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- Allen, Rodney, et al.
(författare)
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Setting of Zn-Cu-Au-Ag massive sulfide deposits in the evolution and facies architecture of a 1.9 Ga marine volcanic arc : Skellefte district, Sweden
- 1996
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Ingår i: Economic geology and the bulletin of the Society of Economic Geologists. - : Society of Economic Geologists. - 0361-0128 .- 1554-0774. ; 91:6, s. 1022-1053
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Tidskriftsartikel (refereegranskat)abstract
- Skellefte mining district occurs in an Early Proterozoic, mainly 1.90-1.87 Ga (Svecofennian) magmatic province of low to medium metamorphic grade in the Baltic Shield in northern Sweden. The district contains over 85 pyritic Zn-Cu-Au-Ag massive sulfide deposits and a few vein Au deposits and subeconomic porphyry Cu-Au-Mo deposits, The massive sulfide deposits mainly occur within, and especially along the top of: a regional felsic-dominant volcanic unit attributed to a stage of intense, extensional, continental margin are volcanism. From facies analysis we interpret the paleogeography of this stage to have comprised many scattered islands and shallow-water areas. surrounded by deeper seas. All the major massive sulfide ores occur in below-wave base facies associations: however, some ores occur close to stratigraphic intervals of above-wave base facies associations, and the summits of some volcanoes that host massive sulfides emerged above sea level. Intense marine volcanism was superceded at different times in different parts of tile district by a stage of reduced volcanism, uplift resulting in subregional disconformities, and then differential uplift and subsidence resulting in a complex horst and graben paleogeography. Uplift of the are is attributed to the relaxation of crustal extension and the emplacement of granitoids to shallow crustal levels. A few massive sulfide ores formed within the basal strata of this second stage. The horst and graben system was filled by prograding fluvial-deltaic sediments and mainly mafic lavas, and during this stage the Skellefte district was a transitional area between renewed are volcanism of more continental character to the north, and subsidence and basinal mudstone-turbidite sedimentation to the south. This whole volcanotectonic cycle occurred within 10 to 15 m.y. We define 26 main volcanic, sedimentary, and intrusive facies in the Skellefte district. The most abundant facies are (1) normal-graded pumiceous breccias, which are interpreted as syneruptive subaqueous mass flow units of pyroclastic debris, (2) porphyritic intrusions, and (3) mudstone and sandstone turbidites. Facies associations define seven main volcano types, which range from basaltic shields to andesite cones and rhyolite calderas. Despite this diversity of volcano types, most massive sulfide ol es are associated with one volcano type: subaqueous rhyolite cryptodome-tuff volcanoes. These rhyolite volcanoes are 2 to 10 km in diameter, 250 to 1,200 m thick at the center, and are characterized by a small to moderate volume rhyolitic pyroclastic unit, intruded by rhyolite cryptodomes, sills, and dikes. Massive sulfide ores occur near the top of the proximal (near vent) facies association The remarkable coincidence in space and time between the ores and this volcano type indicates an intimate, genetic relationship between the ores and the magmatic evolution of the volcanoes.Many of the massive sulfide ores occur within rapidly emplaced volcaniclastic facies and are interpreted to have formed by infiltration and replacement of these facies. Some of the ore deposits have characteristics of both marine massive sulfides and subaerial epithelial deposits. We suggest that massive sulfides in the Skellefte district span a range in ore deposit style from deep-water sea floor ores, to subsea-floor replacements, to shallow-water and possible subaerial synvolcanic replacements. Facies models are provided for the mineralized rhyolite volcanoes and volcanological guides are provided for exploration for blind ores within these volcanoes.
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| 2. |
- Carlsson, Bengt Å., et al.
(författare)
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Alpine and subalpine vegetation
- 1999
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Ingår i: Swedish plant geography. - Uppsala : Svenska växtgeografiska sällskapet. - 9172100842 ; , s. 75-89
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Bokkapitel (refereegranskat)
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| 4. |
- Matero, A, et al.
(författare)
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Alkyl polyglucosides as hydrotropes
- 1998
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Ingår i: Journal of Surfactants and Detergents (JSD). - 1097-3958 .- 1558-9293. ; 1, s. 485-489
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Tidskriftsartikel (refereegranskat)abstract
- The hydrotropic effect of sugar-based surfactants has been studied and compared with totoul-4-sulphonic acid, which was used as as model hydrotrope. The effect has been assessed as the cloud point elevation of a solution containing different nonionic surfactants upon addition of the hydrotrope. Sugar-based surfactants with intermediate alkyl chain lenths were proven to be very effective in elevating the cloud point, while surfactants with a short or a long hydrophobic part had a lesser effect. The influence of the sugarbased surfactants on the phase behaviour and stability of a microemulsion of water, sodium dodecyl sulphate and pentanol was determined. The effects on the phase behaviour and the cloud point elevation on addition of a sugarbased surfactant are highly dependent on the structure of the surfactant. However, no correlation could be found between the structural effects as observed in the two studied functions.
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| 5. |
- Rasmusson, Allan G., et al.
(författare)
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Homologues of yeast and bacterial rotenone-insensitive NADH dehydrogenases in higher eukaryotes : Two enzymes are present in potato mitochondria
- 1999
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Ingår i: Plant Journal. - 0960-7412. ; 20:1, s. 79-87
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Tidskriftsartikel (refereegranskat)abstract
- Two different cDNAs, homologous to genes for rotenone-insensitive NADH dehydrogenases of bacteria and yeast, were isolated from potato. The encoded proteins, called NDA and NDB, have calculated molecular masses of 55 and 65kDa, respectively. The N-terminal parts show similarity to mitochondrial targeting peptides and the polypeptides are in vitro imported into potato mitochondria. Import processing to a smaller polypeptide is seen for the NDA but not the NDB protein. After import, NDA is intramitochondrially sorted to the matrix side of the inner membrane, whereas NDB becomes exposed to the intermembrane space. Imported proteins are associated to membranes upon digitonin permeabilization. On expression in Escherichia coli, NDB is released from the bacterial membrane in the absence of divalent cations whereas detergents are necessary for solubilization of NDA. Both deduced amino-acid sequences contain the dual motifs for nucleotide binding with the characteristics of the core criteria, similar to the bacterial homologues. Unique among NADH dehydrogenases, the NDB amino-acid sequence contains a nonconserved insert, which is similar to EF-hand motifs for calcium binding. Phylogenetic analyses group the rotenone-insensitive NADH dehydrogenases largely by species, but suggest ancient gene duplications.
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