Gold deposits in northern Finland - Arkisto.gsf.fi

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cal gradations between the types and (3) similar REE patterns to those of the Sattasvaara komatiites. Mass balance calculations have shown that biotite schists have been enriched in CO 2 , K, Fe, Au, Ba, S, W, Te, Sr and Mn, and depleted in Mg, Ca, Co, Si and Zn, accompanied by a 10– 100 m Main ore zone Secondary ore (quartz and quartz-baryte veins) Proximal alteration zone (intense biotite ± talc alteration) Distal alteration (talc-chlorite altered komatiite) Outline of A-pit Figure 9. Geological map of the Pahtavaara Mine open pit (compiled by N. Patison in 2000). North up. F2-related gold lodes Dykes at Länsi Rigid (competent) rock Schistosity Gold mineralization The Green Fault Figure 10. Fold model for the Pahtavaara gold deposit. View to the NW. Image courtesy Warren Pratt (Geologcal Mapping Ltd) and Lappland Goldminers AB. 26 Pasi Eilu & Tero Niiranen (ed.)
30% decrease in net volume. Amphibole rocks record a marked increase in volume, with gains in Ca, Si, Au, Na, Ba, Te, S, W, Sr and P, and losses in CO 2 , Co, Mg, Fe and Zn. The two major altered rock types reflect two stages of hydrothermal alteration (Fig. 9) which, on the basis of textural and geochemical evidence, include: (1) earlier biotitisation (K alteration) and (2) later amphibole overgrowth (Ca-Si alteration). The former has been interpreted to have taken place during or immediately after the peak of regional metamorphism, and during ductile deformation. Its distribution was controlled by a combination of high permeability in the originally pyroclastic komatiites, and north-east-trending deformation zones. Later amphibole growth was related to the north-north-east-trending shearing resulting in the formation of zones of dilation into which hydrothermal fluids were focused under conditions straddling the brittle-ductile transition. Note that this interpretation of timing of alteration by Korkiakoski (1992) is in contrast to the later suggestions of premetamorphic alteration described above. Mining The gold ore at Pahtavaara forms narrow lodes generally 5–10 m wide, that strike almost east– west and, in the upper parts at least, dip westwards at about 70–80° (Figs. 11 and 12). Presently, the ore is mined by sub-level caving. The only economically recoverable metal is gold. Sulphides are relatively rare, with pyrite being the most abundant, comprising about 1% of the ore. Magnetite can constitute up to 5–10% of the ore grade material, particularly in the biotite schists. Gold is free milling and occurs as discrete grains that are highly variable in size between silicate grains and along fracture surfaces. Some 50–60% of gold grains are less than 50 μm in diameter. In addition to pyrite and gold, trace amounts of chalcopyrite, rutile, chromite, hematite, pentlandite, pyrrhotite, violarite, miller Z Y X Resource classification Measured resources Indicated resources Inferred resources Figure 11. Open pits (grey) and resource blocks, as of 1 January 2013, in the Pahtavaara gold mine. View to the NW. Image courtesy Lappland Goldminers AB. Excursion Guidebook FIN1 27
Page 1 and 2: 12th Biennial SGA Meeting 12-15 Aug
Page 3: Excursion Guidebook FIN1 Gold depos
Page 7 and 8: Contents Programme ................
Page 9 and 10: Saattopora Levi Suurikuusikko (Kitt
Page 11 and 12: Timanide orogen 500 km Murmansk Lap
Page 13 and 14: Metallogenic Areas and Mineral Depo
Page 15 and 16: 24°0'0"E 26°0'0"E 68°0'0"N Suuri
Page 17 and 18: 24°0'0"E 25°0'0"E 26°0'0"E N Rom
Page 19 and 20: Table 2. Selected, potentially sign
Page 21 and 22: stone Belt (CLGB). The CLGC is geol
Page 23 and 24: schist to upper amphibolite facies.
Page 25 and 26: of Ag, Au, As, CO 2 , K, Rb, S, Sb
Page 27: 3472000 3476000 3480000 3484000 750
Page 31 and 32: 7525300 A’ 3391900 3390500 A 200
Page 33 and 34: eralisation took place at 300-350
Page 35 and 36: comm. 2002). Ore-grade rock was fou
Page 37 and 38: Figure 18. Loading ore. Underground
Page 39 and 40: from progressive alteration of mafi
Page 41 and 42: least 25 km (Fig. 15). The dip of t
Page 43 and 44: Table 4. Alteration minerals presen
Page 45 and 46: tober 15, 2012 (Fig. 28). The prese
Page 47 and 48: 3 395 000 mE 3 400 000 mE 3 405 000
Page 49 and 50: ciated with the gold and uraninite.
Page 51 and 52: Table 6. North Rompas drilling inte
Page 53 and 54: Grönholm, P., 1999: The mesotherma
Page 55 and 56: J.S., Siedlecka, A. & Solli, A., 19
Page 57: Sorjonen-Ward, P., Ojala, V.J. & Ai

Gold deposits in northern Finland - Arkisto.gsf.fi

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