Marttalanniemi - Gold Database

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Name	Marttalanniemi	DATA UPDATED	12.1.2007
Alternative names
Deposit summary	MARTTALANNIEMI, in Southern Ostrobothnia, is a Palaeoproterozoic orogenic gold occurrence with no resource estimate available. It is formed by a set of tourmaline-quartz veins in felsic plagioclase porphyry. The occurrence is close to a major NW-trending shear zone. Native gold both in tourmaline-quartz veins and in the enveloping, altered host rock.
LOCATION
Geological domain	Svecofennian	Belt	Southern Ostrobothnia
Site photo		Regional map
Map sheet	222207
Northing (kkj)	6957670	Easting (kkj)	2449500
Latitude	62.71967N	Longitude	23.00933E
Municipality	Nurmo
Nearest town, roads	10 km SE from Seinäjoki. A sealed road 5 km from the area, a gravel road to the area.
MINING
Exploration licence no	4354/1	Mining concession no
Present holder	OPEN FOR ACQUISITION
Previous holders	Geological Survey of Finland (GTK) (1977-1980, 1987-1991)
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	50-80 m wide and 800 m long [5].
Lodes
Best sections	1 m @ 14.8 ppm Au [3].
EXPLORATION
Discovery year	1987
Discovery	As a follow-up of the Sb exploration in the Seinäjoki area, located by percussion drilling into three anomalies in till by GTK [3,4].
Exploration history	GTK (1977-1990) [1,2,3,4,5]: Regional (1981) and localised (1983-) till geochemical survey, till stratigraphy, bedrock mapping, percussion 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
Drilling	GTK (1988) [3]: percussion drilling: 17 holes, total of 360 m.
Elements analysed	As, Au, S, Sb [2].
Primary dispersion	Au, As and Sb anomalies probably envelope the mineralisation [2].
Secondary dispersion	Extensive Au anomalies in the region in till, regional Sb and As anomalies in till are, apparently, unrelated to gold mineralisation [1,5]. Two local, distinct As-Au-Sb anomalies which relate to the Au mineralisations in the bedrock [2].
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
Exploration geologist in charge	GTK: Niilo Kärkkäinen, Paunu Oivanen.
ORE
Siting of gold	Gold both in tourmaline-quartz veins and in the enveloping, altered host rock [3,4]. Gold seems to follow As-rich bands [5].
Fineness
Major opaques	Pyrite, pyrrhotite, arsenopyrite [3,4].
Minor opaques	Galena, sphalerite, gold [5].
Gangue	Quartz, tourmaline, scheelite [3].
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	Au, As, B, CO2, K, Pb, S, W [3,4].
Ore fluid
Stable isotopes
Pb isotope data
GEOLOGY
Geological setting	A sequence of metapelites and metagreywackes intruded by the intermediate plagioclase and plagioclase-uralite porphyry sills(?) dominates the geological setting in the area [5].
Major host rocks	Dacitic plagioclase porphyry [2,3].
Minor host rocks	Quartz-sericite schist, mica gneiss, greywacke, pegmatites [2,3].
Intrusives	Pegmatite dikes, several minor (<1 m wide) and one large (40-100 m wide), whose relationship with Au mineralisation is unclear [2].
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
Metamorphic grade	Mid-amphibolite facies [2,4].
Metamorphic mineral assemblage	Plagioclase–hornblende–quartz–biotite±cummingtonite [4].
Metamorph photo 1		Metamorph photo 2
STRUCTURE
Structural style
Closest major shear	A NW-trending shear zone extending from Seinäjoki to Peräseinäjoki, >30 km long, 1 km(?) wide [2,5].
Controlling structure	A set of 1-15 m wide shear zones which are conform to the dominant foliation in the area and are within the main shear zone [3,5].
Deformation history
Ore fabric
Veins	Auriferous tourmaline-quartz veins [3].
Structure photo 1		Vein photo 1
Structure photo 2		Vein photo 2
Structure photo 3		Vein photo 3
ALTERATION
General alteration	Sulphidation, biotitisation, carbonation, formation of Ca silicates ± tourmaline [2].
Proximal alteration	The Ca-silicate bands possibly reflect the most intense alteration. These comprise: diopside, K feldspar, calcite, epidote, pyrrhotite, and arsenopyrite [2]. There are, also, tourmaline-bearing quartz-sericite rocks in the northern part of the area [2]; these could reflect early epithermal alteration and be unrelated to Au mineralisation.
Intermediate alteration	Intense biotitisation? [2].
Distal alteration	Low-grade biotitisation? [2].
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
TIMING
GENETIC MODEL	Orogenic "mesothermal" deposit.
GENETIC TYPE	Orogenic	References
Alternative genetic type 1		References
Alternative genetic type 2		References
References 1. Lestinen, P. 1988. Seinäjoen alueen geokemialliset tutkimukset vuosina 1983–1986. Geol. Surv. Finland, Report S/41/2222/1/1988. 40 p. (in Finnish, 1.4 MB) 2. Kärkkäinen, N. 1989. Kulta-aiheen jatkotutkimukset Poka-kairauksella v. 1988 Nurmon Marttalanniemessä. Geol. Surv. Finland, Report M19/2222/89/1/10. 6 p. (in Finnish, 2.9 MB) 3. Kärkkäinen, N. 1990. Tutkimustyöselostus Nurmon kunnassa valtausalueella Marttalanniemi, kaiv. rek. n:o 4354, suoritetuista malmitutkimuksista. Geol. Surv. Finland, Report M19/2222/-90/1/10. 5 p. (in Finnish, 640 KB) 4. Oivanen, P. 1982. Antimonitutkimukset Seinäjoen-Nurmon alueella vuosina 1975–1982. Geol. Surv. Finland, Report M19/2222/-82/1/10. 123 p. (in Finnish, 109 MB) 5. Lestinen, P., Kontas, E., Niskavaara, H. & Virtasalo, J. 1991. Till geochemistry of gold, arsenic and antimony in the Seinäjoki district, western Finland. Journal of Geochemical Exploration 39, 343–361. 6. Appelqvist, H. 1993. Ore mineralogy in the Proterozoic Kalliosalo gold occurrence, western Finland, with preliminary data on an unspecified mineral, Ag ₃Au ₃Sb ₁₀S ₁₀. Geol. Surv. Finland, Special Paper 18, 37–44.
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