Browsing by discipline "Geologia"

Kalliojärvi, Ania and Erkkilä gold deposits are located in the Pirkanmaa migmatite belt in southern Finland. Nearest city is Tampere, approximately 15 km northeast of the deposits. The native gold occurs with sulphide dissemination in quartz veins and shear zones in hydrothermally altered mica schist, gneiss and granite-pegmatite intrusions and black schist. Black schist is common in Erkkilä deposit. Tourmaline pegmatite is common in Ania deposit. Gold grades are in the range of 0,1-26,7 g/t. The peak of metamorphism has reached upper amphibolite fasies in Erkkilä deposit (K-feldspar + sillimanite isograd). In Kalliojärvi the metamorphic index mineral is staurolite, which indicates middle amphibolite facies conditions. In Ania the metamorphism has progressed to the lower amphibolite facies stability field of garnet. These metamorphic associations indicate pressure of 8 kb to 6 kb and temperature of 790 to 525 °C. The hydrothermal alteration is strong in the mineralized zones, demonstrated by silicification and potassium metasomatism, which altered feldspars to sericite and biotite to chlorite. Plagioclase has also altered to albite and potassium feldspar, epidote and calcite and ilmenite has altered to rutile. In the mineralisation process fluids have enriched in the same ore forming elements in all three deposits. These elements include Fe, Cu, Ni, Co, Au, Ag, Hg, Pb, Bi, Sb, Te, S, Se, As. The major ore minerals are arsenopyrite, löllingite, pyrrhotite, pyrite and chalcopyrite. Other ore minerals are native bismuth, gold, bismuth tellurides, maldonite and oxide minerals. The major ore forming process has been open space filling. The ore minerals have crystallized as disseminations in intergranular spaces between silicates and carbonates, in quartz- and epidote-clinozoisite veins and walls of the fluid channels. The arsenopyrite geothermometry shows crystallization temperature from 438 to 609 °C with pyrrhotite and löllingite. The sulfur activity (logS2) has been from -3,70 to -8,30. Fluids transported gold predominantly as a reduced sulphur complex and a thioarsenide complex. The first generation native gold is intergrown and as inclusions in arsenopyrite and in grain borders of composite löllingite and arsenopyrite grains. The second generation native gold occurs as open space fillings in the gangue fractures, intergranular spaces between silicates and as inclusion in potassium feldspar and sulphides, Bi-, Sb- Te-minerals and metallic bismuth. The main crystallization of native gold and tellurides took place in the epizonal temperature range from 150 to 300 °C. According to the mineral liberation analyses in Ania the grain size of gold, 86,10 wt. %, is from 32 to 106 µm, in Erkkilä 98,22 wt. % is from 32 to 355 µm and in Kalliojärvi 76,02 wt. % is from 32 to 106 µm. In heavy mineral concentrates gold occurs as free grains and also intergrown with arsenopyrite and bismuth. A small portion of gold is as inclusions in other minerals in arsenopyrite and silicates. The mineralisation and crystallization of the ore minerals is epigenetic i.e. it was active after the last metamorphic event in shear zones of the host rock. All three gold deposits have crystallized after a complex, accretionary to collisional orogenic evolution of Svekofennian. The ore mineral crystallization occured in the hypozonal-epizonal temperature range from 600 to 150 °C.

Tässä tutkimuksessa perehdytään CMP-luotauksen teoriaan ja käytäntöön maatutkaluotausten profiililinjojen syvyyskalibroinnissa. CMP-luotaus on Suomessa harvoin käytetty nopeusanalyysimenetelmä ja tutkimuksessa haluttiin selvittää CMP-luotauksen tuomia mahdollisuuksia. Tutkimuskohteet sijaitsevat Etelä-Suomessa, Helsingissä ja Hollolassa. Tutkimuskohteet valikoitiin toisistaan poikkeavan geologian vuoksi. Patolassa metsässä maakerrokset olivat pääosin moreenia ja kalliomaata. Tattarisuon pohjavesialueella kerroksissa vaihtelivat hiekkaiset ja saviset kerrosrakenteet. Hollolan deltamuodostumalla maakerrokset vaihtelivat karkeasta sorasta hiekkaan. Sekä Tattarisuolla että Hollolassa saatiin myös aineistoa pohjavesikerroksesta. Kohteissa tehtiin sekä profiililuotaukset että CMP-luotaukset. Tutkimuksissa hyödynnettiin Malå:n ja GSSI:n maatutkalaitteistoja, joita käyttökokemuksen perusteella vertailtiin myös keskenään. CMP-luotauksella saatuja kerrosnopeuksia verrattiin kohteiden referenssiaineistoihin, keskiarvoiseen 0,1 m/ns:n nopeuteen, taulukkoarvoihin sekä Patolassa hyperbelianalyysin tuottamaan tulokseen. Tulokset olivat rohkaisevia, joskin myös poikkeavia arvoja löytyi. Patolassa haasteena oli moreenin ja rikkonaisen kallionpinnan tunnistaminen profiililuotauksista. Tämä aiheutti hajontaa CMP-luotauksella ja muilla referenssiaineistolla saatujen tulosten välillä. Osa tuloksista oli hyvinkin lähellä referenssiaineistoja, mutta moreeni-kallio-rajapinnan tulkinnan haasteellisuuden vuoksi myös huomattavia poikkeamia saatiin. Tattarisuolla tulkinnan haasteena oli monimutkainen kerrosrakenne ja paikoin profiililuotauslinjoja häiritsevät heijasteet. CMP-luotauksen kerrosnopeudet vastasivat hyvin hiekkaisten kerrosten nopeuksia. Lisäksi CMP-luotauksella voitiin varmistaa luotauslinjalla 2 oleva pohjavesikerros ja että luotauslinjalla 1 pohjavettä ei CMP-luotauksella saatujen nopeuksien perusteella ollut. Hollolassa CMP-luotausaineisto kärsi päällisin puolin huomattavasti häiriösignaaleista. Aineiston prosessoinnin jälkeen saadut kerrosnopeudet vastasivat kuitenkin erinomaisesti referenssiaineistojen kerrossyvyyksiä. Kahden maatutkalaitteiston ja useamman antennikonfiguraation hyödyntäminen profiililuotauslinjoissa mahdollistivat hyvän luotausresoluution niin matalammilla kuin paksummilla kerrospaksuuksilla. Malå:n ja GSSI:n luotauslaitteistot toimivat pääosin hyvin eikä kumpikaan laitteisto ollut selkeästi toista parempi. Tässä tutkimuksessa saadun kokemuksen perusteella CMP-luotauksella voidaan saada merkittävää hyötyä maatutkalinjojen tulkintaan. Kun CMP-luotauksen heikkoudet osataan tunnistaa ja aineiston tulkitsija omaa riittävän hyvän kokemuksen, voidaan CMP-luotauksen avulla tehdyillä syvyyskalibroinneilla saada luotettavia tuloksia tutkimusalueen kerrospaksuuksista.

The Archean Hattu schist belt in eastern Finland is host to several orogenic gold occurrences. One of these deposits is the Pampalo gold deposit located in Hattu, Ilomantsi. Major and trace element characteristics of biotite and chlorite were analyzed from a representative collection of rock types of different degrees of alteration from the Pampalo deposit. The main aim of this study was identifying possible correlation of changes in the elemental composition of biotite and chlorite with distance to gold ore mineralization and testing the two minerals’ use as proxies for mineralization in Pampalo. Biotite and chlorite were chosen for being represented in altered and unaltered ore and adjacent country rock units. Samples were prepared from half and quarter drill core rocks and analyzed with hyperspectral imaging, electron micro probe analysis (EMPA) and laser ablation inductively coupled plasma mass spectrometer (LA-ICP-MS). Hyperspectral imaging and thin section microscopy were used for mineral identification and mineral grain sampling. EMPA and LA-ICP-MS data found weak correlation with distance to mineralization for Mg, Al, Ti, Fe, Zn, Sr and Cs in biotites and Li, B, Mg, Al, Si, P, Sc, Ti, Mn, Fe, Ni, Zn, Ga, As and Sr for chlorite. Moderate correlation was found for Pb and Tl in biotites and Co in chlorites. Strongest correlation was found for Mn, W and Ba in biotites. These three elements all deplete in biotites with decreasing distance to mineralization. Changes in concentrations of manganese are likely variation in host rock chemistry. Tungsten concentrations seem to be linked to fluid flows, but only indirectly related to gold ore mineralization. Barium was found to be the most promising element within biotites due to its high mobility, and its depletion could indicate approaching gold ore mineralization. Changes in As concentrations of chlorites also point to two different types of chlorite grains, one of which indicate an ore mineralization event having taken place.

Dredging of the seafloor is often a prerequisite for keeping seaways and harbours operational in the coastal area of Finland. This leads to a need to transport and dispose of the dredged material, which in turn creates environmental concerns. The influences of sea disposal can usually be clearly observed during the process. There has not been as much research on the long term effects, due to difficulties in observing material at the bottom of the sea and in separating the effects of sea disposal from background conditions and other changes that might have taken place in the area. The objective of this study is to gather research data to help in assessing the effects of sea disposal and defining the preconditions for environmentally sustainable disposal projects. The research focuses on two disposal sites for soft dredged material, located in Naantali and Hamina. The site in Naantali is very close to the mainland and a busy harbour, with heavy sea traffic. The site in Hamina is in a location with markedly calmer current conditions, within a scarce archipelago. The effects of the sea disposal were examined three years after the disposal operation. Special attention was paid to how well the disposed material had remained at the disposal sites. Surface sediment samples were taken from both study areas. Based on sedimentation signals observed in these samples, the study aims to determine how well the disposed material had remained in place. The movements of the material were also assessed by observing the topographical changes that had taken place at the sites over three years. The study additionally utilizes monitoring reports and previous research to assess the identified effects on the environment and the factors that influence them in the context of the Baltic Sea area. According to the results, the disposal site at Hamina is an exemplary one, because the disposed material has settled and become part of the existing seafloor. The material is also physically of a superior quality to the original surface sediment, which suffered from oxygen depletion. Sea disposal has managed to isolate the original, heavily oxygen consuming layer of sulphide mud from the bottom water. At the Naantali site, the disposed material appears to have stabilized rather well, but the result is not as obvious as at Hamina. This is largely due to the strong slipstreams in the area causing resuspension of the surface mud. Furthermore, characterization of the disposed material was relatively difficult at the Naantali site due to the strong physical resemblance between original and disposed sediment. Surface sediment samples and basic physical characterization proved to be a useful method in researching the settling of disposed material. When looking for possible signs of sedimentation, the topmost surface layer of samples is especially important. Depth data can also be used in monitoring disposal sites, although based on depth data alone it is difficult to draw conclusions on the reasons for changes in topography.

The Paleoproterozoic volcanically hosted massive sulfide deposits of the Skellefte district, northern Sweden has been subjected to regional metamorphism in greenschist to amphibole facies conditions at 1.84 – 1.82 Ga, resulting in the remobilization of ore minerals and formation of ore-bearing quartz and sulfide veins. The aim of this project is to study the mineralogy and mineral chemistry of the Storliden VHMS deposit in the Skellefte district and determine the conditions the remobilization of ore minerals took place in. The sulfide-rich remobilization veins in the deposit consist of two types: ones composed mostly of pyrrhotite and chalcopyrite, and ones composed mostly of galena and bournonite, often as symplectitic intergrowths, with gudmundite and tetrahedrite occurring in notable amounts as well. Arsenopyrite and sphalerite were found in multiple veins of both types. Additionally, sulfide-poor quartz- and calcite veins occur in the deposit. There are also sulfide-bearing calcite veins that post-date the metamorphism, and were not included in this study. Sphalerite and chlorite from the veins both have lower Fe-content than same minerals in the massive ore and the host rock of the ore, respectively. Sphalerite form the veins also has a significantly higher Cd-content compared to the massive ore. The tetrahedrite from the veins also has a clearly different composition than in the massive ore, with considerably lower As-content and higher Fe/(Fe+Zn) ratio. Arsenopyrite geothermometry was used to determine that the remobilization took place at temperature of 325 – 480 °C, with mean T of 425 °C for the massive ore and 412 °C for the remobilization veins. The composition of sphalerite from the massive ore was used to determine that the pressure during metamorphism was 6.3 – 8.5 kbar, with mean of 7.5 kbar. Thermometric data obtained from chlorite in the quartz veins and the host rock of the ore indicates lower temperatures than the data from arsenopyrite, with mean T of around 200 °C or less for the veins and around 300 °C for the host rock (exact temperature depending on the geothermometer used). The lower range of temperatures likely reflects formation or re-equilibration during the retrograde stage of the metamorphism. The δ18O-data for water calculated from the quartz veins range from 4.7 to 8.8 ‰ with mean δ18O of 7.2 ‰, which is within the δ18O-range of metamorphic water. The values for pressure and temperature obtained conform to data reported by other authors from various deposits in the Skellefte district, which mostly fall between temperatures of 300 – 500 °C and pressures of 5 – 8 kbar for the massive ore, and 200 – 450 °C and 0.5 – 5 kbar for the veins. The δ18O-data is likewise within the range reported from quartz veins elsewhere in the Skellefte district (ranging from 3.7 to 11.6 ‰).

Yeniyaylacık and Sofular localities in southeast of Central Anatolia are yielded with rich and wellpreserved late Neogene mammal fossils including bovids, equids, suids and rhinos. Faunal compositions of these sites are distinct from each other and biostratigraphy is still under study. The age and correlation of the Sofular ignimbrite underlying the studied Sofular section has been contentious in previous studies. For Yeniyaylacık section there are no previous detailed ages published. In this study, the magnetostratigraphic results are presented for the Yeniyaylacik and Sofular sites. The sampled Sofular section (located in 38°43’35” N, 35°00’30” E) is overlaying the Sofular Ignimbrite. In total 83 samples were taken from this ca. 51-meters-thick section, which is composed of thinly bedded and laminated siltstones and siliceous claystones with a few sandstone intercalations. Upper parts are more calcareous and dominated with limestone and claystone beds containing gypsum crystals. In total 32 samples were taken from ca. 8-meters-thick Yeniyaylacık section (located in 38°45’35” N, 34°37’04” E), comprised of muddy-clayey sediments with few thin limestone-sandstone units interbedded in the succession. Grain size of the samples was estimated based on Udden-Wentworth scale and color based on Munsell color chart. Carbonate content of the samples was estimated using 10 % hydrochloric acid. Magnetic susceptibility of each sample was measured using SM 150 susceptibility meter. 2G SQUID magnetometer was used to stepwisely demagnetize the samples. Thermomagnetic analyses were done using KLY-3S kappabridge for selected samples to identify magnetic mineralogy of the sections. Rock magnetic studies revealed that samples located at higher levels were clearly less magnetic in both of the sections, which correlates well with the increased carbonate content. Magnetic mineralogy of the samples consists mostly of Ti-poor titanomagnetite, but some of the samples also contained some hematite. AF-demagnetization results indicated that reversed polarity dominates the lower ca. 15 m in the Sofular section. The upper 35 m of the section is dominated by normal polarity. In the Yeniyaylacık section, reversed polarity dominates the whole section. Based on earlier studies and paleomagnetic results from this study, correlation with chron C4n.2n (8,1–7,7 Ma) or C3An.2n (6,7–6,4 Ma) is suggested for the long period of normal polarity in Sofular section. Less derived morphology of the Yeniyaylacık fauna suggests older age for the Yeniyaylacık fauna, so correlation with chron C4r (8,8–8,1 Ma) is suggested for long period of reversed polarity in the Yeniyaylacık section.

Mustaliuskeet ovat tummia ja helposti rapautuvia sedimenttikiviä, jotka sisältävät runsaasti hiiltä ja metallisulfideja. Niiden rapautuessa ympäristöön vapautuu metalleja ja vetyioneja. Turpeen on todettu sitovan tehokkaasti eri alkuaineita ja läheisestä kallioperästä rapautuneet metallit pidättyvät usein turpeeseen. Talvivaaran mustaliuskeisiin on rikastunut Co, Cu, Mn, Ni ja Zn, ja esiintymälle on tunnusomaista kohonnut Ni-pitoisuus. Mustaliuskealueiden moreeneista on mitattu korkeita Cu- ja Zn-pitoisuuksia, ja pintavesille on tyypillistä alhainen pH ja kohonneet Cd-, Cu-, Mn-, Ni- ja Zn-pitoisuudet. Liuskealueilla myös kaivovesistä ja purosedimenteistä on mitattu kohonneita pitoisuuksia samojen alkuaineiden osalta. Tähän tutkimukseen koealoilta otettiin turvenäytteitä, joista määritettiin turvelaji, maatuneisuus ja sähkönjohtavuus. Laboratoriossa näytteistä määritettiin tuhkapitoisuus TGA-menetelmällä ja kokonaishiilen määrä CHN-menetelmällä. Näytteille tehtiin myös monialkuaineanalyysit ICP-MS (503M)- ja ICP-AES (503P)- menetelmillä, ja Hg- pitoisuus määritettiin CVAFS-analyysillä. Tuloksista laskettiin pistekohtaisesti painotetut keskiarvot ja -hajonnat, sekä koealakohtaisesti Spearmanin korrelaatiokertoimet PASW Statistics 18-ohjelmalla. Osalle aineistosta tehtiin regressioanalyysi. Kartat tehtiin ArcGIS10-ohjelmistolla Geologian tutkimuskeskuksen ja Maanmittauslaitoksen kartta-aineistojen pohjalta. Mustaliuskealueilla turpeiden keskimääräiset Al-, As-, Cd-, Co-, Fe-, Mn-, Ni-, S-, Zn- ja tuhkapitoisuudet ovat huomattavasti korkeammat kuin granitoidi- ja kvartsiittialueilla, kun taas Cu- ja U-pitoisuudet ovat mustaliuskealueilla huomattavasti alhaisemmat. Tuhka- ja alkuainepitoisuudet ovat kvartsiitti- ja granitoidialueilla kohonneita lähinnä pohjanäytteissä, kun taas mustaliuskealueilla monien alkuaineiden pitoisuudet ovat korkeita myös pintanäytteissä. Parhaimmat riippuvuudet havaittiin Cu- ja U-pitoisuuksien, sekä Cr- ja tuhkapitoisuuksien välillä. Mustaliuskealueilla merkittäviä riippuvuuksia oli havaittavissa As-, Fe-, S- ja tuhkapitoisuuksien välillä, mikä voisi olla yhteydessä mustaliuskeiden rautasulfideihin. Poikkeuksellisesti yhdellä kvartsiittialueen koealalla alkuainepitoisuudet muistuttivat mustaliuskepisteitä. Tämä saattaa johtua osaltaan voimakkaasta reunavaikutuksesta, mutta koealalle on myös saattanut kulkeutua mustaliuskepitoista materiaalia jäätikkökuljetuksen seurauksena. Eräällä mustaliuskekoealalla alkuainepitoisuudet ovat sitä vastoin poikkeuksellisen alhaisia. Tämä johtunee turpeen rahkavaltaisuudesta, heikosta kontaktista kallioperään tai sijainnista vedenjakaja-alueella. Mustaliuskealueilla turpeiden alkuainepitoisuudet näyttäisivät olevan suurelta osin yhteydessä Talvivaaran mustaliuske-esiintymän koostumukseen, ja joillakin tutkimuspisteillä erilaiset mustaliuskeiden mineralisaatiot voisivat kuvastua anomaalisina Mn-, Ni-, Zn- ja Fe-pitoisuuksina. Turpeen kemialliseen koostumukseen saattaa kallioperän lisäksi vaikuttaa erilainen turvelajikoostumus mustaliuske- ja granitoidipisteiden välillä, voimakkaampi reunavaikutus mustaliuskekoealoilla, tulvavaikutus tai tien läheisyys. Lisäksi joillakin alkuaineilla epävarmuutta voi aiheuttaa niiden geokemiallinen luonne. Ympäristössä Cu lähtee heikosti liikkeelle ja se pidättyy nopeasti humukseen. Siten Cu ei välttämättä ehdi kulkeutua kallioperästä turpeeseen asti. Zn sitä vastoin on hyvin liikkuva, mutta se pidättyy heikosti turpeeseen. Jatkotutkimuksissa kannattaisi tarkastella keskenään mahdollisimman samankaltaisia turvemaita, jotka eivät ole altistuneet ihmistoiminnalle, tulville tai muille ulkoisille häiriötekijöijlle.

This work explores the lateral spreading of hot, thick, Paleoproterozoic crust via a series of 2D thermomechanical numerical models based on two geometrical a priori models of the thickened crust: plateau and plateau margin. High Paleoproterozoic radiogenic heat production is assumed. The material viscosity is temperature-dependent following the Arrhenius law. The experiments use two sets of rheological parameters for the crust: dry (granite/felsic granulite/mafic granulite) and wet (granite/diorite/mafic granulite). The results of the modeling are compared to seismic reflection sections and surface geological observations from the Paleoproterozoic Svecofennian orogen. Numerical modelling is performed with Ellipsis, a particle-in-cell finite element code suitable for 2D thermo-mechanical modelling of lithospheric deformation. It uses Lagrangian particles for tracking material interfaces and histories, which allow recording of material P-T-t paths. Plateau-models are based on a 480 km long section of 65 km-thick three-layer plateau crust. In the plateau margin-models, a transition from 65 km thick plateau to 40 km thick foreland is imposed in the middle of the model. The models are extended symmetrically from both ends with slow (1.9 mm/a) and fast (19 mm/a) velocities. Gravitational collapse is simulated with an additional set of fixed boundary plateau margin models. The models are studying the effect of free moving boundaries on the crustal structure and the conditions for mid-crustal flow. Strong mid-crustal channel flow is seen in plateau margin models with dry rheology and slow extension or with fixed boundaries. With fast extension or wet rheology channel flow grows weaker/diminishes. In models with slow extension or fixed boundaries, partial melting controls the style of deformation in the middle crust. Vertical movement of the partially molten material destroys lateral flow structures in plateau regions. According to P-T-t paths, the model materials do not experience high enough temperatures to match HT-LP metamorphic conditions typical for Svecofennian orogenic rocks. Metamorphic conditions in the dry rheology models have counterparts in the LT-LP (>650 °C at ≤600 MPa) amphibolite facies rocks of the Pielavesi area. Plateau margin models with dry rheology and slow extension or fixed boundaries developed mid-crustal channel flow, thinning of middle crust, exhumation of mid-crustal domes and smooth Moho, all of which are found in crustal scale reflection sections. Results of this work suggest plateau margin architecture prior to extension that took place at slow velocities or through purely gravitational collapse, although peak temperature of Svecofennian HT-LP metamorphism was not attained.

The Cu-Rautuvaara iron-oxide copper gold (IOCG) deposit is located in the western part of the Central Lapland Greenstone belt. Cu-Rautuvaara and several other IOCG deposits are located next or within of the SSW-NNE trending Kolari-Pajala Shear Zone. Deposits are formed in the contacts of the ca. 1860 Ma Haparanda Suites monzonite-diorite intrusions and the >2050 Ma Savukoski Group supracrustal rocks. At Cu-Rautuvaara deposit Cu-Au ore is hosted by magnetite-disseminated albitite. Host rocks for the other deposits in the Kolari area are skarns and ironstones. The wall and the host rocks are hydrothermally altered. Alterations can be roughly divided to proximal and distal zones which are displaying widespread and irregular alteration zones. The distal alteration is characterized by albite ± biotite ± K-feldspar and the proximal alteration albite + magnetite ± phlogopite ± gedrite ± amphibolite ± sulphides ± clinopyroxene. Based on the mass balance calculations Zr, TiO2 and Al2O3 were immobile during the alteration. Calculations indicated that main gains for albitites were Na2O, Fe2O3, Cu and Ni. For diorites and metavolcanites gains were CaO, K2O, Ce and Ba. Albitite protolith determination by its texture and mineral assemblage is unreliable because of the intense hydrothermal alteration. Based on immobile element correlation data suggest that metavolcanites are the most preferential protolith for albitites. The main oxide in the deposits is magnetite, which locally has accessory ilmenite exsolved from it. The main sulphides are chalcopyrite, pyrite and pyrrhotite. Oxides and sulphides element contents were determined by electron microprobe analyses. Based on analyses Au occurs as native Au-Ag grains in chalcopyrite. Major trace element in pyrrhotite is Ni (0.1– 0.8 wt. %). Based on major trace elements there are two types of pyrites with Co (<3 wt. %) and Ni (<3.5 wt. %). Major trace elements in magnetites are Al2O3 (0.01 – 0.71 wt. %), V2O (<0.23 wt. %) and Cr2O3 (<0.27 wt. %). Some magnetites have also MnO (<0.18 wt. %) as trace element. The trace element contents and ore mineral textures suggest that there were two stages of mineralization events for both sulphides and oxides.

Gold from orogenic deposits represents one third of the world's total gold production. Most orogenic gold ores contain significant amounts of barren waste rocks that are costly to process. The aim of this work was to evaluate the potential of sensor-based sorting (SBS) of quartz vein hosted orogenic gold ores. Jokisivu is an orogenic gold deposit operated by Dragon Mining Oy. A diorite to gabbro intrusion host the ore body that is located in Häme-belt near to Pirkanmaa belt, which are characterized by metamorphic sedimentary and igneous rocks. The deformed and boudinaged quartz vein ore zone thickness varies from centimeters to few meters and is constrained to a shear zone in WNW-ESE- and WSW-ENE- directions. Variably thick pegmatite veins occur often in close contact within the ore zone. The statistical diamond drill core database evaluation showed a clear correlation between gold and quartz veins. According to the drill cores photos auriferous quartz veins and barren host rocks have sharp visually observable contacts. The quartz rocks are white and diorite waste rocks are black. From the two development ores bulk samples were collected: one 18-ton marginal-grade sample from the Arpola ore body and 29-ton high-grade sample from the Kujankallio ore body. A jaw crusher was used for primary crushing. The bulk samples were crushed and screened, which resulted in an approximately 50/50 coarse to fine particles ratio. Over 1.5 tons of screen overflow (> 30 mm) was sampled for SBS tests. Additionally 900 kg of underflow were collected for a secondary sorting study. The SBS tests were done at Tomra in Germany. PRO (Processing) series chute-type optical sorter was used. It divides a conditioned materials feed to ore and waste rocks by color difference. A rock was sorted waste if its surfaces contained less than two percent white pixels. Similarly five percent sorting threshold was tested. Results showed that 41 – 61 wt% of waste was removed from the marginal-grade Arpola ore with 96 % to 93 % gold recovery. In addition, the gold grade improved from 5.1 ppm to 8.2 – 12.0 ppm. The high-grade Kujankallio ore showed 15 – 31 wt% waste rock removal and 97 to 92 % gold recoveries. The gold grade rose from 7.2 ppm to 8.2 – 9.6 ppm. In addition, the quality of the products improved when harmful minerals such as arsenopyrite and pyrrhotite were reduced. Hand sorting was used for evaluation of the SBS results. Approximately 1.5 tons of sorted rocks were classified according to increasing quartz-vein content and the rock type features. The hand sorting showed that optical sorting is sensitive and adjustable even to subtle materials features. The diorite waste, altered rocks and low-grade quartz rocks were easily separated from the sorting feed material. The gold concentration in the waste rocks was low in the Arpola SBS sample (0.5 – 0.6 ppm) and slightly higher in the Kujankallio sample (0.8 – 1.7 ppm) Economic evaluation of SBS is challenging, because a valid calculation needs to account for the entire production chain from mining to tailings handling. Decreased waste rock dilution (WRD) has the most significant impact on economy as it reduces milling, transportation and tailings costs. More importantly, a significant reduction in mill capacity requirements is achievable by SBS. Numerous positive effects of sorting are significant increment in head grade, homogenous feed, various environmental aspects, decreased chemicals and water usage. The SBS is suitable for marginal- and low-grade orogenic gold ores where sharp and detectable contact between the ore and waste rocks exists. The results indicate that certain low-grade deposits, which were previously considered uneconomic mineralizations, are convertible to ore by SBS. In Brownfield mines, SBS can allow the utilization of the marginal mineral resources more accurately. Greenfield projects may benefit from smaller concentrator sizes and time related savings, which reduce CAPEX costs. The economic benefits are always case dependent.