Elinsuo - Gold Database

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Name	Elinsuo	DATA UPDATED	24.5.2007
Alternative names
Deposit summary	ELINSUO, in the Ilomantsi greenstone belt, is an Archaean orogenic gold occurrence with no resource estimate available. It is hosted by a felsic porphyry, and located in the NE-trending Korvilansuo shear zone. Native gold disseminated in the host rock and quartz±tourmaline veins, intergrown with tellurides and pyrite.
LOCATION
Geological domain	Archaean	Belt	Ilomantsi
Site photo		Regional map
Map sheet	424408
Northing (kkj)	6969050	Easting (kkj)	4560800
Latitude	62.82040N	Longitude	31.18941E
Municipality	Ilomantsi
Nearest town, roads	30 km NE from Ilomantsi, 95 km NE from Joensuu. A sealed road 1 km from the area, a gravel road to the area.
MINING
Exploration licence no	7742/4	Mining concession no
Present holder	Endomines (2006-)
Previous holders	Geological Survey of Finland (GTK)
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	Lodes are N-NE trending, subvertical [2].
Best sections	2 m @ 3.05 ppm Au, 6 m @ 1.1 ppm, 1 m @ 2.6 ppm Au [1,2,6,9].
EXPLORATION
Discovery year	1989
Discovery	By GTK; the first indication was an Au anomaly in till [1,2].
Exploration history	GTK (1987–) [1,2,3,6,7]: 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 [5] 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	[2]: 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.
Drilling	GTK: (1987–1993) [1,2,6,9]: 3 diamond-drill holes, total 396 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 [2,3]
Primary dispersion	Au and Te show good correlation; Ag and Bi show moderate correlation with Au. No consistent chemical zoning found yet [2,3].
Secondary dispersion	[2]: 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.
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 host rocks, veins and "tourmaline-quartz rock". Gold occurs intergrown with tellurides, in the host rocks also intergrown with pyrite and in veins also as inclusions in pyrite [2,5].
Fineness	89–92% Au, 6–7% Ag [5].
Major opaques	Pyrrhotite, pyrite [2,5].
Minor opaques	Native gold, tellurobismuthinite, hessite, volynskite, arsenopyrite, chalcopyrite, pentlandite, rutile, ilmenite [5].
Gangue	Quartz, albite, K feldspar, biotite, muscovite, garnet, calcite?, chlorite, scheelite, titanite, tourmaline [2,3,5].
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 + Te, Bi, As, Mo, Ag, B, S, CO2 [2,3].
Ore fluid
Stable isotopes	[2]: δ18O (SMOW): +10.0 per mill (tourmaline); δD (SMOW): -97 per mill (tourmaline).
Pb isotope data
GEOLOGY
Geological setting	The mineralisation is in the central part of the 2754–2726 Ma Hattu Schist Belt [10]. The mica schists are intruded by felsic porphyry dikes [2].
Major host rocks	Felsic porphyry [8].
Minor host rocks	Mica schist [2].
Intrusives	Felsic porphyry dikes, predate gold mineralisation [2].
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	[2]: Progressive regional metamorphism on ca. 2750–2700 Ma, apparently peaked soon after gold mineralisation, at a temperature of about 550±50°C. Thermal peak was synchronous or outlasted deformation. A relatively strong, but unevenly distributed Palaeoproterozoic overprint [4].
Metamorphic grade	Greenschist-amphibolite facies transition [2].
Metamorphic mineral assemblage
Metamorph photo 1		Metamorph photo 2
STRUCTURE
Structural style	Dominantly ductile [2].
Closest major shear	Korvilansuo-Muurinsuo Shear Zone system adjacent to the deposit [2].
Controlling structure	Korvilansuo shear zone [2].
Deformation history	Rapid and extensive crustal generation and progressive deformation between 2.76–2.73 Ma, in a transpressional regime [10].
Ore fabric
Veins	Quartz-tourmaline veins. Tourmaline-quartz rock: vein-dominated material? [2].
Structure photo 1		Vein photo 1
Structure photo 2		Vein photo 2
Structure photo 3		Vein photo 3
ALTERATION
General alteration	Formation of tourmaline, quartz, biotite, muscovite, albite, chlorite, K feldspar, epidote, rutile, titanite. Tourmalinisation of the metatuffite is the most prominent feature [2,5].
Proximal alteration	Tourmalinisation: tourmaline replaces biotite [2,3].
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	[2]: Probably, an Archaean post-mineralisation metamorphic overprint at about 500±50°C with weak deformation and porphyroblast overgrowth. On ca. 1800 Ma, a Proterozoic regional metamorphic overprint which is shown by K-Ar and Rb-Sr ages of micas.
TIMING	[2]: 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 peak metamorphism).
GENETIC MODEL	[2]: 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. Note, in any case, that the presence of gold-bismuth-tellurium mineral assemblages indicate crystallisation temperatures for these minerals chiefly in the range 250–350°C [5].
Genetic type	Orogenic	References	[2]
Alternative genetic type 1		References
Alternative genetic type 2		References
References 1. Nurmi, P. A. 1993. Archaean Au in Finland. Engineering and Mining Journal, Nov., 32–34. 2. 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. 3. 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. 4. 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. 5. 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. 6. 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) 7. Hartikainen, A. & Niskanen, M. 2001. Maaperägeokemialliset kultatutkimukset Hatun liuskejaksolla Ilomantsissa vv. 1983–1995. Geol. Surv. Finland, Report S/41/4244/1/2001. 22 p. 8. 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. (0.8 MB) 9. 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) 10. 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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