Rämepuro - Gold Database

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Name	Rämepuro	DATA UPDATED	12.9.2008
Alternative names
Deposit summary	RÄMEPURO, in the Ilomantsi greenstone belt, has an in situ resource estimate of 1250 kg gold (no JORC-compliant resource calculation is available). It is an Archaean orogenic gold deposit comprising one subvertical, quartz- and tourmaline-rich lode in a tonalitic porphyry dyke, close to the N-S trending Tsurkkila shear zone. Chiefly free native gold.
LOCATION
Geological domain	Archaean	Belt	Ilomantsi
Site photo		Regional map
Map sheet	424409
Northing (kkj)	6977700	Easting (kkj)	4564500
Latitude	62.89736N	Longitude	31.26530E
Municipality	Ilomantsi
Nearest town, roads	35 km NE from Ilomantsi, 100 km NE from Joensuu. A sealed road 500 m from the area.
MINING
Exploration licence no	3831/1, 6577/1, 7418/1–2	Mining concession no	3831/1a
Present holder	Endomines (2006–)
Previous holders	Outokumpu Oyj (1985–2003), Polar Mining (2003–2006)
Mine photo 1		Mine photo 2
Mine photo 3		Mine photo 4
Status of development	Prospect
When mined
Resources	0.919 Mt @ 1.6 ppm Au [22]. 0.25 Mt at 5 ppm Au (down to 50–70 m depth) [3,9,13]. Indicated 0.16 Mt @ 4.3 ppm Au, inferred 0.06 Mt @ 4.1 ppm Au: a JORC-compliant resource
Deposit size (Mt)	0.919	Reference (size)	[22]
Total in-situ gold (kg)	1480	Reference (in-situ Au)	[22]
Total gold production (kg)		Reference (gold prod)
Production of other metals
Extent of mineralisation	One km long, 20–30 m wide, open at 70 m depth [3,4,9,13,14], open along strike at both ends (to S and N) [17,22]. Auriferous veins in a zone 300 m wide [7].
Lodes	The N-S trending, subvertical lode is formed by discontinuous auriferous quartz-tourmaline veins and dissemination in tonalitic porphyry dike [3,4].
Best sections	5.8 m @ 15.2 ppm Au, 10.3 m @ 12.7 ppm Au, 2.8 m @ 6.8 ppm Au [9]. 1.5 m @ 8.1 ppm, 1.0 m @ 6.2 ppm, 0.85 m @ 9.5 ppm, 1.0 m @ 16.1 ppm Au [22].
EXPLORATION
Discovery year	1984
Discovery	By Outokumpu Oy [2,4,5,7,9,13]: reanalysis of a sulphide-bearing outcrop sample. The sample was originally found by an amateur prospector on 1970. The sample contained 93 ppm Au, 75 ppm Ag and 0.4% Cu.
Exploration history	Outokumpu (1985–1988) [1,3,4,5,7,9,11,13,15]: Outcrop mapping, ground magnetic, electric and IP survey, trenching, diamond drilling in profiles 50-100 m apart. 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. GTK (1988–1993) [3,6,11,12]: 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 [11] and geochemistry, and petrogenesis. Endomines (2007–) [20,21,22]: Ground IP survey, 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	Shear zone and shear-related alteration envelope has a weak response on IP (ground survey). Gold mineralisation also has an response on IP [3,9]. A strong IP anomaly continues for 700 m to the north from the known gold mineralisation [21].
Drilling	Outokumpu (–1993) [3,4,5]: 29 drill holes, total 4043 m, traverse interval 50–100 m. 1997: a set of short diamond-drill holes. In total, about 50 drill holes with 5 km of drilling in profiles across 1 km of strike [18]. Endomines (2007): 19 diamond-drill hole, total 1437 m [22].
Elements analysed	[8]: Main components, Cl, Sn and Zr by XRF; Ag, As, Au, Bi, Pd, Sb, Se and Te by GFAAS; Hg by wet-chemical method; B by DCP; Ba, Cd, Co, Cr, Ga, La, Li, Mo, Nb, Ni, Pb, Rb, Sb, Sc, Sr, Th, Tl, U, V, W, Y and Zn by ICP; S by Leco. [7]: Major elements and certain trace elements by XRF, most of the trace elements by AAS.
Primary dispersion	Au and Te show good correlation; Ag and Bi show moderate correlation with Au; no consistent chemical zoning found [3,7]. Good correlation between Au and Te, S, B, Bi, Zn and Cu [13].
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.
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 evaluation by Outokumpu during 1990's [1], and by Endomine in 2007– [22].
Exploration geologist in charge	Outokumpu: Esa Sandberg. GTK: Martti Damsten. Endomines: Jaakko Liikanen
ORE
Siting of gold	Chiefly free gold which occurs between quartz and tourmaline grains and their fractures, associated with sulphides, bismuth and tellurides [7,9,11]. Some gold occurs as inclusions in pyrite and pyrrhotite [7,9,11].
Fineness	86–99% Au, 0–12% Ag, 0.02–0.53% Cu [7,11].
Major opaques	Pyrrhotite, pyrite [4,7,11].
Minor opaques	Native gold, native bismuth, chalcopyrite, cubanite, sphalerite, hedleyite, arsenopyrite, molybdenite, mackinawite, molybdenite, ilmenite, rutile [4,7,11,13].
Gangue	Quartz, albite, K feldspar, biotite, muscovite, garnet, calcite, siderite, chlorite, scheelite, titanite, tourmaline [7,11,13].
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 [8]: 4.70 ppm Au, 4.10 ppm Ag, 20 ppm As, 1830 ppm B, 859 ppm Ba, 361 ppm Bi, 38 ppm Co, 140 ppm Cu, 91 ppb Hg, 56 ppm Li, <1.0 ppm Mo, 121 ppm Ni, <2 ppm Pb, 65 ppm Rb, 15400 ppm S, 0.2 ppm Sb, 0.32 ppm Se, 290 ppm Sr, 3.70 ppm Te, 4.2 ppm Th, 0.80 ppm Tl, 1.9 ppm U, 120 ppm V, 12 ppm W, 8 ppm Y, 90 ppm Zn, 88 ppm Zr; 67.2% SiO2, 0.57% TiO2, 15.0% Al2O3, 7.46% Fe2O3, 1.92% MgO, 0.90% CaO, 1.95% Na2O, 2.70% K2O, 0.05% P2O5.
Enriched elements	Au, Te, Bi, B, Ag, As, W, Se, B, K, Li, Rb, S, CO2 [3,6].
Ore fluid	Fluid inclusions indicate two fluids: 1) H2O–CH4, 4–9% NaCl eq., S-rich, reducing, 310–350°C; 2) H2O–CO2, 8–12% NaCl eq., 220–250°C, XCO2=0.05–0.20 [14].
Stable isotopes	δ18O (SMOW): +6.3 – +8.7 per mill (quartz), +9.0 per mill (tourmaline); δD (SMOW): -96 per mill (tourmaline), -82 per mill (muscovite) [3].
Pb isotope data
GEOLOGY
Geological setting	The mineralisation is in the central part of the 2754–2726 Ma [19] Hattu Schist Belt, in the porphyry between an andesitic pyroclastic metavolcanic rock and a mica schist of sedimentary origin both deposited in an island-arc environment [7,14]. All igneous rocks in the area have a calc-alkaline character [3,7].
Major host rocks	Tonalitic porphyry dyke [2,3,4,5,7].
Minor host rocks	Metagreywacke, sulphide-facies iron formation [7,14].
Intrusives	The tonalitic porphyry host rock predates mineralisation. Tonalite intrusions bound the greenstone belt in the area. In the east, a pre-mineralisation(?) intrusion with U-Pb zircon age of ca. 2.750 Ga cut across the greenstone belt rocks. Post-mineralisation Proterozoic dolerites cross cut all the other rocks, mineralisation and alteration in the area. [2,3,4,5]
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	Progressive regional metamorphism on ca. 2750–2700 Ma, apparently peaked soon after gold mineralisation, at a temperature of about 550±50°C [3]. Garnet-biotite pairs indicate metamorphic temperature variation from 390 to 580 °C, suggesting polyphase metamorphism with a strong retrograde content [3,7]. The thermal peak was synchronous or outlasted deformation [3]. A relatively strong, but unevenly distributed Palaeoproterozoic overprint [10].
Metamorphic grade	Greenschist-amphibolite facies transition [3].
Metamorphic mineral assemblage	Quartz-plagioclase-biotite-chlorite-muscovite-actinolite-garnet-K feldspar [3,7].
Metamorph photo 1		Metamorph photo 2
STRUCTURE
Structural style	Brittle-ductile.
Closest major shear	Tsurkkila Shear Zone adjacent to the deposit [3,10].
Controlling structure	N-S trending Tsurkkila shear zone to the west of the deposit [3].
Deformation history	Rapid and extensive crustal generation and progressive deformation between 2.76–2.73 Ma, in a transpressional regime [2,14].
Ore fabric
Veins	Discontinuous quartz-tourmaline veins, 1 mm to one metre wide, containing minor to trace amounts of biotite, chlorite, muscovite, plagioclase, sulphides, and gold [3,7,9,11,13]. Post-gold mineralisation veins filled by albite and laumontite [7].
Structure photo1		Vein photo 1
Structure photo 2		Vein photo 2
Structure photo 3		Vein photo 3
ALTERATION
General alteration	Formation of the assemblage quartz-muscovite-albite-biotite-chlorite-tourmaline-calcite-garnet- epidote [3,7]. Alteration envelope is 20–30 m wide (containing the main mineralisation and the mineralised shear zone in both the porphyry and metagreywacke) [3,11]. Apparent zoning only within 1 cm of the veins [7].
Proximal alteration	Quartz-sericite-biotite-chlorite-tourmaline-calcite-rutile-garnet-epidote; slightly more intense formation of quartz in the innermost parts of the shear zone [3,6].
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	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) [2,6]. Post-peak metamorphic, retrograde [7,13].
GENETIC MODEL	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. Gold probably 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 [3]. According to [7], auriferous veins were formed during the intrusion of syn- or late-orogenic granitoids when sets of conjugate Reidel faults and/or tensional fractures were formed. Main stage at 450–500 °C, 2.5–3 kbar (Archaean), second stage (remobilisation?) at 400°C, 2.5 kbar (Proterozoic?) [14,16].
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. Ojala, V. J., Pekkarinen, L. J., Piirainen, T. & Tuukki, P. 1990. The Archaean gold mineralization in Rämepuro, Ilomantsi greenstone belt, eastern Finland. Terra Nova 2, 240–244. 5. Pekkarinen, L. J. 1988. The Hattuvaara gold occurrence, Ilomantsi: a case history. Annales Universitatis Turkuensis, Sarja C. Tom 67, 79–87. 6. 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. 7. Ojala, J. 1988. Ilomantsin Hattuvaaran Rämepuron Au-mineralisaation geologia. Unpublished MSc thesis. Department of Geology, University of Oulu. 78 p. (in Finnish) 8. Bornhorst, T. & Nurmi, P. 1999. Personal communication 20/1/1999. 9. Pekkarinen, L. 1988. The Hattuvaara gold occurrence, Ilomantsi: a case history. A paper presented in the Gold '87 Symposium, Turku, Finland, May 12–13, 1987. Outokumpu Exploration. 4 p. 10. 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. 11. 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. 12. Hartikainen, A. & Niskanen, M. 2001. maaperägeokemialliset kultatutkimukset Hatun liuskejaksolla Ilomantsissa vv. 1983–1995. Geol. Surv. Finland, Report S/41/4244/1/2001. 22 p. 13. Pekkarinen, L. 1988. Rämepuron kultaesiintymä. Vuorimiesyhdistys. Sarja B, 54, 22–26. (in Finnish) 14. Poutiainen, M & Partamies, S. 2003 Fluid evolution of the late Archaean Rämepuro gold deposit in Ilomantsi greenstone belt in eastern Finland. Mineralium Deposita. 38, 196–207. 15. 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) 16. Poutiainen, M. and Partamies, S. 2003. Fluid inclusion characteristics of auriferous quartz veins in Archean and Paleoproterozoic greenstone belts of eastern and southern Finland. Econ. Geol. 98, 1355–1369. 17. Dragon Mining NL 2005. Annual Report 2004. Perth. 80 p. (5.8 MB) 18. Sandberg, E. 2005. Personal communication 26/09/2005. 19. 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. 20. Endomines 2007. Pressmeddelande den 20 juni 2007. (in Swedish) 21. Endomines 2007. Pressmeddelande den 14 augusti 2007. (in Swedish) 22. Endomines 2008. Pressmeddelande den 7 januari 2008. (in Swedish) 23. Endomines 2008. Press release 14 July 2008.
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