A Cobalt.Bearing Sutfide

Canadian Mineralogist Vol. 21, pp. 129-136(1983)

A COBALT.BEARINGSUTFIDE - ARSENIDE ASSEMBTAGE FROM THE NORDMINE (FINNSHYTTEBERG),SWEDEN: A NEW OCCURRENCE OF CLINOSAFFLORITE

E. A. J. BURKE AND M. A. ZAKRZEWSKI Institute of Earth sciences,Free (Jniversity,De Boelelaan 1085,l08l HV Amsterdam, The Netherlands

Ansrnecr folots-clds: clinosafflorite, thiospinelles, cattierite, min6raux de cobalt, analysesi la microsonde Three mineral assemblageshave been recognized 6lectronique,Bergslagen, Sudde. in the Nord mine, a small abandoned iron-ore deposit at the proterozoic western edge of the INtnopucnoN Bergslagen province in central Sweden. The arsenide- bearing assemblage (clinosafflorite, cobaltite. bis- In the course of regional metallogenic inves- muth, molybdenite and siegenite) and the magnetite- tigations carried out between 1975 and 1980 in bearing assemblage with pyrite, pyrrhotiie and chalcopyrite are regarded as the early phases of the the Hiillefors area, western Bergslagen, central mineralization. Later mobilization of Cobalt and its Sweden, our attention was drawn to the Nord reaction with the primary iron sulfides resulted in mine becauseof a remark of Magnusson (1929) the formation of a cobalt-bearing thiospinel-disul- about the occurrence there of economic quanti- fide assemblage with carrollite-linnaeiti, cattierite ties of native bismuth. In spite of a search of and cobaltian pyrite. The average composition of the dumps, native bismuth was found only as clinosafflorite, as determined by electron-microprobe microscopicinclusions in samplescontaining co- analysis is Co 27.4, Ni 0.7, Fe 0.4, As 70.4, S 0.4, balt minerals (Zakrzewski et al. 1980). These tota'l 99.3 trrt.V^o. Optically, clinosafflorite is very similar to safflorite; reflectance (nm, minerals include cobaltite. members of the %): 47t5, - 58.3*58.0; 546, 55.3-57.8; 589. 52.8-56.2: 650. carrollite linnaeite series, siegenite of unusual 48.7-53.2: its microhardness ZI{N1ro is in the range composition, members of the cattierite * cobal- 724-933. tian pyrite series,and the rare mineral clinosafflorite. Keywords: clinosafflorite, thiospinels; cattierite, gobalt minerals, electron-microprobe analysis, Bergslagen, Sweden. Grolocrcar SntnNc The Nord mine is a small iron deposit in SovrIvternp the Finnshytteberg ore field (Fig. 1), southern Nordmark district of the western Bergslagen - Trois assemblages min6ralogiques ont 6t6 iden- metallogenic province. The Finnshytteberg ore tifi6s I Ia mine Nord, petit gisement de fer aban- field is located in an isolated enclave (1500 X donn6, situ6 i I'extr6mit6 ouest de la province 700 m) of supracrustal rocks surrounded by the Prot6rozo-ique de Bergslagen dans la partie-centrale postorogenicFilipstad granite. The entire enclave de la Sudde. L'assfmblage clinosaffloriteo cobaltite, bismuth, molybd6nite, siegenite et l,assemblage is literallv covered with dumps from the iron magn6tite, pyrite, pyrrhotine, chalcopyrite sont mines: very few outcrops are present. The consid6r6s comme phases pr6coces de ia min6rati- general geology and the ore deposits of the sation. La mobilisation subs6quentedu cobalt et sa district have been studied by Magnusson (1929), r6action avec les sulfures de fer -thiospinelles_primaires ont and his views are summarizedhere. {9oll u" assemblage cobaltifbre b The supracrustal rocks are the oldest rocks disulfures avec carrollite-linnaeite, cattierite er of the area: thev consist of felsic metavolcanic pyrite cobaltifdre. La composition moyenne de la rocks of guartz-keratophyric to rhyolitic compo- clinosafflorite, d6termin6e i la microsonde 6lectro- sition (called leptite in Sweden) with intercala- nique, est: Co 27,4, Ni 0.7, Fe 0.4, As 70.4, S 0.4, pourcentage pond6ral total 99.3. I_a clinosafflorite tions of greenstone. limestone, skarn and iron est optiquement trbs semblable i la safflorite: r6flec_ ore. The present state of these metasedimentary 91*_-(1m, Vo): 470, 58.3-58.0; 546, 553-57.8; and metavolcanic rocks is the result of repeated 589, 52.8*56.2; 650, 48.7-5j.2; microduretE VHNno folding and metamorphism-related to the intru- entre 724 et 933. sion of granite bodies of several generations. t29

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Frc. 1. Location of the Bergslagen province and geological map of tle Filipstad area, simplified after Magnusson (1925)' (l) postorogenrc g.uiit., (2) late-orogenic palingenetiC granite, (3) synorogenic granite' (7) limestone and Ia) -"iuriui.entary-rocks,- (5) greenstone, (6) leptite, dolomite.

in the According to Magnusson (1929), the oldest (Fig. 1). As the association of elements identical, it synorogenic granite gave rise to the occurrence iqoiArnart< and Nord mines is mineraliza- of magnetite and garnet-pyroxene skarns, to the should also be possible to relate the gran- so-called'omagnesia-metasomaticprocess", which tion of the Nord mine to this palingenetic body formed a number of Mg-rich minerals, and to ite. However, the distance to the nearest such an assumption the "invasion" of the sulfides chalcopyrite, ga- of this granite, 6 km, makes ore field; the lena, pyrite, pyrrhotite and sphalerite. This dubiousl In the Finnshytteberg age synorogeniq granite is exposed 1.5 km east of postorogenic Filipstad granite of Gothian 1977'tcaused th9 the Nord mine @ig. 1). The younger late- tteSS Mu: Welin et al. $tgt- to hornblende- orogenic palingenetic granite (1841 Ma: Oen tion of garnet-pyroxene skarn and cum- et al, 1982) is, in Magnusson'sview, the cause epidote skarn and of anthophyllite formation of of formation of more skarn minerals and of the mingtonite to hypersthene; the scap- strlfide mineralization in the Nordmark mine grosiular-hedenbergite-wollastonite skarn,

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'I}IE olite, brucine-spotted limestone, spinel and TABLE1. MI}IEMLASSEMBLAGES OF NORDMINE mica is also related to this granite (Magnusson 1970). ARSENIDE-SULFIDE Magnetlte Fe304 Clinosafflorite OccunnrNcr CoAs2 EARLY ChalcopyriteCuFesz Cobaltlte CoAss Pyr.ite FeS2 Slegenite (Co,Ni)3S4 The Nord mine is located near the contact Pymhotit€ Fe1_xs Bisnuth Bl between the supracrustal rocks and the Gothian Molybdenite l.tos2 granite. Intrusion of the granite divided the THIOSPINEL-DISULFlDE original orebody into several smaller masses Carrollite (Fig. 2); originally the body was CuCoZS4 lenticular, with Cattlerite CoSz a length of 50 m and a width of up to 12 m; LAIE Cobaltlan pyrite (Fe,Co)Sz mine workings reached a depth of 80 m (fegen- Linnaeite Co3S4 gren l9l2). The mine was closed becauseof Marcasite FeS2 technical problems in 1892 atter 12 years of (Hematite) Fe203 production that yielded (together with several (Magnetite) Fe304 smaller mines of the ore field) 65,000 tonnes of iron ore containing 52-54 wt.Vo Fe. Mag- (1929) nusson mentionedthat somebismuth was clues either, but enablesa reconstructionof the found in 1890 and that the ore produced at spatial relation with regardto the iron ores.Our that time graduallybecame more sulfide-bearing. conclusion is that two primary assemblages The dumps were reworked in 1897 (fegengren (magnetite-sulfideand arsenide-sulfide)reacted 1912);at presentthey contain only about 5,000 to form the later thiospinel-disulfideassemblage tonnes of rock. The material on the dumps (Table l). consistsof dark greenhornblende-epidote skarn, magnetite and granite. Sulfides, mainly pyrite M agnetit e-sulf id e asse m bl age pyrrhotite, and are rare, and only a few blocks Magnetite constitutes,on average,75 vol. % containing cobalt minerals have been found. of the iron ores, the remainder being the skarn minerals clinopyroxene, chlorite, feldspar and MrNEner-AssrMurecrs eNo garnet. Magnetite forms equidimensionalgrains TEXTURALRnlerrous np to 1.5 mm in diameter. Locally it contains disklike exsolutionbodies of spinel and blebsof The descriptionsof the Nord mine by Tegen- pyrrhotite and pyrite (Fig. 3). Nests up to l0 cm gren (1912) and Magnusson(1929) shed no light in diameter in the iron ores contain up to 30 on the location of the cobalt mineralizationin vol. Vo sulfides and only l0 vol. Vo magnetite the mine. A study of dump material providesno disseminated in dark-colored clinopyroxene

TEBERGE& + + w E ELD ++++++\iA++d Nord mine ++++++ I+Fr h{Rlz +++++++ ffie mine* +++ FIrTIila +++ FLW*.'ffis .6

+++ + +

Frc. 2. Geological map of the Finnshytteberg field and cross section through the Nord mine (after Magnusson 1929). (l) postorogenic granite. (2) skarn, (3) greenstone, (4) leptite, (5) iron ore, (6) mine.

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Frc. 3. pyrrhotite (Po) and pyrite (Py) enclosed in magnetite (Mt) with exsolved spinel (Spn). Pyrite in the upper part is secondaryafter pyrrhotite. Frc. 4. Two textural varietiesof carrollite. Grain Car 8, in contact with chalcopyrite (Cp)- and-secondary marcasite (Mc), correspondsto composition 8 in Table 3, The porous Car 9 (conrposition9, Table 3) has been formed from Pyrrhotite. Fro. 5. Cobaltian pyrite (Co-Py) developed on pyrite (Py) along grain borders and cracks. The darker zones are richer in cobalt. Frc. 6. X-ray scanningphotograph for Co of mosaicJike pyrite - cobaltian pyrite intelgrowths similar to those of marcasite-pyrite. Frc. 7. Intergrowths of clinosafflorite (CS) and cobaltite (Cb):, (Cb)' Frc. 8. Schematic representation (not to scale) of intergrowths of clinosafflorite (CS)' cobaltite native bismuth (Bi) and molybdenite (Mo). Note the freezing cracks around native bismuth in cobaltite (upper left corner). Grey is gangue.

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skarn. The presenceof magnetite in these nests TABLE2. REFLECTANCE*AND VICKERS HARDNESSTT OF NORDIiIINE MINERALS as inclusions in pyrite, pyrrhotite and bhalco. pyrite shows it to be the oldest mineral. Magnet- R% ite occurring in intimate intergrowths with lavelength (nn) pyrite and containing marcasite and hematite 470 546 589 650 llEfl no has been forrned at a later stage: small relics of C1inosafflorite ^1 58.3 55.3 52,8 48.7 pyrrhotite 724_g33 suggest that the intergrowths have R^ 58.0 57.8 56.2 53,2 been formed by oxidation of pyrrhotite, possibly Cobaltite 48.9 52.7 53.6 54,4 1168-1288 during retrograde metamorphism, according to Linnaeite-carrol l i te 39.3 4L.5 42,4 44.1 483- 514 a reaction 6FeS * 2Oz: FegOa* 3FeSr. Cobaltian pyrlte 43.5 46.8 48.0 51.2 1309-1343 Pyrite 45.7 49,3. 52.1 53.1 r402-L452 T hio spin el4isullid e assembl age rl4easured wlth a Leltz MPVnlcroscope photoreter equiDDedwith A reaction of the magnetite-sulfide assemblage Knott 9592Aphotmu]tiplier. Veril 8-200 contifluois bind inter- with Co-bearingsolutions resulted ferencefi'lter, obJective16:I,0,40 N.A., andHC standard. in thiospinels .rMeasured with a Leltz Durinet-pol applylng a load of 100 g for of the carrollite-linnaeite series and Co-bearing 15 s. disulfides. In the chalcopyrite-bearingsulfide assemblageincluded in the iron ores, carrollite- linnaeite occurs in two textural varieties (Fig. 4): I) as isolated grains up to 2 mm across and this assemblagewith the highest contents of in intergrowths with pyrite, sometimes with a Co, Ni, Fe and Cu. zone of cobaltian pyrite in between. Relics of The disulfides are members of the pyrite- pyrite and pyrrhotite are present. This type cattierite series,with compositionsranging from shows a cleavage in three directions along pyrite with only 0.2 wt. Vo Co to cattierite with {100} and takes a poor polish (Fig. 4, Car 9); 31.8 wt. % Co (fable 3). The highest Co con- 2) as grains up to 0.5 mm across accompanying tents commonly are presentat the rims of the chalcopyrite;the larger grains of this type occur grains in contact with gangue minerals (Fig. 5) at the contacts with gangue minerals. They are and in bravoite-like zoned crystals. The reflec- hypidiomorphic, have no visible cleavageand tance and microhardnessof members of the good take a polish; smaller grains are found on pyrite-cattierite series Clable 2) decrease with the contacts between chalcopyrite and pyrite increasingCo content, and their color gradually (Fig. 4, Car 8). The members of the carrollite- changesfrom yellowish white for pyrite to more linnaeite serieshave a yellowish white color and distinctly brownish for cattierite. Cobaltian pyrite are isotropic; their reflectance (Iabte 2) is some- also occurs in mosaiclike intergrowths with what lower than the values given by Craig et al. pyrite (Fig. 6); this texture resembles that of (1979), which reflects the varying contents of secondary marcasite in pyrite and probably Fe and Ni in material from the Nord mine. formed by replacement of pyrrhotite during Compositions4-10 in Table 3 refer to grains of retrograde metamorphism.

TABLE 3. RESULTSOF ELECTRON-MICROPROBEANALY5ES OF ARSENIDESAND SULFIDES FROM TtE NORDMINE Weight % Atomlc proportlons Sample Mineral Co Fe Cu S Total co l{i As S Remarks l87C 2 Clinosafflorlte 27.4 i7 0.4 70.L 0.6 2A7f 99.2 0.98 0.02 0.01 1.96 0,04 As+S.2.00 2 Clinosafflorite 27.4 0.7 0.3 n.a. 70.7 0.2 99.3 0.98 0,02 0.01 1.99 0.01 As+S.2.00 387C nt 2 Cobaltite 35.2 0.1 n.d. 45.4 19.6 100.6 0.98 0.01 0,00 1.00 1.00 As+S'2.00 487A Z Nickelian linnaeite 48.9 4.6 1.8 n.d. 41.1. 98.7 2.59 0.?5 0.13 0.09 4.00 lorcst Cu 587A2 Nickelian llnnaeite 47.3 6.2 ln 4.0 n.d. 41.4 99.9 2.49 0.33 687A 0,06 0.19 4.00 highestNi Cuprlan linnaeite 45.8 a.J 2.5 6.1 n.d. 40.7 98.0 0.16 0.14 0.30 4.00 1A 7874 Carolllte 43.5 2,3 9.9 n.d. 40.0 97.3 a .51 887A 0.13 0.09 0.50 4.00 CarrolI i te 43.6 2.t no 12.7 n.d. 41,9 101.2 2.27 0.11 0.05 0.61 987A CafrolI lte 4,00 Fig. 4, Car8 40.8 l.J 2.C tL.7 n.d. 39,0 95.2 2.28 0.07 0.14 U.OI 4.00 Flg. 4, Car9 1087A Fefroancarrollite 41.4 1? 4.4 10.5 n.d. 41.0 98.6 2.20 0.07 0.25 11 87 rB o.52 4.00 Siegenlte 41.3 16.5 0.0 0.8 n.d.42.4 101.0 2.tz nqE 0,00 0.04 4.00 ln cobaltlte L2 87 TR Cuprianslegenite 36.4 11.8 a.o 8.4 n.d. 41.2 100.4 1.92 0.62 0.14 0.41 13 87 TB 4.00 in cobaltite Fe-rlch slegenite 20.0 23.2 L3,7 n.d. 42.4 99.3 I.02 1.20 0.74 4.00 in cobaltlte 1487A Cattierite 31.8 16.3 n.d. 52.2 100.3 0.67 n?6 1587A pyrite ?.00 Cobaltian 2L.9 )EO n,d. 53.7 101.6 0.45 0.00 2.00 rim 1687A Pyri n? around16 te 46.2 n.d. 53.2 99.7 0.01 noo ?.00 relic ln 7 Analyses perfonmd 1-3 uith a CambrldgeMl-croscan, corrected,HJth.a progfan modified after sprlnger (1967), i,Jth.a markg, iorreiGi-withthe 6n:ir* inF prosra;. Analysts:il11::::.4;tg"p:rformed1-13 c. (ieft, 14-16 N,J..qaprlas9 Lu;tenaouw;;r-;.i:-;i;;6;i;;; :'ilt-d"t5!ffi:

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A rsenid e-sulfid e ass e m blage e.g., Bou-Azzer and Aghbar (Picot & Johan The arsenide-sulfide assemblageis related to re77). Under the microscope,clinosafflorite is very the light-colored actinolite-tremolite skarn. Co- similar to safflorite and to nickelian clino- baltite usually is the main mineral but, in some safflorite (Picot & Johan 1977). Zoned crystals, places,clinosafflorite prevails. Textural relations as usually reported for safflorite and also des- betweenthe two minerals are shown in Figure 7 cribed in nickelifdre". have not been and schematically in Figure 8. Clinosafflorite, "safflorite observed.The reflectanceof clinosafflorite has in contact with silicates and cobaltite, forms been measuredon a grain showing the largest grains as much as 0.5 mm in diameter, and bireflectance(Table 2). The spectralcuryes for blebs up to 0.03 mm acrossin cobaltite. Other Rr and Rs crosSat a wavelengthof about 480 inclusionsin cobaltiteconsist of bismuth,molyb- phenomenonhas also been observed denite and siegenite.Columns 1l-13 in Table 3 nm. This in members of the safflorite-loellingite series, give compositionsof siegenitefrom such inclu- the curves for Ioellingite FeAsr crossing at sions. Bismuth and molybdenite also occur as the ones for safflorite interstitial grains between silicates and opaque about 530 nm and (Co,Fe)As: about510 nm (Petruket al. 1971, minerals (Fig. 8). at Picot & Johan 1977). RammelsbergiteNiAs, Clinosat'llorite does not show this feature (Petruk et al. 1971); in contrast to the Synthetic Co-rich diarsenidesin the safflorite- it is interestingto note that, Ni-bearing Moroccan loellingite seriescontaining more than about 80 low-Ni clinosafflorite,the show this crossingof thc mole Vo CoAszare monoclinic (Roseboom1963, clinosaffloritedoes not Radcliffd & Berry 1968).Natural clinosafflorite spectralcurves. polishing is is rare and has only been reported from Cobalt, The hardncss of clinosafflorite hard- Ontario (Radcliffe & Berry 1971)and as "safflo- lower than for cobaltite.Microindentation (VHN) on clinosafflorite rite nickelifbre" from severalMoroccan deposits, ness measurements (Table 2) yield strongly elongateconYex impres- sions. the result of a considerable hardness anisotropyalso known to exist in safflorite. The TABLE4. X-MY POIIDER-DIFFRACTIONDATA FOR mineral is very brittle. CLINOSAFFLORITE'ITDSYNTHETIC COAS2 Microprobe analysesof the Nord mine clinosafflorite (Table 3) indicate a compositionclose SyntheticCoAs2 Cllnosafflorit€. Clinosafflorite*r to CoAsr, with only minor amounts of Fe, Ni PDF14-412 Cobalt, ont. Nordmlne, Sweden and S. X-ray-diffraction data for clinosafflorite hkl qobs. I/I 1oo qb.J^m dobs. dcalc. t/Iro have been obtainedon powder drilled out under Iu b 3.824 3.823 the microscopeand taken into a rubber solution. 020 2.936 12 2.932 10 2.929 2.93L 2 l1t 2.758 18 2.768 2.764 2 The powder pattern and the unit-cell data are 002 2.666 45 2.671 40 2.669 2.673 ? given in Table 4 along with the pattern of ?00 2.648 45 2.657 40 2.652 2.65r I21 2.536 100 2.531 100 2.533 2.534 10 synthetic CoAs, (PDF lMlz) and that of 0r2 2.429 60 2.427 80 2.432 2.432 4 2r0 2.4r3 50 2.422 S0 2,419 2.416 4 clinosafflorite from Cobalt Gadcliffe & Bery 212 t 110 25 2.313 20 2.312 2.3L6 3 22r 2.083 4 te71). L02 2.045 z.osa{!'!!! I 022 I.974 6 , ^.^ t 1.975 220 1.966 4 t't" 1r.973 28 Gr,NErrc CoNsroenatroNs 222 1.913 10 1.911 1.91r 113 1.870 30 1.865 30 1.869 1.870 311 1.856 30 1.861 30 1.85s 1.855 The rnineral assemblages(Table 1) and their 2'13 1.829 16 I31 1.825 t.aul!'.lll textural relations indicate that pyrite, pyrrhotite 013 L.702 2 131 I'658 35 1.656 30 1.658 1.658 and chalcopyrite included in the iron ores re- 1.23 1.6370 l4 1.636 10 l.oJ6 L.637 acted with Co-bearing solutions to form the 3zL L.6274 i8 1.631 t0 L.626 L,627 1.6176 18 thiospinel-disulfideassemblage. The thiospinel 032 1.5777 10 tL.577 230 L,5744 16 1.570 5 r,.s72lr.57z associatedwith the iron sulfides is carrollite- 20? 1.5637 t6 tr-567 linnaeite,whereas it is siegenitein the Co assem-

a - 5.916A a - 5.914+ o.oosI blage (Table 3). The compositionsof the disul- b = 5.872 b=5.862+0.003 fides adjacent to or intergrown with different c = 5.960 c.5.962 + 0.003 thiospinelgrains in the presenceof chalcopyrite I = Lrn"27' 8"116'16'+04' are in accordancewith the phaserelations in the proposed by Craig et al, .Data from Radcllffe & Berry (1971). Cu{o-Fe-S system as .*Stramanls-type 114.57 m Debye-Scherrercarera, mn-fl ltered (1979). It is assumed that the two textural FeKsradiation. varieties of carrollite-linnaeite occurrine with

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the sulfides(Fig. ) are replacementproducts of associationof elementsof the Nordmark and pyrrhotite and chalcopyrite, respectively. In the Nord mines points to a possible proximal absenceof chalcopyrite,disulfide crystals with character in relation to an exhalative centre; zonesof different Co contentshave been formed. the Pb-Zn-Ag mineralization west of Nordmark Completesolid solutionbetween FeSs and Co$ (Magnusson 1929) and the mineralization in existsonly'above 600'C (Klemm 1965); solid carbonate beds east of Filipstad (Magnusson soh.rtionin the carrollite-linnaeiteseries extends 1925) would then represent the distal ores in at 700'C from 16.5 to 2 wt. Vo Cu, and at the carbonatefacies, 600'C from 18 to 0 wt. Vo Cu (Craig et al. 1979). This temperaturerange is also suitable ACKNowLEDGEMENTs for coexisting cobaltite and clinosafflorite (Maurel & Picot 1974), and is in agreementwith The ar"rthors are grateful to Dr. C. Kieft and conditionsof amphibole-and pyroxene-hornfels Mr. W.J. Lustenhouwer for carrying out elec- facies deduced from Magnusson's(1929) des- tron-micropobe analyses. Facilities for these criptions of the skarns related to the intrusion analyses were provided by the Free University of the Gothian postorogenicgranite. and the WACOM, a working group for analy- The theoriesof Magnusson(1929) concerning tical geochemistry subsidized by the Netherlands the "invasion of sulfides" cannot be upheld any Organization for the Advancement of pure longer. As the Nordmark mine is located close Research (7:WO). to a late-orogenicgranite (1841 Ma) and the Nord mine close to a postorogenic granite RrFnnsNcas (1665 Ma), it is unlikely that the granites sup- plied the metals.The almostidentical association Cneto,J.R., VeucseN, D.J. & HlcctNs, J.B. (1979): of elementsin both mines points to a common Phase relations in the Cu-Co-S system and source for both cases of mineralization. The mineral associations of the carrollite (CuCorS4).- granites can only have served as a motor of finnaeite (CorSo)series. Ecorr. Geol. 74, 657-671. mobilization of elements and recrvstallization Klruv, D.D. (1965): Synthesen of mineralsalready present in the older und Analysen in volcano- den Dreieckdiagrammen FeAsS-CoAsS-NiAsS sedimentarycomplex of supracrustal rocks. und FeS2-{oS2-NiS2.Neues lahrb. Mineral, Abh. The different types of iron ores and asso- 103. 205-255. ciated basemetals are believedto haveseparated from a common volcanogenicsource Uy geo- MacNussoN, N.H. (1925): Berggrunden inom de chemicaldifferentiation (Zakrzewski 1982). iwo centrala delarna av Filipstads Bergslag. Persbergs associations of elements have been recognized Malmtrakts malmfyndigheter. Kungl. Kommers- kollegiunt & Sver. (ieol. (Jnders. Beskr. in Bergslagenprovince: the Sikfors type, 6ver with ntineralfyndigheter 2, 1-231, 459-464. Cu-Bi-Co-Mo-Au*Se-Te-W{e-As, and the Hiillefors type, with Pb-Zn-Ag-Sb-Sn-Hg-Mn (1929): Nordmarks Malmrrakt, geologisk As; the Cu-Bi{o-Mo-bearing examples of beskrivning.Sver. Geol. (Jnders.Ser.'Ca I3.- mineralizationof the Nord and Nordmark mines (1970): would thus representthe Sikfors type. In western The origin of the iron ores in central Sweden and history Bergslagen, this group is related the of their alterations.Syer. to iron ores Geol. Unders. Ser. C 643. interpreted to be chemical sediments formed under conditionsof the iron silicategeochemical MAUREL,C. & Prcor, p. (1974): Stabilit6 de I'allo- facies @akrzewski 1982). This is supported by clasite et de la cobaltite dans les svstdmes the presenceof 0.06-0.07 wt, Vo p in the iron Co-As-S et Co-Ni-As-S Soc. frailg. Mindral. ores of the Nord mine (Magnusson1929), an Crist. Bull. 97" 251-256. order of magnitude higher than in other skarn OrN, rron ores. I.S., Hrlurns, H., Venscnunr, R.H. & WrrleNorn, U. (1982): Ore deposition The occurrence in a of a cobalt mineralizationin Proterozoic incipient rift zone environment: a the Nord mine in skarn outside the iron ores tentative model for the Filipstad-Grythyttan- probably reflects a premetamorphicspatial rela- Hjulsjti region, Bergslagen,Sweden. Geol. Rundsch. tion in which cobalt minerals and associated 7t, 182-194. phasesformed an outer zone around the sedi- PETRUK,W., Hennrs,D.C. (1971): mentsthat were the progenitorsof the iron ores. & Srewanr, J.M. The silver-arsenide deposits of the Cobalt- The iron ores were also enriched in Co as Gowganda region, Ontario, Characteristics of the manifestedby the presence of 0.012 wt.Vo Co arsenides, sulpharsenides, and antimonides. Car. in the nearby Ang mine (Magnusson1929). The Mineral. 11, 150-186.

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Prcor, P. & JoneN, Z. (1977): Atlas des min6raux Wrr.rr, E., GonserscHEv, R. & Lullorcinon, P.H. m6talliques.Bur. Rech. Glol. Mini?res Mdm.90. (1977): Rb-Sr dating of rocks in the Viirmland granite group in Sweden. Geol. Fiiren. Stockholnt RADcLTFFE,D. & Bsnnv, L.G. (1968): The safflo- Fi;t'h. 99, 363-367. rite-loellingite solid sotution series. Amer, Min' eral.53, 1856-1881. ZernzEwsru, M.A. (1982): Ceochemical facies model of ore formation in the Grythyttan- & - (1971): Clinosafflorite: a mono- Hiillefors area, Bergslagen.central Sweden.Geol. clinic polymorph of safflorite. Can. Mineral. 10, Rtmdsch. 71, 195-205. 877-88l. Rosrnoou, E.H. (1963): Co-Ni-Fe diarsenides: BURKE,E.A.J. & NuctrnEN, H.W. (1980): compositions and cell dimensions. Anter, Mineral, Cobalt minerals in the Hiillefors area, Bergslagen, 48,271-299. Sweden: new occurrences of costibite, paraco- stibite. nisbite and cobaltian ullmannite. Can. Min' SrRINGER,G. (1967): Die Berechnung von Korrek- eral. 18. 165-171. turen fiir die quantitative Elektronenstrahl- Mikroanalyse. Forlschr. Minerul. 45, lO3-124. TEctNcnru, F.R. (1912): Jilrnmalmstillgingerna i mellersta och sijdra Sverige. Utredning verkstiilld Receivedluly 21, 1982,revised manuscript accepterl 6ren 1907-1909. Sver. Geol, Unders, Ser, Ca 8. September17, 1982.

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