Browsing by study line "Petrology and Economic Geology"

The metamorphosed Kutemajärvi gold deposit is located near the town of Orivesi, at the eastern flank of the Tampere Schist Belt, which constitutes part of the Svecofennian domain of southern Finland, and it is hosted in the volcanic rocks of the Koskuenjärvi formation. Previous isotopic studies have mainly focused on the igneous and metamorphic rocks of the Tampere Schist Belt and only a few of them have presented ages for the area of Kutemajärvi. This study aims to shed light on the timing of mineralization by employing the single-grain U-Pb dating method of monazite and zircon, in order to evaluate the relationship between the ore and its host rocks. Based on the results from the SEM mineral identification, monazite grains are divided into metamorphic and hydrothermal grains. In the case of zircon grains, a third magmatic type has been identified. Results from U-Pb dating of single monazite and zircon grains are well constrained and document four distinct stages of geodynamic evolution in the region. Ages older than 1.91 Ga represent detrital material transported during the stage of rifting that led to the opening of the Tampere basin. Subsequent subduction resulted in active volcanism which is expressed with the extrusion of the Koskuenjärvi formation at 1904 Ma. At the late stages of subduction or at the outset of the collision stage, the subvolcanic Pukala porphyry intruded into the volcanic sequence of the Tampere Schist Belt at 1890 Ma, which provides the maximum mineralization age. Release of hydrothermal fluids, due to the crystallization of the Pukala intrusion caused pervasive hydrothermal alteration of the Kutemajärvi host rocks and deposition of epithermal gold and other elements. However, the participation of hydrothermal fluids, released by high-temperature metamorphism of the lower crust, cannot be ruled out. Ages between 1890‒1878 Ma record the syn-collision stage, during which the deposit, the Pukala intrusion and its adjoining rocks were deformed and metamorphosed at greenschist to lower-amphibolite facies. The majority of ages fall within the 1880‒1878 Ma time-interval, characterizing the metamorphic peak that marks the culmination of the Svecofennian orogeny and provides a minimum age of the mineralization. This major orogenic event is partly overlapped by the collision of the Central Svecofennian Arc Complex with the Southern Svecofennian Arc Complex that transpired at 1880‒1860 Ma, as indicated by ample age data. Monazite and zircon also yield lower ages (<1860 Ma), which record retrograde metamorphic and subordinate cooling events, and resonate recurring tectonothermal activity, associated with the syn- and post-collisional magmatism of Southern Svecofennia and the emplacement of rapakivi intrusions in southern Finland. Single-grain U-Pb dating of monazite and zircon from polished thin sections, in tandem with collation of the obtained ages with earlier published data, establishes a spatial and temporal framework with respect to the tectonometamorphic evolution of the Kutemajärvi gold deposit and the Tampere Schist Belt. Precise temporal constraints substantiate the intricate geological history of the area and can be used to discriminate magmatic, metamorphic and hydrothermal events, with a view to breaking ground on the exploration of other epithermal deposits in the metamorphic terranes of southern Finland.

Aim of this study is to develop biogeochemical exploration methods for cobalt. Several different samples were collected from study area, analyzed, and compared to each other. This study took place at Rautio village at North Ostrobothnia and more accurately over the Jouhineva mineralization. Jouhineva is well-known high-grade cobalt-copper-gold mineralization. Elements examined in this study are cobalt, copper, arsenic, zinc, selenium, and cadmium. Samples were collected from three different study profiles from the area. From these three profiles samples collected are: soil, pine, lingonberry, birch, rowan, and juniper. Water samples were collected around the study area from every location possible. Soil samples were analyzed with four different methods: Ionic leaching, aqua regia, weak leaching and pXRF. Ionic leaching and aqua regia had both elevated concentrations of cobalt, but in different locations depending on study profile. Ionic leaching detects rising ions from the ore and therefore elevated concentrations are found at different locations compared to aqua regia. Aqua regia results proved how different orientation of study profile, direction of the ore and glacial flow can affect to the anomalies of elemental concentration. Profile-2 was oriented differently to ore and glacial flow than Profile-1, and therefore elevated concentrations of cobalt and copper were not drifted away from the ore on Profile-2 like they were on Profile-1. Aqua regia and pXRF have very similar copper, arsenic and zinc results. Pine and lingonberry turn out to be the most promising plant species applied for cobalt exploration, and rowan appears to be most suitable for copper exploration. Lower detection limit could significantly improve pine analyses as exploration method and more extensive sampling could remove some of the uncertainties about the method. Lingonberry samples have elevated concentration of copper and arsenic. Birch and juniper produced somewhat unclear results. Despite this, cobalt and copper concentrations in birch leaves were elevated when compared to concentrations found in other studies. In addition to this birch is suitable for arsenic exploration. Juniper had elevated copper concentration in the study area compared to other studies. Water samples collected from the Jouhineva area yielded concentrations of cobalt, copper and arsenic that were above the average concentration in the Kalajoki area waters. Copper and arsenic were above the average concentration of the Kalajoki area in every sample collected from the study area. Cobalt was above the average concentration in all samples that were not collected directly from the pond formed in the old test mine. Zinc concentration was below the average limit in all samples collected from the area. Zinc concentration in the water samples collected from the pond is significantly lower compared to the other samples collected from the area.

Aijala-Metsämonttu volcanogenic massive sulphide ore deposit belongs to Orijärvi regional volcanogenic massive sulphide mineralisation, localised within the schist zone southwestern Finland. Aijala-Orijärvi zone is an island-arc structure formed during the Paleoproterozoic (1895-1891 Ma). The mining operation in Aijala took place in 1949–1958 and Metsämonttu in 1952–1958 and 1964–1974. The Aijala and Metsämonttu deposits were 1 km apart. The main ore types were massive vein-like pyrite, sphalerite, pyrrhotite, chalcopyrite, and galena. The purpose of this thesis was to produce modern geological 3D models of the Aijala and Metsämonttu volcanogenic massive sulphide ore deposits and numerical grade models of the utilised minerals (copper, lead, zinc, silver, and gold) using historical material and to interpret the occurrences and emplacements of precious metals and base metals. In addition, compare the accuracy of the 3D models with digitised historical material. Geological 3D and numerical grade models were created using implicit modelling. Historical data used in this thesis consist of 266 drill holes from Aijala and 274 drill holes from Metsämonttu. Also, 61 mine tunnel maps and 47 cross-sections were used to create the geological models. The Aijala-Metsämonttu volcanogenic massive sulphide ore deposits are in the same stratigraphic zone between the footwall quartz-feldspar-porphyry and hanging wall amphibolite. Sulphide lenses of both deposits are vertically on the south side of the footwall and hanging wall contact. The main host rocks to sulphide ores are skarn and cordierite-gneiss. Several local faults intersect the deposits. The most significant faults displaced overlying blocks to the south in Aijala and to the north in Metsämonttu. The Aijala-Metsämonttu deposit belongs to the Zn-Pb-Cu group. The occurrence style and concentrations of metals vary between deposits. Copper ore is present in Aijala but absent in Metsämonttu, whilst zinc-lead ore is present in Metsämonttu but absent in Aijala. Precious metals occur in both deposits with a companion of base metals. The Metsämonttu deposit is rich in precious metals compared to the Aijala deposit, and the presence of high content of precious metals correlates with the incidence of lead ore. Precious metals concentrations increase from east to west and deeper in Metsämonttu.

This study consists of a comprehensive characterization of the geology, geochemistry, alteration, and mineralization at the Ronaldo prospect as well as an evaluation of its ore potential. Previous mapping campaigns of the prospect, which lies in the Central Andes in Peru at an elevation of 4300 metres, have identified intrusions overlain by a volcanic package. The intrusions are crosscut by silicified ridges that host epithermal mineralization. Satellite imagery reveals that the topographically elevated areas exhibit strongly altered rocks identified as an advanced argillic-altered lithocap. The methods used to define and better understand the geology and the evolution of the hydrothermal system included reconnaissance field mapping, whole-rock geochemistry, short-wave infrared spectroscopy, petrography, and geochronology. Previous studies have shown that only high-sulfidation epithermal mineralization can be spatially and temporally linked to porphyry Cu mineralization, and therefore this study investigates – among other aspects – what type of epithermal mineralization is present at Ronaldo in order to evaluate the potential for concealed at-depth porphyry Cu mineralization. Two separate lower Miocene intrusive units were identified, a porphyritic diorite and a porphyritic granodiorite, whose average age difference is 1.79 Ma. The intrusive units display intermediate argillic alteration. The overlying extrusive units are Sacsaquero Formation basaltic andesites and ignimbrites that are either unaltered or display propylitic alteration. The basaltic andesite roof pendants observed at Ronaldo indicate that the tops of the intrusions are preserved. At high elevations, advanced argillic alteration composed of pyrophyllite, kaolinite, and dumortierite was observed. This area is the remnant, deeper zone of a larger lithocap. The steeply dipping silicified ridges that display sericitic alteration were inferred to be the root zone of this lithocap. Elevated values of trace elements such as Te, Bi, As, and Sb suggest that the Ronaldo prospect is mostly situated in a sericitic alteration zone related to a porphyry-like magmatic-hydrothermal source located at greater depth. Isolated magnetite aggregates were observed in magmatic-hydrothermal breccia, which indicates that the sericitic alteration may have overprinted potassic alteration. A few intermediate-sulfidation epithermal veins and porphyry-related veins, including a banded molybdenite quartz vein, were observed in the creek near the major fault. At Ronaldo, high silica content and sericitic alteration correlate well with elevated concentrations of Ag, Au, and Mo, whereas Cu concentration does not correlate well with any alteration type or with silica content. Quartz veinlets in the silicified ridges that host abundant Ag and Au mineralization were interpreted to have formed at a slightly later stage and to be unrelated to the magmatic-hydrothermal system. This mineralization was interpreted to be low-sulfidation epithermal in origin due to features such as abundant adularia, lattice-textured bladed calcite replaced by quartz, crustiform banding, banded quartz-chalcedony veins, druse-lined cavities, and high Ag/Au ratios. In conclusion, the Ronaldo prospect comprises a hydrothermal system in which the deep, root zone of an advanced argillic lithocap is exposed. The exploration potential for low-sulfidation epithermal mineralization in the silicified ridges is rather significant, whereas the potential for porphyry Cu mineralization is minor due to the lack of appreciable Cu and Mo mineralization, typically shallow-depth porphyry-related hydrothermal alteration, and the lack of high-sulfidation epithermal mineralization.

Kimberlites are a primary source of diamonds. However, not all kimberlites contain diamonds, let alone in the abundance that enable economically profitable exploitation. To assess the diamond potential of kimberlites, the study of kimberlite/diamond indicator minerals (i.e. mantle-derived xenocrysts) can be utilized. In this study the diamond potential of Liqhobong kimberlite cluster in Lesotho, Southern Africa, was studied. Indicator mineral grains (chromian diopside, garnet, chromite, ilmenite) from Liqhobong kimberlites were analysed for major and minor elements using electron microprobe. Results were used to examine formation conditions (P/T) and chemical characteristics of indicator minerals, to define local geotherm and diamond window and to provide general overview to diamond potential of the Liqhobong kimberlite cluster. Based on single clinopyroxene thermobarometry (using Cr-diopside grains as a thermobarometer), the local Liqhobong geotherm is estimated to be ~41 mW/m². It corresponds reasonably accurately to the reference geotherm 40 mW/m², which is widely considered being a decent “average” geotherm at Kaapvaal-Kalahari Craton area. Analysed xenocrysts are principally from the peridotitic source rock. Geochemistry of the indicator minerals show that there is a significant diamond potential in Liqhobong kimberlites. Specifically, Ni-in-garnet thermometry, using the formation depth of the G10 garnets combined to the relevant 40 mW/m² reference geotherm, displays the existence of a significant diamond window at the depth interval of ~140-230 km below the Liqhobong area.

Vulkaanisten kaarten magmaattinen aktiivisuus nostaa maankuoren lämpötilaa ja laskee sen kestävyyttä, mutta näiden muutosten suuruutta tai muutosten erinäisiä tekijöitä, kuten latenttilämpöä, sulamisesta aiheutunutta viskositeetin laskua sekä intruusioiden koostumusta, lämpötilaa ja sulan määrää ei ole laajemmilta osin tutkittu. Pro gradu tutkielman tarkoitus on kvantifioida näitä kuoressa tapahtuvia muutoksia sekä tutkia erinäisten tekijöiden vaikutusta kallioperän kestävyyteen, kuten sitä kuinka kestävyys muuttuu lämpötilan nousun seurauksena kiinteässä tilassa verrattuna siihen miten se muuttuu kiven sulaessa. Näitä näkökulmia tutkitaan mallilla, joka perustuu kaksiulotteiseen lämpöyhtälöön, joka ratkaistaan differenssimenetelmällä. Kuoren kestävyyden muutoksia lasketaan sarjalla yksiulotteisia kuoren kestävyyskriteerimalleja. Kivien sulamislämpötilat saadaan termodynaamisella ohjelmalla, joka laskee sulafraktiot eri paine ja lämpötilaolosuhteissa ja näitä sulia käytetään hyväksi mallissa, joka laskee efektiivisen viskositeetin osittain sulaneelle kivelle. Kuoren kestävyyttä ja lämpötilan muutoksia tarkastellaan tekemällä useampia simulaatioita, jotka jäljittelevät magmaattisen kaaren vulkanismia. Maankuoren integroitu kestävyys laskee magmakammioiden läheisyydessä jo muutaman miljoonan vuoden kuluttua ~80 % eikä tämä arvo muutu huomattavasti jatkuvan magmaattisen aktiivisuuden seurauksena. Magmakammioita ympäröivä maankuori kuitenkin jatkaa heikentymistä koko magmaattisen aktiivisuuden ajan (10 Ma) eikä tämä ei ole ainoastaan seurausta hitaasta lämmönjohtumisesta. Magmaattisen aktiivisuuden päätyttyä maankuori jäähtyy ja kiteytyy, jolloin intruusioiden mekaaniset ominaisuudet saattavat joko heikentää tai kestävöittää kallioperää suhteessa maankuoren alkuperäiseen kestävyyteen riippuen intruusioiden ja niitä ympäröivän kiven mekaanisista ominaisuuksista. Mafiset intruusion kykenevät kestävöittämään kallioperää helpommin syvemmällä, missä kuori alun perin deformoitui plastisesti, kun taas felsiset intruusiot kykenevät mekaanisesti heikentämään maankuorta matalammilla syvyyksillä. Pitkällä aikavälillä intrudoituvan magman lämpötila on vähemmän tärkeä tekijä kuoren kestävyydelle, kuin intruusioiden mekaaniset ominaisuudet. Kiven sulamisella ei näytä olevan huomattavaa vaikutusta kuoren kestävyyden muutoksiin. Suurin osa simulaatioista osoittaa, että kuoren integroitu kestävyys on pudonnut jo yli 99.9 % lämpötilan nousun seurauksena ennen kuin kuori alkaa sulamaan. Jopa äärimmäisimmissä skenaarioissa kuoren sulamisesta aiheutuva integroidun kestävyyden lasku pysyy pääsääntöisesti 0.5 % alapuolella. Mitä enemmän magmassa on sulaa, sitä suurempi vaikutus latenttilämmöllä on kuoren lämpötiloihin. Magmaattisen aktiivisuude aikana intrudoituvalla magmalla minkä sulamäärä on 10–100 %, latenttilämmön osuus lämpötilan noususta on 12–34 %. Latenttilämpö vaikuttaa enemmän kuoren kestävyyteen magmakammioiden läheisyydessä ja laskee kuoren kestävyyttä enemmän magmaattisen aktiivisuuden päätyttyä. Maximissaan latenttilämmöstä aiheutunut kuoren integroidun kestävyyden lasku on 10–30 % magmakammioiden läheisyydessä ja keskiarvo on 5–17.5 % 50 km säteellä magmakammioista, riippuen magman alkuperäisestä sulan määrästä. Tektoniikan kannalta on tärkeää ymmärtää miten magmaattinen aktiivisuus vaikuttaa maankuoren kestävyyteen. Maankuori on heikoimmillaan suoraan magmakammioiden läheisyydessä magmaattisen aktiivisuuden aikana, joka saattaa aiheuttaa paikallisia muutoksia kuoren deformaatiossa ja hiertovyöhykkeiden muodostumisessa, mutta pitkällä aikavälillä intruusioiden koostumus ja niiden mekaaniset ominaisuudet saattavat vaikuttaa huomattavasti kuoren kestävyyteen. Koska kuoren sulamisesta aiheutunut viskositeetin lasku ei ole huomattava tekijä kuoren kestävyydelle, niin muut magmaattiseen aktiivisuuteen ja vulkanismiin liittyvät tekijät ovat todennäköisesti tärkeämmässä osassa, kuten kiven sulamiseen liittyvä tiheyden lasku ja tilavuuden kasvu, joka taas johtaa uusiin maankuoreen syntyviin jännityskenttiin, kallioperän murrosten syntymiseen sekä magman liikkumiseen.

The Kiimala Trend in Central Ostrobothnia, western Finland hosts orogenic gold de-posits. According to earlier studies conducted in the area by the GTK and Ou-tokumpu Exploration, the orogenic gold deposits contain varying amounts of gold ranging from 1.19 to 2.5 ppm and minor amounts of sulfides. In the Kiimala Trend area, the gold deposits of interest are Kiimala, Ängesneva, Vesiperä, and Pöhlölä. Fel-sic porphyries located in these areas are host rocks for orogenic gold, but little petro-logical and mineralogical information on the porphyries exists, and the available in-formation lacks both details and up-to-date data. During this study, the rocks in the Kiimala trend were mainly categorized as plagio-clase porphyries, plagioclase-porphyritic amphibolites, amphibolites, schists, sulfide veins, and diorites. Geochemically the rocks represent various types of gabbros and diorites. The rocks have been metamorphosed in amphibolite facies conditions during the Svecofennian orogeny. During the metamorphic events, low-salinity hydrothermal fluids altered the rocks resulting in saussuritization, sericitization, alkalization, calcifi-cation, epidotization, and chloritization. Hydrothermal fluids also caused the minerali-zation of gold-, iron-, arsenic-, and copper-bearing sulfides as well as the mineraliza-tion of various metals, most common being bismuth, lead, electrum, silver, and anti-mony. Common oxides are rutile that appears often as rims surrounding ilmenite, and hematite that is associated with hydrothermal veins. Most sulfides and oxides can be found as inclusions or in association with quartz and feldspars, exception being ilmen-ite, that can be found in biotite or chlorite.

The Paleoproterozoic (1.87 Ga, ɛNd -3.7) Suvasvesi granitoid intrusion in southeastern Finland is considered to be a part of the Heinävesi intrusive suite. Inner parts of the lithologically zoned Suvasvesi intrusion are variably alkali feldspar porphyritic biotite granitoid rock and the margins are composed of a more biotite-rich equigranular granitoid rock variety. The Paleoproterozoic metasedimentary rocks of the Viinijärvi suite adjacent to the Suvasvesi intrusion are intruded by leucocratic pegmatite dikes. Potential sources and possible contamination of the granitoid melt are considered with the help of structural and textural observations, petrography, whole-rock geochemistry, mineral chemistry, and petrophysical data. The data were acquired from 34 rock samples collected during a bedrock mapping campaign and combined with the pre-existing mapping, petrographic, and geochemical data from the Suvasvesi and surrounding areas. The Suvasvesi granitoid intrusion is compared to other members of the Heinävesi suite to verify the hypothesis of their petrogenetic connection. The compositions of both Suvasvesi intrusion and Heinävesi suite are also compared to the potential proximal sources, the adjacent Paleoproterozoic metasedimentary rocks and Archean units in the area. In addition, the compositions of the Suvasvesi intrusion and Heinävesi suite rocks are compared to other granitoids from Eastern and Northern Finland with suggested Archean sources, and to regional granitoids of same age. Based on the similarity of major and trace element compositions, it is suggested that the Suvasvesi granitoid is part of the Heinävesi suite. The granites and granodiorites of the Suvasvesi granitoid and the Heinävesi suite are ferroan, calc-alkalic, and peraluminous with average ASI value of 1.08 (n = 73). Although the Heinävesi suite is postkinematic, it shows very few similarities to other rocks of same age. The εNd values of the Heinävesi suite and the paragneiss enclaves within the Suvasvesi intrusion indicate metasedimentary source component or assimilation. Conversely, the I-type mineralogy and geochemistry suggest igneous/meta-igneous source component for the Heinävesi suite. Potential infracrustal sources for the granitoid magma are the Archean TTGs and amphibolites. The conclusion for the magma source is ambiguous. For further studying additional isotope analyses and thermodynamic modelling of the Suvasvesi and Heinävesi magmas are suggested.

Kaapelinkulma is an orogenic gold deposit located in the Paleoproterozoic Vammala Migmatite Belt (1.91 – 1.79 Ma) in Valkeakoski municipality in Southwestern Finland, and it is considered to have been formed in microcontinent collision during Svecofennian orogeny and has been classified as an orogenic gold deposit. Kaapelinkulma comprises a set of sub-parallel lodes in a tight array hosted within a sheared quartz-diorite unit inside a tonalitic intrusion. Gold occurrence is hosted by an en echelon type sheared quartz-dioritic dyke which forms a large xenolith inside synorogenic tonalite intrusion, surrounded by mica gneiss. It is estimated that Kaapelinkulma gold deposit contains at least, 168 Kt of ore containing 3.8 g/t Au. Textural setting, mineralogical association form and assemblage of gold, sulphides and telluride grains in Kaapelinkulma were studied with field-emission scanning electron microscopy, with electron probe microanalyzer and scanning electron microscopy. Ore minerals observed in Kaapelinkulma are: arsenopyrite, löllingite, pyrrhotite, pyrite and chalcopyrite. Other ore minerals identified are native bismuth, gold, scheelite, bismuth-tellurides and maldonite, which were all found in abundant amounts. Ore minerals occur as dissemination in intergranular spaces between silicate matrix, as polycrystal aggregates in quartz-veins and quartz clusters; and within shear zones. Gold in Kaapelinkulma is present as two generations: as single free native gold grains and as polycrystalline gold aggregates. Polycrystalline gold aggregates are grains formed from several mineral association and their combinations. Most common polycrystalline gold aggregates are formed from combination of: maldonite-native Au, Au-Bi alloys, Au-Ag grains and Au-hedleyite. Single free native gold grains are pure gold or gold-silver alloys. Free native gold grains can be found as intergranular, single grains in silicate matrix and adjacent or as a part of disseminated ore together with polycrystalline gold aggregates, bismuth and bismuth tellurides. Polycrystalline gold aggregates are found in disseminated ore, which are in close contact with quartz-veins and sulphide aggregates, or as inclusions in arsenopyrite-löllingite contact zones- or in other sulphides. Concentration of Au varies in native-gold grain from 76.83 to 97.87 wt% according to EPMA analyzes and from 50.03 to 100 wt% according to FE-SEM analyzes. Minor to moderate amounts of silver and copper were identified within the grains. Grain sizes of gold varies significantly from 7µm2 to 5mm2. Ore mineral paragenesis were observed to start when arsenopyrite and löllingite crystallized first, followed, partly simultaneously by pyrrhotite, pyrite and chalcopyrite. This was followed by crystallization of maldonite, first occurrence of native gold and bismuth, bismuth-tellurides, hedleyite and finally tellurides and main occurrence of gold. General ore forming process in Kaapelinkulma has been open space filling.

Tiivistelmä/Referat – Abstract The Geological Survey of Finland (GTK) conducted extensive bedrock mapping and sampling along the southern border of the Central Finland Granitoid Complex (CFGC) between 2016–2017. The 40000 km2 complex was formed during the early stages of the 1.92–1.77 Ga Svecofennian orogeny and is dominated by felsic plutonic rocks. The main crust-forming phase at 1.91–1.87 Ga generated the felsic syn- and postkinematic suites during active subduction. Jyväskylä suite corresponds to the synkinematic rocks (1.89–1.88 Ga) and Saarijärvi and Rautalampi suites to the postkinematic (1.88–1.87 Ga). Previous studies have divided the postkinematic rocks into Types 1, 2, 3a and 3b, of which Types 1–3a represent the Saarijärvi suite and Type 3b the Rautalampi suite. The postkinematic suites are bimodal because of the local mafic association. Volcanic rocks associated to a continental margin setting are especially found along the southern-southwestern margin of the CFGC. Abundant metasediments with a mainly turbiditic origin surround the complex. The purpose of this thesis is to classify the granitoids and dioritoids of the Jämsä region into either the syn- or postkinematic types, discuss their petrogenesis and compare the data to the adjacent volcanic rocks. New petrographical, geochemical and geochronological data are used to set the plutonic rocks into the regional geological framework. Six distinct types are recognized from the study area: Mettisuo, Akkasuo, Linjamaa, Haavistonmäki, Kalaoja and Hangasjärvi. The first three were found to be synkinematic (Jyväskylä) and the last three postkinematic (Saarijärvi) with respect to the orogenic stages. The synkinematic Mettisuo (1890 ± 4 Ma) and Akkasuo-type (1880 ± 6 Ma) equigranular to inequigranular granitoids are metaluminous to peraluminous with Akkasuo being slightly more mafic. They have higher CaO and Sr and lower K2O and FeOt/MgO than the postkinematic types. The Linjamaa-type inequigranular dioritoids represent the Vaajakoski quartz diorite lithodeme (Jyväskylä suite) owing to their more juvenile character. However, there are discrepancies within the Linjamaa division. Partial melting of biotite- and hornblende-rich high-K calc-alkalic rocks by basaltic underplating produced the synkinematic types, leaving behind a granulitic residue. The Haavistonmäki-type (1876 ± 7 Ma) alkali feldspar-porphyritic granites are postkinematic Type 1 with a sedimentary component from the Pirkanmaa migmatite belt. They are peraluminous with low Na2O and FeOt/MgO and high FeOt and Al2O3. The Kalaoja-type inequigranular to porphyritic granitoids are transitional between postkinematic Types 2 and 3. The lack of fluorite and pyroxenes complicate the classification. They are metaluminous to peraluminous with relatively low FeOt, MgO and CaO and higher FeOt/MgO and K2O. The Hangasjärvi-type (1885 ± 5 Ma) granitoids are silica-rich, resembling postkinematic Type 2. They differ from the Kalaoja rocks by their equigranular to inequigranular character, but the same mineralogical restrictions apply in the classification. A mantle-derived basaltic magma assimilated variable amounts of the lower crust, producing the postkinematic magmas. A depleted granulitic residue likely does not produce sufficient amounts of K2O and LILE contents for the postkinematic magmas. The postkinematic types are bimodal because of the locally associated mafic rocks. The volcanic rocks of the study area belong to the same continental subduction environment, are locally coeval and share a partially similar origin as the Jyväskylä suite and the mafic members of the Saarijärvi suite.