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By F R. A Jorgensen, G W. Jensen

A pilot scale experimental investigation of the condensation of zinc vapour from smelter off-gases was performed in conjunction with a mathematical modelling study of the system. The work investigated the feasibility of using the high heat and mass transfer rates associated with a fluidised bed to condense zinc directly from smelter off-gases containing zinc vapour. Of particular interest was whether zinc would revert to zinc oxide during the process of condensation, and whether a zinc fog would form and be carried out of the condenser. A 0.1 m diameter fluidised bed condenser was mounted on the top of a 200 kVA DC electric arc furnace in which mixtures of vapours and gases were generated at 1150 - 1300¦C. The gas/vapour mixtures investigated included Zn/N2, Zn/N2/CO/CO2 and Zn/N2/H2/H2O. Greater than 90 per cent of the zinc was deposited on the zircon sand bed of the condenser, and there was no sign of zinc oxide formation, suggesting that the rate of heat transfer was faster than the reaction rate for zinc oxide formation. There was also no evidence that fog was being formed in the condenser. Using the methods of Kunii and Levenspeil (1991), a mathematical model was developed to predict the behaviour of the fluidised bed condenser. The model enabled the distribution of gas/vapour temperature and bed temperature to be determined as a function of distance from the condenser inlet. Similarly the partial pressure of zinc vapour in the gas mixture, and hence the mass transfer rate of zinc to the particles, was determined. Experimental data allowed validation of the predicted bed and gas/vapour temperatures.

Jan 1, 2000

By J Player, G Sweby

The material properties and hence performance of saturated alluvial sediments slope can be incorrectly forecast if the water content is not preserved, and materials properties not correctly determined. The occurrence of saturated sediments in the Western Australia (WA) Goldfields, while not common, should be a significant investigation focus. Geotechnical engineers new to the area may be unaware of this and hence the importance of correct testing and determination of the material strength. Application of appropriate analysis to determine stable pit slopes to an acceptable level of risk, is not possible unless the appropriate strength and hydrogeological parameters have been established at the outset. A back analysis is presented of a pit that had extensive slope failures in alluvial clay-rich sediments with discussion on the approach adopted by the original design engineers to assess pit wall stability and consequent poor slope performance. Learnings from a full pit 3D back analysis are presented, with an approach to geotechnical and hydrogeological investigations and analysis for slopes in similar materials.

Jun 22, 2022

By A P. Wilkinson

This paper reports on the implementation of the critical control concept to manage material risks in the mining and metals industries. The critical control management (CCM) approach assumes it is better to identify weaknesses in risk controls before an incident happens as opposed to discovering weaknesses from an investigation after an incident occurs. The first is sometimes referred to as active monitoring and the second as reactive monitoring (Health and Safety Executive and Chemical Industries Association, 2006). Both are needed. However, whilst methods for both active and reactive monitoring of risk controls are well established in many high hazard industries, such as oil and gas, petroleum and chemical industries, until the publication in 2015 of the International Council on Mining and Metals (ICMM) guides, (Good Practice Guide and the subsequent Implementation Guide) (ICMM, 2015), there was no specific mining and metals industry guidance on critical control management. This paper reports on progress in implementing the ICMM guidance drawing on two main sources. First, a benchmarking survey of a representative sample of coal and metalliferous mines, both underground and open cut/pit), sponsored jointly by the Queensland Resources Council and the Queensland Commissioner for Resources Safety and Health in the context of a recommendation that the Queensland mining industry adopts high reliability organisation (HRO) principals (Queensland Resources Council and Commissioner for Resources Safety and Health, 2022). Second, it draws on Noetic’s experience of implementing critical control management in mining and other high hazard industries in Australia, Africa, China and North America (Wilkinson, 2018). The paper describes good practices found and where significant improvements can be made, providing specific and actionable examples of both. From this it also identifies how future guidance on this topic could be improved.

Apr 16, 2024

By D David

The development of Western Australian magnetite deposits has lead to the design of some of the largest grinding mills and plants in the world. One of the projects demonstrates the efficiency gains possible by developing a simple yet thorough test program for circuit design. By drawing on the experience of current magnetite operations in Australia and the Mesabi and Marquette iron ranges in the United States, a basic flowsheet was developed. Through comprehensive testwork with AG, ball and stirred milling the flowsheet was optimized to take full advantage of each grinding mill’s strengths to reach the required final grind size. Laboratory work was verified in the pilot plant to optimize the energy efficiency of each grinding step while ensuring adequate liberation at each step for sufficient gangue rejection. By using three stages of grinding, the ball mill can best be employed in ensuring all top size gangue material is liberated and removed in the second magnetic separation step. The inclusion of the IsaMill, with its inherent steep product size distribution, as the tertiary grinding stage ensured that maximum grade was achieved and simplified the downstream process while giving further improvements in total grinding capital and operating costs. In this way the combination of the two technologies downstream from the AG mill is far more efficient than either would be on its own by reducing the total installed power by 1/3 and annual grinding media cost by 2/3.

Aug 8, 2011

By J Hartnett, B Tarrant, A Rayner, D O’Toole, P Davies

Since 2009, the Northern Territory and Australian governments have been working under a national partnership arrangement to inform a rehabilitation plan for the former Rum Jungle uranium mine. Part of the rehabilitation strategy is to backfill a flooded former pit (Pit), which extends down to 100m below the current pit lake surface and was historically partially backfilled with uranium tailings. It is proposed to utilise the remaining pit volume below water level to sub-aqueously store Potentially Acid Forming (PAF-I) waste rock which currently occupies large stockpiles across the site. The rehabilitation design and planning process undertaken to develop a strategy commensurate to project objectives and construction constraints involved the establishment of key constraints derived from the analysis of historic data sources and preliminary design efforts. Tabled strategies were balanced against dependent project tasks and project objectives, especially surrounding minimising disturbance of highly contaminated materials within the Pit. Ideas were developed in conjunction with industry input and review of case histories to develop a remediation solution that is constructible within the project timeframe and constraints.

Jul 1, 2021

By A Innis, A Bye, B McCarthy, S Glover

Technology adoption in the mining industry has been steadily increasing over the past decade, driven by the need to improve operational efficiency, safety, sustainability, and profitability. As mining companies wish to implement solutions to improve mining safety and productivity, various technologies are being integrated into mining operations to enhance processes, reduce risks, and optimise resource utilisation. Adoption of new technologies such as autonomous trucks requires a strong focus on foundational operational technology (OT) and a systems-thinking approach. OT support is critical however, OT is traditionally not considered or integrated into standard maintenance activities. Consequently, sourcing and applying service support to OT systems in real-time has posed significant challenges to date. Neglecting the monitoring and upkeep of these operational technologies and equipment can lead to a host of adverse consequences. Operating instability becomes more prevalent, necessitating reactive measures, and the vulnerability to cybersecurity threats increases significantly. To address OT monitoring and maintenance challenges, a systems wide mindset and remote support discipline must be utilised. Remote operations support refers to real-time, 24/7 monitoring, control and support of site OT: network, production systems, maintenance systems, enterprise systems and mobile and fixed plant through a single interface remote from site. The presence of a disciplined team, grounded in a systems-oriented approach, is of the utmost importance to remote monitoring, given the intricate interdependencies of OT systems. The ability to understand the relationships among multiple systems, coupled with the capacity to distinguish between symptoms and root causes, assumes a pivotal role in operations. Through diligent monitoring and the astute understanding of system thresholds, remote operations support can actively identify and alleviate constraints, in turn, serving as the enabler for transformative advancements in technology output.

Sep 1, 2024

By CorrOa de Araujo A, Salum MJG

The treatment of mining and metallurgical liquid effluents is becoming, everyday, a necessity felt by these industries. Physical-chemical and chemical methods for treating such effluents are generally necessary whenever heavy-metals and other toxic compounds such as cyanide are present. The present paper discusses the use of precipitate flotation as an alternative physical- chemical method that can be applied for the treatment of effluents containing heavy-metals (mainly zinc and cadmium) and cyanide. Examples of laboratorial scale applications on real effluents are given. In both cases precipitate flotation was able to reduce the concentration of toxic components of the effluents at a very high removal rate, generating a solid waste that can either be disposed, re-used or recycled. A cationic collector - dodecylamine hydrochloride - demonstrated to be the best choice of surfactant for the two systems investigated. Sodium sulphide and dithizone were selected for the precipitation of the zinc bearing effluent whereas a copper salt was preferentially used for precipitating cyanide in a form adequate for its recycling envisaging the use of an AVR (acidification - volatilisation - regeneration) technique.

Jan 1, 1993

By A Melloy, D Holt, M Jurak

Oaky North is AustraliaÆs highest producing underground coal mine. In 2011, the mine produced 8.7 Mt of high-quality coking coal. The high quantities are a result of the constant strive for optimising the operating time of major production units, which involves investing numerous resources, including diesel equipment, in supporting and maintaining their operation.In July 2011 it was identified that the diesel particulate matter (DPM) levels in the underground workings were above acceptable levels, due to the high level of diesel activity. Over the next 12 months, several controls were implemented to reduce exposure to personnel: the main ventilation system was upgraded; the production forecast was adjusted to better manage the diesel fleet, removing surges in diesel usage; and an electronic diesel tag board was introduced to centrally manage the distribution of diesel usage around the mine.From the start of the campaign in emission reduction, an intense DPM monitoring regime was established. Within a few months of the introduction of the centralised tag board, there was a major reduction in emission levels. After the installation and commissioning of the new main fans, the emission levels dropped further, such that over-exposures are now a rarity.Oaky North continues to explore new systems to better utilise their diesel fleet while still maintaining control over DPM emissions.CITATION:Melloy, A, Holt, D and Jurak, M, 2013. Reduction in diesel particulate matter at Oaky North, in Proceedings The Australian Mine Ventilation Conference , pp 187-190 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Jul 1, 2013

By S Jahanshahi

In an earlier LCA study, the authors showed that the electricity consumption of the electric furnaces used in the production of the ferronickel and ferrochrome feedstocks made significant contributions towards the Gross Energy Requirement (GER) of stainless steel production, on a æcradle-to-gateÆ basis. Given the relatively low efficiencies associated with electrical power generation, substantial reductions in the GER for stainless steel production could be anticipated if more direct use of thermal energy was made in the ferronickel and ferrochromium smelting stages.In view of these findings, a follow-up study was undertaken to investigate the likely environmental benefits of using bath smelting processes for the production of ferronickel and ferrochromium compared to the traditional rotary kiln-electric furnace processes, but still utilising the electric furnace process for stainless steel production. The METSIM process simulation software package was used to set up models of the two bath smelting processes and provide process energy requirements that were incorporated into the LCA. The environmental impacts considered in the LCA were greenhouse (Global Warming Potential, GWP) and acid rain gas (Acidification Potential, AP) emissions and solid waste emissions.The results of the study showed that the bath smelting route reduced the GER for ferronickel production by about 37 per cent over the traditional route, which translated to about a 21 per cent reduction in the GER for stainless steel. The corresponding reduction for ferrochromium was about half that for ferronickel, and when combined with the ferronickel result gave a 25 per cent reduction in the GER for stainless steel production. Similar reductions were also observed for the GWP and to a lesser extent the AP for both feedstocks, as all primary energy inputs were essentially fossil fuel based. Substantial reductions in solid waste emissions were also indicated for the direct use of ores in smelting. By utilising bath smelting processes for the production of the ferronickel and ferrochromium feedstocks, stainless steelÆs suitability for meeting many of the goals necessary for sustainable development, already recognised because of its particular properties, would be even further enhanced.

Jan 1, 2004

By P Ramsaywok

The use of saline water for mineral beneficiation in arid regions is general practice and also the case with Exxaro Namakwa Sands, situated on the west coast of South Africa. Although it is ‘cost effective’ to use sea water for mineral beneficiation, downstream process separation efficiencies may be negatively affected. This is more specific to surface dependent separation techniques such as electrostatic and high tension (HT) separation. If minimal fresh water is available then, proper washing is often neglected. Salt crystals can form on particle surfaces during the drying process before electrostatic separation.This paper describes a study that has been conducted to determine the effect of upfront salt water processing on downstream electrostatic/HT separation. The study indicated that minor quantities of salt can cause the separation efficiency to decrease substantially.

Oct 5, 2011

By B King

Processing expansion options and mining fleet purchases are major cost items that receive due focus in most cost management analyses. If these items are not needed, they can significantly reduce a project’s short-term capital spend and improve profitability and value to shareholders. When conditions change prior to purchasing equipment, the purchase may no longer represent the best decision for the project.This paper outlines a structured approach for making major cost decisions to improve the value of a project, determining which items should be kept and which should be eliminated.CITATION:King, B, 2014. Cost management optimisation, in Proceedings Orebody Modelling and Strategic Mine Planning Symposium 2014 , pp 7–12 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Nov 24, 2014

As students progress further into a degree, the decision of vocation selection, and even more importantly û securing employment in a particular industry sector, can become quite daunting. However, with a little initiative, students can overcome these issues by not only researching what employment opportunities exist, but by applying for summer vacation employment. Undergraduate vacation employment, especially with a world-leading hydrometallurgy research organisation such as the Parker Centre, can dramatically alter a studentÆs perspective of particular industries and possibly even alter their selection of vocation pursuits upon graduating. Students can also use vacation employment to enhance their networking capabilities, technical skills and knowledge by dealing with challenging new topics such as sulfur dioxide leaching, which is also discussed in this article.

Jan 1, 2005

By A Romanel, M S. Kato, M P. Piermatei, P Artioli

"Brazil is the sixth worldwide producer of aluminum and Votorantim (Metals) has been operating three bauxite open pit mines in a particular way of working. In those the deposits occur on the top of hills, under forest, coffee, eucalyptus plantation or pasture area.The deposits are not large and normally mining takes an average of two months to be completed before starting the rehabilitation process, which demands a good strategy in mining planning to achieve the production goals.The benefit function developed to select feasible areas uses, beyond production costs, fees from the owner by using their area and rehabilitation cost. Both are based on land use and occupation field survey data. In this process each area with different land use receives a specific rehabilitation cost as input into a block model.Once the selection is made the mining schedule begins, taking into consideration the following premise: the orebody needs to be mined in a short period of time because during this time, the surface owners receive from Votorantim a compensation based on the expected profits from their plantation or pasture, plus royalties related to the ore amount existing in their area.Not all operations have waste dumps. Waste is pushed down by bulldozers to the lower part of the ore border. After loading and transporting ore, the waste is handled back to the mined area to fit the topography. With this step concluded, the mined area is directed to the environmental team who, alongside university partners, develop land reclamation to return them to their owners, eg in 2011, 110 ha were rehabilitated of which 29 per cent is native forest.Votorantim closes many mined areas a year and currently the entire mine planning considers this particular way of operation, making profit with minimum interference with the community and the environment.CITATION:Artioli, P, Kato, M S, Romanel, A and Piermatei, M P, 2012. Environmental variables at bauxite mine, in Proceedings Life-of-Mine 2012 , pp 171-178 (The Australasian Institute of Mining and Metallurgy: Melbourne)."

Jul 10, 2012

By S Schwarz, D Alexander

The mining industry, and in fact the world, has undergone significant changes in the past five to ten years, ranging from the metals boom, the global financial crisis and the rise and fall of national economies, to name just a few. There has been a focus on sustainable development for projects and operations in the mining industry, mainly pushed onto the industry by communities, governments and other agencies. While sustainable development and operation is a worthy priority for mining operations, discussions with mining industry personnel (with a strong slant on the mineral processing perspective) have shown other issues have surpassed the typical issues of water resources, energy availability and the environment. These include staff turnover and skills shortages, extracting metal from more complex orebodies and the uptake of new step-change technology.A number of key operating mineral processing personnel were interviewed to determine their perspective on the current issues facing the mining industry. This paper details the findings of this survey and highlights some of the topics that have been identified as the top issues from a mineral processing perspective.CITATION:Schwarz, S and Alexander, D, 2012. Current issues in the mining industry - From the operational mineral processorÆs perspective, in Proceedings 11th AusIMM Mill OperatorsÆ Conference, pp 369-372 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Oct 29, 2012

By J J. Moreno, J Willis, P Garvey

Many of the tailings storage facilities (TSFs) in Australia are upstream raised facilities for which the consolidation of the hydraulically deposited tailings is essential to the stability of the TSF. While much operational consideration is given to limiting the rate of rise of TSFs through careful management of deposition rates to achieve desired consolidation, the rate of embankment raise construction (RoC) is often not given the same level of consideration. Loading the tailings at too high a rate during construction could lead to upstream and potentially downstream failure of the embankment. The Tailings Retention System (TRS) at the BHP Olympic Dam Mine comprises upstream raised TSFs that are continually raised with a zoned embankment. Improving on 20 years of successful embankment raising, there was a desire to understand the acceptable RoC under varying operating conditions and assess upper construction limits to improve operational risk management. To understand the RoC, trial embankment raise construction pads were constructed at different rates and the pore pressure response of the underlying tailings material was monitored. The pore pressure data were used to calibrate the permeability and consolidation characteristics of the tailings in a finite element model (FEM) that replicated a typical embankment raise. The rate of material placement, location of the phreatic surface and construction load were varied in the FEM until failure was initiated. The results were presented as a period (in days) over which the various zones for the embankment raise could be safely constructed. The results indicate direct sensitivity to the depth to the phreatic surface prior to commencement of an embankment raise, as well as the point of application of the construction traffic load. This paper presents the study approach, challenges experienced in modelling the construction methodology, the study results and their relevance in the improvement of understanding of RoC at the BHP Olympic Dam TRS.

Jul 1, 2021

By G K. N Subasinghe

"In the design and operation of mineral processing plants, knowledge of the variability of ore properties and that of the expected metallurgical performance within the orebody is of great importance in order to avoid both production constraints due to inadequate design and less than expected metallurgical performance during operation. Of the many properties that determine the performance of downstream separation processes, such as flotation, gravity separation and leaching etc the liberation characteristics are of primary importance.Current methods of evaluating liberation characteristics of ores such as the use of Mineral Liberation Analyzer (MLA) and QEMSCAN techniques are expensive and suffer from the drawback that these tests are performed on comminuted particles at a given grind size and/or samples of product streams. This problem could be overcome by developing predictive models of liberation that can predict the grade distribution of comminuted products at any grind size based on texture of the parent rock. This paper discusses a procedure that has been developed to predict liberation using information obtained from a sample of the parent rock such as drill core, based on Barbery’s liberation models. The required characteristic statistical functions have been evaluated from image analysis techniques using scanning electron microscope (SEM) images of the parent rock and narrowly sized comminuted particles. Such information can then be used in a predictive model to predict or explain the variability of metallurgical performance at various grind sizes used in future operating plants. The model will predict not only the valuable mineral liberation but also gangue liberation, which will be useful to those who are looking to remove liberated gangue from comminution circuits.CITATION:Subasinghe, G K N, and Dunne, R, 2016. Predictive Model of Mineral Liberation for Geometallurgical Applications, in Proceedings The Third AusIMM International Geometallurgy Conference (GeoMet) 2016, pp 347–350 (The Australasian Institute of Mining and Metallurgy: Melbourne)."

Jun 15, 2016

By F Sahlström, E M. Jolis, V R Troll, E Jonsson, K Högdahl, C Harris

"An EXTENDED ABSTRACT is available for download. A full-length paper was not prepared for this presentation. The Bastnäs-type magnetite-skarn-hosted rare earth element (REE) mineralisations are located in the Palaeoproterozoic Bergslagen ore province, central Sweden, and occur along a ca 100 km long belt of 1.90–1.87 Ga metavolcanosedimentary rocks. Ten different Bastnäs-type deposits have been sampled in order to assess the origin of ore-forming fluids in these systems. Magnetite and quartz have d18O values ranging from -2.3 to +1.1‰ and +7.2 to +8.3‰ respectively. Mineralised carbonates have d18O values between +5.8 and +7.2‰ and d13C values between -5.4 and -3.3‰. Temperature calculations based on the O-isotope composition of mineral pairs, combined with available fluid inclusion data, suggest primary mineralisation at ca 650–400°C. For these temperatures, calculated equilibrium fluids have d18O values that range from those typical of magmatic fluids (+6 to +8‰) to lower values (down to +3‰). Variation in carbonate O and C isotope data are consistent with interaction between local Palaeoproterozoic carbonate rocks (d18O = +12.5 to +19.6‰ and d13C = -1.8 to +1.7‰) and fluids of a magmatic origin. It is suggested that the Bastnäs-type REE-magnetite mineralisations formed as a result of reactions between local carbonate units and high-temperature, magmatic-dominated hydrothermal fluids during 1.90–1.87 Ga (Svecofennian) syn-volcanic activity.CITATION:Sahlström, F, Jonsson, E, Högdahl, K, Harris, C, Troll, V R and Jolis, E M, 2015. O and C isotope study of Bastnäs-type rare earth element mineralisation, Bergslagen, Sweden, in Proceedings PACRIM 2015 Congress, pp 439–444 (The Australasian Institute of Mining and Metallurgy: Melbourne)."

Mar 18, 2015

By T N. Little

This review paper presents an integrated and practical insight to blasting geology and its importance. This approach involves developing blasting objective up front and implementing geology specific blast designs. The author refers to this approach as ‘starting at both ends’. There are many human-imposed controls on blasting operations, such as: safety, security, legislative, company standards, heritage, and environmental constraints. Thus it is possible for some operators to lose sight of the controls imposed by nature. This paper demonstrates how site geology controls or influences many aspects of the rock breaking processes and how a focus on this aspect has potential to add considerable value to mining operations. It is obvious that mining companies concentrate their efforts on economic/ore geology (good rock geology). However it is the author’s experience that they also concentrate on engineering geology (bad rock geology) only when forced to do so by the ground conditions, but seem to run out of puff before they apply blasting geology (big rock geology). This paper contains five main sections. In the first section, the impact of geological controls on blasthole drilling is briefly discussed in terms of drill selection, penetration rates, bit wear, blasthole stability, blasthole deviation, and health precautions. In the second section the geological controls on aspects of geometric design are reviewed. These include: hazardous minerals, valuable minerals, selection of the blasting techniques, geological structures, blasting direction, and blasting geometry. Section three overlaps with the geometric design section and deals with aspects related to explosives. Topics addressed include selecting the explosive type based on geology, distribution of explosive charge in space and time, explosive performance, and the rock response to explosive loading. In the fourth section, examples are given of the operational complexity needed to implement a blast to cater for difficult bench geologies, environment constraints, past mining (voids) and need for a high degree of quality control. Section five demonstrates geological controls on blast results. Blasting results include the muck pile characteristics, downstream handling and processing, damage to the remaining rock, and blasting emissions.

Nov 8, 2011

By M Wortley, J Korteniemi, D La Rosa, L Rajavuori

Geometallurgical modelling of an orebody provides benefits to a mine by gaining a better understanding of the ore characteristics and how they affect the performance of the concentrator. With this knowledge, plant operating conditions can be adjusted to optimise throughput and recovery in advance of the arrival of particular ore types. Therefore, it is extremely important that the origin of the ore being processed is known as accurately as possible. Depending on the homogeneity of the ore characteristics, reliance on assumptions about stockpile residence times, scheduling and material handling can render the best geometallurgical models useless.The solution adopted at Agnico Eagle’s Kittilä mine was to utilise Metso SmartTags™ and in-house expertise to develop a system that continuously and accurately links geotechnical and lab data from the mine to the performance of the plant. This application presented several unique opportunities and challenges. For example, this was the first installation of a SmartTag™ system for geometallurgical modelling in an underground mine. Challenges included the fact that the system installation is routinely subjected to temperatures below -20°C.The system was installed and commissioned in early 2013 and has been operating continuously since. Kittilä has begun to see the benefits of the system, with an increased understanding of how different ores are processed in the concentrator. Other advantages include the ability to alert operators about the arrival of difficult ores and a better understanding of the ore handling systems.This paper describes the installation and use of the system at Kittilä and details some of the geometallurgical relationships that have been developed using the data collected so far.CITATION:La Rosa, D, Rajavuori, L, Korteniemi, J and Wortley, M, 2014. Geometallurgical modelling and ore tracking at Kittilä Mine, in Proceedings Orebody Modelling and Strategic Mine Planning Symposium 2014 , pp 291–298 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Nov 24, 2014

By C M. Rebagliati, J G. Payne, K Roberts

The Pebble deposit, located in south-west Alaska, is one of the largest Copper- Gold-Molybdenum (Cu-Au-Mo) porphyry systems in the world, with a current resource of >8 billion tonnes which contain 73.7 billion pounds of copper, 87.1 million ounces of gold and 4.16 billion pounds of molybdenum. The Pebble deposit formed at ~90 Ma, during emplacement of subduction-related hornblende granodiorite porphyry intrusions emplaced into Jurassic-Cretaceous sedimentary, volcanic and subvolcanic intrusive rocks of the Kahiltna Terrane. The Pebble West and Pebble East Zones represent two thermal and fluid centres in a single large magmatic-hydrothermal system. The West Zone extends from surface to about 500 m depth, has thin zones of oxide and supergene mineralisation overlying hypogene chalcopyrite mineralisation, and is amenable to open pit extraction. The East Zone extends to at least 1700 m depth, is higher grade, occurs beneath an eastward-thickening cover of younger sedimentary and volcanic rocks, lacks oxide and supergene mineralisation, and is being evaluated for underground block-cave mining. Most Cu-Au-Mo was introduced with early K-silicate alteration and related quartz-sulfide veins. In the East Zone, a structurally-controlled overprint by advanced argillic alteration significantly increased Au and, to a lesser extent, Cu grades. Exploration potential at Pebble and its surrounding district remains high. Several other porphyry, skarn and epithermal deposits have been discovered in the district, but only limited exploration has been conducted. The eastern, higher grade part of the Pebble deposit remains open in several directions, with significant potential for resource expansion by ongoing, aggressive drill exploration. An EXTENDED ABSTRACT is available for download. A full-length paper was not prepared for this presentation.

Jan 1, 2008