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| Name | Enonkoski | DATA UPDATED | 2.7.2007 | |||
| Secondary names | Laukunkangas | |||||
| Map sheet | 421106C | |||||
| Northing (kkj) | 6882700 | Easting (kkj) | 4435800 | |||
| Northing (Uni) | 6883361 | Easting (Uni) | 3592760 | |||
| Latitude | 62.045174N | Longitude | 28.769821E | |||
| Municipality | Enonkoski | |||||
| Nearest town | Savonlinna, 20 km SE | |||||
| Access | 3 km from the road 468 by a blacktop | |||||
| Status | Closed mine | Discovery year | 1980 | |||
| Discovery | By Outokumpu Oy. The deposit was discovered in 1969, but the main ore body was found in 1980 as a result of the second drilling campaign directed by lithogeochemical studies (Outokumpu Oy, nickel program) and ground geophysical surveys. | |||||
| Reservation | ||||||
| Exploration licence no | Mining concession no | 2570/1a–b, 3087/1a | ||||
| Present holder | Outokumpu Mining Oy | |||||
| Previous holders | Outokumpu Oy 1969– | |||||
| ENVIRONMENT | ||||||
| Population centre | Enonkoski village c. 10 km NE | |||||
| Protection areas | Large lake areas in Natura program in about 5 km distance. | |||||
| Water system | Ground water area about 2 km west. | |||||
| Overburden | ||||||
| Hazards | ||||||
| Restoration | ||||||
| GEOLOGY | ||||||
| Eon | Proterozoic | |||||
| Domain | Svecofennian | Province | Savo schist belt | |||
| Geological setting | The differentiated and layered Laukunkangas intrusion body is elongated, pipe-shaped, approximately 1 km long, 200 m wide and >800 m deep. The deposit is associated with the mafic to ultramafic parts in the eastern margin of the intrusion [1]. | |||||
| Country rock | Migmatitic mica gneiss with black schist [2] | Isotope age | 1880 ± 3 Ma [3] | |||
| Age group | Svecofennian – 1.9 Ga | Deposit classification | Intrusive | |||
| Lithological map of the Enonkoski-Savonlinna area |
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Local geology |
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| Deformation history | Polyphase folding | |||||
| Metamorphic grade | Upper amphibolite facies [9] | |||||
| Metamorphic history | Peaked at upper amphibolite facies during D2 | |||||
| Regional metamorphic mineral assemblage | ||||||
| Alteration of host rock | 1) Serpentisation. 2) Contact alteration in the intrusion and in the wall rock. A narrow zone of hornblende gabbro and diorite passes into gneiss and the rock grades fine-grained and oriented with increasing garnet content. The alteration of norite begins locally with metanorite followed by garnetiferous hypersthene gneiss or kinzigite. Occasionally norite grades into the wall rock through cummingtonite-bearing pyroxene gabbro [2]. | |||||
| Alteration minerals | 1) Serpentine, chlorite, biotite; 2) Cummingtonite, garnet [2]. | |||||
| Post-mineralisation modifications | ||||||
| Structure of hosting formation | A distinct differentiation series from peridotites to quartz diorites. Cryptic layering dips steeply towards NW [1]. | |||||
| Parental magma composition | Estimated from the highest analysed Fo (81.6 m-%) [2] MgO content of the magma was 10.1 w-%. | |||||
| Contamination | Indicated by a low ε Nd (1.9 Ga) of +0.2 ± 5 and LREE enrichment in norite [3] and abundance of orthopyroxene-rich cumulates [4]. | |||||
| Whole rock Zr vs MgO |
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| Depletion | Limited nickel depletion in olivine. Depletion indicated by whole rock Ni vs MgO plot. | |||||
| Olivine Ni vs Fo |
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Whole rock Ni vs MgO |
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| HOST ROCKS | ||||||
| Field name | Peridotite | |||||
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Modal name
(Streckeisen / conventional) |
Harzburgite | |||||
| CIPW-normative rock name | ||||||
| Modal rock name (cumulus) | Olivine-orthopyroxene cumulate | |||||
| Normative rock name (cumulus) | ||||||
| Description | The peridotite zone consists of olivine, olivine-plagioclase and olivine-orthopyroxene cumulates [5]. Olivine in peridotite is largely serpentinised and orthopyroxene altered into cummingtonite. The main minerals include also phlogopite, chlorite, hornblende and sulphides. In metaperidotite the main minerals are hornblende, phlogopite and serpentine [1,2]. | |||||
| Field name | Norite | |||||
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Modal name
(Streckeisen / conventional) |
Norite | |||||
| CIPW-normative rock name | ||||||
| Modal rock name (cumulus) | orthopyroxene-plagioclase cumulate | |||||
| Normative rock name (cumulus) | ||||||
| Description | The most common rock type in the intrusion. Grain size varies from coarse to fine. The main minerals are orthopyroxene, hornblende, plagioclase, biotite and sulphides [2]. | |||||
| Field name | Olivine gabbro, olivine norite | |||||
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Modal name
(Streckeisen / conventional) |
Olivine gabbronorite | |||||
| CIPW-normative rock name | ||||||
| Modal rock name (cumulus) | Plagioclase-olivine- orthopyroxene cumulate | |||||
| Normative rock name (cumulus) | ||||||
| Description | Coarse-grained, fairly equigranular rocks. The main minerals are olivine, orthopyroxene, hornblende, plagioclase and sulphides [2]. In metanorite olivine has completely altered into serpentine and the rock often contains coarse phlogopite [1]. | |||||
| Field name | Metagabbro | |||||
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Modal name
(Streckeisen / conventional) |
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| CIPW-normative rock name | ||||||
| Modal rock name (cumulus) | ||||||
| Normative rock name (cumulus) | ||||||
| Description | ||||||
| Field name | Mica gneiss | |||||
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Modal name
(Streckeisen / conventional) |
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| CIPW-normative rock name | ||||||
| Modal rock name (cumulus) | ||||||
| Normative rock name (cumulus) | ||||||
| Description | Hosts together with the trondjhemite and black schist the offset-ore [1]. | |||||
| MAJOR ORE MINERALS | ||||||
| Mineral name | Description | |||||
| Pyrrhotite | Euhedral or subhedral inclusions and exsolution "flames" of pentlandite [2]. | |||||
| Pentlandite | Alteration to violarite is more common in peridotite than in norite. Alteration took place during serpentinisation [2]. | |||||
| Chalcopyrite | ||||||
| Polished section |
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| MINOR ORE MINERALS | ||||||
| Mineral name | Description | |||||
| Magnetite | Secondary | |||||
| Ilmenite | ||||||
| Violarite | After pentlandite | |||||
| Rutile | ||||||
| Graphite | ||||||
| Anatase | ||||||
| Gersdorffite | In veins in the contact zone and in the peridotite hosted ore [2]. | |||||
| OTHER MINERALS | ||||||
| Mineral name | Description | |||||
| WHOLE ROCK COMPOSITIONS | ||||||
| Whole rock composition |
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| MINERAL COMPOSITIONS | ||||||
| Mineral name | Element or ratio | Value | Unit | |||
| Olivine [2] | Fo | 74.9–81.6 | mole % | |||
| Olivine [2] | Ni | 778–1519 | ppm | |||
| Orthopyroxene [2] | Ni | 134–296 | ppm | |||
| ISOTOPES | ||||||
| Description | Average δ34S in ores hosted by norite and gabbro is -0.2 (from -4.3 to +3.1) and in graphite schist -2.6 (from -6.5 to -0.5) [5]. | |||||
| ε Nd (1.9 Ga) in norite is +0.2 ± 0.5 [3]. | ||||||
| EXPLORATION | ||||||
| Geochemical dispersion | ||||||
| Description | ||||||
| Geophysics | ||||||
| Measurement type | Response | |||||
| Grav+magn map of the Enonkoski area |
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| Petrophysics | ||||||
| Rock name | Quantity | Result | Unit | |||
| EXPLORATION HISTORY | ||||||
| Organisation | Outokumpu Oy | |||||
| Years | ||||||
| Operations | ||||||
| Geologists | Leo Grundström, Tapio Karppanen, Risto Juhava, Jorma Eeronheimo | |||||
| Drilling | ||||||
| Storage | GTK, National Drill Core Depot Loppi (part of the cores) | |||||
| Assay data | ||||||
| ORE | ||||||
| Ore composition | The PGE contents of the sulphide-bearing samples are low. One massive sulphide sample (Ni = 3.49 w-%) contained 320 ppb Pd, the other ore samples (0.5–1 kg) 17, 19 and 67 ppb Pd [6]. | |||||
| Ore composition table |
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| Ore mineral composition | Ni content in pentlandite is 33.22–38.54 w-% and Co content 0.02–3.17 w-%. Ni in pyrrhotite is 0.29–0.50 w-% and Co 0.01–0.06 w-% [1]. | |||||
| Ore types | Disseminated ores in norites and gabbros, disseminated ores peridotites, breccia ores, massive ores and sulphide-bearing graphite schists and gneisses [1]. | |||||
| Ore sample 1 |
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Ore sample 2 |
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| Ore sample 3 |
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Ore sample 4 | ||||
| PGE pattern |
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PGE pattern |
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| Primary textures | Intercumulus sulphides | |||||
| Secondary textures | Remobilated sulphide veinlets or stringers and massive ore [7]. | |||||
| Fluid | ||||||
| Zoning | ||||||
| Genetic model | Magmatic sulphides. Possible concentration of sulphides during deformation/metamorphism [7]. | |||||
| Timing of mineralisation | Syntectonic. | |||||
| Supergene alteration | Insignifigant. | |||||
| Gangue | ||||||
| RESOURCES AND MINING | ||||||
| Extent | The main orebody has a horizontal section of about 150x250 m in maximum and extends down to about 350 m level. The slope orebody extends down to 150 m level. The deep orebody has been traced down to a depth of 800 m [1]. | |||||
| Best sections | ||||||
| Ore bodies | Four orebodies: 1) The main orebody hosted by peridotite and norite, 2) The slope orebody hosted mainly by norite, 3) The deep orebody, 4) The offset-orebody in the mica gneiss [1]. | |||||
| Cross section figure 1 |
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Cross section figure 2 |
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| Economic evaluations | ||||||
| Resources (including production) | 7.9 Mt @ 0.72 % Ni, 0.20 % Cu (cut off 0.3-0.4 % Ni) [15] | |||||
| Nickel content (t) | 55720 | Grade (Ni %) | 0.72 | |||
| Total production | 6.7 Mt @ 0.78 w-% Ni, 0.22 w-% Cu [11] | |||||
| By products | Cu, Co | |||||
| Further potential | Main resources between the levels +300 m to +400 m [15]. | |||||
| Mining | 1984–1994 | |||||
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REFERENCES 1. Grundström, L. 1985. The Laukunkangas nickel-copper deposit. In: Papunen, H. & Gorbunov, G. I. (eds.) Nickel-copper deposits of the Baltic Shield and Scandinavian Caledonides. Geol. Surv. Finland. Bull. 333, 240–256.2. Grundström, L. 1980. The Laukunkangas nickel-copper occurrence in southeastern Finland. Bull. Geol. Soc. Finland 52 (1), 23–53. 3. Huhma, H. 1986. Sm–Nd, U–Pb and Pb–Pb isotopic evidence for the origin of the Early Proterozoic Svecokarelian crust in Finland. Geol. Surv. Finland. Bull. 337. 48 p. + 2 app. 4. Geonickel. Final technical report, Vol. 1. 5. Papunen, H., Mäkelä, M. 1980. Sulfur isotopes in Finnish nickel–copper occurrences. Bull. Geol. Soc. Finland 52 (1), 55–66. 6. Papunen, H. 1989. Platinum-group elements in metamorphosed Ni–Cu deposits in Finland. In: ed. M. D. Prendergast & M. J. Jones Magmatic sulphides – the Zimbabwe volume. London: The Institution of Mining and Metallurgy, 165–176. 7. Juhava, R., Karppanen, T., Papunen, H. 1989. The Enonkoski Ni–Cu deposit. In: Alapieti, T. (ed.) 5th International Platinum Symposium. Guide to the post-symposium field trip, August 4–11, 1989. Geol. Surv. Finland. Guide 29, 257–263. 8. Puustinen, K., Saltikoff, B., Tontti, M. 1995. Distribution and metallogenic types of nickel deposits in Finland. Geol. Surv. Finland. Report of Investigations 132. 38 p. 9. 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 1:1 000 000. Espoo: Geol. Surv. Finland. 10. Hill, R. & Barnes, S. & Dowling, S. & Makkonen, H. & Peltonen, P. 2005. Chalcophile Element Distribution in Mafic and Ultramafic Metavolcanic Rocks of the Svecofennian Kotalahti and Vammala Nickel Belts Finland – A Test for a Geochemical Signature of Subvolcanic Magmatic Ore Forming Processes. Regional Area Selection Criteria for Intrusive Ni/Cu Sulfide Ore Deposits. Final Report. CSIRO, GTK. 217 s. Geol. Surv. Finland, Archive report, M 10.4/2005/2 (18 MB). 11. Isomäki, O-P. 2004. Personal communication. 12. Mäkinen, J., Makkonen, H.V. 2004. Petrology and structure of the Palaeoproterozoic (1.9 Ga) Rytky nickel sulphide deposit, central Finland : a comparison with the Kotalahti nickel deposit. Mineralium Deposita 39 (4), 405–421. 13. Makkonen, H. & Forss, H. 2004. Nikkelimalmitutkimukset Enonkosken-Savonlinnan-Kerimäen alueella vuosina 1998–2002. 15 s., 3 liites. Geol. Surv. Finland, Archive report, M 19/4211/2004/1/10 (in Finnish, 2.9 MB). 14. Lamberg, P. 2005. From genetic concepts to practice – lithogeochemical identification of Ni–Cu mineralised intrusions and localisation of the ore. Geol. Surv. Finland. Bull. 402. 264 p. + CD-ROM. 15. Isomäki, O-P. 1996. Enonkosken kaivoksen loppuraportti. Outokumpu Finnmines Oy, Enonkosken kaivos. Report 090/4211 06/OPI/96. Geol. Surv. Finland. 16. Makkonen, H., Halkoaho, T. 2007. Whole rock analytical data (XRF, REE, PGE) for several Svecofennian (1. 9 Ga) and Archean (2. 8 Ga) nickel deposits in eastern Finland. 49 p., 13 app. Geol. Surv. Finland, Archive report, M19/3241/2007/1/10/32 (92.65 MB). |
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