Semi-automated geological mapping and target generation from geochemical and magnetic data in Halkidiki region, Greece

This study focuses on using multivariate analyses to generate semi-automated geological maps and exploration targets associated with porphyry Au-Cu mineralization within the Kassandra mining district, Greece. We use principal component analysis (PCA) and self-organizing maps (SOM) to reveal variations in geochemical and magnetic signatures within the input datasets. We visualize the results as pseudo-geological maps reflecting the associated geological processes and their end products. In specific, we utilize the potential of these two methods through an integrated interpretation and comparison of the results. We test the validity of the unsupervised PCAand SOM-derived lithological and prospectivity models by comparing them with existing geological observations and interpretations. The results of this investigation show that both PCA and SOM are able to reproduce the key features of existing geological observations within the study area, but more importantly, also provide useful information that can be used to recognize prospective geological units and exploration targets from previously unknown locations.Peer reviewe

Constraints over the age of magmatism and subsequent deformation for the Neoarchean Kukkola Gneiss Complex, northern Fennoscandia

The Archean crust in northern Fennoscandia preserves a fragmentary geological record, making direct correlation among Archean domains challenging. This study presents two new zircon U-Pb age determinations from the Archean Kukkola Gneiss Complex (KGC) that straddles the border between Finland and Sweden. The results indicate that crystallization of tonalites within the magmatic core of the complex occurred at 2711 +/- 8 Ma, somewhat earlier than previously considered. A new pulse of magmatism occurred at 2675 +/- 10 Ma as demonstrated by hornblende-tonalites cutting the 2.71 Ga rocks. The results further indicate that the first deformation event responsible for development of penetrative foliations occurred after the first magmatic event at 2.71 Ga and prior to the subsequent tectonothermal event at 2.68 Ga. These findings are in concert with the known major periods of magmatism (2.8-2.7 Ga) and deformation (2.7 Ga) within better-known Archean domains in northern Fennoscandia, and hence support their correlation with KGC. Three complementary age determinations on the Haparanda-suite granites and tonalites were conducted: the results indicate crystallization ages of 1.90-1.89 Ga, overlapping with the known age range of the suite and supporting its predominance over the 1.8 Ga Lina suite granites in the Tornio-Haparanda area.Peer reviewe

New digital learning materials for teaching in geosciences

Non peer reviewe

Semi-automated geological mapping and target generation from geochemical and magnetic data in Halkidiki region, Greece

This study focuses on using multivariate analyses to generate semi-automated geological maps and exploration targets associated with porphyry Au-Cu mineralization within the Kassandra mining district, Greece. We use principal component analysis (PCA) and self-organizing maps (SOM) to reveal variations in geochemical and magnetic signatures within the input datasets. We visualize the results as pseudo-geological maps reflecting the associated geological processes and their end products. In specific, we utilize the potential of these two methods through an integrated interpretation and comparison of the results. We test the validity of the unsupervised PCAand SOM-derived lithological and prospectivity models by comparing them with existing geological observations and interpretations. The results of this investigation show that both PCA and SOM are able to reproduce the key features of existing geological observations within the study area, but more importantly, also provide useful information that can be used to recognize prospective geological units and exploration targets from previously unknown locations

Constraints over the age of magmatism and subsequent deformation for the Neoarchean Kukkola Gneiss Complex, northern Fennoscandia

The Archean crust in northern Fennoscandia preserves a fragmentary geological record, making direct correlation among Archean domains challenging. This study presents two new zircon U-Pb age determinations from the Archean Kukkola Gneiss Complex (KGC) that straddles the border between Finland and Sweden. The results indicate that crystallization of tonalites within the magmatic core of the complex occurred at 2711 +/- 8 Ma, somewhat earlier than previously considered. A new pulse of magmatism occurred at 2675 +/- 10 Ma as demonstrated by hornblende-tonalites cutting the 2.71 Ga rocks. The results further indicate that the first deformation event responsible for development of penetrative foliations occurred after the first magmatic event at 2.71 Ga and prior to the subsequent tectonothermal event at 2.68 Ga. These findings are in concert with the known major periods of magmatism (2.8-2.7 Ga) and deformation (2.7 Ga) within better-known Archean domains in northern Fennoscandia, and hence support their correlation with KGC. Three complementary age determinations on the Haparanda-suite granites and tonalites were conducted: the results indicate crystallization ages of 1.90-1.89 Ga, overlapping with the known age range of the suite and supporting its predominance over the 1.8 Ga Lina suite granites in the Tornio-Haparanda area

Structural evolution and strain partitioning within the Palaeoproterozoic Peräpohja Belt, northern Finland

Peräpohjan vyöhyke koostuu arkeeisen Pudasjärven kompleksin päälle kerrostuneista paleoproterotsooisista suprakrustisista kivistä, jotka ovat poimuttuneet ja hiertyneet sedimenttialtaan inversiossa. Vyöhykkeen stratigrafia on suhteellisen hyvin tunnettu, mutta alueen malmipotentiaalistakaan huolimatta perusteellista koko vyöhykkeen kattavaa rakennegeologista analyysiä ei ole aiemmin tehty. Tämän työn tarkoituksena on systemaattinen Peräpohjan vyöhykkeen deformaatiotyylien, rakennegeologisen kehityksen ja deformaation jakautumisen analyysi, jota voidaan käyttää esimerkiksi laajempien kuoren kehityksen tulkintojen ja malminetsinnän kohdentamisen apuna. Työhön liittyvän maastokartoituksen aikana tutkittiin noin 500 havaintokohdetta ja mitattiin yli 1000 geologista rakennetta. Käytössä oli myös aiemmista havainnoista koostuva tietokanta, jonka laatua tarkistettiin kartoitusten yhteydessä. Pisteaineiston lisäksi käytössä oli koko vyöhykkeen kattavasti erilaisia geologisia karttoja, geofysiikan rasteriaineistoa (magneettiset, sähkömagneettiset ja Bouguer-anomaliat), digitaalinen korkeusmalli ja jonkin verran timanttikairausaineistoa. Aineistojen pohjalta laadittiin paikkatieto- ja 3D-ohjelmissa rakennegeologisia muotoviivakarttoja ja poikkileikkauksia, jotka toimivat paikallisten ja koko vyöhykkeen kattavien rakennetulkintojen sekä rakennegeologisen analyysin tukena. Erilaisten rakennetulkintojen lisäksi varsinkin vyöhykkeen pohjoisosien stratigrafisiin yksiköihin tehtiin suuria korjauksia ja yksiköiden välisiä korrelointeja. Peräpohjan vyöhykkeen monimutkaiset ylityöntörakenteet ovat syntyneet pitkittyneen samansuuntaisen tektonisen pääpuristussuunnan seurauksena, jossa kompleksin rakenteen syntyä kontrolloivat vaihtelevien tektonisten suuntien sijaan arkeeisen pohjan lohkorakenteiden aiheuttamat paikalliset jännityskentät. Noin itä-läntinen tai koillis-lounainen suuri siirrosvyöhyke jakaa Peräpohjan vyöhykkeen kahtia. Siirroksen eteläpuolen merkittävät rakenteet liittyvät thin-skinned-tyyliseen deformaatioon, jossa vyöhykkeenlaajuinen hiertopinta erottaa stratigrafian ylä- ja alapuoliset osat rakenteellisesti toisistaan. Sen sijaan siirroksen pohjoispuolta vallitsevat thick-skinned-tyyliset rakenteet, joissa siirrokset alkavat arkeeisesta pohjasta jatkuen pitkälle ylempiin stratigrafisiin yksiköihin. Ensimmäiset thin-skinned tyyliset rakenteet syntyivät jo deformaation alkuvaiheessa, mutta thick-skinned-rakenteet aktivoituivat suuremmassa mittakaavassa vasta selvästi myöhemmin.The Peräpohja Belt comprises Palaeoproterozoic supracrustal rocks deposited on the faulted and subsided Archean Pudasjärvi Complex. The Peräpohja Belt was folded and sheared during the following basin inversion. The stratigraphy of the belt is relatively well known but, despite the potential for mineral deposits, the area is still missing a thorough analysis of the geological structures. This work aims at providing a systematic analysis of the deformation style, structural evolution and strain partitioning of the Peräpohja Belt. The results can be further used in wider-scale interpretations on crustal evolution and in refining the prospectivity models of the Peräpohja Belt. During the field mapping of this work, some 500 outcrops were examined and over 1000 individual geological structure orientations were measured. The most critical parts of a database consisting of earlier observations were verified during the mapping, and several geological maps, geophysical raster data (magnetic, electromagnetic and Bouguer anomalies), digital elevation model and a few diamond drill core logs were also used in the work. Based on available data, structural form-line maps and cross-sections were made in GIS and 3D software and further used in belt-scale structural interpretations and structural analysis. In addition to new structural interpretations, major revisions to stratigraphical units and their inter-correlations were made especially on the northern side of the Belt. The complex fold-and-thrust patterns of the Peräpohja Belt were formed during a single prolonged tectonic event. Instead of highly varying belt-scale stress orientations, the complex structure mostly results from localized stress fields caused by block structures of the Archean basement. A large E-W- or NE-SW-trending fault zone cuts the belt in half, with southern side expressing structures mainly controlled by thin-skinned deformation, whereas the northern side is dominated by thick-skinned features originating deep in the basement. The earliest thin-skinned structures already formed during the beginning of the compressional deformation, but the thick-skinned structures were clearly mostly activated during later stages

Linkage of crustal deformation between the Archaean basement and the Proterozoic cover in the Peräpohja Area, northern Fennoscandia

Constraints from restoration of minor rift-related faults preserved from subsequent Palaeoproterozoic overprint along the southern margin of the Peräpohja Belt, northern Fennoscandia indicate local NE-SW extension directions prevailed at the time of 2.44 Ga rifting of the Archaean continent. This palaeostress field is attributed to pull-apart setting of the Peräpohja Belt at a left overstepping zone of major sinistral N-S trending deformation zones. Consequently, the variably overprinted NW-SE trending structures of the Peräpohja Belt, including the NW-SE central graben were originally generated as normal faults. The proposed setting is compatible with a conducted reconnaissance sandbox analogue model where the orientation of the major normal faults was controlled by the ambient stress field within the step-over zone between strike-slip faults. By contrast, the faults bounding E-W to ENE-WSW trending basement horsts are the result of reactivation of older basement structures underlying the pull-apart basin. Based on the results, we infer that the final break-up of the Archaean continent in northern Fennoscandia utilized the 2.44 Ga rift-related NW-SE trending crustal anisotropy (parallel with dyke swarms), with pre-existing Archaean N-S trending structures reactivated as second-order shear zones in-between. The voluminous syn-rift 2.5-2.4 Ga and later pulses of mafic magmatism (2.32-1.98 Ga) are considered indicative of active-type rifting which onset was controlled by a mantle plume centred within a supercraton formed by the Superior, Hearne and Karelian (-Kola) cratons. The presented model supports the continuity of the Archaean craton beyond the Caledonian Orogen towards north-west and explains its segmentation, suggesting a model for the localization of the Palaeoproterozoic supracrustal belts of Northern Fennoscandia. Moreover, this paper provides an approach to understand the basement-cover relationships and the structural signatures within these relatively shallow supracrustal belts which are highly prospective for mineral deposits.</p

2.45 Ga break-up of the Archaean continent in Northern Fennoscandia: Rifting dynamics and the role of inherited structures within the Archaean basement

Constraints from restoration of minor rift-related faults preserved from subsequent Palaeoproterozoic overprint along the southern margin of the Peräpohja Belt, northern Fennoscandia indicate local NE-SW extension directions prevailed at the time of 2.44 Ga rifting of the Archaean continent. This palaeostress field is attributed to pull-apart setting of the Peräpohja Belt at a left overstepping zone of major sinistral N-S trending deformation zones. Consequently, the variably overprinted NW-SE trending structures of the Peräpohja Belt, including the NW-SE central graben were originally generated as normal faults. The proposed setting is compatible with a conducted reconnaissance sandbox analogue model where the orientation of the major normal faults was controlled by the ambient stress field within the step-over zone between strike-slip faults. By contrast, the faults bounding E-W to ENE-WSW trending basement horsts are the result of reactivation of older basement structures underlying the pull-apart basin. Based on the results, we infer that the final break-up of the Archaean continent in northern Fennoscandia utilized the 2.44 Ga rift-related NW-SE trending crustal anisotropy (parallel with dyke swarms), with pre-existing Archaean N-S trending structures reactivated as second-order shear zones in-between. The voluminous syn-rift 2.5-2.4 Ga and later pulses of mafic magmatism (2.32-1.98 Ga) are considered indicative of active-type rifting which onset was controlled by a mantle plume centred within a supercraton formed by the Superior, Hearne and Karelian (-Kola) cratons. The presented model supports the continuity of the Archaean craton beyond the Caledonian Orogen towards north-west and explains its segmentation, suggesting a model for the localization of the Palaeoproterozoic supracrustal belts of Northern Fennoscandia. Moreover, this paper provides an approach to understand the basement-cover relationships and the structural signatures within these relatively shallow supracrustal belts which are highly prospective for mineral deposits.</p