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|Deposit summary||PAHTAVAARA is an active gold mine (in production 1996–2 000, 2003–), with a total in situ size estimate of 15 t gold (production + resource, February 2006). It is sited in an altered komatiitic sequence at the eastern part of the Central Lapland greenstone belt. A swarm of subparallel lodes; nearly all gold is free native. It has many of the alteration characteristics of amphibolite-facies orogenic gold deposits and an obvious structural control, but has an anomalous barite-gold association and a very high fineness (>99.5 % Au) of gold. The geometry of high-grade quartz-barite lenses and amphibole rock bodies relative to biotite-rich alteration zones is also anomalous, as is the d13C of alteration carbonate minerals. Pahtavaara is best interpreted as a metamorphosed seafloor alteration system with ore lenses as either carbonate- and barite-bearing cherts or quartz-carbonate-barite veins. The gold may have been introduced later, but its grain size, textural position (nearly all is free, native, and occur with silicates, not sulphides) and high fineness point to a pre-peak metamorphic timing which is highly anomalous for orogenic gold.|
|Geological domain||Lapland||Belt||Central Lapland|
|Site photo||Regional map|
|Northing (kkj)||7504900||Easting (kkj)||3475300|
|Nearest town, roads||25 km NW from Sodankylä. 5 km from a sealed road, a gravel road to the mine.|
|Exploration licence no||3921/1, 4061/1, 4995/1–3, 5047/1, 5053/1–4, 5383/1||Mining concession no||3921/1a|
|Present holder||ScanMining (2002–)|
|Previous holders||Geological Survey of Finland (GTK) (–1991)
Terra Mining (1991–2002)
|Mine photo1||Mine photo2|
|Mine photo3||Mine photo 4|
|Status of development||Open pit and underground, active|
|When mined||1996–2000, 2003–|
|Resources||2.975 Mt @ 3.2 ppm Au . 3.18 ppm Au 1.007 Mt @ 4.82 ppm + 0.256 Mt @ 2.33 ppm Au [26,27]; 2002: 0.73 Mt @ 2.3–4.0 ppm Au ; 2 Mt @ 2.5 ppm Au [13,18,19].|
|Deposit size (Mt)||3.5||Reference (size)||[13,18,19,26,27,30]|
|Total in-situ gold (kg)||15,201||Reference (in-situ Au)||[13,18,19,27,30]|
|Total gold production (kg)||7733||Reference (gold prod)||[13,19,21,29,31,35]|
|Production of other metals|
|Extent of mineralisation||The set of lodes extend >400 m along a NW trend and dip to the north at about 70–80° . The undergroud resource is at the depth of from 80 to 330 m below the surface .|
|Lodes||The lodes are 5–10 m wide , have an E-W strike and dip to the N at about 70–80° [18,34]. Two lodes beyond the established ore of 2004, one to the west and another to the east of the mine, within the alteration halo of the ore .|
|Best sections||6.5 m @ 32.6 ppm Au . 10 m @ 11.7 ppm Au, 6 m @ 10.7 ppm Au, 7 m @ 6.6 ppm Au .
Beneficiation tests: At least 1 Mt waste rock @ 0.4–1.2 ppm Au can be processed with a profit .
|Discovery||By GTK: high gold grade and visible gold in outcrop. The discovery was preceded by detection of Au anomalies in till and the discovery of the extensive "skarn" zone in the bedrock during regional exploration [1,3,8].|
|Exploration history||GTK (1984–1991) [1,3,4,5,7,8,17]: Regional and detailed till geochemistry and stratigraphy, systematic sampling from bedrock surface below the overburden by percussion drilling, detailed outcrop mapping, trenching, diamond drilling, detailed thin section studies, microprobe analyses on silicates and gold, C and O isotopes on carbonates; low-altitude airborne magnetic, electromagnetic and radiometric survey; systematic ground magnetic and slingram survey, also ground gravity, ATM, IP and VLF-R surveys were tested in the area, biogeochemical survey of gold.
Terra Mining (1991–) [5,9,10]: Diamond and RC drilling.
Scan Mining (2002–) [26,27,28,29,30,31]: Diamond and percussion drilling.
|Section figure 1||Plan figure 1|
|Section figure 2||Plan figure 2|
|Section figure 3||Plan figure 3|
|Trench fig 1||Trench fig 4|
|Trench fig 2||Trench fig 5|
|Trench fig 3||Trench fig 6|
|Explor site photo 1||Explor site photo 2|
|Geophysical response||No response or a weak negative anomaly by electromagnetic methods for the mineralisation . Good response for unaltered metakomatiite and weak response for altered metakomatiite in magnetic survey .|
|Drilling||GTK (1986–87): 114 diamond-drill holes, total 3639 m .
Terra Mining (1991–2000): A large number of diamond-drill and RC holes , total drilling by 16/9/1998 more than 45 km .
Scan Mining (2002–2003): 7665 m [26,27].
|Elements analysed||Major components by XRF; CO2, H2O, S by Leco; Ba, Co, Cr, La, Ni, Rb, Sb, Sc, Sm by NAA; Ag and Cu by ICP; Au by GFAAS .
Major components by XRF and ICP; CO2, H2O, S by Leco; Au, Ce, Cr, Eu, La, Lu, Nd, Sc, Sm, Tb, Yb by INAA; Cu, V, Zn by DCP; Ba, Cr and Sr also by XRF; Co, Sc, V, Zn also by ICP; Au and Te by GFAAS . Au, Co, Cu, Mn, Ni, Pb and Zn by AAS and Fire Assay .
By GFAAS: Ag, Au, Co, Cu, Mo, Ni, Pb, Te, Zn, by fire assay: Au, by ICP: Ag, Al, As, B, Ba, Ca, Cd, Co, Cr, Cu, Fe, K, La, Li, Mg, Mn, Mo, Na, Ni, P, Pb, S, Sb, Sc, Si, Sr, Th, Ti, V, Y, Zn .
|Primary dispersion||Ba- and Mn-anomalies apparently cover most of the altered rocks [1,7]. Moderate positive correlation between Au and Ba in samples with >20 ppb Au . Along strike to the WNW-NW, local(?) enrichment of gold in bedrock up to 6 km from the deposit .|
|Secondary dispersion||A combined Au-Cu-Co-Ni anomaly in till: arcuate, E-W trending, 15 km long [1,8]. This includes an inner anomaly formed by the combination Au-Ba-Sr-Mn, which envelopes the Au deposit and the most altered rocks .
In vegetation, Au is enriched in juniper and crowberry, and defines an anomaly around the deposit .
|Primary anomaly fig 1||Secondary anomaly fig 1|
|Primary anomaly fig 2||Secondary anomaly fig 2|
|Primary anomaly fig 3||Secondary anomaly fig 3|
|Primary anomaly fig 4||Secondary anomaly fig 4|
|Primary anomaly fig 5||Secondary anomaly fig 5|
|Economic evaluations||Preliminary feasibility study by GTK on 1990 . Feasibility study by Terra Mining (1991–1996) [5,10]. Feasibility study by Scan Mining (2002–2003) .|
|Exploration geologist in charge||GTK: E. Pulkkinen, E. Korkiakoski; Terra Mining: M. Kilpelä.|
|Siting of gold||Nearly all is free native gold, chiefly between silicate, carbonate and baryte grains, but locally also as inclusions in magnetite; minor gold as inclusions in pyrite and chalcopyrite [1,3,8,16,36]. Visible gold occurs in coarse-grained amphibole rock with quartz-baryte veins .|
|Fineness||99.7% Au . 99.02% Au, 0.07% Ag, 0.25% Bi .|
|Major opaques||Magnetite, pyrite [1,3,4,5,8,16,36].|
|Minor opaques||Chalcopyrite, rutile, chromite, haematite, pentlandite, pyrrhotite, violarite, millerite, cubanite, gold, clausthalite, merenskyite [1,3,4,8,16,36].|
|Gangue||Quartz, baryte, tremolite, dolomite, scheelite [1,2,3,4,8,33].|
|Ore miner. photo 1||Ore miner. photo 5|
|Ore miner. photo 2||Ore miner. photo 6|
|Ore miner. photo 3||Ore outcrop photo 1|
|Ore miner. photo 4||Ore outcrop photo 2|
|Ore composition||23.00 ppm Au, 0.2 ppm Ag, 1000 ppm Ba, 41 ppm Co, 427 ppm Cr, 3 ppm Cu, 0.43 ppm La, 605 ppm Ni, 60 ppm Rb, 0.2 ppm Sb, 14 ppm Sc, 0.66 ppm Sm; 54.81% SiO2, 0.10% TiO2, 1.64% Al2O3, 11.70% Fe2O3, 17.10% MgO, 10.95% CaO, <0.00% Na2O, 0.48% K2O, <0.00% P2O5, 2.16% H2O, 0.30% CO2 .
1.00–33.00 ppm Au, 45–80 ppm Co, 18–31 ppm Sc, 20–260 ppm Sr, 0.01–0.08 ppm Te, 180–215 ppm V, 6–150 ppm W, 15–40 ppm Zn, 44–54% SiO2, 0.10–0.76% TiO2, 1.88–6.84% Al2O3, 12.9–24.9% Fe2O3, 16.5–26.0% MgO, 1.8–10.0% CaO, <0.00–0.95% Na2O, <0.00–2.97% K2O, <0.00–0.07% P2O5, 0.25–6 .64% CO2, 0.01–0.81% S .
|Ore composition table 1||Click here|
|Enriched elements||Au, Ag, B, Ba, CO2, Fe(?), K, Mn, Na (locally), S, Sr . Au, Ba, Ca, CO2, K, Na, P, Si, Sr, Te and W in the proximal and intermediate areas; in addition, LREE in the most carbonate-rich parts [3,5].|
|Ore fluid||Biotitisation stage: CO2–H2O fluid, slightly reducing, Au-, K- and S-bearing; S content was relatively low, however .
Amphibole-overgrowth stage: CO2-undersaturated, silica-saturated, Ba-rich?, slightly oxidising .
|Stable isotopes||Ore: δ18O: +11.36 – +11.86 per mill, δ13C: -4.11 – -1.18 per mill . Alteration halo: δ18O: +10.19 – +12.84 per mill, δ13C: -4.42 – -1.23 per mill . Carbonates throughout the alteration halo: δ18O: +10.82 – +11.47 per mill, δ13C: -3.17 – -0.40 per mill . Unaltered: δ18O: +10.06 – +10.26 per mill, δ13C: -8.74 – -1.97 per mill .|
|Pb isotope data||Mantle-derived lead . Pb-Pb age for whole rock 1814±32 Ma, and for pyrite and magnetite 1811±87 Ma .|
|Geological setting||The deposit is in an E-W trending, 40 km long, 5 km wide and several kilometres thick sequence of Geluk-type komatiitic lavas and pyroclastic rocks and komatiite-related mafic metavolcanic rocks, the Sattasvaara Formation, in the Palaeoproterozoic Central Lapland Greenstone Belt [1,3,5,11,17,36]. The deposit is near the northern margin of the sequence, in the contact zone between a komatiitic pyroclastic and a komatiitic lava unit [1,3].|
|Major host rocks||Al-depleted(?) metakomatiites [3,34].|
|Minor host rocks|
|Regional geol map 1||Outcrop photo 1|
|Regional geol map 2||Outcrop photo 2|
|Local geology map 1||Outcrop photo 3|
|Local geology map 2|
|Metamorphic history||Progressive regional metamorphism peaked during the crystallisation of tremolite and recrystallisation of minerals produced by the early alterations, like carbonate(s) and talc . Metamorphic peak during D2, thrusting during D3 was at least partly post-peak, late metamorphic .|
|Metamorphic grade||Upper-greenschist facies, based on mineral assemblages given in the references [1,3]. At the regional boudary between lower-amphibolite and greenschist facies rocks .|
|Metamorphic mineral assemblage||Pyroclastic rock: serpentine-chlorite-tremolite-antophyllite ; tremolite-talc-chlorite-dolomite(?)-antophyllite [2,3,11].
Lava: tremolite-antophyllite(?)±chlorite, carbonate, plagioclase [1,3,11].
|Metamorph photo 1||Metamorph photo 2|
|Structural style||Brittle-ductile [1,3].|
|Closest major shear|
|Controlling structure||Crossing of NW- and NE-trending fault or shear zones [1,3].
A set of SW-NE trending faults which dip to the north by 80° [8,34].
|Deformation history||At least two stages of folding, the older characterised by E-W trending and the younger by NE-trending schistosity . Two major stages, the D1 and D3 of the regional deformation history, recorded in the area .|
|Ore fabric||Massive, nemato-lepidoblastic to granoblastic [1,3].|
|Veins||Distal and intermediate talc-carbonate ± pyrite and proximal quartz-baryte ± carsbonate, tourmaline, gold veins [1,3]. A continuum exists between these two vein types which both may contain variable volumes of actinolite .|
|Structure photo 1||Vein photo 1|
|Structure photo 2||Vein photo 2|
|Structure photo 3||Vein photo 3|
|General alteration||Early carbonation, chloritisation, intense biotitisation ± tourmalinisation, and pyritisation predate peak metamorphism while the following alterations post-date peak metamorphism: the late formation of talc, chloritisation, albitisation, formation of richterite, minor biotitisation and minor tourmalinisation .
Syn-peak deformation biotitisation and post-peak tremolite overgrowth [3,34]. The extent of the alteration envelope (intermediate + proximal alteration?) is 100x600 m .
The extent of the alteration envelope is 100x500 m [5,34].
The extent of the alteration halo is 30–120 m x 600 m .
: Three possible stages of alteration:
1. Albitisation and part of carbonation may have preceded gold mineralisation.
2. Biotitisation, formation of nematoblastic tremolite and additional carbonation, with formation of abundant quartz veins, are most probably related to the syn-peak metamorphic gold mineralisation.
3. Formation of overprinting tremolite porphyroblasts took place after gold mineralisation – this is, in fact, not an alteration stage.
|Proximal alteration||Unfoliated, biotite-talc-dolomite/ankerite-tremolite/actinolite-quartz-pyrite-rutile ± albite, richterite, barite, magnetite, tourmaline; also coarse-grained, nearly mono-mineralic amphibole rock with locally abundant quartz and barite and minor amounts of dolomite or ankerite, talc and albite [1,2,3,15].|
|Intermediate alteration||Talc-carbonate-chlorite-biotite-rutile-tremolite-quartz ± albite, magnetite, tourmaline [1,2,3,15].|
|Distal alteration||Discontinuous, about 8 km long, 100–300(?) m wide, generally E-W trending "skarn"  zone charcterised by the mineral assemblage chlorite-calcite-talc-tremolite ± albite [1,2]. At Pahtavaara, the domain of continuous alteration and formation of penetrative foliation is WSW-trending, >500 m long (open to the WSW) and 100–2 00 m wide [1,2,15].|
|Zonation figure||Prox alteration photo 1|
|Alteration photo 1||Prox alteration photo 2|
|Alteration photo 2||Intermed alteration photo|
|Alteration photo 3||Distal alteration photo1|
|Post-mineralisation modifications||Tremolite overgrowth ? .|
|TIMING||Pb-Pb age for whole rock 1814±32 Ma, and for pyrite and magnetite 1811±87 Ma; if these represent the second stage of mineralisation, the age of ca. 1820 Ma can be considered as the minimum age for the main stage of gold mineralisation .|
|GENETIC MODEL||: Biotitisation-dominated, reducing alteration in a komatiitic sequence was the main mineralising stage during peak- to slightly post-peak deformation. This was followed by amphibole overgrowth with partial decarbonation of rocks altered during the first stage under oxidising conditions; this was another mineralising stage, possibly just remobilising gold. The coarse, visible gold was formed during the latter stage.
[23,24]: Palaeomagnetic indications from remanent magnetism suggest that the main alteration stage took place during 1880–1840 Ma.
: Mineralisation took place at ca. 1840–1870 Ma indicating the formation of late-orogenic metamorphic fluid with lead form mantle that was responsible for the gold mineralisation.
: Albitisation and part of carbonation may have preceded gold mineralisation, "preparing ground", i.e. making the komatiitic host rock locally more competent than the surrounding talc-chlorite schist and, hence, a structurally favourable site for the mineralising fluids to precipitate gold. Biotitisation, formation of nematoblastic tremolite and additional carbonation, with formation of abundant quartz veins, are most probably related to the syn-peak metamorphic gold mineralisation. Formation of overprinting tremolite porphyroblasts took place after gold mineralisation.
: Early, synvolcanic, submarine alteration with a significant metamorphic fluid component: carbonation, biotitisation, chloritisation, sulphidation, tourmalinisation and Au-mineralisation (most of gold). This was followed by syn-metamorphic formation of tremolite porphyroblasts and retrograde(?) formation of talc, quartz-baryte veins, minor chloritisation and tourmalinisation, oxidation of Fe sulphides, replacement of other Ti-bearing minerals by rutile, and mobilisation and re-precipitation of gold into the association of the quartz-baryte veins.
|Alternative genetic type 1||References|
|Alternative genetic type 2||References|
References1. Hulkki, H. 1990. Sodankylän Sattasvaaran komatiittikompleksin Au-kriittinen muuttumisvyöhyke. Unpubl. MSc thesis. Dept of Geology, Univ. of Helsinki. 190 p. (in Finnish)
2. Niiranen, K. 1998. Personal communication 22/2/98.
3. Korkiakoski, E. 1992. Geology and geochemistry of the metakomatiite-hosted Pahtavaara gold deposit in Sodankylä, northern Finland, with emphasis on hydrothermal alteration. Geol. Surv. Finland, Bull. 360. 96 p.
4. Korkiakoski, E., Karvinen, A. & Pulkkinen, E. 1989. Geochemistry and hydrothermal alteration of the Pahtavaara gold mineralization, Finnish Lapland. Geol. Surv. Finland, Special Paper 10, 83–89.
5. Korkiakoski, E. & Kilpelä, M. 1997. The komatiite-hosted Pahtavaara gold mine near Sodankylä, northern Finland. In: E. Korkiakoski & P. Sorjonen-Ward (eds) Ore deposits of Lapland in northern Finland and Sweden. Geol. Surv. Finland, Guide 43, 27–29.
6. Korkiakoski, E. & Räsänen, J. 1993. Komatiites and gold: the two-stage alteration of the Pahtavaara gold deposit, northern Finland. In: IAGOD International Symposium on Mineralization Related to Mafic and Ultramafic Rocks with a special session on Alkaline and carbonatitic magmatism and associated mineralization, Orleans, France, 1–3 September, 1993. Terra Abstracts. Abstract supplement no. 3 to Terra Nova 5, p. 24.
7. Pulkkinen, E., Ollila, J., Manner, R. & Koljonen, T. 1986. Geochemical exploration for gold in the Sattasvaara komatiite complex, Finnish Lapland. In: Prospecting in areas of glaciated terrain 1986: papers presented at the Seventh International Symposium organised by The Institution of Mining and Metallurgy and The Geol. Surv. Finland, Kuopio, 1–2 September, 1986. London: The Inst. of Mining and Metallurgy, 129–137.
8. Karvinen, A. 1990. Pahtavaaran kultatutkimukset Sodankylässä vuosina 1987–1989. Geol. Surv. Finland, Report M19/3714/-90/1/10. 19 p. (in Finnish)
9. William Resources Inc. 1997. Press release 16/4/1997.
10. William Resources Inc. 1997. Press release 2/7/1997.
11. 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.
12. Parkkinen, J. 1990. Sodankylän Pahtavaaran kulta-aiheen arviointi. Geol. Surv. Finland, Report M19/3714/-90/2/10. 13 p. (in Finnish)
13. Alaniska, H. 1998. Personal communication (March 1998).
14. Mänttäri, I. 1995. Lead isotope characteristics of epigenetic gold mineralization in the Palaeoproterozoic Lapland greenstone belt, northern Finland. Geol. Surv. Finland, Bull. 381. 70 p.
15. Eilu, P. 1997. Orogenic lode-gold deposits: Notes to accompany samples from deposits located on the Fennoscandian Shield. Univ. of Turku, Dept of Geology and Mineralogy, Publ. 35, 1st edition. 14 p.
16. Kojonen, K. & Johanson, B. 1988. Pahtavaaran Au-malmiaiheen malmimineraaleista. Geol. Surv. Finland, Report M40/3714/-88/1/41.2. 2 p. (in Finnish)
17. Lanne, E. 1995. Sattasvaaran komatiittimuodostuman geofysikaalinen rakennetutkimus. Geol. Surv. Finland, Report Q19/3714/95/1/22.86. 27 p. (in Finnish)
18. Kilpelä, M. 1998. Personal communication. 16/9/1998.
19. Alaniska, H. 1999. Personal communication (July 1999).
20. Patison, N.L. & Oliver, N.H.S. 2001. Structural features associated with Palaeoproterozoic gold deposits in the Central Lapland Greenstone Belt, northern Finland. In: P.J. Williams (ed) 2001: A Hydrothermal Odyssey. May 17–19th, 2001, Townsville. Extended abstracts. EGRU and JCU. 162–163.
21. Vartiainen, H. 2001. Personal communication 28/08/2001.
22. 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.
23. Airo, M.-L., Mertanen, S. 2001. Magnetic signatures related to Precambrian greenstone-hosted Au mineralizations, northern Fennoscandia. In: Vietnam 2001: IAGA–IASPEI joint scientific assembly, 19–31 August 2001, Hanoi, Vietnam : abstracts. Hanoi: IAGA : IASPEI, 263.
24. Mertanen, S. 2001. Sekundääriset remanenssit kallioperän geologisten prosessien ilmentäjänä. Abstract: Secondary remanent magnetization reflecting the geological processes in bedrock. In: XX Geofysiikan päivät Helsingissä 15–16.5.2001. Geofysiikan Seura, Helsinki. 81–86.
25. ScanMining 2002. Press release 09/09/2002. (in Swedish)
26. ScanMining 2003. Press release 21/08/2003. (23 KB)
27. ScanMining 2003. Press release 15/10/2003. (in Swedish)
28. Scanmining 2004. Press release 18/11/2004. (in Swedish)
29. Scanmining 2005. Press release 12/01/2005. (in Swedish)
30. Scanmining 2005. Press release 03/05/2005. (in Swedish)
31. Scanmining 2006. Press release 24/02/2006. (in Swedish)
32. Nurmi, P. A., Lestinen, P. & Niskavaara, H. 1991. Geochemical characteristics of mesothermal gold deposits in the Fennoscandian Shield, and a comparison with selected Canadian and Australian deposits. Geol. Surv. Finland, Bull. 351. 101 p.
33. Jakobsson, P. 2006. Personal communication 17 May 2006.
34. Ojala, V.J., Patison, N. & Eilu, P. 2007. Day 2, Stop 1 Pahtavaara Au mine. Geol. Surv. Finland, Guide 54. 45–47.
35. ScanMining 2007. Årsredovisningen 2006. ScanMining, Karlstad. 52 p. (in Swedish)
36. Eilu, P., Pankka, H., Keinänen, V., Kortelainen, V., Niiranen, T. & Pulkkinen, E. 2007. Characteristics of gold mineralization in the greenstone belts of northern Finland. Geol. Surv. Finland, Special Paper 44, 57–106.
37. Hölttä, P., Väisänen, M., Väänänen, J. & Manninen, T. 2007. Paleoproterozoic metamorphism and deformation in Central Lapland, Finland. Geol. Surv. Finland, Special Paper 44, 7–5 6.
38. Lappland Goldminers 2008. Press release June 18 2008.
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