Abramovite, Pb2SnInBiS7, a new mineral species from fumaroles of the Kudryavy volcano, Kurile Islands, Russia

Abramovite, a new mineral species, has been found as fumarole crust on the Kudryavy volcano, Iturup Island, Kuriles, Russia. The mineral is associated with pyrrhotite, pyrite, würtzite, galena, halite, sylvite, and anhydrite. Abramovite occurs as tiny elongated lamellar crystals up to 1 mm long and 0.2 mm wide (average 300 × 50 μ m), which make up chaotic intergrowths in the narrow zone of fumarole crust formed at ～600°C. Most crystals are slightly striated along the elongation. The new mineral is silver gray, with a metallic luster and black streak. Under reflected light, abramovite is white with a yellowish gray hue. It has weak bireflectance; anisotropy is distinct without color effects. The chemical composition (electron microprobe) is as follows, wt %: 20.66 S, 0.98 Se, 0.01 Cu, 0.03 Cd, 11.40 In, 12.11 Sn, 37.11 Pb, 17.30 Bi; the total is 99.60. The empirical formula calculated on the basis of 12 atoms is Pb_1.92Sn_1.09In_1.06Bi_0.89(S_6.90Se_0.13)_7.03. The simplified formula is Pb₂SnInBiS₇. The strongest eight lines in the X-ray powder pattern [d, Å (I)(hkl)] are 5.90(36)(100), 3.90(100)(111), 3.84(71)(112), 3.166(26)(114), 2.921(33)(115), 2.902(16)(200), 2.329(15)(214), 2.186(18)(125). The selected area electron diffraction (SAED) patterns of abramovite are quite similar to those of the homologous cylindrite series minerals. The new mineral is characterized by noncommensurate structure composed of regularly alternated pseudotetragonal and pseudohexagonal sheets. The structure parameters determined from the SAED patterns and X-ray powder diffraction data for pseudotetragonal subcell are: a = 23.4(3), b = 5.77(2), c = 5.83(1) Å, α = 89.1(5) °, β = 89.9(7)°, γ = 91.5(7)°, V = 790(8) ų; for pseudohexagonal subcell: a = 23.6(3), b = 3.6(1), c = 6.2(1) Å, α = 91(2)°, β = 92(1)°, γ = 90(2)°, V = 532(10) ų. Abramovite is triclinic, space group P(1). The new mineral is named in honor of Russian mineralogist Dmitry Abramov. The type material of abramovite has been deposited in the Fersman Mineralogical Museum, Russian Academy of Sciences, Moscow.     

Paleomagnetism of Ordovician–Silurian Volcanics on the Western Slope of the Southern Urals

Doklady Earth Sciences - This work presents new paleomagnetic data on previously dated Ordovician–Silurian volcanics from four sections in the western framework of the Taratash massif...     

Paleomagnetism of sedimentary strata and the origin of the structures in the western slope of South Urals

Paleomagnetic data may contribute to studying the formation history of orogens; in particular, these data can promote identifying the pattern and scales of deformations at the final stages of orogeny. We have conducted paleomagnetic studies of the Paleozoic and Neoproterozoic sediments in the western part of the Western Ural Megazone in South Urals. The detailed thermal demagnetization revealed the intermediate temperature magnetization component in most samples. This magnetization has a reversed polarity and has been acquired before folding or at the early stages of the deformations. The directions of this component are narrowly grouped in rocks of a different age in all the segments of the studied part of South Urals, and the regional average direction closely agrees with the reference paleomagnetic direction of 270 Ma for the East European Platform. The results of our study suggest the following conclusions: (1) the main magnetization component in the studied sedimentary rocks has a secondary origin; (2) this component has an age of ~270 Ma and has been formed during the Kungur deformations (279–272 Ma ago) of the western part of South Urals; (3) neither a general rotation of the studied part of the Urals relative to the East European Platform nor local rotations of the individual tectonic blocks relative to each other are revealed; (4) the changes in the strike of the structures from NE within the Karatau uplift to the submeridional in the remaining part of the Urals is not an oroclinal bend.     

Observations on New Approaches for the Determination of Platinum-Group Elements, Gold and Silver in Different Geochemical Samples from Siberia and the Far East

Some recent experiments on the determination of Au and the platinum-group elements (PGE) in geochemical samples are reviewed. Emphasis is given to the determination of ultra-low levels of PGE concentrations in resistant matrices, including chromites, molybdenites and ultrabasic ores. The problems and features of PGE determination in samples of various chemical composition are considered. For each sample type studied, a series of sample preparation techniques are proposed. These techniques included acid digestion, fusion with sodium peroxide, cold sintering with an oxidizing mixture of Na₂O₂+ Na₂CO₃ and also oxidizing fluorination with bromine trifluoride. A new approach for preparing geochemical material prior to digestion, based on mechano-chemical activation with simultaneous hyperfine grinding, is proposed and studied. The instrumental determination of PGE contents was carried out directly by AAS from extracted organic phases. It was found that a combination of digestion processes was required to achieve geochemical background levels of Au and PGE concentrations with the following detection limits: Pd, Rh - 1 ng g⁻¹, Pt, Ru - 10 ng g⁻¹, Au - 0.2 ng g⁻¹, Ag - 0.1 ng g^−1. The uncertainty in PGE and Au determination in geochemical samples is dependent on metal concentration, and also on their distribution in samples. The total analytical uncertainty of the proposed method is between 15-30%.     

Ultra-Low Geomagnetic Field Intensity in the Devonian Obtained from the Southern Ural Rock Studies

Izvestiya, Physics of the Solid Earth - Abstract—In order to determine the Earth’s magnetic field intensity in the Devonian, a collection of rocks of the Baymak-Buribay formation of the...     

The late Cenomanian paleoecological event (OAE 2) in the eastern Caucasus basin of Northern Peri-Tethys

The Cretaceous sections of the eastern Caucasus contain rich in organic matter (OM) sediments corresponding to the late Cenomanian Oceanic Anoxic Event 2. They are marked by positive δ¹³C and negative δ¹⁸O isotopic anomalies, which are characteristic for this level in many areas of the world. The sediments exhibit distinct cyclic patterns reflected in an alternation of black OM-rich and gray more calcareous layers. The rocks are enriched with many chemical elements, although concentrations of some of them (Mo, Se) are lower than in typical sediments of anoxic basins. It is inferred that anoxic environments in the paleobasin were unstable and locally developed. Nannofossil assemblages from OAE 2 sediments are dominated by the highly resistant eurytropic taxon Watznaueria accompanied by common cool-water Eprolithus and rare warm-water Rhagodiscus representatives, which implies the development of environments unfavorable for the normal marine nannoflora and short-term cooling in the basin during OAE 2. The OM-rich sediments were deposited against the background of the rapid eustatic transgression due to a significant increase in productivity of phytoplankton in the paleobasin. The OAE 2 duration is estimated to be approximately 400 ka.