Timing of magmatic-hydrothermal activity in the Variscan Orogenic Belt: LA-ICP-MS U–Pb geochronology of skarn-related garnet from the Schwarzenberg District, Erzgebirge

[EN] Here, we present in situ U-Pb laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) ages of andradite-grossular garnet from four magmatic-hydrothermal polymetallic skarn prospects in the Schwarzenberg District, Erzgebirge (Germany), located in the internal zone of the Variscan Orogenic Belt. Within the geochronological framework of igneous rocks and hydrothermal mineralization in the Erzgebirge, the obtained garnet ages define three distinct episodes of Variscan skarn formation: (I) early late-collisional mineralization (338-331 Ma) recording the onset of magmatic-hydrothermal fluid flow shortly after the peak metamorphic event, (II) late-collisional mineralization (similar to 327-310 Ma) related to the emplacement of large peraluminous granites following large-scale extension caused by orogenic collapse and (III) post-collisional mineralization (similar to 310-295 Ma) contemporaneous with widespread volcanism associated with Permian crustal reorganization. Our results demonstrate that the formation of skarns in the Schwarzenberg District occurred episodically in all sub-stages of the Variscan orogenic cycle over a time range of at least 40 Ma. This observation is consistent with the age range of available geochronological data related to magmatic-hydrothermal ore deposits from other internal zones of the Variscan Orogenic Belt in central and western Europe. In analogy to the time-space relationship of major porphyry-Cu belts in South America, the congruent magmatic-hydrothermal evolution in the internal zones and the distinctly later (by similar to 30 Ma) occurrence of magmatic-hydrothermal ore deposits in the external zones of the Variscan Orogenic Belt may be interpreted as a function of their tectonic position relative to the Variscan collisional front.Open Access funding enabled and organized by Projekt DEAL. This study was funded by the Federal State of Saxony and the European Social Fund (Grant no. 100339454 received by M. Burisch

Ore-forming processes of hydrothermal vein-type deposits, SW Germany

This thesis focuses on ore-forming processes and the provenance of involved fluids, solutes and gases of epithermal to mesothermal Pb-Zn-(Cu)-fluorite-quartz and Ag/Bi-Ni-Co-(Fe)-As-(U)-calcite vein-type deposits of the Schwarzwald and the Odenwald, SW Germany. These veins occur across basement-cover unconformities due to mixing of two or more chemically contrasting fluids. A fluid component (fluid-type A), which originates from deeper crustal levels (high salinity; low Cl/Br (by mass)) of the upper crust is invariably recognised in the ore fluids, while the other fluid component is of basinal, sedimentary and/or meteoric origin (fluid-type B). Although extensive data is available for unconformity-related hydrothermal veins, several important aspects are still poorly constrained. These aspects include a precise understanding of the processes that result in the observed compositions of deep-seated crustal fluids, alteration processes in root zones (below actual vein), regional and temporal variations in the composition of the ore fluids of the Schwarzwald and the genesis of the enigmatic five-element veins of the Odenwald, SW Germany. To attain a better understanding of the presented aspects, we carried out leaching experiments on common igneous, metamorphic and sedimentary rocks including their mineral separates at variable temperatures (25 to 350°C), pressures (0.01 to 1.9 kbar), grain-size fractions and fluid/rock ratios. Leachates were analysed by ion chromatography and total reflexion X-ray fluorescence (TXRF). The samples were characterized prior to the experiments by X-ray fluorescence, microthermometry, electron microprobe analyses, pyrohydrolysis and TXRF. Furthermore, numerous hydrothermal veins of the Schwarzwald and the Odenwald were characterized with respect to their ore geology, vein mineralogy, mineral chemistry, fluid inclusion composition (microthermometry, crush-leach, LA-ICPMS and Raman spectroscopy), stable isotopic composition and radiogenic isotopic composition. This comprehensive analytical and experimental approach yields new and profound insights into processes relevant for hydrothermal vein-type deposits. Halogens fractionate during fluid-rock interaction, since they are distributed between two reservoirs in the rock: as highly soluble phases and as low soluble phases. Lowest Cl/Br ratios, similar to natural basement brines are obtained by short leaching of medium- to fine-grained rock. Still, the maximum salinities that can be obtained by selective leaching of the low soluble phases are limited to ~10 wt.%. Consequently, at least an additional chlorine source is required for natural basement fluids having high salinities (~26 wt.%) and low Cl/Br ratios. Furthermore, the experiments confirm that substantial amounts of Pb, Zn, Cu, Ni, As and W are released by alteration of common rock-forming minerals. Time resolved trace element, Rb/Cs and Cl/Br variations of vein-hosted fluid inclusions of the Jurassic Brandenberg vein near Todtnau (Germany) were used to monitor alteration processes that occur in cataclastic root zones below the actual hydrothermal vein. On the other hand, the sedimentary aquifers involved in ore-forming processes and their associated fluids are inhomogeneous in their composition on the scale of the Schwarzwald. The combined study of the regional geology, basement brines, sedimentary brines and the ore fluids (mixture) of different vein-types and ages enabled a reconstruction of the evolution and origin of the involved fluids during the last 300 million years. A new genetic model for five-element veins is proposed, which seems to be universally valid for most occurrences of five-element veins. Five-element veins form where strongly reducing methane or methane-bearing fluids are introduced into an active hydrothermal sulphide system. This is the first genetic model for five-element veins, which is in total agreement with all textural and chemical features that are typical of five-element veins

The Niederschlag fluorite-(barite) deposit, Erzgebirge/Germany—a fluid inclusion and trace element study

The Niederschlag fluorite-barite vein deposit in the Western Erzgebirge, Germany, has been actively mined since 2013. We present the results of a first comprehensive study of the mineralogy, petrography, fluid inclusions, and trace element geochemistry of fluorite related to the Niederschlag deposit. Two different stages of fluorite mineralization are recognized. Stage I fluorite is older, fine-grained, associated with quartz, and forms complex breccia and replacement textures. Conversely, the younger Stage II fluorite is accompanied by barite and often occurs as banded and coarse crystalline open-space infill. Fluid inclusion and REY systematics are distinctly different for these two fluorite stages. Fluid inclusions in fluorite I reveal the presence of a low to medium saline (7–20% eq. w (NaCl+CaCl2)) fluid with homogenization temperatures of 140–180 °C, whereas fluorite II inclusions yield distinctly lower (80–120 °C) homogenization temperatures with at least two high salinity fluids involved (18–27% eq. w (NaCl+CaCl2)). In the absence of geochronological data, the genesis of the earlier generation of fluorite-quartz mineralization remains enigmatic but is tentatively related to Permian magmatism in the Erzgebirge. The younger fluorite-barite mineralization, on the other hand, has similarities to many fluorite-barite-Pb-Zn-Cu vein deposits in Europe that are widely accepted to be related to the Mesozoic opening of the northern Atlantic Ocean.European Social Fund http://dx.doi.org/10.13039/50110000489

The Niederschlag fluorite-(barite) deposit, Erzgebirge/Germany—a fluid inclusion and trace element study

<jats:title>Abstract</jats:title><jats:p>The Niederschlag fluorite-barite vein deposit in the Western Erzgebirge, Germany, has been actively mined since 2013. We present the results of a first comprehensive study of the mineralogy, petrography, fluid inclusions, and trace element geochemistry of fluorite related to the Niederschlag deposit. Two different stages of fluorite mineralization are recognized. Stage I fluorite is older, fine-grained, associated with quartz, and forms complex breccia and replacement textures. Conversely, the younger Stage II fluorite is accompanied by barite and often occurs as banded and coarse crystalline open-space infill. Fluid inclusion and REY systematics are distinctly different for these two fluorite stages. Fluid inclusions in fluorite I reveal the presence of a low to medium saline (7–20% eq. w (NaCl+CaCl<jats:sub>2</jats:sub>)) fluid with homogenization temperatures of 140–180 °C, whereas fluorite II inclusions yield distinctly lower (80–120 °C) homogenization temperatures with at least two high salinity fluids involved (18–27% eq. w (NaCl+CaCl<jats:sub>2</jats:sub>)). In the absence of geochronological data, the genesis of the earlier generation of fluorite-quartz mineralization remains enigmatic but is tentatively related to Permian magmatism in the Erzgebirge. The younger fluorite-barite mineralization, on the other hand, has similarities to many fluorite-barite-Pb-Zn-Cu vein deposits in Europe that are widely accepted to be related to the Mesozoic opening of the northern Atlantic Ocean.</jats:p&gt

Li-Co–Ni-Mn-(REE) veins of the Western Erzgebirge, Germany—a potential source of battery raw materials

Situated in the western Erzgebirge metallogenetic province (Vogtland, Germany), the Eichigt prospect is associated with several quartz-Mn-Fe-oxyhydroxide veins that are exposed at surface. Bulk-rock geochemical assays of vein material yield high concentrations of Li (0.6–4.1 kg/t), Co (0.6–14.7 kg/t), and Ni (0.2–2.8 kg/t), as well as significant quantities of Mn, Cu, and light rare earth elements, a very unusual metal tenor closely resembling the mixture of raw materials needed for Li-ion battery production. This study reports on the results of a first detailed investigation of this rather unique polymetallic mineralization style, including detailed petrographic and mineralogical studies complemented by bulk rock geochemistry, electron microprobe analyses, and laser ablation inductively coupled mass spectrometry. The mineralized material comprises an oxide assemblage of goethite hematite, hollandite, and lithiophorite that together cement angular fragments of vein quartz. Lithiophorite is the predominant host of Li (3.6–11.1 kg/t), Co (2.5–54.5 kg/t), and Ni (0.2–8.9 kg/t); Cu is contained in similar amounts in hollandite and lithiophorite whereas light rare earth elements (LREE) are mainly hosted in microcrystalline rhabdophane and florencite, which are finely intergrown with the Mn-Fe-oxyhydroxides. 40Ar/39Ar ages (~ 40–34 Ma) of coronadite group minerals coincide with tectonic activity related to the Cenozoic Eger Graben rifting. A low-temperature hydrothermal overprint of pre-existing base metal sulfide-quartz mineralization on fault structures that were reactivated during continental rifting is proposed as the most likely origin of the polymetallic oxyhydroxide mineralization at Eichigt. However, tectonically enhanced deep-reaching fracture-controlled supergene weathering cannot be completely ruled out as the origin of the mineralization.Lithium AustraliaEuropean Social Fund http://dx.doi.org/10.13039/501100004895Technische Universität Bergakademie Freiberg (3135

Li-Co–Ni-Mn-(REE) veins of the Western Erzgebirge, Germany—a potential source of battery raw materials

<jats:title>Abstract</jats:title><jats:p>Situated in the western Erzgebirge metallogenetic province (Vogtland, Germany), the Eichigt prospect is associated with several quartz-Mn-Fe-oxyhydroxide veins that are exposed at surface. Bulk-rock geochemical assays of vein material yield high concentrations of Li (0.6–4.1 kg/t), Co (0.6–14.7 kg/t), and Ni (0.2–2.8 kg/t), as well as significant quantities of Mn, Cu, and light rare earth elements, a very unusual metal tenor closely resembling the mixture of raw materials needed for Li-ion battery production. This study reports on the results of a first detailed investigation of this rather unique polymetallic mineralization style, including detailed petrographic and mineralogical studies complemented by bulk rock geochemistry, electron microprobe analyses, and laser ablation inductively coupled mass spectrometry. The mineralized material comprises an oxide assemblage of goethite hematite, hollandite, and lithiophorite that together cement angular fragments of vein quartz. Lithiophorite is the predominant host of Li (3.6–11.1 kg/t), Co (2.5–54.5 kg/t), and Ni (0.2–8.9 kg/t); Cu is contained in similar amounts in hollandite and lithiophorite whereas light rare earth elements (LREE) are mainly hosted in microcrystalline rhabdophane and florencite, which are finely intergrown with the Mn-Fe-oxyhydroxides.<jats:sup>40</jats:sup>Ar/<jats:sup>39</jats:sup>Ar ages (~ 40–34 Ma) of coronadite group minerals coincide with tectonic activity related to the Cenozoic Eger Graben rifting. A low-temperature hydrothermal overprint of pre-existing base metal sulfide-quartz mineralization on fault structures that were reactivated during continental rifting is proposed as the most likely origin of the polymetallic oxyhydroxide mineralization at Eichigt. However, tectonically enhanced deep-reaching fracture-controlled supergene weathering cannot be completely ruled out as the origin of the mineralization.</jats:p&gt