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By Shinji Shirakawa

The gold wire bonding technology is widely used for electrically connecting aluminum pads on IC devices to external terminal of semiconductor. In 1960?s, the tensile strength of gold bonding wire was about 100 MPa only. However, recently the wire with 300 MPa in strength has been developed. Since the gold bonding wire was started to use for IC package in early 1960?, the many types of gold bonding wire has been developing continuously in order to meet market?s needs, such as high density, small size and thin type of IC packages. Moreover, electronic equipments were used in automobile applications and also demanded good reliability under severe temperature environment. Thus Au-Pd alloy wire has been introduced instead of the wire with 4N(99.99wt%) purity gold to provide excellent reliability in Au-Al bond interface. The phenomena at Au-Al interface in the high temperature storage have been already explained by several studies as follows. There are five phases of inter metallic compound (IMC) between gold and aluminum. Just after bond gold ball on aluminum pad, Au5Al2 phase was formed and occupied almost all of IMC area. During high temperature storage test, Au5Al2 phase transformed to Au4Al phase, then this phase was corroded by Bromide (Br) ion that was isolated from molding resin. Thus the reliability between Au and Al degraded. In case of Au-Pd alloy wire, the concentrated palladium phase (Au-Pd-Al) was formed at the interface between Au alloy ball and Al pad. The Au-Pd-Al phase prevented from transforming between Au and Al, therefore Au5Al2 phase was hard to transform to Au4Al phase. Consequently the reliability at the interface between Au alloy ball and Al pad was less degradation. However, in recent study using several advanced analysis technique, Au4Al phase was found at the interface between Au alloy ball and Al pad same as the case of conventional gold wire (4N purity gold bonding wire). It was suggested that the formation of concentrated palladium phase (Au-Pd-Al) related the excellent reliability at ball bonding process.

Oct 1, 2003

By A. Singh

"The flotation of fine minerals less than 10 µm in size is an age old challenge spanning both the precious metal and industrial mineral sectors across a range of commodities. This problem has been brought into sharper focus by the emergence of the practice of fine grinding of flotation feed to effect better liberation of the targeted minerals. However, the ability of conventional flotation cells to effectively float the liberated fines remains questionable. In order to overcome this problem, Gold Ore postulates the “Bringing the Mountain to Mohamed” hypothesis which comprises the steps of gas nucleation on particle surfaces, aggregation of particles and levitation of aggregates. Testing of this hypothesis at Mintek, South Africa, showed a ~180% increase in the Kelsall kfast factor coupled with a projected recovery improvement of ~4 % for the Mach Reactor case coupled with a final concentrate grade of ~2 times that of conventional flotation. These fundamentals were then extrapolated to plant scale with Mach Reactors installed on the flotation feed at Platmin’s Tailings Scavenger Plant (TSP) with the objective of scavenging the fine minerals lost to tailings by the main plant. This paper details the theory, pilot plant results as well as key aspects of the full scale plant design supplemented by operational plant observations after commissioning. This game changing application is regarded as being pivotal to future flotation plant design whilst providing the technology leverage required for the survival of mineral operations in an economically unfriendly environment.INTRODUCTION - THE CONUNDRUM OF FINE PARTICLE FLOTATION“If the mountain won't come to Mohamed then Mohamed must go to the mountain” is an age old saying written into the book of proverbs in 1670. Legend has it that Mohamed promised his people that he would summon a mountain to come over to him so that he could offer up his prayers from its summit. After numerous attempts at moving the mountain went in vain, Mohamed, quite unabashed, said “Well if the mountain will not come to Mohamed, then Mohamed will go to the Mountain.” In this analogy, Mohamed is a fine particle <10 µm and the mountain is a bubble within a flotation system. The age old challenge is how to bring these two together to achieve attachment?"

Jan 1, 2016

By S. Nakamura, K. Fujiwara, S. Hirosawa, S. Tsukamoto, Y. Koshino, Y. Aruga

"In this study, hardness test, differential scanning calorimetry(DSC)and transmission electron micros copy were carried out to investigate the age-hardening behavior of Al-Mg-Si alloy with a Mg+Si concentration of 1.5mass%, and a Mg/Si ratio of 1.0. Pre-aging treatment was conducted for the solution-treated and then water-quenched specimen at 100, 80, 60, 40, 20 (natural aging), 0 and -20°C for 20min or 5h, followed by artificial aging at 170°C for 20min. It was found that when pre-aging time is prolonged from 20min to 5h, the bake-hardening response is deteriorated irrespective of the pre-aging temperature. In particular, the specimens subjected to pre-aging at 20-40°C for 5 h hardly increased the hardness with the subsequent artificial aging. From the results of DSC measurement, it was suggested that as pre-aging temperature is lowered, the amount of solute clusters formed during pre-aging, i.e. Mg-Si clusters and Si-rich clusters, is decreased, but the ratio of Si-rich clusters is increased, resulting in the deteriorated bake-hardening response.INTRODUCTIONIn recent years, Al-Mg-Si alloys have been widely used forautomotive body panels due to their excellent characteristics such as high strength-to-weight ratio and good formability. Their strength is increased not only by artificial aging during paint-bake treatment; i.e. “bake-hardening”, but also when kept at room temperature(RT);i.e. “natural aging”, in association with the suppressed bake-hardening response. Such a “negative effect of two-step aging” has been a serious problem because Al-Mg-Si alloy coils are unavoidably maintained at RT in the manufacturing process of body panels; e.g. shipping and storage. However, it was reported that pre-aging above 70°C before the two-step aging can restore the bake-hardening response, and such an improvement is related to the formation of solute clusters(Sato, 2006; Abidet al., 2010; Takaki et al., 2014; Zandbergen et al., 2015). From the comprehensive analysis by three-dimensional atom probe (Aruga et al., 2014 and 2015), it is believed that Mg-Si clusters formed during pre-aging transform into the strengtheningß"" phase, whereas Si-rich clusters formed during pre-aging act as a detrimental precursor of ß""phase. In this study, it was aimed to investigate the effect of pre-aging conditions, especially pre-aging temperature and time, on the formation of solute clusters during pre-aging, in order to elucidate the mechanism of the age-hardening behavior of an Al-Mg-Si alloy."

Jan 1, 2018

By Alexandre Desbarats, Michel David

"All optimum pit design studies start from the geological are reserves inventory, the estimated grades of all blocks of potential are within the interpreted limits of the deposit. The actual optimization procedure is then carried out on block valuations based on these estimated grades. Thus, the relevance of any pit design can be seen to depend directly on the ore reserve estimation . To insure a proper pit design, a first step would be to use a geostatistical reserve estimation technique such as kriging, however, this is not enough. A frequently neglected fact is that the blocks of ore estimated during the planning stage of the mine are usually considerably larger than those on which the ore-waste selection will be made at the time of mining. Experience in the exploitation of large low-grade deposits has shown that large blocks, estimated to be are, when mined selectively in smaller blocks, often yield significant amounts of waste material. This phenomenon, known as internal waste, is a function of the variability of the grades, the size of mining unit and the amount of sampling information on which ore-waste decisions are made.In this study, it was proposed to consider the effect of internal waste caused by selective mining, on. pit design, using geostatistical methods to predict the tonnage and grade of recoverable reserves within large blocks.Optimum pits obtained using a block valuation formula taking into account the recoverable reserves within large blocks were compared with optimum pits obtained using a conventional block valuation formula. It was found that the optimum pits obtained by the proposed method had the highest total valuations and thus were, in fact, ""more optimum”. These pits were characterized by greater are tonnages at a lower average grade, the additional ore more than compensating for the drop in grade. It was also found that the consideration of internal waste in pit design could considerably alter pit limits in marginal areas of the deposit.It was concluded that selective mining had a significant, potentially critical, impact on the design of optimum pits especially in the case of large low-grade deposits."

Jan 1, 1984

By C. Chongo, L. Little, Q. Mclennan

Since commissioning in 2005, First Quantum Minerals’ Kansanshi Mine in Zambia has produced over three million tons of copper and 1.8 million ounces of gold from a deposit with highly varied copper mineralization. The processing plant is complex with three independent flotation circuits, gold gravity concentration, atmospheric and high pressure leaching, solvent extraction, and electro-winning. For the first ten years of operating the plant, copper mineralogy was inferred from total copper and acid soluble copper assays, and various misconceptions developed about the mineralogy which impacted operational strategy and project decisions. In 2015, an on-site mineralogy section was set up with an Automated Scanning Electron Microscope, the Zeiss MinScan. This instrument has provided detailed mineralogical data that have debunked some of the mineralogy myths that had developed, highlighting the key underlying issues affecting processing performance. This has enabled the development of projects targeting losses of specific copper minerals in defined size classes, unlocking significant value. This paper describes some of the early misconceptions around mineralogy at Kansanshi processing plant, outlining projects that have benefitted from understanding copper mineral distribution. Learnings from Kansanshi are to be applied at other FQM sites, with a similar mineralogy program being set up at the Cobre Panama project. INTRODUCTION The deposit Kansanshi Mine is located in the North Western Province of Zambia, and it has been the largest copper producer in Africa for over a decade. The deposit occurs within a broad northwest trending antiform that can be traced for 12 km, hosted in a zone of complicated faulting, abundant vein injection, breccia development and down-dropped rock units that lies within Kansanshi’s mining license. The copper mineralization within the deposit is predominantly vein-hosted, although some is strata-bound, occurring in thin bands and veinlets parallel to foliation, and some is disseminated associated with albite-carbonate alteration (Gray, 2015). Supergene enrichment has led to significant variety in the copper mineral speciation. This alteration is complex, and has not followed the text-book principles with a neat layer of supergene mineralization overlying fresh hypogene ore. Rather, the occurrence and extent of oxidation and supergene enrichment is highly irregular throughout the deposit, sometimes occurring at significant depth in localized pockets and along fault lines. Gold mineralization tends to follow the copper within the deposit, but it is dominated by coarse-grained, free-milling native gold. The extent of copper oxidation – measured as the fraction of total copper that assays as acid soluble – is used to classify ore into three main ore types, named Sulphide, Mixed, and Oxide, which are then fed to three different primary crushers for processing in independent circuits.

Jan 1, 2019

By Nabeel Khan

Annual oil production from the Canadian Oil Sands in Northern Alberta has been rising for several decades, and more ore and overburden are excavated each year from an increasing number of open pit mines. Overburden meeting certain specifications will be used to dam tailings and fill open pits, but the remaining material must be stored in overburden storage structures (OBSS). Well-designed overburden storage structures are more stable and cost less in the short- and long-term. The purpose of this paper is to explore OBSS designs that will be stable yet economical in the short- and long-term. The geological background of the site is briefly discussed, including the effect of each of the main geologic layers (recently deposited till and muskeg, Clearwater Formation clay shales, McMurray Formation oil sands, and the Devonian limestone) on the slope stability of the OBSS. Cost is considered in the analysis when balancing between minimizing costs (steeper slopes) and acceptable factors of safety (flatter slopes), all the while considering the financial consequences of failure. Potential failure planes are identified and probabilistic analysis is conducted on the critical failure surface. The variations in the factor of safety caused by varying pore water pressure, friction angle, and cohesion, are plotted and discussed.

Jun 1, 2012

By W. A. Jones

THE Ross mine, a subsidiary operation of Hollinger Consolidated Gold Mines, Limited, is situated near the north end of lot 1, concession 2, Hislop township, Ontario. The property comprises the north half of lot 1, concession 2, and the south one-third of lot 1, concession 3. It is readily reached by a good motor road from the village of Ramore, 7.5 miles to the southeast on the Temiskaming and Northern Ontario railway. The-mine has been developed to a depth of 900 feet and the current daily production rate is about 260 tons. From the inception of operations in March, 1935, until December 31st, 1942, 455,720 tons of ore with a total value of $4,169,-316 have been milled. The silver to gold ratio of 1.48 to 1 is unusually high for Ontario gold mines. The deposit is interesting because the relationship between hydrothermal metamorphism and three successive stages of fracturing and mineralization is marked with considerable clarity. During the past seven years, detailed geological maps of the mine have been kept up to date, many thousands of feet of diamond-drill core have been logged, and numerous thin and polished ore sections have been studied. The present paper describes the structure and mineralogy of the orebodies.

Jan 1, 1944

By Y. Long

The deep-hole surface blasting technique is a prime method of iron ore mining. Blasting fragmentation is one of the important economic indicators that measures the blast method to obtain the iron ore. To improve the efficiency of the blasting method and further reduce the cost of the subsequent processing of iron ore, this paper summarizes measured data gained from a certain amount of blasting test conducted in an iron ore mine in Guangdong province, China. According to the data analysis, there are differences on iron ore blasting fragmentation by different indicators of deep-hole blasting, such as decoupling coefficient of charge, contact state between charge and borehole wall, and change of detonation position in charge. These factors were compared in terms of relevance and impact. Research shows: under certain rock conditions, the decoupling coefficient of the charge has a best range related to blasting fragmentation. Since the detonation position in charge determines the direction of propagation of the explosion stress wave through ore and rock, bottom initiation and mid initiation will help to improve the iron ore blasting fragmentation in joints fractured rock and ore. The research conclusions have important application value for program design of iron ore surface blasting and to guide other types of rock surface blasting.

Aug 1, 2013

By H. T. Michels

Recent laboratory studies show that several bacteria, known to be human pathogens, die when they come in contact with copper and copper alloy surfaces. The amount of live bacteria drops by several orders of magnitude, to zero, on copper alloys in a few hours. In contrast, no reduction is seen in the concentration of live organisms on stainless steel during the six-hour test period. Aluminum painted and coated surfaces and plastics would show behavior similar to stainless steel and show no effect. Coatings and other surfaces claiming to be antimicrobial showed little to no effect. These results suggest the selection of copper alloys for surfaces exposed to human touch can materially assist in reducing the transmission of infectious organisms. In order to make antimicrobial claims in the United States, the approval of the US Environmental Protection Agency (EPA) is required. The EPA-required efficacy testing is described and the test results are summarized. It is anticipated, that once regulatory approval is obtained, that this will facilitate the introduction of antimicrobial copper alloys in hospitals, nursing homes and other healthcare facilities, as well as schools, and public buildings. Some of the application and barriers, to entry into the healthcare markets are mentioned.

Jan 1, 2007

By Par G. Jönsson, Joachim von Scheele, D. S. Sarma, Mukul Goyal

Dust from flue gas cleaning systems at iron and steel production is frequently considered as a waste problem, but it is actually a potential raw material source. By using a technology like the oxyfuel based OXYFINES technique, it can be melted into a suitable form. The product from this processing, however, needs to meet the requirements of a recyclable raw material, here particularly a top-charged blast furnace feed. The present work has been focused on characterization of the product produced from these dusts by OXYFINES technology. The investigation has been carried out on samples of processed dusts from a European integrated steel mill. It was done by means of chemical analysis, density measurement, light optical microscopy, X-ray diffraction, scanning electron microscopy combined with energy dispersive spectroscopy, and micro indention hardness measurement. Special attention was paid to the presence of zinc, an element that might be harmful while recycling the material (e.g., in a blast furnace). The results show that the product contains four different regions with different morphologies and properties in the material, which are discussed in detail. The overall conclusion is that by processing the dusts in this way, a raw material suitable for recycling in a blast furnace can be obtained.

Jan 1, 2004

By A. Jeffkins

Visibility is restricted when operating load haul dump vehicles resulting in a number of serious accidents in the Ontario Mining Industry. One of the leading causes of these accidents is the inability of the equipment operator to see clearly people, objects or hazards around the machine. Previous line of sight testing by the research team found specific machine characteristics were responsible for blind spots and impaired visibility. In order to identify feasible design modifications a computer simulation program, Classic JACK 3.1, was utilized. Program features include human factors analysis, which allows evaluation of line of sight and operator posture in order to decrease risk of musculoskeletal injury. Research within the virtual computer environment consisted of a Visibility Audit and a Target Audit in order to quantitatively determine how certain components of the LHD design affected the line of sight around the vehicle. Results indicate that modifying the LHD light brackets, engine profile, cab posts and other components will enhance visibility. The addition of cameras located on the front and rear of the vehicle were able to enhance the operator?s sight lines to previously obstructed areas. Modifications to seat height and the operators orientation both improved sightlines and decreased risk factors associated with back and neck musculoskeletal disorders.

May 1, 2003

By A. A. Abdul-Latif, A. Sahin

"The phosphate deposit, located in the Abu Tartur plateau between the Kharga and the Dakhla Oases in the southern part of the Western Desert of Egypt, is the largest of its kind in the country. The phosphates are found in two horizons referred to as the Lower and Upper Phosphate Horizons within the Late Campanian Sibaiya Formation which belongs to the Nubia Group.This paper presents the results of a geostatistical study on the main phosphorite bed at the base of the Lower Phosphate Horizon which contains almost all the commercial reserves in the area. After semivariogram modeling for the phosphate thickness and accumulation, ordinary block kriging was employed to estimate the values of these variables in blocks of400 m by 400 m dimensions. The kriging results, which are presented in the form of contour maps, can be of considerable use in both future exploration and exploitation of the deposit. The grade-tonnage relationship based on the grade estimates derived from the corresponding thickness and accumulation estimates indicates the existence of 453.9 x 105 tonnes of phosphate above a cut-off grade of 18% P2O5. The mean grade of this tonnage has been estimated to be 25.77% P205"

Jan 1, 1990

By X. Cao, M. Xiao, M. Jahazi

Magnesium alloys have low hardness, wear, erosion and corrosion resistance. The repair of service-damaged aerospace components made of magnesium alloys is an attractive solution in terms of time and cost saving. The feasibility of applying laser beam technology to repair ZE41A-T5 magnesium alloy sand castings in the machined surface conditions was studied using a continuous wave 4 kW Nd:YAG laser system. The influence of process parameters such as laser power, cladding speed, wire feed rate and defocusing distance on the shape, size and area of single cladding beads is discussed using a process optimization software. Sound single clad beads with good geometric characteristics were obtained using strictly controlled laser process parameters. The overall results indicate that laser surface cladding using filler wire has the potential for repairing aerospace components made of cast magnesium alloys.

Jan 1, 2006

By Jr. Wilkinson

Suncor Energy currently mines approximately nine hundred thousand tonnes of ore and waste per day at its open pit operations in the Athabasca Oilsands near Fort McMurray, Alberta. Modeling these deposits for planning purposes is particularly challenging given the characteristics associated with the deposit - stratigraphic deposition coupled with gradational grade distribution. The identification of ore and waste is a combination of bitumen cutoff grade, minimum mining thickness and separable waste thickness subject to criteria established by provincial regulatory agencies. Suncor along with Mincom Inc. have collaborated on this project to derive a methodology, automated by computer software, to streamline the ore and waste identification process. This paper explains the methodology and programs created to identify ore and waste in use at Suncor Energy and how this identification is used to categorize reserves and to generate mine design surfaces.

Apr 1, 2005

By L. Jiang

The evolution of twinning in an AM30 Mg alloy was examined by uniaxial tension and compression testing at temperatures from ambient to 250°C and a strain rate of 0.1/s. The samples were cut along the extrusion direction from extruded AM30 Mg alloy tubes. Specimens deformed to various strain levels were examined by optical microscopy and electron backscattered diffraction (EBSD) techniques. The results indicate that the initial extrusion texture plays an important role in the formation of different types of twins and that the twinning behavior also depends on the strain path. Contraction and double twinning are the dominant twinning mechanisms in uniaxial tension, while extension twinning prevails in uniaxial compression. The different twinning behaviors are shown to be responsible for the sharply contrasting strain hardening characteristics of the experimental flow curves.

Jan 1, 2006

By M. Bigdeli Karimi

In this study, the effect of strain level and holding time in semisolid temperature range via SIMA process on AS21 Mg alloy was investigated. Some cylindrical samples of this alloy with 1cm in height and 2.5cm in diameter (H/D=0.4) were compressed to 10%, 20%, 30% and 40% at 300-C. Then, the samples were reheated in semisolid temperature range at 614°C for various times. The results of optical microscopy and image analysis showed that with increasing of strain and holding time, dendritic structure changed to equi-axed structure, gradually. Also, the best conditions to obtain good globular structure were achieved. Furthermore, it was seen that after compression and reheating, Mg2Si intermetallics with Chinese script morphology converted to dispersed-fine particles which were distributed into the ci-Mg grains.

Jan 1, 2007

By F. Golestani-Fard, A. A. Nourbakhsh

In this paper microstructural development of nitride-Bonded SIC refractories is reported in presence of Al203, Mg() and Urea additives .The samples were prepared by mixing, shaping and firing at 1400-1500°c in a controlled atmosphere furnace. Phase analysis, microscopic observation and mechanical evaluation were taken for microstructural investigations. The strength of samples doped with Al203 was first increased and then decreased at higher amount of Al2O3 additions. The addition of MgO decreased the strength while the urea showed an improving effect on strength. These phenomena could be attributed to microstructural evolution and mainly to liquid phase formation and grain morphology. It was found that the additives such as Al203, MO and urea could modify the microstructure in terms of phase formation and texture modification, which in terms influences the mechanical behavior.

Jan 1, 2004

By Chao Yang, Liguo Tian, Yan Yang

"The Jinfeng gold mine is one of the three gold mines that Eldorado Gold has in China and it is the second largest gold mine in China. The mine is located in a relatively remote and mountainous area in the southwestern Guizhou province. The orebody is similar to the Carlin type deposit in Nevada. The mill throughput was designed to treat 3,600 tones per day. The ore comes from open pit mining and underground mining, and is fed to one-stage jaw crushing. The crushed ore is stockpiled, reclaimed and then fed to the SABC grinding circuit. After classification with hydrocylones, the ore is floated, and the resultant concentrate is oxidized biologically in a process known as BIOX®. The oxidized concentrate is then washed in a CCD circuit and finally leached with cyanide in a CIL circuit for gold extraction. Jinfeng produces about 180,000 oz of gold per year.This paper introduces operations and modifications of SABC circuit over the past three years, and then describes some technical characteristic of the SAG mill and other circuits in the processing plant.Major modifications and improvements on the SABC circuit are described in the paper, including:1. Impacts of grinding ball and mill liner with respect to material selection, quality, hardness, manufacturing methods, and interactions between mill liner and grinding ball.2. Effect of milling operation parameters on milling efficiency.3. Impacts of SAG mill scats and modifications of grate size to improve mill throughput.4. Design and construction of a pebble crushing system, and recycle the crushed scats to the SAG mill to improve mill throughput.With the above-mentioned modifications, 20% increase over the design in mill throughput has been realized over the past three years, and operating cost has been significantly reduced. However, some issues still remain, and thus process modifications and technical innovations are still needed."

Jan 1, 2012

By S. Sagar

In September 1996, Dofasco commissioned a 165 Mt twin shell EAF furnace and an associated ladle fleet. During and after this startup, refractory performance in the ladles was optimized on a holistic approach through several initiatives that increased ladle refractory retention times from 7000 to over 16000 mins (160 heats). This dropped the overall refractory costs by 40% while ensuring a consistent and predictable ladle performance. One initiative that drove enhancements was the proper brick selection for each particular refractory area and it&apos;s process conditions. The work concentrated on the selection of a resin bonded alumina magnesia carbon (AMC) brick in the barrel area of the ladle, upgrades to the 2 piece monolithic alumina cast ladle bottom and increasing the slagline refractory brick quality with the appropriate zoning/paneling. The adoption of a magnesia alumina carbon (MAC) brick in the transition area of the barrel/slagline has also improved performance and predictability. The design developments have lowered the overall wear rates and balanced the service life of the entire ladle. Safety was improved and breakout potential reduced by changing the safety lining from a high alumina brick to a state of art technology - monolithic shotcrete lining. This initiative decreased the overall manpower required to brick a ladle and increased shop ladle availability. The ladle bricking area environment was also improved by adopting a post combustion device to burn phenol fumes from ladle preheating practices. This has improved the overall health & safety of the reline teams. The consistent and predictable performance of the ladle on a whole has allowed the shop to decrease the number of working ladles in operation from 5 to 4. This further decreased wear rates from over-oxidation and excessive thermal cycling, saving approximately $500,000 in natural gas from pre-heater operations.

Jan 1, 2004

By C. D. M. Chisholm

Introduction The Sullivan orebody is a sulphide replacement deposit in beds of argillaceous quartzites. The general strike of the vein is north and south, with rather an abrupt change to northwest in the north limits, and a pronounced steepening of the dip in the same area. An east-west section across the orebody in the vicinity where the change in strike occurs will show the dip-to the east-to be about 10° to 20° above the 4500 level, 20° to 30° between the 4500 and 3900 levels, and 35° to 45° between the 3900 and 3500 levels. It is this last section, averaging 75 feet in thickness, that is being mined by the blast hole method discussed in this paper. Typically, the mineralization throughout this section follows the same general pattern between footwall and hanging-wall, there being solid sulphides for a width of 30 to 50 feet, above which lie quartzite beds of varying widths separated by ore bands which also vary in width and in grade. This banded part of the vein usually extends for 30 to 40 feet above the solid sulphides, with commercial ore terminating on reaching a siltstone bed. Development is generally carried to the highest ore band which, when averaged with the underlying quartzite band, will assay about the marginal limit in lead and zinc. When wide stopes are opened, sloughing to the siltstone usually occurs and, although the values are too low to carry the cost of developing and mining, the caved muck can be handled profitably with only haulage and treatment to be considered.

Jan 1, 1946