Understanding the thermal behavior of nonsteady state subsurface geosystems, when temperature changes over time, requires knowledge on the speed of heat propagation and, thus, of the rock's thermal diffusivity as essential thermo‐physical parameter. Mixing models are commonly used to describe thermo‐physical properties of polymineralic rocks. A thermal diffusivity‐porosity relation is known from literature that incorporates common mixing models into the heat equation and properly works for unconsolidated, clastic clayey, and sandy marine sediments of high porosity (35%–80%). We have proofed the relation's applicability for consolidated, isotropic sedimentary rocks of low porosity (<35%). The performance of this approach was evaluated for consolidated quartz‐dominated sandstones containing air, water, and heptane as pore‐ and/or fracture‐filling medium. For these rocks, the reliability of the relation was confirmed for the entire range of porosity and all three media, with water‐saturated rocks displaying an almost perfect fit between measured and modeled thermal diffusivity. Additional measurements conducted on a larger suite of low‐porous siliciclastic and carbonate rocks imply that it is also suitable to acceptably good to infer the thermal diffusivity of mineralogically more diverse sedimentary rocks. In contrast to other common mixing models, this relation is appropriate to convert thermal‐diffusivity data obtained on air‐saturated samples into such reflecting water‐saturated conditions. This is of particular importance for handling data acquired from methods limited to the measurement of dry samples, for example, laser‐flash analysis. In conclusion, the applied relation is suited to model thermal‐diffusivity data of isotropic sedimentary rocks of different porosity and independent of the pore fluid.

A re-examination of the El Dragón vein-type Se deposit using polarized light microscopy and scanning-electron microscopy combined with electron-microprobe analyses revealed the following results: the detection of (a) petříčekite, krut’aite and penroseite close to endmember composition; (b) a yet unknown mineral of the ideal composition CuNi2Se4; (c) intermediate members of the vaesite-pyrite solid-solution series; and (d) a mineral with a composition intermediate between athabascaite and its yet unknown S-equivalent, Cu4S5. Triggered by volcanic-hydrothermal activities around the Porco caldera, formation of the mineralization involved five episodes of fault formation and re-opening, fluid-mediated metal mobilization, metalliferous fluid infiltration, and mineral precipitation, re-deposition, and alteration that probably extended from 12 Ma until today. The origin of the Se-vein was accomplished by the multiple injection of highly oxidized, metal-rich fluids into a fault at the interface between black shale and siltstone. These low-T solutions (estimated max. temperature 100 °C, max. pressure 1 bar) possessed high to exceptionally Se fugacities (log fSe2 fluctuating between of −14.5 and −11.2) that prevailed for most of the evolution of the deposit, only interrupted once, during the episode of deposition of sulfides of Cu and Fe and resulting partial alteration of the pre-existing selenides. Formation of end-member krut’aite and native selenium implies a minimum log fSe2 of −11.2 at the final stage of vein formation. The likely source of Se and the accompanying metals (Cu, Ag, Ni, Co, Au, Pb, Hg, Cd, Fe and Bi) is the neighboring Kupferschiefer-type (possibly Devonian) black shale rich in framboidal pyrite, Cu-sulfide aggregates, and organic matter. Deposition of Se-minerals occurred where the oxidized metal-bearing solutions became in contact with a reductant, associated with the reduction of mobile selenate to immobile selenide or elemental Se.

The late-collisional Erzgebirge granites (∼325–318 Ma) were emplaced at shallow crustal levels in the Variscan metamorphic basement shortly after large-scale extension caused by orogenic collapse. These granites comprise mildly peraluminous transitional I—S-types and strongly peraluminous S-type rocks, which can be subdivided into three major groups: low-F biotite granites; low-F two-mica granites; and high-F, high-P₂O₅ Li-mica granites. The highest degree of differentiation is reached in the Li-mica granites, which exhibit strongly elevated concentrations of P, F, Li, Rb, Cs, Ta, Sn, W and U; but very low Ti, Mg, Co, Ni, Sr, Ba, Y, Zr, Hf, Th and rare earth elements. Crystal—melt fractionation is the dominant process controlling the bulk composition of all groups of granites. However, metasomatic processes involving late-stage residual melts and high-T orthomagmatic fluids became increasingly more important in highly evolved units and have modified the abundances of mobile elements (P, F, Li, Rb, Cs, Ba, Sr) in the Li-mica granites particularly. Isotopic and geochemical characteristics suggest that the three granite groups cannot be derived from a common precursor magma. Their discrete compositions are source related, and are attributed to melting of quartzo-feldspathic and pelitic crustal lithologies in different proportions. Granites are common in the central European Variscides, but the Erzgebirge is unusual for the predominance of evolved Li-mica granites associated with economically important Sn, W and U deposits. The abundance of Li-mica granites is attributed to a combination of favourable factors: (1) low degrees of anatectic melting of crustal protoliths; (2) wide distribution of fertile lithologies rich in large-ion lithophile elements and ore elements; (3) extended magmatic differentiation by crystal—melt fractionation and subsequent autometasomatism.