Tomáš Mikuš

Cuprobismutite, kupčíkite, hodrushite and associated sulfosalts from the black shale hosted Ni-Bi-As mineralization at Čierna Lehota, Slovakia

Three sulphosalts from the cuprobismutite homologous series have been found in a hydrothermal Ni-Bi-As mineralization at Cierna Lehota (Slovakia). Kupcikite (second world occurrence) has a significant content of Pb (2.73 wt.%) and Fe (0.85 wt.%), with the structural formula (Cu 3.92 Fe 0.24 ) Σ4.16 (Bi 4.60 Pb 0.19 Ag 0.04 Sb 0.01 ) Σ4.84 S 9.58 . Hodrushite has a higher content of Ag (mean 1.27 wt.%), but less Fe (0.59 wt.%) and Pb (0.23 wt.%), with structural formula (Cu 7.79 Fe 0.38 ) Σ8.17 (Bi 11.34 Ag 0.43 Pb 0.04 Sb 0.02 ) Σ11.83 S 22.13 . Two varieties of cuprobismutite have the highest Ag content (3.8 and 2.3 wt.%), with Fe 0.6 and 0.2 wt.%, and Pb 0.1 and 6.7 wt.%, giving two formulas (Cu 7.42 Fe 0.47 ) Σ7.87 (Bi 12.56 Ag 1.55 Pb 0.02 ) Σ14.13 S 24.68 and (Cu 7.67 Fe 0.14 ) Σ7.81 (Bi 11.95 Pb 1.37 Ag 0.85 Sb 0.02 ) Σ14.19 S 24.13 . Chemical variations between these sulphosalts are compared with published data, that emphasizes the role of minor cations. Associated sulphosalts are described: aikinite, and Bi-rich tennantite (Bi up to 9.7 wt.%).

Eclogites overprinted in the granulite facies from the Ďumbier Crystalline Complex (Low Tatra Mountains, Western Carpathians)

Eclogites overprinted in the granulite facies from the Ďumbier Crystalline Complex (Low Tatra Mountains, Western Carpathians) Metabasites with evidence for breakdown of former eclogites and recrystallization under granulite facies conditions occur in the Ďumbier Crystalline Complex of the Low Tatra Mountains, Central Western Carpathains. Textural relationships, phase equilibrium modelling and thermobarometry have been used to determine the P-T evolution of these rocks. Omphacite diagnostic for the eclogites facies stage is absent but its former presence is inferred from the symplectitic intergrowths of clinopyroxene + plagioclase. The re-equilibration in high-pressure granulite facies conditions is demonstrated by the assemblage garnet + clinopyroxene (< 10 % Jd) + plagioclase + quartz. The phase equilibrium modelling using THERIAK-DOMINO program and conventional geothermobarometry suggest the P-T conditions of 750-760 °C and 1.1-1.5 GPa for the high-pressure granulite stage. Orthopyroxene formed in the clinopyroxene + plagioclase symplectites and kelyphites and coronas around garnet at P-T conditions of ca. 0.7-1.0 GPa and 650-700 °C. P-T evolution of granulitized eclogites is interpreted as the result of two metamorphic events; early Variscan eclogite facies metamorphism was followed by granulite facies thermal overprint in the Carboniferous time. The second metamorphic event was crucial for breakdown of eclogites, these are only seldom preserved in the pre-Alpine basement of the Western Carpathians.

TAPHONOMIC CLOCK AND BATHYMETRIC DEPENDENCE OF CEPHALOPOD PRESERVATION IN BATHYAL, SEDIMENT-STARVED ENVIRONMENTS

Abstract: The dependence of skeletal alteration on time spent in the taphonomic active zone (TAZ) can generate a taphonomic clock, which can be used to quantify scales of time averaging and rates of skeletal production and recycling in the fossil record. However, the strength of the taphonomic clock is variable in present-day shallow marine environments and it is unclear how this strength varies with depth. Here, we assess the strength of the taphonomic clock in Nautilus macromphalus dead shells that were collected in cool-water, sediment-starved, epi- and mesobathyal environments off New Caledonia and range in postmortem age from few decades to several millennia. We find that, first, differences in the onset and extent of alteration states in the epibathyal zone (< 750 m) segregate well-preserved shells with red stripes (less than ∼ 200 years) from encrusted shells with faded colors and extensively bored by sponges (∼ 400 years), and from strongly fragmented, bored, and coated shell relicts (> 1,000 years). The onset of dissolution and formation of clay-goethitic coating occurs earlier (∼ 200 years) in the mesobathyal zone (> 750 m) than in the epibathyal zone. Clay-goethitic rims and boring infills show signs of microbial binding, pelletization, and coccolith dissolution and can represent nascent stages of glauconitization. Second, shells several centuries old show differences between right and left flanks (1) in the degree of encrustation and sponge bioerosion in the epibathyal zone and (2) in the extent of clay-goethitic coating in the mesobathyal zone. The upper flanks are ultimately removed in both depth zones, leaving relict half-shells that are millennia old. Third, the depth dependence of alteration can reflect a bathymetric decline in disintegration rates by heterotrophic borers due to a reduced productivity in the mesobathyal zone and an increase in dissolution rates due to the proximity of the aragonite compensation depth. The between-flank asymmetry in preservation implies (1) horizontal position of shells close to the sediment-water interface for several decades or centuries without being overturned or subjected to reworking and (2) shell exposure to two distinct taphonomic regimes separated by few centimeters, with the upper flank located in the TAZ and the lower flank facing a less aggressive sediment zone. The stable exposure of shells in the taphonomic active zone and slow alteration rates in bathyal environments allow discriminating between within-habitat time-averaged assemblages on one hand and environmentally or stratigraphically condensed assemblages on the other hand.

Garavellite and associated sulphosalts from the Strieborná vein in the Rožňava ore field (Western Carpathians)

Abstract The article presents the first description of a complete and continuous series from berthierite to garavellite sulphosalts in the Western Carpathians. Berthierite is a common main or accessory phase of Sb mineralizations in the Western Carpathians, and occurs at many localities and ore deposits as well. On the other side, garavellite or Bi-rich berthierite is a relatively rare accessory phase. The highest Bi content in garavellite reaches up to 38.04 wt. % which represents 0.90 apfu, and its crystallochemical formula can be written as Fe0.97Sb1.07Bi0.90S3.98. Raman band shifts were observed in the isomorphic berthierite–garavellite series. Garavellite occurs in the younger stages of sulphidic mineralization, and associates with tetrahedrite, berthierite, Bi-chalcostibite, Sb-bismuthinite, Bi-stibnite, ullmanite and cinnabarite. It creates irregular grains and veinlets in pre-existing tetrahedrite, or forms myrmekite intergrowths with chalcopyrite in tetrahedrite. Bi content in chalcostibite is up to 0.20 apfu. Besides the tetrahedrite, pre-existing sulphosalts are the members of the tintinaite–kobellite series, Bi-jamesonite and bournonite. The Sb/(Sb+Bi) ratio of minerals of the tintinaite–kobellite series varies from 0.37 to 0.80. The maximum content of Bi in jamesonite is up to 1.22 apfu. A vertical zonation at the ore vein body (mining levels 6 / 180 a.s.l., 8 / 80 a.s.l., 10 / 20 b.s.l.) is represented by the Sb decrease along with the Bi increase with increasing depth. Bi content continuously decreases during the older ore mineralization stage and Sb increases at the younger mineralization stage. Both of the stages have been enriched by Sb as well.