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Koivusaarenneva |
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Finland |
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Ti V
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Super Porphyry Cu and Au
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The Koivusaarenneva ilmenite and vanadium-magnetite deposit is hosted by the 1881 ±6 Ma Svecofennian, sill like, layered Koivusaarenneva gabbro at Kälviä in north-western Finland.
The Koivusaarenneva gabbro intrudes 1.9 Ga tonalitic bedrock near the boundary of the Mid Finland granitoid complex and occurs at the southern margin of the large Ylivieska gabbro province that includes the northern extension of the Kotalahti Nickel Belt. The Koivusaarenneva gabbro is part of a 12 km long belt of mafic intrusions emplaced within a NE-SW oriented fault zone, a branch of the major Kinturi Fault that extends across Finland in a NW-SE direction. The intrusion was influenced by a regional amphibolite facies metamorphism and has since experienced retrograde metamorphish related to faulting activity.
The intrusion dips south-east at a sub-vertical angle and is mainly composed of even grained metamorphosed gabbro and gabbronorite which has been subdivided into three layers, as follows:
i). Lower Zone, 150 to 500 m thick - monotonous, sub-ophitic gabbro and gabbronorite (plagioclase-pyroxene cumulates) with layering on the scale of a few metres and local concentrations of Fe-Ti oxides, with coarse gabbro near the base and homogenous medium grained gabbro at the top.
ii). Middle Zone, 150 m thick - characterised by voluminous massive and disseminated ilmenite, even grained gabbro and minor coarse grained pyroxenite. This zone carries the bulk of the ilmenite resource. A 1.5 to 4 m thick layer of magnetite rich high grade ilmenite is found near the base of the zone. This is overlain by a few layers, each of 10 to 30 m of pyroxenite with orthopyroxene as the main cumulus minerals and lesser clinopyroxene and plagioclase intercumulus. Then follows a 5 to 20 m ilmenite rich gabbro grading up into an up to 50 m thick gabbro with abundant disseminated ilmenite.
iii). Upper Zone, 200 to 500 m thick - non-magnetic, poorly layered apatite rich gabbro, noritic gabbro and leucogabbro. Ilmenite is the dominant Fe-Ti oxide, although ilmenite enrichments are sparse.
The ilmenite deposit, which comprises ilmenite rich rocks with >4% TiO2 (ie, cut-off of 8% ilmenite), can be followed continuously for 2 km, almost the entire length of the intrusion and has an average thickness of 50 to 60 m. The hosts are predominantly gabbro and pyroxenite within the Middle Zone. Sulphide are most abundant in the oxide rich rocks and averaging 1.1% sulphide (for 0.44% Cu, 0.25% Ni). The ore is divided into high grade, averaging 26% ilmenite and 9% magnetite (9% TiO2 cutoff) and low grade (4 to 9% TiO2) averaging 12% ilmenite.
The stated resource in 2002 was: 44 Mt @ 15% ilmenite, 6% vanadiferous magnetite [=0.7% V] to a depth of 150 m.
For detail consult the reference(s) listed below.
The most recent source geological information used to prepare this decription was dated: 2002.
This description is a summary from published sources, the chief of which are listed below.
© Copyright Porter GeoConsultancy Pty Ltd. Unauthorised copying, reproduction, storage or dissemination prohibited.
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Selected References:
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Karkkainen N K, Bornhorst T J 2003 - The Svecofennian gabbro-hosted Koivusaarenneva magmatic ilmenite deposit, Kalvia, Finland: in Mineralium Deposita v38 pp 169-184
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Porter GeoConsultancy Pty Ltd (PorterGeo) provides access to this database at no charge. It is largely based on scientific papers and reports in the public domain, and was current when the sources consulted were published. While PorterGeo endeavour to ensure the information was accurate at the time of compilation and subsequent updating, PorterGeo, its employees and servants: i). do not warrant, or make any representation regarding the use, or results of the use of the information contained herein as to its correctness, accuracy, currency, or otherwise; and ii). expressly disclaim all liability or responsibility to any person using the information or conclusions contained herein.
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