Pahkosuo - Gold Database

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Name	Pahkosuo	DATA UPDATED	24.5.2007
Alternative names	Pahkolampi
Deposit summary	PAHKOSUO, in the Suomussalmi greenstone belt, has an in situ resource estimate of 150 kg gold (unclear if the resource calculation is JORC-compliant). It is an Archaean orogenic gold deposit in tholeiitic metabasalt comprising several narrow lodes in a second-order, D3 to D4, N-trending, brittle-ductile shear zone close to the contact between greenstones and TTG terrain. Native gold associated with scheelite in quartz veins.
LOCATION
Geological domain	Archaean	Belt	Suomussalmi
Site photo		Regional map
Map sheet	451303
Northing (kkj)	7248800	Easting (kkj)	4469400
Latitude	65.33343N	Longitude	29.33966E
Municipality	Suomussalmi
Nearest town, roads	50 km NNE from Suomussalmi, 12 km from sealed road, a gravel road to the area.
MINING
Exploration licence no	5621/1 6272/1–2, 6410/1, 7500/37	Mining concession no
Present holder	Polar Mining (2003–)
Previous holders	Geological Survey of Finland (GTK) (1995–2001), Outokumpu Oyj (2002–2003)
Infra fig 1		Infra fig 2
Mine photo 1		Mine photo 2
Mine photo 3		Mine photo 4
Status of development	Prospect
When mined
Resources	0.1 Mt @ 1.6 ppm Au [3,4,5].
Deposit size (Mt)	0.1	Reference (size)	[3,4,5]
Total in-situ gold (kg)	152	Reference (in-situ Au)	[4]
Total gold production (kg)		Reference (gold prod)
Production of other metals
Extent of mineralisation
Lodes	Several 1–5 m wide lodes dipping at 80° to the east [5].
Best sections	In 31 drill holes 1 m sections @ >1 ppm Au; 5 m @ 1.7 ppm, 4 m @ 3.5 ppm, 4 m @ 2.92 ppm, 2.1 m @ 4.2 ppm, 1 m @ 16.6 ppm, 1 m @ 10.1 ppm, 1 m @ 8.18 ppm, 1 m @ 6.7 ppm, 1 m @ 6.1, 1 m @ 5.2 ppm Au [4,6].
EXPLORATION
Discovery year	1995
Discovery	By GTK by drilling into a structurally favourable location in a combined till geochemical and ground IP anomaly [1,5]. First indication was an extensive Au anomaly in till detected in early 1990's [4,5].
Exploration history	GTK (1991–1999) [1,4,5,6]: Bedrock mapping, till geochemical and transport survey, ground IP, VLF-R and magnetic survey, RC and diamond drilling. Outokumpu (2002–2003) [7]: diamond 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	The two main IP anomalies indicate Au lodes and metakomatiitic units in the area [5]. The trends of the IP anomalies also suggest the presence of NW-trending faults [5,6].
Drilling	GTK (1995–1998): 43 diamond-drill holes and 19 RC holes, total drilling 4732 m [4,5,6]. Outokumpu (2002–2003): five diamond-drill holes [7].
Elements analysed
Primary dispersion	A strong positive correlation between Au and scheelite [4,5,6].
Secondary dispersion	Au-As-Te anomaly in till 200–400 m wide, extends along strike several km to the N and S from the detected Au occurrence; total length of the Au-As-Te anomaly in till is, at least, 10 km [4,5].
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
Exploration geologist in charge	GTK: Kimmo Pietikäinen. Outokumpu: Markku Kilpelä.
ORE
Siting of gold	Close association with scheelite(?) [4].
Fineness
Major opaques	Pyrrhotite, pyrite [5,6].
Minor opaques	Arsenopyrite, chalcopyrite, native gold [5,6].
Gangue
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
Enriched elements	Au, S, W [4,5].
Ore fluid
Stable isotopes
Pb isotope data
GEOLOGY
Geological setting	The deposit is in the northeastern part of the late Archaean Suomussalmi Greenstone Belt, in contact zone between the greenstones and a TTG-series granitoid [1].
Major host rocks	Mafic, tholeiitic metavolcanic rock [1,5,6].
Minor host rocks	Quartz porphyry, granodiorite, tonalite [1,4,5].
Intrusives	A TTG granitoid, with an age of 2740–2720 Ma, at the contatc of the mineralised zones [1], sets of gtranitoid and felsic porphyry dykes, that have intruded the mafic volcanic sequence, predate mineralisation as also they host gold [5,6].
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
METAMORPHISM
Metamorphic history
Metamorphic grade	Amphibolite facies [1,2].
Metamorphic mineral assemblage
Metamorph photo 1		Metamorph photo 2
STRUCTURE
Structural style	Brittle-ductile [5]
Closest major shear	N-trending shear zone along the eastern contact between greenstone belt and TTG terrain [5,6].
Controlling structure	The mineralisation is within a second-order D3 or D4 fault or shear zone [1], in N-trending shear zone in the contact zone between the Suomussalmi Greensotne Belt and adjacent granitoids, possibly also controlled by NW-trending faults [5,6].
Deformation history	At least, four deformation stages during the late Archaean and two deformation stages during the Palaeoproterozoic time detected in the area [1,2]. Age of D2 is probably 2820±15 Ma [4] or 2843±18 Ma [8]. Syn-D3 granodiorite suggests an age of ca. 2718 Ma for the D3 stage [4].
Ore fabric
Veins	Auriferous, pyritic, quartz veins are common [5].
Structure photo 1		Vein photo 1
Structure photo 2		Vein photo 2
Structure photo 3		Vein photo 3
ALTERATION
General alteration	Sericitisation and sulphidation [4,5].
Proximal alteration
Intermediate alteration
Distal alteration
Zonation figure		Prox alteration photo 1
Alteration photo 1		Prox alteration photo 2
Alteration photo 2		Intermed alteration photo
Alteration photo 3		Distal alteration photo 1
Post-mineralisation modifications
TIMING	Syn- or slightly post-peak metamorphic [1].
GENETIC MODEL	[1]: Formed soon(?) after the peak metamorphic event under slightly retrograde conditions near the ductile-brittle transition; formed during late-Archaean cratonisation [3].
GENETIC TYPE	Orogenic	References	[1,3]
Alternative genetic type 1		References
Alternative genetic type 2		References
References 1. Halkoaho, T. & Pietikäinen, K. 1999. Ni and Au prospects of the Kuhmo and Suomussalmi greenstone belts. In: H. Papunen & P. Eilu (eds.) Geodynamic Evolution and Metallogeny of the Central Lapland, Kuhmo and Suomussalmi Greenstone Belts, Finland. University of Turku, Inst. Geol. Mineral. Publ. 42, 60–63. 2. Luukkonen, E. 1992. Late Archaean and Early Proterozoic structural evolution in the Kuhmo-Suomussalmi Terrain, eastern Finland. Annales universitatis Turkuensis. Ser. A. II 78, 1–37. 3. Papunen, H., Halkoaho, T., Liimatainen, J. & Luukkonen, E. 2001. Metallogeny of the Archaean Tipasjärvi-Kuhmo-Suomussalmi greenstone belt, Finland. AGSO – Geoscience Australia, Record 2001/37, 456–458. 4. Luukkonen, E., Halkoaho, T., Hartikainen, A., Heino, T., Niskanen, M., Pietikäinen, K. & Tenhola, M. 2002. Itä-Suomen arkeeiset alueet –hankkeen (12201 ja 210 5000) toiminta vuosina 1992–2001 Suomussalmen, Hyrynsalmen, Kuhmon, Nurmeksen, Rautavaaran, Valtimon, Lieksan, Ilomantsin, Kiihtelysvaaran, Enon, Kontiolahden, Tohmajärven ja Tuupovaaran alueella. Geol. Surv. Finland, Report M19/4513/2002/1. 265 p. (in Finnish, 130 MB) 5. Heino, T. 2001. Mineral Resource Assessment of the Pahkosuo gold mineralization, claims Pahkosuo (mine reg. N:o 5621/1), Pahkosuo 2 (N:o 6272/1), Pahkosuo 3 (N:o 6272/2) and Pahkosuo 4 (N:o 6410/1). Geol. Surv. Finland, Report M19/4513/2001/1. 3 p. (2.3 MB) 6. Tenhola, M., Pietikäinen, K., Hartikainen, A. & Niskanen, M. 2001. The Pahkosuo gold prospects in Suomussalmi, eastern Finland in 1991–1998 (registen numbers of claims: Pahkosuo 1, 5621/1; Pahkosuo 2, 7272/2; Pahkosuo 3 6272/2; Pahkosuo 4, 6410/1. Geol. Surv. Finland, Report M 06/4513/2001/1. 15 p. (3.8 MB) 7. Dragon Mining NL 2004. Quarterly Activities Report for the Quarter Ended 31st December 2003. Perth, Australia. 8 p. (116 KB) 8. Sorjonen-Ward, P. & Luukkonen, E.J. 2005. Archean rocks. In: Precambrian Geology of Finland – Key to the Evolution of The Fennoscandian Shield. Elsevier Science B.V., Amsterdam, 19–9 9. 9. Goode, K. 2004. Dragon Mining NL (DRA) – Bringing Scandinavian Gold Mines into Production. 12 p. (938 KB)
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