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By M. Menéndez

Enhanced gravity separation appears to be one of the most promising methods for processing all types of <200-µm coal feeds and tailings. Systems based on this technology are reviewed, and the results of investigations based on C900 Multi-Gravity Separator tests conducted to assess the treatment of <200-µm, extremely difficult-to-wash coal settling pond tailings are presented. Multi-Gravity Separator processing tests of ultra-fine tailings with a high clay particle size content (22.6% <10 µm and 60.1% <40 µm) and a 69.56% ash content show that this material can be effectively treated after desliming (<10 µm) of clay-size particles to produce a coal with a 20.6% ash at a separator combustible material recovery of 69.3%. Desliming is shown to be critical in reducing coal ash content and combustible material recovery. Similar improvements are anticipated in the recovery and separation pro-cesses for other enhanced gravity separation systems from the desliming of feeds. Although not a conventional form of treating Multi-Gravity Separator data, the existence of well-defined polynomial relationships based on the product of drum shake amplitude and shake frequency relative to product coal recovery, product ash content and yields at varying wash water flows is demonstrated. Low-amplitude and intermediate- to high-frequency bed agitation are shown to produce optimum ash reduction results.

Jan 1, 2007

By A. T. Iannacchione

From 1990 to 1996, 16 states reported 92 injuries from falls of roof, rib or face in the more than 90 underground stone mines in the United States (Fig.1). Missouri, Pennsylvania and Kentucky accounted for 48% of the total number of injuries (Fig. 2). Of this total, 11 miners were killed. Of the 11 fatalities, 10, or 91%, were associated with unrecognized loose or failed rock within the roof beam. Additionally, unrecognized roof beam failures resulted in a majority of the falls of ground injuries occurring in underground US stone mines from1990 to 1996. This number is not large in magnitude. But a workforce of fewer than 2,000 miners makes for a high fatal-accident rate. The severity of the typical fall-of-ground injury is, in general, very high. About three-fifths of all roof, face and rib fall injuries were designated by the US Mine Safety and Health Administration (MSHA) as some kind of lost time accident. MSHA assigns each accident a severity value from one to six. A one represents a fatality, a two, a permanent disability and three, a lost time accident (Fig. 3).

Jan 1, 2000

By P. C. Holloway

La Oroya zinc ferrite (19.5% Zn, 26.6% Fe, 0.052% Ga, 0.075% In) was roasted with coal under conditions more oxidizing than normally used in a Waelz kiln, and the roasted residues were leached with 200 g/L H2SO4. Overall zinc recoveries of up to 97% were achieved, with 35% of the zinc reporting to the fume after roasting at 1,100°C with a bituminous coal addition of 20%. Under these conditions, 93.2% of the Cd, 13.4% of the Cu, 33% of the Ga, 61% of the In and 18.2% of the Pb were recovered either in the fume or in the leach solution. At 2006 metal prices, the value of the recovered metals is comparable to that obtained from commercial Waelz kiln processing of this residue. Zinc in the franklinite (ZnFe2O4) mineral is reduced to zinc vapor, and, after oxidation, some of the zinc is found as ZnO or as Zn2SiO4 in the roasted residue. Iron reacts to form either hematite (Fe2O3) or magnetite (Fe3O4), with no metallic iron detected in the roasted residue, and less than 2% of the iron is solubilized during leaching. The residue produced after roasting and leaching is, therefore, much more stable than the residue from Waelz kiln processing and should be suitable for disposal in a landfill.

Jan 1, 2008

By Hassan Madani

Kushk lead-zinc mine is located in central part of IRAN. The mine is owned by Bafgh Mines Co., which is a nationalized company. Exploration results show that ore occurs in the area that extends for 800m length and 180m depth. The approved, probable and possible reserves of the mine is 900,000 tons, 1,120,000, tons and 1,450,000 tons respectively with average grade of 17.7% zinc and 4.3% lead. The total annual output of the mine all was by underground mining, is in the order of 100. 000 tons. The main entry to the mine is via an inclined shaft with a cross-sectional arp of 8 m2, length of 263m which dips at 20°. The ore is mined mostly by sublevel stopinq method. The major difficulty in ventilating the mine was that related to spontaneous combustion of pyrite, which was more serious in some parts of the mine than others. In order to reduce this risk, a new ventilation system for the mine was designed, using 4 exhusting fans.

Jan 1, 1991

By Jon J. Indall

I. INTRODUCTION The challenge of moving the use of nuclear energy from military to civilian use was first issued by President Dwight Eisenhower in his December 8, 1953 “Atoms for Peace” speech delivered at the United Nations. Eisenhower stated: “The United States knows that if the fearful trend of atomic military build up can be reversed, this greatest of destructive forces can be developed into a great boon, for the benefit of all mankind. * * * * The more important responsibility of this Atomic Energy Agency would be to devise methods whereby this fissionable material would be allocated to serve the peaceful pursuits of mankind. Experts would be mobilized to apply atomic energy to the needs of agriculture, medicine, and other peaceful activities. A special purpose would be to provide abundant electrical energy in the power-starved areas of the world. In the 1950’s and 1960’s, the Atomic Energy Commission promoted the use of nuclear power as the answer to our nation’s energy problems. Nuclear power would provide energy too cheap to meter. The utility industry responded and numerous plants were planned with over one hundred constructed from the 1970’s to the 1990’s. Capital costs for nuclear power plants escalated due to permitting changes and public opposition, and the Three Mile Island incident caused new nuclear plant construction to cease. Today, we once again are experiencing a nuclear renaissance. Concerns over global warming and rapid projected increases in the demand for electricity have caused many nations to begin construction of new nuclear fleets. The price of uranium to fuel these reactors, which had dropped to an historical low of $7.10 in 2001, has surged to $56.00 as of October 2006. This paper will review some of the social, environmental, and government issues that are all playing a role in the resurgence of the nuclear fuel industry.

Jan 1, 2007

By Kevin Andrews, Terry Hamric, Scott Nelson

"Mining conditions in underground coal mines are dictated by the environment in which the coal seams were geologically deposited. Depositional features can change rapidly, significantly affecting mining conditions. Mine geologists understand factors affecting mining conditions, predict future conditions, and provide guidance to mine management. A case study demonstrates how a mine in Appalachia merged an understanding of depositional environments with mining conditions and drilling data to make informed decisions as the mine encountered geologic anomalies. The assessment included drilling, mapping of geologic hazards and mine productivity, and creation of a conceptual depositional model. Metallurgical coal quality and clean tons per foot served as incentives for continued advance. Mining in the south was historically favorable, with good production and advance rates. As mining advanced north, changing geologic conditions caused the upper seam split to abruptly disappear. The mine ramped down into the lower seam split. Mining in the north area encountered unfavorable conditions, including transition roof, “horsebacks,” sandstone intrusions, roof rolls, and bony floor, resulting in low rates of mining advance. The mine geologist characterized the features and created a predictive model for future mining. Most of the adverse conditions were attributed to the coal in the north being part of an incised, transgressive valley fill environment, as compared to the favorable conditions in the south resulting from a floodplain depositional environment. Geologic conditions, low productivity, and unfavorable future predicted conditions in the north ultimately resulted in mine closure and reallocation of resources to a new mine with better forecasted conditions.INTRODUCTIONThe role of a geologist in assisting coal mining operations to understand and predict the impact of varying geological factors on mining productivity is a critical one, especially when management decisions must be made about the future prospects of a mine operating in difficult conditions. Chase, Newman, and Rusnak (2006) provide a very thorough discussion of the evolution of the role of the coal mine geologist and emphasizes the importance of understanding geology with regard to mine management decisions. Using actual mining performance data to determine which geologic factors are the most critical for mining is a powerful tool for making informed mine management decisions. For example, Nelson, Mullennex, and Miller (1988) provide a case study of analyzing the geologic factors impacting productivity of a Kentucky longwall mine to predict future mining conditions for the operation. In that case, the difficult geologic factors for longwall mining were prevalent across much of the remaining permit area and, in response, mine management converted the operation from a longwall operation to a continuous miner (CM) operation to better adapt to the geology. In another example, Keim and Miller (1999) evaluated geologic conditions impacting a West Virginia longwall mine. In both examples, significant geotechnical and geological information was available, including the opportunity to compare predicted mining conditions against actual conditions as mining progressed. Numerous examples of advanced Geologic Hazard Mapping (GHM) methodologies have come from government agencies and academia. For example, development of the Coal Mine Roof Rating (CMRR) system (Molinda and Mark, 1994) provided a standard means for geologists and engineers to communicate quantitatively with regard to mine roof conditions, and the introduction of the Stability Mapping System (SMS) provided an efficient means for analyzing numerous factors affecting coal mine stability (Wang and Heasley, 2005)."

Jan 1, 2019

By J. Garretson

When mining accidents occur, workers often become trapped and/or incapacitated. Current rescue operations can be dangerous and too slow to produce favorable outcomes. Currently, no method exists for rescue crews to scout ahead at critical times to assess the situation. Sandia National Laboratories (SNL), through a National Institute for Occupational Safety and Health (NIOSH) sponsored program has developed the Gemini-Scout mine rescue platform. The Gemini-Scout was created to assist in underground mine rescue missions. It has been designed to go into potentially hazardous environments to assess the conditions (structural, air quality, temperature). In addition, it will enable two-way communications with potential survivors prior to human rescue teams being able to enter the area. The Gemini platform is a dual tracked-chassis design, which gives the robot excellent mobility in unstructured environments. The design includes a passive 2-degree of freedom joint between two identical bodies allowing for ±30deg of pitch and roll. In addition to the base mobility platform, the Gemini-Scout incorporates many other features to help it succeed in its underground mission. The electronics are mounted in explosion proof housings to ensure safe operations in hazardous gas environments. The platform is also able to operate in up to 18in of standing water with its elevated pan/tilt cameras for navigation. A four-channel video link and Two-way audio on the vehicle help to ensure located survivors can communicate with the robot operators. The platform also incorporates a Mine Safety and Health Administration (MSHA) approved multi-gas sensor to monitor air quality. SNL believes that this technology is broad enough to be appealing to other first responders, such as police, firefighters and medical personnel. Gemini could easily be fitted to handle earthquake and fire scenarios, and it could provide relief in currently inaccessible situations.

Jan 1, 2012

By T. Seal

Hydro-Jex© releaching was undertaken during the summer of 2010 at the Valley Leach Facility (VLF) at AngloGold Ashanti?s Cripple Creek & Victor Gold Mine. Several advancements to the technique were made in response to the technical design and operational challenges posed by the unique site conditions. New geophysical resistivity monitoring techniques were developed to monitor solution migration during the injections. These developments are presented along with discussion of gold production resulting from the project.

Jan 1, 2011

By Tim O’Neil

Caterpillar has introduced its 5090B front shovel, to work with 40 to 70 st (36 to 63 t) trucks. The new unit replaces Cat’s 5080 hydraulic excavator. The 5090B offers more engine horsepower, higher flow, greater digging forces, higher swing torque, faster swing speed and more drawbar pull than its predecessor. It can also handle larger bucket sizes than the previous model. These improvements enhance productivity and make the 5090B a high-volume material handler for hard rock and aggregates producers.

Jan 1, 2003

In the dimension stone industry, workers in processing shops may be exposed to harmful levels of respirable silica dust when conducting the different tasks in stone preparation, which include cutting, grinding, polishing, and thermaling. To protect workers from this health hazard, operators sometimes ventilate processing shops using fan-powered dust collectors to capture and filter dust. To investigate this issue, NIOSH, Pittsburgh Research Laboratory, in cooperation with a dimension stone operation, upgraded an off-the-shelf dust collector the operator was utilizing in a polishing/cutting shop. Initial dust surveys showed that the unit was under-designed for the amount of dust being generated in the shop. The objective of the research was to cost-effectively increase the air cleaning volume and improve dust capture efficiency of the unit with a larger motor and blower. The unit?s original stock 0.56 kw motor and blower was replaced with a 2.24 kw motor and matching blower to increase airflow. The unit was evaluated both in the laboratory and the shop before and after the retrofit to determine the improvement of the upgrade. The study showed that the 2.24 kw upgrade improved the performance over the original 0.56 kw motor resulting in more dust being cleaned from the ambient air in the shop. The 2.24 kw unit cleaned 19% more air and captured 32% more respirable dust than the 0.56 kw unit.

Jan 1, 2009

By Geoffrey Hughes

The Narragansett Bay Commission (NBC) is a regional sewer authority that serves ten communities in the Providence, Rhode Island metropolitan area. From 1992 to 1999, the NBC developed a comprehensive facilities plan to abate Combined Sewer Overflow (CSO) pollution in the Upper Narragansett Bay. The plan underwent many major evolutions during this period, most notably the addition of a stakeholder?s process by which NBC demonstrated a site-specific plan to control the pollutants and meet water quality standards. The favored solution consisted of deep tunnel storage with treatment at existing wastewater facilities that had been recently upgraded. In 1999, a final plan was accepted which included two tunnels, five CSO interceptors, twelve sewer separation projects, a wetland facility, and a wastewater treatment facility upgrade. The program is to be constructed over 20 years in three sequential phases (Figure 1). Phase I of the program includes a 4,963 m (16,284 ft) long, 7.9 m (26 ft) diameter, 70.1 m (230 ft) deep storage tunnel; seven drop shafts with connecting adits; ancillary facilities; and a pump station. Construction of Phase I began in 2001 and is expected to be operational by October 2008. This paper focuses on design and construction of the Fields Point Tunnel Pump Station (FPTPS)located at the south end of the main spine tunnel. A189 Ml/day (50 MGD) pump station is required to lift CSO flows from the tunnel to the Fields Point Wastewater Treatment Facility (FPWWTF). The pumps are to be housed in a 35.6 m × 18.6 m ×20.7 m (117 ft × 61 ft × 68 ft), 91.4 m (300 ft) deep cavern excavated in a complex meta-sedimentary rock of the Rhode Island Formation, and connected to the surface by 9.7 m (32 ft) and 3.4 m (11 ft) diameter shafts. Factors which influenced selection of the size, configuration and location of facilities included the preferred arrangement of pumps, critical aspects of site geology, and estimated cost. Technical and value engineering reviews also affected the final design. Following Notice to Proceed (NTP), concerns were raised by the contractor regarding constructability and design. Additional geotechnical investigation and independent engineering review were employed to validate the design assumptions. The cavern was successfully excavated and sup-ported in rock, completed on schedule and within budget in 2005. In 1992 the NBC retained Louis Berger Group (LBG) as Program Manager (PM) for the CSO Abatement Program. LBG thereafter formed a design team including: Jacobs Engineering Group(JEG) as the designer for underground structures and near surface collection facilities; Black and Veatch(B&V) to design the pumping system and associated facilities; Haley and Aldrich (H&A) to oversee the geotechnical program; and Malcolm Pirnie to design the system-wide instrumentation and control system. Construction management, resident engineering, and inspection services were provided by the joint venture Gilbane/Jacobs Associates (G/J).

Jan 1, 2008

By W. S. Fyfe, G. Southam, T. J. Beveridge

Sporosarcina ureae was able to grow in the presence of tip to 10-ppm L-asparagine complexed gold. However, 10 ppm Au3+ was found to be highly toxic to Sporosarcina ureae, killing 109 bacteria/mL within a few seconds. To compare the effects of these responses on gold mobility, an in vitro bacterial biofilm model was developed to examine the interaction be¬tween Sporosarcina ureae and ionic gold or L-asparagine gold complexes in gravity fed columns. The immobilization of ionic gold was between 80% and 90% over a period of one week. But, as the available cellular reactive sites became saturated, immobilization decreased to 14% within two weeks. In the L¬asparagine-gold system, gold immobilization in the cytoplasm occurred at a high rate (80% to 90%) throughout the experi¬ment, with limited toxicity towards Sporosarcina ureae. The bacterial immobilization and detoxification of L-asparagine¬complexed ionic gold was associated with a low molecular weight, i.e, <5,000 dalton (atomic mass unit), intracellular protein fraction. This peptide-complexed gold would allow for the continued biogeochemical cycling of gold under ambient (<100°C) surface or near-surface conditions.

Jan 1, 2000

By J. Kang

To obtain microbial cultures with the ability to efficiently leach copper ion from chalcopyrite, microbial samples from acid mine drainage sites were mixed and then subjected to mutation using sodium nitrite (NaNO2), diethyl sulfate (DES), ultraviolet light (UV) and their combinations. Mixed cultures with a much stronger ability to leach copper ion (identified as mixed cultures A, B, C, D and E) were obtained by screening on leaching media. Leaching tests showed that mixed culture E had the best leaching performance and increased the Cu2+ content by 120.5% in 20 days, compared to a control without mutation treatment. Mixed culture E grows well on Leathen leaching medium supplemented with Cu2+ (at a final concentration of 32 g/L), reaching 3.2 × 107 cells/L after 15 days, while the unmutated control culture cannot survive beyond 15 days, indicating that mixed culture E is more tolerant of high concentrations of Cu2+. In addition, continuous leaching by mixed culture E is very effective at a pulp density of 1%. These results suggest that it has the potential for industrial applications.

Jan 1, 2008

By Dr. Peter J. Conroy

The current study is part of the U.S. Department of Energy&apos;s (DOE) on-going subsidence research program. The long-term objective of the DOE program is to develop analytical methods of subsidence prediction applicable over a broad range of geologic and mining conditions encountered in the United States. The DOE currently has several contracts in progress to develop a sound data base that can be used in the development of predictive models. Dames & Moore is currently under contract to the DOE to collect and analyze detailed subsidence and hydrologic data from a coal mine employing longwall mining methods in the Eastern Coal Province. Work under Contract No. DE-AC22-80PC 30335 began in October of 1980 and will continue through September of 1984. This paper summarizes the work that has been completed through September of 1981 and presents the results that have been achieved during this period. Technical difficulties encountered during both the installation and monitoring phases are discussed, and recommendations for future work are presented.

Jan 1, 1982

By Jon Y. Kaneshiro, Gregory E. Korbin, Stephen J. Navin, Larry J. Stout

Sewage presently being discharged into the Tijuana River Valley pollutes the valley as well as the beaches in the South Bay of San Diego, making the beaches unusable nearly year round. The SBTO will convey flows down a 8.5 m (28 ft.) by 58 m (190 ft.) deep drop shaft, through a 3.35 m (11 ft.) by 5.8 km (3.6 mile) long tunnel, and up a 46 m by 2.7 m (150 ft. by 9 ft.) riser shaft connecting to a 1.5 km (0.95 mile) of seafloor pipeline and 1.2 km (0.76 mile) of diffusers on the ocean floor. The drop shaft will be sunk through 38 m (125 ft.) of saturated sands and gravels and 20 m (65 ft.) into the dense fine sands of the San Diego Formation. The tunnel liner has been designed as a five piece, single pass, gasketed, bolted, reinforced concrete liner designed to withstand an external head of 76 m (250 ft.) of water and internal operating head of up to 27 m (89 ft.) and to accommodate movement at the numerous fault crossings. The tunnel is contemplated to be driven with a state-of-the-art Earth Pressure Balance Machine (EPBM) or slurry shield machine through a wide range of conditions from clay to gravel with boulders.

Jan 1, 1995

By W. Lin, M. J. McPherson

When a large area of open gob collapses suddenly, a windblast is produced that can cause considerable damage throughout the infrastructure of a mine. In a few cases, the windblast has been accompanied by ignitions of methane and/or coal dust. This paper describes the conduct and results of laboratory tests involving the compression of mixtures of air, methane and coal dust under a falling weight and while allowing controlled escape of the mixture. The transient responses on pressure and temperature sensors were recorded. In addition to an analysis of those records, the paper highlights those conditions in which ignitions occurred.

Feb 24, 1997

By J. Noll, D. Yantek, B. Kendall, J. A. Organiscak

"A self-tramming remotely controlled mobile Dry Scrubber (DS) was developed by J. H. Fletcher and Co. under a contract with the National Institute for Occupational Safety and Health’s Office of Mine Safety and Health Research (NIOSH OMSHR) to reduce exposure of miners to airborne dust. NIOSH OMSHR laboratory testing showed that the DS averaged greater than 95% dust removal efficiency with the disposable filters and averaged 88% and 90%, respectively, for the optional washable filters in their pre-washed and post-washed test conditions. Although the washable filters could be reused, washing them generated personal and downstream respirable dust concentrations of 1.2 and 8.3 mg/m3, respectively, for a 10-minute washing period. The DS’s velocity pressure regulated variable frequency drive (VFD) fan maintained a relatively consistent airflow near the targeted 1.43 and 4.25 m3/s (3000 and 9000 ft3/min) airflow rates during most of the laboratory dust testing until reaching its maximum 60 Hz fan motor frequency or horsepower rating at 2610 Pa (10.5 in. w.g.) of filter differential pressure and 3.97 m3/s (8420 ft3/min) of scrubber airflow quantity. Laboratory sound level measurements of the DS also showed that the outlet side of the scrubber was noisier and the loaded filters increased sound levels as compared to clean filters at the same airflow quantities. With loaded filters the scrubber reached a 90 dB(A) sound level at 2.83 m3/s (6000 ft3/min) of scrubber airflow, indicating that miners should not be overexposed in relation to MSHA’s permissible exposure level (PEL) of 90 dB(A) at or below this airflow quantity (1). The DS’s washable filters were not used during field testing because of their lower respirable dust removal efficiency and the airborne dust generated from filter washing. Field testing the DS with the disposable filters at two underground coal mine sections showed that it can clean a portion of the section return air and provide about a 50% dust reduction at the face area downstream of the continuous miner (CM) operation. INTRODUCTION Coal mine worker overexposure to coal and quartz dust continues to be a problem at underground coal mining operations in the U.S. The U.S. Mine Safety and Health Administration (MSHA) recently changed the standard for coal mine worker respirable dust exposure from 2.0 mg/m3 average during an eight-hour shift to 1.5 mg/m3 average over the actual working shift, effective as of August 1, 2016 (1). If more than 0.1 mg/m3 quartz mass is found in the coal mine worker dust sample, the applicable respirable dust standard is further reduced to the quotient of 10 divided by the percentage of the quartz in the sample (1). Over 90% of the mechanized mining units operating in U.S. underground coal mines are continuous mining machines (2). MSHA inspector dust samples from 2009 to 2012 showed that 3.7% of continuous miner operators exceeded the 2.0 mg/m3 dust standard, while 8.8% of these dust samples exceeded the new 1.5 mg/m3 dust standard and 9.7% of these samples exceeded the reduced quartz standard (3). Additionally, roof bolter dust samples at these mechanized mining units during this same period have exceeded the 2.0 mg/m3, 1.5 mg/m3, and reduced quartz levels at 1.1%, 3.7%, and 10.6%, respectively (3)."

Jan 1, 2016

By R. P. Killmeyer, W. W. Wen, B. K. Parekh

A continuous pilot-scale test of the GranuFlow Process was conducted using a screen-bowl centrifuge for the dewatering and reconstitution of column -flotation concentrate at a coal preparation plant in Virginia. In this test, a slipstream of the fine clean-coal slurry from the column flotation con¬centrate was treated with a bitumen emulsion before dewatering. The treated products from the screen-bowl centrifuge appeared to be dry and in a free flowing granularform, while the untreated products were wet, sticky and difficult to handle. Test results indicated that the average moisture contents of the dewatered coal products were 35.7%, 35.5%, 32.6%, 29.9% and 26.5% (by weight) with Orimulsion additions of 0.0%, 0.7%, 3.2%, 4.8% and 6.4% (by weight), respectively. The handleability and dust reduction of the dewatered coal products were also vastly improved.

Jan 1, 2000

By J. T. Hollow

The Fort Knox Mine is located in Alaska?s interior, where the average ambient air temperatures range from -24°C (-11°F) in January to 16°C (61°F) in July. The mill processes a free-milling gold ore utilizing both a gravity recovery circuit and conventional cyanide leach/carbon-in-pulp circuits. Mathematical models have been developed to accurately predict the impact of leach circuit slurry temperature on gold leaching, carbon adsorption and cyanide destruction kinetics. Additionally, an energy-balance approach has been used to model the seasonal variations in slurry temperatures throughout the Fort Knox mill. The energy-balance model, combined with the kinetics models previously developed to predict plant performance, was used to justify a tailing thickener installation at the Fort Knox Mine. This paper describes the development of the energy-balance model and its prediction of plant performance assuming a tailings wash thickener to reduce heat loss from the mill. Also presented is an analysis of the post-project plant performance that validates the model and shows that the mine produced an additional 596 kg (19,155 oz) of gold while reducing mill reagent costs by $6,302,000 during the first 38 months of operation.

Jan 1, 2007

By G. Deschênes

Following a successful investigation on the Central Zone sample, a cyanidation study was conducted on an ore sample from the AD-MW Zone of Clarence Stream Property, owned by Freewest Resources Canada, to develop a leaching strategy to extract gold. At a grade of 6.48 g/t, gold is present in the forms of aurostibite, free gold and electrum. The ore contains 4.3% berthierite/gudmundite, 1.3% pyrrhotite, 0.7% pyrite, 0.07% stibnite and 0.9% arsenopyrite. Similar to the Central Zone, the extraction of gold from the AD-MW Zone can be performed at atmospheric pressure, pH 10.5 and with a low concentration of cyanide. The grind size had no effect on gold extraction between a P80 of 28 to 71 µm. The oxygen and cyanide requirement significantly increased with a ?ner grind. Consequently, a very close control of cyanide addition is required to minimize passivation of gold. Lead nitrate, added in the pretreatment, increased the extraction of gold by 2.3%. Leaching at pH < 10 improved gold extraction but increased the cyanide consumption by 5%. Passivation of gold occurred when the pretreatment was longer than 2 hours. A longer pretreatment reduced the cyanide consumption by 5%. Mineralogical characterization of the leach residue with no gravity pretreatment prior to leaching indicated the presence of unleached gold grains and passivated gold grains. Removal of coarse gold by gravity increased the extraction by 2.8% (leach residue at 0.74 g/t Au). Increasing the DO to 16 ppm or the lead nitrate from 500 to 1,000 g/t increased the overall gold extraction to 90.4% (leach residue at 0.62 g/t), which is the maximum gold extraction obtained. The leaching parameters were 800 ppm NaCN, DO 16 ppm and pH 10.5 for a duration of 120 hours. The associated cyanide consumption was 4.0 kg/t. Gold leaching was not sensitive to cyanide concentration. Reducing the cyanide concentration to 250 ppm resulted in a gold extraction of 89.5% with a cyanide consumption of 2.6 kg/t.

Jan 1, 2009