Pb isotope constraints on fluid flow and mineralization processes in SW Germany (original) (raw)
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Overbank sediments from the River Weser provide a record of geochemical anomalies which vary distinctively from the regional background as far back as 3500 years BP. The use of Pb isotopes, measured by inductively coupled plasma mass spectrometry (ICP-MS), in combination with the determination of heavy metal concentrations has identified the mining and smelting activities that took place early in the Harz Mountains. as the source of contamination. The regional background was defined from sediments deposited prior to 3500 years BP with Pb and Zn concentrations of about 23 ^ 7 and 109 ^ 38 mg g21; 206Pb/207Pb ratios of 1:215 ^ 0:002 and 208Pb/206Pb ratios of 2:044 ^ 0:002: The isotopic characteristics of the Pb in the sediments can be easily explained by a simple two-component mixing model involving: (i) the background component; and (ii) Pb derived from the Harz Mountain ore bodies characterised by 206Pb/207Pb ratios of 1.167–1.187 and 208Pb/206Pb ratios of 2.075–2.096. The rapid determination of isotopic ratios by ICP-MS has advantages over Thermal Ionisation Mass Spectrometry. It enables large-scale investigations in prospecting archaeology or more-recent history.
Stable isotope relationships of mineralisation in theNorth Eastern German Basin
Journal of Geochemical Exploration, 2003
JOURNAL OF GEOCHEMICAL EXPLORATION www.elsevier.comJlocate/j geoexp Abstract Stable isotope systematics (634S, 6180, ~13C) of carbonates, sulphates and sulphides of hydrothermal veins and t~acture infills in the North Eastern German Basin (NEGB) give evidence of a complex history of fluid input from at least two sources: fluids equilibrated with the Zechstein evaporites and fluids ascending from deeper sources such as the Rotliegend and Upper Carboniferous volcanics. The different fluid events can be related to mineralising events of vein deposits in the Harz Mountains and the polymetallic Kupferschiefer mineralisations.
Chemical Geology, 2015
We studied an aragonitic section of ca. 6 cm length of stalagmite HBSH-1 from the Hüttenbläserschachthöhle, western Germany. 230 Th/U-dating revealed that this section grew between~210 and~190 ka, with a relatively uniform growth rate of 3.1 μm a −1 . For the first time, we determined Pb isotope ratios ( 207 Pb/ 206 Pb and 208 Pb/ 206 Pb) in a stalagmite by laser ablation (LA)-ICP-MS. In addition, we analyzed various trace element (Mg, Al, Si, P, Mn, Sr, Pb and Th) concentrations.
Lead isotope behaviour in a polyphased Pb-Zn ore deposit: Les Malines (Cévennes, France)
Mineralium Deposita, 1991
Les Malines Mine (C6vennes, France) provides an example of Pb-Zn ore bodies that underwent a polyphased evolution. On the Pb-Pb diagram, experimental points of the Les Malines ore types always plot in the central part of the field defined for the C6vennes metallogenic province. This homogeneity, the similarities with the Pb isotopic compositions of the surrounding rocks and the comparison with Pb isotopes evolution of whole rocks and minerals of the neighbouring continental lands, which emerged during Triassic and Liassic times, rule out the participation of extraneous Pb during the successive concentration stages and agree with an initial metal stock transformed and mobilized in a Pb closed system. Hercynian K-feldspars are the main source of the Pb preconcentrated during Triassic times. Most of the C6vennes Pb-Zn ore bodies could derive from this Triassic metal stock; nevertheless, local Pb isotopic anomalies suggest hydrothermal sources for some Pb-Zn ore bodies located along the C6vennes fault.
Large-scale tectonic cycles in Europe revealed by distinct Pb isotope provinces
Lead isotopic systematics of U-poor minerals, such as sulfides and feldspars, can provide unique insights into the origin and evolution of continents because these minerals ''freeze in'' the Pb isotopic composition of the crust during major tectonothermal events, allowing the history of a continent to be told through Pb isotopes. Lead model ages constrain the timing of crust formation while time-integrated U/ Pb, Th/Pb, and Th/U ratios shed light onto key geochemical processes associated with continent formation. Using 6800 Pb isotope measurements of primarily lead ores and minor K-feldspar, we mapped out the Pb isotope systematics across Europe and the Mediterranean. Lead model ages define spatially distinct age provinces, consistent with major tectonic events ranging from the Paleozoic to the Proterozoic and latest Archean. However, the regions defined by time-integrated U/Pb and Th/Pb ratios cut across the boundaries of age provinces, with high U/Pb systematics characterizing most of southern Europe. Magmatic influx, followed by segregation of dense sulfide-rich mafic cumulates, resulted in foundering of U-and Th-poor lower crust, thereby changing the bulk composition of the continental crust and leading to distinct time-integrated U-Th/Pb provinces. We show that the tectonic assembly of small crustal fragments leaves the crust largely undifferentiated, whereas the formation of supercontinents results in fundamental changes in the composition of the crust, identifiable in time and space by means of Pb isotope systematics. Observations based on Pb isotopes open up a new perspective on possible relationships between crustal thickness and geodynamic processes, in particular the role of crustal foundering into the mantle and the mechanisms responsible for the existence of cratons.
Ore Geology Reviews
Fe sulfide and F-Ba mineralization occur as open space fillings, veins, and fracture coatings in various parts of the North German Basin in Paleozoic sedimentary rocks and volcanic units at depths of up to four kilometers. We present a petrographic and geochemical (fluid inclusion, mineral and formation water geochemistry) inventory of the mineralized zones and review the basin architecture, evolution, and stratigraphy in order to decipher the timing, extent, fluid pathways, and fluid-rock interactions associated with the ore formation. A particular focus lies on the sediment-hosted Zn-Fe-Pb sulfides in the western part of the North German Basin, the Lower Saxony Basin. Samples from hydrothermal veins from the Pre-Permian basement are also being investigated and compared to the North German Basin-style mineralization to uncover possible genetic links between them. The sediment-hosted sulfide mineralization in the Lower Saxony Basin in the Permian Stassfurt Carbonate unit (Ca2) shares many characteristics that are typical for carbonate-hosted base metal sulfide deposits such as MVT deposits. Petrographic observations, fluid inclusion and isotope data provide evidence that Zn-Fe-Pb sulfides were deposited by highly saline metal-rich basinal brines at temperatures of ∼160°C. Carbon and oxygen isotope data point toward fluid mixing augmented by structurally-controlled fluid migration during the late Cretaceous basin inversion as the primary ore precipitation mechanism with no magmatic component. In the Altmark-Brandenburg Basin, steeply-dipping F-Ba (calcite, anhydrite, quartz) veinlets in Permo-Carboniferous sandstones and volcanic units are evidence for enhanced post-Variscan structurally-controlled fluid flow. Sulfides are, apart from rare occurrences of chalcopyrite, absent. This is interpreted to reflect the paleogeographic position of the Altmark-Brandenburg Basin (deeper paleogeographic basin position without carbonate aquifers), the lack of reductants, and the predominance of nitrogen-rich fluids as documented by fluid inclusions. Measurements on formation waters from the NGB show geochemical similarities to fluid inclusions in ore and gangue minerals and could represent a potential future exploration tool for hydrothermal ore deposits. This has the potential to aid future research and exploration of deeply covered sediment-hosted deposits and to meet future mineral resources demands.
Chemical Geology, 1991
Lead isotopic data of alkaline volcanic rocks and carbonatites from the Kaiserstuhl are presented in combination with Sr isotopic ratios. As a whole the initial lead ratios cover the range typical for other Tertiary to Recent alkaline rock provinces in Europe: 2°6pb/2°4pb= 18.9-19.7, 2°7pb/2°apb= 15.61-15.70 and 2°SpbF°4Pb= 38.7-39.7. Especially in the 2°SpbF°4pb vs. 2°6pb/2°4pb diagram the data reveal a linear array which is interpreted in terms of mixing of two mantle components. In detail the data comprise three distinct groups which are correlated with different magmatic rock types: unfractionated primary mantle melts (olivine nephelinites, olivine melilitites), fractionated alkaline rocks (tephrites, phonolites), and a group with carbonatites, bergalites and hauynophyres. These results are interpreted to reflect either derivation from different mantle sources, or the data trace a mixing line between two mantle reservoirs, one of them being more enriched. Contamination with crustal lead is unlikely: it may have affected the tephritic magma series, but not the carbonatitic rocks. The uppermost part of the updomed mantle beneath the Kaiserstuhl, which is known by petrographic evidence to be partially metasomatized, probably is the site of the enriched reservoir. A "plume'Mike structure within the deeper mantle is suggested as the initial source of this mechanism.
Economic Geology
The Southern Permian basin in central Europe contains a number of important high-grade sediment-hosted Cu deposits. Laterally extensive stratabound Cu and Zn-Pb sulfide mineralized rocks are located at a major stratigraphic redox boundary, where coarse-grained continental sandstones of the uppermost Rotliegend Group are overlain by carbonaceous mudstones (T1) and limestones (Ca1) of the Zechstein Formation. This study investigates the diagenetic evolution and style of sulfide mineralization in three drill cores that intersect Cu and Zn-Pb sulfide mineralized rocks at three locations (Sangerhausen, Allstedt, and Wallendorf) in the Saale subbasin (Eastern Germany), which is located at the southern margin of the Southern Permian basin. We combine macro- to microscale petrographic data (binocular, transmitted and reflected light, and scanning electron microscopy) with quantitative X-ray diffractometry and bulk-rock geochemical analyses. Petrographic results show extensive, primary-poros...
The significance of galena Pb model ages and the formation of large Pb-Zn sedimentary deposits
Chemical Geology, 2021
In an attempt to clarify the significance of Pb model ages in Pb-Zn sedimentary deposits, we report high-precision Pb isotopic compositions for 64 galenas and 52 K-feldspars, the former from ores and the latter separated from granites. All samples are from Spain and the French Pyrenees. Lead from galena ores is of unequivocal continental origin. With few exceptions, Pb model ages systematically exceed emplacement ages by up to 400 Ma, a gap which is well outside the uncertainties of ~30 Ma assigned to the model. The histogram of the new high-precision Pb isotope data shows prominent peaks of galena Pb model ages at 94±38 Ma and 392±39 Ma. When the data are consolidated with literature data and examined in 3-dimensional Pb isotope space, cluster analysis identifies five groups. The model ages of the peaks occur, in order of decreasing peak intensity, at 395±40 (Middle Devonian), 90±34 Ma (Middle Cretaceous), and 613±42 Ma (Neoproterozoic), with two minor peaks at 185+26 Ma (Jurassic) and 313±41 (Upper Carboniferous). To a large extent, the model ages centered around these peaks correspond to distinct localities. The ages of the peaks do not coincide with any of the Betic, Variscan, or Pan-African tectonic events, which are the main tectonic episodes that shaped Iberian geology, but rather match well-known global oceanic anoxic events. It is argued that surges of metals weathered from continental surfaces scorched during anoxic events accumulated and combined in anoxic water masses with unoxidized marine sulfide released by submarine hydrothermal activity to precipitate the primary Pb-Zn stock. Frozen Pb isotope compositions require that galenas from black shales are the source of the final ores. The Revised manuscript with no changes marked Click here to view linked References 2 sulfides were later remobilized by large-scale convective circulation of basinal and hydrothermal fluids. The peaks of K-feldspar Pb model ages are distinct from those of galenas and do not correlate with magmatic emplacement ages. It is suggested that they instead reflect local circulation in Paleozoic sediments surrounding individual plutons. While Pb isotopes can be used as a regional provenance tool, such an approach requires that the data are considered in a fully 3-dimensional space.
Chemical Geology, 1991
Lead isotopic data of alkaline volcanic rocks and carbonatites from the Kaiserstuhl are presented in combination with Sr isotopic ratios. As a whole the initial lead ratios cover the range typical for other Tertiary to Recent alkaline rock provinces in Europe: 2°6pb/2°4pb= 18.9-19.7, 2°7pb/2°apb= 15.61-15.70 and 2°SpbF°4Pb= 38.7-39.7. Especially in the 2°SpbF°4pb vs. 2°6pb/2°4pb diagram the data reveal a linear array which is interpreted in terms of mixing of two mantle components. In detail the data comprise three distinct groups which are correlated with different magmatic rock types: unfractionated primary mantle melts (olivine nephelinites, olivine melilitites), fractionated alkaline rocks (tephrites, phonolites), and a group with carbonatites, bergalites and hauynophyres. These results are interpreted to reflect either derivation from different mantle sources, or the data trace a mixing line between two mantle reservoirs, one of them being more enriched. Contamination with crustal lead is unlikely: it may have affected the tephritic magma series, but not the carbonatitic rocks. The uppermost part of the updomed mantle beneath the Kaiserstuhl, which is known by petrographic evidence to be partially metasomatized, probably is the site of the enriched reservoir. A "plume'Mike structure within the deeper mantle is suggested as the initial source of this mechanism.