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Online oxygen (δ 18 O) and hydrogen (δ 2 H) isotope analysis of fluid inclusion water entrapped in minerals is widely applied in paleo-fluid studies. In the state of the art of fluid inclusion isotope research, however, there is a scarcity of reported inter-technique comparisons to account for possible analytical offsets.Along with improving analytical precisions and sample size limitations, interlaboratory comparisons can lead to a more robust application of fluid inclusion isotope records.Methods: Mineral samples-including speleothem, travertine, and vein materialwere analyzed on two newly setup systems for fluid inclusion isotope analysis to provide an inter-platform comparison. One setup uses a crusher unit connected online to a continuous-flow pyrolysis furnace and an isotope ratio mass spectrometry (IRMS) instrument. In the other setup, a crusher unit is lined up with a cavity ringdown spectroscopy (CRDS) system, and water samples are analyzed on a continuous standard water background to achieve precisions on water injections better than 0.1‰ for δ 18 O values and 0.4‰ for δ 2 H values for amounts down to 0.2 μL.Results: Fluid inclusion isotope analyses on the IRMS setup have an average 1σ reproducibility of 0.4‰ and 2.0‰ for δ 18 O and δ 2 H values, respectively. The CRDS setup has a better 1σ reproducibility (0.3‰ for δ 18 O values and 1.1‰ for δ 2 H values) and also a more rapid sample throughput (<30 min per sample). Fluid inclusion isotope analyses are reproducible at these uncertainties for water amounts down to 0.1 μL on both setups. Fluid inclusion isotope data show no systematic offsets between the setups. Conclusions:The close match in fluid inclusion isotope results between the two setups demonstrates the high accuracy of the presented continuous-flow techniques for fluid inclusion isotope analysis. Ideally, experiments such as the one presented in this study will lead to further interlaboratory comparison efforts and the selection of suitable reference materials for fluid inclusion isotopes studies.

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Hydrothermal fluid flow along fault zones in the Harz Mountains led to widespread formation of economic vein-type Pb-Zn ore and Ba-F deposits during the Mesozoic. We reconstruct the fluid flow system responsible for the formation of these deposits using isotope ratios (δ 2 H and δ 18 O) and anion and cation contents of fluid inclusions in ore and gangue minerals. Building forward on extensive studies in the 1980s and 1990s, our new geochemical data reveal that seawater evaporation brines, which most likely originated from Zechstein evaporites, descended deeply into Paleozoic rocks to leach metals at depth. In Jurassic times, these metal-rich brines episodically recharged along fault zones and mixed with shallow crustal H 2 S-bearing brines. Primarily in the Upper Harz Mountains, this mixing system led to the formation of economic Pb-Zn-Cu mineralization, which locally shows banded textures with alternations of sulfide minerals and quartz or carbonate (mostly calcite). In the Middle and Lower Harz Mountains, Zechstein-derived brines interacted with K-and F-bearing basement rocks and/or magmatic rocks to deposit fluorite mineralization upon ascent in the Upper Cretaceous. The proposed model of mineralizing fluids originating as (evaporated) seawater has been shown to hold for numerous basin-hosted base-metal sulfide and fluoride deposits elsewhere in Europe.