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Sulfides in upper mantle lherzolite xenoliths from Cretaceous alkaline-ultramafic rocks in the Jetty Peninsula (East Antarctica) were studied for their major and trace-element compositions using SEM and LA-ICP-MS applied in situ. Modal abundance of sulfides is the lowest in Cpx-poor lherzolites ≤ Spl-Grt lherzolites << Cpx-rich lherzolites. Most sulfides are either interstitial (i-type) or inclusions in rock-forming minerals (e-type) with minor sulfide phases mostly present in metasomatic veinlets and carbonate-silicate interstitial patches (m-type). The main sulfide assemblage is pentlandite + chalcopyrite ± pyrrhotite; minor sulfides are polydymite, millerite, violarite, siegenite, and monosulfide solution (mss). Sulfide assemblages in the xenolith matrix are a product of the subsolidus re-equilibration of primary mss at temperatures below ≤300 °C. Platinum group elements (PGE) abundances suggest that most e-type sulfides are the residues of melting processes and that the i-type sulfides are crystallization products of sulfide-bearing fluids/liquids. The m-type sulfides might have resulted from low-temperature metasomatism by percolating sulfide-carbonate-silicate fluids/melts. The PGE in sulfide record processes are related to partial melting in mantle and intramantle melt migration. Most other trace elements initially partitioned into interstitial sulfide liquid and later metasomatically re-enriched residual sulfides overprinting their primary signatures. The extent of element partitioning into sulfide liquids depends on P, T, fO2, and host peridotite composition.

Geological mapping and regional geochemical prospection on a scale of 1:50,000, covered an area of about 4,000 km 2 in the Zamtyn Nuruu region of the eastern Mongolian Altay. Northern part of the region is formed by the Lake Zone Terrane, the southern by the Gobi Altay Terrane; these two units are separated by the Bogd fault. The panned-concentrate heavy mineral survey was combined with the dry stream-sediment geochemistry, both being complemented by lithogeochemical sampling. The dry stream-sediment geochemistry proved to be a suitable method for regional prospection in semiarid to arid areas of Mongolia. The morphology and composition of placer gold grains were studied in order to estimate the distance from the primary source, and to constrain the nature of prospective primary mineral deposits. Based on the results of the regional geochemical survey and geological mapping, follow-up works were focused on prospective areas including the reconnaissance field works, detailed geochemical sampling, and geophysical measurements. New occurrences and signs of Au, Cu, Zn and (Ba)-As-Sb-Hg mineralizations were discovered. The ascertained goldbearing mineralizations are represented namely by Au and Au-(Ag) quartz veins in basic metavolcanic rocks of the Neoproterozoic Khan Taishir and volcanic rocks of the Permian Delger Khangay formations. Gold locally accompanies vein-disseminated base metal mineralization in some Proterozoic and Lower Palaeozoic formations. A prospective occurrence of clastic gold in Mesozoic conglomerates and sandstones was found at the northern edge of the Zamtyn Nuruu around the Samoandamba Uul. The geochemical survey has revealed a contrast in occurrence of ore indices between the two terranes formig the studied area. While the Lake Terrane and, especially, the Neoproterozoic Khan Taishir Formation are rich in gold and base metal showings, the Gobi Altay Terrane is barren.

The Nýřany Member in the Pilsen Basin records the evolution of a broad paleotropical alluvial plain that preserves amalgamated lenticular to sheet sandstone bodies separated by basin-wide floodplains. Facies and architectural element analysis in conjunction with well-log correlation was employed in order to reconstruct fluvial system stacking patterns and decipher the controls responsible for the preserved fluvial architectures and identify the possible influence of allogenic processes on basin fill architectures. The main architectural components identified include: 1) sheet-like and lenticular pebbly to cobbly conglomerate thalweg fill representing the lowermost portion of channels that are preferentially preserved; 2) inclined gravel-sand and sandy strata of barforms and rarely preserved (3) mudstone units representing floodplains and abandoned channel fills. These architectural elements combine to form a hierarchy of alluvial cycles represented by channel-bar systems (3-10 m thick), channel-belts (4-15 m thick) and stacked channel-belt complexes (10-35 m thick). Autogenic processes of lateral migration and local and regional avulsion of braided channels of intermediate sinuosity (1.5) controlled the formation of the smaller scale cycles. While the geometry of stacked channel belt complexes (sandbodies) appear to be driven by variations in subsidence rates, their cyclic alternation with extensive floodplains is considered to be related to allogenic processes of variable seasonality of precipitation, which affected sedimentation rates and water-table level in the basin. Their maximum periodicity of 140 k.y. indicate that eccentricity paced changes of Earth's orbit may be a driving force controlling climate stability in the Pennsylvanian paleotropics.•