Palosuo - Gold Database

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Name	Palosuo	DATA UPDATED	24.5.2007
Alternative names	Rämepalo
Deposit summary	PALOSUO, in the Ilomantsi greenstone belt, is a Neoarchaean gold occurrence with no resource estimate available, to the SSE of the Rämepuro deposit. It is hosted by intermediate tuffite, immediately to the east of the N-trending Tsurkkila Shear Zone. Native gold disseminated in the host rock. No information on siting of gold.
LOCATION
Geological domain	Archaean	Belt	Ilomantsi
Site photo		Regional map
Map sheet	424409
Northing (kkj)	6977500	Easting (kkj)	4565000
Latitude	62.89548N	Longitude	31.27505E
Municipality	Ilomantsi
Nearest town, roads	35 km NE from Ilomantsi, 100 km NE from Joensuu. A sealed road 1 km from the area.
MINING
Exploration licence no	5027/1, 6577/1	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
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
Best sections	1 m @ 2.7 ppm, 1 m @ 1.1 ppm Au [1,9].
EXPLORATION
Discovery year	1993
Discovery	By GTK in early 1993: drilling into a till geocemical anomaly in the structural continuation of the Rämepuro deposit [1].
Exploration history	GTK (1988–1993) [1,7,8]: Low-altitude air- and ground-magnetic, slingram and IP survey. Bedrock mapping, ground-magnetic, slingram and IP survey, diamond drilling; 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. Outokumpu (1994–1999) [9]: "surface survey".
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
Drilling	GTK (1990's) [1,8]: 5 diamond-drill holes, total 142 m.
Elements analysed
Primary dispersion
Secondary dispersion
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].
Exploration geologist in charge	GTK: Martti Damsten; Outokumpu: Esa Sandberg. Endomines: Jaakko Liikanen
ORE
Siting of gold
Fineness
Major opaques
Minor opaques
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
Ore fluid
Stable isotopes
Pb isotope data
GEOLOGY
Geological setting	A sequence of andesitic tuffites, minor silicate-facies iron formations [1]. The mineralisation is in the central part of the 2754–2726 Ma Hattu Schist Belt, at a contact zone between an andesitic pyroclastic metavolcanic rock and a mica schist of sedimentary origin both deposited in an island-arc environment [3,10]. All igneous rocks in the area have a calc-alkaline character [2,3].
Major host rocks	Intermediate metatuffite [1]
Minor host rocks
Intrusives	Tonalites to the east of the deposit [1]. 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 cuts across the greenstone belt rocks [10]. Post-mineralisation Proterozoic dolerites cross cut all the other rocks, mineralisation and alteration in the region [2,4].
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	Progressive regional metamorphism on ca. 2750–2700 Ma, apparently peaked soon after gold mineralisation, at a temperature of about 550±50°C [2]. Garnet-biotite pairs indicate metamorphic temperature variation from 390 to 580 °. C, suggesting polyphase metamorphism with a strong retrograde content [2,3]. The thermal peak was synchronous or outlasted deformation [2]. A relatively strong, but unevenly distributed Palaeoproterozoic overprint [5].
Metamorphic grade	Greenschist-amphibolite facies transition [2].
Metamorphic mineral assemblage
Metamorph photo 1		Metamorph photo 2
STRUCTURE
Structural style
Closest major shear	Tsurkkila Shear Zone adjacent to the deposit [2].
Controlling structure	The N-S trending Tsurkkila shear zone to the west of the deposit [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
Structure photo1		Vein photo 1
Structure photo 2		Vein photo 2
Structure photo 3		Vein photo 3
ALTERATION
General alteration
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	[2]: Probably, an Archaean post-mineralisation metamorphic overprint at about 500±50°C with deformation and porphyroblast overgrowth. At 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].
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 [2].
GENETIC TYPE	Orogenic	References	[2]
Alternative genetic type 1		References
Alternative genetic type 2		References
References 1. Damstén, 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) 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. Ojala, J. 1988. Ilomantsin Hattuvaaran Rämepuron Au-mineralisaation geologia. Unpublished MSc thesis. Department of Geology, University of Oulu. 78 p. (in Finnish) 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. 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. 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. 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. (790 KB) 9. Sandberg, E. 2000. Kaivoslain 19 §:n mukainen tutkimustyöselostus: Ilomantsi "Palosuo 1" ja "Korpilampi", kaiv.rek.n:o 5027/1 ja 5498/2. Outokumpu Oy, Report 080/4244 09/EAS/2000. 3 p. (in Finnish, 8.2 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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