Marble-hosted sulfide ores in the Angouran Zn-(Pb–Ag) deposit, NW Iran: interaction of sedimentary brines with a metamorphic core complex

The Angouran Zn-(Pb–Ag) deposit, Zanjan Province, NW Iran, is located within the central Sanandaj-Sirjan Zone of the Zagros orogenic belt. The deposit has proven and estimated resources of 4.7 Mt of sulfide ore at 27.7% Zn, 2.4% Pb, and 110 g/t Ag, and 14.6 Mt of oxidized carbonate ores at 22% Zn and 4.6% Pb. It is hosted by a metamorphic core complex that is unconformably overlain by a Neogene volcanic and evaporite-bearing marine to continental sedimentary sequence. The sulfide orebody, precursor to the significant nonsulfide ores, is located at the crest of an open anticline at the contact between Neoproterozoic to Cambrian footwall micaschists and hanging wall marbles. ⁴⁰Ar–³⁹Ar data on muscovite from mineralized and unaltered footwall micaschists suggest a rapid Mid-Miocene exhumation of the metamorphic basement (∼20 Ma) and yield an upper age constraint for mineralization. The fine-grained sulfide ore is massive, replacive, often brecciated, clearly postmetamorphic and dominated by Fe-poor sphalerite, with minor galena, pyrite, anhydrite, quartz, muscovite, dolomite, and rare calcite. Sphalerite contains Na–Ca–Cl brine inclusions (23–25 mass% total dissolved solids) with homogenization temperatures of 180–70°C. Fluid inclusion chemistry (Na–K–Li–Ca–Mg–Cl–Br), ore geochemistry, S, and Pb isotope data suggest that the Angouran sulfide ore formed by the interaction of modified, strongly evaporated Miocene seawater and the lithotypes of an exhumed metamorphic core complex. Minor contributions of metals from Miocene igneous rocks cannot be excluded. Mineralization occurred in a collisional intra-arc setting with high heat flow, probably during the transition from an extensional to a compressional regime. The Angouran deposit may represent a new type of low-temperature carbonate-hosted Zn–Pb ore that is distinct from Mississippi Valley type and sedimentary-exhalative deposits.Editorial handling: B. Lehmann     

Qualitative and Quantitative Characterization of Mangrove Vegetation Structure and Dynamics in a Peri-urban Setting of Douala (Cameroon): An Approach Using Air-Borne Imagery

Qualitative and quantitative characterization of mangrove vegetation structure and dynamics is required for assessment of coastal habitat vulnerability. Changes in mangrove forests around Douala, Cameroon, have been documented using aerial photography between 1974 and 2009. The distribution pattern of tree species was also assessed in 2009 following the point-centered quarter method (PCQM+) protocol. Pristine mangroves observed in 1974 had been disturbed markedly in 2003 and 2009. Some of the pre-existing mangroves were entirely replaced by settlements, road, and crops (maize, bean, banana, oil palm, green vegetables, and sugar cane plantations). From 1974 to 2003, 39.86 % of mangrove forests have disappeared; the net loss of 22.10 % occurred between 2003 and 2009 alone. Mangrove forest area had decreased 53.16 % around Douala over a 35-year period from 1974 to 2009 concurrent with a substantial increase of settlements (60 %), roads (233.33 %), agriculture areas (16 %), non-mangrove areas (193.33 %), and open water (152.94 %). Field survey showed that almost one third of the quadrants in the remaining mangrove forest were empty. The disrupted mangrove forest has an overall mean height, absolute density, and basal area of 19.80 m, 158 trees ha^?1, and 110.44 m² ha^?1, respectively. In comparison with scientific literature on mangrove degradation, this puts the mangroves around Douala at the top of the “peri-urban mangrove degradation” list. In addition, beyond listing of mangrove plants on the Red List of Threatened Species which will seldom lead to widely distributed species being listed, we call for the creation of a Red List of Locally Threatened Ecosystems, which in contrast is likely to list mangroves as an ecosystem under critical risk of (local) extinction in many countries around the globe, in particular, peri-urban sites.     

The development of the Space Environment Viability of Organics (SEVO) experiment aboard the Organism/Organic Exposure to Orbital Stresses (O/OREOS) satellite

The Space Environment Viability of Organics (SEVO) experiment is one of two scientific payloads aboard the triple-cube satellite Organism/ORganic Exposure to Orbital Stresses (O/OREOS). O/OREOS is the first technology demonstration mission of the NASA Astrobiology Small Payloads Program. The 1-kg, 1000-cm³ SEVO cube is investigating the chemical evolution of organic materials in interstellar space and planetary environments by exposing organic molecules under controlled conditions directly to the low-Earth orbit (LEO) particle and electromagnetic radiation environment. O/OREOS was launched on November 19, 2010 into a 650-km, 72°-inclination orbit and has a nominal operational lifetime of six months. Four classes of organic compounds, namely an amino acid, a quinone, a polycyclic aromatic hydrocarbon (PAH), and a metallo-porphyrin are being studied. Initial reaction conditions were established by hermetically sealing the thin-film organic samples in self-contained micro-environments. Chemical changes in the samples caused by direct exposure to LEO radiation and by interactions with the irradiated microenvironments are monitored in situ by ultraviolet/visible/near-infrared (UV/VIS/NIR) absorption spectroscopy using a novel compact fixed-grating CCD spectrometer with the Sun as its light source. The goals of the O/OREOS mission include: (1) demonstrating key small satellite technologies that can enable future low-cost astrobiology experiments, (2) deploying a miniature UV/VIS/NIR spectrometer suitable for in-situ astrobiology and other scientific investigations, (3) testing the capability to establish a variety of experimental reaction conditions to enable the study of astrobiological processes on small satellites, and (4) measuring the chemical evolution of organic molecules in LEO under conditions that can be extrapolated to interstellar and planetary environments. In this paper, the science and technology development of the SEVO instrument payload and its measurements are described.     

Challenges of value chain actors for vegetable production and marketing in North-East Bangladesh

GeoJournal - Vegetable farming in Northeast Bangladesh has developed rapidly over the last 10 years, with limitations to field management and marketing. A survey was conducted in...     

Application of environmental tracers to study groundwater recharge in a semi-arid area of Central Tunisia

Abstract

Groundwater of the Tertiary-Quaternary Formations in the Jeloula basin (Central Tunisia), together with rain and surface waters, were analysed to investigate the mineralization processes, the origin of the water and its recharge sources. The water samples present a large spatial variability of chemical facies which is related to their interaction with the geological formations. The main sources of the water mineralization are the dissolution of evaporitic and carbonate minerals and cation exchange reactions. Stable isotopes indicate that most groundwater samples originate from infiltration of modern precipitation. Surface water samples from small dam reservoirs show a ¹⁸O/²H enrichment, which is typical of water exposed to open-surface evaporation in a semi-arid region. Considerable data of ³H and ¹⁴C allow the qualitative identification of the present-day recharge that is probably supplied by infiltration of recent flood waters in the Wadi El Hamra valley, and by direct infiltration of meteoric water through the local carbonate outcrops.

Editor D. Koutsoyiannis; Associate editor S. Faye     

Chlorophyll concentration and surface temperature changes associated with earthquakes

The preparation process of an impending earthquake may leave fingerprints on the earth??s surface. Elastic strain in rocks, formation of micro-cracks, gas releases and other chemical or physical activities in the earth??s crust before and during earthquakes has been reported to cause rises in temperature, surface latent heat flux (SLHF), upwelling index and chlorophyll-a (Chl-a) concentration on the ground or sea surface. Changes in surface temperature can be monitored with thermal infrared sensors such as NOAA-AVHRR and microwave radiometers like AMSR-E/Aqua. SLHF data and upwelling indices are provided by National Centers for Environmental Prediction (NCEP) Reanalysis Project and Pacific Fisheries Environmental Laboratory, respectively. This study examines behaviors of the above four factors prior to the past three oceanic and coastal earthquakes occurred at the Pacific Ocean (Northern California of June 15, 2005, Central California of September 28, 2004, and December 22, 2003). We were successful in detecting pre-earthquake anomalies prior to all three earthquakes. Our detailed analysis revealed 1?C5?°C rises in surface temperature in epicentral areas. Considerable anomalies in Chl-a concentration, 1?C2?weeks before the day of the main earthquakes, were spotted, which are attributed to the rise in upwelling index. Time series of SLHF showed meaningful rises from 1?month to a fortnight before the earthquake events. One problem in our research was the low resolution of the data which makes the graphs that are generated from NCEP database affected by all sources of anomalies, other than seismic activities, within an about 1.8°?C2.5° (200?km) area.     

Hydrogeochemical assessment of groundwater in Isfahan province, Iran

Groundwater quality in five catchment areas in Isfahan province of Iran is assessed by measuring physicochemical parameters including major cation and anion compositions, pH, total dissolved solid, electrical conductivity and total hardness. For this purpose, 567 piezometric well samples were collected in October 2007. The abundance of major ions in four of the catchment areas including Gavkhuni, Ardestan, Salt lake and Central Iran desert basins is similar and follows Cl^??>?SO₄ ^2??>?Na⁺?>?HCO₃ ^??>?Ca²⁺?>?Mg²⁺?>?K⁺?>?CO₃ ^2? trend, while in the fifth basin (Karoon), the trend changes into HCO₃ ^??>?Ca²⁺?>?Cl^??>?SO₄ ^2??>?Mg²⁺?>?Na⁺?>?K⁺?>CO₃ ^2?. In general, four water facies are determined and it is shown that alkali elements and strong acids are dominating over alkaline earth and weak acids. Statistical analysis including Mann?CWhitney U test indicate that physicochemical parameters in three of the five investigated basins [Gavkhuni, Ardestan and Central Iran desert (CID)] are similar, while Karoon and salt lake basins display different characteristics. The result indicate that groundwater west of the province is suitable for irrigation, while in the central and eastern parts of the province the groundwater loses its quality for this purpose. It is concluded that mineral dissolution and evapotranspiration are the main processes that determine major ion compositions.     

Modeling of subduction components in the Genesis of the Meso-Cenozoic igneous rocks from the South Shetland Arc, Antarctica

Isotope data and trace elements concentrations are presented for volcanic and plutonic rocks from the Livingston, Greenwich, Robert, King George and Ardley islands (South Shetland arc, Antarctica). These islands were formed during subduction of the Phoenix Plate under the Antarctica Plate from Cretaceous to Tertiary. Isotopically (⁸⁷Sr/⁸⁶Sr)_o ratios vary from 0.7033 to 0.7046 and (¹⁴³Nd/¹⁴⁴Nd)_o ratios from 0.5127 to 0.5129. εNd values vary from +2.71 to +7.30 that indicate asthenospheric mantle source for the analysed samples. ²⁰⁸Pb/²⁰⁴Pb ratios vary from 38.12 to 38.70, ²⁰⁷Pb/²⁰⁴Pb ratios are between 15.49 and 15.68, and ²⁰⁶Pb/²⁰⁴Pb from 18.28 to 18.81. The South Shetland rocks are thought to be derived from a depleted MORB mantle source (DMM) modified by mixtures of two enriched mantle components such as slab-derived melts and/or fluids and small fractions of oceanic sediment (EM I and EM II). The isotopic compositions of the subduction component can be explained by mixing between at least 4 wt.% of sediment and 96 wt.% of melts and/or fluids derived from altered MORB.