Gahnite composition as a means to fingerprint metamorphosed massive sulfide and non-sulfide zinc deposits

Gahnite occurs in and around metamorphosed massive sulfide (e.g., Broken Hill-type Pb–Zn–Ag (BHT), volcanogenic massive sulfide Cu–Zn–Pb–Au–Ag (VMS), sedimentary exhalative Pb–Zn (SEDEX)), and nonsulfide zinc (NSZ) deposits. In addition to occurring in situ, gahnite occurs as a resistate indicator mineral in unconsolidated sediments (e.g., glacial till) surrounding such deposits. The spatial association between gahnite and metamorphosed ore deposits has resulted in its use as an empirical exploration guide to ore. Major and trace element compositions of gahnite from BHT, NSZ, SEDEX, and VMS deposits are used here to develop geochemical fingerprints for each deposit type. A classification tree diagram, using a combination of six discrimination plots, is presented here to identify the provenance of detrital gahnite in greenfield and brownfield terranes, which can be used as an exploration guide to metamorphosed massive sulfide and non-sulfide zinc deposits. The composition of gahnite in BHT deposits is discriminated from gahnite in SEDEX and VMS deposits on the basis of plots of Mg versus V, and Co versus V. Gahnite in SEDEX deposits can be distinguished from that in VMS deposits using plots of Co versus V, Mn versus Ti, and Co versus Ti. In the Sterling Hill NSZ deposit, gahnite contains higher concentrations of Fe3+ and Cd, and lower amounts of Al, Mg, and Co than gahnite in BHT, SEDEX, and VMS deposits. Plots of Co versus Cd, and Al versus Mg distinguish gahnite in the Sterling Hill NSZ deposit from the other types of deposits

The Engineering of Practical Gas Phase Air Cleaning

SUMMARY This is one of two CLIMA 2007 papers on gas phase air cleaning by this author. The Science of Gas Phase Air Cleaning' covers aspects of air quality, gas phase air cleaning (particularly adsorption) limitations and opportunities, capital and energy saving impacts, and the role of Standards. This paper discusses application parameters, deals with testing of gas phase air cleaners and presents odour removal efficiency test results for a product. Economics of use are discussed. ACKNOWLEDGEMEN

PCC Pavement Deterioration and Expansive Mineral Growth

In order to evaluate the importance of newly-formed minerals in the premature deterioration of Iowa highway concrete, a two-phase study was undertaken. In the first phase, we performed petrographic and SEM/EDAX analyses to determine chemical and mineralogical changes in the aggregate and cement paste of samples taken from Iowa concrete highways that showed premature deterioration. In the second phase, we experimentally simulated environmental changes occurring in highway concrete after different deicer chemicals were applied in order to evaluate the role of deicers in premature deterioration. In highways exhibiting premature concrete deterioration, ettringite, 3CaO. Al2O3 . 3CaSO4 .32H2O, completely fills many small voids and lines the walls of larger voids. Microscopic ettringite is also commonly disseminated throughout the paste of many samples. Severe cracking of cement paste is usually associated with ettringite locations, and strongly suggests that ettringite contributed to deterioration. Pyrite, FeS2, is present in coarse/fine aggregates in several concretes. Sulfate ions released by its oxidation contribute to ettringite formation. In poorly performing concretes containing reactive dolomite aggregate, brucite, Mg(OH)2, resulting from partial dedolomitization of the aggregate, was most common. No cracking was observed to be spatially associated with brucite, but most brucite crystals are microscopic in size and widely disseminated in the cement paste of less durable concretes. Expansion stresses associated with its growth at many microlocations may be relieved by cracking at weaker sites in the concrete. In the experimental phase of the study we found that each deicer salt can cause characteristic concrete deterioration by altering dedolomitization rims at the coarse-aggregate paste interface, by altering cement paste, and/or by forming new expansive minerals in the paste. Magnesium in deicer solutions produces the most severe paste deterioration by forming noncementitious magnesium silicate hydrate and brucite. Chloride in deicer solutions promotes decalcification of paste and alters ettringite to chloroaluminate. Acetate seems to accentuate Mg-induced deterioration. Magnesium chloride, calcium magnesium acetate (Ca3Mg7Ac), and magnesium acetate were the most deleterious

Tellurides and bismuth sulfosalts in gold occurrences of Greece: mineralogical and genetic considerations

Pre-Tertiary to Tertiary gold deposits in Greece occur in a wide range of genetic types including volcanic massive sulfides, orogenic, intrusion-hosted, skarn, manto-, porphyry- and epithermal-type ores. Almost all of the gold mineralization hosts various Bi-tellurides and Bi-sulfosalts, which in addition to Au-Ag-tellurides, are indicators of specific physicochemical conditions of ore formation. The Bi-bearing mineralization can be subdivided into three groups regarding their spatial relationship to gold: (a) mineralization which lacks tellurides but includes Bi-sulfosalts and native gold, (b) mineralization where Bi-tellurides of the reduced-type (joseite-A, joseite-B, pilsenite) accompany Bi-sulfosalts, native bismuth and native gold, (c) deposits/prospects where Au-Ag-tellurides are abundant and Bi-tellurides and Bi-sulfosalts are absent. Bi-telluride and -sulfosalt mineralization in Greece underwent several stages of remobilization during successive accretionary episodes in active continental margins and arc terranes during the Carboniferous to Pleistocene

Effects of Various Deicing Chemicals on Pavement Concrete Deterioration

The deleterious effects of deicers on concrete pavements and bridges have concerned concrete researchers for several decades. The present study experimentally investigates the effects of different deicers on concrete deterioration. Laboratory simulations of environmental conditions (wet/dry and freeze/thaw cycling) were conducted on highway concrete samples with various deicer chemicals (NaCl, CaClv MgC12, calcium magnesium acetate (CMA) of 5 different Ca/Mg ratios, Ca-acetate, and Mg-acetate). Each deicer produced characteristic effects on the concrete samples by physically and chemically altering the dolomite coarse aggregate, the dolomite coarse aggregate-paste interface, and cement paste. Chloride solutions commonly promoted decalcification of paste and altered ettringite to chloroaluminate. Magnesium-bearing deicer solutions ( e.g., CMA, Mg-acetate and MgC12) caused severe paste deterioration by forming brucite and noncementitious magnesium silicate hydrate. For acetate solutions, the effects caused by Ca-acetate on concrete deterioration was much less severe than those caused by Mg-bearing acetates. For the experimental conditions utilized herein, NaCl solution was the least deleterious to the cement paste and aggregate

The Formation of Rims on Dolomite Aggregate in Iowa Highway Concrete

Rims have formed on the margins of dolomite (Ca,Mg(C03 ) 2 ) aggregate in Iowa highways due to dedolomitization reactions between aggregate and concrete paste. These dedolomitization reactions are usually accompanied by a volume change, due to a conversion of dolomite to a calcitic dolomite, that results in the development of micro-cracks in the aggregate and the concrete paste. These cracks become channelways for solutions, often saline in nature due to the application of deicing salts, that result in further deterioration of highway concrete. Rim development on aggregate particles commonly results in highway concretes with short service lives. The most complete sequence of rims on aggregate in Iowa highway concretes occurs where individual reaction zones are up to 200 μm wide and consist of an inner dark-colored dolomite rim, an outer light-colored dolomite rim, and an outer light-colored Portland cement paste rim. These rims are superimposed on unaltered dolomite aggregate particles and cement paste. Nondurable concretes (service life of\u3c I 6 years) exhibit better developed and more abundant rims and a higher density of microcracks and contain dolomite with a more variable grain size and higher porosity than durable concretes (service life of \u3e 40 years). The rims of lightcolored dolomite aggregate show an increase in Ca content and a concomitant decrease in Mg adjacent to the aggregate-paste interface, along with the formation of calcite, brucite, and portlandite. The ability to distinguish dolomites that are susceptible to deterioration from those that are less likely to deteriorate should save expenditures since highway maintenance costs will be reduced

Cervelleite, Ag4TeS: solution and description of the crystal structure

Examination of the type specimen of cervelleite throws new light on its structure demonstrating how earlier researchers erred in describing the mineral as cubic. It was found to be monoclinic, space group P21/n, with a = 4.2696(4), b = 6.9761(5), c = 8.0423(7) Å, β = 100.332(6)°, V = 235.66(3) Å3, Z = 4. The crystal structure [R1 = 0.0329 for 956 reflections with I \u3e 2σ(I)] is topologically identical to that of acanthite, Ag2S, and aguilarite, Ag4SeS. It can be described as a body-centered array of tetrahedrally coordinated X atoms (where X = S and Te) with Ag2X4 polyhedra in planes nearly parallel to (010); the sheets are linked by the other silver position (i.e., Ag1) that exhibits a three-fold coordination. Crystal-chemical features are discussed in relation to other copper and silver sulfides/tellurides, and pure metals. A SEM study of the cervelleite crystal used for the structural investigation showed that it is intergrown with an unnamed Ag2FeS2 phase in the type material

Concrete Deterioration by Deicing Salts: An Experimental Study

Concrete with dolomite coarse aggregate was obtained by coring existing Iowa highways. The concretes were of two types, those which were very durable under highway conditions and those which were low durability. Samples were experimentally deteriorated using wet/dry, freeze/thaw, and continuous soak conditions in solutions of magnesium chloride, calcium chloride, sodium chloride, magnesium acetate, magnesium nitrate, and distilled water in order to determine relative deterioration activities. Magnesium chloride was most destructive. Calcium chloride was next, and sodium chloride was relatively benign. Magnesium acetate produced severe crumbling and moderate fracturing, and magnesium nitrate caused moderately severe deterioration by crumbling and discoloration. Low durability concrete was somewhat more affected by distilled water freeze/thaw conditions than more durable material, but generally both types were severely damaged by magnesium and calcium salts. These results suggest that magnesium and calcium deicers may accelerate highway concrete deterioration

Trace Elements in Magnetite from the Pagoni Rachi Porphyry Prospect, NE Greece: Implications for Ore Genesis and Exploration

Magnetite is a common accessory phase in various types of ore deposits. Its trace element content has proven to have critical implications regarding petrogenesis and as guides in the exploration for ore deposits in general. In this study we use LA-ICP-MS (laser ablation-inductively coupled plasma-mass spectrometry) analyses of trace elements to chemically characterize magnetite from the Pagoni Rachi Cu–Mo–Re–Au porphyry-style prospect, Thrace, northern Greece. Igneous magnetite mostly occurs as euhedral grains, which are commonly replaced by hematite in fresh to propylitic-altered granodiorite porphyry, whereas, hydrothermal magnetite forms narrow veinlets or is disseminated in sodic/potassic-calcic altered (albite + K-feldspar + actinolite + biotite + chlorite) granodiorite porphyry. Magnetite is commonly associated with chalcopyrite and pyrite and locally exhibits martitization. Laser ablation ICP-MS analyses of hydrothermal magnetite yielded elevated concentrations in several trace elements (e.g., V, Pb, W, Mo, Ta, Zn, Cu, and Nb) whereas Ti, Cr, Ni, and Sn display higher concentration in its magmatic counterpart. A noteworthy enrichment in Mo, Pb, and Zn is an unusual feature of hydrothermal magnetite from Pagoni Rachi. High Si, Al, and Ca values in a few analyses of hydrothermal magnetite imply the presence of submicroscopic or nano-inclusions (e.g., chlorite, and titanite). The trace element patterns of the hydrothermal magnetite and especially the decrease in its Ti content reflect an evolution from the magmatic towards the hydrothermal conditions under decreasing temperatures, which is consistent with findings from analogous porphyry-style deposits elsewhere

Alkalic-Type Epithermal Gold Deposit Model: Chapter R of Mineral Deposit Models for Resource Assessment

This report summarizes the primary characteristics of alkalic-type epithermal gold (Au) deposits and provides an updated descriptive model. These deposits, primarily of Mesozoic to Neogene age, are among the largest epithermal gold deposits in the world. Considered a subset of low-sulfidation epithermal deposits, they are spatially and genetically linked to small stocks or clusters of intrusions containing high alkali-element contents. Deposits occur as disseminations, breccia-fillings, and veins and may be spatially and genetically related to skarns and low-grade porphyry copper (Cu) or molybdenum (Mo) systems. Gold commonly occurs as native gold, precious metal tellurides, and as sub-micron gold in arsenian pyrite. Quartz, carbonate, fluorite, adularia, and vanadian muscovite/roscoelite are the most common gangue minerals. Alkalic-type gold deposits form in a variety of geological settings including continent-arc collision zones and back-arc or post-subduction rifts that are invariably characterized by a transition from convergent to extensional or transpressive tectonics. The geochemical compositions of alkaline igneous rocks spatially linked with these deposits span the alkaline-subalkaline transition. Their alkali enrichment may be masked by potassic alteration, but the unaltered or least altered rocks (1) have chondrite normalized patterns that are commonly light rare earth element (LREE) enriched, (2) are heavy rare earth element (HREE) depleted, and (3) have high large ion lithophile contents and variable enrichment of high-field strength elements. Radiogenic isotopes suggest a mantle derivation for the alkalic magmas but allow crustal contamination. Oxygen and hydrogen isotope compositions show that the fluids responsible for deposit formation are dominantly magmatic, although meteoric or other external fluids (seawater, evolved groundwater) also contributed to the ore-forming fluids responsible for these deposits. Carbon and sulfur isotope compositions in vein-hosted carbonates and sulfide gangue minerals, respectively, coincide with magmatic values, although a sedimentary source of carbon and sulfur is evident in several deposits. Deep-seated structures are critical for the upwelling of hydrous alkalic magmas and for focusing magmatic-hydrothermal fluids to the site of precious metal deposition. The source of gold, silver (Ag), tellurium (Te), vanadium (V), and fluorine (F) was probably the alkalic igneous rocks themselves, and the coexistence of native gold, gold tellurides, and roscoelite in several deposits is primarily a function of similar physicochemical conditions during deposition (for example, overlapping pH and oxygen fugacity (fO2). Potential environmental impacts related to the mining and processing of alkalic-type epithermal gold deposits include acid mine drainage with high levels of metals, especially zinc (Zn), copper, lead (Pb), and arsenic. However, because alkalic-type gold deposits typically contain carbonates, which contribute calcium and magnesium ions that increase water hardness, aquatic life may be afforded some protection. Impacts vary widely as a function of host rocks, climate, topography, and mining methods. Geologic mapping to (1) highlight the distribution of potassic alteration; (2) define fault density and orientation of structures; (3) determine the distribution of alkaline rocks and hydrothermal breccias; and (4) identify uniquely colored gangue minerals, such as fluorite and roscoelite, will be critical to exploration and future discoveries. Geophysical techniques that identify potassium (K) anomalies (for example, radiometric and spectroscopic surveys), as well as magnetic, resistivity, aeromagnetic, and gravity surveys, may help locate zones of high-permeability that control advecting hydrothermal fluids. Geochemical surveys that include analyses for Au, Ag, barium, Te, K, F, V, Mo, and mercury, which are key elements in these deposits, should be undertaken along with the measurement of other pathfinder elements such as arsenic, bismuth, Cu, iron, nickel, Pb, antimony, selenium, and Zn