Gold deposits in northern Finland - Arkisto.gsf.fi

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Figure 25. A. Colour photo from Etelä pit at Kittilä Mine, August 27th 2011. B. Structural interpretation of the same
area. Photograph shows chert boudins, and both sinistral and dextral shear zones. Marker pen for scale. North to
right. Photo and interpretation Juhani Ojala.
Figure 26. An underground 3D image across ore. Distance between inner green markings is 5.5 metres. Image courtesy
Agnico Eagle Mines.
Alteration in and around the deposit appears
typical for deposits of this type. Visually, intense
carbonate and albite alteration are associated with
gold-rich arsenopyrite and pyrite. Albite occurs
as a matrix overprint that typically extends from
a few tens of metres to up to 100 m into barren
rock, and as brecciating micro veinlets. Barren
carbonate alteration includes distal calcite veins,
and dolomite-ankerite veins and infilling tectonic
or hydrothermal breccia within proximal alteration
zones and ore lodes, respectively. Table 4
presents a summary of progressive alteration of
mafic pillow lavas; missing in this table is amorphous
carbon. The abundance of this ‘graphitic’
carbon correlates with the intense shearing that
bounds most mineralised zones. The presence of
such carbon suggests extremely reducing fluid
conditions during shearing and possibly mineralisation.
Gold-bearing sulphides commonly nucleated
on shear planes, stylolitic cleavage, and
on fractures bearing amorphous carbon (Fig. 27).
Carbon isotope data indicate that this material is
sourced from carbon-rich sediments within the
host sequence (Patison, unpublished data). Ar­
40 Pasi Eilu & Tero Niiranen (ed.)