Pahtavuoma - ZINC Database

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Name	Pahtavuoma	DATA UPDATED	6.3.2007
Secondary names
Site photo 1		Site photo 2
LOCATION
Geological domain	Karelian	Province	Central Lapland Greenstone Belt
Regional map 1		Regional map 2
Map sheet	274104
Northing	7523650	Easting	2510750
Latitude	67.79920N	Longitude	24.25052E
Municipality	Kittilä
Nearest town, access	30 km NW from Kittilä. 14 km to a sealed road, gravel road to the deposit.
MINING
Mine photo 1		Mine photo 2
Mine photo 3		Mine photo 4
Exploration licence no	2240/1–4	Mining concession no	2240/1a
Present holder	Outokumpu Oyj (1970–)
Previous holders
Status of development	Modern test mining
When mined	1974–76, 1989–1993 [17,22].
Resources and grades	17 Mt @ 0.81% Zn, 0.11% Cu, 0.09% Pb, 0.02% Ni, 0.01% Co, 7 ppm Ag, including 4.1 Mt @ 1.5% Zn; 6.53 Mt @ 0.84% Cu and 21 ppm Ag (cutoff @ 0.3% Cu); and 0.14 Mt @ 0.39% U, 0.24% Cu, 0.08 % Zn, 0.09% Pb, 0.02% Ni, 0.01% Co, 24 ppm Ag, 240 ppm Mo [2,3,17,23]. Cu ore bodies (cutoff @ 0.6% Cu): 4.4 Mt @ 1.04% Cu, 0.12% Zn, 0.02% Pb, 0.03% Ni, 0.02% Co, 23 ppm Ag [23].
Total production	0.3 Mt @ 1.07% Cu, 26 ppm Ag [22].
Total in-situ content	143,100 t Zn, 64,800 t Cu, 16,300 t Pb, 4750 t Ni, 2600 t Co, 224 t Ag, 546 t U [23].
Size of the deposit (Mt)	21,54	Size reference	[23]]
Best sections
Extent of the deposit
Ore bodies	Six Zn lodes, four Cu lodes, and three U lodes; the Cu and U lodes are separate from the Zn lodes; all lodes have a E-W trend and a dip of 60–80° to the N [2,3,7,13,23]. The Cu ore bodies are sited along sedimentary-volcanic contact zone [23].
Plan figure 1		Plan figure 2
Plan figure 3		Plan figure 4
Section figure 1		Section figure 2
Section figure 3		Section figure 4
EXPLORATION
Explor. site photo 1		Explor. site photo 2
Discovery year	1970
Discovery	By Outokumpu: sulphide dissemination detected in outcrop during regional exploration [3,6]. The first regional indications were the numerous Cu anomalies detected in stream-sediment survey by Outokumpu [23].
Exploration history	Outokumpu (1961–1985) [2,3,4,6,7,8,10,17]: Bedrock mapping, till, stream-water and -sediment geochemical survey, ground magnetic, VLF-EM and slingram survey, diamond drilling, pilot-plant tests, mineralogical studies, S-isotope study, structural study, pilot plant tests. GTK (since 1950's) [5,9,11,18]: Regional bedrock mapping and till geochemical survey, regional till stratigraphy and glacial erratic boulder survey, high- and low-altitude airborne magnetic, electric and radiometric survey.
Drilling	Outokumpu (1971–74): 121 diamond-drill holes [3].
Elements analysed	SiO2,TiO2, Al2O3, Fe2O3, MnO, CaO, C, S, Ag, As, Au, Ba, Bi, Cd, Cl, Co, Cr, Cu, Hg, Mo, Ni, Pb, V, Zn by XRF + AAS [2]. SiO2,TiO2, Al2O3, Fe2O3, MnO, MgO, CaO, Na2O, K2O, P2O5, Ag, As, Au, Br, Co, Cs, Cu, Ba, Cr, La, Lu, Mo, Ni, Pb, Rb, S, Sc, Sb, Sm, Sr, Ta, Th, U, W, Zn, Zr by XRF, AAS, INAA [14,15].
Economic evaluations	By Outokumpu during the 1980's [17].
Geophysical response	Graphite-rich units, which host all ore, give a strong response on electric methods [2].
Geophys. anomaly fig. 1		Geophys. anomaly fig. 2
Petrophysics
Primary geochemical dispersion	Strata-bound Ba, Cd, Mn and Pb haloes surround the Zn lodes, and Ag, As and Co haloes surround the Cu lodes [2,15]. In the area, only Fe and Pb have significant positive correlation coefficients with Zn [2]. An extensive Br anomaly surrounds all sulphide mineralisation [15].
Secondary geochemical dispersion	Distinct As, Cu and Zn anomalies in till [7]. U-rich boulder trains start from the Pahtavuoma U lodes [9,11,18].
Primary anomaly fig. 1		Secondary anomaly fig. 1
Primary anomaly fig. 2		Secondary anomaly fig. 2
Primary anomaly fig. 3		Secondary anomaly fig. 3
Exploration geologist(s) in charge	Outokumpu: Osmo Inkinen
ORE
Ore outcrop photo 1		Ore outcrop photo 2
Major ore minerals	Pyrrhotite, sphalerite [2,3,14,20].
Minor ore minerals	Galena, chalcopyrite, ilmenite, arsenopyrite, gersdorffite, pyrite, marcasite, magnetite, graphite, uraninite, cobaltite, cobalt pentlandite, argentian pentlandite, niccolite, tucolite, gold, molybdenite, mackinawite [2,3,14,20].
Ore mineral photo 1		Ore mineral photo 2
Ore mineral photo 3		Ore mineral photo 4
Gangue	Quartz, calcite, ankerite [2,14,20].
Zoning	Cu-lodes in lower (southern) part and Zn lodes in upper (northern) part of the sequence [3,13].
Ore composition	Click here	Ore mineral compositions	Click here
Primary structures	Primary banding (layering) and pillows in the wallrocks [3,14].
Ore fabric	Chiefly, the sulphides are in breccia veins, but also occur as dissemination [2,3]. Grain size of sphalerite is in veins 0.2–0.5 mm and 0.05–0.1 mm in dissemination
Enriched components	As, Au, Ba, Cd, Co, Hg, K, Mg, Mn, Ni, Pb, Rb, Zn [14,15,20].
Geothermo- and barometry	Sphalerite: 4.6–6.7 kbar [19].
Ore fluid
Stable isotope data	δ34S in sulphides, Cu-ore: -4 – -15.5 per mill (median -8 per mill), hanging wall: +10 – +31.2 per mill [2,4,12]. In calcite in chl schis brecciated by Fe-carb veins: δ18O = 12.88 per mill, δ13C = -8.35 [21].
Pb isotope data
GEOLOGY
Regional geology map 1		Regional geology map 2
Local geology map 1		Local geology map 2
Geological setting	The deposit is in the metasedimentary rock-dominated, >2130 Ma, Matarakoski Formation of the Savukoski Group of the Central Lapland Greenstone Belt (CLGB) [1]. The deposit is in a sedimentary- and pyroclastic-dominated subsequence, right above mafic metavolcanic rocks [2,3,4,13]
Major host rocks	Metamorphosed black shale, mica schist [2,14,17,20].
Minor host rocks	Metagreywacke [4,14].
Intrusives	Subconformable dolerites in the sequence [1].
Outcrop photo 1		Outcrop photo 2
Outcrop photo 3		Outcrop photo 4
METAMORPHISM AND DEFORMATION
Metamorphic history
Metamorphic grade	Upper-greenschist facies (interpreted from mineral assemblages given in [2,3]), Chalcopyrite-sphalerite-pyrrhotite: 360–425°C, 4±1 kbar; silicates: 500±50°C, 5.0±0.5 kbar [2,3].
Metamorphic mineral assemblages	Mafic metalavas and dolerites: albite-actinolite-biotite-ilmenite ± scapolite, quartz, titanite, carbonate + locally, relict cpx [2,3,20]. Mafic tuffites: plagioclase-chlorite-quartz-biotite [3]. Phyllites: quartz-albite-biotite ± garnet, actinolite, scapolite, tourmaline [3]. Black shales, graphite-rich tuffites: biotite-albite-quartz-graphite ± garnet, actinolite, tourmaline [3].
Metamorph photo 1		Metamorph photo 2
Deformation history	Five stages of deformation detected in the CLGB [1]; at least two dominant stages at Pahtavuoma [3]. Stage D4 has produced the present setting [14].
Structure photo 1		Structure photo 2
ALTERATION
Regional alteration	Extensive albitisation and scapolitisation with a variable intensity in the region – these most probably postdate the sulphide mineralisation at Pahtavuoma [13,14,16,20]. Presence of scapolite-rich rocks above the sulphide-rich horizon(s) may indicate the formation of Cl-rich chemical sediments above the mineralisation [20].
Local alteration	Sericitisation, chloritisation, tourmalinisation [13,14].
Alteration figure 1		Alteration figure 2
Alteration figure 3		Alteration figure 4
Post-mineralisation modifications	Polyphase deformation, pervasive recrystallisation and partial, local, remobilisation of ore metals into breccia veins [2].
TIMING	Palaeoproterozoic [1,2].
SUPERGENE ALTERATION
GENETIC MODEL	Mineralisation is a product of submarine tholeiitic volcanism and related hydrothermal system in a sediment-dominated rift basin [2,20]. Magmatism and syngenetic mineralisation took place in a submerged rift, precipitation of ore metals and S at sea floor [1,2,15]. Sulphur of the ore was derived from sulphates sea-water or marine-sediment origin [2,13].
GENETIC TYPE	Stratabound and stratiform, syngenetic	References	[2,12,15,17]
Alternative genetic type 1	Guaymas-type	References	[20]
Alternative genetic type 2	Red Sea-type	References	[20]
Schematic model 1		Schematic model 2
References 1. Lehtonen, M. I., Airo, M-L., Eilu, P., Hanski, E., Kortelainen, V., Lanne, E., Manninen, T., Rastas, P., Räsänen, J. & Virransalo, P. 1998. Kittilän vihreäkivialueen geologia. Lapin vulkaniittiprojektin raportti. Summary: The stratigraphy, petrology and geochemistry of the Kittilä greenstone area, northern Finland. A report of the Lapland Volcanite Project. Geol. Surv. Finland, Report of Investigation 140. 144 p. 2. Inkinen, O. 1979. Copper, zinc, and uranium occurrences at Pahtavuoma in the Kittilä greenstone complex, northern Finland. Economic Geology 74, 1153–1165. 3. Latvalahti, U. 1974. Kittilän Pahtavuoman malmigeologiasta. Unpubl. MSc thesis. Dept of Geology, Univ. of Turku. 90 p. (in Finnish) 4. Mäkelä, M. & Tammenmaa, J. 1978. Lapin rikki-isotooppitutkimus vuosina 1974–1976. Summary: Sulfur isotope studies in Finnish Lapland, 1974–1976. Geol. Surv. Finland, Report of Investigation 24. 64 p. 5. Ristiluoma, S. & Mattila, P. 1972. Pohjois-Suomen malminetsintää palveleva maaperätutkimus. 3. Pahtavuoman osaprojekti. Geol. Surv. Finland, Report P 13.2.001. 8 p. (in Finnish, 309 MB) 6. Korkalo, T. 1979. Kittilän Pahtavuoman uraaniesiintymä. In: Parkkinen, M. (ed.) Uraaniraaka-ainesymposiumi (1979). Vuorimiesyhdistys. Sarja B 27, 80–87. (in Finnish) 7. Kokkola, M. & Korkalo, T. 1976. Pahtavuoma: copper in stream sediment and till. Journal of Geochemical Exploration 5, 280–287. 8. Ketola, M. 1979. On the application of geophysics in the indirect exploration for copper sulphide ores in Finland. In: Hood, P.J. (ed.) Geophysics and Geochemistry in the Search for Metallic Ores. Geological Survey of Canada. Economic Geology Report 31, 665–684. 9. Hirvas, H. & Mäkinen, K. 1989. Tracing of uranium-rich boulders at Pahtavuoma, northern Finland. In: DiLabio, R. N. W. & Coker, W. B. (eds.) Drift Prospecting. Geological Survey of Canada. Paper 89–20, 7–12. 10. Korkalo, T. 1977. The Pahtavuoma Cu-mineralisation. Studies conducted in the area. In: Prospecting in areas of glaciated terrain, August 1977, Finland. Excursion Guide, 14–17. 11. Pääkkönen, K. 1988. Uraanimalmitutkimukset Pahtavuoman-Kolvakeron alueella Kittilässä ja Muoniossa vuosina 1982–1985. Geol. Surv. Finland, Report M19/2741/-88/1/60. 34 p. (in Finnish, 6.8 MB) 12. Mäkelä, M. 1977. Sulfur isotope stratigraphy in some Finnish ore deposits. Geologiska Föreningens i Stockholm Förhandlingar 99, 163–171. 13. Papunen, H. (ed.) 1990. Sinkkiprojektin loppuraportti. Univ. of Turku, Inst. of Geology and Mineralogy, Publication 22. 143 p. (in Finnish) 14. Roos, S. 1987. Pahtavuoma. In: Papunen, H. (ed.) Lapin vulkaniittien tutkimusprojekti. Loppuraportti. Dept of Geology, Univ. of Turku, Report. 14–19. (in Finnish). 15. Papunen, H. 1987. Pahtavuoman geokemiasta ja malmimallista. In: Papunen, H. (ed.) Lapin vulkaniittien tutkimusprojekti. Loppuraportti. Dept of Geology, Univ. of Turku, Report. 20–46. (in Finnish). 16. Eilu, P. 1987. Muuttumisilmiöiden keskinäistä vertailua. In: H. Papunen (ed.) Lapin vulkaniittien tutkimusprojekti. Loppuraportti. Dept of Geology, Univ. of Turku, Report. 165–170. (in Finnish) 17. Korvuo, E. 1997. The Saattopora gold ore and the Pahtavuoma Cu-Zn-U occurrences in the Kittilä region, northern Finland. Geol. Surv. Finland, Guide 43, 21–25. 18. Pääkkönen, K. 1988a. Tutkimustyöselostus Kittilän ja Muonion kunnissa valtausalueilla Kolvakero 1–3, kaiv.rek. n:o 3315 sekä Laavivuoma 1–2 ja Kolvakero 4, kaiv.rek. n:o 3572 suor. malmitutkimuksista vv. 1982–1985. Geol. Surv. Finland, Report M06/2741/-88/1/60. 6 p. (in Finnish, 8.2 MB) 19. Törnroos, R. 1982. Sphalerite geobarometry of some metamorphosed sulphide ore deposits in Finland. Geol. Surv. Finland, Bull. 323. 42 p. 20. Aatos, S. 1992. Geokemiallisen muuttumisindeksin soveltaminen metamorfoituneiden vulkaanis-sedimenttisten sinkkiesiintymien sivukiviin. Unpublished MSc thesis. Dept of Geology, Univ. of Turku. 114 p. (in Finnish) 21. Hölttä, P. & Karhu, J. 2001. Oxygen and carbon isotope compositions of carbonates in the alteration zones of orogenic gold deposits in central Finninsh Lapland. Geol. Surv. Finland Special Paper 31, 25–29. 22. Puustinen, K. 1995. Suomen malmikaivokset vuosina 1530–1994. Geol. Surv. Finland, Report M10.1/-95/1. 96 p. (in Finnish) 23. Korkalo, T. 2006. Gold and copper deposits in Central Lapland, northern Finland, with special reference to their exploration and exploitation. Acta Univ. Oulensis, A Scientiae Rerum Naturalium 461. 122 p.
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