Au-Ag selenide-telluride deposits in Finland

Category Mineral processing
Group GSI.IR
Location International Geological Congress,oslo 2008
Author Kojonen, Kari
Holding Date 21 September 2008

Au-Ag selenide-telluride deposits are common in Finland in the Archean and Proterozoic bedrock. They were discovered in: 1) Tampere schist belt, southern Finland, 2) central Finland Osikonmäki-Laivakangas zone, 3) Kuusamo greenstone belt, NE Finland, 4) Oijärvi schist belt, western central Finland and 5) schist belts in Ilomantsi and Kuhmo, Eastern Finland. The gold provinces include six major Au-Ag selenide-telluride deposits: 1) the Kutemajärvi mine, Orivesi, 2) the Jokisivu gold deposit, Huittinen, 3) the Osikonmäki gold deposit, Rantasalmi. 4) the Juomasuo gold deposit, Kuusamo, 5) the Ilomantsi gold prospects and Pampalo test mine, and 6) the Kylmäkangas gold deposits, Oijärvi.
The gold ore of Kutemajärvi has native gold in fractures and as inclusions in pyrite, arsenopyrite and quartz, and intergrown with altaite, rucklidgeite, tetradymite, tellurobismuthite, joseite, frohbergite, melonite, petzite, hessite, coloradoite, calaverite, krennerite, sylvanite, kostovite and an unknown (Bi,Sb,Se)-telluride.
The Jokisivu deposit has free gold grains in quartz veins in gabbro-diorites associated with arsenopyrite, ullmannite, costibite, loellingite, chalcopyrite, sphalerite, pyrite, marcasite, galena, altaite, tsumoite, tellurobismuthinite, rucklidgeite, maldonite, hedleyite, joseite-B, pilsenite, tetradymite, aurostibite, ilmenite and magnetite.
The Osikonmäki deposit is hosted by a 3-km long shear zone and has native gold occurring with arsenopyrite, quartz, plagioclase and pyrrhotite, arsenopyrite, loellingite, chalcopyrite, marcasite, sphalerite, galena, cubanite, covellite, molybdenite, native bismuth, native antimony, maldonite, ikunolite, hedleyite, kawazulite, pilsenite, dyscrasite, tetrahedrite, stannite, ilmenite and rutile.
The Juomasuo test mine has native gold in albite-quartz- sericite-amphibole-chlorite-talc associated with pyrite, cobaltite, uraninite, altaite, calaverite, frohbergite, melonite, rucklidgeite, tellurobismuthite, mattagamite, kawazulite, and clausthalite.
The Ilomantsi greenstone has gold in quartz-carbonate veins and shear zones in tonalites, quartz-feldspar porphyries, quartz-tourmaline veins and hydrothermal alteration zones in sericite schists. In the Pampalo test mine gold occurs in quartz-feldspar porphyries in contact with ultramafic rocks. Native gold is intergrown with pyrite, arsenopyrite, rutile, native bismuth and tellurides including altaite, tsumoite, hedleyite, tellurobismuthite, unnamed Bi3Te2, rucklidgeite, volynskite, hessite, thallian silver telluride, frohbergite, melonite and NiSbTe. Minor amounts of gold are incorporated in electrum, calaverite, petzite and an AuSbTe phase. The Kylmäkangas Au-Ag deposit is hosted by a sheared quartz vein and quartz-sericite schist in Archean Oijärvi greenstone belt. Native gold occurs with hessite, petzite, altaite, Bi-telluride, probable krennerite with sulfides (chalcopyrite, pyrite, galena, terahedrite-tennantite, sphalerite, bornite, chalcocite, covelline).