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This work evaluates an exceptionally complex natural laboratory, the Middle Triassic Latemar isolated platform in the northern Italian Dolomite Mountains and explores spatial and temporal gradients in processes and products related to contact metamorphism, dolomitization and dedolomitization of marine limestones. The relation between petrographic change and re‐equilibration of geochemical proxy data is evaluated from the perspective of carbonate‐archive research. Hydrothermal dolomitization of the limestone units is triggered by dykes and associated hydrothermal fluids radiating from the nearby Predazzo Intrusion. Detailed petrography, fluid inclusion analysis, δ13C and δ18O data and 87Sr/86Sr isotope ratios shed light on the extreme textural and geochemical complexity. Metamorphic and diagenetic patterns include: (i) peak‐metamorphic and retrograde‐metamorphic phases including three dolomite marbles, two dedolomite marbles, brucite, magnesium silicates and late‐stage meteoric/vadose cement at the contact aureole; (ii) four spatially defined episodes of dolomitization, authigenic quartz, low magnesium calcite and late‐stage meteoric cement at the Latemar isolated platform; and (iii) kilometre‐scale gradients in δ13C values from the contact aureole towards the platform interior. Results shown here are relevant for two reasons: first, the spatial analysis of alteration products ranging from high‐grade metamorphic overprint of marbles at temperatures of 700°C in the contact aureole to moderately altered limestones in the platform interior at temperatures <100°C, allows the observation of processes that commonly occur along vertical (prograde) gradients from shallow burial to metamorphism at depths >20 km. Second, under rock‐buffered conditions, and irrespective of metamorphic to diagenetic fluid−rock interactions, both marbles, and low‐temperature hydrothermal dolomites have conservative marine δ13C and δ18O values. The fact that metamorphism and hydrothermal dolomitization of precursor limestones and early diagenetic dolostones did not per se reset environmental proxy data is of interest for those concerned with carbonate archive research in Earth's deep time. [ABSTRACT FROM AUTHOR]

Native arsenic is an occasional ore mineral in some hydrothermal base metal deposits. Its rarity (compared to pyrite, arsenopyrite, galena, sphalerite, or chalcopyrite, for example) is surprising, as arsenic is a common constituent of upper crustal fluids. Hence, the conditions of formation must be quite special to precipitate native arsenic. An ideal location to investigate the formation of native As and to explore the parameters constraining its crystallization is the Michael vein near Lahr, Schwarzwald, southwest (SW) Germany. Here, galena, sphalerite, and native arsenic are the most abundant ore minerals. The two important ore stages comprise (1) galena-barite and (2) sphalerite-native arsenicquartz, the latter with a general mineral succession of pyrite → sphalerite ± jordanite-gratonite solid solution → galena → native As. The native arsenic-bearing mineralization formed by cooling of an at least 130 °C hot saline fluid accompanied by a reduction due to the admixing of a sulfide-bearing fluid. Thermodynamic calculations reveal that for the formation of native arsenic, reduced conditions in combination with very low concentrations of the transition metals Fe, Co, and Ni, as well as low sulfide concentrations, are essential. "Typical" hydrothermal fluids do not fulfill these criteria, as they typically can contain significant amounts of Fe and sulfide. This results in the formation of arsenides, sulfarsenides, or As-bearing sulfides instead of native arsenic. Very minor amounts of pyrite, sulfarsenides, and arsenides record the very low concentrations of Fe, Co, and Ni present in the oreforming fluid. High concentrations of aqueous Zn and Pb lead to early saturation of sphalerite and galena that promoted native arsenic precipitation by decreasing the availability of sulfide and hence suppressing realgar formation. Interestingly, native arsenic in the Michael vein acted as a trap for uranium during supergene weathering processes. Infiltrating oxidizing, U+VI-bearing fluids from the host lithologies reacted under ambient conditions with galena and native arsenic, forming a variety of U+VI (±Pb)-bearing arsenates such as hügelite, hallimondite, zeunerite, heinrichite, or novacekite together with U-free minerals like mimetite or anglesite. Some parts of the vein were enriched to U concentrations of up to 1 wt% by this supergene process. Reduced (hypogene) uranium phases like uraninite were never observed. [ABSTRACT FROM AUTHOR]

Security of supply of "hi-tech" raw materials (including the rare earth elements (REE) and some high-field-strength elements (HFSEs)) is a concern for the European Union. Exploration and research projects mostly focus on deposit- to outcrop-scale description of carbonatite- and alkaline igneous-associated REE-HFSE mineralization. The REE-HFSE mineral system concept and approach are at a nascent stage, so developed further here. However, before applying the mineral system approach to a chosen REE-HFSE metallogenic province its mineral system extent first needs defining and mapping. This shifts a mineral system project's foundation from the mineral system concept to a province's mineral system extent. The mapped extent is required to investigate systematically the pathways and potential trap locations along which the REE-HFSE mass may be distributed. A workflow is presented to standardize the 4-D definition of a REE-HFSE mineral system at province-scale: (a) Identify and hierarchically organize a mineral system's genetically related sub-divisions and deposits, (b) map its known and possible maximum extents, (c) name it, (d) discern its size (known mineral endowment), and (e) assess the favorability of the critical components to prioritize further investigations. The workflow is designed to generate process-based perspective and improve predictive targeting effectiveness along under-evaluated plays of any mineral system, for the future risking, comparing and ranking of REE-HFSE provinces and plays. [ABSTRACT FROM AUTHOR]