Bladed Texture and Exploration Implications. A Case Study from the Kuklitsa Deposit,Krumovgrad Goldfield,SE Bulgaria

This study demonstrates that the bladed texture, which is common in epithermal, low-sulfidation (adularia-sericite) precious metal deposits, can serves as exploration vector towards precious metal mineralization. The paper presents two styles of bladed texture in the Kuklitsa gold deposit (Krumovgrad goldfield, SE Bulgaria) observed at both different altitude and lateral position in respect to regional low-angle detachment fault. The first style has formed as a crackle breccia just above the detachment fault where bladed texture consists of 10–20 vol % pseudorhombic adularia, 90-80 vol % quartz, scarce pyrite, and electrum, which is often observed under optical microscope. The second style is present in steep veins which fill listric faults of sharp tectonic contacts. It is developed at a higher level relative to the detachment fault. Bladed texture there consists of 1–2 vol % pseudorhombic adularia, 99-98 vol % quartz, and scarce both electrum and pyrite. Electrum of the two styles of bladed texture comprises only gold and silver but in different proportions with a higher gold content for the first style: fineness of 765, on average, for the first style vs. fineness of 692 for the second one. In this way, it is found that the adularia abundance correlates positively with the electrum one and negatively with the quartz abundance. The author uses the proportions of adularia, quartz and electrum, the fineness of electrum, and the relative distance to the detachment fault to conclude that the first style of bladed texture has been formed at higher temperature relative to the second style. The author infers that the first style is promising for mineralization of higher grade. Methods used comprise field observations and sampling, optical and electron microscopy, powder X-ray diffraction and electron microprobe analysis.

     

In the footsteps of Alexander the Great: searching for the origins of ancient zooplankton on the wild steppe of Central Asia

Rising above the modern town of Nurata, in Navoiy Province, eastern Uzbekistan is the ancient fortress of Alexander the Great, built as part of Alexander's campaigns to subjugate the Persian‐speaking Sogdian peoples that lived in this province of the Persian Empire in the 4th Century bc . Alexander passed this way in 327 bc , marching his ancient army through this beautiful but desolate landscape, and conquering all before him. His fortress was built in a strategic place at the boundary between fertile agricultural lands and a dry and uncompromising vastness of steppe that lies to the east. From Nurata, about one hour drive by car along a road that cuts eastwards across the desert, is the sleepy town of Jo'sh. In the mountains beyond Jo'sh sits the hamlet of Kanda, a few mud‐brick houses nestling at the head of a small valley where a spring emerges miraculously from a bone‐dry landscape. Hereabouts are telltale signs of ancient marine deposits yielding graptolites from rocks of the Silurian system. And in these rocks are the fossils of tiny arthropods that mark a fundamental shift in the marine arthropod zooplankton 425 million years ago. It is these fossils that we have chased halfway across the world to the steppe of Central Asia.     

A New Interlaboratory Characterisation of Silicon,Rare Earth Elements and Twenty‐Two Other Trace Element Concentrations in the Natural River Water Certified Reference Material SLRS‐6 (NRC‐CNRC)

The natural river water reference material SLRS‐6 (NRC‐CNRC) is the newest batch of a quality control material routinely used in many international environmental laboratories. This work presents a nine‐laboratory compilation of measurements of major and trace element concentrations and their related uncertainties, unavailable in the NRC‐CNRC certificate (B, Cs, Li, Ga, Ge, Hf, Nb, P, Rb, Rh, Re, S, Sc, Se, Si, Sn, Th, Ti, Tl, W, Y, Y, Zr and REEs). Measurements were mostly made using inductively coupled plasma‐mass spectrometry. The results are compared with equivalent data for the last batch of the material, SLRS‐5, measured simultaneously with SLRS‐6 in this study. In general, very low concentrations, close to the quantification limits, were found in the new batch. The Sr isotopic ratio is also reported.     

Multi-proxy climate and environmental records from a Holocene eutrophic mire,southern taiga subzone,West Siberia

Palaeoenvironmental reconstructions from peat are strongly focused on ombrotrophic mires, but this study demonstrates that eutrophic mires can also be used. A multi-proxy approach was applied to a eutrophic mire on a floodplain terrace in the southern taiga of West Siberia. The results of the reconstruction were considered in the wide geographic context of the surrounding regions, including Siberia and Central Asia. Different palaeoecological proxies (analysis of plant macrofossils, testate amoebae, oribatid mites, molluscs, peat humification, ash content and spectral characteristics of humic acids) were used in this study. The results of different proxies showed a high level of consistency among themselves, which allowed for a robust interpretation of Holocene mire development. Throughout the ~7800 years history of the mire, there was a high level of surface wetness. The presence of mineral matter in the peat between 7800 and 5100 cal. a BP indicates regular flooding caused by the intensive fluvial activity, apparently resulting from increased precipitation. This was followed by a trend towards a gradual decrease in surface wetness from conditions of high surface moisture (stagnant water) between 5100 and 3000 cal. a BP to present day conditions of moderate surface moisture with a water table slightly below the mire surface. This pattern is consistent with the well-documented long-term trend from palaeoecological records throughout the taiga and arctic zones in West Siberia and central arid Asia. Our data further support the idea that the westerlies were the dominant driver of climate for the southern taiga of West Siberia during the Middle to Late Holocene.     

δ53Cr values of catchment runoff exhibit seasonality regardless of bedrock Cr concentrations: Role of periodically changing chromium export fluxes

One pre-requisite for the construction of a global chromium isotope mass balance is detailed understanding of Cr isotope systematics in the critical zone where redox-processes can modify the isotope signature of geogenic Cr input into the hydrosphere. A Cr isotope inventory of bedrock, soil, and runoff was performed in a Central European headwater catchment underlain by amphibolite, situated in the vicinity of two previously studied catchments underlain by different bedrock types (serpentinite and leucogranite). Fresh bedrock in the amphibolite catchment NAZ contained ~300 mg/kg Cr, serpentinite at PLB contained ~800 mg/kg Cr, and leucogranite at LYS contained ~2 mg/kg Cr. Monthly hydrochemical monitoring at all three sites revealed higher Cr(VI) export fluxes in winter than in summer. NAZ was characterized by a distinct seasonality in the δ⁵³Cr values, with minima during winter/spring snowmelts (−0.35‰) and maxima during dry summers (0.40‰). Similar seasonality in δ⁵³Cr values had been reported from PLB and LYS. Bedrock at all three sites had similar Cr isotope composition close to −0.10‰, a value indistinguishable from the δ⁵³Cr value of bulk silicate Earth (BSE). Positive mean δ⁵³Cr value of NAZ runoff indicated Cr-isotope fractionations during weathering of geogenic Cr(III), combined with adsorption of the resulting Cr(VI) on soil particles during pedogenesis. However, the mass-weighted mean δ⁵³Cr of NAZ runoff was lower (−0.08‰), indistinguishable from the Cr isotope signature of bedrock. The same pattern of lower mass-weighted mean δ⁵³Cr values of runoff, compared to arithmetic mean δ⁵³Cr values of runoff, were observed also at PLB and LYS. We suggest that elevated Cr runoff fluxes in winter remove some of the residual isotopically light Cr that accumulated in the soil during summer. Seasonality in runoff δ⁵³Cr values appears to be a relatively widespread phenomenon, de-coupled from Cr availability for chemical weathering.     

Mid-Miocene thermal impact on the lithosphere by sub-lithospheric convective mantle material: Transition from high- to moderate-Mg magmatism beneath Vitim Plateau,Siberia

High-Mg lavas are characteristic of the mid-Miocene volcanism in Inner Asia.In the Vitim Plateau,small volume high-Mg volcanics erupted at 16-14 Ma.and were followed with voluminous moderate-Mg lavas at 14-13 Ma.In the former unit,we have recorded a sequence of(1) initial basaltic melts,contaminated by crustal material,(2) uncontaminated high-Mg basanites and basalts of transitional(K-Na-K) compositions,and(3) picrobasalts and basalts of K series;in the latter unit a sequence of(1) initial basalts and basaltic andesites of transitional(Na-K-Na) compositions and(2) basalts and trachybasalts of K-Na series.From pressure estimation,we infer that the high-Mg melts were derived from the sublithospheric mantle as deep as 150 km,unlike the moderate-Mg melts that were produced at the shallow mantle.The 14-13 Ma rock sequence shows that initial melts equilibrated in a garnet-free mantle source with subsequently reduced degree of melting garnet-bearing material.No melting of relatively depleted lithospheric material,evidenced by mantle xenoliths,was involved in melting,however.We suggest that the studied transition from high-to moderate-Mg magmatism was due to the mid-Miocene thermal impact on the lithosphere by hot sub-lithospheric mantle material from the Transbaikalian low-velocity(melting) domain that had a potential temperature as high as 1510℃.This thermal impact triggered rifting in the lithosphere of the Baikal Rift Zone.     

Hydrochemistry of Salt Lakes in Southeastern Transbaikalia(Russia) in the Time of Arid Phase of Climate Change at the Beginning of the XXI Century

正1 Introduction In the south of Eastern Transbaikalia in the border area with China and Mongolia,there are at least 300 saline without outlet lakes.They are confined to the semi-arid zone Daurian steppes with pronounced continental salinization processes and are mostly located on the bottoms of the intermountain basins.Their origin is related to evaporative concentration of fresh waters lakes filling.