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  • 1. Denisova, Nikola
    et al.
    Allan, Åsa
    Martinsson, Olof
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    Sulfide distribution and its relation to different types of skarn alteration at the Tapuli deposit, northern Sweden2013Inngår i: Mineral deposit research for a high-tech world: proceedings / [ed] Erik Jonsson, Uppsala: Sveriges Geologiska Undersökning , 2013, s. 1539-1542Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The Tapuli deposit is a skarn iron ore located in the Pajala municipality in Northern Sweden. It is situated at the margin of the Karelian craton, at the stratigraphic contact between Karelian and Svecofennian rocks. The ore forms stratabound lenses concordant with the metasedinnentary sequences and dips 45 - 60 degrees towards NW. Footwall rocks are dolomitic marbles, phyllites and graphitic phyllites; the hanging wall comprises phyllites and quartzites. Mafic dykes and sills crosscut the stratigraphic succession. Magnetite is the only ore mineral. The skarn minerals are serpentine, diopside, tremolite and actinolite. The skarn altered rocks show a zonation with serpentine skarn closest to or as part of the ore, thereafter, tremolite-diopside skarn and, finally, actinolite skarn closest to the phyllites and quartzites in the hanging wall. Sulfides occur in minor amounts, but their content generally increases with proximity to the footwall rocks. The dolomitic marble was the precursor of the serpentine and tremolite-diopside skarn. Immobile element data suggests that mafic dykes and sills were the precursors of the actinolite skarn. Possible controls of the sulfide distribution are the presence of sulfide-bearing source rocks (dolomitic marble, graphitic phyllite) and rennobilization of sulfides during the intrusion of mafic dykes.

  • 2.
    Edfelt, Åsa
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    Geology, alterations and mineral chemistry of the Tjårrojåkka Fe-oxide Cu-Au occurrences, northern Sweden2003Licentiatavhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    The Tjårrojåkka area is located about 50 km WSW of Kiruna, northern Sweden, and hosts one of the best examples of spatially related Fe-oxide Cu-Au occurrences (the Tjårrojåkka-Fe and Tjårrojåkka-Cu). The bedrock, depositional environment and tectonic evolution of the area were studied through petrological, geochemical and geophysical-petrophysical investigations. The bedrock is dominated by intermediate and basic extrusive and intrusive rocks. The intermediate andesites and basaltic andesites are cut by diabases which acted as feeder dykes for the overlying basalts. The intrusive rocks range from gabbro to quartz-monzodiorite in composition. The area is metamorphosed to epidote-amphibolite facies and has been affected by scapolite, K-feldspar, epidote and albite alteration that is more intense in the vicinity of deformation zones and mineralisations. Based on geochemistry the andesites and basaltic andesites are similar to the Svecofennian Porphyrite Group intermediate volcanic rocks, but have also features common with the intermediate volcaniclastic unit in the underlying Kiruna Greenstone Group. Chemically the basalts and diabases have the same signature, but cannot directly be correlated with any known basaltic unit. Some of the samples have characteristics comparable to the basalts of the Kiruna Greenstone Group. Whether the volcanic sequence at Tjårrojåkka represents the Porphyrite Group or is part of the greenstones could not be unequivocally determined without geochronological data. Three events of deformation have been distinguished in the Tjårrojåkka area; the first one involving NW-SE compression creating NE-SW-striking steep foliation corresponding with the strike of the Tjårrojåkka-Fe and Cu bodies, followed by the creation of an E-W deformation zone. Finally a second compressional event resulted in folding and the formation of a NNW-SSE striking and gently dipping structure possible related to thrusting from SW. The Tjårrojåkka apatite-magnetite ore (52.6 Mt of iron ore @ 51.5% Fe) is a blind ore consisting of a massive magnetite core surrounded by an ore- breccia containing low-grade Cu-mineralisation. Apatite, amphiboles and carbonate occur disseminated and as veins within the massive ore and in the wall rock. The Tjårrojåkka-Cu mineralisation is located 750 m from the Tjårrojåkka-Fe and contains 3.23 Mt ore @ 0.87% Cu. The main ore minerals are chalcopyrite and bornite occurring both disseminated and in veinlets. Minor pyrite, molybdenite and gold have also been observed. The host rock has been affected by strong albite, scapolite, amphibole and K-feldspar alteration. The alteration assemblages at Tjårrojåkka are highly variable with several of the alteration minerals occurring in several generations and settings, and with multiple reactivations of already existing veins and overlapping alteration stages indicating a complex, long history of fluid activity in the area. Similarity in alteration minerals and paragenesis in the iron and copper mineralisation is described in terms of whole rock geochemistry, mineral chemistry and paragenesis. This may partly be explained by the common host rock to the mineralisations, but indicates also similarities in fluid composition. Within the massive magnetite ore apatite, tremolite and carbonate veinlets fill fractures probably formed during cooling of the magnetite body. The wall rock has been affected by extensive pervasive albite and plagioclase alteration. Scapolite occurs locally as porphyroblasts and later veins. The albitised and scapolitised rocks are overprinted by pervasive K-feldspar alteration and veins of K-feldspar + Mg-hornblende ± titanite ± quartz ± magnetite ± sulphides along the foliation. Epidote is common in veins together with K-feldspar. Allanite occurs as an accessory mineral associated with epidote, otherwise REE-minerals are rare. Carbonate and zoelites were the last phases to form in vacancies. The area between the apatite-iron and copper bodies is strongly albite + magnetite altered. The footwall of the copper body is characterised by pervasive albite alteration spatially associated with magnetite and apatite veins cut by later carbonate veinlets. Scapolite (porphyroblasts and veins) is formed in an early stage in the hanging wall overprinted by pervasive K-feldspar alteration. Amphiboles (tschermakites, Mg-hornblende and actinolite) occur in several generations as porphyroblasts, in veins on its own, or together with K-feldspar ± titanite ± quartz ± carbonate ± chalcopyrite ± bornite. Epidote, REE- carbonate, zeolites and fluorite are the latest alteration phases in the copper mineralisation. Ba, Cl, S and F are enriched in the alteration minerals in the Tjårrojåkka occurrences. Barium-rich varieties of K-feldspar (max. 3.5% BaO) occur in the Cu-mineralised breccia surrounding the apatite-magneitie body indicating high concentrations of Ba in the hydrothermal fluids. Absence of sulphate in the fluids probably caused the formation of Ba-feldspars instead of barite. Scapolite shows a trend with more Cl-rich varieties around the magnetite body gradually getting more SO3 and CO2-rich in the Cu-mineralisation. The presence of accessory barite in the copper mineralisation also indicates that the SO3 content in the fluids were higher than in the iron ore. The biotites are rich in Ti while Cl and F contents are more moderate and do not show great variation in different parts of the systems. All amphiboles are Ca-rich ranging from tschermakites, Mg-hornblende to actinolite and tremolite. The apatites are F-dominate with higher Cl content in the apatite- iron ore than in the copper occurrence. Overall the alteration minerals related to the apaite-iron ore are more rich in Cl and Ba than the ones in the Cu-mineralisation that show higher contents of F, SO3 and CO2.

  • 3.
    Edfelt, Åsa
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    The Tjårrojåkka apatite-iron and Cu (-Au) deposits, northern Sweden: products of one ore forming event2007Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    The Tjårrojåkka area is located about 50 km WSW of Kiruna, northern Sweden, and hosts one of the best examples of spatially related apatite-iron (Kiruna type) and Cu (-Au) deposits in Sweden. The results from this project show that the two deposits are genetically related and indicate the presence of a younger, previously unknown, 1780 Ma generation of apatite- iron ores in northern Sweden. The bedrock in the Tjårrojåkka area is dominated by intermediate and basic extrusive and intrusive rocks. The 1880 Ma intermediate volcanic rocks, belonging to the Porphyrite Group, formed in association with subduction- related magmatism in a volcanic arc environment close to the Archaean continental margin. The overlying basalts and related feeder dykes formed through extrusion of mantle derived magma during a local extensional event in a subaquatic back arc setting. The area was metamorphosed at epidote- amphibolite facies and deformed during at least three stages, creating NE- SW, E-W, and NNW-SSE striking structures. The Tjårrojåkka deposits can be considered as belonging to the Fe-oxide-Cu- Au (IOCG) group of deposits representing two "end-members" of the class. Several generations and overlapping hydrothermal alteration stages indicate a long, complex history of fluid activity between 1780 and 1700 Ma related to the formation and post ore modification of the deposits. The strongly altered host rock shows enrichment of alkalis related to mineralisation due to the formation of albite, scapolite, and K-feldspar. It is not obvious whether the massive part of the apatite-iron ore formed from an iron rich melt or through hydrothermal replacement, but a hydrothermal system was active at least at a late stage during the deposition of the iron ore, producing the apatite-magnetite-actinolite breccia, the copper mineralisation, as well as the extensive hydrothermal alterations. The ore forming fluids were CO2-bearing, moderately to highly saline CaCl2- NaCl-rich fluids of most likely magmatic origin. The magnetite ore deposited at around 500 to 650°C followed by the copper mineralisation between 150 and 450°C. Cooling along with decrease in salinity were important factors for metal precipitation at Tjårrojåkka. A NE trending shear zone acted as a major fluid channel and a structurally favourable location for the deposition of the copper (-gold) mineralisation. From apatite chemistry, it is evident that there is a fundamental difference between typical Kiruna type apatite-iron ores and copper mineralised apatite-iron deposits of IOCG character and could potentially be used as a tool for distinguishing copper mineralising apatite-iron systems from barren.

  • 4. Edfelt, Åsa
    et al.
    Armstrong, Robin N.
    Natural History Museum, London.
    Smith, Martin
    University of Brighton.
    Martinsson, Olof
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    Alteration paragenesis and mineral chemistry of the Tjårrojåkka apatite-iron and Cu (-Au) occurrences, Kiruna area, northern Sweden2005Inngår i: Mineralium Deposita, ISSN 0026-4598, E-ISSN 1432-1866, Vol. 40, nr 4, s. 409-434Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The northern Norrbotten area in northern Sweden, is an important mining district and hosts several deposits of Fe-oxide Cu-Au-type. One of the best examples of spatially, and possibly genetically, related apatite-iron and copper-gold deposits in the region is at Tjårrojåkka, 50 km WSW of Kiruna. The deposits are hosted by strongly sheared and metamorphosed intermediate volcanic rocks and dolerites and show a structural control. The Tjårrojåkka iron deposit is a typical apatite-iron ore of Kiruna-type and the Tjårrojåkka copper occurrence shows the same characteristics as most other epigenetic deposits in Norrbotten. The host rock has been affected by strong albite and K-feldspar alteration related to mineralisation, resulting in an enrichment of Na, K, and Ba. Fe and V were depleted in the altered zones and added in mineralised samples. REE were enriched in the system, with the greatest addition related to mineralisation. Y was also mobile associated with albite alteration and copper mineralisation. The Tjårrojåkka iron and copper deposits show comparable hydrothermal alteration minerals and paragenesis, which might be a product of common host rock and similarities in ore fluid composition, or overprinting by successive alteration stages. Mineralogy and mineral chemistry of the alteration minerals (apatite, scapolite, feldspars, amphiboles, and biotite) indicate a higher salinity and Ba/K ratio in the fluid related to the alterations in the apatite-iron occurrence than in the copper deposit, where the minerals are enriched in F and S. The presence of hematite, barite, and in SO4 in scapolite suggests more oxidising-rich conditions during the emplacement of the Tjårrojåkka-Cu deposit. From existing data it might be suggested that one evolving system created the two occurrences, with the copper mineralisation representing a slightly later product.

  • 5. Edfelt, Åsa
    et al.
    Broman, C.
    Martinsson, Olof
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    A preliminary fluid inclusion study of the Tjårrojåkka IOCG-occurrence, Kiruna Area, northern Sweden2004Inngår i: The 26th Nordic Geological Winter Meeting: abstract volume / [ed] Joakim Mansfeld, Uppsala: Geological Society of Sweden , 2004, s. 148-Konferansepaper (Fagfellevurdert)
  • 6. Edfelt, Åsa
    et al.
    Martinsson, Olof
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    Fennoscandian Shield: iron oxide-copper-gold deposits. Tjårrojåkka, northern Sweden: Lat 67° 40′ N, Long. 19° 10′ E2005Inngår i: Ore Geology Reviews, ISSN 0169-1368, E-ISSN 1872-7360, Vol. 27, nr 1-4, s. 328-329Artikkel i tidsskrift (Fagfellevurdert)
  • 7. Edfelt, Åsa
    et al.
    Martinsson, Olof
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    The Tjårrojåkka Fe-oxide and Cu-Au occurrences northern Sweden: products of one ore forming event?2004Konferansepaper (Annet vitenskapelig)
  • 8. Edfelt, Åsa
    et al.
    Martinsson, Olof
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    The Tjårrojåkka Fe-oxide Cu(-Au) occurrence, Kiruna area, northern Sweden2003Inngår i: Mineral Exploration and Sustainable Development: proceedings of the Seventh Biennial SGA Meeting, Athens, Greece, 24-28 August 2003 / [ed] D.G. Eliopoulos, Rotterdam: Millpress , 2003, s. 1069-1071Konferansepaper (Fagfellevurdert)
  • 9. Edfelt, Åsa
    et al.
    Sandrin, Alessandro
    Luleå tekniska universitet.
    Evins, Paul
    EGRU, School of Earth Sciences, James Cook University.
    Jeffries, Teresa
    Natural History Museum, London.
    Storey, Craig
    Open University, Walton Hall, Milton Keynes.
    Elming, Sten-åke
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    Martinsson, Olof
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    Stratigraphy and tectonic setting of the host rocks to the Tjårrojåkka Fe-oxide Cu-Au deposits, Kiruna area, northern Sweden2006Inngår i: GFF, ISSN 1103-5897, E-ISSN 2000-0863, Vol. 128, nr 3, s. 221-232Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The Tjårrojåkka area is located about 50 km WSW of Kiruna, northern Sweden, and hosts one of the best examples of spatially and possibly genetically related Fe-oxide and Cu-Au occurrences in the area. The bedrock is dominated by intermediate and basic extrusive and intrusive rocks. An andesite constrains the ages of these rocks with a U-Pb LA-ICPMS age of 1878±7 Ma. They are cut by dolerites, which acted as feeder dykes for the overlying basalts. Based on geochemistry and the obtained age the andesites and basaltic andesites can be correlated with the 1.9 Ga intermediate volcanic rocks of the Svecofennian Porphyrite Group in northern Sweden. They formed during subduction-related magmatism in a volcanic arc environment on the Archaean continental margin above the Kiruna Greenstone Group. Chemically the basalts and associated dolerites have the same signature, but cannot directly be related to any known basaltic unit in northern Sweden. The basalts show only minor contamination of continental crust and may represent a local extensional event in a subaquatic back arc setting with extrusion of mantle derived magma. The intrusive rocks range from gabbro to quartz-monzodiorite in composition. The area is metamorphosed at epidote-amphibolite facies and has been affected by scapolite, K-feldspar, epidote, and albite alteration that is more intense in the vicinity of deformation zones and mineral deposits. Three events of deformation have been distinguished in the area. D1 brittle-ductile deformation created NE-SW-striking steep foliation corresponding with the strike of the Tjårrojåkka-Fe and Cu deposits and was followed by the development of an E-W deformation zone (D2). A compressional event (D3), possible involving thrusting from the SW, produced folds in the central part of the area and a NNW-SSE striking deformation zone in NE.

  • 10. Edfelt, Åsa
    et al.
    Smith, M.
    University of Brighton.
    Armstrong, R.N.
    Natural History Museum, London.
    Martinsson, Olof
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    Apatite chemistry - a potential tool for IOCG exploration2006Inngår i: The 27th Nordic Geological Winter Meeting, January 9-12, 2006, Oulu, Finland: abstract volume / [ed] Petri Peltonen ; Antti Pasanen, Helsinki: Geological Society of Finland , 2006, s. 29-Konferansepaper (Annet vitenskapelig)
    Abstract [en]

    Northern Norrbotten is an important mining region of Sweden and is regarded as an iron-oxide copper-gold (IOCG) district hosting several apatite-iron oxide and copper-gold sulphide ores (e.g. Hitzman et. al., 1992). The IOCG group of deposits is diverse with respect to age, host rock, ore and alteration mineralogy as well as ore-forming processes and there is still an ongoing debate regarding a possible genetic link between "classical" Kiruna type ores and copper dominated end-members within this class of deposits. Apatites from Kiruna-type apatite-iron deposits (Kiirunavaara, Rektorn, Nukutus, Ekströmsberg, Tjårrojåkka-Fe), IOCG copper occurrences (Tjårrojåkka-Cu and Nautanen), a 1.89 Ga andesite and a Perthite-monzonite group intrusion were collected and analysed for their mineral chemistry and rare earth elements using electron microprobe and LA-ICPMS analysis. The apatite chemistry can subsequently be used as an indicator of the composition of fluids involved in the formation of the deposits (Korzhinskiy, 1982). Different trends with regard to F-Cl content as well as REE pattern in the apatites were observed for apatite-iron ores with no spatial relation to copper mineralisation compared to the apatite-iron ore spatially related to a copper occurrence. The apatites from the former were almost pure F-apatites with steep REE patterns, while the apatites from the latter and the copper mineralisations themselves contained a large Cl-component and showed depletion in LREE.It can be concluded that apatite chemistry could be a potential tool for distinguishing copper mineralising apatite-iron systems from barren ones. However, so far only one apatite-iron deposit spatially related to a copper occurrence has been studied and more studies are needed to confirm the results.

  • 11.
    Martinsson, Olof
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    Allan, Åsa
    Envipro Miljöteknik AB, Linköping.
    Niiranen, Tero
    Northland Exploration Finland.
    Wanhainen, Christina
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    Eilu, Pasi
    GTK.
    Ojala, Juhani
    GTK.
    Nykänen, Vesa
    GTK.
    Weihed, Pär
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    Iron oxide-Cu-Au deposits in the northern part of the Fennoscandian shield2008Konferansepaper (Annet vitenskapelig)
    Abstract [en]

    The northern part of the Fennoscandian Shield, which formed during repeated extensional and compressional events at 3.1-1.8 Ga, is an ore province characterized by regionally developed albite and scapolite alteration and the occurrence of world class Fe-oxide (Kiirunavaara) and Cu-Au deposits (Aitik). It host several styles of Fe-oxide-Cu-Au deposits, including skarn and apatite-iron style deposits, many of them with features that also warrant classification as iron oxide-copper-gold (IOCG) deposits.The apatite-iron ores are economically most important with a total production of c. 1900 Mt from 10 mines during the last 100 years and with a total pre-mining resource of c. 4100 Mt. In these deposits, the Fe and P content vary between 30-70 % and 0.05-5 %, respectively. The ore minerals magnetite and hematite occur in lenses or as breccia infill. The ores are usually enriched in LREE, sulphides are rare but subeconomic amounts of Cu may occur.Skarn-like iron occurrences consisting of magnetite and Mg and Ca-Mg silicates have been less important with c. 20 Mt mined from 6 deposits and a pre-mining resource of 760 Mt. Most of them occur as conformable lenses with a banded internal structure. Pyrite, pyrrhotite and minor chalcopyrite are commonly present disseminated or as veinlets. Typical grades are 30-55% Fe, 0.2-3.5 % S, 0.05-0.3% Cu, 0.005-1g/t Au and 0.02-0.2% P. A few of the deposits are also enriched in LREE. Epigenetic Cu±Au occurrences include the porphyry-style giant Aitik deposit with a pre-mining resource of 2000 Mt at 0.3% Cu and 0.2 g/t Au and a total production of 465 Mt. Other deposits vary in style from disseminated to breccia infill or veins. Chalcopyrite is the most important ore mineral but bornite, pyrite, pyrrhotite, magnetite, molybdenite and native gold may occur in varying amounts. The skarn-like ores occur in 2.1Ga Karelian greenstones in association to carbonate rocks, BIF and graphite schist. The apatite iron ores are hosted by 1.9 Ga Svecofennian intermediate to felsic porphyries. The epigenetic Cu±Au deposits occur in both Karelian and Svecofennian volcanic and sedimentary rocks and 1.9 Ga intrusive rocks. The two last type of deposits show similar alteration styles including albite, K-feldspar, biotite, scapolite, carbonate, amphibole and tourmaline, whereas the skarn-like deposits are associated with diopside, amphibole, scapolite and biotite alteration.Deposit studies and geochronological data reveal a multiphase origin of the Fe oxide and Cu±Au occurrences with multiple sources of the ore fluids and peaks of mineralization at c. 1.88 and 1.77 Ga. These events are temporally related to major orogenic stages in the evolution of the Fennoscandian Shield. This implies that mineralization formed in different tectonic settings, and with different magmatic associations. Thus, the IOCG deposits are not uniform in origin, which may well explain their diverse features and also makes a simple genetic model for them dubious.

  • 12.
    Sandrin, Alessandro
    et al.
    Luleå tekniska universitet.
    Edfelt, Åsa
    Waight, Tod E.
    University of Copenhagen.
    Berggren, Robert
    Elming, Sten-åke
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    Physical properties and petrologic description of rock samples from an IOCG mineralized area in the northern Fennoscandian Shield, Sweden2009Inngår i: Journal of Geochemical Exploration, ISSN 0375-6742, E-ISSN 1879-1689, Vol. 103, nr 2-3, s. 80-96Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The Tjårrojåkka Fe-Cu prospect in northern Sweden is considered an example of a Fe-oxide Cu-Au (IOCG) deposit and is hosted in metamorphosed Paleoproterozoic volcanic and intrusive rocks. Rock samples from 24 outcrops were collected for petrophysical analysis (magnetic susceptibility, remanent magnetization, variation of magnetic susceptibility with temperature, Curie temperature and density). The major Cu-prospect in the area has been studied by magnetic and electron microprobe analyses of four selected rock samples. The samples are from an exploration well that intersects the main Cu-mineralized body.The magnetic analyses show that magnetite is the dominant magnetic mineral, while hematite and other Fe-minerals are present in minor amounts. The electron microprobe observations confirm the presence of magnetite and further indicate that hematite is an alteration product of magnetite. Moreover, microprobe observations indicate that Fe-sulfides are present in negligible amounts in the samples from the Tjårrojåkka area. The strong spatial relationship of Cu-minerals (e.g., chalcopyrite) and the oxidation of magnetite to hematite suggest that the presence of rocks with low magnetic susceptibility in areas dominated by high susceptibility rocks may be a signal of related Cu-prospects.

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