Search Documents

By K. Sawada

Along with the expanding demand of copper concentrate in Asian countries, custom-smelters have confronted with difficulties of low TC/RC. Now, Japanese Copper Industry have 2 options; investment in mine development and/or recycling of copper scraps. The strategy of global mining companies is analyzed, and implications for Japanese Copper Industry will be discussed from the viewpoint of sustainability of smelters in Japan.

Jan 1, 2014

By B. Dubreuil, J. -M. Lalancette, D. Lemieux

Arsenical bearing deposits are posing an increasing challenge for the mining industry. In particular, mineral processing of arsenical sulfidic ores for base and precious metals recovery tend to produce problematic arsenical tailings. This arsenic being present as sulphide or oxide, tends to dissolve, contaminating surface and underground waters. To meet the environmental regulations, it is often required to stabilize the arsenic in a more insoluble form. Dundee Sustainable Technologies has developed a new patented technology using vitrification of the arsenic oxide in an economical way, giving a stable solid, well below the environmental regulations upon leaching. This technology involves oxidation of As (III) to As (V), by using a low cost natural oxidizer and transformation of the produced arsenic oxide into calcium arsenate, which is not volatile at the melting temperature of the glass. This technology would be advantageously applied on most cases around the world where sulphide concentrates are oxidized in a fluidized bed or smelted.

Jan 1, 2014

By R. Carpenter, H. Muntanion, P. Kleespies, E. Flood, M. Tansey

Abstract - BHP Minerals discovered the Archean lode gold ULU deposit on the western margin of the High Lake Volcanic Belt in 1989. The greenschist to amphibolite facies mafic volcanic and sedimentary rocks on the property are folded into a 5 km-long anticline. There is a close spatial association of Au-As zones to the trace of this F2 ULU anticline. The largest of these auriferous zones, the Flood zone, is localized at the core of the fold. The southeast-trending Flood zone consists of several anastomosing lenses that have been traced for 435 m on surface. Overall, it dips steeply (70° to 80°) to the southwest and has been intersected to depths below 600 m. The hosting high-iron tholeitic basalt displays a lower amphibolite mineral assemblage of ferrohornblende + plagioclase + ilmenite with accessory quartz and epidote. Alteration minerals include biotite, chlorite, hornblende, actinolite-tremolite, and potassium feldspar (microcline) with minor calcite, epidote, tourmaline, and titanite. The highest gold values occur where brecciated basaltic wall-rock clasts are replaced by acicular arsenopyrite + quartz + K-feldspar. BHP Minerals completed 54,783 m of both exploration and resource development drilling before selling the ULU property to Echo Bay Mines in 1995. Development of ULU as a satellite deposit to Echo Bay’s Lupin mine began in 1996. A -15% ramp was extended to the 155-meter level, and 16,011 m of underground drilling were completed before the decline in gold prices forced a suspension of activities at ULU in August 1997. The current owners, Wolfden Resources Inc., drilled 18,569 m in 2004 to increase confidence in the resource blocks. Following this drill program, a revised resource calculated by an independent consultant determined that the ULU deposit contains an inferred/indicated mineral resource of 1,130,000 t grading 11.34 g/t gold (373,748 oz) to the 360-m level. The portal was re-opened in 2005 and a prefeasibility study is underway.

Jan 1, 2004

By R. D. Clark, Heinz Althoff

"The advantages and disadvantages of a mobile crushing plant with a belt conveyor system compared to a stationary crushing plant with haulage by heavy trucks are described. The capital expenditure and operational expenses are compared and the individual cost factors are explained.Every open-pit mine or quarry, however, is different and has to be assessed and analyzed individually in order to find the optimum and most economical solution. Due to the high truck haulage costs, many open-pit mines tend to the more economical solution with mobile crushing plants and continuous belt conveyor operation. IntroductionFor the material haulage within an open-pit mine the heavy truck is the most flexible means of transportation. However, due to the high fuel consumption, wear and labour costs, it is also the most expensive one. Therefore, many open-pit mines are looking for alternative solutions for the material transport A mobile belt conveyor system is most likely to meet the requirements because it is efficient and economical with regard to the power consumption. The material , however, has to be crushed at the mining face to lumps which are suitable for conveyor operation. For this purpose a mobile crushing plant is required.In some open-pit mines the crusher is also used to crush the material to lumps of smaller particle sizes in order to save crushing costs in the preparation plant.Although a cost comparison between a system with stationary crusher and truck haulage and a system with mobile crusher and belt conveyors favours in most cases the belt conveyor system, up till now only a few open-pit mines and quarries benefit world-wide from the advantages of the mobile crushing plant with continuous belt conveyor operation."

Jan 1, 1986

By J. C. Moreno, G. Rios, M. Palacios

The Huelva smelter was commissioned in 1970 coinciding with the shutdown of the old smelter in the Rio Tinto mine site. That new smelter consisted of two Momoda blast furnaces with a capacity of 500 dmtpd of concentrate. Nevertheless, soon after their start-up, it was clear that an increase in the smelting capacity was needed. After an analysis of the existing alternatives at that time, the flash smelting technology was chosen. The new Outokumpu Flash Smelting Furnace (FSF) came into operation on 18 September1975, with an initial capacity of 900 dmtpd of concentrate, using four Venturi-type burners and preheated atmospheric air. Since that date the Huelva Smelter team, together with Outokumpu (now called Outotec), have continuously improved our FSF design, process conditions and operational practices, leading to a present capacity of 3,500 dmtpd of concentrate. Since 1975, five smelting campaigns have been completed, the last ending in November 2013 with the rebuilding of the original FSF hearth. This paper describes the history of these improvements and the lessons learned.

Jan 1, 2014

The control of carbon concentration in a counter current carbon absorption circuit is critical to optimise gold recovery. MINTEK has developed a carbon movement controller to address this potentially problematic area in gold extraction. This controller reduces operator interaction by automating carbon movement. Elution schedules are entered into the control system, which then moves the carbon through the circuit into the first adsorption tank until enough carbon is available for elution. This is done while maintaining the specified carbon profile within the circuit. MINTEK has also developed an online-carbonconcentration- meter to measure carbon concentration in pulp. The meter uses an ultrasonic measurement technique. Long term testing has shown the measurement to be robust and require minimal maintenance. Results from a gold mine in South Africa’s well known Witwatersrand gold producing area has shown a decrease in soluble gold loss between 30 - 50% when the controller was used.

Jan 1, 2014

This document presents estimates of future "total cash cost per ounce" and "minesite cost per tonne" that are not recognized measures under United States generally accepted accounting principles ("US GAAP"). This data may not be comparable to data presented by other gold producers. These future estimates are based upon the total cash costs per ounce and minesite costs per tonne that the Company expects to incur to mine gold at the applicable projects and do not include production costs attributableto accretion expense and other asset retirement costs, which will vary over time as each project is developed and mined. It is therefore not practicable to reconcile these forward-looking non-GAAP financial measures to the most comparable GAAP measure. A reconciliation of the Company's total cash cost per ounce and minesite cost per tonne to the most comparable financial measures calculated and presented in accordance with US GAAP for the Company's historical results of operations is set forth in the notesto the financial statements included in the Company's Annual Information Form and Annual Report on Form 20-F, for the year ended December 31, 2009, as well as the Company's other filings with the Canadian Securities Administrators and the SEC.

May 1, 2011

By Chandrakala Kari, Divyang Shah, Lakshmi Kanth Reddy, Kaushik Vakil, Sanjay Sarkar, Bhavin Desai

Gases rich in sulfur dioxide generated as a by-product of smelting and converting operations of copper concentrate contain selenium apart from zinc, lead, copper, cadmium, bismuth, antimony, and arsenic. The gaseous stream is heat exchanged in waste heat boiler, dust collected in electrostatic precipitator followed by cleaning in reverse jet scrubber to remove fumes, halogens and fine dust before passing to DCDA Monsanto catalytic converter to produce commercial grade sulfuric acid. The gas cleaning section of the acid plant uses water to scrub the smelting gases. During scrubbing, precipitated solids, known as sludge, settles at the bottom of the reverse jet scrubber containing 30 to 40 wt% copper and selenium up to 40 wt% selenium. In the existing process, the sludge collected during scrubber cleaning process is directly recycled to the smelter for copper recovery. However, the selenium is expected to again vaporize due to high oxidation potential during smelting and converting, causing accumulation of selenium in sludge. In present investigation, a roasting process has been developed to recover the selenium from acid plant sludge before charging it to smelter for copper recovery. Selenium is associated with copper in acid plant sludge as copper selenide, as determined by X-ray diffraction and electron microscopy. Thermodynamic and thermo-gravimetry study revealed that the copper selenide phase present in the sludge was amenable to oxidation at 600°C forming oxides of copper and selenium (Cu-Se-O). However, the dissociation of selenium from the copper oxide was made possible by sulfatation using sulfur dioxide between 450°C to 600°C, resulting into the formation of CuSO4(s) and SeO2(g). Lab scale experiments were carried out in vertical tubular furnace to determine the optimum roasting conditions with respect to roasting time, temperature and molar ratio of O2:SO2. Using these optimum conditions, selenium up to 90 wt. % in the form of SeO2 vapors could be recovered from the acid plant sludge in a large scale commercial roaster. Roasted sludge free from selenium and containing oxides and sulfates of copper could now be recycled in the smelter for copper recovery. INTRODUCTION There is an increasing demand for minor metals due to their use in innovative technologies. Similarly, the increase in demand for selenium is expected due to disruption in sectors related to renewable energy and photovoltaic battery. Selenium is a chalcogen and a non-metal with black or red crystalline appearance. Selenium is used in the glass industry to decolorize glass and to make red-colored glasses and enamels. It is also used in solar cells and as a photographic toner. Selenium is used as a brasses in stainless steel to improve its machinability. Selenium sulfide is used in anti-dandruff shampoos. In spite of the toxicity of its compounds, selenium is also an essential trace element for humans and animals. Selenium occasionally occurs free in nature, but more often occurs as selenides of iron, lead, silver and copper. There is an urgent need for the development of new methods for selenium recovery from the existing resources. Commercially, selenium is obtained only from anode mud produced during electrolytic refinery of copper.

Jan 1, 2019

By P. Espinoza, I. Yutronic, J. Olivares

"Compañía Minera Doña Inés de Collahuasi's (CMDIC) Concentrator Plant is located at 4300 meters above sea level, approximately 2000 kms north from Santiago, Chile. The concentrator has three grinding lines. Each one, Lines 1 and 2, have one SAG mill at the primary grinding stage followed by a secondary grinding and classification stage consisting of one ball mill, two hydrocyclone batteries and a sump with two pumps. Line 3 has one SAG mill (Gearless Mill Drive), followed by a secondary grinding and classification consisting two ball mills, four hydrocyclone batteries and a sump with four pumps. Average throughput for these three lines is 150 Ktons per day. Peak values of 180 ktons per day have been achieved.Since late 2008 and throughout 2009 and 2010, Operations and Automation areas developed an optimization program for the grinding process, considering the implementation of Model Predictive Controllers (MPC) for the three SAG mills, and later, extending MPC to the secondary grinding and classification stages. The implementation of a MPC solution was based on stability considerations (high variability of the SAG process, high interaction between sump level control and classification efficiency, etc), requirements for an automated and consistent operation, the need to maximize throughput under timevarying scenarios and, in the long term, optimization of grinding process considering Specific Energy Consumption, among other parameters. MPC solutions had proven control robustness and strong optimizing capabilities in terms of helping in discovering new operational points and so achieving all of the aforementioned goals.On the first stage of the program, MPC implementation considered identification of dynamical process control models based mainly on historical data, in order to know the impact of a group of Manipulated Variables over Controlled Variables. Also, the impact of measured Disturbance Variables was modeled in order to take into account the high impact and interaction of these variables over the processes. At the end of this stage, 4 controllers were successfully operating for the 3 SAG mills and the secondary grinding and classification process. In response to challenges made by the working group, the second stage of the development of control applications in the grinding process required to achieve a design and implementation of a solution capable of governing the milling process, in addition to stabilization and optimization of both processes (SAG milling and secondary grinding), to integrate from a point of view of process control and automation. Therefore, in the second stage, MPC performance was continuously monitored and optimized through advanced tuning, inclusion of more process models (with proper step tests), redefinition of specific optimization criteria and adjustment to new process needs.Finally, successful MPC implementation at Collahuasi has proved that fast development and deployment of process control solutions is possible and allows immediate process stability, higher throughput, specific energy consumption reduction, and successful product size control, among many others."

Jan 1, 2012

By Douglas A. Sloan

"Recently, a number of major mining companies seemed unable to find a president from within the industry, and were searching outside the industry. From this, one could conclude that managers within the industry are either not being prepared or are not preparing themselves for presidential responsibility. Opinions were sought from a number of senior executives, to attempt to define the skills a prospective president should acquire and what actions a company could take or that a prospective president could take to acquire these skills.This paper contains summaries of the opinions obtained, along with the author's comments. The paper also describes the actions some companies are taking and the actions that an aspiring president can take to prepare himself for corporate management.IntroductionA manager is promoted up the management ladder when the manager's superiors believe that he is capable of handling a more senior position. Normally, the manager acquires this credibility by outstanding performance in his current management post, whether it be in a junior management (supervisory) or in a vice-presidential capacity.In most instances, the skills required for promotion can be acquired in the current position or, at worst, the abilities exhibited in a candidate's current role will convince his superiors that the necessary expertise for the more senior position can be acquired on-the-job. This is particularly the case when the new skills are felt to be an extrapolation of the old skills.However, in the case of appointment to presidential rank, there appears to be a need for new expertise which often is not acquired in normal management progression or, at least, boards of directors of some mining companies seem to believe this to be the case. The objective of this paper is to attempt to define the new skills that should be acquired by a manager who aspires to be the president, and to describe what actions might be taken by him to acquire them."

Jan 1, 1982

By H. Ikeman

"The highly specialized communication systems used in the mining industry place exacting demands on equipment and transmission media. Safely and reliability of services are perhaps the two most important factors. Fibre optics is ideally suited 10 meet these stringent requirements. Aside from being an intrinsically safe, non-sparking and EMI/RFI immune medium , fibre optics offers greater reliability , higher quality of services and superior flexibility over conventional copper or radio-based communication systems.This paper wilt show how fibre optics can be applied in mining industry applications. Emerging trends and concepts will be presented to show how fibre-optic-based integrated service communication networks and local distribution systems can be implemented.IntroductionCommunication requirements in today's mine s are varied and extensive. The communication system must be rugged , safe and reliable, yet provide an ever increasing amount of high quality services. Presently, these systems are implemented using conventional copper cable. As mining method s and technology advance and the demand for better and more communication services increases, traditional systems quickly reach their limitations. It is under these circumstances that we turn to fibre optic communication systems.Fibre optics is a mature technology which is finding its way into more and more applications worldwide. A fibre optic communication system can provide a level of performance unattainable by conventional cable systems yet ca n be cost competitive. As is well known, fibre optics provides a noise-free, noise-immune, high -capacity communications channel. Glass fibre, being dielectric and non-sparking, is an intrinsically safe communications medium. Clearly, it is ideally suited to the harsh environment present in a mine.From a communication systems point-of-view, the topology of a deep mine is unique. The objective of the systems engineer is to implement a total communications capability throughout this wide spread area. Ideally all classes of services should be accessible throughout the network-an integrated network concept. Recent advances in communications technology combined with fibre optics make this realizable."

Jan 1, 1984

By Ken Musgrave

"A program is described that helps managers and supervisors control maintenance more effectively. Work- order generation, preventive maintenance, repair parts inventory, planning and scheduling, reporting, analyzing costs, printing purchase orders and other functions are covered. Flexibility often permits integration with other programs such as payroll, cost accounting and materials management.The Role of MaintenanceMaintenance provides a service to allow the rest of the operation to do its job effectively. Its success should not be measured by maintenance cost alone, but also by its effectiveness in reducing downtime and maximizing production. It can make sense to spend more maintenance dollars if this results in an even greater contribution from increased production.The Cost of MaintenanceIn mining companies, maintenance costs can be as much as half of operating costs. Maintenance has generally not been given the management attention that an expenditure of this magnitude deserves."

Jan 1, 1986

By P. R. Brito-Parada, G. Bhutani

"The physical processes occurring in flotation columns are very complex as they take place at different scales over a range of sizes and multiple phases. Column design and optimum operating parameters are usually obtained from empirical studies and although progress has been made on its numerical modelling, most column models rely on simplifications that do not fully capture the hydrodynamics. In particular, Computational Fluid Dynamics (CFD) models of the pulp phase in flotation usually assume the bubble population to be monodispersed. While this assumption may be reasonable in some situations, the polydispersed nature of the gas phase can have a significant impact on the predicted flotation rates.Techniques to model size distribution do exist in the literature and have been rigorously analysed in the past two decades for bubble columns, which are very similar to flotation columns from a hydrodynamics point of view. In fact, available CFD models of flotation columns are an extension of bubble column models, sometimes including additional equations for solids treated as passive scalars. This work focuses on the development of an efficient CFD model for flotation columns. The bubble size distribution in the column has been modelled using the Population Balance Equation (PBE), which is solved using the Direct Quadrature Method of Moments (DQMOM). Coupled with the PBE, the multiphase flow equations in the column have been modelled using the standard Eulerian–Eulerian approach. The solution of this coupled system has been made tractable in this work with the implementation of a highly parallelised adaptive-mesh finite element method. This powerful framework has been implemented in the open source CFD code Fluidity and it allows the carrying out of detailed simulations of flotation columns in 2D and 3D, with important implications for industrial column evaluation and design."

Jan 1, 2016

By Jean-François Lagueux

Goldex Mine is an underground mine located near the town of Val-d?Or. Multiple innovations were required to work the mine. Due to its low grade, it was important to develop a bulk mining method to economically extract the ore. The method used is a combination between shrinkage stope and long hole stope methods. This modified method is more than adequate; however, all of the ore body must be liberated in a very short period of time. Therefore, to bring down 23 Mt of ore, large blasts up to 1.8 Mt are required. The situation is also complicated by the fact that the mine is located in a residential area. No less that 40 homes are built within a 1 km radius of the mine site. In addition to managing mass blasts, means must also be found to mitigate the vibrations produced by the blast to diminish the disturbance to the neighbourhood. Therefore, the mine used numerous tools to properly plan the blasts and reduce the impacts. A program to control vibrations was one of the first tools put in place. The program?s aim was to draw up an action plan to ensure a follow-up of the homes by inspecting them. The second tool was to develop a methodology to plot a reliable attenuation curve and to adequately determine the maximum charge weight for each blast. Finally, effective communication tools were developed to inform the neighbourhood. There was a huge amount of work to be done in relation to the bench. Reliable and fast loading techniques had to be found to load large blasts in a very short period of time. Adequate logistics had to be developed to send underground more than 20,000 kg of emulsion per day while performing the daily underground operations. Technology had to be developed to adapt the i-kon electronic blasting system to large blasts. Since the control of the charges was the major factor to reduce surface vibrations, it was important to employ loading techniques that would permit decking of the long holes to reduce the charge weight per delays without adversely affecting the loading. All of this work requires an enormous amount of energy but also close collaboration between the different stakeholders (various departments, suppliers and consultants).

May 1, 2011

By P. Keller, T. E. Lister, G. G. Clark, L. A. Diaz

As electronic technology continues to evolve there is a growing need to develop processes which recover valuable material from antiquated technology. This need follows from the environmental challenges associated with the recovery of raw materials and fast growing generation of electronic waste. Although present in small quantities in electronic devices, the availability of raw materials such as rare earths and precious metals becomes critical for the production of high tech electronic devices and the development of green technologies (i.e. wind turbines, electric motors, and solar panels). Therefore, the proper recycling and processing of electronic waste presents an opportunity to stabilize the market of critical materials, providing a proper disposal and treatment of a hazardous waste stream. This paper describes the development and techno-economic assessment of a comprehensive process for the recovery of value and critical materials from electronic waste. This hydrometallurgical scheme aims to selectively recover several value streams (base metals, precious metals, and rare earths) present in electronic waste. The economic feasibility for the recovery of rare earths from electronic waste is mostly driven by the efficient recovery of precious metals, such as Au and Pd (ca. 80 % of the total recoverable value). Rare earth elements contained in magnets (speakers, vibrators, and hard disk storage) can be recovered as a mixture of rare earth oxides which can later be reduced to the production of new magnets.

Jan 1, 2016

By Eric Best

"In the past two to three years, all continuous mining machines at the Potash Corporation of Saskatchewan Mining Limited, Lanigan Division, have been changed over to a new cutting pattern using 1 -inch- and 1-3/l6-inch-diameter self-sharpening pencil bits. The bits are arranged in a cone-type pattern across the face on 2 1/2 -inch and 3-inch spacing. The result is that the ore is removed by chipping and flaking. Previously, rap-lock bits were used, with the pattern being several bits in single rows at wide spacings. The cutting action was grinding and breaking.Besides improved penetration rates and lower bit costs, there are many other advantages. The ore size is much smaller, resulting in less wear and tear on conveyors and other associated equipment. Feeder-breakers are no longer routinely set up at the head end of every extensible belt, as the banana-shaped chunks of ore that used to require breaking are no longer produced. Also, less dust is generated by the cutting heads and fewer stops are required for bit changes. Even the mill operation has been improved, as fewer fines are produced.Further improvements are still sought after, but, all in all, the new cutting pattern is considered to be a giant step forward from the old method."

Jan 1, 1981

By Ken Musgrave

"What Most Effective Management Does?It must satisfy the demands, of three groups of people: owners, employees and the public.OwnersOwners want profitable operations that will pay them a return on their investment, plus operations managed for long life. Many owners are also concerned with employee's well being and their company's public image.EmployeesJob security and a good income are probably still the most important demands, however, as time goes by, employees are also demanding more involvement in safety issues, working conditions, and even how work is done.The PublicThe public requires acceptable environmental standards, as well as enjoying the prosperity supplied by a successful operation.How are Mines Managed?Most mines are managed very traditionally. The basic credo is that the managers make the decisions, and the hourly, and junior salaried employees do what they are told. Clearly this is the extreme case, epitomized by the long service shift boss who might say ""It took twenty-years to become a shift boss, and no miner is going to tell me what to do"" .There are some exceptions, two notable ones being Campbell-Chibougamau, and T.G.S. (now Kidd Creek Mines) which, in very different circumstances, decided on a more participative style.Campbell-Chibougamau, having closed down due to unprofitable operations, reopened, using a team structure with working leaders, and a system for sharing gains against cost targets with employees. Although the system has some problems, and development miners are bonused conventionally, this has been a basically successful program.Texasgulf Sulphur, a company with a history of non-union operations, and a participative management style, made a corporate decision to operate their Kidd Creek Mine in the same way. The orebody was rich enough to allow them the luxury to do this, but they have never had a strike, so perhaps they have more than saved the cost of the benefits and salaries they needed to pay. They also reward employees with a stock distribution scheme based on service and earnings."

Jan 1, 1985

By G. Dubé, A. Leclerc, P. Quinn, G. E. Agar, J. Y. Clouthiér, J. D. McLaughlin

"Gold dissolution by cyanide requires the presence of oxygen which is usually supplied by sparging compressed air into the gold containing slurry. For those ores that contain certain obnoxious substances that consume oxygen, maintaining the required minimum level of dissolved oxygen can be troublesome. One of the most economical solutions to the problem of low dissolved oxygen, especially in plants that have air compressors installed, is to enhance the rate of oxygen mass transfer.The oxygen mass transfer rate was measured in a two phase system using two different sparger arrangements, and with addition of a frother that is known to reduce the bubble size produced by the sparger. The common sparger system was shown to be inefficient compared to a readily available but under utilized method of gas dispersion which introduces air directly below the reactor turbine. Transfer of this technology to an operating plant confirmed the beneficial effect of the improved sparger system. The addition of the frother did decrease the bubble size, but it also reduced the oxygen mass transfer rate."

Jan 1, 1993

By R. S. James, S. P. Goff, A. E. Armitage

"Abstract - Oxide-facies banded iron formation in the Third Portage Lake area is hosted by ultramafic and calc-alkaline volcanic rocks and related sedimentary rocks of the Archean (2.8 Ga) Woodburn Lake Group, 80 km north of Baker Lake. These rocks record at least two phases of metamorphism/ metasomatism. Greenschist facies metamorphism, in the temperature range of 370°C to 520°C and at pressures above 2.3 kbar, has affected all rocks on a regional scale. Later mineralization and alteration of banded iron formation (BIF) and associated volcanic rocks resulted from metasomatic fluids which carried Mg, K, Ca, S, As, Cu and Au. These fluids were confined to ductile to brittle, cross-cutting and layer-parallel micro-shears developed in the thickened hinge region of a shallow plunging recumbent fold. Metasomatic reactions yielded cummingtonite + biotite-bearing assemblages which are associated with strongly mineralized iron formation. Pyrrhotite is the dominant sulfide phase and occurs within ductily deformed iron formation where it pervasively replaces magnetite. Minor fine-grained chalcopyrite and arsenopyrite generally occur as inclusions within pyrrhotite and recrystallized magnetite, and rarely as individual grains. Pyrite is restricted to brittlely deformed iron formation, and to the contact between iron formation and altered ultramafic rocks, where it is associated with quartz veins. Pyrite typically replaces pyrrhotite. Native gold is associated with both pyrrhotite and pyrite, but higher gold concentrations are associated with pyrite. Grunerite/Ca-amphibole + stilpnomelane and sparse pyrrhotite and pyrite characterize weakly mineralized iron formation. Within adjacent ultramafic rocks, metasomatic reactions yielded assemblages of interlayered Ca-amphibole + biotite, and talc + Ca-amphibole + carbonate + biotite. K-Ar geochronology on metasomatic biotite from mineralized BIF yielded a 1791 ± 32 Ma age.An epigenetic model is favored for the emplacement of gold. The age of the gold mineralization in the Third Portage Lake area is uncertain, but may be Proterozoic based on the preliminary isotopic age and by analogy with Proterozoic gold deposits elsewhere in this part of the Churchill Structural Province."

Jan 1, 1996

By R. S. James, S. P. Goff, A. E. Armitage

"Oxide-facies banded iron formation in the Third Portage Lake area is hosted by ultramafic and calc-alkaline volcanic rocks and related sedimentary rocks of the Archean (2.8 Ga) Woodburn Lake Group, 80 km north of Baker Lake. These rocks record at least two phases of metamorphism/ metasomatism. Greenschist facies metamorphism, in the temperature range of 370°C to 520°C and at pressures above 2.3 kbar, has affected all rocks on a regional scale. Later mineralization and alteration of banded iron formation (BIF) and associated volcanic rocks resulted from metasomatic fluids which carried Mg, K, Ca, S, As, Cu and Au. These fluids were confined to ductile to brittle, cross-cutting and layer-parallel micro-shears developed in the thickened hinge region of a shallow plunging recumbent fold. Metasomatic reactions yielded cummingtonite + biotite-bearing assemblages which are associated with strongly mineralized iron formation. Pyrrhotite is the dominant sulfide phase and occurs within ductily deformed iron formation where it pervasively replaces magnetite. Minor fine-grained chalcopyrite and arsenopyrite generally occur as inclusions within pyrrhotite and recrystallized magnetite, and rarely as individual grains. Pyrite is restricted to brittlely deformed iron formation, and to the contact between iron formation and altered ultramafic rocks, where it is associated with quartz veins. Pyrite typically replaces pyrrhotite. Native gold is associated with both pyrrhotite and pyrite, but higher gold concentrations are associated with pyrite. Grunerite/Ca-amphibole + stilpnomelane and sparse pyrrhotite and pyrite characterize weakly mineralized iron formation. Within adjacent ultramafic rocks, metasomatic reactions yielded assemblages of interlayered Ca-amphibole + biotite, and talc + Ca-amphibole + carbonate + biotite. K-Ar geochronology on metasomatic biotite from mineralized BIF yielded a 1791 ± 32 Ma age.An epigenetic model is favored for the emplacement of gold. The age of the gold mineralization in the Third Portage Lake area is uncertain, but may be Proterozoic based on the preliminary isotopic age and by analogy with Proterozoic gold deposits elsewhere in this part of the Churchill Structural Province. Copyright"

Jan 1, 1996