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By Z. Xie

Gas diffusion electrodes (GDEs) for high temperature polymer electrolyte fuel cells (PEFCs) have been prepared using ZrP-modified Nafion ionomer. The performances of these GDEs as cathodes and anodes were evaluated and compared with conventional Nafion ionomer GDEs using Nafion 112 as the PEM under elevated temperature and reduced relative humidity. ZrP-modified Nafion ionomer was incorporated into the catalyst layer to enhance water retention and/or increase the protonic conductivity. The fabrication of ZrP-GDEs was implemented by the ion exchange of Nafion solution with zirconyl chloride, followed by the impregnation of GDEs in H3PO4 solution. The composite electrolytes in the catalyst layer possessed a ZrP content of 20% by weight. GDEs were characterized by TGA, SEM, XRD, and CV. Scanning electron microscopy (SEM) indicated evenly distributed elemental Zr and P within the catalyst layer. Cyclic voltammetry shows a reduced electrochemically-active surface area when the ZrP is incorporated into GDEs. Polarization and impedance analyses indicate the cathode with ZrP-modified Nafion ionomer did not show an enhanced or decreased performance, compared with conventional Nafion ionomer GDEs under elevated temperature and decreased humidity. However, when GDEs with ZrP¬Nafion ionomer were used as the anode, an improved performance was observed. Preliminary experiments show that the anode is more sensitive to dehydration than the cathode under elevated temperature and/or low humidity. Improving the anode water retention capability will help to reduce losses at the anode. However, the incorporation of hygroscopic agents in the cathode catalyst layer is not essential because it is self-humidified by electrochemically-produced water even under elevated operating temperature and lower humidity.

Jan 1, 2005

By Christopher R. Davis

Resource modelling is the basis for any economic appraisal of a mining project and includes a number of steps from data acquisition and validation to resource reporting and classification. At each step in the modelling process it is necessary to define the specific objectives, the methodology proposed to achieve those objectives and to establish a set of checks and validation tools to assess the effectiveness of the proposed methodology. The data used has to be both reliable and relevant for the purpose of the modelling. QA/QC for database validation requires verification of sample location; including correct collar location, topographic modelling and down-hole surveying. Validation is also performed on assaying information such as checks for sampling bias and accuracy of core splits, proper use of pulp duplicates and standards, handling of calculated values, explicit/implicit absent data and data entry errors. The second step involves identifying the mineralized domains resulting from the mineralization process. This step requires a geometric interpretation of all relevant geological features that have influenced the spatial distribution of the mineralization including dykes, faults and alteration. In addition, a geologic reference system rather than a standard Cartesian system is established to measure distances between samples. Once the mineralized domains are established and the database has been validated, statistical and spatial description of the mineralized samples are examined in order to establish the histogram and the variogram of all variables of interest and their correlation. Results are also used to calibrate the global resource estimate within the mineralized domain and to establish the search strategy for grade interpolation. The mineral envelope is filled with polyhedral cells representing mining blocks. The average grade of these blocks is estimated using kriging techniques in order to eliminate global bias and to minimize the local error in the block grade estimate. Visual checks are made to validate the spatial trends in grade distribution while global bias and smoothing effect are assessed from the declustered sample statistics. When required, smoothing correction may be applied using ?change of support? techniques. Simulations are used to perform sensitivity analysis and the simulation models are used if severe smoothing of spatial variability makes the interpolated model inappropriate for mine planning. The keys to successful resource estimation are an integrated team of geologists, geophysicists, geostatisticians and mine engineers using the best available technology and reviews by independent auditors. The resource team is also responsible for performing a QA/QC program in order to measure the effectiveness of the methods in meeting the specific objectives at each step of the modelling process.

May 1, 2001

By A. A. Nourbakhsha

The main application of refractories based on andalusite in ferrous metallurgy are in air heaters of blast furnaces, mobile mixers, and hot-metal transfer, pig iron ladle, steel-casting, and intermediate ladles. Three specific properties of andalusite are very interesting for the production of high-quality shaped and unshaped mullite refractories: being free of water, its crystal a remains stable without changing its density or volume after firing and therefore has no internal porosity .Graphite additives due to its great wetting ability play an important role in raising the property of refractory bodies. In order to improve properties of andalusite graphite bodies, oxidant agent for increasing in hot strength and oxidation resistance can not be avoided. In this research, firstly 8 pig iron ladles from ESC(esfahan Steel company) with different conditions selected and monitored during usage to determine of main factors affecting on corrosion of refractories. Results showed that tap to tap time, undischarged pig iron ,penetrated pig iron are the main ones.Literature studies showed that the graphite addition help to thermal shock resistance and liquid penetration(steel,pig iron) effect. In this research particle size distribution of aggregates containing andalusite and graphite determined by andreazen equation. Then different mixes with different percentage of graphite,Si, FeSi, SiC prepared by uniaxially pressing under 1500kgf/cm2 pressure by adding 4%wt novalak resin and 0.4%wt HMTA as hardner. Samples fired at 1100-1500oC under reduction atmosphere. According to specific standards density, porosity and CCS measured. Analytical tests such as XRD, SEM were carried out on sample selected from point of view of mechanical properties at different temperatures. Results showed that optimized amount of Si and Fe-Si for _-SiC formation in body is 4 and 6 %wt respectively at 1500OC. XRD and SEM analysis on sample with Fe-Si additives showed no destructive phase through the matrix, also SiC additives not only increase oxidation resistance but also no effect on thermo-mechanical properties.

Oct 1, 2011

By Richard W. Hutchinson, Christopher Osterman

The Selebi-Phikwe deposits are hosted by amphibolite to granulite facies gneisses of the Limpopo belt. The sulfide orebodies are generally stratiform and conformable to the foliation of the wallrock gneiss. Sulfide remobilization has occurred during metamorphism and has produced discordant sulfide veins, called piercement structures, which project into the hanging wall and footwall gneisses. These piercement structures are compositionally similar to the stratiform sulfides, consisting mainly of pyrrhotite, pentlandite and chalcopyrite. However, texturally the piercement sulfides are coarse grained and inclusion-free, whereas the stratiform sulfides are fIne grained and packed with tectonically produced wallrock inclusions. The piercement structure sulfides and adjacent stratabound sulfides were sampled and analyzed for major base metals and PGE's for comparative purposes. Most of the piercement structures were enriched in Cu, Ag and Au, whereas they were generally depleted in Ni, Co, Fe and PGE's. Changing elemental associations were observed from the stratabound sulfides and along the length of the piercement structures. This and the degree of depletion or enrichment of various major and minor elements in the sulfide piercement structures may reflect the relative mobilities of metals under metamorphic conditions. The similarities between sulfIde piercement structures and the footwall Cu-PGE veins in some Sudbury deposits are reviewed.

Jan 1, 1994

By S. Kamado

Development of new SF6 alternative cover gas with low global warming potential is strongly desired for melting and casting of magnesium alloys. We have tried to apply several kinds of HFC and HFE gases with low potential from 30 to 950 as protection gases to AZ91D alloy melt in the temperature range of 650 to 800°C. As a result, protective film consisted of MgF2 and MgO is formed on the melt surface and ignition-proof effect is sufficiently obtained at all the temperature ranges even when flow rates of mixed gases containing CO2 as a carrier gas are almost the same as those using SF6 gas. Reduction of global warming potential exceeds 98% at 650°C and 89% at 800°C in comparison with a mixed gas of CO2 and SF6.

Jan 1, 2006

By E. H. Hall

"Perhaps .I should start this talk on Arsine poisoning, by giving a brief background and history of the Bralorne Mill.The present Bralorne company started milling operations in 1932, with amalgamation and flotation, and operated continuously until 19 61 . In 19 59, it was decided to change over to cyanidation, and to use double filtration rather than counter current. The cyanide portion of this new plant was completed and went on stream in August 1961 utilizing the grinding circuit of the old flotation plant. The new grinding circuit was completed and started operating December 15, 1961.The grinding circuit consists of a 7 1 x 101 Hardinge Rod Mill, and a 7 1 x 101 Hardinge Ball Mill. In series with the rod mill is a 16"" x 24"" Denver Duplex Jig, and two of these jigs are also in parallel with the ball mill. The rod mill product is classified by a Kreb cyclone, the oversize going to the ball mill. The ball mill is in closed circuit with this same cyclone. The jig products are amalgamated daily, and the amalgam barrel tails are returned to the ball mill for regrind. Arsenious oxide (As203) is one of the reagents used in amalgamation. Approximately 39 ozs. per day is used.The cyanide circuit consists of a 481 x 121 thickener, three 24' x 24' agitators, two 141 x 161 drum filters and a Merrill Crowe precipitation unit.The Krebcone overflow is thickened to 60 - 62% solids. Hydrated lime, along with a settling agent is added to the thickener. Some of the overflow water from the thickener is returned for use in the jigs. The balance of this overflow water goes to waste. To the thickened pulp entering No. 1 agitator, barren solution is added, along with sodium cyanide and hydrated lime. Cyanide strength is held at 0. 9 - 1. 0 lbs/ ton solution and lime at 0. 8 lbs/ ton solution. The lime content usually drops to 0. 5 lbs/ ton in No. 3 agitator. The two drum filters are in series and are washed with barren solution. The discharge of No. 3 agitator is fed to No. 1 filter and the discharge of No. 1 filter is repulped in barren solution and feeds No. 2 filter. No. 2 filter discharges to tails, The filtrate is clarified, deaerated and the gold precipitated. One hundred to two hundred tons of barren solution are bled to waste each day. The ore contains 1 % Arsenopyrite and 1. 5% Pyrite."

Jan 1, 1964

By G. W. H. Norman

Introduction During the past few years emphasis has been placed on the importance of major faults, fault zones, and associated structures in localizing ore deposition. This interest has developed partly through experience in mining camps in other parts of the world, and partly by the discovery of such structures associated with ore deposits in the Abitibi region, northwestern Quebec. The recognition of these structures has been brought about chiefly by detailed mapping that has been gradually extended along most of the southern gold belt of Quebec and across adjacent parts of Ontario. In the Chibougamau region of northern Abitibi, progress has been made in the mapping of major faults by using aeroplane photographs with a scale of about 1,000 feet to one inch for field mapping. These studies have shown that many large faults occur in the Abitibi region; also that there is a relationship, direct or indirect, between faults and mineral deposition. The faults are, however, of more than one type and age, and this should be clearly appreciated in any planned programme for prospecting this great region adequately. The information regarding faults and structure is so widely scattered that it is difficult to obtain a clear picture of the essential features, either for planned prospecting or for analysis and development of ideas for further study. This paper, as originally conceived, was intended only to discuss and compare the regional structure of southern Abitibi county-where detail mapping and diamond drilling have been carried on intensively for the past ten years-and of the less well-known Chibougamau district, in order that the experience gained in the one area could be usefully applied in the other. However, a comparison of the two districts leads naturally to a consideration of their common relationship to certain major late-Precambrian structures that form an important northeast system across the southeastern part of the Canadian Shield.

Jan 1, 1946

By Rob Kelso

The PISCES Goals ? To conduct research and develop programs to enable and promote planetary surface exploration ? To host international tests and technology demonstrations at the PISCES Test Site. ? To promote STEM education, inspiring students by connecting Hawaiian culture to space exploration and settlement. - economic and workforce development ? To involve the commercial sector, spinning off technologies to help the local Hawaiian economy. ? To develop a full-scale, technically valid, analog lunar/Martian outpost on Hawai`i Island.

May 1, 2013

By S. F. Dudka, T. Dang, M. L. Wong

Abstract - The Nui Phao W-F-Cu-Au-Bi deposit is located in one of the poorest regions of northern Vietnam. The deposit is currently undergoing a pre-feasibility study by Tiberon Minerals Ltd., with a view to developing what would be the largest WO3 mine and one of the five largest fluorite mines in the world. The project is being planned in close compliance with World Bank and national guidelines for environmental and social protection. Development of the mine is anticipated to bring the following benefits: remediation of serious pre-existing environmental conditions (natural and anthropogenic heavy metal contamination and acid rock drainage); provision of employment and training, and thereby wealth, to local communities; significant tax and royalty payments to government, which will be reinvested as social spending; and development of municipal and industrial infrastructure to build sustainable post-mining communities. The role of governments at all levels is critical in guiding and facilitating this process. This paper was written prior to development of the mine, and relays the intentions of the developers. Future studies will be needed to evaluate the degree of attainment of sustainable development objectives, both during mine operation and after closure.

Jan 1, 2003

By Xuanxue Mo, Kaihui Yang

"The Laochang mine, located in the Sanjiang area of southwestern Yunnan Province of China, is a volcanogenic massive Pb-Zn-Cu sulfide deposit. It is hosted by a pyroclastic sequence of Early Carboniferous age, namely the lower member of the Yiliu Group, which was intruded by syenite and rhyolite porphyry. The volcanic suite is basaltic or basaltic-andesitic in composition, has alkaline affInities, and is associated with the initial rifting along the margin of the Baoshan-Shanstate continental microplate (Yang, 1989). The ores are typically Pb>Zn>Cu in composition, averaging 3.820/0 Pb, 3.51% Zn, from 0.01% to 1.85% Cu (0.107% av.), a high average content of Ag (113 glt) and recoverable amounts of Au, n, Gd, Ga, Ge, In. A massive sulfide zone, in which lenticular and stratiform orebodies are localized in a sulfide-<:arbonate-silica shale unit or sulfidic tuffIte horizon that usually overlies coarse-grained pyroclastic rocks, is underlain by a stringer sulfide zone developed in a subvolcanic intrusion or volcanic sequence. The sulfIde mineral assemblages, from the top to the bottom of the deposit, are: realgar + orpiment - galena + sphalerite + pyrite - chalcopyrite + pyrite + pyrrhotite + arsenopyrite. Oxide and sulfate minerals occur rarely in the massive ores. The massive ores are generally fme-grained and banded, but coarse-grained ore, colloform and framboidal texture, and growth-zoned pyrite and sphalerite are common. Sedimentary features such as graded bedding, brecciated and deformed ore clasts, and chaotically emplaced blocks, are well preserved, indicating that the massive orebodies have undergone slumping and displacement. Alteration is weak in the hanging-wall rocks, but strong in the stringer zone. Two distinctive alteration zones have been identifIed: the upper zone, characterized by an assemblage of quartz, carbonates, chlorite, albite, zeolite and sericite, and the lower zone containing diopside, tremolite, actinolite, gamet, clinozoisite, and epidote.The general features of the Laochang deposit are in accord with the descriptive model of VMS deposits (Lydon, 1984). However, it falls into neither the Zn-Cu group nor the Zn-Pb-Cu group chemically (Franklin et al., 1981). The depositional setting of the Laochang deposit is quite different from Cyprus or Besshi-type massive sulfide deposits. Laochang is hosted by alkaline lavas that were erupted in a submarine continental rift. Although some features of the Laochang deposit are similar to those of Kuroko-type deposits, there are remarkable differences in the alteration mineral assemblage, the proportion of ore-forming elements (lead enriched) and the amounts of oxides and sulfates. These suggest corresponding differences in ore fluid composition and the associated ore-forming environment. Thus, the authors suggest that the Laochang deposit may be a distinct type of VMS deposit."

Jan 1, 1993

By A. J. Basu

Air quality in underground mining operations can fluctuate significantly during the working day, but until recently the only way to ensure a mine had sufficient air quality was to over-ventilate and, with significant delay in adjusting the volume or direction of the airflow, working conditions were tolerable but rarely ideal. Underground ventilation management systems have been considered to achieve improved energy efficiency since at least 1995 in Canada. However, Mine Ventilation Optimization, (MVO) and integrating it with Ventilation on Demand (VOD) is only becoming more of a reality in the last seven (7) years. A systems approach to MVO takes into account all the elements from the point the power is distributed into the ventilation fans through to the actual quality and quantity of fresh air to the working face. Opportunities exist throughout the system for energy savings but not all of them are cost-effective. Depending on the application, these opportunities can be easily realized by properly sizing, streamlining, maintaining and operating the ventilation system using premium mine proven energy efficient components throughout. Implementation of VOD is a key step in achieving the MVO objective. However, VOD is a concept, and it requires various tools, procedures, and strategies for cost-effective and operationally viable implementations. This paper provides a historical background in the development of VOD and provides a framework for proper and cost effective implementation. In addition, an optimized ventilation system will also allow increased airflow by reducing resistances and shock losses. This turn in would allow production target improvement, which could be an attractive objective compared to energy savings. Mine ventilation is the life support system of an underground mine, and contributes to sustainable development and corporate social responsibility goals assuring health and safety aspects of strategic planning. The proposed framework addresses implementing mine ventilation optimization integrating ventilation on demand as a vehicle for energy, health and safety improvement and overall productivity gains in the mining cycle efficiency while significantly reducing carbon footprint of a mine.

Aug 1, 2013

By DALE MacGREGOR, VERA TUREK

lndusmin Limited acquired the St. Donat quartzite deposit in 1967 to produce high-quality silica for use in the sandblasting and silicon carbide industries. The quartzite, of Grenville age, is highly friable and porous. This is due to numerous small, kaolinite-coated cavities in the quartzite; the cavities were formed through leaching, probably by rising hot solutions.

Jan 1, 1984

By D. Embury

The construction and utilization of oil and gas pipelines is a vital aspect of the Canadian economy. The evolution of materials for this application can be considered as part of an evolutionary process in which the processing of the materials is linked to the design requirements of the pipeline. The evolution of both materials and designs will be considered in terms of parameters such as yield strength, work hardening characteristics including strain path changes such as the Bauschinger Effect and toughness. The final portion of the presentation will consider the possible uses of non-metallic materials, composites and &apos;smart &apos;systems in pipeline construction.

Jan 1, 2005

By Lauri Gregg

How Can Man Meet the Carbon-Free Energy Challenge ? ? Increases in Energy Efficiency can displace 1/2 to 2/3 of the Carbon-Free Energy required to stabilize at 550 ppmv ? Renewable Energies require too much land and thus can displace 5 to 10 % of the energy requirement ? Large new sources of carbon free energy are needed ? Conservation is desirable but provides only a small and variable contribution ? People will have to adjust to higher levels of CO2 in the atmosphere as energy demand continues to grow

Nov 1, 2002

By A. Farzanegan, D. A. Lowther, A. R. Laplante

"Off-line optimization studies are often necessary to improve the efficiency of grinding circuits. These studies are primarily based on the mathematical modelling of processing units (e.g., ball mills and hydrocyclones) and computer simulations. To complete an optimization task, process engineers must possess skills and knowledge of different subtasks involved in such efforts, e.g., plant audit, laboratory tests, and data analysis. Such know-how can be in part provided by Knowledge-Based Systems (KBSs). One such system, being developed in C Language Integrated Production System (CLIPS), is presented here, with focus on the estimation of ball mill selection functions for the purpose of both diagnostic and simulation, and its use for the optimization of ball size. Some of the interpretation and diagnostic rules will be presented, as well as grinding kinetics and classification data likely to fire them.IntroductionSince the late eighties there has been a growing trend in applying Knowledge-Based Systems (KBSs) to mineral processing [Meech 1990, Bearman and Milne 1992). Table l lists some KBS (often referred to as expert systems) applications that have been used mainly as tools for improving on-line monitoring and control of grinding circuits. However, there has been fewer attempts to add the symbolic processing powers of KBSs to conventional off-line grinding simulators. Figure 1 shows a relatively standard procedure to perform an off-line optimization study [Napier-Munn and Lynch 1992]. In brief, a typical program includes taking representative samples from a number of streams, running laboratory tests on collected samples, estimating model parameters which describe physical processing units (e.g. ball mills and hydrocyclones) validating model predictions and using models for simulation trials. One inevitably needs to be familiar with concepts of process modelling and simulation as well as various computer programs to be able to complete all steps of the study. Much of this ""expertise"" can be captured by KBSs, given their inherent capabilities for symbolic knowledge representation and manipulation."

Jan 1, 1997

By J. B. C. Wu, B. McKee

"Mining along with subsequent processing of the minerals often presents conditions where a wear- and/or corrosion-resistant alloy is needed to minimize downtime and maximize efficiency. This paper is intended to give an overview of the alloys that are currently being used, as well as those developed in recent years that could be used in the mining industry. Emphasis will be put on the iron-, nickel-,cobalt-based alloys and composites containing a variety of carbides. The characteristics, properties, product forms, and methods of application are presented. In addition, examples of the actual use of these wear-resistant materials are illustrated.IntroductionPreventing wear and corrosion is important in any industrial operations. In the mining industry, the process equipment typically suffers many different types of material degradation. Abrasion, impact, erosion, metal-to-metal wear and corrosion are typically encountered. Each situation requires different material characteristics to retard the degradation process. Therefore, it is essential to understand the characteristics of the materials and the effects of the alloying elements.There are four common classes of metallic materials for resisting wear and corrosion; namely, iron-based alloys, nickel-based alloys, cobalt-based alloys, and carbide-containing composites. Each class of material has its own characteristics. Depending on the chemical composition, the materials within each class can be vastly different in properties. In recent years, there have been materials developed in each of the four classes using the knowledge of the metallurgical principles and the effects of the alloying elements on the material degradation process.To use a wear-resistant alloy, it is also necessary to understand the available product forms and their application methods. Weld overlaying is a traditional way of using these alloys (Wu and Redman, 1994). In recent years, thermal spray is becoming popular. For applications where over-laying and spraying are impractical, solid components can be made by a variety of casting and powder metallurgy techniques. They can also be fabricated from the wrought products.To select a proper material for an application, it is important to understand not only the characteristics of the wear-resistant materials but also the degradation process. Due to the complexity of the processing environments, past experience is also helpful in making the decision on the material selection."

Jan 1, 1997

By Victor Dolmage

"The localization of orebodies by geological structures is well demonstrated at the Copper Mountain mine of southwestern British Columbia. These extensive deposits; owned and workd by the Granby Consolidated Mining; Smelting and Power Company; are at Princeton; abo!lt 150 miles east of Vancouver and 40 miles north of the International boundary. The geology of the deposits and the surrounding district is described by the present writer in Memoir 171 of the Geological Survey of Canada; pub1ished in 1934.The main geological feature is a gabbro stock, elliptical in plan, with a major axis about 5 miles in length extending in a northwest-southeast direction. The stock varies in composition from syeno-gabbro (gabbro plus orthoclase) through diorite and syenite to a core of syenite pegmatite. All the members contain orthoclase, which ·increases greatly in amount toward the centre, but all are devoid of quartz. The stock has been injected into a steeply folded series of volcanic flows, breccias, and tuffs that strike more or less parallel with the major axis of the stock. On its northeast side the stock is flanked by a band of fairly coarse volcanic breccia of andesitic composition and ·having fragments up to several inches in length. Where this breccia is tangential to the stock it is both dynamically and chemically metamorphosed to a marked degree, and within the zone of this metamorphism are enclosed the copper deposit~. The ore consists of bornite, chalcopyrite, and a little magnetite occurring as disseminated grains and small veinlets in the metamorphosed breccias. The only gangue minerals are orthoclase, albite, oligoclase, and biotite. The two most common vein minerals, quartz and pyrite, are conspicuously rare or absent. The dynamic metamorphism has produced two well-defined structures, namely, a strong schistosity parallel with the curved vertical contact of the stock and a very striking set of small, straight, nearly parallel open fractures that stand nearly vertical and at right angles to both the schistosity and the stock contact. These are called the ore fractures."

Jan 1, 1954

By M. Eikerling

The full competition between mass transport and reaction in PEMFC unfolds in cathode catalyst layers (CCLs). Recently developed models provide vital insights into effects of thickness and composition on effectiveness of catalyst utilization and performance. However, the CCL&apos;s key function in liquid water removal is rather unexplored. Studies of water balance in PEMFCs focus mostly on other cell components. Notwithstanding this prioritization, a simple calculation shows that the CCL is the PEMFC&apos;s favourite medium for conversion of liquid water into vapor. Porous structure and wetting properties steer the interplay of evaporation, transport and reaction. A model will be presented, that links pore space morphology, composition, distributed properties (concentrations, pressures, reaction rates, potential) with global performance (critical phenomena). It reveals how problems of flooding in the fuel cell could be mitigated by properly adjusting catalyst layer structure and operation conditions and under which conditions all liquid water arriving in the CCL would leave it as water vapour through the CCL/GDL interface. Results for a simple variant of the model emphasize the role of the CCL as a watershed for the whole cell.

Jan 1, 2005

By B. Andreaus

In spite of tremendous efforts in research and development of polymer electrolyte fuel cells (PEFCs), essential properties of the actual catalyst material, supported Pt or Pt-alloy nanoparticles, are not yet well understood. Fundamental understanding of the catalyst structure and the prevailing kinetic mechanisms is, however, of utmost importance for further progress. In the present study, we investigate catalyst activity for CO oxidation from a theoretical point of view. Electrochemical CO oxidation serves as an important test reaction for the study of the fundamental properties of supported Pt nanoparticles. Recent experiments have revealed strong effects of catalyst particle size and supporting material on catalytic activity. It was found, that the activity towards CO oxidation decreases significantly when the particle diameter drops below 2.5 nm. We perform kinetic Monte Carlo simulations of CO oxidation on supported catalyst particles to elucidate this particle-size effect. The simulations are based on the active site concept, highlighting the role of active site formation and finite surface mobility of adsorbed electroactive species for catalyst activity. For comparison with experimental results, potential step experiments were simulated. The Monte Carlo simulations consistently reproduce effects of particle size and electrode potential found experimentally. In comparison with our simulations, analytical mean field models and nucleation and growth models exhibit inferior agreement with experimental data. In summary, our findings support an oxidation mechanism via active site formation. The reason for the slow reaction kinetics on catalyst particles with diameters below 2.5 nm is a rather low CO surface diffusivity. The rates of active site formation, diffusion and CO oxidation via recombination with adsorbed OH can be determined from the simulations.

Jan 1, 2005

By R. M. Graves, C. B. McKenzie, D. Barbour, D. W. Desnoyers

"The prospective Tulks volcanic belt hosts five significant massive sulfide deposits, Tulks Prospect, Tulks East, Jack&apos;s Pond, Daniel&apos;s Pond and Victoria Mine, as well as numerous showings and indications throughout its 70 km outcrop length. Regionally, the 498 Ma sequence consists dominantly of felsic pyroclastic rocks and flows with interbedded mafic volcanic units and finegrained sediments, commonly graphitic. Contemporaneous granitoid rocks occur in the south half of the belt. Rocks usually display a strong NE-SW, steeply dipping, penetrative foliation and other shear-related high-strain fabrics. Facing directions are normally northwest, although there is local evidence of folding. Sulfide bodies and their alteration systems are deformed and shape-modified in the style of ambient strain.The Tulks, Tulks East and Jack&apos;s Pond prospects appear to occupy a similar stratigraphic level, on or near the contact between a thick felsic pile and an overlying broad, conductive package of graphitic sedimentary rocks. All are pyritic deposits with well-developed footwall alteration systems. The Tulks prospect comprises four polymetallic lenses totalling 750 000 t. Three lenses constituting more than 6 000 000 t of sulfide mineralization are indicated at Tulks East but only the 210 000 t ""B"" lens contains significant base metals. Jack&apos;s Pond consists of a very extensive, zoned alteration complex in which four lenses of massive to semi-massive pyrite + chalcopyrite are known. The central part of the system, characterized by Mg chlorite and carbonate, is enveloped by pervasive sericitization and capped by intensely silicified and pyritized volcanics. The sulfide lenses are interpreted as part of the footwall zone and are beneath that part of the system most likely to hostpolymetallic massive sulfides.Daniel&apos;s Pond differs from the other prospects in such fundamental ways as metal content, associated alteration and structural setting. The deposit comprises strongly tectonized, Ag-rich, Zn-Pb mineralization distinguished by a pronounced Ba-As-Sb signature. Mineralization is confined to a narrow, north-south high-strain zone which separates unstrained mafic volcanic rocks to the east from well-foliated felsic rocks. The deposit lacks an extensive alteration halo and at its north end is associated with a lens of barren, undeformed massive pyrite.The Victoria Mine deposit, the most cupriferous of the five, is related to a moderately dipping structure that separates well-foliated Tulks volcanic rocks from an overlying, less deformed volcanic sedimentary sequence that may be as young as 462 Ma. The structure is also the locus of black chlorite, dolomite and quartz alteration. Structurally remobilized precursor sulfide mineralization is one possible source for the deposit."

Jan 1, 1993