Secondary dispersion haloes in the gold-bearing weathering crust of the Vasilkovskoe gold deposit, Northern Kazakhstan

The formation conditions and characteristics of secondary dispersion haloes in the gold-bearing weathering crust of a gold-sulfide-quartz deposit are considered. The fraction < 0,1mm is demonstrated to be preferable for lithochemical prospecting for the Vasilkovskoe type gold mineralization. The secondary dispersion haloes of gold, identified based on analyses of this fraction, are characterized by the maximum size and productivity.

STUDY OF GOETHITE IN THE ABYSSAL WEATHERING CRUST OF IRON ORES AT THE YUVILEINA MINE (KRYVYI RIH BASIN).

The issue of the formation of iron hydroxides in deep horizons of the vertical weathering crust of the Saksagan iron-ore strip of the Kryvyi Rih basin (the Yuvileina Mine) has been studied. А stable presence of iron hydroxides in the ore strata has been revealed at considerable depths (1300-1400 m) using the method of traditional microscopy and phase analysis of iron. They are represented by goethite. Ontogenic observations have identified four main varieties of goethite. Each variety is characterized by their own forms, conditions and method of formation such as: pseudomorphic, dispersed (earthy), colloform, cementing ones. It was found that martite aggregates were the only source of iron for all four varieties. It has been proven that the depth factor, by itself, does not determine the formation of goethite. The formation of the necessary physical and chemical parameters in the system of mineralogenesis is of decisive importance. Iron hydroxides were suggested to be considered as hypergene-metasomatic formations in the abyssal weathering crust.

TYPOMORPHIC FEATURES OF GOLD FROM OF THE SURSK GREENSTONE STRUCTURE WEATHERING CRUST

Based on the generalization of the actual material of production reports, publications in scientific journals and own research, information on the typomorphic features of native gold from the weathering crust of different mineral composition of gold-bearing rocks within the deposits and ore occurrences of the Sura greenstone structure are given. The change of typomorphic features of gold in the vertical section of the weathering crust is investigated.

Storage and export of microbial biomass across the western Greenland Ice Sheet

The Greenland Ice Sheet harbours a wealth of microbial life, yet the total biomass stored or exported from its surface to downstream environments is unconstrained. Here, we quantify microbial abundance and cellular biomass flux within the near-surface weathering crust photic zone of the western sector of the ice sheet. Using groundwater techniques, we demonstrate that interstitial water flow is slow (~10−2 m d−1), while flow cytometry enumeration reveals this pathway delivers 5 × 108 cells m−2 d−1 to supraglacial streams, equivalent to a carbon flux up to 250 g km−2 d−1. We infer that cellular carbon accumulation in the weathering crust exceeds fluvial export, promoting biomass sequestration, enhanced carbon cycling, and biological albedo reduction. We estimate that up to 37 kg km−2 of cellular carbon is flushed from the weathering crust environment of the western Greenland Ice Sheet each summer, providing an appreciable flux to support heterotrophs and methanogenesis at the bed.

Comparative Study on the Reservoir Characteristics and Development Technologies of Two Typical Karst Weathering-Crust Carbonate Gas Reservoirs in China

Carbonate reservoirs are the main reservoir types in China, which occupy the large ratio of reserves and production at present. The high-efficiency development of carbonate reservoirs is of great significance to assure the stability of national energy supply. The Lower Paleozoic reservoir in Jingbian gas field and the Sinian reservoir in Anyue gas field are two typical carbonate gas reservoirs, and their successful development experiences can provide significant references for other similar carbonate gas reservoirs. For Jingbian gas field, it is a lithological-stratigraphic reservoir developed in a westward monocline and multiple rows of nose-fold structures, and is a stable craton basin with simple palaeognomy distribution and stable connectivity, which has complex gas-water distribution. However, for Anyue gas field, it is a lithological-structural reservoir with multiple tectonic high points and multiple fault systems, and is biological dune beach facies under extensional setting with highly differentiated inside of the block in palaeognomy characteristics, which has limited connectivity and tectonic side water is in a local area. The difference of gas reservoir characteristics leads to the diverse development strategies. For these two gas reservoirs, although there are some similar aspects, such as the screen of enrichment areas, the application of irregular well pattern and reservoir stimulation techniques, the criteria of enrichment areas, the well types, and the means of reservoir stimulation are absolutely different. In addition, due to the differences of control reserves and production capacity for these two kinds of reservoirs, the mode of stable production is also different. The effective development of Jingbian gas field can give some references to the future exploitation on the Sinian gas reservoir. Firstly, the sedimentary characteristics should be studied comprehensively. Secondly, the distribution pattern and distribution characteristics of the palaeognomy should be found and determined. Thirdly, the distribution of fracture system in the reservoir should be depicted finely. Finally, dynamic monitoring on the production performance should be strengthened, and the management for this gas field should be improved further. The findings of this study can help for better understanding of the Karst weathering-crust carbonate gas reservoir formation characteristics and the optimal development technologies that should be taken in practice.

Native gold in the weathering crust of the Nizhneselemdzhinsky gold-bearing node (Amur region)

Research subject. The weathering crust of Proterozoic slates in the Neklya River basin and Paleozoic granites in the Nizh- neselemdzhinsky gold-bearing node (NGBN) in the Tatarka River basin.Methods. The research was carried out using the methods of atomic absorption, X-ray fluorescent and mineralogical analysis of rocks and minerals. The method of raster electron microscopy was used to study the element structure, morphological and microstructural features of minerals.Results. Specific features of native gold from the weathering crust of NGBK were defined. It was established that the NGBN weathering crust contains both hypogene gold, partially changed in the course of hypergenesis, and neogenic gold. A considerable share of gold is of high purity (1000%o). Occasionally, gold in the form of complex accretions from grains of different morphology and structure is present. A specific feature of weathering crust gold is its interpenetrations within the rock matrix of a varying mineral structure. Gold-bearing carbonaceous structures in the form of films and outgrowths on gold grains were revealed; the presence of carbon in rock components associating with the noble metal was defined. In the crust, the participation of carbon in physicochemical processes was established, as a result of which the release of Au, encapsulated in minerals-concentrators, and its redeposition on geochemical barriers occur. Gold nanoparticles can be long-acting growth centres in the host rocks, first coalescing with each other to yield nanoformations, then microforms, etc. In the weathering crust of gold deposits, both the transformation of the hypogenic noble metal and the formation of its new forms occur.Conclusion. This work contributes to the expansion of the mineral resource base of gold in the Amur Region, including through such unconventional sources as the NGBN weathering crust.

Spectral attenuation coefficients from measurements of light transmission in bare ice on the Greenland Ice Sheet

Light transmission into bare glacial ice affects surface energy balance, biophotochemistry, and light detection and ranging (lidar) laser elevation measurements but has not previously been reported for the Greenland Ice Sheet. We present measurements of spectral transmittance at 350–900 nm in bare glacial ice collected at a field site in the western Greenland ablation zone (67.15∘ N, 50.02∘ W). Empirical irradiance attenuation coefficients at 350–750 nm are ∼ 0.9–8.0 m−1 for ice at 12–124 cm depth. The absorption minimum is at ∼ 390–397 nm, in agreement with snow transmission measurements in Antarctica and optical mapping of deep ice at the South Pole. From 350–530 nm, our empirical attenuation coefficients are nearly 1 order of magnitude larger than theoretical values for optically pure ice. The estimated absorption coefficient at 400 nm suggests the ice volume contained a light-absorbing particle concentration equivalent to ∼ 1–2 parts per billion (ppb) of black carbon, which is similar to pre-industrial values found in remote polar snow. The equivalent mineral dust concentration is ∼ 300–600 ppb, which is similar to values for Northern Hemisphere warm periods with low aeolian activity inferred from ice cores. For a layer of quasi-granular white ice (weathering crust) extending from the surface to ∼ 10 cm depth, attenuation coefficients are 1.5 to 4 times larger than for deeper bubbly ice. Owing to higher attenuation in this layer of near-surface granular ice, optical penetration depth at 532 nm is 14 cm (20 %) lower than asymptotic attenuation lengths for optically pure bubbly ice. In addition to the traditional concept of light scattering on air bubbles, our results imply that the granular near-surface ice microstructure of weathering crust is an important control on radiative transfer in bare ice on the Greenland Ice Sheet ablation zone, and we provide new values of flux attenuation, absorption, and scattering coefficients to support model development and validation.

Paleotemperature modeling of hydrocarbon generation centers and their role in the formation of «Paleozoic» oil deposits (Ostaninskoe field, Tomsk region)

Study and exploration of the pre-Jurassic oil and gas complex in Western Siberia is one of the aspects of hydrocarbon raw-material base development. The main scope of this study is to locate the source of Paleozoic hydrocarbons. The problem of modeling and assessing the role of Paleozoic-Mesozoic hydrocarbon generation centers in the formation of «Paleozoic» oil deposits in the section of the Ostaninskoe oil and gas condensate field (Tomsk region) is solved. In the formation of the oil and gas content of the pre-Jurassic basement two reservoirs are involved: the weathering crust and the roof of the bed-rock Paleozoic. The first was formed during the period of 213–208 Ma, and the second is genetically determined by epigenetic processes in the weathering crust. Potential hydrocarbon sources for the weathering crust and bed-rock Paleozoic reservoirs are Domanic type rocks in the crystalline basement: Larinskaya S1lr, Mirnaya D1mr, Chuzikskaya D2cz, Chaginskaya D3cg Formations, as well as Tyumenskaya J1-2tm and Bazhenovskaya J3bg Formations in sedimentary cover. To perform joint paleotemperature modeling of sedimentary basins of the «modern» Jurassic-Cretaceous and Paleozoic «paleobasins», the Ostaninskaya 438P well was selected, which is due to the presence of measured temperatures both in the Jurassic sections and in the pre-Jurassic formations, as well as fluid inflows from the pre-Jurassic horizons into the well. At the first step, the solution of the inverse problem of geothermics was obtained using reservoir temperatures and vitrinite reflectance measurements from the Mesozoic deposits: density of deep heat flow from the base of sedimentary section was determined, which is characterized by a quasi-constant value from the Jurassic to the present. The second step was to solve the inverse problem using vitrinite reflectance measurements from Paleozoic sediments. As a result, the heat flow value was obtained for the key moments of geodynamic history of the stratigraphic section, starting from the Silurian. By solving direct problems of geothermics with the given values of heat flow, the structural-tectonic and thermal history of four Paleozoic potential oil source formations (as well as Jurassic – Bazhenov and Tyumen Formations) has been retraced. The controversial aspects of the heat transfer model in the section of the Ostaninskoe field are considered. It has been established that the Tyumen and Bazhenov oil sources (most likely Bazhenov) are syngenetic (in terms of generation, accumulation and preservation time) for the weathering crust and the Paleozoic reservoirs. The role of the Chaginskaya Formation as gas source is insignificant.

Engineering and geological zoning of the Malmyzhsky deposit weathering crusts (Svoboda area)

Introduction. Interest in the study of weathering crusts arose at a time when geological engineers faced the problem of developing open pits formed by eluvial soils. However, the exact and detailed division of the weathering crusts into engineering-geological zones, especially when studying mineral deposits, is not given due attention even today. Therefore, in the course of prospecting, it is important to correctly determine weathering crust type and profile, and establish the possibility of changing the engineering and geological conditions when opening the rock mass by mine workings for further slope stability prediction of the designed mining structures. Research aim is to determine vertical engineering-geological zoning of the Malmyzhsky deposit weathering crusts (Svoboda area) and identify patterns in alluvial deposits physical and mechanical properties change, which define the safety of mine development. Methodology. A significant number of Russian and foreign scientists have considered the formation of weathering crusts from different positions. They established the geochemical zoning and engineeringgeological zoning of the weathering crusts. Results. The article describes the Svoboda area at the Malmyzhsky gold-copper-porphyry deposit. Engineering and geological zoning of the weathering crust section was carried out according to a set of features, including structural and textural features, mineral composition, physical and mechanical properties of rocks. Within it, three zones are identified at the Malmyzhsky field, the Svoboda area: IV – dispersed, III – litomarge, and II – clastic. Physical and mechanical properties of rock building up the considered weathering crust have been analyzed proving that change in geological conditions within even one zone of the Malmyzhsky gold-copper-porphyry deposit (Svoboda area) entails a change in the choice of projected pit wall angles.