of Harestua, nordmarkite of Haka- dal, ekerite and biotite granite. The relative ages of the biotite granite and other rocks cannot be established as they are nowhere in observable contact. Olerud has shown that the Hakadal nordmarkite intrudes the Storøy- ungen granite just to the north of As Gård, Hakadal. Thus, it may be that the biotite granites are the earlier intrusions.

HYDROTHERMAL ALTERATION AND OTHER AREAS OF POTENTIAL ORE MINERAL DEPOSITION

North-east of Høgbrenna (UTM 008807). Host rock: felsite and porphyritic syenite. Quartz sericitic alternation pre- sent. Pyrite present but no molybdenite found. Extent of area of alteration not determined.

East of Nordre Skotjernfjell (UTM 996793). Host rock: felsite. Small area of quartz sericitic alteration with a little pyrite (approx. 200 m square).

Gåsetjern (UTM 053785). Host rock: ekerite. Small area of alteration beside road. A little pyrite and molybdenite. Road section is approx 20 m long. -1 L-

4 . HeLweell Dalst_ )(4141eLdnd Grims Ljernet bes ide new ruad IMTM und129). Host rock: poLLA.yritic syenite drid biutite ardnite. ch Lott 444: and prubab ly auditz serici lic alleration. A teL ut di ssemi na ted py vi Le Iuund along wi Lh some molybdeni Le .

5. Åsveaen , on ruadn Lde beside KId na ler skole and furthor north Lowa rds Hok: Ina Ier (UTM 096787) . Hos t rock: ekert.Le Severa L vcin-like pd Lches uf very reddened ekerite cut by veinle ts ut white cluy . Reddened ekeli te is surrounded by nurmal ekevi te heavily s Lained with manganese. No sulphides lound.

• 500 m north ul SkL)It jurnet (UTM 089796) . Hos t rock: fe)- site (ur microsyten Lte) . Sume of the rock within the felsi te is cream Lu white duluured and may have been af fected by hydro Lbermal alterdt i on . NU sulphides have been found.

7. Wes L ut Merrat jernet , ,5 km uus t of Råb jørn (UTM 043)92) . liont ruch: ekeri Le. Zune ut reddened ekerite with narrcAN vertida I wb tte ve Id 1n denre 01 reddened zune. Vein is

27 CHIS du and cout a ins abun ant yalena and pyrite.

. Øki iuutei, n()I h-nln tir-wcsL ab II:IkeuKbrenna UTM 0 4 tt Gi . L dred ut iaart_z st:ricitie al tcru-

Li :Jk.) ualpIlid,rH

Wi th the encei4Lion o I nu . 4 dl 1 ot Lhe dYL“5 of hydrothorm41 allertti un dre wl 1411n ei ther Lie eker Lle ur Ule diatreme s L1 udtd Ies . Mure de latled examination 01 these two rock

types n c tes alt Itt tert der areas et alteruLion being tuund.

FUI

Althuugh d cumplete mdt. has been pruduced, SOIRC details (1: boundttries need ex,nuininy and the internal structurcs -12-

of some intrusionsneed examining. Areas where further work is needed before publicationof the map are as follows:

Central part of the ekerite body. Monzonite around Lauvtangen.

The breccia structure is best observed on weathered surfaces as contrastbetween fragmentsand matrix is not usually visible on a freshlybroken surface. In the major felslte/ breccia structurenorth-westof Råbjørn, the breccia com- prises mostly felsite fragments;but, in the structure 500 m north of Skotjernet,large rhomb porphyryblocks are found. Also in the latter structure the felsite is coarser and containsmuscovite (probablythis rock is more correctly called a microsyenite). Two small areas of felsite disconnec- ted from the main structurenorth-westof Råbjørn are thought to have been separated as a result of later intrusionof the porphyriticsyenite.

Western boundary of monzonite south-westof Råsjøen. Central part of diatreme structure north-westof Råbjørn and detail of contact of diatremewith surroundingrocks. Examinationin considerabledetail of all areas with hydrothermalalteration.

Universityof Hull, England September 1979 P.W. Scott (sign.) -13-

REFERENCES

Barth, T.F.W. 1944: Studies on the igneous rock complex of the Oslo region II. Systematic petrography of the plutonic rocks. Skr. Norske Vidensk.-Akad. Oslo I. Mat.-Naturv. Klasse. 9, 104 pp.

Oftedahl, C. 1948: Studies on the igneous rock complex of the Oslo region IX. The feldspars. Skr. Norske Vidensk.-Akad. Oslo I. Mat.-Naturv. Kl. No. 3., 71 pp.

Saether, E. 1962: Studies on the igneous rock complex of the Oslo region XVIII. General investigation of the igneous rocks in the area north of Oslo. Skr. Norske Vidensk.-Akad. Oslo I. Mat.-Naturv. Kl. Ny ser., 1, 148 pp.

Segalstad, T.V. 1975: Cauldron subsidences, ring structures, and major faults in the Skien district, . Norsk Geologisk Tidsskrift, 55, 321-333. •

LEGEND:

1815 I 155.5915555I s Unexposed C Cambrosilurian hornfelses P5 x X )< :(< k>[ :1\2C/55555s ____ 5cs ss5 s 5 5 5s5 3S s sss5 F F p- ps()P5 Ps P5 5 5 s — 5 _ ps vs 96 „x- 5,555 ssss sss- 5P-6FPP;P51:5P6F5r p5ps955p:PssP3pPPS55:15..5555:75 1815 II JS 5 5 5 5 3-5 s 5 -5 Q X ggx KK s 5 5 F F rr PS PS / 5 5 5 s P5 P5 s 5ss5s _5 5 Biotite granite aplite Mapped contacts F r r P5 PsPs Ps sssss._:ss :<‘," X 4 )( "r )( (\/ + 5 . 5 s _ _ _ 5 5 S S - PFFPFFFF \ xx: /\( '>\'' X X ,< )< X 2< < Pc Pc -- .5 s 5 x x g PC Inferred contacts 5 5 S S 5 s < ipc N X X _ 5 5 s - --- PRFFF F.F P6 PS S Ekerite 5 s - - - ,5 r 7 >< ;( )K X Z< z< under thick cover 5 5 $ s 5 r F F5p 75 ;< P rePPC pc Pc /k/ -\" 5 as _ 5 _ s 5 5 t) s -- - _ - _ s 5 5 S - )<" xx 4-k X Intrusive contact. Arrow points 5 5 G5 S PSAPS 1 55\S K X Fine grained ekerite dominant _ _ _ 55 5 s 0 .• from intruding rock into its host rock \1/4/\ z _ _ - _ - s - - \ -- Fs- „ p ps P5 Åj X is 55‘12C S ,C X X ----5----51:53-55:e5 >, , / ‘,„ S„5 3„ , Peralkaline quarts \ \ - - - 5 PP5:57357PIPS; PP5;55;56/:\S:#\ 5 5 sS ///S. ./ Pss Whereno boundarybetween rockunits ——- CSJ, syeniteE Nordmarkite < — _ ps RS P3 PS *. is shown the contactisdiffuse ps x x -)< ->< X -5( 5 s — 25 Ps ps `j 1:\\\ \)\ 5 F5F5T—FtiS)15\ S‘:PPSCC P5 P4 ps y SS s \ - -‘< N X "Vt< ›S/ IS5555 Syenite porphyry (Byvatn type) 5 S 5 5 XXX X „<' X/xx Xx -X x 5 I — ® Areas of hydrothermal alteration z \ n ros ' 5"5 s s, pS ps ps x / 2,;/ Ca _553-5,5 Syenite porphyry. Coarser .15 5:5 5 PS Ps xx grained than Byvatn type .ps x x 5 5 5 5 1 553.515 / ~. 7.5 -54 55555 N. X s - 5 5' 5 4 s \f\,, 5 5 5 -555 5153p;I; ' I 1 Syenite. Non - peralkalkaline (,5s 5555 \/ < tikeN / 77 ss 5 S / -/1" -1- _A/ sl L ( 5 5 //\ LL sss -\/ a. s s \— 1 + 75 P — \- 5 «t'll 5 - Porphyritic syenite \\ 4>c; 6 S $ ts s + 1- _, \\\ \ --S s)(:11): 17e,s, -+ + P5 PS PS :/ P )1: 5)1/415 -SC ")( \' Non- P \ \51`) 5,5 < a:X X 1111 5 5 / / \\ "- 3 t / ps - 5 X X s re• 55551:511÷ peralkaline X ' F.5 Fs F \ • s - \ _ - PSPs ss )( ")( sss sssssss + Fine-grained syenite , \ , \- \ 5Pspp6:3psp5, \\\ _ 55 5s s 55 !rs-` Cs\' e 5 / S55 s s5:55-555 rs F.5 __ 5 s s s sss FF F C 5 cs .s 555 F "sts Ps S 5 5 5 c SS 5 5 ,;(53); )(5,55,g53565.5:55.5sSiSs5555:5-05553 t- 1 g — „\ „ \ s C c 5 s __. 5-5-5 S-5.5 555 s ss 35555 5 55 535 + fl ' s 5-5t _ o c s Cs cs 5 5553 SS5SSSSSssi .53S5S Felsite , Felsite porphyry _—- 555 55ss S 3 353555.555ss S RFF ss sss 555555555 + and flow banded felsite Ff FFF g5:3. ;555.5.5- &:" 5: s i•" —Ss 5-5:15-s _ C.C.S5CC155(55CCSSC s -4; - s _ cs cs cs cs C S 5 CS C g 5 s s s s s _ \ r PS F F5 s s s s +- FF CFF F F Quarts feldspar porphyry f / \ FFFF FF-n s + + + -!*". .‹C».* v cFzp.

\4\ • 4t In / V g F N ,, Ortir diatremes \\ 1km 2km 3km 4km 5km _ F" ' Ignimbrite N er — F

Rhomb porphyry

MÂLESTOKK OBS. P.W.S. Aug.-79 Green porphyry US B 1979 TEGN n Sept. -79 P W. Scott , september 1979 Geological mcuo 1:50 000 TRAc Larvikite and other ROMERIKSASEN ,Nov -79 monzonites LUNNER , NITTEDAL , NANNESTAD KFR. S.0 I AKERSHUS , OPPLAND

TEGNING NR. KARTBLAD (AMS) - p Precambrian gneisses NORGES GEOLOGISKE UNDERSØKELSE TRONDHEIM 1750/49G-01 1915 III