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Abstract. The present investigation deals with sulphur isotope distribution in Lower Proterozoic iron and sulphide mineralizations in northern Sweden. The contrastmg sulphur isotope patterns are indicative of different genesis. Some 267 sulphur isotope analyses of pyrite, pyrrhotite, chalcopyrite, sphalerite, galena and bornite from 23 occurrences have been performed. Some deposits exhibit uniform compositions, although the mean 634S values are clearly different, while other mineralizations have widely fluctuating values.The 634S values in syngenetic, exhalative sedimentary skarn iron ores, quartz-banded iron ores and sulphide mineralizations of the 2.0-2.5 Ga old (Lapponian) Greenstone group show a large spread, supporting the existence of bacteriogenic sulphate reduction processes. The spread of the sulphur isotope values (&34S = -8 to + 25%o), and the non-equilibrium conditions, point to a biogenic rather than to an inorganic reduction of seawater sulphate.The isotopic composition of the sulphides in the epigenetic Lannavaara iron ores which were formed by a hydrothermal scapolite-tourmaline-related process, indicates a sulphur source similar to that of the Greenstone group. The &34S values of Cu-(Au) sulphide mineralizations in the Malmberget region (e.g. Aitik), which were formed by a similar process and hosted by the volcanicsvolcanoclastics of the 1.9Ga old Porphyry group, are slightly below zero %0, indicating a magmatic origin. The existence of different sulphur compositions for these mineralization types formed by a similar hydrothermal process, probably reflects the influence of the host rock, the solutions leaching pre-existing sulphides.In southern Norrbotten, epigenetic, Cu-Zn-Pb veintype mineralizations in metavolcanics and metasediments have 634S values close to zero %0 indicating a magmatic origin. The sulphur isotope data of the volcanogenic, massive sulphide ores of the Skellefte district, in particular the ores of the Adak dome, are close to zero %0.The lead and sulphur isotopic features of the sulphides in northern Sweden show that the ore-forming processes were of a different nature on both sides of the ArcheanProterozoic border, implying differences in the crustal development. Lead isotopes show that lead was mobilized from specific sources on each side of the border. The sulphur of the sulphides in the Greenstone group in NE Sweden and Finland was introduced by sedimentary processes, whereas the sulphur of the sulphide occurrences towards the SW, mainly in the Porphyry group, is dominated by a magmatic sulphur component.
Abstract. The present investigation deals with sulphur isotope distribution in Lower Proterozoic iron and sulphide mineralizations in northern Sweden. The contrastmg sulphur isotope patterns are indicative of different genesis. Some 267 sulphur isotope analyses of pyrite, pyrrhotite, chalcopyrite, sphalerite, galena and bornite from 23 occurrences have been performed. Some deposits exhibit uniform compositions, although the mean 634S values are clearly different, while other mineralizations have widely fluctuating values.The 634S values in syngenetic, exhalative sedimentary skarn iron ores, quartz-banded iron ores and sulphide mineralizations of the 2.0-2.5 Ga old (Lapponian) Greenstone group show a large spread, supporting the existence of bacteriogenic sulphate reduction processes. The spread of the sulphur isotope values (&34S = -8 to + 25%o), and the non-equilibrium conditions, point to a biogenic rather than to an inorganic reduction of seawater sulphate.The isotopic composition of the sulphides in the epigenetic Lannavaara iron ores which were formed by a hydrothermal scapolite-tourmaline-related process, indicates a sulphur source similar to that of the Greenstone group. The &34S values of Cu-(Au) sulphide mineralizations in the Malmberget region (e.g. Aitik), which were formed by a similar process and hosted by the volcanicsvolcanoclastics of the 1.9Ga old Porphyry group, are slightly below zero %0, indicating a magmatic origin. The existence of different sulphur compositions for these mineralization types formed by a similar hydrothermal process, probably reflects the influence of the host rock, the solutions leaching pre-existing sulphides.In southern Norrbotten, epigenetic, Cu-Zn-Pb veintype mineralizations in metavolcanics and metasediments have 634S values close to zero %0 indicating a magmatic origin. The sulphur isotope data of the volcanogenic, massive sulphide ores of the Skellefte district, in particular the ores of the Adak dome, are close to zero %0.The lead and sulphur isotopic features of the sulphides in northern Sweden show that the ore-forming processes were of a different nature on both sides of the ArcheanProterozoic border, implying differences in the crustal development. Lead isotopes show that lead was mobilized from specific sources on each side of the border. The sulphur of the sulphides in the Greenstone group in NE Sweden and Finland was introduced by sedimentary processes, whereas the sulphur of the sulphide occurrences towards the SW, mainly in the Porphyry group, is dominated by a magmatic sulphur component.
Recent studies of volcanogenic base metal sulfide deposits and of metalliferous sediments in the Red Sea indicate precipitation of iron and base metals under conditions varying from reducing to oxidizing, at or near sites of fumarolic brine emission onto the sea floor. Differing lithofacies of iron-rich sediments were apparently deposited penecontemporaneously, mainly in response to changing chemical, biological, and sedimentary lithofacies conditions. Iron-rich sediments associated with the cupriferous pyrite bodies of Cyprus have been studied to determine the behavior of Fe, Mn, Cu, Zn, Pb, Ni, Co, Cr, Sn, Mo, Ag, and Au, when these fumarolic brines enter the sea bottom environment. Variations in metal abundances and ratios indicate that rapidly changing Eh is a major factor controlling metal deposition on the sea floor. The FeIMn ratio in these sediments is a useful indicator of the amount of interaction of these fumarolic brines and normal oxygenated sea water. Results suggest that zinc, copper, and gold are concentrated in the high FelMn ratio proximal sediments; nickel is concentrated in the low FelMn ratio distal sediments; and lead, silver, tin, and molybdenum are relatively unaffected by oxidation of the fumarolic brine solution by normal sea water.These concepts of sea floor deposition controlling the distribution of metals may also be applicable to other types of stratabound metalliferous deposits, like certain skarn, greisen, and gold ores, heretofore considered to be of epigenetic origin.Des etudes recentes de gisements de sulfures metalliques d'origine volcanique et de sediments metalliferes dans la mer Rouge indiquent que le fer et les metaux de base precipitent dans des conditions variant de reductrices a oxydantes lorsqu'ils sont localises pres des bouches d'ernissions du fond de la mer. Divers lithofacies de sediments enrichis en fer auraient e t t deposes a ces moments precis comme effet de changements de conditions chimiques, biologiques et de facies sedimentaires.Nous avons etudie des sediments riches en fer associes aux gisements de pyrite cuprifere de Chypre pour determiner le comportement des elements Fe, Mn, Cu, Zn, Pb, Ni, Co, Cr, Sn, Mo, Ag, et Au lorsque les fumerolles arrivent dans le milieu marin. La quantite de chaque metal et leur proportion varient avec un changement rapide du Eh, ce qui semble 6tre un facteur important qui contr8le les depbts metalliques sur le fond de la mer. Le rapport Fe/Mn a l'interieur de ces sediments est un bon indicateur de I'interaction de ces fumerolles et de l'eau de mer normalement oxygenee. Les resultats suggerent que le zinc, le cuivre et I'or sont en plus grande quantite lorsque le rapport FelMn est eleve dans les sediments proximaux; le nickel y est plus abondant si le rapport FelMn est faible dans les sediments plus eloignes; le plomb, I'argent, l'etain et le molybdene ne sont pratiquement pas affectes par I'oxydation des fumerolles par I'eau de mer normale.Ces conceptsdes dep8ts marins contrblant la distribution des metaux peuvent s'appliquer au...
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