Journal of GEOsciences Table of Contents for the Journal of GEOsciences. List of articles from the latest print issue.http://www.jgeosci.orgen-US Journal of GEOsciences <![CDATA[ Editorial ]]> Plášil JK; Vol. 68, issue 1, page: 1
I want to welcome all our readers in the new year 2023, and wish them all the best. I am delighted to serve a portion of a fresh reading. Three of the papers in this volume are focused mainly on processes, from volcanology to thermodynamic modeling of what happens during weathering of ores. The fourth paper focuses on describing the new mineral, fluorpyromorphite, which has been unseen until now but has been expectable!

In Prague, January 16, 2023
Jakub K. Plášil ]]> Editorial
<![CDATA[ Eruptive and magmatic evolution of North Chamo Volcanic Field (southern Ethiopia) ]]> Rapprich V, Janoušek V, Hroch T, Míková J, Erban V, Legesa F, Pécskay Z, Halodová P; Vol. 68, issue 1, pages 3 - 24
A group of pyroclastic cones is dispersed in the North Chamo Volcanic Field, i.e. in the northern surroundings of the Chamo Lake and over neighbouring part of the Nech Sar plains (southern termination of the Main Ethiopian Rift). The activity of scattered cinder cones was partly coeval with that of Tosa Sucha Volcano (Calabrian), but continued also after Tosa Sucha’s extinction until Middle Pleistocene (c. 0.5 Ma). Whereas scoria cones on the Nech Sar plains displayed a rather simple Strombolian eruptive style, the cones located within the northern part of Chamo Lake were characterized by more complex evolution. Ganjulle scoria cone, with a uniform olivine basalt composition, started with a Surtseyan-style eruption, which turned into Strombolian as the volcano grew above the water level. An even more complex history was documented for the Ganta cone. Compositional zoning of pyroclastic rocks is explained by zoned-chamber exhaustion. The transition from magmatic to phreatomagmatic style of the eruption was then most likely linked to syn-eruptive subsidence of the area on the Chamo Lake banks. Subsequent transition back to Strombolian style reflected the growth of the cone above water level.
The Sr-Nd-Pb isotopes, together with major-element-based thermodynamic modelling, demonstrate that magmas parental to the North Chamo alkaline volcanic rocks (alkali basalt, through trachybasalt and trachyandesite to trachyte) evolved initially by closed-system fractionation of olivine, later joined by clinopyroxene, spinel and calcic plagioclase. The subsequent stage was characterized by a substantial (c. 25% by mass) assimilation of country-rock felsic igneous material, perhaps corresponding to the Paleogene ignimbrites. ]]> Original paper
<![CDATA[ From magmatic arc to a post-accretionary setting: Late Palaeozoic granitoid plutons in the northwestern Trans-Altai Zone, Mongolia ]]> Hanžl P, Janoušek V, Hrdličková K, Buriánek D, Gerel O, Altanbaatar B, Hora JM, Čoupek P; Vol. 68, issue 1, pages 25 - 66
The Trans-Altai Zone in the southern tract of the Central Asian Oceanic Belt is composed of Early Palaeozoic oceanic crust preserved in Ordovician to Devonian ophiolite fragments and Devonian-Carboniferous igneous arcs. The Edren and Baaran subzones at the NW tip of the Trans-Altai Zone were intruded by Late Palaeozoic plutons that have been examined by the combined geochronological and geochemical study.
Mississippian subduction-related plutons intruded Devonian and Carboniferous volcano-sedimentary sequences in two magmatic pulses. The older, Tournaisian plutons (dated at 352 ± 1 and 347 ± 4 Ma) occur in both subzones; the younger Visean/Serpukhovian ones (331 ± 1 Ma) are found only at the northern boundary of the Edren Subzone. All Mississippian rocks are high-K calc-alkaline and characterized by a strong enrichment of hydrous fluid mobile lithophile elements over conservative Nb, Ta and Ti relative to normal mid-ocean ridge basalts. Low 87Sr/86Sri (˜ 0.7035-0.7038) and highly positive values (+6.6 to +5.2) suggest a relatively juvenile parental magma source with a short mean crustal residence. This corresponds well with the age of scarce inherited zircons, none of which is older than 530 Ma.
The Early Permian post-tectonic plutons intruded the shallow crust of the Baaran Subzone (Devonian-Carboniferous flysch and Early Carboniferous volcanic arc). The prominent concentric body of the Aaj Bogd Pluton is composed of monzodiorites to monzogabbros (284 ± 1 and 294 ± 3 Ma) in its centre, surrounded by granite with syenite (282 ± 1 Ma) in the main mass of the pluton. Whole-rock Sr-Nd isotopic ratios match those of Carboniferous magmatic rocks, while trace-element patterns point to an intra-plate origin influenced by a fertile asthenospheric mantle component. On the other hand, the slightly older (290 ± 1 Ma) quartz syenites to alkali feldspar granites in the Baaran Subzone have spurious arc-like geochemistry inherited from their arc-related crustal source(s). Regional distribution of the numerous oval-shaped Early Permian alkaline post-orogenic plutons, some with A2-type granite affinity, follows the major Permian strike-slip zones spanning from the Dulate Arc in the west to the Khan Bogd Pluton in the east. These late, transcurrent zones apparently played an important role in late-orogenic magma generation, ascent and emplacement. ]]> Original paper
<![CDATA[ Thermodynamics of the Cu, Zn, and Cu-Zn phases: zincolivenite, adamite, olivenite, ludjibaite, strashimirite, and slavkovite ]]> Majzlan J, Števko M, Plášil J, Sejkora J, Dachs E; Vol. 68, issue 1, pages 67 - 80
Secondary minerals, especially phosphates and arsenates of copper and zinc, form a group of phases with astonishing variability in crystal structures and chemical composition. Some of these minerals are more common than others and one has to ask whether the abundance is linked to their thermodynamic stability or rather to geochemical constraints. In this work, we used calorimetric techniques to determine the thermodynamic properties of synthetic olivenite [Cu2(AsO4)(OH)], zincolivenite [Cu0.95Zn1.05(AsO4)(OH)], adamite [Zn2(AsO4)(OH)], ludjibaite [Cu5(PO4)2(OH)4], natural strashimirite [(Cu7.75Zn0.09)7.84(AsO4)3.89(SO4)0.11(OH)3.79·5H2O], and a slavkovite sample dehydrated to the composition Cu12(AsO4)4(AsO3OH)6·14H2O that is used as a proxy for slavkovite. All thermodynamic data presented are based upon the compositions given above. The enthalpies of formation (at 298.15 K and 1 bar, all in kJ·mol-1) are -1401.7 ± 2.6 (adamite), -1211.6 ± 3.2 (zincolivenite), -3214.3 ± 10.7 (ludjibaite), -5374.9 ± 18.1 (strashimirite), and -12004 ± 34 (dehydrated slavkovite). Entropy was measured only for ludjibaite (389.0 ± 2.7 J·K-1·mol-1) and estimated for other phases. Gibbs free energies of formation (all in kJ·mol-1) were calculated for ludjibaite (-2811.4 ± 10.7), strashimirite (-4477.0 ± 18.3), and dehydrated slavkovite (-9987 ± 35). The dehydrated slavkovite is the consequence of H2O loss from the slavkovite holotype specimens during storage of the samples in air at room temperature. It is triclinic (P-1), with unit-cell parameters a = 6.4042(11) Å, b = 13.495 (2) Å, c = 13.574 (2) Å, α = 87.009(15)°, β = 85.564(14)°, γ = 79.678(15)°. Dehydration of slavkovite results in a collapse of the sheet structure into a framework structure and into reorganization of bonding, including protonation/deprotonation of AsO4 groups. Constructed activity-activity phase diagrams show that the less stable phases are those which are less common in nature, such as euchroite, strashimirite, or slavkovite. Zincolivenite is stabilized with respect to the end-members olivenite and adamite by a small enthalpy difference of -1.95 kJ·mol-1. Ludjibaite is metastable with respect to its polymorph pseudomalachite. Slavkovite is probably restricted to local acidic environments, rich in Cu and As. ]]> Original paper
<![CDATA[ Fluorpyromorphite, Pb5(PO4)3F, a new apatite-group mineral from Sukhovyaz Mountain, Southern Urals, and Tolbachik volcano, Kamchatka ]]> Kasatkin AV, Pekov IV, Škoda R, Chukanov NV, Nestola F, Agakhanov AA, Kuznetsov AM, Koshlyakova NN, Plášil J, Britvin SN; Vol. 68, issue 1, pages 81 - 93
Fluorpyromorphite, ideally Pb5(PO4)3F, a new apatite-group member, an F-dominant analog of pyromorphite and hydroxylpyromorphite. It is a supergene mineral found at two localities: Sukhovyaz Mountain, Ufaley District, Southern Urals (holotype) and Mountain 1004, Tolbachik volcano, Kamchatka (co-type), both in Russia. At Sukhovyaz, fluorpyromorphite forms anhedral grains up to 0.2 mm across (usually much smaller), filling cavities in quartz and sometimes partially replacing fluorapatite. Associated supergene minerals include pyromorphite, hydroxylpyromorphite, fluorphosphohedyphane, mimetite, and nickeltsumcorite. At Tolbachik, fluorpyromorphite occurs in the oxidation zone of paleo-fumarolic deposits in close association with pyromorphite, fluorphosphohedyphane, wulfenite, cerussite, munakataite, vanadinite, chrysocolla, and opal. It forms crude long-prismatic to acicular crystals up to 0.1 mm long and up to 5 μm thick combined in bunches and spherulites up to 0.2 mm. Fluorpyromorphite is colorless (Sukhovyaz) or yellow (Tolbachik), translucent to transparent and has a vitreous luster. It is brittle, with an uneven fracture and poor cleavage on (001). The calculated density values are 7.382 (holotype) and 6.831 (cotype) g/cm3. Fluorpyromorphite is optically uniaxial (-). In reflected light, it is light-grey, weakly anisotropic. The reflectance values (Rmin/Rmax, %) are: 15.8/16.6 (470 nm), 16.2/17.2 (546 nm), 15.9/16.9 (589 nm), 15.4/16.2 (650 nm). The chemical composition is (electron microprobe, wt. %; holotype/co-type): CaO 0.10/3.16, SrO 0.17/0.00, PbO 83.51/77.39, P2O5 16.13/16.35, CrO3 0.00/0.49, SeO3 0.00/0.98, F 1.00/1.35, Cl 0.29/0.40, H2Ocalc 0.13/0.00, -O = (F,Cl) -0.49/-0.66, total 100.84/99.46. The empirical formulae based on 13 anions (O + F + Cl + OH) pfu are Pb4.95Ca0.02Sr0.02P3.00O12F0.70(OH)0.19Cl0.11 (holotype) and Pb4.26Ca0.69P2.83Se6+0.09Cr6+0.06O11.99F0.87Cl0.14 (co-type). Fluorpyromorphite is hexagonal, space group P63/m, unit-cell parameters (from powder X-ray diffraction data; holotype / co-type) are: a = 9.779(5) / 9.732(1), c = 7.241(9) / 7.242(1) Å, V = 599.6(7) / 594.0(2) Å3, and Z = 2. The crystal structure was refined using the Rietveld method to Rp= 0.1764 (holotype). Fluorpyromorphite is isostructural with other members of the apatite group, a subdivision of the apatite supergroup. ]]> Original paper