Hammaslahti
Hammaslahti Belt
The
30+ km long Hammaslahti Belt located in Eastern Finland, comprises a
sequence of Mid-Proterozoic supra-crustal rocks consisting
predominantly of felsic pyroclastics, mafic volcanics and
volcanoclastic sediments. A number of base metal occurrences are known
along the belt, but the only major deposit found to date has been the
Hammaslahti Mine, which was discovered on surface in 1966 during
routine field mapping by the Geological Survey of Finland. The deposit
is located on the west limb of a major folded sequence of felsic
pyroclastics sediments at the north end of the Belt.
Field
geological and geophysical work by Magnus has identified several target
areas for follow-up exploration, including depth and strike extensions
of the Hammaslahti deposit.
Magnus holds several claim applications over the mine as well as extensions to the known mineralization.
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Hammaslahti Mine
Quick Facts:
- Cu-Zn-Au-Ag distal VMS deposit.
- Open pit 1973–1976, underground mine 1976–1986
- Remaining reserves of 0.212 Mt in Zinc Zone and open at depth below 100 m
- Main Copper Zone continues below lowest mining level of 600m
- Total production was 7 Mt of 1.16% Cu from the main zones and
0.283 Mt of 1.55% Zn, 0.52% Cu, 0.59 g/t Au, 5.2 g/t Ag from the Zinc
Zone.
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Exploration History
Geological
Survey of Finland carried out the initial exploration and Outokumpu Oy
mined the deposit. A variety of exploration programs have been carried
out in the area by GTK and Outokumpu, including boulder tracing, till
and stream sediment geochemical surveys, and ground magnetic, slingram
EM, gravimetric and radiation surveys. Regional low-altitude airborne
radiometric, magnetic and EM surveys in the region became available
after the mine was in production. No new mineralization of significance
has been discovered.
The host rocks at Hammaslahti have been
considered to be predominantly sediments (‘arkosites’, ‘conglomerates’,
etc.) and the distal volcanic environment has not been recognized.
Alteration and other characteristics of distal VMS deposits have not
been recognized nor used to explore for or evaluate areas along strike
or in the immediate vicinity of the mine.
Mine Geology
A
W-E cross-section of the geology in the vicinity of the main Copper
Zone (S Zone) is depicted in the insert (source Outokumpu Oy).
The sequence of rocks, including the mineralized horizon, dip to the
west at approximately 60 degrees, while the ore zone has a shallow
plunge of approximately 30 degrees to the SSW. The ore bearing horizon
is capped to the west by a graphitic schist unit which separates the
volcanoclastic complex to the east from a sequence of monotonous ‘mica
schists’ to the west.
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Potential
Down
plunge extension of zinc ore (Z zone) below 100m possibly continues up
to 400m to SSW while the main Copper Zone is open down plunge below the
600m. As well, undiscovered ore bodies may exist down dip of the
ore-bearing horizon far below the mine workings. Similar VMS geological
settings exist in the sequence around the fold nose and along both
limbs of the structure and hold potential for the discovery of new
deposits.
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