Juomasuo - Gold Database

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Name	Juomasuo	DATA UPDATED	12.1.2007
Alternative names
Deposit summary	JUOMASUO is the largest known gold deposit in the Palaeoproterozoic Kuusamo Schist Belt. It has been test mined, is under feasibility study by Polar Mining Oy, and presently (November 2006) has an in situ resource estimated as 3360 kg gold and 1550 t cobalt. The deposit is also enriched in Ag, Cu, Mo, Ni, REE and U. It is mainly hosted by albitised, biotitised and sulphidised sericite quartzite in a metamorphosed, intracratonic, extensively albitised, supracrustal sequence in a failed rift system. Juomasuo comprises one major and a number of smaller lodes controlled by a NW-trending fault crossing an axial culmination in the NE-trending Käylä-Konttiaho Anticline. Native gold chiefly associated with Bi and Te minerals as inclusions in pyrite, cobaltite and uraninite, between silicates, and in tiny Au-Bi-Te rich veinlets oriented parallel with foliation and enveloped by silicates. Orogenic gold with atypical metal association, iron oxide-copper-gold, and syngenetic style have been suggested for the gold-cobalt-copper ± uranium occurrences at Kuusamo. Structural control and timing seem to fit with the orogenic hypothesis, alteration, metal association, necessary mineralising fluid(s) and structural control with the IOCG hypothesis, whereas mineralising fluid(s) and the rift/self and host rock settings with the syngenetic (metamorphosed) hypothesis. Gold fineness may fit with any of the genetic styles proposed. At Juomasuo, the early structures and textures strongly point towards host rocks being deposited in a playa-like setting and at least the early stages of alteration (most of albitisation + carbonatisation) having been taken place in brine-rich, evaporite-related system.
LOCATION
Geological domain	Lapland	Belt	Kuusamo Schist Belt
Site photo		Regional map
Map sheet	461302
Northing (kkj)	7355400	Easting (kkj)	4464230
Latitude	66.28882N	Longitude	29.19952E
Municipality	Kuusamo
Nearest town, roads	37 km N from Kuusamo. 3 km from a sealed road, a gravel road to the area.
MINING
Exploration licence no	3965/1	Mining concession no	3965/1a
Present holder	Polar Mining (2003–)
Previous holders	Geological Survey of Finland (GTK) (1983–90), Outokumpu Oyj (1990–2003)
Mine photo 1		Mine photo 2
Mine photo 3		Mine photo 4
Status of development	Test pit
When mined	1992
Resources	0.7 Mt @ 6 ppm Au and 0.15% Co (cut off 1 ppm Au) [1]. 0.779 Mt @ 4.2 ppm Au with 1 ppm cut off [20].
Deposit size (Mt)	0.8	Reference (size)	[15]
Total in-situ gold (kg)	3360	Reference (in-situ Au)	[15]
Total gold production (kg)	104	Reference (gold prod)	[14]
Production of other metals	24.7 t Co [14].
Extent of mineralisation	Main lode: 100 m long, 30 m wide, at least 300 m deep mineralised zone [6,7,13]. Main lode: oval- or sheet-shaped, 50 x 100 x >300 m (depth) in size, NW-trending, dip approx. 50° to the SW; the satellite lodes have the same strike and dip [4,17]. The lodes are open at depth along plunge [21].
Lodes	The main mineralised zone and a set of smaller, subparallel lodes around the main lode, within an area of 0.5 km2 [17].
Best sections	24 m @ 4.5 ppm Au and 0.20% Co [13].
EXPLORATION
Discovery year	1985
Discovery	By GTK: ground geophysical checking of a low-altitude airborne electric anomaly [2,13,17].
Exploration history	GTK (1983–89) [2,3,4,5,6,11,13,17]: detailed bedrock mapping, low-altitude airborne and ground magnetic, electric, slingram, gravimetry, IP, VLF-R and radiometric survey, till stratigraphy and geochemistry, diamond drilling, thin section investigations, detailed studies on mineralogy and geochemistry. Outokumpu (1990–2003) [18]: test mining and pilot plant tests in 1992, diamond drilling. Dragon (2003–) [19]: 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	Distinct uranium gamma-ray and electric anomalies, defined by low-altitude airborne survey data, and slingram, IP and VLF ground anomalies [2,3,4,17].
Drilling	GTK (1985–89): 44 diamond-drill holes, total 7241 m [13]. Outokumpu (1991–) [18]: diamond drilling for 7000 m, in profiles 12.5 m apart, in 1991; more drilling in 1992 [18]. Dragon: four diamond-drill holes, total 1463 m [19].
Elements analysed	[17]: by XRF: major elements, Ba, Ce, Cl, Cr, Cs, Ga, La, Mo, Nb, Nd, Rb, Sb, Sc, Sr, Th, U, V, Y and Zr; by ICP-AES: As, As, Cd, Co, Cu, Fe, Mn, Mo, Ni, Pb, S, Sb, Zn; by ICP-MS: REE, Sc, Y, Th, U; by GFAAS: Au, Bi, Sb, Se, Te; by Fire assay: Au; by AAS: Co, Cu, Ni, Pb, Zn. By AAS partial leach Ag, As, Co, Cu, Fe, Mo, Ni, Pb, W, Zn, by fire assay: Au and Te, by Leco: S, by MCA: U [7,13].
Primary dispersion	Au, U, W, Te and Se show significant positive correlation; the Te anomaly extends beyond Au anomaly [3,4,13].
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
Primary anomaly fig 6		Secondary anomaly fig 6
Economic evaluations	Preliminary feasibility study by GTK 1989 [9], by Outokumpu in 1990's [17,18].
Exploration geologist in charge	GTK: Heikki Pankka.
ORE
Siting of gold	Native gold is chiefly associated with Bi and Te minerals as inclusions in pyrite, cobaltite and uraninite, between silicates, and tiny Au-Bi-Te veinlets oriented parallel with foliation and enveloped by silicates [3,4,6,11,13,17].
Fineness	95–97% Au, 1–4% Ag, 1.6–1.8% Se, <0.14% Te [4,17].
Major opaques	Pyrrhotite, pyrite [3,4,6,13,17].
Minor opaques	Cobaltite, Co-pentlandite, magnetite, rutile, linneaite, chalcopyrite, molybdenite, uraninite, radiogenic galena, ilmenite, gold, altaite, calaverite, frohbergite, melonite, rucklidgeite, tellurobismuthite, mattagamite, kawazulite, clausthalite [3,4,6,7,11,13,17].
Gangue	Sericite, quartz, Fe dolomite, chlorite, biotite, albite, scheelite [3,4,6,13,17].
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	24 m long, "typical" section [7]: 3.7 ppm Au, 1.0 ppm Ag, 1980 ppm Co, 230 ppm Cu, 120 ppm Ni, 100 ppm Pb, 15 ppm Zn. "Typical ore" [6]: 6 ppm Au, 1500 ppm As, 2000 ppm Co, <500 ppm Cu, 6-7% S, 6-7 ppm Te. Diamond-drill core [8]: 4.10 ppm Au, 0.16 ppm Ag, 1200 ppm As, 54.6 ppm B, 298 ppm Ba, 2.7 ppm Bi, 1820 ppm Co, 226 ppm Cu, 5 ppb Hg, 13 ppm Mo, 122 ppm Ni, 85 ppm Pb, 84 ppm Rb, 58700 ppm S, 0.4 ppm Sb, 78 ppm Se, 10 ppm Sr, 7.00 ppm Te, 8.1 ppm Th, 284 ppm U, 130 ppm V, 390 ppm W, 45.7 ppm Zn; 57.5% SiO2, 0.45% TiO2, 15.0% Al2O3, 13.1% Fe2O3, 2.37% MgO, 0.04% CaO, 0.63% Na2O, 4.41% K2O, <0.002% P2O5, 5.00% LOI.
Ore composition 1	Click here	Ore composition 2	Click here
Ore mineral compositions
Enriched elements	Gain in Ag, As, Au, Ba, Bi, Co, Cu, Fe, K, Li, LREE, Mo, Ni, Pb, Rb, S, Se, Te, Th, U, V, W, Y [3,4,6,7,8,13,17], loss in Ca, Na [17]. In deeper parts, at least locally, a significant MREE and HREE enrichment [17].
Ore fluid
Stable isotopes
Pb isotope data
GEOLOGY
Geological setting	The deposit is in the Sericite Quartzite Formation (of the Kuusamo Schist Belt) containing metasedimentary and metavolcanic rocks, and dolerites [3,4,6,11,13], in the N end of the Käylä-Konttiaho Anticline [17]. The schist belt is an intracratonic, failed rift filled by a subaerial to shallow-water volcanosedimentary sequence deposited on late Archaean (2.6–2.8 Ga) basement [3,4,5,6,11,13,16].
Major host rocks	Sericite quartzite [17]. Mafic metavolcanic rocks [4].
Minor host rocks	Sericite quartzite [3,4,6], mafic and/or ultramafic dykes [13].
Intrusives	Mafic and/or ultramafic dikes: altered, mineralised, conformably related to the metasedimentary rocks [13].
Regional geol map 1		Outcrop photo 1
Regional geol map 2		Outcrop photo 2
Regional geol map 3		Outcrop photo 3
Local geology map 1
METAMORPHISM
Metamorphic history	Peak regional metamorphism at lower-amphibolite facies: staurolite porphyroblasts in Al-rich rocks, during D1? [11]. This was followed by retrograde greenschist-facies metamorphism: sericitisation of staurolite [11], during D2?, related to NW-trending shear zones and gold mineralisation?
Metamorphic grade	Greenschist facies [4].
Metamorphic mineral assemblage	Metasedimentary rocks: quartz-albite-rutile ± carbonate, haaematite, sericite, chlorite [11,17]. Ultramafic sill or lava: chlorite-talc-tremolite-carbonate-albite-magnetite [17].
Metamorph photo 1		Metamorph photo 2
STRUCTURE
Structural style	Ductile [3,5,6,13].
Closest major shear	A collision-related thrust fault 10 km NE of the deposit [4].
Controlling structure	NW-trending ductile shear zone which cut across the regional, N-S to NE-trending Käylä-Konttiaho Anticline [3,4,5,6,17], especially, areas close to the contact between Sericite Quartzite and Greenstone II Formations are critical for mineralisation [11].
Deformation history	At least two major folding stages. D1 is characterised by a major N-S trending antiform whose northern end is bended to the east due to D2; D2 is also presented by S2 foliation and a conjugate set of NW- and NE-trending, chiefly sinistral shear and fault zones [11]. No deformation before 2000 Ma [16].
Ore fabric	Foliated, with the degree of foliation increasing towards the centre of the mineralisation [17].
Veins	In albitised rocks: albite and albite-quartz-carbonate veins [4].
Structure photo 1		Vein photo 1
Structure photo 2		Vein photo 2
Structure photo 3		Vein photo 3
Structure photo 4		Vein photo 4
ALTERATION
General alteration	[17]: 1. Diagenetic albitisation of feldspars and sericitisation of clay minerals. 2. Intense albitisation of clastic sediments and spilitisation of volcanic units when the 2.206 Ga mafic sills and dykes heated the evaporite-bearing sequence and put hot brines into circulation. 3. Carbonation. 4a. Magnetite-albite-quartz-chlorite-phlogopite-biotite-amphibole-talc. 4b. Albite-quartz-chlorite-pyrrhotite-cobaltite-Co pentlandite-chalcopyrite-gold-uraninite. 5. Quartz-sericite-pyrite-gold-uraninite-tellurides. The general sequence of alteration at Kuusamo is as follows [3,4,5,6,10,11,13]: Albitisation is the most extensive alteration type and is, apparently, premetamorphic. Albitisation is followed by a sequence of syn- to late-metamorphic(?) alteration stages. First of them is the Mg-Fe metasomatism which is closely related to gold mineralisation and indicated by formation of chlorite, tremolite-actinolite, magnetite, chloritoid, talc and Fe sulphides. The next stage is retrograde(?) K±S metasomatism indicated by biotite and sericite ± pyrite, additional(?) Au mineralisation and ductile deformation. This is followed by a stage of carbonation, silicification, further Au mineralisation and brittle deformation. According to [11], carbonation and silicification post-dates all significant Au-mineralisation.
Proximal alteration	Outer proximal: Quartz-sericite-chlorite-biotite-albite-magnetite-sulphides [17]. Inner proximal: Quartz-sericite-sulphides ± biotite, chlorite [17]. Fe-Mg silicate and K-silicate alteration: albitisation, chloritisation and sericitisation [4,13]. Mafic metavolcanic rock: sericite (phengitic muscovite)-albite-chlorite-quartz-rutile ± sulphides, biotite, magnetite [3,4,6]. Generally: sericite-chlorite-biotite ± albite, sulphides, gold [13].
Intermediate alteration	Sericite quartzite: albite-Fe dolomite-chlorite-quartz [3,4,6].
Distal alteration	Sericite quartzite: albite-quartz-tremolite-Fe dolomite-rutile ± biotite, chlorite, sericite [4,6,17]. Albitisation has a lateral extent of more than 300 m; it has the widest extent of the alteration types present, but is not related to mineralisation [4,17]. Mafic and/or ultramafic dikes: talc-chlorite-tremolite-actinolite-Fe dolomite-rutile ± biotite, albite, quartz, pyrite [3,4,6,13,17].
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
Alteration photo 4		Distal alteration photo 1
Alteration photo 5		Distal alteration photo 1
Post-mineralisation modifications
TIMING	At 1.85–1.82 Ga [17]. Between 2050 Ma and 1800 Ma [3]. Post-peak metamorphic at 1.8–1.9 Ga [4].
GENETIC MODEL	During the evolution of the greenstone belt, hot hydrothermal fluids altered the host rocks in several stages and precipitated metals in a structurally, and possibly chemically, favourable site during post-metamorphic peak felsic magmatism, as a result of boiling (phase separation), at <2 kbar [17]. Epigenetic mineralisation in rift-filling rocks. Structurally controlled hydrothermal fluid pathways were created during post-depositional tectonic event(s) of regional scale which were related to the closure of the main rift during the Svecofennian (Svecokarelian) orogeny [3,4,5]. The auriferous fluids were transported along deep, rift-tectonic faults up to the greenschist-metamorphic environment, concentrated on the antiform; the metals precipitated in structurally controlled sites close to impermeable dolerites and metavolcanic units or, rather, in the more competent sericite quartzite units between the more plastic mafic units [4,10,11,12]. Minimum temperature for Au mineralisation is 270–310°C [4].
GENETIC TYPE	Orogenic	References	[6,17]
Alternative genetic type 1		References
Alternative genetic type 2		References
References 1. Pankka, H. 1993. Personal communication 7/9/1993. 2. Arkimaa, H. 1997. The fingerprints of known gold occurrences in the Kuusamo schist belt as shown by airborne gamma-ray spectrometric data. Geol. Surv. Finland, Special Paper 23, 25–28. 3. Pankka, H., Puustinen, K. & Vanhanen, E. 1991. Kuusamon liuskealueen kulta-koboltti-uraaniesiintymät. Summary: Au-Co-U deposits in the Kuusamo volcano-sedimentary belt, Finland. Geol. Surv. Finland, Report of Investigation 101. 53 p 4. Pankka, H. 1992. Geology and mineralogy of Au-Co-U deposits in the Proterozoic Kuusamo volcanosedimentary belt, northeastern Finland. A dissertation. Geology. Michigan Technological University. 233 p. 5. Pankka, H. 1997. Epigenetic Au-Co-U deposits in an early Proterozoic continental rift of the northern Fennoscandian Shield: a new class of ore deposit? In: H. Papunen (ed.) Research and Exploration – Where Do They Meet? Proceedings of the Fourth Biennial SGA Meeting, Turku, Finland, 11–13 August 1997. 277–280. 6. Pankka, H. S. & Vanhanen, E. J. 1992. Early Proterozoic Au-Co-U mineralization in the Kuusamo district, northeastern Finland. Precambrian Research 58, 387–400. 7. Vanhanen, E. 1989. Uraniferous mineralizations in the Kuusamo schist belt, northeastern Finland. In: Metallogenesis of uranium deposits: proceedings of a technical committee meeting on metallogenesis of uranium deposits, Vienna 9–12 March 1987. Vienna: International Atomic Energy Agency, 169–186. 8. 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. 9. Parkkinen, J. 1989. Kuusamon kulta-aiheiden arviointi: Juomasuo, Sivakkaharju, Meurastuksenaho. Geol. Surv. Finland, Report M19/4611,4613/-89/2/10. 14 p. (in Finnish) 10. Vanhanen, E. 1991. Cobalt-, gold- and uranium-bearing mineralizations and their relation to deep fractures in the Kuusamo area. Geol. Surv. Finland, Special Paper 13, 91–97. 11. Korteniemi, J. 1993. Kultaesiintymien ympäristön hydroterminen muuttuminen Käylän alueella Kuusamossa. Unpublished MSc thesis. Department of Geology, University of Turku. 90 p. (in Finnish) 12. Sorjonen-Ward, P. 1992. Kultamalmien rakennegeologiaa. Geol. Surv. Finland, Report M10.2/-92/1. 45 p. (in Finnish) 13. Pankka, H. 1989. Kuusamon Juomasuon Co-Au esiintymän malmitutkimukset vuosina 1985–1989. Geol. Surv. Finland, Report M19/4613/-89/1/10. 28 p. (in Finnish, 959 KB) 14. Kauppa- ja Teollisuusministeriö, 1998. Kertomus Suomen vuoritoimesta 1991–1995. 84 p. (in Finnish) 15. Mäkelä,T. 2001. Personal communication 30/01/2001. 16. Pankka, H. & Vanhanen, E. 2001. Personal communication 04/06/2001. 17. Vanhanen, E. 2001. Geology, mineralogy and geochemistry of the Fe-Co-Au-(U) deposits in the Paleoproterozoic Kuusamo Schist Belt, northeastern Finland. Geol. Surv. Finland, Bulletin 399. 229 p. 18. Lahtinen, J. 1988. Outokumpu Finnmines Oy:n malmitutkimukset Juomasuolla. Vuorimiesyhdistys. Sarja B, 54, 44–45. (in Finnish) 19. Dragon Mining NL 2004. Quarterly Activities Report for the Quarter Ended 31st December 2003. Perth, Australia. 8 p. (116 KB) 20. Dragon Mining NL 2005. Annual Report 2004. Perth. 80 p. (5.8 MB) 21. Haga, I. 2005. Dragon Mining's activities and strategies in Fennoscandia. FEM2005 Congress, Rovaniemi, 1–2. Dec 2005. (8.4 MB)
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