Genesis of massive sulfide deposits in the Verkhneural’sk ore district, the South Urals, Russia: Evidence for magmatic contribution of metals and fluids

Melt inclusions and aqueous fluid inclusions in quartz phenocrysts from host felsic volcanics, as well as fluid inclusions in minerals of ores and wall rocks were studied at the Cu-Zn massive sulfide deposits in the Verkhneural’sk ore district, the South Urals. The high-temperature (850–1210°C) magmatic melts of volcanic rocks are normal in alkalinity and correspond to rhyolites of the tholeiitic series. The groups of predominant K-Na-type (K₂O/Na₂O = 0.3–1.0), less abundant Na-type (K₂O/Na₂O = 0.15–0.3), and K-type (K₂O/Na₂O = 1.9–9.3) rhyolites are distinguished. The average concentrations (wt %) of volatile components in the melts are as follows: 2.9 H₂O (up to 6.5), 0.13 Cl (up to 0.28), and 0.09 F (up to 0.42). When quartz was crystallizing, the melt was heterogeneous, contained magnetite crystals and sulfide globules (pyrrhotite, pentlandite, chalcopyrite, bornite). High-density aqueous fluid inclusions, which were identified for the first time in quartz phenocrysts from felsic volcanics of the South Urals, provide evidence for real participation of magmatic water in hydrothermal ore formation. The fluids were homogenized at 124–245°C in the liquid phase; the salinity of the aqueous solution is 1.2–6.2 wt % NaCl equiv. The calculated fluid pressure is very high: 7.0–8.7 kbar at 850°C and 5.1–6.8 kbar at 700°C. The LA-ICP-MS analysis of melt and aqueous fluid inclusions in quartz phenocrysts shows a high saturation of primary magmatic fluid and melt with metals. This indicates ore potential of island-arc volcanic complexes spatially associated with massive sulfide deposits. The systematic study of fluid inclusions in minerals of ores and wall rocks at five massive sulfide deposits of the Verkhneural’sk district furnished evidence that ore-forming fluids had temperature of 375–115°C, pressure up to 1.0–0.5 kbar, chloride composition, and salinity of 0.8–11.2 (occasionally up to 22.8) wt % NaCl equiv. The H and O isotopic compositions of sericite from host metasomatic rocks suggest a substantial contribution of seawater to the composition of mineral-forming fluids. The role of magmatic water increases in the central zones of the feeding conduit and with depth. The dual nature of fluids with the prevalence of their magmatic source is supported by S, C, O, and Sr isotopic compositions. The TC parameters of the formation of massive sulfide deposits are consistent with the data on fluid inclusions from contemporary sulfide mounds on the oceanic bottom.     

Basaltic melts in olivine from alkaline pumice of Primor’e: Evidence from the study of melt inclusions

Doklady Earth Sciences -     

Problem of the Application of Mathematical Methods in Geology

The most characteristic errors in the application of mathematical-statistic and modeling methods encountered periodically during the peer reviewing of geological scientific journals are analyzed, and recommendations for their elimination are given. Problems of the determination of relative errors in the simplified mathematical models are discussed. Necessity of calculating parameters of the background value and eliminating its influence on computation of the “useful signal” is shown. A graphic method for determining the minimum anomalous content is also proposed for discussion and testing. Characteristic errors and necessity for maintaining constraints of the application of correlation analysis are demonstrated.     

Adakites and adakitic melts: Compositions of rocks,quenched glasses,and inclusions in minerals

Data set of rocks and glasses whose compositions correspond to the term “adakite” (SiO₂ > 56 wt %, Sr > 400 ppm, Sr/Y > 18) was compiled from two large geochemical data bases. It was revealed that the adakitic melts are characterized by extremely low abundance as compared to adakitic rocks. Only 50 adakitic compositions (~0.5%) were identified in the data base that includes the major and trace element compositions of over 9700 quenched and melt inclusion glasses. It was established that only 22 of selected analyses characterize melt inclusion glasses, while other analyses represent residual glass or “pocket melts” in ultramafic mantle xenoliths. The question of a genetic relationship between adakitic rocks, adakitic melts, and melting of subsiding plate remains open. Original data on the Shiveluch volcanic center (Kamchatka) were used to demonstrate the formation of adakitic signatures through mineral accumulation.     

Evidence for the volcanoclastic genesis of the Carnian diamondiferous bed in the Ust’-Olenek area (from petrographic and geochemical data)

A detailed petrographic study of a 0.4–1.2 m thick Carnian diamondiferous bed of the Angardam-Tasa Ridge (Ust’-Olenek area, northern Siberia) was performed. It showed that the bed earlier referred to as a terrigenous deposit might be interpreted as an intensely altered volcanoclastic lapilli tuff of basic and, probably, ultrabasic composition. The tuff occurs within a 100 m thick Ladinian–Carnian volcanosedimentary sequence. It consists mainly of resurgent material: altered lithoclasts (nodules of basic-ultrabasic? lithology), devitrified volcanic glass, fragments of autolithic breccia, etc. The thin volcanoclastic sheet is supposed to have formed within a sedimentation basin as a result of phreatomagmatic eruptions of kimberlite volcanoes. The substantiation of the volcanogenic origin of the Carnian diamondiferous bed might be a new approach to elucidate the primary source of widespread placer diamonds in Arctic Siberia.     

Towards the question of the movement of hydrothermal solutions: The case of the Schlema-Alberoda vein deposit

The paths of the movements of hydrothermal solutions are considered in the case of one of the world’s largest uranium vein deposits, the Schlema-Alberoda, which was mined by the Soviet-German corporation Wismut JSC in the second half of the 20th century. Detailed geological exploration to a depth of 2 km was accompanied by specialized research, the results of which have remained practically unpublished due to confidentiality. The data obtained show that the region adjoining the largest fault was draining rather than ore-conducting. This circumstance specifies and supplements the current concept concerning the movement of hydrothermal fluids.     

Silicate and salt melts in the genesis of the industrial’noe tin deposit: Evidence from inclusions in minerals

The data obtained on melt and fluid inclusions in minerals of granites, metasomatic rocks, and veins with tin ore mineralization at the Industrial’noe deposit in the southern part of the Omsukchan trough, northeastern Russia, indicate that the melt from which the quartz of the granites crystallized contained globules of salt melts. Silicate melt inclusions were used to determine the principal parameters of the magmatic melts that formed the granites, which had temperatures at 760–1020°C, were under pressures of 0.3–3.6 kbar, and had densities of 2.11–2.60 g/cm³ and water concentrations of 1.7–7.0 wt %. The results obtained on the fluid inclusions testify that the parameters of the mineral-forming fluids broadly varied and corresponded to temperatures at 920–275°C, pressures 0.1–3.1 kbar, densities of 0.70–1.90 g/cm³, and salinities of 4.0–75.0 wt % equiv. NaCl. Electron microprobe analyses of the glasses of twelve homogenized inclusions show concentrations of major components typical of an acid magmatic melt (wt %, average): 73.2% SiO₂, 15.3% Al₂O₃, 1.3% FeO, 0.6% CaO, 3.1% Na₂O, and 4.5% K₂O at elevated concentrations of Cl (up to 0.51 wt %, average 0.31 wt %). The concentrations and distribution of some elements (Cl, K, Ca, Mn, Fe, Cu, Zn, Pb, As, Br, Rb, Sr, and Sn) in polyphase salt globules in quartz from both the granites and a mineralized miarolitic cavity in granite were assayed by micro-PIXE (proton-induced X-ray emission). Analyses of eight salt globules in quartz from the granites point to high concentrations (average, wt %) of Cl (27.5), Fe (9.7), Cu (7.2), Mn (1.1), Zn (0.66), Pb (0.37) and (average, ppm) As (2020), Rb (1850), Sr (1090), and Br (990). The salt globules in the miarolitic quartz are rich in (average of 29 globules, wt %) Cl (25.0), Fe (5.4), Mn (1.0), Zn (0.50), Pb (0.24) and (ppm) Rb (810), Sn (540), and Br (470). The synthesis of all data obtained on melt and fluid inclusions in minerals from the Industrial’noe deposit suggest that the genesis of the tin ore mineralization was related to the crystallization of acid magmatic melts. Original Russian Text@ V.B. Naumov, V.S. Kamenetsky, 2006, published in Geokhimiya, 2006, No. 12, pp. 1279–1289.     

Observations of extrasolar planet transits with the automated telescopes of the Pulkovo Astronomical Observatory

Exoplanet observations have been performed on the automated Pulkovo Observatory telescopes. We have obtained 33 transit light curves for 16 known exoplanets and six transit observations for three exoplanet candidates discovered by the Kepler telescope. Based on our observations, we have reliably confirmed the existence of an exoplanet with an extremely large radius, R _pl = 1.83 ± 0.16R _Jup, in the system KOI 256 and detected a strong deviation of its orbital revolution from the theoretically predicted one. During the transit of the exoplanet WASP-12b across the stellar disk, we detected bursts that could be caused by the planet transit across spots on the star or by the presence of a satellite around this exoplanet. We detected possible periodic variations in the duration of the exoplanet transit across the stellar disk with time for HAT-P-12b that could be caused by variations in orbital inclination. The transit duration and depth, the central transit time, and the radius and orbital inclination of the planet have been estimated. The equilibrium temperature and albedo have been estimated for several exoplanets.     

Chemical composition of melts of the Early Eocene volcanic center at Cape Khairyuzova,western Kamchatka: Evidence from inclusions in minerals

Original authors’ data on the mineralogy and composition of melt inclusions in two samples show that the Early Eocene magmatic rocks at Cape Khairyuzova were formed by mixing melts of mafic, intermediate, and acid composition, which were derived from different sources. The mafic melt was rich in MgO, and its temperature was 1100–1150°C. The temperature of the acid melt varied from 1070 to 1130°C. The melts are also different in concentrations of trace elements and in their ratios. All three melt types are enriched in LILE and LREE and depleted in HFSE and were likely derived in suprasubductional environments. The mafic and intermediate magmas were formed by melting a mantle wedge and subsequent fractionation of the melts. The acid melts could be formed by melting crustal rocks when they were overheated in the newly formed orogen of significant thickness. When ascending, the mantle melts could mix in variable proportions with acid melts in crustal chambers.