Hydrodynamic and geochemical conditions of the formation of stratiform Zn-Pb ore mineralization by chloride solutions

Ore mineralization is formed by postsedimentary (concentrated by evaporation to stage SW2) chloride brines metamorphosed in hydrogeochemical systems that are closed with respect to CO₂, evolve according to “calcic” trend, and have high 2mCa²⁺ > mHCO ₃ ^? + 2mCO ₃ ^2? ratios. In these situations at high R/W ratios (10–100) and temperatures (100–200°C), these brines concentrate ore elements (Zn, Pb, Fe, and Mn) that are geochemical analogues of Ca. The sulfide precipitation of these elements occurs under the effect of carbonate rocks at the abiogenic sulfate reduction of S(VI) of the original brines at low Eh values, which are created in carbonate rocks at higher (>100°C) temperatures. This origin of sulfide mineralization is intensified at decreasing R/W ratios during the dilution of the original brines by elision waters and an increase in the temperature. The hydrodynamics of these ore-forming brines is controlled by the elision hydrogeological regime, which is defined in hydrogeological structures by the geostatic pressure. The brines migrate into the zones of geochemical barriers during the relaxation of hydrogeological structures toward their equilibrium hydrostatic state. Hydrogeological structures, optimal for the precipitation of ore mineralization, are hydrodynamically active and able to maintain a steady (during 10⁵-10⁶ years) inflow of ore-forming brines into the zones of geochemical barriers and the maximum number of water-exchange cycles at these barriers. Modern analogues of these structures are miogeosyncline foredeeps with Cl-Na-Ca chloride brines with high concentrations of ore elements and overall flow rates ranging from 0.n to n m³/year. Stagnate hydrogeological platform structures in hydrostatic equilibrium cannot ensure water exchange needed for ore formation, and, hence, the brines of these structures are not able to deposit the ore elements contained in them, in spite of the high concentrations of these elements.     

Age of Detrital Zircons from Sandstones of the Mesozoic Flysch Formation in the South Anyui Suture Zone (Western Chukotka)

The South Anyui fold zone (western Chukotka) is considered a suture zone related to closure of the South Anyui oceanic basin and collision of Eurasia with the Chukotka–Arctic Alaska microcontinent in the Early Cretaceous. The existence of a compensatory sedimentation basin (foredeep) during folding in the terminal Jurassic–initial Cretaceous remains debatable. This work presents first data on age estimates of detrital zircons from Upper Mesozoic terrigenous sequences of the South Anyui suture zone obtained by the fission-track method. The distal flysch of presumably Late Jurassic age and the proximal flysch of probably Late Triassic age were sampled in the Uyamkanda River basin. The fission-track dating showed that sandstones from the flysch sections contain detrital zircons of two different-age populations. Young zircon populations from sandstones of distal turbidites in the upper course of the Uyamkanda River (two samples) are 149 ± 10.2 and 155.4 ± 9.0 Ma old (Late Jurassic), whereas those from coarse-grained proximal turbidites sampled in the lower course of the Uyamkanda River (one sample) is 131.1 ± 7.5 Ma old (Early Cretaceous). The data obtained indicate that the Late Mesozoic folding in the South Anyui suture zone was accompanied by the formation of a marginal sedimentary basin. Sediments accumulated in this basin compose tectonic nappes that constitute a fold–thrust structure with the northern vergence.     

Directionality of surface high-frequency geoacoustic emission during deformational disturbances

Changes in the directionality of surface high-frequency geoacoustic emission during periods of deformational disturbances on the diurnal time scale prior to strong seismic events on Kamchatka have been investigated. It has been shown that while the emission intensity grows by over an order of magnitude, sharp maxima appear in the direction of longitudinal acoustic oscillations. Based on their position, the orientation of the major compression axis can be determined, whose chaotic motion exhibits two metastable states around the direction to the epicenter of the earthquake.     

Swelling behaviour of expansive soil treated with fly ash–GGBS based binder

In this article, the potential of a binder developed by admixing fly ash and ground granulated blast furnace slag (GGBS) to stabilise expansive soils is evaluated. Laboratory tests included determination of free swell index, swell potential and swelling pressure tests of the soil/binder mixtures at different mixing ratio. The test results showed decrease in the swelling behaviour of the soil with increase in binder content. The percent swell–time relationship was observed to fit the hyperbolic curves enabling us to predict the ultimate percent swell from few initial test results. Addition of 1% of lime to the binder showed further improvement in reducing swelling. A good linear relationship is established between percent oedometer swell and modified free swell index (MFSI) for soil/binder mixtures without lime but the same has not been observed in the presence of lime. The compressibility characteristics of the soil/binder mixtures reduced nominally with increase in binder content but in the presence of lime, the compressibility reduced significantly. Binder used in this study has been found to be effective and economic to stabilise expansive soils with lesser amount of chemical additives such as lime.     

Primitive island arc and oceanic lavas from the hunter ridge-hunter fracture zone. Evidence from glass,olivine and spinel compositions

Summary At its southernmost end, the main spreading centre of the North Fiji Basin is propagating into arc crust of the poorly-known Hunter Ridge. We define nine magmatic groups from major element glass chemistry and olivine and spinel compositions in samples dredged from twenty six sites in this area by the R/V Academician A. Nesmeyanov in 1990. These include groups of boninites, island arc tholeiites (IAT), mid-ocean ridge basalts (MORB), enriched mid-ocean ridge basalts (E-MORB), olivine porphyritic andesites and basaltic andesite and Na-rhyolites. Primitive lavas containing highly forsteritic olivine phenocrysts are common in all the groups, except for the rhyolites.We report over 100 glass analyses for dredged rocks from this region, and about 300 olivine-spinel pairs for representatives of all the magmatic groups identified, except the Na-rhyolites.The MORB in this region are probably produced at the propagating spreading centre in the southern part of the North Fiji Basin. Juxtaposition of shallow, hot MORB-source diapirs supplying the MORB in this area, and the sub-arc damp, refractory upper mantle beneath the Hunter Ridge, provides suitable petrogenetic conditions to produce a range of magma types, from island arc tholeiites through to high-Ca boninites. The latter were recovered in eleven dredges.The E-MORB lavas recovered from the extreme southern margin of the North Fiji Basin are shown to be essentially identical to those dredged from adjacent older South Fiji Basin crust. It is hypothesized that the former were either scraped off the South Fiji Basin crust during an episode of oblique subduction that may have generated the Hunter Ridge during the last 5 Myr, or alternatively, that slices of the South Fiji Basin crust were trapped and incorporated into the North Fiji Basin as the subduction zones fronting the Vanuatu arc stepped or propagated southward.

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Primitive Inselbogen- und ozeanische Laven von Hunter Rücken und der Hunter BruchZone: die Bedeutung der Zusammensetzung von Glas, Olivin und Spinell

Zusammenfassung Das spreading centre des Nord-Fidschi-Beckens setzt sich an seinem südlichsten Ende in die Inselbogen-Kruste des noch wenig bekannten Hunter-Rückens fort.Wir definieren 9 magmatische Gruppen auf der Basis der Hauptelement-Zusammensetzung von Gläsern und der Zusammensetzung von Olivin und Spinell in Proben die das Forschungsschiff R/V Akademiker A. Nesmeyanov von 26 Stellen im Jahr 1990 aufgesammelt hat. Zu diesen gehören Gruppen von Boniniten, Inselbogentholeiiten (IAT), Basalten zentralozeanischer Rücken (MORB), angereicherte zentralozeanische Rücken (E-MORB), Olivin-porphyritische Andesite und basaltische Andesite, sowie Na-Rhyolite. Primitive Laven mit Olivinkristallen, die reich an Forsterit-Komponenten sind, kommen in allen diesen Gruppen, mit Ausnahme der Rhyolite, vor.Wir legen über 100 Glas-Analysen von Gesteinen aus diesem Gebiet vor und über 300 Olivin-Spinell-Paare für Vertreter aller der hier identifizierten magmatischen Gruppen, mit Ausnahme der Natriumrhyolite.Die MORB in diesem Gebiet sind wahrscheinlich an dem aktiven Spreading Center im Südteil des Nord-Fidschi-Beckens entstanden. Das nebeneinander Vorkommen von seichten heißen MORB-Quellen Diapiren, die MORB in diesem Gebiet erzeugen, und der Sub-Inselbogen, wasserhaltige, refraktäre obere Mantel unter dem Hunter Rücken führen zu geeigneten petrogenetischen Bedingungen für die Entstehung einer Vielfalt von Magmatypen, von Inselbogentholeiiten bis zu sehr Kalziumreichen Boniniten. Die letzteren wurden in 11 Dredge-Proben gefunden.Die E-MORS Laven, die aus dem extremen Südteil des Nord-Fidschi-Beckens entnommen wurden, sind im wesentlichen mit jenen identisch, die aus der benachbarten älteren Kruste des Süd-Fidschi-Beckens stammen. Es wird vermutet, daß die letzteren entweder aus dem Süd-Fidschi-Becken während einer Episode obliger Subduktion, die in den letzten 5 Millionen Jahren zur Entstehung des Hunter Ridge geführt hat, abgeschert wurden, oder auch daß Teile der Kruste des Süd-Fidschi-Beckens in das Nord-Fidschi-Becken inkorporiert wurden als Subduktionszonen gegenüber dem Vanuato-Bogen sich nach Süden fortbewegten.

     

Date of minimum of the “protracted” solar cycle 23

We offer an interpretation of the now widely discussed protracted onset of the epoch of solar activity minimum after cycle 23. The interpretation appeals to the Gnevyshev-Ohl rule, but in the context of a new statistical quantity-the product of the cycle amplitude by its duration. Considering this quantity, which has the same physical meaning as that of the integrated characteristic used by Gnevyshev and Ohl, yields a probable estimate for the onset of the minimum of the current cycle in the interval 2009.0–2012.4.     

Changes in phytoplankton production and upwelling intensity off A Coruña (NW Spain) for the last 28 years

Ocean Dynamics - The analysis of a 28-year-long (1989–2016) series of monthly measurements of chlorophyll concentrations and primary production rates at a shelf station off A Coruña (NW...     

The Water Vapour Continuum: Brief History and Recent Developments

The water vapour continuum is characterised by absorption that varies smoothly with wavelength, from the visible to the microwave. It is present within the rotational and vibrational–rotational bands of water vapour, which consist of large numbers of narrow spectral lines, and in the many ‘windows’ between these bands. The continuum absorption in the window regions is of particular importance for the Earth’s radiation budget and for remote-sensing techniques that exploit these windows. Historically, most attention has focused on the 8–12?μm (mid-infrared) atmospheric window, where the continuum is relatively well-characterised, but there have been many fewer measurements within bands and in other window regions. In addition, the causes of the continuum remain a subject of controversy. This paper provides a brief historical overview of the development of understanding of the continuum and then reviews recent developments, with a focus on the near-infrared spectral region. Recent laboratory measurements in near-infrared windows, which reveal absorption typically an order of magnitude stronger than in widely used continuum models, are shown to have important consequences for remote-sensing techniques that use these windows for retrieving cloud properties.     

Mineralogy and fluid inclusion study of polymetallic veins in the Madjarovo ore field,Eastern Rhodope,Bulgaria

Summary The formation of the Madjarovo polymetallic ore deposit is closely related to Paleogene magmatism of intermediate character represented by subvolcanic and volcanic rocks. Six stages of vein type mineralization were established: 1. quartz-pyrite-chalcopyrite with Bi-sulphosalts; 2. quartz-hematite-chlorite with gold; 3. quartz-galena-sphalerite; 4. quartz-barite-chalcedony with Sb-sulphosalts; 5. quartz-arsenic sulphosalts; 6. calcite-siderite. Ag-bearing galena and Fe-poor sphalerite are the main minerals. Galena of early formation is Bi-bearing, while in late stages it carries more Sb. Gold was found in two generations in different parageneses. The early gold is Ag-poor and related to hematite, while the late one is Ag-rich and closely associated with quartz and sulphosalts. Three groups of sulphosalts were established: Se-bearing Bi-sulphosalts; Sb-sulphosalts, a part of them Cl-bearing, and As-sulphosalts with more or less Ag. Fluid inclusion data obtained in quartz, amethyst, sphalerite and barite from several representative ore veins show formation temperatures in the range of 370° to 150°C for different stages of mineralization. Evidence of boiling fluids suggests pressures of 70 to 180 bars which correspond to an average depth of mineralization near 1.000 m. The low salinities of the fluids (a/v 3.5 eq. wt% NaCI) indicate influx of meteoric waters during mineralization. On the basis of mineralogical and fluid inclusion data physicochemical conditions and source of the ore forming fluids are discussed.

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Mineralogie und Flüssigkeitseinschlüsse in polymetallischen Erzgngen der Lagerstätte Madjarovo, Ost-Rhodopen, Bulgarien

Zusammenfassung Die Bildung der polymetallischen Lagerstätte Madjarovo war eng verknüpft mit einem Paläogenen Magmatismus von intermediärem Charakter, der durch Subvulkanite und Vulkanite repräsentiert wird. Es wurden sechs Bildungsstadien der Gangvererzung festgestellt: 1. Quarz-Pyrit-Chalcopyrit mit Bi-Sulfosalzen; 2. Quarz-Hämatit-Chlorit mit Gold; 3. Quarz-Galenit-Sphalerit; 4. Quarz-Baryt-Chalzedon mit Sb-Sulfosalzen; 5. Quarz-As-Sulfosalze; 6. Calcit-Siderit. Ag-führender Galenit und Fe-armer Sphalerit sind die Hauptminerale. Früh gebildeter Galenit is Bi-haltig, während Galenite der späteren Bildungsstadien mehr Sb führen. Gold wurde in zwei Generationen in unterschiedlichen Paragenesen gefunden. Das Früh-Gold (Ag-arm) ist verknüpft mit Hämatit, während das Spät-Gold (Ag-reich) mit Quarz und Sulfosalzen eng assoziiert ist. Es wurden drei Gruppen von Sulfosalzen festgestellt: Se-führende Bi-Sulfosalze; Sb-Sulfosalze, die z.T. Cl-führend sind, und As-Sulfosalze mit mehr oder weniger Ag-Gehalten. Flüssigkeitseinschlüsse in Quarz, Amethyst, Sphalerit und Baryt aus mehreren repräsentativen Erzgängen zeigen Bildungtemperaturen von 370°–150°C für unterschiedliche Mineralisationsstadien. Siedende Lösungen weisen auf einen Druckbereich von 70–180 Bar hin, der einer durchschnittlichen Bildungstiefe von 1.000 m entspricht. Die durchweg niedrige Salinität der Lösungen (durchschnittlich 3.5. Gew.% NaCl äq.) wird auf einen Zufluß von meteorischen Wässern während der Mineralisation zurückgeführt. Auf der Basis der mineralogischen Ergebnisse und der Daten fluider Einschlüse werden die physikochemischen Bedingungen und die Herkunft der Erzlösungen diskutiert.

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With 4 Figures