Revista Brasileira de Geociências 17(4):571-5 77, dezembro de 1987

Mo AND Zn MINERALlZATIONS RE LATED TO GRANITES IN CALDERA ROOTS IN TH EELSJAE-AREA, OSLOPALEOR IFT,

SVEIN OLERUD*

ABS T ~ AC T Th e Paleorift evolved in th e Pro terozoic basement of southeastern Norway and the Skagerak Sea in the Permian ; it form s a par t of a larger system of taphrogenic elements occurring at th e margin of th e Balt ic Sh ield . It consists of alkaline igneous rocks and Carnbro-Silurian sedim ents. Th e mo st prominent epigenetic mineralization ty pes are: A. intramagmatic Mo-depo sits; B. contact metasom atic c eposits (Zn , Pb , Fe etc.); C. rift margin deposits (Ag etc). Th e Elsjae area shows good examples of the A and B types. The Elsjae area is situated in th e northern part of the paleorift at the point of intersection be tween tw o dee ply erode d cald era struc tures. Cambro-Ordovician shales and Iimestones form a 2 krn 2 inlier enclosed in Permian ín tru sives. The sedime nts are co ntact metamorphosed and altered by met asomatic processes. Th e sphalerite mineralization is found in skarnaltered Iimestone layers an d lenses at severa l leveis in th e Cambro-Ordovician hornfelsed sedim ents. The Elsjae are a is unde rlain b y Permian granites which are hydrothermally altered and brecciated and carry low-grade molybdenite min erali zation in zones dominated by quartz-sericite-pyrite alte ration . Field evid en ces indicat e that th e Zn-skarn mineralization are related to the Storasyungen gran ite , which was intruded earlier th an the ring d yk e syste rn of th e calderas, while the Mo-mineralization was formed at a lat e stage in th e development of th e calderas.

RESUMO O Paleo-rifte de Oslo , desen volvido no emba samento proterozóico na regrao Sud este da Noruega e no Permiano do mar Skag erak, representa uma das unidades do ex te nso sistema de eleme ntos tafrogênicos qu e ocorrem na marg em do Escudo Báltico. Compõe-se de ro cha s íg neas alca linas de idade perm ian a e de rocha s sedime ntares cambro-silurianas.Os t ipos de min er alizações epigené ticas mais proeminentes são : A. depósito de Mo intramagmático ; B. depósitos metassomá ticos de contato (Zn , Pb , Fe etc .); e C. depó sitos em margem de riftes (Ag etc.) . A área de Elsjre apresenta bo ns exe mplos dos tipos A e B. A região de Elsjee situa-se na porção norte do paleo-r ift e, na zona de in terseção entre duas estru turas de caldeiras pro fun daménte ero didas . Cerca de 2 km 2 de folhelhos e calcários cambro-ordovicianos jazem encaixados na s intrusivas perm ian as. Os sedime ntos mo stram metamorfismo de contato e alteraçã o po r pro cessos metassom ático s. A mineraliz ação de esfalerita enco ntra-se em camadas e lentes car bonáticas escarn itizadas , e em vários níveis do s sed imen tos cambro-ordovicianos transfor mad os em hornfelses. Subjacentes à área de Elsjee há granito s permiano s hidroterminalizados e brechados, e portam mlneralízação de baixo teor de molibdenita nas zonas com predomínio da alte ração quartzo-seri cita-pirita. Evidê ncias de cam po indi cam qu e os escarnitos mineralizados co m Zn se relacionam ao Granito Stor teyungen , o qu al é mais antigo que o sistema de diq ues anelares das cald eiras, enquanto a min eralização de Mo se formou no s estádios tardios do dese nvo lvime nt o das caldeiras.

IN T RODUCT ION This paper reports the results of a Cambro-Ordovician sedimentary rocks which occur as a 2 stu dy of the hydrothermal molybdenum and zink km 2 large rift in Permi an int rusives (Olerud 1984) (F ig. mine ralization within the Elsjee area in the Oslo Paleorift I). The area is located on the eastern margin of the Stryken in Sou th Nor way. ring complex, interpreted as a cauldron root by Scott The Oslo Paleorift evolved in the Proterozoic basement (1979), where syenite porphyry and felsites make up a of southeastern Norway and the Skagerak Sea duríng the system ofring dykes. To the north , a circular alkali granite Permian, and forms part of a larger system of intrusion occurs with remnants ofporphyric syen ite along taphrogenic elements occurring at the margin ofthe Baltic th e borders forming an incorn plete circular structu re Shield in northwest Europe (Fig . 1). It mainly consists of (Scott 1980). No supracrustal Permian rocks are prese rved alkaline Permian igneous rocks and Cambro-Silurian inside this ring structure, as it is in the Stryken ring sedimentary rocks. complex. The alkali granite is ínterpreted as a late A great variety of mineralization types, bo th intrusion in the central, deeper part of the caldera, where orthomagmatic and epigenetic, is related to the magm a­ it has completely destroyed the sup racrustal and tism of the Oslo Paleorift. The most prominent epigenetic subvolcanic rocks found elsewhere in the Oslo Rift mineralization ty pes are: A. intramagmatic Mo-deposits; calderas. The Elsjre area is situated at the point of B. contact metasomatic deposits (Zn , Pb, Fe etc.); C. rift intersection ofthese two main ring structures (Fig. 1). The margin deposits (Ag etc.) (Ihlen 1986a). The Elsjee area Carnbro-Ordovician rocks are in contact with five shows good examples of the A and B types. The different intrusives (Scott 1979 , Olerud 198 2a) (Fig . 2) metallogeny of the Oslo Paleorift is rece ntly described in and are underlain by various Perm ian granites, which have detail in a volume edited by Olerud & Ihlen (1986). produced extensive contact metamorphism and skarn The Elsje area is situate d in the deeply eroded northern alteration in the limes tone s. part of th e paleorift. It con sists of contact-rnetarnorphic

* Geological Survey ofNorway. Box 3006 , N-7002 Trondheim, Norway 572 Revista Brasileira de Geociências. Volume 17, 1987

NORWAY

EL5J0 AREA FIG.2

i i , , i I i LEGEND O 5 10km PERMIAN CAMBRO- SILURIAN XX Alkali gran ite(ekerite) ~~-~~ 5edimentary rocks,contact metamorphosed ++ Granite and granite porphyry (biotite granite) --- near the mtrusives 5yenite (nordmarkite. grefsen-syenite.etc.! PRECAM BRIAN Monzonite (larvikite. kjelsãsite ,etc) c=J Gneiss Gabbro ("Oslo-essexite'; etc) 5ubvolcanic rocks (syenite por phyry, felsite etc) - Main faults Volcanic rocks (rhomb porphyry, basalts. ek.l

Figure 1 - Geologieal map of the northern part of the Oslo Region eompiled and simplif ied from Broegger& Seh etelig (1923), Saether (1962), Larsen (1978), Seott (1980), and Olerud (19 82a). Index map shows the loeation of the Oslo Graben and the eontinuation to the south in the Skagerak Sea. Local rock-type nam es in parentheses.

Sphalerite mineralization occurs in skarn horizones nodules to discoid-formed lenses with maximum sizes of2 within the Cambro-Ordovician sequence of carbonaceous x 40 x 50 m (Ihlen 1980). The zinc mineralizations were and mar1y shales and limestones. The limestone beds and described by Goldschrnidt (1911) and recent1y in more fault zones are part1y replaced by zink bearing skarn. detail by Ihlen (1980). Sphalerite occurs in a medium­ Skarn alteration with associated Zn·W mineralization aiso grained skarn rock dominated by hedenbergite, garnet, occur along fault zones in the argillaceous hornfelses. and small amounts of calcite, amphibole sulphides, and Scattered molybdenite mineralization is found related to scheelite. Between the skarn rock and the surrounding hydrothermal alteration zones in the under1ying Permian Cambrian graphitic shales there is always a zone of granites. This molybdenite mineralization is found in one garnet-graphite rock. This characteristic zonation is found deep (475 m) drill hole (DDH2, Fig. 2), and the all over the Elsjae area. The zinc content of the skarn description of the mineralization is based on data from lenses seldom exceeds 10%, and the average is estimated to this drill hole. to be 5%(Mathiesenetal. 1976). Underground mapping and drilling show that only a SPHALERITE SKARN MINERALlZATIONS Uno small fraction of the limestone lenses is altered to skarn. derground mapping in the abandoned mines by Ihlen The Zn-mineralized skarn lenses are to widespread and low (1980) and surface mapping by Olerud (1984) show that grade to be recoverable. the most important zinc mineralizations in the western Other sphalerite occurences in the eastern part of the part of the Elsje area are related to limestone lenses at a Elsjee area are described as mineralízed fault zones and as single stratigraphic levei in the Cambrian graphitic shales. thin skarn-altered limestone beds (Goldschmidt 1911 , The limestones lenses have irregular shapes from small Mathiesen et ai. 1976, Ihlen 1978). Revista Brasileira de Geociências. Volume 17, 1987 573

-~''-'\'''''-~ ' \-' '-' ~- ' ~- ' '-' :- , -;:- ,,-'~ ',.. \ ..\ .. ', ... \ x x x x x X l..'c' !5.:!-\;,/~":!-~!-':~~~:~-\;.!_~-!._'\l,.. X ',~~:,'.!f,'J:·;:;tk XX ~~ ~~ " : " : " ! " : , ~ ;;':;,-':;;':;,-.:;} J. -..." -': ' -':" -..""/ '" ,":},~-',::),~_j,J DIAMOND DRILL HOLE 2 X 'J .. I \ '-!._\/:~,!~_'.!~~'" X ':f_~:f~:'~_~~_;;~~> X X X x~ \'..."'-:\','..','.!,'--:"'-"-'~"", .. -,:},~-'.,:~,.~~,~-,,"'"",",,..,,,)~ ~ X XX X \'~~::~-~:..~,~:t:~ ·\ - ~ ... , "'~_~~_'\;~5:f5:f5::y' X X o XX: : X1~~!~tt~i~wi~i 't.#J)~' i;fl~E~tf*~~~l~1~,X ~ ., ~ ,_'-----">~ X X " " " ,~ , ." ." ." ,,, .,, .,, ., ,,,, ,,, .,, ,, , ,, , ,, , ,, , ,,, .,, ,, , ,, ,, x "" ~ i

õ · I"

100

L- --' --l'lkm

PERMIAN ROCKS CAMBRO-ORDOVICIAN ROCKS Diabasedyke Hornfelsed graphitic shales Alkali granite and shales with some Syenite marble layers Granite porphyry II Phyllic alteration of the Stor évunqen granite rocks Granite porphyry I Sphalerite-bearing skarn Granite I mineralization Syenite porphyry Molybdenite. scattered mineralization in altered intrusives Faults

Figure 2 - Geological map ofthe Elsja:area.from O/erud (1984)

PERMIAN ROCKS. ALTERATION ANO MOLYBOE­ rock ranging from medium to coarse grained. It comprises NITE MINERALlZATION Permian Rocks Core alkali fe1dspar , a variable amount of quartz (10-30%) and drilling through the Cambro-Ordovician rocks (Ole rud one or more alkali pyriboles and dark mineral. The alkali 1983) showed that the Elsjee area is underlain by per mian granite has a peralkaline chemical composition and is the intrusives (Figo 2)0These rocks are hydrothermally alt ered youngest known intrusive of the area. It is probably and breccia ted and carry low grade mol ybdenit e intru ded into the deeper parts of a now destroyed mineralization locally, cau1dron complex (Figo1). Based on field observations of the in trusive contacts by Scott (1980), Gaut (1981 ) and Olerud ( 1982b, 198 4) and THE SYENITE lt is coarse grained, equigranular drillcore data by Olerud (1983, 1984) th e relative ages can in trusive with a orange colour. A porphyritic variety with be outlined: dark bluish fe1dspar phenocrysts is known frorri the • Youngest : A1kali granite, Syenite, Granite porphyry 11 , southern border of the Cambro-Ordovician rocks of the Storzeyungen granite, Granite porphyry I; and Elsjae area . The rock consists a1kali feldspar, plag íoclase, • Oldest: Granite I. and less than 10%quartzo Biotite and hornblende are the main dark mineraIs. The syenite probably formed the ring THEALKALIGRAN1TE It is a pale pinkish granular dyke of a later destroyed cau1dron complexo The intrusion 574 Revista Brasileira de Geociências, Volume 17, 1987 post-date the propylit ic alteration and Zn- skarn minerali­ which often are zo ne d and mantled by plagioc1 ase. The zation of the Elsjre area, and pre-date the ph yllic plagioc1 ase grains are hypidiomorphic, partly rou nded alte ration with molybden ite m ineralization. with grain size of 2-6 rnrn. The quartz oc curs as part1y rounded and co rroded grai ns less than 3 mm. The matrix is THE GRANITE PORPHYR Y II It is an allotriomor­ dominated by quartz and plagioc1ase with grain sizes less phic granular rock with grain size 0.1-1.0 mm. lt occurs than 0.1 mm. The granite porphyry I is in truded by the with and without phenocry sts of partly rounded quartz of granite porphyry 11 but intrudes the granite I. hypidiomorphic alkali feldspar and often shows granophy­ ric texture with irregular intergrowths of quartzo The rock GRANITE I It is a medium to coarse grained gra nite is characterized by red spots, which occur as haloes around with equigranular texture. lt is only found in the DDH 2. disseminated pyrite grains. The gran ite porphyry II The fresh red coloured alkali feldspar constitute intrudes the granite porphyry I in DDH 2 and is found as approximately 50%of th e rock, while the quartz content is dykes and irregular bodies in side the Storreyungen granite. ca 20% The plagio c1ase appears as white to grey crys tals. Wholerock chemistry (Table 1) of the granite porphyr y II The rock appears very similar to the Storeeyungen granite, and the Storreyungen granite also confirm the close but the whole rock chemistry is c1ear1y different (Ta ble 1 relationship. andFig.3). Rb Table 1 - A verage analy ses ofintrusive rocks in the Elsja: area. A nalysed by X-ray fluorescence at the Geological Survey of Norway , ex cept the alkaligranite, wh ich is analysed by the same m eth ode by Dr. P. W. Sc ott, University ofHull, U.K. GI - Granite I, average of three samples; GP I ­ Granite porphyry I, average of five samples; St.gr, ­ Storteyungen granite, average of two samples; GP II ­ Granite porphyry Il, average ofsix samples; Sy - Syenite, one sample of dy ke south ofElsjte area; A1. gr. - Alkali granite, average of seven samples; 1.0.i. - Losson ignition ; * A verage of two samples. (~ G I GP I St.gr . GP II Sy. Al.gr . wei ght Si02 67.49 70.80 76.23 75 .64 61.62 74 .09 Ah03 15.77 13.81 12.33 12.40 17.7 8 13.08 Fe2 03 2.03 2.39 1.3 3 1.14 3.44 1.78 TiO2 0.5 1 0.42 0.20 0.14 0.84 0. 27 MgO 0.57 0.5 5 0.12 0.09 0.67 0.23 CaO 1.51 1.22 0 .50 0.53 1.72 0.3 4 o Alkali granite Na 20 4.2 3.9 3.6 3.7 5.2 5.1 K20 5. 24 4.48 4 .75 4.64 6.09 5.13 x Syenite MnO 0. 06 0.09 0.06 0.05 0.10 0.1 2 + Granite porphyry 11 P20S 0.11 0.09 0.0 1 < 0.0 1 0.2 3 0.01 6 Stor0yungen granite l.o .i. 1.14 0.94 0.36 0.58 0.79 - 'V Gnmite porphyry I CIPW D Granite I nor m (%) o Dark syenite Q 19.0 27.6 35. 9 34 .8 4.0 25. 3 C 0. 7 0.5 0.4 0.2 0. 1 O Figure 3 - The ternary relationship ofRb, Sr, and Ba in Or 31.0 26.4 28.1 27.4 36 .0 30.3 the intrusive roeks ofthe E lsja:area Ab 35.8 33.1 30.4 31.7 44.0 38.8 An 6.7 5.4 2.4 2.3 7.0 O D.I. 85. 8 87.1 94 .4 93.9 84.0 94.4 Whole rock chemistry Ta ble 1 shows the average PPM whole ro ck chem istry of the actual in trusive rocks in the Rb 170 19 2 324 260 133 242* area. The alk ali fel dspar of these Oslo Region intrusives all Sr 351 216 57 62 400 10* have a high conten t of microperthite, this must be ke pt in Ba 815 4 83 124 146 1,800 92 * mind as it causes c1ear1y different values in th e a lkali feldspar cont en t seen in specimens and the one obtained in the CIPW norm calculation. The Table 1 shows a clear THE STORAJYUNGEN GRANITE At the south of" tendency of increasin g sílica content from the early the Elsjee area it is a coarse gra ined biotite-bearing sub­ (granite I) to the relatively later granite porphyry I an d the solvus granite with hyp idiomorphic granular texture. It latest Storreyungen granite and the granite porphyry 11. consists of alkali feldspar, 25-3 5% quartz and less than The differentiati on index shows the same tendency. The 30% of plagioc1ase. Biotite and magnetite are the most alkali granite is clear1y differen t from this serie of common accessory mineral s (Gau t 1981 ). peraluminous granites (Table 1) as it has only one feldspar and sho ws a peralkaline com position. GRANITEPORPHYR Y I It is only found in the DDH The trace ele me nts Rb , Sr, Ba are plo tt ed in the ternary 2. The phenocrysts of this porphyry make up more than diagrarn of El Bou seily an d El Sokkary (I 975) in figu re 3. 40%of the ro ck volum. The alkali feldspar grains are 3-10 The actu al rock ty pes plo t .in distinct are as. Th e mm across, pa rtly rounded hypidiomorphic cry stals, Storreyungen granite and the granite porphyry II are fo und Revista Brasileira de Geociências. Volume 17, 1987 575 in the area of the mo st differentiated granites and differ mar kedly from the less differentiated granite porphyry 1 and the least differen tiated granite I. The dark syenite occu rs as thin dyk es in DDH 2.

MOLYBDENITE MINERALlZATION Molybdenite occu rs scattered in Permian granitic rocks in DDH 2 between 370 and 26 5 m above sea leveI (a.s.l.) (Fig . 2) and between 170 and 150 m a.s.l, Molybdenite occurs in areas with in tensive phyllic alteration and is deposited the folIowing ways: A. Moly bdenite as a dissemination in zones with phylIic alteration. B. Moly bde nite coatings on fissures. C. Moly bde nite in veinlets of quartz, epidote, an d pyrite. D. Molybdenite as matrix in hydrothermal breccias. The moly bdenum grades found are toa low to be 01' econo mic interest. Figure 4 - Secondary electron image picture tak en by scanning electron m icroscop e. The picture sho ws a quartz HYDROTHERMAL AL TERATION The Permian grain surrounded by sericite, which is the remnants 01 a rocks in DDH 2 show three main types of alteration, i.e. feldspar grain in a sample ofpervasive phy/lic alteration 01 phyllic, argillic, and propylitic alteration. the granite po rphyry I

PHYL LIC A LTERA TION is encountered in the gran ite int rusions beneath the Cambro-Ordovician rocks other places. The alteration is characterized by a clay in DDH 2 as well as in the Storteyungen granite and the mineral alte ration of the plagioclase and a pr ecipi tation of syenite on the western shore of the lake Store Elsje (Fig. hydrothermaI mineraIs such as py rite, carbonates, and 2). In DDH 2 the ph yllic veins are spread along nearly the fluorite alon g the grain bou ndaries of the silicates. The whole length of the core. They are most abundant in the biotite is altered to aggregates of chlorit e, pyr ite, and upper part of the intrusives between 370 and 265 m a.s.l., carbonates. Clay mineraIs also occur as vein-filIing in the whe re approximately 20% of the rock volurn is altered. DDH 2. Dickite and montmorillonite are the main clay Between 230 and 142 m a.s.l. the rock is more weakely mineraIs according to x-r ay diffraction analyses . The alte red, approximately 6-8o/

ARGILLICALTERA TION occurs as a blea ching and DISCUSS ION The succe ssion of geological events in slight green colo uring of the rock and is mainly found in the Elsjte area in the Perm ian is listed in the table the uppermost part of the Permian intrusions in DDH 2, underneath, where the relatively oldest event is at the between 35 1 and 32 8 m a.s.l. In other parts of the core bottom and the youngest is at the topo the argillic alteration is scattered, and it is not foun d any 576 Revista Brasileira de Geociê ncias, Volume 17, 1987

Propylitic alt eration by a later propylitic aIteration which possibly is a low Alkali granite in trusion temperature alteration following the latest intrusive Phyllic alteration and molybdenite mineralization event; the alkali granite. The argillic alteration is difficult Syenite (ring dyke) intrusion to relate to time and space in the system, but is probably a Propylitic alteration and Zn-skarn mineralization late and low temperature alteration. Granite porphyry 11 intrusion The location ofMo-mineralizatíon to calderastructures Storreyungen granite intrusion of different erosion leveIs is an important feature of the Granite porphyry I intrusion ore geology of the Oslo Region. The Nordli deposit is a Granite I intrusion large, subeconomic porphyry like molybdenum deposit The alkali granite is from the existing field data situated in a deeply eroded caldera structure (Pedersen considered to be the latest intrusion of the area. The 1986), Molybdenite occurs dessiminated in three shells, whole rock chemistry (Table 1) of the alkali granite each above different granitic intrusives. The molybdenite clearly indicates that it is unrelated to the other granite mainly occurs in a quartz-sericite-pyrite stockwork of intrusion in the area. veins. In the Glitrevann caldera the Mo mineralization is The succession of intrusives and alteration phenomena associated with the resurgent granitic stock and with vent suggests that the early phase of propylitic alteration and erupted ignimbrites (Scheenwandt 1986). The Mo­ Zn-skarn mineralization are earlier thant the syenite ring mineralization associated with the resurgent stock has dyke and conternporary or later than the Storeeyungen phyllic alteration and Mo-mineralization in the roof zone granite and its dyke rock, the granite porphyry 11. The which resemble the Elsje type, This molybdenite bea ring Zn-skarn is not overprinted by later alteration. The alteration associated with the resurgent granitic stock is, as Storeeyungen granite resembles the biotite granite I group in the EIsjifJ area, clearly later than the ring dyke. ofGaut (1981), which is assumed being the source ofthe In the granite batholith, where no caldera rnetals in a lot of small contact deposits of Zn, Pb, Cu etc, structures are known so far, some small molybdenite in the Oslo Region e.g, the Konnerudkollen mine in mineralization occur in areas with intense quartz-topaz­ Drammen (Ihlen 1986b) and the Grua deposits (Olerud biotite or quartz-sericite alteration. These mineralizations 1977). The Stoneyungen granite is interpreted being the mainly consist molybenite in thin quartz veins and they source of the Zn-skarn mineralization in the Elsje area. occur in apical position to the main intrusives (Ihlen et ai. From the Glitrevann caldera, Pedersen (1975) assume that 1982, Ihlen & Martinsen 1986). These Mo-mineralizations the Zn-mineralízation of the Glomsrudkollen deposit, are in many respect unlike the one related to calderas. which occurs in contact with the ring dyke, is on the The Elsje area is probablylocated to the intersection contrary, later or contermporary with the intrusion of the between two main structures which are interpreted as ring dyke. caldera roots by Scott (1979). The Mo-mineralization of In the Elsjee are a, the early propylitic alteration is cut the Elsjre area is spatially located to the granite I and the by the syenite ring dyke, which again is altered by phyllic roofzone ofthe granite porphyry I. These intrusions seem alteration. This suggests a distinct event of phyllic to be deep leveI intrusions with relative age older than the alteration and Mo-mineralízation, which is clearly later ring dyke system, while the Mo-mineralization and phyllic than the early propylitic alteration and the intrusion of aIteration seem to be related to late events in the deeper the syenite ring dyke. The phyllic alteration is overprinted part ofthe evolving caldera.

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BR~GGER, W.C. & SCHETELIG, J. - 1923 - Geologisk IHLEN , P.M. & MARTINSEN , M. - 1986 - Ore deposits spatially . oversiktskart over Kristianiafeltet i: 250.000. Nor. geol. related to the Drammen batholith. in : S. OLERUD & P.M. unders. IHLEN eds, Metallogeny associated with the Oslo Paleorift, EL BOUSEILY, A.M. & EL SOKKARY, A.A. - 1975 - The Sver. geol. unders. Ser. c«. 59: 38-42. relation between Rb, Ba and Sr in granitic rocks. Chem . geol. , IHLEN, P.M.; TR~NNES , R.; VOKES, F.M. - 1982 ­ 16: 207-220. Mineralization, wallro ck alteration and zona'tion of ore GAUT, A.- 1981 - Field relations and petrography of the biotite deposits associated with the Drammen granite in the Oslo granites of the Oslo Region. Nor. geol. unders., 367: 3'9-64. Region, Norw ay. In: EVANS, A.M. ed. Metalli zation GOLDSCHMIDT, V.M. - 1911 - Die Kontaktmetamorphose in associated with acid magmatism, V. 6. John Wiley & Sons Kristiania Gebiete. Kgl. Nor, Vidensk, Selsk, Skr. I. Mat. ­ Ltd ., London. p. 111 -136 . Naturvidensk, KI. No . I., 483 p . LARSEN, B.T. - 19 78 - Excursíon 5. Krokskogen lava area. In : IHLEN , P.M. - 1978 - Malmgeologisk undersrekelse og J .A. DONS & B.T. LARS EN The Oslo paleorift, A review and kartlegging av Kongen, Sulitjelma, Rzeros, asvre og Nedre guide to excursions. Nor. geol. unders., 337: 143-162. Grubelien og Dalstjern Gruver i Elsjeefeltet, Nannestad , MATHIESEN, C.O.; OLERUD , S.; EIDSVIG, P. - 1976 ­ . 8 p. (Unpubl. NGU-report 1575/16B). Geologiske geofysiske und ersaikelser ved Glom srudkollen . IHLEN, P.M. - 1980 - Geologisk kartiegging av Kongens og , . 30 p. (Unpubl, NGU-repor 1430/17A). Rrero s gruve i Elsjsefeltet, Nannestad, , Akershus. OLERUD, S. - 1977 - En m almgeologisk undersaskelse av Zn-Pb­ 18 p. (Unpubl, NGU-report 1650/16C). Fe forekomstene i Grua omrãdet p ã . Unpubl. IHLEN , P.M. - 1986a - The geological evolution and thesisNTH, Univ, Trondheim. 96 p. metallogeny of the Oslo Paleorift. In: S. OLERUD & P.M. OLERUD, S. - 1982a - Berggrunnskart Nannestad 1915 m, ffiLEN eds Metallogeny associated with the Oslo Paleorift, 1:50000. Foreleepig utgav e.Nor. geol. unders. Sver. geol. unders, Ser. Ca. , 59: 6-17. OLERUD, S.- 1982b - Elsjeefeltets geologi, tektonikk og IHLEN , P.M. - 1986b - The Konnerudkollen skarn deposit - a innhold av sporelementer i kambro-ordovisiske sklfre , road log. In : S. OLERUD & P.M. IHLEN eds . Metallogeny Nannestad /Nittedal, Akershu s, 49 p .(Unpubl. NGU-report associated with the Oslo Paleorift. Sver. geol. unders, Ser. 1650/16D). c«.59: 43-48 . OLERUD, S. - 1983 - Molybdenrnineraliseringer under Revista Brasileirade Geociências, Volume 17, 1987 577

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As floresta s pr ecedem o s povos, o s desertos seguem-no s.

Chateaubriand