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By Laxman M. Amaratunga, Nuri Hrnidi

"Reactive pyrrhotite tailings were agglomerated using the Cold Bond Tailings Agglomeration (CBTA) process with low cost binders; Portland Cement and fly ash. Various chemical additives, were used to retard acid mine drainage (AMD), including acid neutralizers, surfactants, sealants, and bactericides, which were encapsulated into the agglomerates. The choice of these additives was based on their low cost, low toxicity, and environmental friendliness. The main objective of the study was to examine the long term stability of these reactive tailings agglomerates towards AMD when used as aggregates for disposal in underground paste backfill.A carefully controlled kinetic stability test was carried out using specially designed humidity cells suitable for testing pellets. Using the humidity cell test method a 20-30 year AMD test may be accelerated to 50 weeks. During this period the following parameters were monitored: pH, redox potential, conductivity, sulphate, acidity, and dissolved metals.Results indicated that most of the encapsulated additives were successful in retarding AMD, while the control samples produced significant amounts of acid generation. The water soluble surfactant Enviroseal, and the sodium silicate sealant were very effective as a long term retardant for acid generation reactions in the sulphidic tailings when exposed to oxygen, water and iron-oxidizing bacteria.IntroductionThe sulphidic material discharged from concentrators becomes reactive upon exposure to air and/or water. Pyrrhotite (Fe0 S0_1) and pyrite tailings in particular which are discharged from the beneficiation process in the mining and mineral processing activities consist of finely ground particles. Upon exposure to oxygen and moisture, the tailings become reactive due to the instability of the metal sulphide minerals present which undergo spontaneous oxidation, thereby producing a weak sulphuric acid. Therefore, the long-term behaviour of the tailings can have a significant impact on the environment, due to acid mine drainage (AMD). AMD is created during natural atmospheric weathering when leaching action (natural and bacterial) conditions are present in the process wastes discarded during the mining and milling of sulphur bearing ores, and consequently it plays a major role in surface water chemistry."

Jan 1, 1998

By T. P. Meloy

In a recent paper, Gaudin and Meloy1 derived a size distribution function for single, impact fracture. Mular2 extended the use of this size distribution to describe the output of carefully controlled grinding experiments. As it stands, the function is difficult to compute. Consequently, a series of tables of the function are presented below: where M(x) is the cumulative fraction finer than size x when x is particle size. Weight percents are tabulated for the single parameter, r, in three different size ranges: from 0 to 1, from 1 to 10 and from 10 to 100. Tables I, II and III are cumulative percent finer and Tables IV, V and VI are for weight percent passing screen size x, retained on the screen below. A number of conditions from the table are plotted in Figs. 1 and 2. Fig. 1 is a plot of the cumulative percent finer vs. size, and Fig. 2 is the weight per-

Jan 1, 1963

By J. L. Blaylock

Normally, the hydraulic system and structures are considered to be unrelated items. In reality, the two cannot be separated because one affects and depends on the other to function properly. This paper explores the potential failure areas of hydraulic cylinders, and suggests possible methods to prevent failures from occurring. The use of high-strength low-alloy steel in frames is reviewed and the benefits discussed. Fabrication techniques and handling of material are noted in the hope that this knowledge will aid in the repair of frames in the field.

Jan 1, 1979

By J. S. Kennedy, R. G. Omeara

Beryllium is a strategic metal of ever-increasing peacetime importance because of the unusual properties of beryllium-copper alloys. These unusual characteristics are the combination of high strength and hardness, high fatigue resistance, and high wear resistance in alloys that have the corrosion resistance of copper. The principal industrial source of beryllium is the mineral beryl, a beryllium-aluminum silicate that occurs in pegmatites associated with quartz, feldspar, mica, and smaller amounts of various accessory minerals. The beryl is usually recovered in processing the pegmatites for the recovery of some of the other mineral constituents. Pegmatite deposits are found in various parts of the United States, but those in the Black Hills of South Dakota are the source of most of domestic production. The beryl marketed from the South Dakota pegmatite deposits occurs as coarse crystals, which are obtained by hand sorting. These pegmatites also contain other valuable minerals.

Jan 1, 1948

By Y. Wang

Wet magnetic separation methods for recovering hematite and chromite fines and ultrafines are investigated in this paper. These methods include wet high intensity and high gradient magnetic separations, carrier or "piggy-back" magnetic method, magnetic field-induced aggregation and magnetic seeding. This investigation indicates that wet magnetic separation is more efficient for fines and ultrafines whereas other methods can be used to enhance the particle aggregation and/or the magnetic response. The magnetic behaviour of these minerals with respect to magnetizing field, particle size and temperature is also presented.

Jan 1, 1993

By James R. Evans

Forecasting demand is an art as well as a science, and much personal judgment is required. National forecasts made for sand and gravel, crushed stone, and/or aggregate may be misleading or unhelpful locally. This is because of significant variation in demand within different geographic and/or political areas in the US, and/or the use of an inadequate data base and forecasting methodology. The best forecasts may be made for local or regional market areas, irrespective of geographic or political boundaries, provided a proper data base is available.1 The Bureau of Mines compiles detailed statistics on commodities sold or used in the construction industries and, therefore, is in an advantageous position to make national aggregate demand forecasts.

Jan 1, 1979

By Achille Balossi Restelli, Elena Rovetto, Andrea Pettinaroli

"The Station “C13” of Warsaw Underground Line II, with tunnel crown 10m below the water table, required the excavation of three connection tunnels, underpassing a six-lane in service road tunnel, working from two lateral shafts. After the collapse occurred while digging the first tunnel, the use of artificial ground freezing was chosen to ensure the excavation under safe conditions. A complex freezing pipe geometry and excavation sequencing was necessary because of the interferences of the overlying road tunnel diaphragm wall foundations, shaft internal structures and previous grouting activities. A combined freezing method was used: nitrogen for freezing the tunnel arches, brine for freezing the intermediate wall and for maintenance stages. Sandy and silty sandy layers were frozen around the crowns and sides. No treatment was necessary for the inverts, lying in clay. A monitoring system of ground temperatures and structure movements allowed for successful completion of work in 8 months. INTRODUCTION The C13 Station of the Warsaw Underground-Line II is located on the West bank of the Vistula River. It consists of two shafts and three connecting tunnels, passing under the Wislostrada (WS) Road tunnel. According to the initial geotechnical investigation, tunnels should have been excavated in high-plasticity clay, but during the first borings non cohesive soil was encountered. Additional investigations were performed on both shafts and a more detailed stratigraphy was reconstructed (Lombardi et al. 2015). Layers of fine sand, sandy silt and sandy silty clay were present along the tunnels crown arches and in the North East tunnel they extended down to the centre line (-13.735m above the Vistula River medium level). Based on the new stratigraphy, it was decided to stabilize the crown and control the groundwater inflow from the face with jet-grouting columns extending the treatment down to the clayey soil, but a collapse occurred in the North West tunnel with soil and water inflow inside the shaft."

Jan 1, 2016

By R. H. Heinen

Introduction Drilling is the initial operating step In open pit mining. It goes hand-in-hand with the blasting operations to ensure adequately broken material for the excavation equipment employed. The drilling effectiveness is highly dependent on the quality of the drill evaluation. This discussion will center on the parameters that are needed to evaluate drill requirements for a new mine The procedure that is generated can, however, be used to evaluate whether to expand existing operations and replace existing equipment. Methods of breaking ground, other than blasthole drilling and blasting, such as ripping, will not be discussed. The importance of correct drill evaluation extends to the other facets of open pit mining. Inadequate fragmentation, the direct result of poor drilling and blasting techniques, results in oversized, hard digging for the excavating equipment. The result is higher secondary blasting costs, reduced excavation efficiencies, higher excavation costs, higher road repair costs, and higher haulage equipment costs. The main objective of evaluating drill fleet requirements, therefore, is to determine the equipment needed to minimize the operational constraints, caused by blasthole drilling, on other facets of open pit mining at the lowest cash flow costs.

Jan 1, 1979

By D. Harrington

One of the main functions of the United States Bureau of Mines is to obtain and disseminate information that will promote safety in and around mines, and the health and safety of employees engaged in mining. Serious health and safety conditions arising out of contamination of air in metal mines by dust, fumes from explosives and fires, and absorption of oxygen by timber and other causes, led the Bureau of Mines to cooperate with the United States Public Health Service in the study of dust occurrence and ventilation in metal mines in various parts of the country. A. J. Lanza, of the U. S. Public Health Service, and Edwin Higgins, mining engineer of the U. S. Bureau of Mines, in 1915, made a detailed study in the mines around Joplin, Mo.; their reports1 are now available. In 1916, 1917, and 1918, a similar study was made in the Butte, Mont., region by Doctor Lanza and D. Harrington, mining engineer of the Bureau of Mines; the reports of this investigation will be available soon. In 1919, the study was continued in some of the Arizona mines by D. Harrington, of the Bureau of Mines, and G. E. McElroy and R. A. Koronski, of the U. S. Public Health Service, the underground work being completed in June, 1920; these reports are now being prepared for publication. In the spring of 1920, the scope of the work was extended, with D. Harrington in charge as supervising mining engineer, and short studies were made in the mines of the Coeur d' Alenes in Idaho and around Oatman, Ariz. It is hoped soon to extend the work into mines of California, Nevada, Colorado, Michigan, and Minnesota, and ultimately to other states should the mining companies be willing to coöperate. While the coöperation of the mining companies is necessary, the companies are put to practically no expense other than supplying a guide to accompany the investigators underground, the length of time spent

Jan 1, 1922

By B. A. Ridolfi, S. M. Alvarez

The Moon Creek Reclamation Project provides a case study in the development of creative cleanup solutions for an abandoned lead and zinc mine and mill site located in northern Idaho. Innovative design features include construction of a 88,000cubic yard combined waste containment facility on soft in-situ tailings, water-balance cap, limestone gravel drains, a geocell mattress for stability, and a below-grade scour protection berm. The stream, including a wetlands buffer, will be relocated within an existing road alignment and rehabilitated to provide trout habitat. These elements allow for the integration of reclamation and stabilization measures into an effective site design.

Jan 1, 1999

A Novel Diagnosis and Evaluation Procedure for Flotation Plants

Sep 13, 2010

By H. L. Bilhartz, H. F. Dunlap, C. R. Bailey, Ellis Shuler

Data are presented which indicate that the saturation exponent, n, in the equation, R. = R100S-11, relating core resistivity, I:,. to the resistivity at 100 per cent saturation. R100. and to the saturation, S. may vary appreciably from the value of two which is usually assumed for this exponent when interpret ing well logs. Values ranging from one to two and one-half have been found on (.ore sample investigated to date. Attempts to correlate this saturation exponent with porosity or permeability of the core have not been successful. The saturation exponent is apparently not a function of the interfacial tension between the brine and the displacing fluid. Some evidence is given indicating that the resistance of the core is not a unique function of the saturation but depends upon the manner in which this saturation was achieved. Equipment and technique are discussed for measurement of resistivities in core plugs in which water saturation can be varied. lNTRODUCTION A number of investigations of the resistivity-saturation relationship for un-c~~nsolidated sands and consolidated (.ore samples have been reported in the literature. According to most of these: R. = R¹ººS², where R² = the resistivity of a formation at saturation S, and R¹ºº= the resistivity of the formation at 100 per cent water saturation. Much of this work was (lone on unconsolidated sands desaturated by gas or oil. Hen-clerson and Ynster worked exclusively with dynamic systems, flowing oil or gas through consolidated cores. There is some doubt as to how well this reproduces static reservoir conditions. Jakosky and Hopper³ onsidered also the case of consolidated core plugs, but the oil-water distribution in the emulsions which they used to saturate their cores is almost certainly different from that occurring in reservoirs. Recently Guyod quotes the results of some Russian work which indicates that n may vary from 1.7 to 4.3. No experimental details of this work are available. In connection with electric log interpretation it is important to know the value of the saturation exponent. For example, if in a given reservoir it is found that the resistivity is three time.; the resistivity observed when the reservoir is 100 pel. cent 'saturated with water, this fact would be interpreted as indicating a water saturation of 33 per cent if the saturation exponent were 1 and a water saturation of 6-1 per cent if the saturation exponent were 2.5. EXPERIMENTAL METHOD In the work to be described it was assumed that reservoir conditions are most nearly obtained when core plugs are desaturated by the capillary pressure technique referred to in numerous places in the literature, as for example. in Bruce and Welge's paper.' In this technique the core. saturated 100 per cent with brine, is placed in contact with a ceramic disc permeable to brine but not to the displacing medium for the displacement pressures used. Pres-ure is then applied to the displacing medium and brine forced out of the core through the ceramic disc. Fig. 1 shows the core plug in place in the cell in which resistivity and saturation measurements are made. Fig. 2 shows the schematic electrical diagram wed to make resistivity measurements on the core plug. A four-electrode type circuit is used, employing a Hewlett-Packard model 400A. AC vacnum tube voltmeter. The 60-cycle AC current througli the core is adjusted to 1 milliampere and measured by noting the voltage drop across the calibrated 100-ohm resistor. The vo1tages appearing at probes 1, 2, 3, and 4 are then successively measured. Voltage drops across the top, center, and bottom portions of the core are obtained by sublracting the voltages appearing at successive probes. This technique avoids any polarization or other high contact resistance phenomena which may develop at the current input electrodes. Resistances which may develop between the core and the probes, and which are small compared to the 1-megoam input impedance 01' the vacuum tube voltmeter will (obviously not affect the measurements allpreciably. Any very appreciable resistallces which may develop at any of the probe wires are detected and allowed for by inserting a 1-megohm resistor in series with the voltage measuring probe. If the probe resistance is actually zero, the new voltage measured after insertion of the I-megolim resistor will be approximately one-half of that previously measured. since the input impedance of the vacuum tube voltmeter is itself 1 megohm. If an! appreciable probe resistance has developed, the new voltage is found to be appreciably greater than one-half of the previously measured voltage. Such probe resistance; have been found to develop only occasionally and usually can be traced to poor connections betwern the core

Jan 1, 1949

By C. R. Bailey, H. F. Dunlap, Ellis Shuler, H. L. Bilhartz

Data are presented which indicate that the saturation exponent, n, in the equation, R. = R100S-11, relating core resistivity, I:,. to the resistivity at 100 per cent saturation. R100. and to the saturation, S. may vary appreciably from the value of two which is usually assumed for this exponent when interpret ing well logs. Values ranging from one to two and one-half have been found on (.ore sample investigated to date. Attempts to correlate this saturation exponent with porosity or permeability of the core have not been successful. The saturation exponent is apparently not a function of the interfacial tension between the brine and the displacing fluid. Some evidence is given indicating that the resistance of the core is not a unique function of the saturation but depends upon the manner in which this saturation was achieved. Equipment and technique are discussed for measurement of resistivities in core plugs in which water saturation can be varied. lNTRODUCTION A number of investigations of the resistivity-saturation relationship for un-c~~nsolidated sands and consolidated (.ore samples have been reported in the literature. According to most of these: R. = R¹ººS², where R² = the resistivity of a formation at saturation S, and R¹ºº= the resistivity of the formation at 100 per cent water saturation. Much of this work was (lone on unconsolidated sands desaturated by gas or oil. Hen-clerson and Ynster worked exclusively with dynamic systems, flowing oil or gas through consolidated cores. There is some doubt as to how well this reproduces static reservoir conditions. Jakosky and Hopper³ onsidered also the case of consolidated core plugs, but the oil-water distribution in the emulsions which they used to saturate their cores is almost certainly different from that occurring in reservoirs. Recently Guyod quotes the results of some Russian work which indicates that n may vary from 1.7 to 4.3. No experimental details of this work are available. In connection with electric log interpretation it is important to know the value of the saturation exponent. For example, if in a given reservoir it is found that the resistivity is three time.; the resistivity observed when the reservoir is 100 pel. cent 'saturated with water, this fact would be interpreted as indicating a water saturation of 33 per cent if the saturation exponent were 1 and a water saturation of 6-1 per cent if the saturation exponent were 2.5. EXPERIMENTAL METHOD In the work to be described it was assumed that reservoir conditions are most nearly obtained when core plugs are desaturated by the capillary pressure technique referred to in numerous places in the literature, as for example. in Bruce and Welge's paper.' In this technique the core. saturated 100 per cent with brine, is placed in contact with a ceramic disc permeable to brine but not to the displacing medium for the displacement pressures used. Pres-ure is then applied to the displacing medium and brine forced out of the core through the ceramic disc. Fig. 1 shows the core plug in place in the cell in which resistivity and saturation measurements are made. Fig. 2 shows the schematic electrical diagram wed to make resistivity measurements on the core plug. A four-electrode type circuit is used, employing a Hewlett-Packard model 400A. AC vacnum tube voltmeter. The 60-cycle AC current througli the core is adjusted to 1 milliampere and measured by noting the voltage drop across the calibrated 100-ohm resistor. The vo1tages appearing at probes 1, 2, 3, and 4 are then successively measured. Voltage drops across the top, center, and bottom portions of the core are obtained by sublracting the voltages appearing at successive probes. This technique avoids any polarization or other high contact resistance phenomena which may develop at the current input electrodes. Resistances which may develop between the core and the probes, and which are small compared to the 1-megoam input impedance 01' the vacuum tube voltmeter will (obviously not affect the measurements allpreciably. Any very appreciable resistallces which may develop at any of the probe wires are detected and allowed for by inserting a 1-megohm resistor in series with the voltage measuring probe. If the probe resistance is actually zero, the new voltage measured after insertion of the I-megolim resistor will be approximately one-half of that previously measured. since the input impedance of the vacuum tube voltmeter is itself 1 megohm. If an! appreciable probe resistance has developed, the new voltage is found to be appreciably greater than one-half of the previously measured voltage. Such probe resistance; have been found to develop only occasionally and usually can be traced to poor connections betwern the core

Jan 1, 1949

By Di Liu, Yongjun Peng

"It was identified that clay minerals adversely affect fine coal flotation through slime coatings. In the study, it was interesting to find that an anionic polymer dispersant, lignosulfonate, successfully mitigated the negative effect of clay minerals in coal flotation using fresh water, but in saline water, it exacerbated coal flotation.In order to understand the mechanisms underpinning the different behaviour of lignosulfonate in coal flotation using fresh and saline water, the adsorption isotherm, and dynamic light scattering (DLS) measurements were conducted in this study. While DLS monitored the molecular conformation change (swelling or shrinking) of the polymer in fresh and saline water, adsorption isotherms enabled polymer adsorbed amount on clay and coal mineral surfaces to be determined. It was found that lignosulfonate adsorbed on the coal and clay mineral surfaces providing effective electrostatic repulsions and resulting in a mitigation of clay minerals from coal surfaces in deionised water. In the presence of saline water, however, polymer molecular conformation changed. Polymer molecules were compressed and adsorbed in form of aggregates. The adsorption amount of lignosulfonate on clay minerals increased in saline water. A low dosage of lignosulfonate could not provide sufficient electrosteric repulsion to disperse clay minerals. Moreover, the high adsorption amount of the polymer on coal and clay surfaces led to a more hydrophilic coal surface, and coal flotation was therefore depressed in saline water. This study provides a new insight into understanding the role of anionic polymeric dispersants in mineral flotation using different quality water."

Jan 1, 2014

By S. Lee, F. Campero

"Past heap leach design has evaluated hydrodynamic parameters based on a uniform particle size of heap material, but has ignored the equal importance of the instability of fine migration within heap stack in the beginning stages of the irrigation process. The proposed probabilistic model evaluates internal fine erosion and segregation potential of well-graded crushed ores by considering the entire particle size distribution shape and site compaction degree. Using this model, unsaturated flow model parameters were successfully evaluated based on synthesized soil-water characteristic curve (SWCC). Additionally, one-dimensional unsaturated transient flow modeling with Hydrus 1D® showed that the different recovery efficiencies of heap material under unsaturated flow patterns depending on the particle size distribution and compaction degree of heap material. Agglomeration preprocess employed by most heap leach sites can reduce the potential of fine erosion within heap material significantly, but internal stability of crushed ores and hydrodynamic-based analysis of heap material’s pore structure is equally important in the prescreening stage in order to improve efficiency of the heap leach and avoid a costly agglomeration process. INTRODUCTION Accurate estimation of heap leach recovery is a difficult task due to the variety of design parameters that need to be considered - such as geochemistry, hydro-dynamics, and geotechnical design aspects, most notably particle size distribution through the process of agglomeration. After agglomeration techniques were introduced to heap leach design, the influence of particle size distribution and compaction degree in enhanced heap leach recovery has been neglected. The main purpose of agglomeration is to prevent fine segregation and internal erosion during and after heap stacking for well graded crushed ores, which will eventually diminish heap reach recovery. Recent studies show that agglomerated heap materials that had been consolidated at 10 meters below heap surface can release the fines after contact time with lixiviant to the compacted heap material and produce poor drainage performance (Milczarek et al, 2013). It must be noted that engineers and practitioners should investigate feasibility of agglomeration benefit prior to heap leach design because the agglomeration process can incur up to 20 or 30% of project costs. Internal stability of stacked heap material is mainly governed by the particle size distribution of crushed ores. Depending on this stability, segregation and internal erosion of fines can be mitigated by the application of moderate compaction effort during heap construction. Investigation of segregation and internal erosion potential therefore takes precedence for well graded crushed ore since reaction time and contact area with lixivant are greater in finer ores."

Jan 1, 2016

Agenda ?The Context ?The Challenge ?The Solution ?Benefits and lessons learnt from pilots ?Next Steps The Context ?Facilitate management decision making process by supporting the development of value/risk based business cases. ?Large scale investments by extractive industries are expected tobring broad-based benefits to local communities (e.g.: health, education, jobs, infrastructure) ?Investors continue to expect the demonstration of social performance?Specific interventions bring direct value to companies (e.g. skills development) ?Social Investments are key to protecting a company?s license to operate ?Quantifying the value of these investments and planning accordingly, however, has long posed a challenge for the extractive industries and community development practitioners

May 1, 2011

By John MacDonald

An unstable economy has shown businesses what the mining industry has known for decades ? a successful business location today may not succeed in the future. Unexpected expenses, natural events and workforce changes have a big impact on the costs of production. To help focus production and maintenance budgets, mining executives are increasingly turning to production metrics to make key decisions. Role of mine and mill data Companies employ a variety of information systems to allow employees to accomplish their operational tasks, and each worker is focused on the metrics, or key performance indicators (KPI), for his or her individual function. For example, machine operators monitor throughput and cycle time to keep the machines running continuously and to meet daily production quotas. Meanwhile, the maintenance teams monitor machine performance, overall equipment effectiveness (OEE) and meantime between failure to predict and help prevent downtime.

Jan 1, 2013

By Joseph Licavoli, Paul Sanders, Yang Yang

"Al-Sc-Zr alloys form thermally stable L12 precipitates which provide high temperature strength. Although the overall fraction of L12 Al3Sc and Al3Zr may be increased by increasing scandium (Sc) and zirconium (Zr) content, such additions may increase primary phase fractions and do not produce desirable secondary phase morphologies. Rapid solidification techniques, such as melt spinning, increase solute atom concentration within the matrix. When the supersaturated matrix is aged, higher precipitate volume fractions at low Sc and Zr levels can be achieved improving high temperature strength. Melt spinning was used to rapidly solidify (107 k/s) a thin ribbon of Al-0.5Sc-0.4Zr at. %. The ribbon was compacted and extruded into 99.8% dense rods, and then aged using multi-step isochronal heat treatment up to 600°C. Precipitation strengthening was evaluated by ambient hardness measurement. The ambient hardness of melt-spun ribbon after precipitation hardening increased by 450 MPa (~67% increment) during isochronal heat treatment.INTRODUCTION Small Sc and Zr additions to aluminum improve strength and creep resistance above 300°C due to tri-aluminide precipitation of Al3(Sc,Zr) in L12 structures similar to ??, Ni3(Al,Ti) in nickel superalloy, but the Al3(Sc,Zr) particles have a Sc-rich core surrounded by Zr-rich shell (Figure 1). The Al3Zr shell limits atomic transport between the Al3Sc core and the matrix and reduces coherency strain. These factors reduce precipitate coarsening rate at elevated temperature (Bergner & Van Chi, 1977; Fujikawa, 1997; Knipling et al., 2011; Clouet et al., 2006).Figure 1. Simplified schematic model of precipitate Al(Sc,Zr) in Al-Sc-Zr alloy. Shell is rich of Al(Zr) intermetallic phase, particle core is rich of Al(Sc) intermetallic phase (after Voorhees, 2006). Numerous Al3(Sc,Zr) particles increase alloy strength and creep resistance as the precipitates impede dislocation glide and to a lesser extent climb. Previous work on ternary Al-Sc-Zr alloys show large strength increases versus binary Al-Sc, and Al-Zr alloys in Table 1."

Jan 1, 2018

By P Cleary, G K. Robinson, J Hilton, P Wilson

Concern has been expressed that Vezins can be biased when used for sampling fine materials if the cutter speed is as high as the 0.6 m/s which is often used. Using modelling techniques that consider airflow as well as particles, we have endeavoured to investigate sampling bias as a function of the size of fine particles, cutter aperture, cutter speed, shape of cutter blades, and the size of the gap between the inlet pipe and the cutter blades. Using crude estimates of the rate of airflow and a simple model of a single particle moving through air led to an approximate rule that bias will not occur due to mechanisms related to airflow for particles larger than about 200 microns; and bias will always occur for particles smaller than about 40 microns. For particles between these size limits, the extent of bias depends on particle density, cutter speed and cutter geometry as well as particle size.CITATION:Robinson, G K, Wilson, P, Hilton, J and Cleary, P, 2012. Avoiding bias when using vezins for sampling dusty materials, in Proceedings Sampling 2012 , pp 109-114 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Aug 21, 2012

By Jorgensen D. K.

The Bullfrog and Montgomery-Shoshone deposits, outside Beatty, Nevada, have a combined drill-indicated reserve of 17.4 M tons of ore with an average grade of 0.103 oz/t Au and 0.240 oz/t Ag. The deposits occur in Miocene volcanic rocks which underwent large-scale movement within a detachment-faulted terrane. The principal host to gold mineralization is a strongly welded rhyolitic tuff which experienced brittle deformation during plate movement. Open-space fractures and breccia were filled with quartz, calcite, and adularia accompanied by lesser pyrite, gold, and acanthite. Gold occurs as micron-sized particles within and adjacent to the low-angle fault and along associated listric-normal and tear faults.

Jan 1, 1989