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171.
The Kristineberg massive sulfide deposit is hosted by metamorphosed volcanic and subvolcanic rocks of the Palaeoproterozoic
Skellefte Group. The deposit consists of: (1) two main massive sulfide horizons, the A-ores and B-ores, which dip steeply
southwards and are separated by 100–150 m; and (2) the Einarsson Zone, a complex interval of Cu–Au-rich ‘stockwork‘ sulfides
and small massive sulfide lenses in altered and deformed rocks near the 1,000 m level. The Einarsson Zone occurs some 20–100 m
south of the B-ores. There are no definite younging indicators in the mine sequence. In many areas of the mine, the original
host rocks are impossible to identify petrographically due to the abundance of secondary minerals such as quartz, chlorite,
muscovite, cordierite, andalusite, phlogopite, pyrite and talc, combined with variably schistose fabrics. Application of immobile-element
methods to 600 recent whole-rock chemical analyses has, however, allowed the original rock types to be identified and correlated.
Rhyolite X lies immediately north of the A-ore, while andesitic to dacitic to rhyodacitic rocks make up the 100–150 m interval
between the A-ore and B-ore, and massive rhyolite A lies immediately south of the B-ore. The felsic rocks are mostly of calc-alkaline
affinity, excluding rhyolite X, which is transitional. The mine porphyry, which lies north of the A-ore and forms the marginal
phase of the synvolcanic Viterliden Intrusive Complex, is compositionally similar to dacite and rhyodacite. Mass changes calculated
for all rock types indicate that most of the volcanic rocks in the mine area are strongly depleted in Na and Ca, and have
gained variable amounts of Mg and Fe, whereas Si changes range from negative to positive. Gains in Fe and changes in Si are
largest within 5–10 m of the massive sulfide lenses. Cordierite-bearing schists of andesitic to felsic compositions that lie
between massive sulfide lenses A and B are not as altered. The Einarsson Zone commonly shows large gains in Fe and Mg, while
Si shows large gains to large losses. Immobile-element ratios indicate that very different secondary assemblages in the mine,
e.g. andalusite–quartz–muscovite and cordierite–chlorite–talc, can be produced from the same precursor volcanic unit, e.g.,
rhyolite. Conversely, the same secondary mineral assemblage can be produced from different rocks, e.g. weakly altered andesite
and strongly altered rhyolite. The common presence of cordierite + andalusite in the mine area, without anthophyllite, is
unusual in the alteration systems of volcanic-hosted massive sulfide deposits, and is proposed to have formed by the metamorphic
reaction of the synvolcanic alteration minerals kaolinite and chlorite to produce cordierite. Where kaolinite was in excess
of chlorite, andalusite was also formed. We propose that highly acidic alteration fluids locally produced high-Al minerals
such as kaolinite that either overprinted, or occurred in place of, a more typical sericite–chlorite–quartz alteration assemblage
that otherwise formed near the massive sulfide lenses. Application of lithogeochemical methods to the altered, deformed and
metamorphosed Kristineberg rocks has identified specific volcanic contacts with massive sulfide potential, and quantified
the effects of synvolcanic hydrothermal alteration. Such an approach can increase the effectiveness of mineral exploration
in metamorphosed terrains. 相似文献
172.
Kim J. Krahn Mario Tucci Brigitte Urban Julien Pilgrim Peter Frenzel Ingeborg Soulié-Märsche Antje Schwalb 《Boreas: An International Journal of Quaternary Research》2021,50(3):723-745
The archaeological sites in the open-cast mine of Schöningen, Germany, represent outstanding archives for understanding Middle Pleistocene interglacial–glacial transitions and human adaption. Aquatic microfossil and pollen assemblages from the ‘Reinsdorf sequence’, likely correlated to Marine Isotope Stage 9, document environmental changes from a thermal maximum to succeeding glacial conditions recorded in two sequences of excavation sites 12 II and 13 II. Multi-proxy analyses enable detailed reconstruction of lake-shore and landscape developments despite variable microfossil preservation in changing carbonate- and organic-rich deposits. Rich aquatic vegetation with abundant charophytes suggests repeated phases with water depths of 0.5–2 m at site 13 II, while even greater temporary depths are deduced for 12 II DB. Mesorheophilic and mesotitanophilic ostracod species indicate stream inflows with medium–low calcium contents of >18 mg Ca L–1 originating from nearby springs. Diatoms point to meso-eutrophic conditions and an alkaline pH of the lake water. Interglacial conditions with thermophile forests but no aquatic microfossils preserved, suggesting a dry or only temporarily flooded site, mark the beginning of the sequence. Continuous presence of aquatic organisms and overall dominance of small tychoplanktonic diatoms during a subsequent cool steppe phase provide evidence for increased water depths and unstable habitats characterized by erosion and probably prolonged periods of lake ice cover. During the succeeding boreal forest-steppe phase, surface runoff into the productive, shallow lake decreased due to a more extensive vegetation cover. Concurrently, intensified groundwater input in contact with the nearby salt wall caused elevated salinities. Following a lake level drop, stream inflows and lake levels increased again towards the end of the Reinsdorf sequence and promoted development of a diverse fauna and flora at the lake shore; thereby maintaining an attractive living and hunting environment for early humans during a phase of generally cooler temperatures and landscape instability at the transition into a glacial period. 相似文献
173.
The geothermal fields in the Pericaspian, Pripyat, and North German basins are considered. These basins are characterized
by widespread Upper Paleozoic evaporite sequences, which underwent halokinesis with the formation of salt domes and plugs
owing to tectonic and gravity instability. Heat flow refraction occurs at the boundaries of the domes with country rocks due
to the contrast in thermal conductivity of evaporites and terrigenous rocks between the domal zones. This is the main cause
of heat flow variation in the lateral and vertical directions in the salt-dome basins. Close correlation between zones of
elevated temperature in the sedimentary rocks and petroleum occurrences is confirmed by the results of 2D and 3D modeling
of the geothermal field. The previously noted relations of oil and gas fields to the deep faults in the studied basins create
prerequisites for consideration of the geothermal field as a genetic factor controlling the tectonic features and petroleum
resources of the salt-dome basins. 相似文献
174.
175.
Revealing the coastal event-history of the Andaman Islands (Bay of Bengal) during the Holocene using radiocarbon and OSL dating 总被引:1,自引:0,他引:1
Alexander Kunz Manfred Frechen Ramachandran Ramesh Brigitte Urban 《International Journal of Earth Sciences》2010,99(8):1741-1761
Earthquakes that trigger tsunamis are of great geological, ecological and socio-economic importance. The knowledge of the
recurrence interval of these events will give information about the hazard for a region. Coastal sediments on the Andaman
Islands located in the eastern Bay of Bengal were investigated to find evidence for palaeotsunamis and palaeoearthquakes.
Fieldwork was conducted on Red Skin Island and North Cinque Island, south of South Andaman. Sediment material from event-layers
was dated by optically stimulated luminescence and radiocarbon dating method. The results show evidence possibly for one earthquake
at about 1,000 or 3,000 years before the present together with deposits from possible tsunamis and storms. The complex pattern
of co- and post-seismic uplift and subsidence of the Andaman Islands is reflected in the investigated sections and made it
possible to reconstruct an event-history for the last 3,000 years. 相似文献