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  • 501. Weihed, Pär
    et al.
    Schöberg, Hans
    Swedish Museum of Natural History.
    Age of porphyry-type deposits in the Skellefte District, northern sweden1991Ingår i: Geologiska föreningens i Stockholm förhandlingar, ISSN 0016-786X, Vol. 113, nr 4, s. 289-294Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The Skellefte District in northern Sweden consists of metamorphosed Lower Proterozoic submarine volcanic, sedimentary, and intrusive rocks. Several massive sulphide deposits occur in the volcanics, and several small porphyry-type deposits exist in the oldest granitoids, which are coeval with the volcanics. The volcanic rocks have been dated previously at 1.88 Ga while the oldest granitoids have an age of 1.89 Ga. The aim of this study was to establish the timing of the porphyry systems. For this purpose, an intrusive quartz-feldspar porphyry, associated with the Tallberg porphyry-type deposit, has been dated. The U-Pb zircon age is 1886+15-95 Ma which is within the error limits of both the host tonalites (the oldest Jrn granitoids) and the lower Skellefte volcanic rocks, hosting the massive sulphides. While the massive sulphide deposits were formed on the 1.88-1.89 Ga old, early Proterozoic seafloor, the porphyry-type deposits formed farther north inside the marginal arc, both types of deposit occuring in a tectonic regime similar to modern destructive plate margins

  • 502. Weihed, Pär
    et al.
    Vaasjoki, Matti
    Geological Survey of Sweden.
    Regional implications of an age determination of a gneissose granitoid south of the Skellefte District, northern Sweden1993Ingår i: Geologiska föreningens i Stockholm förhandlingar, ISSN 0016-786X, Vol. 115, nr 2, s. 189-191Artikel i tidskrift (Refereegranskat)
  • 503.
    Weihed, Pär
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    Weihed, J. Bergman
    Geological Survey of Sweden.
    Sorjonen-Ward, P.
    Geological Survey of Finland.
    Matsson, B.
    Boliden AB.
    Post-deformation, sulphide-quartz vein hosted gold ore in the footwall alteration zone of the Palaeoproterozoic Långdal VHMS deposit, Skellefte District, northern Sweden2002Ingår i: GFF, ISSN 1103-5897, E-ISSN 2000-0863, Vol. 124, nr 4, s. 201-210Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The Palaeoproterozoic, c. 1.88 Ga old Långdal VHMS deposit is situated in the eastern part of the Skellefte District, northern Sweden. In the stratigraphic footwall to the VHMS ore a sulphidequartz vein system with high gold grades was mined in the second half of the 1990’s. The Långdal VHMS ore is hosted by the uppermost part of the Skellefte Group volcanic rocks, close to the contact with an overlying fine-grained sedimentary unit. Regional structural studies indicate that bedding surfaces in volcanic rocks are parallel to the contact between the volcanic and the sedimentary rocks. Based on the differences in structural style on each side, the contact is interpreted as a major structural break. The Långdal ore is situated close to this break that may have focussed fluid flow during metamorphism and deformation. The orientation of the contact indicates that it either is a D2 structure or that it was at least active during D2. The structural development in the altered footwall rocks to the Långdal VHMS ore indicates that gold-bearing sulphide and sulphide-quartz veins both pre- and post-date the first deformation. Gold associated with the vein system can thus not only be attributed to syngenetic exhalative or replacement processes. The close spatial relationship with the massive sulphide deposits suggests, however, that the gold was remobilized from these syngenetic systems. It is concluded that sulphides were introduced at several stages during the geological evolution of the area as: a) syngenetic disseminations of sulphide and folded, pre-S1 stringer sulphide±quartz veins in the footwall related to the syngenetic VHMS deposit, b) syn-S1 sulphide veins in the footwall gold ore, c) main, post-S1, sulphide-quartz veins associated with the gold ore in the footwall rocks to the Långdal VHMS deposit, and d) post-S1 to pre-S2 galena and sphalerite rich veins post-dating the main, post-S1, sulphide-quartz vein system in the footwall to the Långdal ore. From these relationships it is suggested that gold was re-mobilized from the sulphide rich parts of the VHMS system into post-D1 structures during or slightly after the peak metamorphism. The timing of this event is poorly constrained to post-date the syngenetic ore emplacement by 20–80 m.y.

  • 504.
    Weihed, Pär
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    Weihed, Janette Bergman
    Uppsala University.
    Sorjonen-Ward, Peter
    Geological Survey of Finland.
    Structural Evolution of the Björkdal Gold Deposit, Skellefte District, Northern Sweden: Implications for Early Proterozoic Mesothermal Gold in the Late Stage of the Svecokarelian Orogen2003Ingår i: Economic geology and the bulletin of the Society of Economic Geologists, ISSN 0361-0128, E-ISSN 1554-0774, Vol. 98, nr 7, s. 1291-1309Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The Björkdal gold deposit is situated in the eastern part of the Paleoproterozoic Skellefte district in northern Sweden. The Skellefte district constitutes a 1.89 to 1.88 Ga volcanic arc with numerous volcanic massive sulfide deposits and lode gold deposits of which the Björkdal deposit is the largest, at ca. 20 Mt with 2.5 g/t Au. The gold at Björkdal is associated with centimeter- to meter-wide, subvertical quartz veins at the northwestern contact between a quartz-monzodioritic to tonalitic intrusion and the surrounding supracrustal rocks. The main quartz veins strike north-northeast, and a minor set of veins strike east-northeast. The quartz veins terminate against a major thrust duplex at the contact between the intrusion and the structurally overlying supracrustal rocks. The mylonitic thrust zone has a 20° to 40° dip toward north and trends approximately east-west. A few kinematic observations indicate reverse to obliquely reverse slip on the thrust. Deformed quartz veins exist in lithons between thrusts within the duplex. In the mine, the quartz veins in the footwall to the thrust are spatially and temporally associated with moderately to steeply west dipping reverse shear zones with a northeast strike. It is suggested here that the quartz veins and the steep reverse shear zones are related to the thrust duplex and formed more or less simultaneously. Fluid inclusion and isotopic results from previous studies indicate that juvenile magmatic fluids were responsible for the precipitation of quartz and sulfides at moderate temperatures and pressures. Furthermore, titanites from the quartz veins give ages of ca. 1.78 to 1.79 Ga, whereas the host pluton is dated at ca. 1.90 Ga, indicating a time gap of over 100 m.y. between the emplacement of the host rock and titanite growth in quartz veins. The regional deformation and metamorphism are poorly constrained in the area to some time between 1.87 and 1.80 Ga. As the quartz veins are virtually undeformed and do not exhibit metamorphic fluid inclusions or other evidence of premetamorphic origin, we interpret the titanite ages in the quartz veins as the age of emplacement of the veins. The ca. 1.78 to 1.79 Ga age is also constrained for the crustal-scale, north-south–striking shear zones in the area, and it is suggested here that the thrust duplex and steep reverse shear zones in the mine are third-order structures related to east-west shortening at ca. 1.80 Ga. Gravity data from the Björkdal area indicate the presence of a less dense body at depth beneath the Björkdal pluton. The geophysical signature is best explained by the presence of a 1.80 Ga Skellefte-type intrusion at depth. Magmatic fluids from this S-type granite may have interacted with the host pluton and precipitated gold in the more competent pluton during the east-west shortening. The common occurrence of scheelite in the quartz veins is further evidence for magmatic fluids derived from a younger pluton at depth.

  • 505.
    Westhues, Anne
    et al.
    Department of Earth Sciences, Memorial University of Newfoundland.
    Hanchar, John M.
    Department of Earth Sciences, Memorial University of Newfoundland.
    Whitehouse, Martin J.
    Department of Geosciences, Swedish Museum of Natural History, Stockholm.
    Martinsson, Olof
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    New constraints on the timing of host-rock emplacement, hydrothermal alteration, and iron oxide-apatite mineralization in the Kiruna District, Norrbotten, Sweden2016Ingår i: Economic geology and the bulletin of the Society of Economic Geologists, ISSN 0361-0128, E-ISSN 1554-0774, Vol. 111, nr 7, s. 1595-1618Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    High spatial resolution zircon U-Pb geochronological data obtained directly on the Kiirunavaara iron oxide-apatite (IOA) deposit, related orebodies, and host rocks provide new constraints on the timing of mineralization in these deposits. These data raise new arguments in the debate of a magmatic versus hydrothermal/metasomatic genesis of these major (2,500 Mt, 30-70 wt % Fe) Paleoproterozoic deposits. The main orebody at Kiirunavaara contains Ti-poor magnetite and minor (0.05-5 wt % P) apatite, located between a trachyandesite footwall and a rhyodacite hanging wall, which also hosts smaller orebodies (Nukutus, Rektorn, and Tuolluvaara). The pervasive Na and K metasomatism in the host rock is documented by whole-rock geochemical data and cathodoluminescence (CL) microscopy. Zircon U-Pb data for the metavolcanic rocks in the footwall and hanging wall cluster between 1884 ± 4 and 1880 ± 3 Ma. In the footwall, a syenite-aplite system yields ages of 1880 ± 7 and 1881 ± 4 Ma; a granite pluton exposed underground has an age of 1874 ± 4 Ma. Zircons in two ore samples, never directly dated before this study, yield ages of 1877 ± 4 and 1874 ± 7 Ma. Brecciation at the contacts between the ore and host rocks, the tight age at ca. 1880 Ma for most volcanic and plutonic rocks in the footwall and hanging wall, and the marginally younger age for ore at ca. 1877 to 74 Ma, matching the age of the spatially related granite pluton, suggest a magmatic-hydrothermal emplacement model for the Kiruna area IOA ores

  • 506.
    Wiberg Steen, Tobias
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser.
    Genetic relationships and origin of the Ädelfors gold deposits in Southeastern Sweden2018Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
    Abstract [sv]

    Ädelfors ligger ca 17 km öster om Vetlanda, Jönköpings län, i det N-S strykande Transskandinaviska granit och porfyrbältet och är en del av det NÖ-SV strykande 1,83-1,82 Ga Oskarshamn-Jönköpingsbältet (OJB) bildad i en kontinental subduktionszon i kanten av den Svecofenniska kontinentalplattan. I denna kontinentalbåge ligger Vetlanda supergruppen som är en metasedimentär del av OJB bestående av starkt folierad 1,83 Ga metagråvacka, metasandsten och metakonglomerat med inlagringar av mafiska och felsiska vulkaniter.

    Ädelfors gruvfält består utav ca. 330 kvartsgångar förande mestadels guld men också koppar. Järnmineraliseringar i form av bandad järnmalm finns också i området. Geologin, mineralogin och pyritens kemiska sammansättning från järngruvorna Nilssons järngruva (NFE) och Fe-gruvan (FE), koppargruvan Kamelen (KM) och guldgruvorna Brånadsgruvan (BR), Adolf Fredriks gruva (AF), Gamla Krongruvan (GKR), Gamla Kolhagsgruvan (GKO), Thörngruvan (TH), Nya Galongruvan (NG), Stenborgs gruva (ST), Tyskgruvan (TG), Hällaskallen (HS) och Fridhem (FR) har undersökts för att finna eventuella genetiska likheter. Svavelisotopförhållande har fastställts för pyrit från AF, FE och KM.

    Strukturellt kan gångarna delas in i ett antal grupper. AF, GKR, ST, NG, TH och möjligtvis NFE stryker 10-70° och stupar 55-70°. BR, GKO och KM stryker 110-140° och stupar 80-90° medan TG och HS stryker 90-110° och stupar 85°. Fridhem stryker 70° och stupar 80°. En klorit-kvarts-sericit-biotitrik metapelit utgör värdbergarten i alla gruvor förutom; FR där den utgörs av en beresitiserad felsisk vulkanit rik på plagioklas, sericit, biotit och kvarts med disseminerad pyrit; och NFE, HS, NG vilka har en mafisk tuffitisk moderbergart. Kvartsgångarna är mjölkvita med undantag för FE:s svarta, pyritförande kvarts vilket uppträder som sprickfyllnad i den bandade järnmalmen och är senare bildad. Kvartsen i KM är starkt dynamiskt omkristalliserad. Svag till måttlig foliation är vanlig i sidoberget med undantag av stark foliation i TG och NFE, vilka är lokaliserade i förkastningssprickor med stark kloritförskiffring av värdbergarten. Klorit-, zeolit-, karbonat-, hematit-, amfibol-, kalifältspat-, sericit-, biotit- och epidotomvandling förekommer i majoriteten av lokalerna.

    Malmmineralen är dominerande sprött deformerad subhedral till euhedral pyrit som kataklastiska aggregat eller band, interstitiell kopparkis i pyrit, markasit, magnetkis, guld och sporadiskt kopparkissjuk zinkblände och arsenikkis. I det här arbetet har även tetradymit, staurolit, blyglans och Ce-monazit observerats. Bismutinit och tetradymit i form av inneslutningar i pyrit observerades i AF, GKR, FR och TG. Guld observerades i AF, BR, GKR och TG som inneslutningar i pyrit eller fritt i kvarts med Au/Ag medianvärde på 78,41, avvikande är HS med värden mellan 4,66-5,25.   

    Förhållanden mellan spårelement i pyrit indikerar två typer av pyrit. Typ 1 funnen i FE och KM har följande värden: Co/Ni = 10,94, Bi/Au = 1,79, Bi/S = 0,037, Au/Ag = 11,13, S/Se = 235,96 och As/S = 0,006. Typ 2 funnen i NG, GKO, ST, TH, AF, NFE, HS, GKR, BR, FR, TG och som sliror i KM4 py1 har följande värden Co/Ni = 5,26, Bi/Au = 1,95, Bi/S = 0,031, Au/Ag = 4,19, S/Se = 0 and As/S = 0. δ34S värden styrker denna uppdelning där KM och FE har värdena 1,3-2,6 ‰ och AF 3,6-3,8 ‰.

    Den geologiska utvecklingen av fältet har tolkats som följande: FE-gruvans bandade järnmalm är den tidigaste mineraliseringen vilket följs utav uppsprickning och läkning av kvarts med pyrit typ 1 som också bildar kopparmineraliseringen KM. Senare sprickzoner efter Smålandsgraniternas intrusion läks av kvarts med pyrit typ 2 på mesozonalt djup vilket bildar NG, GKO, ST, TH, AF, NFE, GKR, BR, FR, TG och omkristalliserar och introducerar nya pyritsliror i kvartsen i KM. HS bildas möjligtvis sist eller har blivit omvandlad eftersom den är anrikad på silver. Morfologi, omvandlingar och svavelisotop-signaturer tyder på ett orogent ursprung för Ädelfors guldrika kvartsådror samt den kopparrika kvartsådern i KM.

  • 507.
    Widenfalk, Lennart
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser.
    Corporate strategy, location of investments and competitiveness: the case of Trelleborg/Boliden : comment1992Ingår i: Resources policy, ISSN 0301-4207, E-ISSN 1873-7641, Vol. 18, nr 4, s. 293-Artikel i tidskrift (Övrigt vetenskapligt)
  • 508.
    Widenfalk, Lennart
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser.
    Exhalites and the ore-forming processes in the Skellefte district1986Ingår i: Abstracts: 17e Nordiska geologmötet, Helsingfors universitet, 12-15.5. 1986, 1986Konferensbidrag (Övrigt vetenskapligt)
  • 509.
    Widenfalk, Lennart
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser.
    Kvicksilver som malmindikator vid prospektering1983Ingår i: Berggrundsgeokemi som prospekteringsmetod i Sveriges urberg: föredrag och inlägg från ett symposium i Uppsala [den 17-18 mars 1983] anordnat av Sveriges geologiska undersökning och Svenska gruvföreningen, Uppsala: Sveriges Geologiska Undersökning , 1983, s. 205-206Kapitel i bok, del av antologi (Övrigt vetenskapligt)
  • 510. Widenfalk, Lennart
    Mercury in the Skellefte ore district1981Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
  • 511.
    Widenfalk, Lennart
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser.
    Mercury zoning in the Skellefte ore district illustrated by the Laangsele and Kankberg ore deposits1982Ingår i: Vol. 104, nr 4, s. 372-373Artikel i tidskrift (Övrigt vetenskapligt)
  • 512.
    Widenfalk, Lennart
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser.
    Ore formation and geology of the northern, central part of the Skellefte field, N. Sweden1993Ingår i: Abstracts of lectures and posters: 21:a Nordiska geologiska vintermötet 10-13 Januari 1994 Luleå / [ed] Jan-Anders Perdahl, Luleå: Högskolan i Luleå , 1993, s. 225-Konferensbidrag (Övrigt vetenskapligt)
  • 513. Widenfalk, Lennart
    Provtagning och provtagningsmetoder for berggrundsgeokemiska arbeten1983Ingår i: Berggrundsgeokemi som prospekteringsmetod i Sveriges urberg: föredrag och inlägg från ett symposium i Uppsala [den 17-18 mars 1983] anordnat av Sveriges geologiska undersökning och Svenska gruvföreningen, Uppsala: Sveriges Geologiska Undersökning , 1983, s. 13-19Kapitel i bok, del av antologi (Övrigt vetenskapligt)
  • 514.
    Widenfalk, Lennart
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser.
    Claesson, L.A.
    Naturhistoriska Riksmuseet.
    Skiöld, Torbjörn
    Naturhistoriska Riksmuseet.
    Rocks associated with uplift of a Proterozoic continental margin, N. Sweden1987Ingår i: Proterozoic geochemistry: abstracts, Lund June 3-6 1987, 1987, s. 92-93Konferensbidrag (Övrigt vetenskapligt)
  • 515. Widenfalk, Lennart
    et al.
    Elming, Sten-åke
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    Enmark, Thomas
    A multidisciplinary investigation of the Notträsk Gabbro, northern Sweden1985Ingår i: Geologiska föreningens i Stockholm förhandlingar, ISSN 0016-786X, Vol. 107, nr 2, s. 109-126Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The differentiated, sulfide-bearing gabbro near the city of Boden in northern Sweden has been investigated in order to get a plausible model for its formation, shape and age. The gabbro is associated with a major fault system along which several intrusive bodies occur. The largest of these has been traversed by a gravimetric, magnetometric and geological profile. The investigated intrusion is undeformed and oval-shaped and covers some 20 km2. The outer parts of the body consist of a norite in contact with older meatasediments and granites of varying age. Inside the norite occurs a magnetite-rich gabbro, which forms a ring around the centre of the massif, which in turn consists of leucogabbro-olivine gabbro. Fe, Ti and K are low in the centre where Mg and Cr have their highest contents. Impregnations of sulfides and a massive pyrrhotite vein with some 1 % Ni are located in the norite. A number of intrusion models have been tested by computer modelling combining gravimetric and magnetic field data. The most probable model seems to be a funnel-shaped body pointing downwards. The different gabbro types dip steeply inwards indicating vertical zones rather than horizontal. Palaeomagnetic measurements show that the intrusion has a similar orientation of magnetization as other gabbros of the Haparanda series in northern Sweden (1800-1900 Ga, Rb-Sr). Furthermore, the pole distributions show that the rock cooled slowly, which may indicate that the present outcrop is a deep part of an eroded intrusion. The massif is supposed to have been formed by a diapiric re-emplacement of primary horizontal cumulates formed in the sequence olivine gabbro-leucogabbro-magnetite-bearing gabbro-norite.

  • 516.
    Widenfalk, Lennart
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser.
    Forsberg, Lars-Ole
    MITU.
    PIM - ore geology related to exploration: a national programme1993Ingår i: Abstracts of lectures and posters: 21:a Nordiska geologiska vintermötet 10-13 Januari 1994 Luleå / [ed] Jan-Anders Perdahl, Luleå: Högskolan i Luleå , 1993, s. 226-Konferensbidrag (Övrigt vetenskapligt)
  • 517. Williams, P.
    et al.
    Guoyi, D.
    Pollard, P.
    Broman, C.
    Martinsson, Olof
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    Wanhainen, Christina
    Mark, G.
    Ryan, C.
    Mernagh, T.
    The nature of iron oxide-copper-gold ore fluids: fluid inclusion evidence from Norrbotten (Sweden) and the Cloncurry district (Australia)2003Ingår i: Mineral Exploration and Sustainable Development: Proceedings of the Seventh Biennial SGA Meeting on Mineral Exploration and Sustainable Development / [ed] D.G. Eliopoulos, Rotterdam: Millpress , 2003, s. 1127-1130Konferensbidrag (Övrigt vetenskapligt)
  • 518.
    Winnes, Kaisa
    et al.
    Sveriges Geologiska Undersökning.
    Weihed, Pär
    Antal, Ildiko
    Sveriges Geologiska Undersökning.
    Kartbladen 23J Norsjö2000Ingår i: Regional berggrundsgeologisk undersökning: sammanfattning av pågående undersökningar 1999, Uppsala: Sveriges Geologiska Undersökning , 2000, s. 55-63Kapitel i bok, del av antologi (Övrigt vetenskapligt)
  • 519.
    Wolde, Begashaw
    et al.
    Luleå tekniska universitet.
    Widenfalk, Lennart
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser.
    Petrological and geochemical constraints on cenozoic magnatism in Ethiopia1993Ingår i: Abstracts of lectures and posters: 21:a Nordiska geologiska vintermötet 10-13 Januari 1994 Luleå / [ed] Jan-Anders Perdahl, Luleå: Högskolan i Luleå , 1993, s. 229-Konferensbidrag (Övrigt vetenskapligt)
  • 520.
    Wolde, Begashaw
    et al.
    Luleå tekniska universitet.
    Widenfalk, Lennart
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser.
    The petrology and geochemistry of Ethiopian plateau and rift basalts: Part I, Oligocene and upper Miocene tholeiites1993Ingår i: Vol. 5, nr Suppl. 1, s. 540-Artikel i tidskrift (Övrigt vetenskapligt)
  • 521.
    Yesares, Lola
    et al.
    Department of Geology, University of Huelva, Avenida de las Fuerzas Armadas.
    Aiglsperger, Thomas
    Departament de Cristal·lografia, Mineralogia i Dipòsits Minerals, Universitat de Barcelona.
    Sáez, Reinaldo
    Department of Geology, University of Huelva, Avenida de las Fuerzas Armadas.
    Almodóvar, Gabriel R.
    Department of Geology, University of Huelva, Avenida de las Fuerzas Armadas.
    Nieto, José Miguel
    Department of Geology, University of Huelva, Avenida de las Fuerzas Armadas.
    Proenza, Joaquín A.
    Departament de Cristal·lografia, Mineralogia i Dipòsits Minerals, Universitat de Barcelona.
    Gómez, Carmelo
    Geological Area, Mining Department of Cobre Las Cruces S.A., Gerena, Seville.
    Escobar, Juan Manuel
    Geological Area, Mining Department of Cobre Las Cruces S.A., Gerena, Seville.
    Gold behavior in supergene profiles under changing redox conditions: The example of the Las Cruces Deposit, Iberian Pyrite Belt2015Ingår i: Economic geology and the bulletin of the Society of Economic Geologists, ISSN 0361-0128, E-ISSN 1554-0774, Vol. 110, nr 8, s. 2109-2126Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The Las Cruces deposit is in the eastern end of the Iberian Pyrite Belt (SW Spain). It is currently being mined by Cobre Las Cruces S.A. The main operation is focused on the supergene Cu-enriched zone (initial reserves of 17.6 Mt @ 6.2% Cu). An Au-Ag-Pb–rich gossan resource (3.6 Mt @ 3.3% Pb, 2.5 g/t Au, and 56.3 g/t Ag) occurs in the upper part of the deposit. The Au grade ranges from 0.01 ppm to >100 ppm, and occurs as three different Au ore types: (1) Au mineralization in the upper part of the gossan linked to Fe-oxides lithofacies, (2) Au concentration in the lower part of the gossan associated with leached black shales, and (3) Au ore in the cementation zone related to subvertical fractures.

    A hydroseparation device has been used to obtain heavy mineral concentrates from selected samples of different ore types. Reflected-light microscopy, scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS), and electron probe microanalysis (EPMA) were used to study the separated Au particles. Significant differences between the defined ore types include the Au-bearing lithologies, mineral associations, textural features, particle sizes, morphologies, and fineness. Au-rich minerals include native Au, Au-Ag electrum, and Au-Ag-Hg amalgams. Gold-bearing mineral associations include Pb-oxihalides, Fe-oxides, galena, pyrite, cinnabar, and Ag-sulfosalts.

    The Au enrichment mechanism in the supergene profile involves (1) dissolution of Au from the primary sulfides as chloride-rich ionic complexes during the weathering of the deposit under subaerial exposure; dissolved Au is transported downward through the supergene profile under acidic and oxidized conditions; (2) destabilization of the Au complexes by Fe-controlled redox reactions; as a consequence, coarse-grained, high-fineness Au particles precipitated in association with Fe-oxyhydroxides. This resulted in secondary concentration in the upper gossan; and (3) after deposition of cover sediments took place a progressive change in the system conditions resulting in a later Au remobilization as hydroxidehalide, hydroxide, thiosulfate, and bisulfide complexes in the lowermost gossan and cementation zone. The main pathways for migration of enriched fluids to the cementation zone are secondary permeability zones linked to Alpine reactivated faults. Deposition of Au seems to be related to fluid interaction with reductant lithologies, including black shales and the primary sulfides.

  • 522.
    Yousefi, Fazilat
    et al.
    Department of Petrology and Economic Geology, Faculty of Earth Sciences, Shahrood University of Technology.
    Sadeghian, Mahmoud
    Department of Petrology and Economic Geology, Faculty of Earth Sciences, Shahrood University of Technology.
    Wanhainen, Christina
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    Ghasemi, Habibollah
    Department of Petrology and Economic Geology, Faculty of Earth Sciences, Shahrood University of Technology.
    Frei, Dirk
    Department of Earth Science, Faculty of Natural Science, University of the Western Cape.
    Geochemistry, petrogenesis and tectonic setting of middle Eocene hypabyssal rocks of the Torud–Ahmad Abad magmatic belt: An implication for evolution of the northern branch of Neo-Tethys Ocean in Iran2017Ingår i: Journal of Geochemical Exploration, ISSN 0375-6742, E-ISSN 1879-1689, Vol. 178, s. 1-15Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The Torud–Ahmad Abad magmatic belt is located in the south-southeast of Shahrood (East of Semnan Province, NE Iran) and lies in the northern part of the Central Iran Structural Zone (CISZ), where a thick sequence of Paleocene to middle Eocene volcanic and volcanosedimentary rocks cropped out. This sequence was intruded by numerous dikes, hypabyssal igneous domes and one small gabbrodioritic intrusion, with compositions ranging from trachybasaltic andesite, trachyandesite, dacite, trachyte, gabbro, diorite and syenite. Various enclaves (cogentic and noncogenetic) with different composition, size and shape have been found in these domes and dikes. These enclaves are evidence of magma mixing and crustal contamination. Geochemically, the studied rocks exhibit a calc-alkaline to high potassium calc-alkaline affinity, and are enriched in LREE and LILE and depleted in HREE and HSFE. Other geochemical characteristics, such as a silica content varying between 59–63 wt% and 51–59 wt%, a Na2O content > 3 wt%, Al2O3 content > 16 wt%, Yb < 1.8 ppm, and Y < 18 ppm, make it possible to classify these rocks as high silica adakite in the Ahmad Abad region and low silica adakite in the Sahl-Razzeh region or at least, adakitic like rocks. Also, depletion of Nb and Ti, and high enrichment in Rb, Ba, K and Th, imply crustal contamination of the mentioned adakitic domes. The petrographical and geochemical evidence show that the magma forming of the high silica adakites has been originated from partial melting of the subducted oceanic slab of Neo-Tethys (Sabzevar–Darouneh branch) in amphibolite to eclogite facies and the low silica adakites formed by partial melting of the metasomatized or modified mantle wedge, above the subduction zone. Gabbroic to syenitic rocks are the products of fractional crystallization of basic magma which originated from a nearly non-modified mantle wedge above the subducted oceanic slab. U-Pb dating of the dacitic and andesitic rocks belong to hypabyssal rocks yielded age of 41.4 ± 0.3 Ma, and 35.5 ± 0.2 Ma respectively and consistent to Middle to Late Eocene.

  • 523.
    Yousefi, Fazilat
    et al.
    Faculty of Earth Sciences, Shahrood University of Technology.
    Sadeghian, Mahmoud
    Faculty of Earth Sciences, Shahrood University of Technology.
    Wanhainen, Christina
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    Ghasemi, Habibollah
    Department of Petrology and Economic Geology, Faculty of Earth Sciences, Shahrood University of Technology.
    Lambrini, Papadopoulou
    Department of Mineralogy-Petrology-Economic Geology, Aristotle University of Thessaloniki.
    Bark, Glenn
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    Rezaei-Kahkhaei, Mehdi
    Department of Petrology and Economic Geology, Faculty of Earth Sciences, Shahrood University of Technology.
    Koroneos, Antonis
    Department of Mineralogy-Petrology-Economic Geology, Aristotle University of Thessaloniki.
    Mineral chemistry and P-T conditions of the adakitic rocks from Torud–Ahmad Abad magmatic belt, S-SE Shahrood, NE Iran2017Ingår i: Journal of Geochemical Exploration, ISSN 0375-6742, E-ISSN 1879-1689, Vol. 182, nr A, s. 110-120Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Torud-Ahmad Abad magmatic belt is located 175 km east and southeast of Shahrood in the northern part of the Central Iran Structural Zone and includes a thick sequence of Paleocene to middle Eocene volcanic and volcanosedimentary rocks. This magmatic belt was formed by numerous hypabyssal igneous adakitic domes constituting basaltic andesite, andesite, trachyandesite, dacite, trachydacite, and dacite. The investigated rocks are mainly composed of pyroxene, amphibole, and plagioclase, with minor biotite and opaque minerals. Mineral chemical analysis reveals that plagioclase composition varies from albite to labradorite, clinopyroxene varies from diopside to augite, and amphibole varies from Mg-hastingsite to Mg-hornblende.

    Amphibole geothermobarometry suggests crystallization temperatures of 850–1050 °C, at 2–6 kbar and the temperature of 920–970 °C, at a pressure of 3–4.5 kbar, which are conditions in agreement with andesite and dacite formation. Clinopyroxene crystallized at temperatures of 1020–1170 °C, at 2–10 kbar, indicating crystallization at crustal depths of maximum 30 km for the studied intrusive rocks in the Torud-Ahmad Abad magmatic belt.

  • 524. Zaccarini, Federica
    et al.
    Bakker, Ronald J.
    Garuti, Giorgio
    Aiglsperger, Thomas
    Thalhammer, Oskar A. R.
    Campos, Lolita
    Proenza, Joaquin A.
    Department of Crystallography, Mineralogy, and Ore Deposits, University of Barcelona.
    Lewis, John F.
    Department of Earth and Environmental Sciences, George Washington University, .
    Platinum group minerals in chromitite bodies of the Santa Elena Nappe, Costa Rica: mineralogical characterization by electron microprobe and Raman-spectroscopy2010Ingår i: Boletín de la Sociedad Geológica Mexicana, ISSN 1405-3322, Vol. 62, nr 1, s. 161-171Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    AbstractForty-seven grains of platinum group minerals (PGM) associated with small chromitite bodies of the Santa Elena ultramafic Nappe (Costa Rica) were mineralogically investigated with electron microscope, electron microprobe and Raman spectroscopy. The mineralogical assemblage includes sulfides of the laurite-erlichmanite series (RuS₂-OsS₂), irarsite (IrAsS), osmium, Ir-Rh sulfides containing relevant amounts of Ni, Fe and Cu, and a Ru-As-S compound, possibly ruarsite (RuAsS). Most platinum group element (PGE) sulfides and sulfarsenides represent primary magmatic phases entrapped in chromite at high temperatures, whereas native osmium is probably formed by subsolidus exsolution. The lack of primary PGE alloys suggests relatively high S-fugacity in the chromite forming system. This investigation emphasizes the efficiency of Raman spectroscopy in the identification of PGM of extremely small size, and shows how this technique can be used in revealing distinctive compositional differences among PGM of the laurite-erlichmanite series and irarsite.

  • 525.
    Zaccarini, Frederica
    et al.
    Department of Applied Geosciences and Geophysics, University of Leoben.
    Garuti, Giorgio
    Department of Applied Geosciences and Geophysics, University of Leoben.
    Proenza, Joaquín A.
    Departament de Cristal·lografia, Mineralogia i Dipòsits Minerals, Universitat de Barcelona.
    Campos, L.
    Escuela Centroamericana de Geología, University of Costa Rica.
    Thalhammer, O. A. R.
    Department of Applied Geosciences and Geophysics, University of Leoben.
    Aiglsperger, Thomas
    Departament de Cristal·lografia, Mineralogia i Dipòsits Minerals, Facultat de Geologia, Universitat de Barcelona.
    Lewis, John F.
    Department of Earth and Environmental Sciences, George Washington University, .
    Chromite and platinum group elements mineralization in the Santa Elena Ultramafic Nappe (Costa Rica): Geodynamic implications2011Ingår i: Geologica Acta, ISSN 1695-6133, E-ISSN 1696-5728, Vol. 9, nr 3-4, s. 407-423Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Chromitites associated with strongly altered peridotite from six distinct localities in the Santa Elena ultramaficnappe (Costa Rica) have been investigated for the first time. Santa Elena chromitites commonly display acompositional variation from extremely chromiferous (Cr/(Cr+Al)=0.81) to intermediate and aluminous(Cr/(Cr+Al)=0.54). This composition varies along a continuous trend, corresponding to calculated parental liquidswhich may have been derived from the differentiation of a single batch of boninitic magma with Cr-rich and(Al, Ti)-poor initial composition. Fractional precipitation of chromite probably occurred during differentiation ofthe boninitic melt and progressive metasomatic reaction with mantle peridotite. The distribution of platinum groupelements (PGE) displays the high (Os+Ir+Ru)/(Rh+Pt+Pd) ratio typical of ophiolitic chromitites and, consistently,the platinum group minerals (PGM) encountered are mainly Ru-Os-Ir sulfides and arsenides. Textural relations ofmost of the platinum group elements suggest crystallization at magmatic temperatures, possibly under relativelyhigh sulfur fugacity as indicated by the apparent lack of primary Os-Ir-Ru alloys.The chemical and mineralogical characteristics of chromitites from the Santa Elena ultramafic nappe have astrong affinity to podiform chromitites in the mantle section of supra-subduction-zone ophiolites. Calculatedparental melts of the chromitites are consistent with the differentiation of arc-related magmas, and do not supportthe oceanic spreading center geodynamic setting previously proposed by some authors.

  • 526.
    Zaccarini, Frederica
    et al.
    Department of Applied Geosciences and Geophysics, University of Leoben.
    Tredoux, Marian
    Department of Geology, University of the Free State, Bloemfontein.
    Miller, Duncan E.
    2Department of Geology, University of the Free State, Bloemfontein.
    Garuti, Giorgio
    Department of Applied Geosciences and Geophysics, University of Leoben.
    Aiglsperger, Thomas
    Department of Crystallography, Mineralogy, and Ore Deposits, University of Barcelona.
    Proenza, Joaquin A.
    Department of Crystallography, Mineralogy, and Ore Deposits, University of Barcelona.
    The occurrence of platinum-group element and gold minerals in the Bon Accord Ni-oxide body, South Africa2014Ingår i: American Mineralogist, ISSN 0003-004X, E-ISSN 1945-3027, Vol. 99, nr 8-9, s. 1774-1782Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Two samples from the enigmatic Ni-oxide body of Bon Accord (Barberton greenstone belt, South Africa) have been investigated with the hydroseparation technique to obtain heavy mineral concentrates. The concentrates contain abundant Pt, Pd, and gold minerals never reported before from the Bon Accord Ni-oxide body. The grains occur as: (1) minute inclusions (<3 μm) in trevorite (ideally NiFe3+O4) and (2) larger (5–70 μm) free aggregates liberated from the host phase. The first group comprises several PGM compounds of Pd-Sb, Pd-Sb-As, Pd-Cu-Sb, Pt-Sb, Pt-As-S, Ru-As-S, Ru-S, along with free grains of Ni-Fe-As. The second consists of sperrylite (PtAs2), members of the sobolevskite-kotulskite series, and electrum. These results are in good agreement with previous analyses of PGE-Au in bulk rock. Paragenetic relationships indicate that the PGM and electrum are of secondary origin, probably generated during low-temperature metamorphism of the Ni-rich mineralization. They have a terrestrial origin and are related with a low-sulfidation regime that usually accompanies hydrothermally driven serpentinization of mafic-ultramafic bodies. The ligands in the newly formed PGM (As, Sb, Bi, Te, and O) probably proceed from the same source of the hydrothermal solutions. In this model, the metals Ni-PGE-Au were original components of the primary mineral assemblage of the Bon Accord precursor, whereas As, Sb, Bi, Te, and O might have been contributed by the metasomatizing fluids, during near-surface evolution of the ore body. The data on the high-grade heavy mineral concentrates, obtained by hydroseparation, have provided new knowledge about the mineral deportment of Pd, Pt, and Au.

  • 527.
    Zainy, Maher
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik. Geosurve.
    Geological Report about the Field Work in western part of the Zagros Fold and Thrust Belt, NE Iraq2017Rapport (Övrigt vetenskapligt)
    Abstract [en]

    The studied area is located in the Western part of Zagros Fold and Thrust Belt, northeastern part of Iraq, along the border between Iraq and Iran. It covers an area of about 1600 Km2. It is rugged area, the relief difference ranges from 2526 to 440 m. The high terrain is mainly of structural origin, which is represented by Avroman Range and Qulqula Imbricate structure. The studied area includes twelve geological units of sedimentary rocks, which are ranging in age from Triassic to Late Cretaceous, besides different types of Quaternary sediments. The work, which performed in the area, was field work, which carried out to identify the structural characteristics, via get structural data of the major and minor structures in the area. The field work performed during two periods (Summer-2016 and spring-2017). Performed six geological traverses and studied the structural elements of forty one minor folds during the field work in additional to other minor structures. The goals are build 3D-model for study area using Move and Arc GIS softwares. Moreover, to obtained better understanding of the tectonic history and how many tectonic phases effected the area and explain the relationship between the major and minor structures in the area. The studied area contains a numbers of minor structures that come in different forms, sizes and directions, which indicate their effect in many tectonic phases. Furthermore all most all the structures in the studied area are related with thrusting, which due to the collision between Arabian and Iranian Plates since Miocene till now.

  • 528.
    Zainy, Maher
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    Al-Ansari, Nadhir
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi.
    Bauer, Tobias
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    Ask, Maria
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    The Tectonic and Structural Classifications of the Western Part of the Zagros Fold and Thrust Belt, North Iraq, Review and Discussion2017Ingår i: Journal of Earth Sciences and Geotechnical Engineering, ISSN 1792-9040, Vol. 7, nr 2, s. 71-89Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The Zagros fold and thrust belt represents a tectonically significant area, and one

    of the richest areas in oil and gas reservoirs in the world. The Zagros fold and

    thrust belt is the deformational product of the Cretaceous-present day convergence

    of the Arabian and Iranian (Eurasian) plates (subduction and collision). The belt

    extends more than 2000 km from southern Turkey through the north and

    northeastern Iraq to the Strait of Hormuz in southwestern Iran. The Zagros fold

    and thrust belt is divided into two parts which are; Western part within Iraqi

    region and Eastern part within Iranian region. The western part of the Zagros fold

    and thrust belt has been traditionally subdivided into several structural zones that

    are generally striking parallel to the plate boundary. This is characterized by

    exposure of Late Ordovician to Pliocene - Pliestocene formations with different

    types of Quaternary Sediments. This research will concentrate on Western part of

    Zagros fold and thrust belt and the styles of structural classifications, which will

    aid to clarify and better understand the tectonic and structural history and

    evolution of the region. We have considered the last version of structural

    classification as the most relevant one to the reality, especially within outer

    platform (Unstable shelf). Where it divides the region into four structural zones,

    which are: Low Folded zone, High Folded Zone, Imbricate Zone, and Zagros

    Suture Zone and these zones were further divided to several subzones. This

    classification is based on the structural style and intensity of deformation,

    stratigraphy, mechanicalstratigraphy and tectono-stratigraphy of the deformed

    sequences, Age of deformation, surface physiography and morphology. The data

    used in the classification is more reliable, up to date and relevant.

  • 529.
    Zainy, Maher T.
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    Al-Ansari, Nadhir
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi.
    Bauer, Tobias
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    Ask, Maria
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    The Tectonic and Structural Classifications of the Western Part of the Zagros Fold and Thrust Belt, North Iraq, Review and Discussion2017Ingår i: Journal of Earth Sciences and Geotechnical Engineering, ISSN 1792-9040, E-ISSN 1792-9660, Vol. 7, nr 2, s. 71-89Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The Zagros fold and thrust belt represents a tectonically significant area, and one of the richest areas in oil and gas reservoirs in the world. The Zagros fold and thrust belt is the deformational product of the Cretaceous-present day convergence of the Arabian and Iranian (Eurasian) plates (subduction and collision). The belt extends more than 2000 km from southern Turkey through the north and northeastern Iraq to the Strait of Hormuz in southwestern Iran. The Zagros fold and thrust belt is divided into two parts which are; Western part within Iraqi region and Eastern part within Iranian region. The western part of the Zagros fold and thrust belt has been traditionally subdivided into several structural zones that are generally striking parallel to the plate boundary. This is characterized by exposure of Late Ordovician to Pliocene - Pliestocene formations with different types of Quaternary Sediments. This research will concentrate on Western part of Zagros fold and thrust belt and the styles of structural classifications, which will aid to clarify and better understand the tectonic and structural history and evolution of the region. We have considered the last version of structural classification as the most relevant one to the reality, especially within outer platform (Unstable shelf). Where it divides the region into four structural zones, which are: Low Folded zone, High Folded Zone, Imbricate Zone, and Zagros Suture Zone and these zones were further divided to several subzones. This classification is based on the structural style and intensity of deformation, stratigraphy, mechanicalstratigraphy and tectono-stratigraphy of the deformed sequences, Age of deformation, surface physiography and morphology. The data used in the classification is more reliable, up to date and relevant.

  • 530.
    Zainy, Maher T.
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    Bauer, Tobias
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    Al-Ansari, Nadhir
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi.
    Ask, Maria
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    Geometric Analysis of the Minor Structures in Iraqi Part of the Zagros Belt, NE Iraq2018Ingår i: 9th International Symposium on Eastern Mediterranean Geology 07-11 May 2018 Antalya-Turkey: Abstracts and Proceedings Book / [ed] M. Gurhan Yalcin, Yasemin Leventeli, Turkey: Academic Conferences Publishing, 2018, s. 324-324Konferensbidrag (Övrigt vetenskapligt)
    Abstract [en]

    Geometric analysis was carried out on part of the Zagros Belt, along the border between Iraq andIran, within rocks of Cretaceous age, which are composed of alternative sequences of competentand incompetent layers, and it contains a number of minor structures. The minor folds identifiedwithin the study area have different shapes, orientations and sizes, and exhibit high intensityfolding. Their wave length and amplitude range from few centimeters up to tens of meters. They areranged from gentle to tight according to the Fleuty, 1964 classification. Class 1B is dominated andfollowed by class 1C according to the Ramsay, 1967. The orientation of the minor folds, theirrelation with the major structures, variance in their shapes and sizes and difference interlimb angle,all indicate that they were developed progressively and in harmony with the major structuredevelopment. It can be concluded that the congruous and subcongruous minor folds weredeveloped successively during a single phase of deformation with simulation of variouscompressive stress directions (generally, at NE-SW and E-W), and the reorientation of the stressfield from one direction to another is attributed to the oblique collision between the Arabian andEurasian plates and to the anticlockwise rotation of the Arabian plate relative to Eurasian plate.

  • 531.
    Zeballos, Ariana
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    Geological, geochemical and mineralogical characterization of non-metallic mineral deposits in the La Paz region, Bolivia2018Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    Industrial mineral resources are a promising source of economic development in Bolivia where the mining industry’s main focus is on metalliferous deposits. The industrial mineral resources in Bolivia are of large quantity, even though they remain only locally known, as well as understudied to a large degree.

    This thesis aims to show the industrial mineral mining potential of La Paz and Bolivia as a whole. Bolivia’s resources of industrial minerals can potentially be used for numerous industrial applications. Three deposits have been geologically and mineralogically characterized. In addition, the potential applications of the mined products are addressed.

    Firstly, the Micaya deposit, located at the Micaya village south-west of La Paz city, comprising two whitish kaolinite-bearing occurrences, was investigated. The material is currently used in tableware production. The Micaya deposit is situated in a Palaeozoic sequence in the Altiplano basin. The general mineral composition of the occurrences is 56 vol.% quartz, 21 vol.% muscovite, 18 vol.% kaolinite and <5 vol.% feldspar. The kaolinite-bearing sediments were formed through enhanced weathering of the muscovite-rich siltstones aided by groundwater remobilization along permeable fault zones. Micaya kaolinite is suggested to be suitable for industrial applications.

    Secondly, the Choquetanga deposit, located south-east of La Paz city and currently mined for Sn and W, is associated with a coarse-grained granitic batholith that was studied for its feldspar characteristics in this work. Geologically, the Choquetanga area is dominated by a Palaeozoic sedimentary sequence intruded by the porphyritic granite from the Quimsa Cruz batholith in the south-east of the Eastern Cordillera. The Quimsa Cruz batholith is composed of megacrystalline granite with 5–10 cm long orthoclase, albite and oligoclase crystals that contain a considerable alkali content of YK2O,Na2O=7.84–10.25 wt.%.

    Thirdly, the La Fabulosa deposit, located north-west of the Eastern Cordillera, was studied for its feldspar occurrences hosted in granites and pegmatites. The deposit is composed of a metasedimentary sequence of Palaeozoic age intruded by the Sorata batholith, which comprises two-mica granites, granodiorites and pegmatites with an alkali content of YK2O,Na2O=7.41–14.25 wt.%, hosted in the minerals microcline, orthoclase and oligoclase.

    The potential raw materials from the three studied industrial mineral deposits were evaluated for use in ceramic applications. In addition, nine non-metallic occurrences, most of them currently mined and located at Oruro (one zeolite occurrence), Potosí (one diatomite and one montmorillonite occurrence), La Paz (three clay deposits and one diatomite occurrence) and Santa Cruz (two kaolin deposits) have been sampled. Mineralogical and lithogeochemical characterization of the materials have been performed to address higher-value applications for the deposits.

    X-ray diffraction (XRD) and inductively coupled plasma mass spectrometry (ICP-MS) were used to identify the mineralogical and lithogeochemical composition of the host rocks to the deposits. Scanning electron microscopy (SEM) were performed on the kaolinite-bearing materials to characterize the microstructure in the rocks. This indicates mineral paragenesis and has therefore implications for mineral deposit formation. Physical tests on the ceramic specimens, such as drying shrinkage (Choquetanga 0.20 vol.%, La Fabulosa 0.31 vol.%), firing shrinkage (Choquetanga 1.66 vol.%, La Fabulosa 1.59 vol.%), bending strength (Choquetanga 69.55 N/mm2, La Fabulosa 70.20 N/mm2), water absorption (Choquetanga 2.13 vol.%, La Fabulosa 0.58 vol.%) and Mohs hardness value of 7, demonstrate the potential application of the studied industrial minerals in the production of floor tile ceramics.

    The results of this work show the geological potential for industrial mineral exploitation in Bolivia. It is expected that these investigations will serve as a starting point and encouragement for future geological research and mineral exploration with important implications for the supply of industrial minerals for the growing industrial sector of Bolivia.

  • 532.
    Zeballos, Ariana
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik. Instituto de Geología y del Medio Ambiente, Universidad Mayor de San Andrés, La Paz .
    Weihed, Pär
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    Blanco, Maria
    Instituto de Geología y del Medio Ambiente, Universidad Mayor de San Andrés, La Paz.
    Machaca, Vladimir
    Instituto de Geología y del Medio Ambiente, Universidad Mayor de San Andrés, La Paz.
    Characterization of some nonmetallic resources in Bolivia: an overview of their potentiality and their application in specialized formulations2017Ingår i: Environmental Earth Sciences, ISSN 1866-6280, E-ISSN 1866-6299, Vol. 76, nr 22, artikel-id 754Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Bolivia has several nonmetallic occurrences widespread in the country. Unfortunately, they are poorly studied and slightly characterized. In the present work, several nonmetallic occurrences located in La Paz, Oruro, Potosí and Santa Cruz were studied. The results of the chemical and mineralogical characterization of the materials will be presented, in order to approach their applicability in specialized industrial formulations. A preliminary test of the final products besides an overview of their potentiality will be exposed and a current view of the commercialization as well.

  • 533.
    Zeballos, Ariana
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    Weihed, Pär
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    Blanco, Mario
    IGEMA, Universidad Mayor de San Andres, La Paz.
    Machaca, Vladimir
    IGEMA, Universidad Mayor de San Andres, La Paz.
    Geological, mineralogical and chemical characterization of Devonian kaolinite-bearing sediments for further applications in the ceramic (tiles) industry in La Paz, Bolivia2016Ingår i: Environmental Earth Sciences, ISSN 1866-6280, E-ISSN 1866-6299, Vol. 75, nr 7, artikel-id 546Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Clay minerals are widely distributed in Bolivia; among them, illitic clays are most common in the Altiplano where they are mined for use in the ceramic industry that has been growing in the last few years. In addition to illitic sediments, kaolinitic sediments have been recently discovered in sedimentary units in the Bolivian Altiplano. Residual ball clay occurrences in Devonian sedimentary units were studied as part of this work. Geological mapping and geophysical studies (ERT and GPR) were done for better understanding the origin of the deposits and were part of a preliminary study of the mineral potential to define the relationship with the host rock. Chemical and mineralogical techniques such as X-Ray Diffraction, Scanning Electron Microscopy and Inductively Coupled Plasma analyses were performed in samples from the studied area to verify the presence of kaolinite. Atterberg limits and behaviour of the raw material in ceramic specimens supported by chemical analyses show that this material is suitable for manufacturing tile ceramics. This study provides fundamental knowledge for deposit exploitation and future generation of an alternative source of employment for the inhabitants of Micaya

  • 534.
    Zeballos, Ariana
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    Weihed, Pär
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    Blanco, Mario
    Machaca, Vladimir
    Mullite synthetization at low temperature2013Ingår i: Mineral deposit research for a high-tech world: proceedings / 12th biennial SGA meeting, 12-15 August 2013, Uppsala, Sweden / [ed] Erik Jonsson, Uppsala: Sveriges Geologiska Undersökning , 2013, s. 1784-1786Konferensbidrag (Refereegranskat)
    Abstract [en]

    The mineral nnullite (3Al(2)O(3)2SiO(2)) is frequently used by the industry in the preparation of refractory ceramics. However, it is uncommon in nature and, therefore, synthetically manufactured. The commercial mullite is synthetized from kaolinite + Al2O3 (gibbsite, bauxite), making the synthetization expensive. For that reason, naturally occurring deposits that can be utilized for the process are sought for. The Micaya deposit, located outside La Paz, Bolivia, is composed of a layer of kaolinitic shale hosted within the Vila Vila Formation composed of Devonian coarse-grained sandstones and siltstones. The shale is composed of quartz, kaolinite, muscovite and feldspar. The kaolinite can be separated from the shale by gravity separation, thus decreasing the SiO2 content and obtaining a new product with a higher Al2O3 content. The two major components (quartz and alumina) are then subjected to a calcination process at high temperatures in a suitable ceramic firing programme and results in the formation of mullite without adding extra Al2O3.

  • 535.
    Zoheir, Basem
    et al.
    Department of Geology, Faculty of Science, Benha University.
    Weihed, Pär
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    Greenstone-hosted lode-gold mineralization at Dungash mine, Eastern Desert, Egypt2014Ingår i: Journal of African Earth Sciences, ISSN 1464-343X, Vol. 99, nr 1, s. 165-187Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The auriferous quartz±carbonate veins at Dungash mine, central Eastern Desert of Egypt, are confined to ∼E-trending dilation zones within variably foliated/sheared metavolcanic/volcaniclastic rocks. The vein morphology and internal structures demonstrate formation concurrent with a dextral shear system. The latter is attributed to flexural displacement of folded, heterogeneous rock blocks through transpression increment, late in the Neoproterozoic deformation history of the area. Geochemistry of the host metavolcanic/metavolcaniclastic rocks from the mine area suggests derivation from a low–K, calc–alkaline magma in a subduction-related, volcanic arc setting. In addition, chemistry of disseminated Cr-spinels further constrain on the back-arc basin setting and low-grade metamorphism, typical of gold-hosting greenstone belts elsewhere.Mineralogy of the mineralized veins includes an early assemblage of arsenopyrite-As-pyrite-gersdorffite±pyrrhotite, a transitional pyrite-Sb-arsenopyrite±gersdorffite assemblage, and a late tetrahedrite-chalcopyrite-sphalerite-galena-gold assemblage. Based on arsenopyrite and chlorite geothermometers, formation of gold-sulfide mineralization occurred between ∼365 and 280°C. LA-ICP-MS measurements indicate the presence of refractory Au in arsenian pyrite (up to 53 ppm) and Sb-bearing arsenopyrite (up to 974 ppm). Abundant free-milling gold associated with the late sulfide assemblage may have been mobilized and re-distributed by circulating, lower temperature ore fluids in the waning stages of the hydrothermal system.Based on the isotopic values of vein quartz and carbonate, the calculated average δ18OH2O values of the ore fluids are 5.0±1.4‰ SMOW for quartz, and 3.3±1.4‰ for vein carbonate. The measured carbonate δ13C values correspond to ore fluids with δ13CCO2= -6.7±0.7‰ PDB. These results suggest a mainly metamorphic source for ore fluids, in good agreement with the vein morphology, textures and hydrothermal alteration. The calculated δ34SH2S values for early, transitional, and late sulfide assemblages define three distinct ranges (∼1.5 to 3.6 ‰), (∼0.4 to 1.0‰), and (–3.7 to –1.9‰), respectively. The systematic evolution towards lighter δ34S values may be attributed to recrystallization, or to ore fluid buffering under variable physicochemical conditions.The shear zone-related setting, mineralogy and isotopic characteristics of gold mineralization in Dungash mine are comparable with other orogenic gold deposits in the region (e.g., Barramiya deposit), which may suggest a regional setting controlling gold metallogeny of the region. This setting should guide future exploration programs in the central Eastern Desert province.

  • 536. Åberg, J. A.
    et al.
    Weihed, Pär
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    Geochemical alteration associated with Au-bearing quartz veins at the Björkdal gold deposit, Skellefte district, northern Sweden1999Ingår i: Gold '99 Trondheim: bPrecambrian gold in the Fennoscandian and Ukrainian shields and related areas : abstract volume / [ed] Nigel J. Cook; Krister Sundblad, Trondheim: American Speech-Language-Hearing Association, 1999, s. 173-175Konferensbidrag (Övrigt vetenskapligt)
  • 537. Åberg, J. A.
    et al.
    Weihed, Pär
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    Petrographic- and chemical characteristics of alteration associated with Au-bearing quartz veins at the Bjorkdal gold deposit, Skellefte District, northern Sweden1999Ingår i: Mineral deposits; processes to processing: proceedings of the Fifth biennial SGA meeting and the Tenth quadrennial IAGOD symposium / [ed] C.J. Stanley, Rotterdam: Balkema Publishers, A.A. / Taylor & Francis The Netherlands , 1999, s. 1005-1008Konferensbidrag (Refereegranskat)
  • 538.
    Öhlander, Björn
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    Romer, Rolf L.
    Luleå University of Technology.
    Zircon ages of granites occuring along the Central Swedish Gravity Low1996Ingår i: GFF, ISSN 1103-5897, E-ISSN 2000-0863, Vol. 118, nr 4, s. 217-225Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Two major types of late Svecofennian granitoids occur in south central Sweden. Large homogeneous massifs of coarse-grained granite with trace element characteristics typical of granites formed in tensional settings occur along the Central Swedish Gravity Low (CSGL). The other type comprises smaller intrusions of irregular, heterogeneous, locally derived granites (IHLD granites). We present U-Pb zircon ages are presented of one IHLD granite and of three varieties of the homogeneous intrusions. The result for the IHLD granite is 1779+-8 Ma. One of the samples of the homogeneous type yielded an age of 1769.7 +- 3.4 Ma. The remaining two samples have heterogeneous zircon populations. The emplacement age of these rocks is bracketed by the intercept ages of 1770 +- 6 and 1779 +- 23 Ma.The overlapping ages of granite groups of different types show that different types of granites were formed contemporaneously in the same region as a result of melt formation at various depths and from various sources.

  • 539.
    Öhlander, Björn
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    Weihed, Pär
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    Proterozoic mineralizations associated with granitoids in northern Sweden: Excursion guide no 71986Ingår i: 7th IAGOD symposium and Nordkalott project meeting / [ed] Ebbe Zachrisson, Sveriges Geologiska Undersökning , 1986Konferensbidrag (Övrigt vetenskapligt)
  • 540. Kathol, Benno (Redaktör)
    Weihed, Pär (Redaktör)
    Description of regional geological and geophysical maps of the Skellefte District and surrounding areas2005Rapport (Övrigt vetenskapligt)
    Abstract [sv]

    Beskrivningen ingår i serien Ba - översiktliga jordarts- och berggrundskartor. Syftet med denna beskrivning är att, utifrån SGUs berggrundskartering och geofysiska kartering i området, ge en så heltäckande bild av Skelleftefältets berggrund som möjligt. Tillsammans med norra Norrbotten och Bergslagen utgör Skelleftefältet ett av Sveriges viktigaste malmområden. Beskrivningen bygger på en genomgång och bearbetning av redan insamlad information samt kompletterande fältundersökningar.Beskrivningen innehåller dessutom en presentation av områdets geologiska utveckling, detaljerade geologiska beskrivningar för särskilt viktiga områden, förteckningar över de olika malmfyndigheterna, radiometriska data m.m.Till beskrivningen hör sex separata kartor: berggrundskarta (Ba 57:1), karta över metamorfosgrad, strukturer och isotopåldrar (Ba 57:2), karta över mineral- och bergartsresurser samt hydrotermalomvandlingar (Ba 57:3), magnetisk anomalikarta (Ba 57:4), Bougueranomalikarta (Ba 57:5), samt gammastrålningskarta, elektromagnetisk karta (VLF), Eulerträffar från tyngdkraftsdata och höjdreliefkarta (Ba 57:6).

  • 541. Weihed, Pär
    Williams, Patrick J.
    James Cook University.
    Metallogeny of the northern Fennoscandian Shield: a set of papers on Cu–Au and VMS deposits of northern Sweden2005Ingår i: Mineralium Deposita, ISSN 0026-4598, E-ISSN 1432-1866, Vol. 40, nr 4, s. 347-447Artikel i tidskrift (Övrigt vetenskapligt)
891011 501 - 541 av 541
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