Primary Mineralogy Research Articles

Gas-exchange chamber analysis of elemental mercury deposition/emission to alluvium, ore, and mine tailings

Deposition of mercury (Hg) from the atmosphere is an important source of this contaminant to terrestrial ecosystems. Once deposited, all forms of Hg can be retained or emitted back to the atmosphere. Distinguishing between volatilization of geogenic or indigenous Hg and that deposited from the atmosphere is difficult. Field flux measurements in the general area of two industrial scale gold mining operations, showed local deposition of Hg emitted from point and nonpoint sources, and subsequent re-emission. The work presented in this paper investigated deposition/emission of elemental Hg to and from alluvium and two mine materials before, during, and after exposure to high air concentrations, for both wet and dry conditions, using a laboratory gas exchange chamber and a Hg permeation source. In general, results showed a range in mean elemental Hg deposition velocities ranging from 0.13 to 0.46cms−1 that varied with material. A significant influence of atmospheric ozone (O3) on flux was observed that depended on the material and whether wet or dry. A synergistic relationship existed between O3 and light promoting Hg flux, and flux was also influenced by material grain size, chemistry, and primary mineralogy.

Environmental mineralogy of Cu-porphyry mine tailings, a case study of semi-arid climate conditions, Sarcheshmeh mine, SE Iran

Sarcheshmeh porphyry copper mine is located in semiarid clime conditions, in the Central Iranian Volcano-Plutonic Copper Belt. Hydro-geochemical and climatological conditions produce suites of secondary mineral assemblages in the Sarcheshmeh mine tailings, which are very interesting and important from the environmental point of view. Solid samples were collected from the fresh and weathered tailings and also from the surface evaporative layer formed on top of the old impoundments. Samples were investigated by using X-ray diffraction (XRD), ore microscopy and chemical fractionation methods. The primary mineralogy of fresh tailings, which is controlled by alteration/mineralization in the Sarcheshmeh mine, was mainly composed of quartz, pyrite, muscovite (sericite), albite, orthoclase, ±clinochlore±chalcopyrite and±illite. This mineral assemblage was subjected to the oxidation/weathering reactions in dried impoundments. Acidic conditions of the weathering zone were compatible with the precipitation of jarosite [KFe3+3(SO4)2(OH)6], hydronium jarosite [(H3O)Fe3+3(SO4)2(OH)6], natrojarosite [NaFe3+3(SO4)2(OH)6], alunite [KAl3(SO4)2(OH)6], butlerite [Fe3+(SO4)(OH)2H2O] and gypsum [CaSO4 2H2O]. A great variety of soluble secondary minerals, typical of arid and semiarid environment, were distinguished in the well-developed evaporative layer on top of the old weathered tailings. These minerals, which are formed due to the upward migration of multi-elemental contaminated waters enriched in Al, Ca, Cl, Cu, Fe2+, Fe3+, H, K, Mg, Mn, Na, O, S, and Zn, were mainly from: (1) simple hydrated sulfate salts of the divalent metal cations (gypsum, hexahydrite, kieserite, leonite, poitevinite, and Zinc-melanterite); (2) simple hydrated salts of the trivalent ions (alunogen, kalinite, and tamarugite); (3) mixed divalent–trivalent salts (lishizhenite, römerite, and Zincobotryogen); and (4) chloride containing minerals (eriochalcite, halite, and mitscherlichite). Secondary minerals in the evaporative zone were found in several unique mineral assemblages such as poitevinite–tamarugite–alunogen–hexahydrite. Formation, transformation, and dissolution of evaporative minerals are induced by the wetting/drying cycles. Mineralogical results, which are supported by the hydro-geochemical and sequential extraction data, are useful for the prediction of contamination potential of tailings, the fate of environmental contaminants, and also the possible remediation strategies.

REPLACEMENT PROCESSES INVOLVING HIGH FIELD STRENGTH ELEMENTS IN THE T ZONE, THOR LAKE RARE-METAL DEPOSIT

The Thor Lake rare-element (Y-REE-Nb-Ta-Zr-Be) deposit, Northwest Territories, Canada, is a world-class deposit hosted by alkaline syenite and granite and has two main mineralized zones, namely the Nechalacho and T Zones deposit. The T Zone is shown to have originally been a pegmatite, but has experienced a strong hydrothermal overprint. Coarse-grained to megacrystic, elongate crystals defining the pegmatitic texture are completely pseudomorphed and are interpreted to have originally been nepheline. The T Zone underwent three main alteration stages, which are (from earliest to latest): (I) silicification of the principal phases of the pegmatite and the associated replacement of igneous aegirine and arfvedsonite by quartz + magnetite + high field strength element (HFSE)-bearing minerals; (II) polylithionite [KLi 2 AlSi 4 O 10 (F,OH) 2 ] alteration (Li metasomatism) that caused pervasive replacement of albite by polylithionite; and (III) phenakite (Be 2 SiO 4 ) alteration (Be metasomatism). Replacement of the primary mineralogy resulted in the formation of abundant pseudomorphs that are characterized by various HFSE minerals [typically, bastnasite-(Ce), zircon, rutile, xenotime-(Y), and columbite] and phenakite (the predominant Be mineral). The habit and mineralogy of the pseudomorphs, as well as textural relationships in partially altered crystals, make aegirine and mica-group minerals the most likely precursors of the HFSE-rich and Be-rich pseudomorphs, respectively. Although aegirine and arfvedsonite from alkaline rocks can contain HFSE, LA-ICP-MS analysis of aegirine and arfvedsonite from the T Zone indicates that the HFSE concentrations in these two minerals are insufficient to account for the bulk HFSE concentrations of the HFSE-rich pseudomorphs. Therefore, HFSE must have been added to the pseudomorphs during fluid-mineral interaction, requiring hydrothermal mobility of HFSE. An open-space filling process may have been involved in the precipitation of HFSE minerals, including zircon, rutile, anatase, and REE fluorcarbonates. Initial replacement of aegirine by quartz + magnetite increased porosity in some of the T Zone rocks, which may have facilitated HFSE precipitation. Our study also demonstrates that most hydrothermal zircon shows no association with fluorite and that the fluorite in REE-rich pseudomorphs commonly postdates the REE fluorcarbonate minerals [ e.g. , bastnasite-(Ce)]. These relationships indicate that HFSE precipitation in the T Zone requires a model that does not rely on the mixing of HFSE-, F-bearing fluids with Ca-rich fluids, as has been proposed for other HFSE deposits hosted by alkaline igneous rocks. As the precipitation of HFSE appears to be restricted to pseudomorphs where aegirine and micas have been replaced, the degree of hydrothermal enrichment of HFSE in the T Zone, and possibly in other deposits containing such minerals, may be dictated by the primary abundance of these minerals.

Correlation between magnetic susceptibility and mineral species along NWA-1 well, southern Tunisia: An overlap of the depositional environment, the climate, and the diagenesis

In order to distinguish the effects of diagenesis, the climate and the depositional environment, the magnetic properties were correlated with some minerals along the NWA-1 well, which crosses the southern subsurface from Cretaceous to Silurian successions. The MS along NWA-1 well shows major picks probably indicating a dramatic change of geochemical and mineralogical composition. Minor picks may be attributed to diagenetic transformations affecting some minerals. The mineralogical analysis shows the presence of illite, kaolinite with some traces of chlorite and smectite. Quartz, calcite, white feldspar, anorthite, dolomite, gypsum and pyrite are identified as associated minerals. The PCA of the different minerals and the magnetic susceptibility shows three different heterogeneous populations. In these populations, the traditional classification of magnetic minerals is not respected. For instance, diamagnetic minerals are positively correlated with MS. This correlation is through indirect causal relation extrapolating the temperature caused by the burial diagenesis. The aim is not totally reached because the handicap is twofold. The XRD diffraction is not able to identify the low amounts of magnetic minerals and the primary mineralogy and magnetic properties are radically modified by post-depositional processes. At the productive well of NWA-1, this overlap is further complicated by hydrocarbons, low grade metamorphism and remagnetization modifying the original magnetic signal.

Diagenesis of Paleogene sandstones in the Padesh strike-slip basin, Southwestern Bulgaria

Sandstones are a major rock type in the 2500 m thick Palaeogene sedimentary fill of the Padesh strike-slip basin. The main diagenetic alterations include mechanical compaction and carbonate cementation while dissolution, transformation, recrystallization, replacement and chemical compaction were of lesser significance during burial. These postdepositional processes and their products are discussed in terms of micropetrographic characteristics, spatial distributional patterns, mechanisms of formation, controlling factors, and temporal sequence. The diagenetic changes are related to eodiagenesis, mesodiagenesis, and telodiagenesis but most processes occurred during the mesodiagenetic stage. The sandstone diagenesis was controlled by the depositional facies, climate conditions, primary mineralogy and fabric, distribution and composition of the associated shales, chemistry of the pore fluids, sedimentation and subsidence rates, burial depth, and basin thermal regime. The most peculiar feature is recorded in basal sandstone strata of the Palaeogene succession which display evidence for minor selective dissolution and subsequent kaolinite precipitation in the produced secondary pores as a result of thermal maturation of organic matter in the adjacent black shales. Several lines of evidence indicate a hyperthermal character of the Padesh Basin thus resembling other “hot-type” sedimentary basins. The present study contributes to deciphering the diagenetic pathway of siliciclastic deposits in strike-slip basins characterized by elevated heat flow and can be applied for the evaluation of their hydrocarbon system potential. It also supports previous findings that thermal maturation of kerogene in carbonate-free, organic-rich shales may influence the mesodiagenetic alteration of adjacent sandstones in response to increased temperature.

Preservation of primary lake signatures in alkaline earth carbonates of the Eocene Green River Wilkins Peak-Laney Member transition zone

Significant changes in carbonate mineralogy, texture, and stable isotope composition occur at the transition from the Wilkins Peak Member to the Laney Member in the Eocene Green River Formation, Bridger Basin, Wyoming, which reflect evolution of inflow waters, lake waters, and paleoenvironments.The top of the Wilkins Peak Member contains heterogeneous laminae of calcite and dolomite. Evaporites associated with these layers suggest deposition in hypersaline lakes. Diagenetic carbonate mineral textures include euhedral cement overgrowths and interlocking mosaics of calcite and dolomite crystals, 20–70μm in size. Electron microprobe analyses indicate diagenetic overgrowth of Fe-rich dolomite on cloudy Fe-poor cores. δ18O values of carbonate laminae in the upper Wilkins Peak Member vary by ~6‰ with no depth dependent or mineralogic trends, which also suggests diagenetic overprinting.Alternating organic-rich and primary aragonite, calcite, and dolomite laminae were identified from the lower Laney Member. Primary lacustrine aragonite consists of well sorted, prismatic crystals 5–10μm in length, with micro-lamination defined by crystal size variation. Primary precipitated calcite and dolomite laminae are monominerallic, with well sorted polyhedral crystals, ~10μm in size. Primary mineralogy of the lower Laney Member changes from calcite to aragonite and dolomite stratigraphically upward. Along the same 15m thick stratigraphic interval, δ18O values decrease upward by ~3‰, all of which suggests (1) lake waters underwent evaporative concentration, which together with calcite precipitation increased the lake water Mg/Ca ratios and led to formation of aragonite and dolomite, (2) source waters became lower in δ18O, possibly as inflow changed to higher altitude foreland rivers.The results from this study show that understanding the primary lacustrine versus diagenetic origin of Green River carbonate minerals is essential for paleoenvironmental and paleoclimate interpretations.

Inorganic control on original carbonate mineralogy and creation of gas reservoir of the Upper Jurassic carbonates in the Kopet-Dagh Basin, NE, Iran

The Upper Jurassic Mozduran Formation (Oxfordian–Tithonian) is the main petroleum reservoir in the Kopet-Dagh Basin, northeast Iran, which consists predominantly of carbonate rocks with subordinate evaporites and siliciclastics deposited in platform to deep marine settings of a subtropical sea. Detailed field surveys, petrographic investigations, facies and wire line log analyses were carried out at eight surface sections and four wells in the Kopet-Dagh Basin. Integration of petrographic and isotopic data suggests primary low-Mg calcite mineralogy of Oxfordian and Tithonian ooids. On the other hand, in the wells, Kimmeridgian ooids and cements are dominantly aragonitic and high-Mg calcite mineralogy (HMC). Marine cements with isopachous, fibrous and isopachous bladed fabrics indicate original aragonite and HMC mineralogy, respectively. The domination of aragonite mineralogy could be related to increased hypersalinity, evaporite precipitation and consequently an increase in Mg/Ca ratio, which resulted in formation of aragonite in preference to calcite. Preserved ooids with radial and concentric cortices in shallow-water settings that are nearby siliciclastic source, together with aragonitic and HMC ooids accompanied by evaporites in the drilled fields, suggest original mineralogy was probably controlled inorganically following local salinity variations. This study suggests that Kimmeridgian pay zones are mainly controlled by depositional facies, aragonitic and HMC mineralogy, and diagenetic processes such as dolomitization and dissolution.

More chips off of Asteroid (4) Vesta: Characterization of eight Vestoids and their HED meteorite analogs

Vestoids are generally considered to be fragments from Asteroid (4) Vesta that were ejected by past collisions that document Vesta’s collisional history. Dynamical Vestoids are defined by their spatial proximity with Vesta (Zappala, V., Bendjoya, Ph., Cellino, A., Farinella, P., Froeschle’, C. [1995]. Icarus 116, 291–314; Nesvorny, D. [2012]. Nesvorny HCM Asteroid Families V2.0. EAR-A-VARGBDET-5-NESVORNYFAM-V2.0. NASA Planetary Data System.). Taxonomic Vestoids are defined as V-type asteroids that have a photometric, visible-wavelength spectral, or other observational relationship with Vesta (Tholen, D.J., 1984. Asteroid Taxonomy from Cluster Analysis of Photometry. Ph.D. Thesis, University of Arizona, Tucson; Bus, S.J., Binzel, R.P. [2002]. Icarus 158, 106–145; Carvano, J., Hasselmann, P.H., Lazzaro, D., Mothe’-Diniz, T. [2010]. Astron. Astrophys. 510, A43). We define ‘genetic Vestoids’ as V-type asteroids that are probable fragments ejected from (4) Vesta based on the supporting combination of dynamical, near-infrared (NIR) spectral, and taxonomic evidence. NIR reflectance spectroscopy is one of the primary ground-based techniques to constrain an asteroid’s major surface mineralogy (Burns, R.G. [1993a]. Mineralogical Applications of Crystal Field Theory. Cambridge University Press, Cambridge, UK, 551 p). Despite the reasonable likelihood that many dynamical and taxonomic Vestoids likely originate from Vesta, ambiguity exists concerning the fraction of these populations that are from Vesta as compared to the fraction of asteroids that might not be related to Vesta.Currently, one of the most robust techniques to identify the genetic Vestoid population is through NIR reflectance spectroscopy from ∼0.7 to 2.5μm. The derivation of spectral band parameters, and the comparison of those band parameters with those from representative samples from the Howardite–Eucrite–Diogenite (HED) meteorite types, allows a direct comparison of their primary mineralogies. Establishing tighter constraints on the genetic Vestoid population will better inform mass estimates for the current population of probable Vestoids, will provide more accurate orbital information of Vestoid migration through time that will assist dynamical models, and will constrain the overall current abundance of basaltic material in the main asteroid belt (Moskovitz, N.A., Jedicke, R., Gaidos, E., Willman, M., Nesvorny, D., Fevig, R. [2008]. Icarus 198, 77–90).This work reports high-quality NIR spectra, and their respective interpretations, for eight Vp-type asteroids, as defined by Carvano et al. (Carvano, J., Hasselmann, P.H., Lazzaro, D., Mothe’-Diniz, T. [2010]. Astron. Astrophys. 510, A43), that were observed at the NASA Infrared Telescope Facility on January 14, 2013 UT. They include: (3867) Shiretoko, (5235) Jean-Loup, (5560) Amytis, (6331) 1992 FZ1, (6976) Kanatsu, (17469) 1991 BT, (29796) 1999 CW77, and (30872) 1992 EM17. All eight asteroids exhibit the broad ∼0.9- and ∼1.9-μm mineral absorption features indicative of pyroxene on each asteroid’s surface. Data reduction and analysis via multiple techniques produced consistent results for the derived spectral absorption band centers and average pyroxene surface chemistries for all eight asteroids (Reddy, V., Sanchez, J.A., Nathues, A., Moskovitz, N.A., Li, J.-Y, Cloutis, E.A., Archer, K., Tucker, R.A., Gaffey, M.J., Mann, P.J., Sierks, H., Schade, U. [2012c]. Icarus 217, 153–168; Lindsay, S.S., Emery, J.P., Marchis, F., Enriquez, J., Assafin, M. [2013]. A spectroscopic and mineralogic study of multiple asteroid systems. American Astronomical Society, DPS Meeting #45, #112.04; Lindsay, S.S., Marchis, F., Emery, J.P., Enriquez, J.E., Assafin, M. [2014]. Icarus, submitted for publication; Gaffey, M.J., Cloutis, E.A., Kelley, M.K., Reed, K.L. [2002]. Mineralogy of asteroids. In: Bottke Jr., W.F., Cellino, A., Paolicchi, P., Binzel, R.P. (Eds.), Asteroids III. The University of Arizona Press, Tucson, pp. 183–204; Burbine, T.H., Buchanan, P.C., Dolkar, T., Binzel, R.P. [2009]. Met. Planet. Sci. 44, 1331–1341.). (3867) Shiretoko is most consistent with the eucrite meteorites while the remaining seven asteroids are most consistent with the howardite meteorites. The existing evidence suggests that all eight of these Vp-type asteroids are genetic Vestoids that probably originated from Vesta’s surface.

Hydrothermal alteration and zeolitization of the Fohberg phonolite, Kaiserstuhl Volcanic Complex, Germany

The subvolcanic Fohberg phonolite (Kaiserstuhl Volcanic Complex, Germany) is an economic zeolite deposit, formed by hydrothermal alteration of primary magmatic minerals. It is mined due to the high (>40 wt%) zeolite content, which accounts for the remarkable zeolitic physicochemical properties of the ground rock. New mineralogical and geochemical studies are carried out (a) to evaluate the manifestation of hydrothermal alteration, and (b) to constrain the physical and chemical properties of the fluids, which promoted hydrothermal replacement. The alkaline intrusion is characterized by the primary mineralogy: feldspathoid minerals, K-feldspar, aegirine–augite, wollastonite, and andradite. The rare-earth elements-phase gotzenite is formed during the late-stage magmatic crystallization. Fluid-induced re-equilibration of feldspathoid minerals and wollastonite caused breakdown to a set of secondary phases. Feldspathoid minerals are totally replaced by various zeolite species, calcite, and barite. Wollastonite breakdown results in the formation of various zeolites, calcite, pectolite, sepiolite, and quartz. Zeolites are formed during subsolidus hydrothermal alteration (<150 °C) under alkaline conditions. A sequence of Ca–Na-dominated zeolite species (gonnardite, thomsonite, mesolite) is followed by natrolite. The sequence reflects an increase in $$\log [(a_{{{\text{Na}}^{ + } }} )/(a_{{{\text{H}}^{ + } }} )]$$ and decrease in $$\log [(a_{{{\text{Ca}}^{2 + } }} )/(a_{{{\text{H}}^{ + } }}^{2} )]$$ of the precipitating fluid. Low radiogenic 87Sr/86Sr values indicate a local origin of the elements necessary for secondary mineral formation from primary igneous phases. In addition, fractures cut the intrusive body, which contain zeolites, followed by calcite and a variety of other silicates, carbonates, and sulfates as younger generations. Stable isotope analysis of late-fracture calcite indicates very late circulation of meteoric fluids and mobilization of organic matter from surrounding sedimentary units.

Corpos hipabissais correlacionados à Formação Serra Geral na região do Cerro do Coronel, RS: geologia e petrologia

The Serra Geral Formation is characterized by an expressive volume of tholeiitic basic lava flows and a subordinate presence of acid volcanites. Intrusive bodies (dikes and sills) are correlated to this unit, and, along with volcanic deposits, constitute the Parana Magmatic Province. This research is about the geological and petrological investigation of basic-intermediate intrusions of the Cerro Coronel region, southeast of the city of Pantano Grande, RS. These hypabyssal bodies are stratigraphically linked to the Serra Geral Formation and form an alignment with NW-SE orientation. They are intrusive in sedimentary rocks of Irati and Rio Bonito Formations. All intrusives present columnar disjunctions and are affected by strong NE and NW fracturing. The small facies variation is predominantly constituted by fine equigranular rocks and, rarely, porphyritic terms. Intergranular texture is a very common feature, but subophitic texture is present too. Primary mineralogy is characterized by plagioclase, augite, opaque minerals and, scarcely, olivine. Apatite and quartz occur as accessory minerals. Mesostasis of felsic composition occurs as the final stage of crystallization. Geochemical data of major and trace elements allow the classification of the rocks as basaltic andesite with tholeiitic affinity, whose evolution occurred probably by fractioned crystallization mechanisms, involving mainly plagioclase and augite. The characteristics of the major, trace, and rare earth elements are compatible with those presented for magmatism related to large continental tholeiitic provinces such as Deccan Traps, Paraná-Etendeka, Columbia River, Siberian Traps and Karoo. These rocks have concentrations below 2% of TiO2, showing a tendency to Esmeralda magma-type of the Paraná Magmatic Province.

Gold Sterile Ore Acid Generation Evaluation, San Juan Argentina

One of the problems that mining represents in relation to the natural watercourses is the possible formation of what we call acid mine drainage, which consists in the emission or formation of water effluents of great acidity, usually rich in sulfate and with variable contents in heavy metals. The drainage mentioned is developed from the metal sulfide and sulfate leaching. Researches about the creation of acid drainage suggest that the formation of these depends directly on various factors: primary mineralogy (neutralizer sulfides and minerals), water presence (whether), oxygen diffusion, grain size, microbiological interaction (bacterium), among others. To study these variables and to relate them with geological factors, static (Acid-Base Accounting) and dynamic (Humidity Cell) tests have been developed, among others. The mentioned tests are applied to a case of a gold deposit situated in the Province of San Juan, which is currently very argued because of its mining activity due to its leaching process. In the sterile mineral obtained from the process, kinetics tests were carried out in humidity cells to simulate the natural oxidation of the primary mineral samples. In the obtained leaching, pH values closer to neutrality and a limited solution metal presence were detected, indicating the neutralization ability due to the carbonates ores presence.

Observed CO2-induced reactivity in Werkendam gas field, the Dutch storage analogue

Natural CO2 fields provide important insights in the long-term geochemical behaviour of CO2 in a reservoir and the potential of permanent trapping in carbonate minerals. The Werkendam gas field in The Netherlands, discovered during gas exploration activities in 1991, contains >70% CO2. Core samples were selected from the Werkendam natural analogue (WED) as well as from the nearby Barendrecht-Ziedewij (BRTZ) and Waalwijk-Noord (WWN) CH4-bearing reservoirs. The three gas reservoirs are all Triassic Bunter sandstones, with BRTZ and WWN containing respectively 0.8% and 1.4% CO2. Mineralogical and petrographic analyses were performed to unravel the diagenetic evolution of each field for comparison. Early diagenetic mineral reactions were similar for the three field. Minor differences are attributed to variation in primary mineralogy and the K+/H+ ratio of the formation water. The late stage mineral reactions that are observed in WED which are absent in BRTZ and WWN were interpreted to be induced by the influx of CO2. These include the (additional) dissolution of K-feldspar and anhydrite, and the precipitation of Mg-rich siderite, quartz and barite. Even though carbon isotope analysis could not confirm (but also not exclude) this, petrographic analysis gave strong indications for the precipitation of siderite in WED as a result of the high CO2 partial pressure. The estimated amount of carbon trapping in siderite is 20% to 58% of the total CO2. Barite precipitation was probably the result of K-feldspar and anhydrite dissolution, since barium is a common impurity in K-feldspar. In the overall reaction between the sandstone and carbonized brine, several unknowns remain. A sink for calcium, potassium and aluminium from anhydrite and K-feldspar dissolution was not observed in the samples from WED. In addition, potential sources of magnesium and iron for Mg-rich siderite could not be deduced from the comparison of the fields. Possibly, these sinks and sources can be found in the clay-rich intervals within the sandstone reservoir. Future research should investigate the effect of heterogeneity within storage complexes on mineral trapping.

Depositional and Diagenetic controls on Reservoir Characteristics of X-well and K-well, Ogban Field, Niger Delta

Sedimentological subsurface study of X-well and K-well reservoir sand bodies located in the Niger Delta was carried out to determine the influence of depositional environment and diagenetic control on the reservoir characteristics. Lithofacies analysis reveals the presence of sandstones, siltstones, mudstones and heterolithics. Based on the detailed sedimentological description, wire line logs evaluation and trace fossils analysis, the X-well and K-well reservoirs are interpreted as a barrier complex deposit of fluvio-deltaic—shallow marine environment. Petrographic studies reveal quartz as the dominant mineral with minor amount of feldspars. Cements include silica, quartz overgrowth and siderite. Facies analyses indicate porosity loss due to compaction, and variations in the diagenetic pathway observed in the different facies are closely related to primary mineralogy as influenced by palaeodepositional environments.

Using gamma-ray Spectrometry and Geostatistics for Assessing Geochemical Behaviour of Radioactive Elements in the Lese Catchment (southern Italy)

Gamma-rays emitted from the ground surface relate to the primary mineralogy and geochemistryof the bedrock, and the secondary weathered materials. This information can contribute significantly to anunderstanding of the geochemical and pedogenetic history of a region. The main aim of this paper was to study the relationship between ground gamma-ray data and basement geochemistry in the Lese catchment (Calabria, southern Italy) and to map them, using geostatistics, from in-situ γ-ray spectrometry. The activities of naturally occurring radionuclides were measured at 179 locations by in situ measurements of 40K, 238U, 232Th and total radioactivity and by using gamma-ray spectrometry. Then a multi-Gaussian approach was used to explore and map the activity of naturally occurring radionuclides (40K, 238U, 232Th) and total radioactivity. Locations and lithological compositions of bedrock appear to be responsible for variations in radioelement activity. From radiometric investigations it has emerged that the natural activity of radionuclides in rocks and soils is not equally distributed, but rather influenced by the different geologic conformations of the various examined areas. As expected, high values of 40K, 232Th and total radioactivity were found in rocks of plutonic origin and low values in sedimentary rocks. Uranium radioactivity behaved in a constant manner in these lithologies, albeit with some differences in clayey sites particularly rich in Uranium.

Jadeitite formed during subduction: In situ zircon geochronology constraints from two different tectonic events within the Guatemala Suture Zone

Jadeitite is a rare rock type associated with high-pressure–low-temperature blocks within serpentinite matrix mélanges. Models of formation involve precipitation from subduction-zone aqueous fluids veining the overlying mantle wedge (P-type), or metasomatism of igneous and/or sedimentary protoliths previously emplaced into the mélange (R-type). Age determinations of mélange lithologies provide constraints on the timing of “peak metamorphism” and subsequent exhumation. The timing of jadeitite formation, particularly in the rich source of the Guatemala Suture Zone (GSZ), is a controversial subject needing further attention.Over 80 in situ zircon crystals from three jadeitites and two mica–albite rocks from the North Motagua Mélange and one phengite jadeitite from the South Motagua Mélange of the GSZ were studied for age and trace-element determination. Most of these zircons are characterized by low Th/U ratios, depleted chondrite-normalized REE patterns relative to zircons from oceanic gabbros, and contain fluid and mineral inclusions that reflect the primary mineralogy (i.e., jadeite) and context (i.e., crystallization from an aqueous fluid) of the host rock, and thus formed during jadeitite crystallization. The SHRIMP-RG and LAM-ICP-MS U–Pb dates from zircon indicate that jadeitites and mica–albite rocks from the GSZ were formed through vein precipitation at ~98−80 and ~154–158Ma, respectively. These data show (a) older ages that indicate jadeitite crystallization occurred ~10–30Ma before the preserved subduction-zone peak metamorphism (e.g., exhumed eclogite), and (b) a second group of ages slightly younger than, or similar to, exhumation ages given by Ar–Ar dates from micas. Similar relationships occur at other jadeitite occurrences, such as the Syum-Keu ultramafic complex in the Polar Urals (Russia) and the serpentinite mélanges of the Río San Juan complex (Dominican Republic). The data argue for formation of jadeitite within the mantle wedge during active subduction. Thus, jadeitite provides a record of fluid introduction into the mantle wedge during subduction rather than during exhumation.

Mobility and fractionation of REEs during deep weathering of geochemically contrasting granites in a tropical setting, Malaysia

In this study we describe the mobility and fractionation of REEs in two deep (up to 30m) tropical weathering profiles developed on two granites from the Kuala Lumpur pluton, Malaysia, sampled at Cheras and Rawang. On the basis of Na2O and K2O both are S-type granites, but Rawang has higher CaO, MgO and FeO than Cheras and lower SiO2. With respect to Al-saturation Rawang is I-type and Cheras is S-type. We compared the two profiles in terms of total REEs, magnitude and changes in Ce and Eu anomalies, REE mobility and LREE/HREE fractionation. Rawang profiles have higher REE contents, display lower mobility for most except the heaviest REEs and show higher LREE/HREE fractionation than those from Cheras. These differences can be linked to differences in primary mineralogy and degree of weathering, the latter controlling the type and volume of secondary minerals. Specifically, bowl-shaped parent-rock-normalised patterns in the Cheras saprolites appear to be a result of apatite dissolution. Moreover, moderate weathering evident in lower Mineralogical Indices of Alteration (MIA) at Cheras has conserved parent rock REE patterns and fractionation factors in the saprolites. By contrast, more intense weathering observed in Rawang profiles has produced abundant kaolinite group minerals that have preferentially retained LREE, which consequently display high LREE/HREE fractionation. This study provides important insights into the factors controlling REE mobility during tropical weathering, and its potential as an indicator of weathering intensity.

Petrological vestiges of the Late Jurassic-Early Cretaceous transition from rift to back-arc basin in southernmost Chile: New age and geochemical data from the Capitán Aracena, Carlos III, and Tortuga ophiolitic complexes

The ophiolitic remnants of the Upper Mesozoic Rocas Verdes basin in southernmost South America were studied from the perspectives of petrography, chemistry of minerals, bulk-rock geochemistry, and U-Pb geochronology. The study aimed to unravel the tectonic, magmatic, and metamorphic evolution of a suprasubduction rift zone that underwent a transition to a back-arc basin. The rifting phase and bimodal magmatism within the Rocas Verdes basin started prior to or during the Late Jurassic, as indicated by a gabbro in contact with pillow basalts that dated at 154 Ma. In the Late Jurassic Capitán Aracena and Carlos III complexes, tholeiitic basalts are geochemically comparable to enriched mid-oceanic ridge basalts. Back-arc basin development continued for 35 myr until the Early Cretaceous, as suggested by the ages of detrital zircons in cherty layers within pillow basalts and metamorphic titanite that crystallized during seafloor metamorphism near the spreading/magmatic axis. In the Early Cretaceous Tortuga Complex, tholeiitic basalts are comparable to normal mid-oceanic ridge basalts. Non-deformative metamorphism converted the primary mineralogy of the ophiolites to low- to intermediate-grade metamorphic assemblages formed during ocean-floor type alteration in a suprasubduction setting. Fossilized bacteria, preserved as rounded aggregates of titanite microcrystals, were identified in the pillow basalts up to the Early Cretaceous. The Rocas Verdes basin closed during the Andean orogeny, which started during the Late Cretaceous, and ophiolites were tectonically juxtaposed and thrust over the sedimentary infill of the quasi-oceanic basin in which they developed. The tectonic emplacement of the ophiolitic complexes was complete before the latest Cretaceous, as indicated by crystallization ages of granites intruded into the ophiolitic complexes.

Alteration assemblages in the Miller Range and Elephant Moraine regions of Antarctica: Comparisons between terrestrial igneous rocks and Martian meteorites

AbstractThe weathering products present in igneous terrestrial Antarctic samples were analyzed, and compared with those found in the four Miller Range nakhlite Martian meteorites. The aim of these comparisons was to determine which of the alteration phases in the Miller Range nakhlites are produced by terrestrial weathering, and what effect rock composition has on these phases. Antarctic terrestrial samples MIL 05031 and EET 96400, along with the Miller Range nakhlites MIL 03346 and 090032, were found to contain secondary alteration assemblages at their externally exposed surfaces. Despite the difference in primary mineralogy, the assemblages of these rocks consist mostly of sulfates (jarosite in MIL 05031, jarosite and gypsum in EET 96400) and iddingsite‐like Fe‐clay. As neither of the terrestrial samples contains sulfur‐bearing primary minerals, and these minerals are rare in the Miller Range nakhlites, it appears that SO42−, possibly along with some of the Na+, K+, and Ca+ in these phases, was sourced from wind‐blown sea spray and biogenic emissions from the southern ocean. Cl enrichment in the terrestrially derived “iddingsite” of MIL 05031 and MIL 03346, and the presence of halite at the exterior edge of MIL 090032, can also be explained by this process. However, jarosite within and around the olivine‐bound melt inclusions of MIL 090136 is present in the interior of the meteorite and, therefore, is probably the product of preterrestrial weathering on Mars.

Geochemical constraints on komatiite volcanism from Sargur Group Nagamangala greenstone belt, western Dharwar craton, southern India: Implications for Mesoarchean mantle evolution and continental growth

We present field, petrographic, major and trace element data for komatiites and komatiite basalts from Sargur Group Nagamangala greenstone belt, western Dharwar craton. Field evidences such as crude pillow structure indicate their eruption in a marine environment whilst spinifex texture reveals their komatiite nature. Petrographic data suggest that the primary mineralogy has been completely altered during post-magmatic processes associated with metamorphism corresponding to greenschist to lower amphibolite facies conditions. The studied komatiites contain serpentine, talc, tremolite, actinolite and chlorite whilst tremolite, actinolite with minor plagioclase in komatiitic basalts. Based on the published Sm-Nd whole rock isochron ages of adjoining Banasandra komatiites (northern extension of Nagamangala belt) and further northwest in Nuggihalli belt and Kalyadi belt we speculate ca. 3.2–3.15 Ga for komatiite eruption in Nagamangala belt. Trace element characteristics particularly HFSE and REE patterns suggest that most of the primary geochemical characteristics are preserved with minor influence of post-magmatic alteration and/or contamination. About 1/3 of studied komatiites show Al-depletion whilst remaining komatiites and komatiite basalts are Al-undepleted. Several samples despite high MgO, (Gd/Yb)N ratios show low CaO/Al2O3 ratios. Such anomalous values could be related to removal of CaO from komatiites during fluid-driven hydrothermal alteration, thus lowering CaO/Al2O3 ratios. The elemental characteristics of Al-depleted komatiites such as higher (Gd/Yb)N (>1.0), CaO/Al2O3 (>1.0), Al2O3/TiO2 (<18) together with lower HREE, Y, Zr and Hf indicate their derivation from deeper upper mantle with minor garnet (majorite?) involvement in residue whereas lower (Gd/Yb)N (<1.0), CaO/Al2O3 (<0.9), higher Al2O3/TiO2 (>18) together with higher HREE, Y, Zr suggest their derivation from shallower upper mantle without garnet involvement in residue. The observed chemical characteristics (CaO/Al2O3, Al2O3/TiO2, MgO, Ni, Cr, Nb, Zr, Y, Hf, and REE) indicate derivation of the komatiite and komatiite basalt magmas from heterogeneous mantle (depleted to primitive mantle) at different depths in hot spot environments possibly with a rising plume. The low content of incompatible elements in studied komatiites suggest existence of depleted mantle during ca. 3.2 Ga which in turn imply an earlier episode of mantle differentiation, greenstone volcanism and continental growth probably during ca. 3.6–3.3 Ga which is substantiated by Nd and Pb isotope data of gneisses and komatiites in western Dharwar craton (WDC).

Hydrothermal Ni: Doriri Creek, Papua New Guinea

The Doriri Creek (DC) Ni–Pd–Pt prospect was discovered in 1966 in the Papuan Ultramafic Belt (PUB) in PNG. The DC was interpreted as a hydrothermal Ni accumulation. The DC is located in the southern proximity of Mt Suckling (~180km SE of Port Moresby), where local intrusive rocks are intermediate to acid dykes and small stocks, within the tec tonized contact zone of the Australian and Woodlark Plates. The active volcanoes of Mount Victory and Waiowa indicate recent thermal activity in the area.The Doriri Creek prospect is the result of episodic hydrothermal fluid flow running through the Doriri prospect, that resulted in Ni concentration of up to 1.55wt.%, formed by alteration of an ultramafic unit of peridotites/pyroxenites within a Mg-rich gabbronorite envelope. Ni was concentrated in chlorite and serpentine group minerals in addition to Fe oxides, with a minor amount in pentlandite in locally sulfidic samples. Ore mineralogy is also associated with a high phosphorous content as apatite, that concentrates LREE (light rare earth elements). Palladium concentrations are up to 0.37ppm. Platinum is present in concentrations up to 0.06ppm within the ore.The alteration halo associated with Doriri Creek mineralization is ~100m in width. Primary mineralogy comprises pyroxene, olivine and plagioclase, which have been altered extensively to amphibole and chlorite–serpentine group minerals. This halo is characterized by enrichments of U, K and W over background values.Local magnetite concentration is up to ~35% of whole rock, which is very pronounced in the sulfide rich area of the system. The top part of the DC system is overprinted by tropical weathering at metric scale, which displays LREE enrichment and positive Ce anomalies.The Papuan Ultramafic Belt is described as a highly prospective ground for hydrothermal Ni systems based on its availability of Ni, active thermal flow engines, and the geologic regional context dominated by mafic rock suites and the presence of carbonate/siliciclastic units.