Tervasmäki - Gold Database

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Name	Tervasmäki	DATA UPDATED	12.1.2007
Alternative names
Deposit summary	TERVASMÄKI, in Southern Ostrobothnia, is a Palaeoproterozoic orogenic, antimony-rich, gold occurrence with no resource estimate available. It is hosted by plagioclase porphyry and mica schist. The occurrence is within a regional NW-trending shear zone, locally controlled by minor shears within the main shear zone.
LOCATION
Geological domain	Svecofennian	Belt	Southern Ostrobothnia
Site photo		Regional map
Map sheet	222208
Northing (kkj)	6960050	Easting (kkj)	2445200
Latitude	62.74040N	Longitude	22.92451E
Municipality	Nurmo
Nearest town, roads	4 km south from Seinäjoki. 3 km from a sealed road, a gravel road across the area.
MINING
Exploration licence no	2711/1	Mining concession no
Present holder	OPEN FOR ACQUISITION
Previous holders	Geological Survey of Finland (GTK) (1975–1982)
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	At surface, 3–23 m wide, 150 m long, open in depth [1].
Lodes
Best sections	5 m @ 1.3 ppm Au and 0.55% Sb [1].
EXPLORATION
Discovery year	1977
Discovery	Sb-rich erratic boulders found by amateur prospectors led to discovery of a Sb-mineralisation in outcrop by GTK [1].
Exploration history	GTK (1975–1982) [1,2,3]: Detailed bedrock mapping, trenching, diamond drilling, till stratigraphic and geochemical studies, IP ground 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	A consistent magnetic and electric anomaly about 1 km long, because the wallrock on both sides is a pyrrhotite- and graphite-bearing mica schist.
Drilling	GTK (1977–1979) [1]: 10 diamond-drill holes. One or two holes per profile, profiles about 50 m apart.
Elements analysed
Primary dispersion
Secondary dispersion	Extensive Au anomalies in the region in till; the regional Sb and As anomalies in till are, apparently, unrelated to gold mineralisation [3].
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: Paunu Oivanen.
ORE
Siting of gold
Fineness
Major opaques	Antimony, arsenopyrite [1].
Minor opaques	Loellingite, pyrrhotite, chalcopyrite, gudmundite [1].
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	Au, Ag, As, Cu, K, S [1].
Ore fluid
Stable isotopes
Pb isotope data
GEOLOGY
Geological setting	A sequence of Palaeoproterozoic metapelites and metagreywackes intruded by the intermediate plagioclase and plagioclase-uralite porphyry sills(?)[1,3].
Major host rocks	Plagioclase porphyry, mica schist [1].
Minor host rocks
Intrusives	Post-mineralisation(?) pegmatite dikes within the host rock [1].
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	Amphibolite facies [1].
Metamorphic mineral assemblage	Plagioclase-hornblende-quartz-biotite±cummingtonite [1].
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 [3].
Controlling structure	A set of minor shear zones which are within the main shear zone [3].
Deformation history
Ore fabric
Veins
Structure photo 1		Vein photo 1
Structure photo 2		Vein photo 2
Structure photo 3		Vein photo 3
ALTERATION
General alteration	Sericitisation and silicification in the mica schist [1].
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
TIMING
GENETIC MODEL	Orogenic "mesothermal" deposit.
GENETIC TYPE	Orogenic, Au-Sb subtype	References
Alternative genetic type 1		References
Alternative genetic type 2		References
References 1. 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) 2. 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) 3. 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.
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