Muurinsuo - Gold Database

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Name	Muurinsuo	DATA UPDATED	12.9.2008
Alternative names
Deposit summary	MUURINSUO has an in situ resource estimate of 1330 kg gold (a JORC-compliant resource). It is an Archaean orogenic gold deposit comprising a set of subvertical disseminated lodes in intermediate volcanogenic metasedimentary rock, close to the NE-trending Korvilansuo shear zone. Chiefly native gold, disseminated in the host rock, intergrown with pyrrhotite, pyrite, arsenopyrite, gersdorffite and tellurides.
LOCATION
Geological domain	Archaean	Belt	Ilomantsi
Site photo		Regional map
Map sheet	424408
Northing (kkj)	6970040	Easting (kkj)	4562900
Latitude	62.82893N	Longitude	31.23096E
Municipality	Ilomantsi
Nearest town, roads	30 km NE from Ilomantsi, 95 km NE from Joensuu. A sealed road 500 m from the area, a gravel road to the area?
MINING
Exploration licence no	4273/1, 5359/1–2, 6540/1, 7417/1, 7977/1	Mining concession no
Present holder	Endomines (2006–)
Previous holders	Geological Survey of Finland (GTK), Outokumpu Oyj (–2003), Polar Mining (2003–2006)
Mine photo 1		Mine photo 2
Mine photo 3		Mine photo 4
Status of development	Prospect
When mined
Resources	0.923 Mt @ 1.4 ppm Au, cut off grade at 0.5 ppm Au: a JORC-compliant resource [13,15]. 0.60 Mt @ 2.7 ppm Au [10]. Indicated 0.2 Mt @ 2.6 ppm Au, inferred 0.8 Mt @ 1.5 ppm Au: a JORC-compliant resource [17].
Deposit size (Mt)	0.923	Reference (size)	[13]
Total in-situ gold (kg)	1331	Reference (in-situ Au)	[13]
Total gold production (kg)		Reference (gold prod)
Production of other metals
Extent of mineralisation	Width: 11 m, length >300 m [5,10].
Lodes	A set of N-NE striking, subvertical, apparently pipe-formed, lodes which comprise dissemination in the host rocks [3,10].
Best sections	1 m @ 9.7 ppm, 2 m @ 6 ppm, 5 m @ 4.9. ppm, 6 m @ 2.63 ppm, 5 m @ 2.6 ppm, 8.5 m @ 1.2 ppm Au [1,3,8,10]. 4.2 m @ 6.4 ppm, 4.9 m @ 4.9 ppm, 4.5 m @ 4.6 ppm, 6.5 m @ 4.0 ppm, 4.2 m @ 7.1 ppm Au [15]. 3.8 m @ 2.7 ppm Au, 4.8 m @ 6.7 ppm Au, 4.5 m @ 2.9 ppm Au [16].
EXPLORATION
Discovery year	1987
Discovery	By GTK; the first indication was an Au anomaly in till [5].
Exploration history	GTK (1987–1994) [3,4,5,8,9,10,11]: 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 [7] and geochemistry, and petrogenesis. Outokumpu (1994–1999) [12]: "surface survey". Endomines (2007–) [15]: 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	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 [3].
Drilling	GTK (–1993) [1,3,8,10,11]: 30 diamond-drill holes, total 2838 m, drilling profile spacing: 50 m. Endomines (2007): 21 diamond-drill holes, total 1891 m [15].
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 [3].
Primary dispersion	Au and Te show good correlation; Ag and Bi show moderate correlation with Au. No consistent chemical zoning found yet [3,4].
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	Preliminary resource estimation [12].
Exploration geologist in charge	GTK: Martti Damsten; Outokumpu: Esa Sandberg. Endomines: Jaakko Liikanen
ORE
Siting of gold	Dissemination in host rocks. Gold is intergrown with pyrrhotite, pyrite, arsenopyrite, gersdorffite and tellurides [3].
Fineness	83–97% Au, 4–15% Ag, 0.01–2.8% Sb [3,5]
Major opaques	Pyrrhotite, pyrite [7].
Minor opaques	Native gold, electrum, tellurobismuthinite, tsumoite, altaite, hessite, petzite, volynskite, chalcopyrite, pentlandite, galena, arsenopyrite, gersdorffite (in mafic rocks), molybdenite, cubanite, mackinawite, ilmenite, rutile [7].
Gangue	Quartz, albite, K feldspar, biotite, muscovite, garnet, calcite, siderite, scheelite, titanite, tourmaline [3,7].
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	Diamond-drill core [3]: 2.6 ppm Au, 0.152 ppm Ag, 18.0 ppm As, 410 ppm B, 593 ppm Ba, 1.4 ppm Bi, 27 ppm Co, 55 ppm Cu, <5 ppb Hg, 4 ppm Mo, 139 ppm Ni, <2 ppm Pb, 94 ppm Rb, 7470 ppm S, <0.2 ppm Sb, 0.18 ppm Se, 285 ppm Sr, 1.02 ppm Te, 7.0 ppm Th, 2.4 ppm U, 200 ppm V, 3.0 ppm W, 120 ppm Zn; 59.0% SiO2, 0.89% TiO2, 18.4% Al2O3, 7.77% Fe2O3, 3.50% MgO, 1.40% CaO, 1.88% Na2O, 2.64% K2O, 0.15% P2O5, 3.25% LOI.
Enriched elements	Au + Te, Bi, As, Ag, Cu, B, K, Rb, S, CO2 [3,4,5].
Ore fluid
Stable isotopes	[3]: δ18O (SMOW): +10.8 – +11.4 per mill (quartz), +6.6 – +8.6 per mill (biotite), -0.6 per mill (epidote), +10.3 – +10.7 per mill (albite); => T = 400–5 80°C; δD (SMOW): -67 – -55 per mill (biotite), -88 per mill (actinolite).
Pb isotope data
GEOLOGY
Geological setting	The mineralisation is in the central part of the 2754–2726 Ma [14] Hattu Schist Belt. The hosting mica schist (greywacke schist) units are interbedded with mafic metatuffites and dikes, and intruded by felsic porphyry; the mineralisation is in the NW hanging wall of the northern tip of the Kuittila tonalite [3,5,8,10].
Major host rocks	Mica schist (volcanogenic metasedimentary rock) [2,3,4,5].
Minor host rocks	Mafic or ultramafic schist, mafic dykes, felsic porphyries [2,3,4,5,10].
Intrusives	The late-orogenic Kuittila tonalite, felsic porphyries and mafic dikes predate gold mineralisation [3,8].
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	[3]: Progressive regional metamorphism on ca. 2750–2700 Ma, apparently peaked soon after gold mineralisation, at a temperature of about 550±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 [3].
Metamorphic mineral assemblage	Mica schists: andesine-quartz-biotite-muscovite-chlorite(-tourmaline-garnet-apatite-zircon) [3,5]. Mafic or ultramafic schist: hornblende-biotite(-tourmaline-calcite-opaques) [5].
Metamorph photo 1		Metamorph photo 2
STRUCTURE
Structural style	Brittle-ductile to ductile [3].
Closest major shear	Korvilansuo-Muurinsuo Shear Zone system adjacent to the deposit [3].
Controlling structure	Korvilansuo shear zone, dominantly ductile [3].
Deformation history	Rapid and extensive crustal generation and progressive deformation between 2.76–2.73 Ma, in a transpressional regime [14].
Ore fabric
Veins	Quartz-calcite and quartz-siderite veins commonly occur in the felsic porphyries and contain arsenopyrite and tellurides. Auriferous quartz-tourmaline veins in the main host rock [3,5,7].
Structure photo 1		Vein photo 1
Structure photo 2		Vein photo 2
Structure photo 3		Vein photo 3
ALTERATION
General alteration	Formation of the assemblage quartz-albite-muscovite-chlorite-tourmaline-calcite-rutile-K feldspar-epidote-hornblende-titanite-siderite-garnet [3,4,7].
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	[3]: Probably, an Archaean post-mineralisation metamorphic overprint at about 500±50°C with deformation and porphyroblast overgrowth. This also affected δ18O values of minerals. On ca. 1800 Ma, a Proterozoic regional metamorphic overprint which is shown by K-Ar and Rb-Sr ages of micas.
TIMING	[3]: 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	[3]: 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 [7].
Genetic type	Orogenic	References	[3]
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., 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. & 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. 4. 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. 5. Ojanen, H. 1993. Ilomantsin Kuittilan ja Muurinsuon Au- ja Mo-W-mineralisaatioiden petrografia ja malmimineralogia. Unpublished MSc thesis. Department of Geology, University of Oulu. 108 p. (in Finnish) 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. Sandberg, E. 2000. Kaivoslain 19 §:n mukainen tutkimustyöselostus: Ilomantsi "Muurinsuo 2 ja 3", kaiv.rek.n:o 5359/1 ja 5359/2. Outokumpu Oy, Report 080/4244 08B, 09A/EAS/2000. 3 p. (in Finnish, 7 MB) 13. Micon International ltd 2007. Muurinsuo mineral resources at 4th April 2007 classified following the guidelines of the JORC code (2004). 1 p. 14. 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. 15. Endomines 2007. Pressmeddelande den 6 november 2007. (in Swedish) 16. Endomines 2008. Press release 16 June 2008. 17. Endomines 2008. Press release 14 July 2008.
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