Pekka Sipilä’s research while affiliated with Geological Survey of Finland and other places

The Western Finland (WF) supersuite, characterized by supracrustal rocks and intruding plutonic rocks, forms the core component of the coupled Bothnian oroclines in the central part of the Svecofennian orogen. We present here geochemical-isotope data, detrital zircon age data on sedimentary rocks and age data on granitoid plutons within the WF supersuite in the Pirkanmaa (PB) and Pohjanmaa (PoB) belt representing the southernmost limb of the southern and the hinge zone of the northern Bothnian orocline, respectively. The Tampere belt (TB) in the north and Häme belt (HB) in the south bound the PB.

This paper summarises the results of probabilistic estimates of the amounts of Cu, Zn, Pb, Ni, Co, Pt, Pd, Au, Ag and Mo in undiscovered orogenic Au, volcanogenic massive sulphide (VMS), porphyry Cu, Outokumpu-type Cu-Zn-Co, synorogenic intrusion-related Ni-Cu, komatiite-related Ni, and layered intrusion-hosted contact-type and reef-type PGE deposits in Finland. The assessments were carried out down to the depth of one kilometre using the three-part quantitative assessment method.

Undiscovered resources of copper, zinc, lead, gold and silver in volcanogenic massive sulphide (VMS) deposits, undiscovered resources of copper, molybdenum, gold and silver in porphyry copper deposits, and undiscovered resources of copper, zinc, nickel and cobalt in Outokumpu-type deposits were estimated down to the depth of one kilometre in the bedrock of Finland using the threepart quantitative assessment method. Grade-tonnage models were constructed for felsic, bimodal-mafic and mafic VMS deposits using data from known Fennoscandian deposits. A grade-tonnage model for porphyry copper deposits was constructed using global data from Precambrian deposits. For the Outokumpu-type deposits, a grade-tonnage model was developed using data from wellknown deposits within the Outokumpu area. Thirty-one permissive tracts were delineated for VMS deposits, 10 for porphyry copper deposits, and one for Outokumpu- type deposits. The VMS tracts cover an area of 41,600 km2, the porphyry copper tracts cover 38,400 km2, and the Outokumpu tract covers 9800 km2. The mean estimates of the numbers of undiscovered VMS, porphyry copper and Outokumpu-type deposits within the permissive tracts are 45, 11 and 6, respectively. At 50 % probability, the undiscovered VMS deposits are estimated to contain at least 730,000 t Cu, 1.6 Mt Zn, 150,000 t Pb, 1100 t Ag and 16 t Au, and the undiscovered porphyry copper deposits are estimated to contain at least 2.4 Mt Cu, 100,000 t Mo, 1000 t Ag and 170 t Au. The estimated median undiscovered resources in Outokumpu-type deposits are at least 580,000 t Cu, 220,000 t Zn, 53,000 t Co and 41,000 t Ni. About 71 % of the copper and 68 % of the zinc endowment in VMS and Outokumpu-type deposits, and at least 98 % of the copper endowment in porphyry copper deposits in Finland occurs in poorly explored and undiscovered deposits. The undiscovered VMS resources are estimated to be distributed between several permissive tracts, with the Vihanti and Pyhäsalmi tracts having the largest undiscovered resources. Felsic deposits are estimated to contain 53 % of the undiscovered VMS-type copper-zinc resources and 95 % of the undiscovered VMS-type lead resources in Finland. The undiscovered porphyry copper resources are estimated to be concentrated in the Central Ostrobothnia, Tampere, Häme and Haaparanta tracts, with 86 % of the resources in central and southern Finland. At the 50 % level of probability, the undiscovered copper-zinc resources in VMS, porphyry copper and Outokumpu-type deposits in Finland are at least 3.7 Mt of copper and 1.8 Mt of zinc. This is 38 % of the total estimated undiscovered copper resources and 100 % of the total estimated undiscovered zinc resources in Finland.

The~1.88 Ga VaasaVaasa Batholith in western Finland is a large granitoid area (8 000 km 2) with gradational contacts against the garnet- and cordierite-bearing diatexite and metatexite migmatites of the Pohjanmaa Belt. It is located in the middle part of the Fennoscandian Shield and was formed during the Svecofennian orogeny (1.9-1.8 Ga). The Batholith area consists of porphyritic and even-grained granodiorite with smaller proportions of granite and pyroxene granitoid. The various phases in the Vaasa Batholith mainly grade into each other and usually contain relicts of Ca concretions and schists, biotite and garnet, locally resembling uniform diatexites. All the phases are peraluminous in composition. The Mg# of biotite in the granodiorites and pyroxene tonalites is high (50-60), in contrast to lower values in the granite (20-35). Orthopyroxene in the tonalite has an elevated Mg# value and Al2 O3 concentration. In Harker diagrams, bulk composition of the tonalites, granodiorites and granites of the Vaasa Batholith evolves along the same path, but the metatexites are beyond or cutting the path. The textural, mineralogical and chemical continuity between the granodiorites of the Vaasa Batholith and the adjacent diatexites indicate that the Vaasa Batholith represents a magma layer formed by extensive in situ melting of the crust. The diatexites are mainly from the inhomogeneous magma, although they texturally grade to the metatexites. The Vaasa Batholith and adjacent diatexites are separated from the metatexites of the Pohjanmaa Belt by 'magma interface' (MI). The metatexites formed in a conduction heat flow zone above the MI. The Vaasa Batholith is an exceptional type example of the voluminous and diverse granitoids in Finland.

The Kedonojankulma Cu-Au occurrence was discovered by diamond drilling after systematic till geochemical studies in the Forssa region, Southern Finland. The starting point for the study was a Te-Cu-As anomaly in the regional till geochemical data. The till geochemical exploration was carried out in two main phases, first in regional-scale anomaly mapping, followed by local-scale anomaly checking and target-scale exploration. The discovered Cu-Au(-Ag-Mo) occurrence is hosted by a porphyritic tonalite intrusion in the Palaeoproterozoic volcanic-intrusive Häme belt, part of the Southern Svecofennian Arc Complex in southern Finland. The fiune-grained Cu-Au(-Ag-Mo) mineralization is controlled by a sheared and fractured, strongly altered zone in the quartz-plagioclase porphyrite. The highest metal contents in one-metre-long samples of drill core are 2.4% Cu, 8 ppm Au, 120 ppm Ag, 0.13% Mo, 0.15% Sb, 0.33% Bi and 1.27% Zn. The Kedonojankulma occurrence has a complex mineralogy, including various Cu, Ag, Au, Bi, Mo, Sb, Sn and Zn minerals. The main ore mineral is chalcopyrite. Other notable ore minerals are arsenopyrite, bornite, chalcocite, sphalerite, pyrite, pyrrhotite, molybdenite, silver sulphides and bismuth. The Kedonojankulma occurrence has several features that are typical of porphyry-style Cu deposits. Most prominent are the metal contents and zoning, with Cu-Au-Ag-As-Mo in the core, Mo and Cu in quartz veins outside of the core and Zn-Cu-Ag in the outer zone of the intrusion. Various alteration assemblages in the mineralized zone have been identified, with silicification, chloritization, sericitization and epidotization being common.

Inventories of bedrock outcrops suitable for aggregate production have been carried out at the Geological Survey of Finland since 1989 and now include over 12,000 outcrops. Initially, the aim of the inventories was to locate outcrops for high quality aggregate production but the work has developed with regional co-operative POSKI projects seeking to reach a balance between groundwater protection and aggregate supply. Based on evaluation in the field and mechanical–physical tests, about 1% of the bedrock outcrops studied meet the highest quality requirements. As an example of the societal implication of the inventories, 44 areas with regionally significant aggregate reserves were identified in the 1st Complementary Stage of the Uusimaa Regional Land Use Plan, in order to secure the supply of aggregates with good quality. In 2008, GTK opened a web based aggregate accounting service to provide information on available reserves in high demand regions in Finland.

This report consists of results of bedrock mapping in Pohjanmaa covering three 1:100 000 map sheets: Oravainen (1334), Lapua (2311) and Alahärmä (2312). The fieldwork was carried out during 2002-2006 by the staff of GTK. In addition, most of the mapping in the Alahärmä map sheet area was carried out by University of Turku in 2004. The map area is part of the Palaeoproterozoic Pohjanmaa schist belt, and the bedrock is clearly divided into two main parts. The main rock type in the region is a heterogeneous rock called Vaasa granite. It has formed from mica gneisses through melting to various degrees and re-crystallization. Eastern and southern parts of the mapped area form part of the Evijärvi schist belt where the dominant rock types are psammitic and pelitic metasediments. Chemical compositions indicate that the Vaasa granite has evolved from Evijärvi-type metagreywackes almost isochemically. In terms of mineralogical and chemical composition Vaasa granite is mainly granodioritic, but granitic areas also exist. The appearance of the rocks is very variable, but can roughly be divided into even-grained and porphyritic types. Garnet and quartz aggregates are common, though not present throughout the Vaasa granite. Locally, there is also orthopyroxene. In the Lapua-Alahärmä region, the main rock type is unoriented and its appearance is similar to intrusive rock. In the more western Oravainen and Vöyri-Maksamaa regions, the rocks are more heterogeneous and include abundant mica gneiss remnants melted to variable degrees, biotite-rich restites and skarn concretions. In these areas, the rock is commonly ductilely deformed and in places migmatitic. Inside the domain of heterogeneous granodiorite, there are several localities of homogeneous, even-grained to porphyritic granites which in this report are given the common name of Vöyri-type granites. On the basis of age determination from the Isomäki granite, at Vöyri-Maksamaa, they belong to the granites of the 1.88 Ga age group. Ultramafic Ni-critical intrusions have been discovered on the bottom of the Bay of Oravainen in diamond drilling by exploration companies. Metasedimentary rocks in the Evijärvi schist belt, in eastern and southern parts of the map area, are migmatitic. They are mainly psammitic and pelitic mica gneisses with graphite-sulphide interbeds. Metacherts, graphite-sulphide schists and banded metavolcanic rocks dominate in the Simpsiö area and its surroundings. The schist belt also contains several small tonalitic and granitic intrusions and minor volcanic-sedimentary interbeds. Metamorphic grade in the schist area is mainly at amphibolite facies, though in the Kauhava-Kortesjärvi region it has in places increased to granulite facies. Vaasa granite has developed from sedimentary rocks by gradual melting under PT conditions varying between amphibolite and granulite facies. Large volumes of bedrock aggregate are used in the map area to replace glacial gravel as building material. Hence, there are numerous aggregate quarries. The local aggregates are, at best, of moderate quality but still suitable for normal building. High-quality bedrock aggregates have not been detected from the area. The Punakari granite has been quarried for building material outside the mapping area. In addition, small volumes of porphyritic Vaasa granite have been used in building house bases and facades. There are no metal mines, historic or recent, in the area. The nickel deposit under the Bay of Oravainen is the most intensely investigated metal deposit in the map area. The text is in Finnish, with figure and table captions and conclusions in English.