Trace elements in pyrite from the Petropavlovsk gold–porphyry deposit (Polar Urals): Results of LA-ICP-MS analysis

The first study of the pyrite composition from gold deposit in the Urals by the LA-ICP-MS method has been carried out. In the pyrite high contents of Au (up to 49 ppm), Ag (105 ppm), and other micronutrients (As (417 ppm), Ag (105 ppm), Co (2825 ppm), Ni (75 ppm), Cu (1442 ppm), and Zn (19 ppm)) were detected. Furthermore, an increase in the concentrations of trace elements from early to later generations of pyrite (from Py-1 to Py-3) Au, Ag, Te, Sn, Te, and Bi and depletion of Co, As, and Ni have been revealed. Gold is mainly concentrated in the pyrite of the second generation (Py-2) and occurs mostly as an “invisible” form with prevalence of nano-sized particles of native Au, similar in composition to electrum AuAg, as well as Au- and Au–Ag tellurides. The presence in the pyrite of admixtures of Cu, Co, Ni, Pb, As, and Te, possibly favors the entrance of Au into it (up to 5–50 ppm), while in common pyrite, poor in the mentioned impurities, the gold content is <1 ppm.     

Zoogeography and imperial defence: Tracing the contours of the Nearctic region in the temperate North Atlantic, 1838–1880s

This paper focuses on the ‘zoogeographic region’ and the ‘zoogeographical boundary-line’ as key biogeographical constructs of empire. More specifically, it investigates how army and navy officers stationed at Halifax and Bermuda on the North America and West Indies Station helped to create an imperial, militarized ‘New World’ region in the North Atlantic through zoogeography in the British post-emancipation era. The tracing of the boundary-line between the temperate (Nearctic) and tropical (Neotropical) North Atlantic involved designating Bermuda and Halifax as strategic winter and summer ‘homes’ on the Station, and highlighting the ‘natural’ connections between the two sites through mobile fauna, ocean currents, and weather systems. Making visible the geographic distribution of migratory animals, the Gulf Stream, and hurricanes – through maps, natural collections, sketches, and travel-writing – provided new ways of seeing and thinking about British imperial defence in the North Atlantic. This paper also considers the role of non-human mobilities in animating these regions.     

Early Jurassic Magmatism of the Kobyumé Graben System (Verkhoyansk Framing of the Siberian Craton) and Its Geodynamic Nature

Doklady Earth Sciences - Data on the Early Jurassic volcanic rocks of the Kobyumé graben system, which formed at the Verkhoyansk passive margin of the Siberian Craton, are presented. The...     

Iron–titanium sands of the Atlantic beaches between Tan-Tan and Tarfaya (southwest Morocco): Characterisation and origin

In Morocco, the most important placers of ferrotitanium minerals are found along the Laâouina–Cape Juby Atlantic coastline, where they accumulate in the upper parts of the foreshores. The heavy minerals would come from the dismantling of the acidic to intermediate magmatic rocks of the Precambrian Anti-Atlasic buttonholes and from the Meseta basement where crystallophyllous rocks predominate. The sands emanating from this erosion, once ejected by the rivers in the Atlantic, are transported by the littoral drift in the direction of the south before being trapped at the level of the great virgation of the shoreline of Laâouina–Cape Juby. The wind deflation, in its turn, reinforces this sorting by carrying away the white sands towards the continent and also the black sands sometimes. The cliffs along the coast of Laâouina–Sidi Akhfenir are, however, barriers against wind loss unlike the sector of Sidi-Akhfenir–Cape Juby where the continuous migration of sands to the hinterland is facilitated by the absence of cliffs. The conjunction of these factors has the consequence of weakening the retention of sands' ferrotitanium in the sector Sidi Akhfenir–Cape Juby compared with its counterpart of Laâouina–Sidi Akhfenir. In general, the Laâouina–Cape Juby coastline can be considered a morphological and hydrodynamic trap whose concentrations in ferrotitanium minerals are likely to earn the quality of a mining district despite its seasonal instability and the difficulty of estimating reserves. Indeed, in this supposed district, heavy minerals total about 95 % of the raw sediments and ilmenite predominates and its alteration state is only superficial.     

Marine radiocarbon reservoir corrections (∆R) for Chesapeake Bay and the Middle Atlantic Coast of North America

Radiocarbon dates from known age, pre-bomb eastern oyster (Crassostrea virginica) shells provide local marine reservoir corrections (?R) for Chesapeake Bay and the Middle Atlantic coastal area of eastern North America. These data suggest subregional variability in ?R, ranging from 148 ± 46 ¹⁴C yr on the Potomac River to ? 109 ± 38 ¹⁴C yr at Swan Point, Maryland. The ?R weighted mean for the Chesapeake's Western Shore (129 ± 22 ¹⁴C yr) is substantially higher than the Eastern Shore (? 88 ± 23 ¹⁴C yr), with outer Atlantic Coast samples falling between these values (106 ± 46 and 2 ± 46 ¹⁴C yr). These differences may result from a combination of factors, including ¹⁴C-depleted freshwater that enters the bay from some if its drainages, ¹⁴C-depleted seawater that enters the bay at its mouth, and/or biological carbon recycling. We advocate using different subregional ?R corrections when calibrating ¹⁴C dates on aquatic specimens from the Chesapeake Bay and coastal Middle Atlantic region of North America.     

40Ar/39Ar Age of the Burinda Gold–Silver Deposit and Its Relationship to Magmatism (Northeastern Part of the Argun Superterrane)

Doklady Earth Sciences - Our investigations have made it possible to estimate the age of hydrothermal ore metasomatic rocks at the Burinda Au–Ag deposit, one of the best known in East Asia,...     

Radon in “nonradonic” ground waters of the Baikal region: Spatial and temporal variations

Based on the analysis of radon concentrations in several dozen springs and wells, three groups were distinguished for the waters classified as “nonradonic.” The spatial regularities of the distribution of these groups were revealed, along with the quantitative characteristic of the anomalies and the background, in view of their belonging to the Baikal and Transbaikal hydromineral provinces of the region.     

The nephelinitic–phonolitic volcanism of the Trindade Island (South Atlantic Ocean): Review of the stratigraphy,and inferences on the volcanic styles and sources of nephelinites

Trindade Island is located in the South Atlantic Ocean, 1170 km from the Brazilian coast, and represents the eastern end of the E–W Vitória–Trindade Chain. It shows the youngest plume-induced (ca. 3.7 to <0.17 Ma) subaerial volcanism on the South American plate, associated with the Trindade plume activity. Almeida (1961) recognized five volcanogenic successions at Trindade (in decreasing age): the Trindade Complex (TC, >2.4 Ma) and the Desejado (DF, ∼2.4 to 1.5 Ma), Morro Vermelho (MV, <0.17 Ma), Valado (VF, no age) and Paredão (PF, no age) formations, composed of effusive–pyroclastic deposits and subvolcanic intrusions associated with nephelinite–phonolite volcanic episodes. We revised the original Almeida's (1961) stratigraphy with additional field work and petrography to recognize eruptive styles and processes within the nephelinite–phonolite volcanism. Also, available geochemical databases were used to improve the stratigraphic correlation between nephelinites from different units and to characterize their mantle sources.The nephelinitic volcanism may represent Strombolian and Hawaiian–type activity of low viscosity and volatile–rich lavas interlayered with pyroclastic successions (fall–out deposits). Phonolitic deposits record explosive Vulcanian–style episodes of volatile–rich and higher–viscosity lavas interlayered with pyroclastic deposits (mostly pyroclastic flows). Geochemical data allowed the individualization of nephelinites as follows: (1) MV olivine–rich nephelinites and all olivine–free varieties are low K₂O/Na₂O, K₂O/TiO₂ and intermediate CaO/Al₂O₃ that may be derived from N–MORB and HIMU mantle components; (2) the VF olivine–rich nephelinites have high K₂O/Na₂O, K₂O/TiO₂ and CaO/Al₂O₃ that indicates both EM and HIMU mantle sources and; (3) the PF olivine–rich nephelinites show high K₂O/TiO₂ similar to those from VF, and intermediate CaO/Al₂O₃ as nephelinites from MV rocks, suggesting a mixed source with EM + HIMU > N–MORB components.We suggest that the HIMU and EM mantle types resulted from metasomatic episode(s) in the peridotitic mantle beneath the Trindade Island during the Brasiliano Orogeny and later, as previously pointed out by Marques et al. (1999). Thus, the major HIMU component would relate to recycled oceanic crust or lithospheric mantle (mostly CO₂–eclogites) whereas the less important EM component to recycled marine or continental sediments.     

Sources of Matter and Ore-Producing Fluid of the Tamunyer Gold–Sulfide Deposit (Northern Urals): Isotope Results

The Tamunyer deposit is a typical example of gold–sulfide mineralization located in the lower lithologic–stratigraphic unit (S₂–D₁) of the Auerbach volcanic–plutonic belt. The latter comprises island–arc andesitic volcano–sediments, volcanics, and comagmatic intrusive formations. Carbonates have demonstrated intermediate values of δ¹³C between marine limestone and mantle. The quartz δ¹⁸O is in the range of 15.3–17.2‰. The δ³⁴S of sulfides from the beresitized volcano-sedimentary rocks and ores varies widely from –7.5 to 12‰. The calculated isotope compositions of H₂O, CO₂, and H₂S of the ore-bearing fluid imply two major sources of matter contributing to ore genesis: local rocks and foreign fluid. The ore-bearing fluid was formed by interaction and isotope equilibration between a deep magmatic fluid and marine carbonates (W/R ~ 1), with the contribution of sulfur from the volcano-sedimentary rocks.     

Territory and territorial transformation: the rural properties of the Dávalos-Bracamontes family in the Compostela region (Seventeenth Century)

This investigation seeks to analyse the territorial transformations, land uses, and land tenures in the region of Compostela, Nueva Galicia during the seventeenth century, using land grants for sites of cattle and sheep husbandry and farmland granted as the rural properties to the Dávalos-Bracamontes family, who in 1690 obtained the title of the Counts of Miravalle. The novohispanas haciendas served as territorial control mechanisms of the use and incorporation of new forms of exploitation of the area’s natural resources. The methodology is based on the analysis of the archival data, historical cartography, supplemented by information collected in fieldwork and use of historical modality of geographic information systems. The haciendas of La Lagunilla, Miravalle and San José were located and together represented 33,736.60 ha of land for livestock and agriculture. The territorial extension was possible due to the disappearance of villages, parse indigenous populations in the surroundings and commitments made by the Spanish Crown to the Dávalos-Bracamontes family.

     

Geologic stages of the Paleogene and Neogene evolution of the Arctic shelf in the Ob’ region (West Siberia)

The paper is concerned with the structure of the Arctic shelf sediments in the Ob’ region in the Paleogene and Neogene, sampled from boreholes drilled on the Yamal Peninsula, in the lower reaches of the Pur and Taz Rivers. The specifics of Paleogene marine sedimentation in the central and northern West Siberian Plain are studied. The effect of abiotic (tectonic) factors on the completeness of the geologic record is considered as well as the effect of recent (Oligocene-Neogene) tectonic processes on topography and sedimentation. The borehole sections are compared with the main seismic sections of the Kara Sea and Lomonosov Ridge.     

Early island-arc granitoids of the Shchuchinskaya zone of the Polar Urals: U–Pb (SIMS) zircon isotope data

Granitoids of the Rechnoy and Yalya-Pe paleovolcanoes, which were ascribed to the Silurian Khoimpe complex during a geological mapping, and granitoids of the Nganotsky-1 and Nganotsky-2 plutons that were ascribed to the Early Devonian Yunyaga complex were studied in the Shchuchinskaya zone of the Polar Urals. It was established that according to the mineral and chemical compositions the rocks of the plutons studied correspond to island-arc granitoids of I-type. Zircons from granitoids of the Rechnoy and Yalya-Pe paleovolcanoes and the Nganotsky-1 pluton yielded concordant U–Pb (SIMS) isotope ages of 456 ± 6, 454 ± 4, and 463 ± 3 Ma, respectively, which indicates the existence of an island arc within the Shchuchinskaya zone starting from the Middle–Late Ordovician. Based on the obtained zircon ages of granitoids, the country volcanics were ascribed to the Syaday Formation; the upper stratigraphic boundary of their formation was specified as the Middle–Upper Ordovician.     

Dry gas vents (“mazuku”) in Goma region (North-Kivu,Democratic Republic of Congo): Formation and risk assessment

The word “mazuku” in Swahili means “evil wind”. It corresponds to lowland (depressions) where carbon dioxide is released and, being heavier than air, accumulates at high – often lethal – concentrations (10 vol.% of CO₂ in atmosphere can be considered as the deadly threshold, even for a short time exposure). Mazuku are abundant in Goma and surrounding areas and particularly in the area south of the large volcanic edifices of Nyiragongo and Nyamulagira volcanoes located in the most eastern part of DR Congo, W branch of the East African Rift System (EARS). Our extensive field surveys have indicated that mazuku are concentrated within to and around the densely populated city of Goma close to the N shores of Lake Kivu, mainly near fault or fissure networks. At a more local scale, depressions allowing CO₂-rich gas accumulation are created by lava flow superposition, lava tunnels or cavity collapses, or directly associated with open fractures. People are killed by mazuku every year. Given political and social unrest coupled with the current important demographic and urban growths around Goma, the risks associated to mazuku are increasing accordingly. Mazuku are currently the most important natural risk in terms of human loss for the area and there is an urgent need for further research, more systematic mapping and monitoring of mazuku and for appropriate risk management to be implemented. This paper summarizes the current scientific knowledge on mazuku as well as new advances and a preliminary risk assessment performed recently in the frame of the GORISK project.     

Structure and Geodynamic Evolution of the Maksyutov Metamorphic Complex (Southern Urals): Structural Analysis and Results of U–Pb Dating of Detrital Zircons

Geotectonics - Detailed structural analysis of the formations of the Maksyutov eclogite–glaucophane–schist complex in the Southern Urals has been carried out. U–Pb (LA-ICP-MS)...     

Geomorphology and geomorphological heritage of the Ifrane–Azrou region (Middle Atlas,Morocco)

Geomorphological heritage is a widely used term in European and North-American countries, but is still scarcely mentioned in Africa. Nevertheless, the attractiveness of the African countries is often intimately connected to its breathtaking and endless geological landscapes. Morocco is one of those countries that has the widest diversity in landscapes and landforms, ranging from the Mediterranean and Atlantic coasts over the Rif, Middle Atlas, High Atlas and Anti-Atlas mountain chains to the great rocky and sandy deserts in the South. A wide variety of geological units hosting different types of important economic mineral deposits cover a temporal range from Late Precambrian to Quaternary. A detailed geomorphological study has been carried out in the region of Ifrane and Azrou (Middle Atlas, Central Morocco) using a combination of high resolution satellite data and direct field observations integrated by geological maps and scientific literature. In order to describe and evaluate the geomorphological heritage of this area, 40 geomorphosites have been selected comprising springs, karst landforms (polje, dolines, caves, sinkholes, stone forests, cryptokarstic dolines), carbonate depositional landforms (travertines and waterfalls), fluvial landforms (meanders, canyons, palaeo-valleys, etc.), structural landforms (triangular facets, hogbacks, cuestas, residual outcrops, etc.) and volcanic landforms (volcanoes, caldeira, pyroclastic cones, lava tube). The results of this research have been summarised in a thematic map, representing the geomorphosites related to various landscape units.