Korvilansuo - Gold Database

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Name	*Korvilansuo*	DATA UPDATED	24.5.2007
Alternative names
Deposit summary	KORVILANSUO, in the Ilomantsi greenstone belt, is an Archaean orogenic gold occurrence with no resource estimate available. It comprises subvertical lodes formed by dissemination and auriferous tourmaline-quartz veins in intermediate volcanogenic metasedimentary rock, close to the NE-trending Korvilansuo shear zone. Native gold disseminated in the host rock and quartz veins as inclusions in biotite, pyrrhotite, pyrite and arsenopyrite, free between silicate grains, intergrown with bismuth, tellurides and rutile.
LOCATION
Geological domain	Archaean	Belt	Ilomantsi
Site photo		Regional map
Map sheet	424408
Northing (kkj)	6966600	Easting (kkj)	4560000
Latitude	62.79856N	Longitude	31.17285E
Municipality	Ilomantsi
Nearest town, roads	30 km NE from Ilomantsi, 95 km NE from Joensuu. A sealed road 500 m the area.
MINING
Exploration licence no	4165/1, 5510/1–5, 6357/1, 7558/1–2	Mining concession no
Present holder	Endomines (2006–)
Previous holders	Geological Survey of Finland (GTK), Outokumpu Oyj (1995–2 003), Polar Mining (2003–2006)
Mine photo 1		Mine photo 2
Mine photo 3		Mine photo 4
Status of development	Prospect
When mined
Resources
Deposit size (Mt)		Reference (size)
Total in-situ gold (kg)		Reference (in-situ Au)
Total gold production (kg)		Reference (gold prod)
Production of other metals
Extent of mineralisation
Lodes	The N-NE striking, subvertical lodes are formed by dissemination in the host rock and auriferous tourmaline-quartz veins [4].
Best sections	5.5 m @ 2.7 ppm Au [3,4], 2.5 m @ 5.1 ppm Au, 2 m @ 4.5 ppm Au, 0.5 m @ 15 ppm Au [8,11], 1 m @ 8.4 ppm, 0.7 m @ 9.8 ppm, 0.5 m @ 15.2 ppm Au [1].
EXPLORATION
Discovery year	1986
Discovery	By GTK: arsenopyrite-bearing outcrop samples assayed 4–8 ppm Au. These samples were from an exploration pit excavated into one of the peak areas of a local till anomaly [4].
Exploration history	GTK (1987–1994) [1,4,7,8,9,10,11]: Detailed geochemical till sampling: sampling grid 250x250 m over the greenstone belt covering 400 km2. Follow-up as till-bedrock interface geochemistry, samples collected across the Au anomaly along traverses 100 m apart with sampling distance 10–30 m. Low-altitude air- and ground-magnetic, slingram and IP survey. Bedrock mapping based on outcrops, geophysics, trenching and diamond drilling. Special studies on Quaternary geology, ore mineralogy [1,7] and geochemistry, and petrogenesis.
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 on magnetic, slingram or IP methods. Magnetic and electric methods do show the structural features of the area, including those which control gold mineralisation [4].
Drilling	GTK (–1993) [3,4,8,10,11]: 14 diamond-drill holes, total 2083 m in 50–100 m traverse intervals, total 2202 m.
Elements analysed	Ag, Al, As, Au, B, Ba, Bi, Ca, Cd, Co, CO2, Cr, Cu, Fe, K, LOI, Mg, Mo, Na, Nb, P, Pb, Rb, REE, S, Sb, Sc, Se, Si, Sr, Te, Ti, Th, U, V, W, Y, Zn, Zr [2,4].
Primary dispersion	Au and Te show good correlation; Ag and Bi show moderate correlation with Au. No consistent chemical zoning found yet [4,5].
Secondary dispersion	[3]: Regional Au, As and B till anomaly, local Au, Te and Bi anomaly. Au content within the till anomaly is from tens of ppb to >1 ppm. Best combination for defining exploration targets: Au + Te + Bi- better than Au alone. A 0.5–1 km wide Au anomaly in till along the western-southwestern contact of the Kuittila tonalite.
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: Martti Damsten. Endomines: Jaakko Liikanen
ORE
Siting of gold	Dissemination in mica schist and in tourmaline-quartz veins and breccia. Gold is as inclusions in biotite, pyrrhotite, pyrite and arsenopyrite, free between silicate grains, intergrown with bismuth, tellurides and rutile and in petzite [1,4,7].
Fineness	78–96% Au, 4–17% Ag [7].
Major opaques	Pyrite, pyrrhotite [1,7].
Minor opaques	Native gold, frohbergite, altaite, hessite, tellurobismuthinite, petzite, melonite, rucklidgeite, volynskite, bismuth, arsenopyrite, chalcopyrite, sphalerite, galena, native bismuth, molybdenite, cubanite, pentlandite, mackinawite, rutile, ilmenite [1,7].
Gangue	Quartz, tourmaline, albite, K feldspar, biotite, muscovite, garnet, calcite, chlorite, scheelite, titanite [1,5,7].
Ore miner. photo 1		Ore miner. photo 6
Ore miner. photo 2		Ore miner. photo 7
Ore miner. photo 3		Ore miner. photo 8
Ore miner. photo 4		Ore outcrop photo 1
Ore miner. photo 5		Ore outcrop photo 2
Ore composition	Diamond-drill core [2]: 6.25 ppm Au, 0.519 ppm Ag, 870 ppm As, 2270 ppm B, 689 ppm Ba, 3.9 ppm Bi, 31 ppm Co, 51 ppm Cu, 17 ppb Hg, 1.0 ppm Mo, 155 ppm Ni, 2.1 ppm Pb, 124 ppm Rb, 5640 ppm S, 19.4 ppm Sb, 0.14 ppm Se, 213 ppm Sr, 2.250 ppm Te, 5.2 ppm Th, 2.3 ppm U, 170 ppm V, 7.0 ppm W, 109 ppm Zn; 59.9% SiO2, 0.76% TiO2, 16.3% Al2O3, 8.56% Fe2O3, 4.02% MgO, 1.25% CaO, 1.38% Na2O, 3.97% K2O, 0.18% P2O5, 0.62% LOI.
Enriched elements	Au + Te, As, Bi, Ag, B, K, S, CO2 [4, 5].
Ore fluid
Stable isotopes	[4]: δ18O (SMOW): +10.40 – +15.07 per mill (calcite), +10.1 – +12.3 per mill (quartz), +10.9 per mill (calcite), +1.7 per mill (scheelite), +10.5 per mill (tourmaline), +8.2 (muscovite); => T = 411–473°C; δD (SMOW): -96 per mill (tourmaline), -77 (muscovite), -96 per mill (chlorite); δ13C (PDB): -12.41 – 8.67 per mill (calcite).
Pb isotope data
GEOLOGY
Geological setting	The mineralisation is characterised by quartz-tourmaline vein and breccias and is in the central part of the 2754–2726 Ma [12] Hattu Schist Belt. The mica schists of sedimentary and/or volcano-sedimentary origin are intruded by felsic porphyry, gabbroidic dikes and tonalite [1,4].
Major host rocks	Mica schist [4,7].
Minor host rocks	Mafic metatuffite and dolerite(?) [4], tonalite [10].
Intrusives	Felsic porphyry, gabbroidic dikes and tonalite which all predate gold mineralisation, are affected by gold mineralisation-related alteration [4].
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	[4]: Progressive regional metamorphism on ca. 2750–2700 Ma, apparently peaked soon after gold mineralisation, at a temperature of about 539–595±50°C (garnet-biotite thermometer). Thermal peak was synchronous or outlasted deformation. A relatively strong, but unevenly distributed Palaeoproterozoic overprint [6].
Metamorphic grade	Greenschist-amphibolite facies transition [4].
Metamorphic mineral assemblage	Andalusite-chlorite-biotite-quartz-plagioclase-garnet-K feldspar(-staurolite) [5,7].
Metamorph photo 1		Metamorph photo 2
STRUCTURE
Structural style	Brittle-ductile to ductile [4].
Closest major shear	Korvilansuo-Muurinsuo Shear Zone system adjacent to the deposit [4].
Controlling structure	Korvilansuo shear zone [4].
Deformation history	Rapid and extensive crustal generation and progressive deformation between 2.76–2.73 Ma, in a transpressional regime [12].
Ore fabric	Granoblastic [1].
Veins	Auriferous tourmaline-quartz veins up to a few tens of centimetres wide, tourmaline-quartz breccia [1,4].
Structure photo 1		Vein photo 1
Structure photo 2		Vein photo 2
Structure photo 3		Vein photo 3
ALTERATION
General alteration	Formation of quartz, biotite, muscovite, albite, chlorite, tourmaline, rutile, calcite, garnet; locally, intense tourmaline formation; the alteration envelope is several hundreds of metres wide [1,4,5].
Proximal alteration	Chlorite-sericite-biotite; destruction of andalusite [4,5] + tourmalinisation [8].
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	[4]: Probably, an Archaean post-mineralisation metamorphic overprint at about 500±50°C with deformation and porphyroblast overgrowth. This also affected δ 18O values of minerals. On ca. 1800 Ma, a Proterozoic regional metamorphic overprint which is shown by K-Ar and Rb-Sr ages of micas. Kyanite, probably a Proterozoic overprint, is replacing sericite formed during alteration.
TIMING	[4]: Either pre-peak metamorphic and formed under greenschist-facies conditions, or syn-peak metamorphic. Minimum age 2708–2693 Ma (U-Pb of titanite and monazite indicating peakmetamorphism).
GENETIC MODEL	[4]: Formed in a structurally favourable, the most competent lithological units in the area. Precipitation of gold by desulphidation of fluid and, possibly, by decomposition of Au-bisulphide, -thiosulphide and -telluride complexes of fluid due to cooling and/or changes in pH and fO2. Probably, gold precipitated just below 500°C with sulphides due to reaction between the mineralising fluid and wall-rock (chiefly by sulphidation). The formation of the present low-temperature Te and Bi minerals probably took place as subsolidus reactions with cooling temperature. The combination of arsenopyrite and oxygen isotope thermometry, sphalerite geobarometry, with the dominance of pyrrhotite and calcite instated of pyrite and dolomite, respectively, suggests uppermost-greenschist facies or conditions transitional between greenschist and amphibolite facies for mineralisation: T = 450–500°C, p = 2–3 kbar. Arsenopyrite indicates crystallisation at about 400°C, bismuth below 271°C and Ag-Au tellurides at 120–250°C [1,7].
Genetic type	Orogenic	References	[4]
Alternative genetic type 1		References
Alternative genetic type 2		References
References 1. Kojonen, K., Johanson, B., Pakkanen, L. & O'Brien, H. 1991. Ilomantsin Korvilansuon Au-malmiaiheen mineralogiaa ja petrografiaa. Geol. Surv. Finland, Report M19/4244/-91/1/42. 40 p. (in Finnish, 10 MB) 2. 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, Bulletin 351. 101 p. 3. Nurmi, P. A. 1993. Archaean Au in Finland. Engineering and Mining Journal, Nov., 32–34. 4. Nurmi, P. A. & Sorjonen-Ward, P. (eds) 1993. Geological Development, Gold Mineralization and Exploration Methods in the Late Archaean Hattu Schist Belt, Ilomantsi, Eastern Finland. Geol. Surv. Finland, Special Paper 17. 386 p. 5. Rasilainen, K. 1996. Alteration geochemistry of gold occurrences in the late Archean Hattu Schist Belt, Ilomantsi, Eastern Finland. Academic dissertation: synopsis and four research papers. Geol. Surv. Finland. 140 p. 6. Korsman, K. (ed.) & Glebovitsky, V. (ed.) 1999. Raahe-Ladoga Zone structure-lithology, metamorphism and metallogeny: a Finnish-Russian cooperation project 1996–1999. Map 2: Metamorphism of the Raahe-Ladoga Zone 1:1000000. Geol. Surv. Finland. 7. Kojonen, K., Johanson, B., O'Brien, H. E. & Pakkanen, L. 1993. Mineralogy of gold occurrences in the late Archaean Hattu schist belt, Ilomantsi, eastern Finland. In: P. Nurmi & P. Sorjonen-Ward (eds) Geological development, gold mineralization and exploration methods in the late Archaean Hattu schist belt, Ilomantsi, eastern Finland. Geol. Surv. Finland, Special Paper 17, 233–271. 8. Damsten, M. & Nurmi, P. 1994. Alustava raportti kultamalmitutkimuksista ns. Kuittilan vyöhykkeellä Ilomantsin kunnassa. Geol. Surv. Finland, Report M 19/4244/94/1/10. 14 p. (in Finnish, 1.9 MB) 9. Hartikainen, A. & Niskanen, M. 2001. maaperägeokemialliset kultatutkimukset Hatun liuskejaksolla Ilomantsissa vv. 1983-1995. Geol. Surv. Finland, Report S/41/4244/1/2001. 22 p. 10. Damsten, M., Hartikainen, A., Koistinen, E. & Nurmi, P.A. 1994. Tutkimustyöselostus Ilomantsin kunnassa valtausalueilla Muurinsuo (kaivosrekisterinro 4273/1), Korvilansuo 1 (4165/1), Kelokorpi 1 (4165/2), Palosuo (5027/1), Muurinsuo 2 (5359/1), Muurinsuo 3 (5359/2) sekä valtausvarausalueilla Elinsuo (156/93), Kiimasuo (156/93) ja Viinivaara (25/94) suoritetuista kultamalmitutkimuksista vuosina 1984–1993. English summary: Report on exploration in Ilomantsi during 1984–1993 in claims Muurinsuo (Mine Reg. No. 4273/1), Korvilansuo 1 (4165/1), Kelokorpi 1 (4165/2), Palosuo (5027/1), Muurinsuo 2 (5359/1), Muurinsuo 3 (5359/2) and claim reservation areas Elinsuo (156/93), Kiimasuo (156/93) and Viinivaara (25/94). Geol. Surv. Finland, Report M06/4244/-94/1/10. 14 p. (790 KB) 11. 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) 12. 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, 19-99.
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