Search Documents

By R. Hipsley, D. Arbonies, P. J. Dobak, M. Visher

The Storm deposit is a high grade breccia hosted “Carlin-type” gold deposit located at the north end of the Carlin Trend. Storm consists of 3 smaller deposits: 1) 49er Zone, 2) End Zone, 3) Discovery Zone. Structural intersections and favorable stratigraphy at the Paleozoic Popovich/Rodeo Creek formation and Bootstrap limestone formation contact are the primary known controls to gold mineralization at Storm. High grade silica-sulfide breccia occurs in the footwall of the north-south trending, dike filled, Dee fault. This mineralization cross-cuts silicified heterolithic breccia zones localized above the Bootstrap limestone where northwest, dike filled, reverse faults cut this structural-stratigraphic horizon. 40Ar/39Ar dates of 37.57+ 0.34 Ma (basalt dike) and 162 Ma (lamprophyre dike) have been obtained from dikes in the Dee pit which are locally mineralized by the same event as Storm. This paper will focus on the descriptive aspects of the Storm deposits.

Jan 1, 2001

By Yuting Xue, Taghi Sherizadeh, Mark Van Dyke, Dogukan Guner, Khaled Mohamed

The Coal Pillar Rib Rating (CPRR) technique has been developed to assist in rib support design in underground coal mines. One major challenge of the data collection process is the measurement of coal strengths in the field. Schmidt hammer has been verified as a useful tool to determine coal strength. An alternative approach is to obtain the representative strength of coal mass by determining the coal lithotypes in the field based on the coal brightness profile by experienced geologists or mining engineers. In this paper, image processing techniques have been used to quantify the texture of coal images of different lithotypes with the purpose of classifying coal lithotypes. The coal images were collected from the pillar ribs with exposed surfaces in underground coal mines, and the coal lithotypes were identified when taking the images. The method of Gray-Level Co-Occurrence Matrix (GLCM) was used to analyze the textures of coal images of different lithotypes, and the texture parameters, such as contrast, homogeneity, energy, and entropy, were compared. The results show that the images of coal with different lithotypes have different textures, which can be quantified through the image processing. The results from this study demonstrate the potential of classifying coal lithotypes using rib photos and easing the data collection process of CPRR.

Feb 1, 2024

By Fickera M. A, Marshall S, Burgeese F. L, Burgees J, Estrina H

A new high intensity flotation process FASTFLOT was deployed to recover residual zinc from the zinc circuit tailings at Pasminco Mining's Concentrator, Broken Hill. Performance of the FASTFLOT process is discussed with respect to various size fractions. Results suggest that the process has an affinity not only for fine particles but also for +200 ¦m particles which the conventional flotation cells failed to recover. Various strategies for FASTFLOT deployment are also discussed.

Jan 1, 1995

In common with general experience in the iron-making industry overseas, Australia has in recent years suffered a deterioration in the physical quality of her iron ores in their suitability as a direct blast furnace feed. The increasing amounts of fines and the more friable nature of lump ore, especially in the ore from the Cockatoo Island deposits in Yampi Sound, Western Australia, have focused attention on problems of ore preparation and agglomeration, particularly sintering.Although very small pilot scale Dwight-Lloyd type sinter machines were operated at the steel-making centres at Newcastle and Port Kembla during World War II, no sizeable capacity was installed, so that ore was charged to the blast furnaces almost entirely unscreened, and the resultant flue dust was stockpiled.Towards the close of the war, the pilot plant at Newcastle was replaced by a small machine, adjacent to the flue dust stockpile, with a rated capacity of some 20 tons per hour. After approximately five months of part-time operation, this plant was closed down in January, 1945. Production was not resumed until December, 1950, when, due to a temporary ore shortage, it was decided to supplement available ore with sinter produced from the large flue dust stocks of about 300,000 tons. In spite of mechanical and process difficulties, inherent to the design of the plant, operation was continued on a two-shift basis, with several shutdowns for extensive overhaul and plant alterations, until September, 1954, when production was put on a three-shift basis. Addition of Yampi ore fines to the sinter machine burden was not commenced...

Jan 1, 1957

By Hidefusa Takahara, Koichi Miyake, Dierk Raabe

"Mechanical properties of copper wires were examined. The copper wires containing 5-10 mass % chromium and 1-3 mass % silver were produced through heavily cold deformation. It was expected that the copper wire was easily fractured during cold deformation because of the existence of brittle chromium phase in the alloy. In fact, the copper wire was fractured due to large work hardening, when the true strain [n] exceeded 5. However, the copper wire annealed at 1273K for 6 ks ·in the middle of deformation process could be smoothly drawn to 11=8. After precipitation treatment for silver phase at 473k for 1.8 ks, the wire was able to further drawn to n=8.4. The final deformed wire showed tensile strength higher than 1200MPa.IntroductionDownsizing of electronic devices has led to the demand of finer and higher strength materials for cables. Conventional copper alloys have about 800MPa in ultimate tensile strength. These strength are mainly obtained by precipitation hardening. Nowadays, a process for higher strength wire has been developed, where dual phase copper alloy is used. When it is drawn heavily, the' second phase is elongated along drawing direction and the wire gets high strength due to fiber reinforcement (1). That alloy is so called in-situ formed fiber reinforced ·alloy. Cu-Ag(2), Cu-Nb(3) and Cu-Cr(4) systems are well known as such alloys. It is also well known that chromium is brittle material except single crystal and high purity of chromium. However, Mihara et al. C5l have achieved 1 GPa in ultimate tensile strength in the Cu-Cr-Zr and Cu-Cr-Ti alloys by appropriate thermo-mechanical processing.In this study, the Cu-Cr-Ag systems were investigated: The alloys contained 10 or 5% chromium and 3 or 1 % silver. It was demonstrated that silver precipitated in copper matrix contributed on further hardening."

Jan 1, 2000

By D. M. Wagner, G. Biggs, M. Osmundson, C. J. Twaroski

Potential air emission impacts to federal Class I areas from distant sources are receiving increasing scrutiny by federal land managers (FLMs). This paper provides summary results of the impact analyses conducted for FLMs and PSD permitting of a proposed expansion for a taconite processing facility. Results from air quality increment, acid deposition, mercury deposition, and visibility analyses for Class I areas located 50 to 162 km from the facility showed the project would meet the respective regulatory and guideline values for the specific analyses. During the course of the air quality analyses, potential new requirements from the FLMs’ Air Quality Related Values Workgroup (FLAG) efforts and USEPA’s Regional Haze Program were brought into the PSD discussions. The implications for these future guidelines and regulations as they may affect future expansions at other mineral processing facilities are also discussed.

Jan 1, 2001

By G K. N Subasinghe

Metallurgists operating Knelson Concentrators (KC) often rely on manufacturerÆs recommendations for selecting operating parameters, such as fluidising water flow rate and cycle time. Recent studies have shown that these parameters are not only dependent on the machine parameters but also on the feed characteristics, such as size distribution of the gold and gangue particles and the composition of its constituent minerals. It is known that a particle entering a KC initially traverses a circular path within the bowl. For a particle to maintain a given orbit, the required centripetal force must be supplied by external means. It has been argued that this centripetal force, which is dependent on the mass of the particle, its radial position and the rotational speed of the bowl, is provided by the fluid drag force created by inwardly moving fluidising water and the BagnoldÆs force created by the particle/particle collisions. Depending on the fluidising water flow rate, one of two situations can occur where the porosity of the bed increases or decreases, which influences the amount of material retained within the bowl. The amount of material of a given size and density retained in the bowl is thus dependent on the extent of the centripetal force provided. Based on the above concept, a criterion that can be used to predict the amount of material recovered in the bowl has been derived and validated by experimental data. It may also be construed that this criterion demarcates the transition of the bed from a packed-bed state to a fluidised state. By identifying the transition values for the different constituent mineral particles in the feed, it is possible to estimate the optimal fluidising water flow rate that would maximise gold recovery while minimising gangue recovery. In addition, the kinetics of gangue displacement by incoming heavy mineral particles were also studied using synthetic mineral mixtures. The experimental data suggests that this process follows first order kinetics and that the build-up of heavy mineral reaches a maximum. A model has been proposed to predict the optimal batch cycle time for a KC in terms of the feed characteristics and machine operating parameters.

Jan 1, 2006

Recent developments in diamond drilling practice have been chiefly 'concerned with modifications in drill design and 'operating technique whereby an increase in daily footage rates and reduced footage costs have been achieved without any marked improvements in the recovery of core. This trend is perhaps due to the general acceptance by the mining and drilling engineer alike of the belief that diamond drilling has definite limitations in exploratory work on mineral deposits characterized by irregularities in continuity and grade, such a belief arising from the fact that drilling technique has not yet evolved coring devices to ensure the full recovery of the rock and mineral formations penetrated.Current diamond drilling operations at Moonta and Wallaroo Mines, carried out by the South Australian Department of Mines, have attained remarkable results in completely eliminating core-loss by the use of a special double-tube core barreI.It is considered that assays of borehole samples taken with this special barrel have a reliability comparable, if not superior to that of similarly situated mine samples and, provided they are spaced satisfactorily, can be used as, a basis for calculating tonnage and grade. Formerly, with only partial core-recoveries, positive borehole results on narrow irregular lodes, such as those in the Moonta and Wallaroo Mines, could be accepted mainly as indications of the presence of mineralization, and could have only a limited bearing on estimates of ore reserves.The value of this special double-tube core-barrel lies In the fact that it guarantees good core recovery and, therefore, good samples, and eliminates the need for sludge-sampling, which is prone to give unreliable assay results from several causes, such as gravity concentration in the bottom of the hole and return water losses which cannot be overcome.In view of the increasing demand for minerals and the probability that the search for them will be carried on largely by boring, it is felt that it would be of interest and value to direct the attention of mining engineers to core-recovery results obtained by diamond drilling plants in South Australia and the features of the special core-barrel, designed by the writer, which has made this possible. Also, the writer is desirous of placing on record two other core-recovery devices designed to extract accurate samples in relatively soft or unconsolidated formations. The latter are used with percussion and calyx plants, respectively and their value has been proven on phosphate rock and coal deposits in South Australia.

Jan 1, 1943

By J. H. Starkey

SAGDesignTM Testing for grinding mill design was introduced commercially in 2004. Up to January 2008, 18 projects have been completed and 99 samples have been tested using this method. Two papers have been published describing the patented test procedure and one of these shows how the results compare with other grinding test methods. This paper will briefly discuss the theory on which this technology is based, and explain the procedures used to develop the calibration equation. Case studies are also included to demonstrate the effectiveness of the test work being done. These case studies show how the SAGDesign test is being used today: to design new grinding circuits for commercial full scale use; to calculate throughput in existing mills for production planning; and to accurately define grinding mill requirements at the scoping, pre-feasibility or feasibility study stage of project development, in order to economically identify the size and cost of the grinding mills that will be needed for the project. This is important because if the full rec-ommended SAGDesign testing program is done at an early stage in the project, the definitive cost for a guaranteed throughput, grinding mill design (by Outotec if their mills are purchased) is available. New grinding mill design for final engineering will be represented by the test work done on the Climax Molybdenum Project for Phelps Dodge (now FMI) in Colorado, USA. The SAG mill and ball mill for Climax are now in fabrication with project start up in late 2009. Next, the sizing of grinding mills at the scoping, pre-feasibility or feasibility study stage of mine development will be represented by a large metal mining property in Russia. Finally, calculation of the throughput for existing mills will be represented by work done at a base metal mine, in eastern Canada. Test work for designing SAG mills is now done in four laboratories at the time this paper was written. One in the USA at Dawson Metallurgical Laboratories, Inc. in Salt Lake City, two in Russia at the TOMS Research and Design Institute and at the Irgiredmet Research Institute, both in Irkutsk, and a fourth mill has been installed in Australia at AMMTEC Limited?s lab in Perth. A fifth SAGDesign test mill for radioactive ores has been built by Starkey & Associates, specifically for testing uranium ores and can be moved to any licensed lab in the world on a project basis.

Jan 1, 2014

By Bill Cain, David F. Tsztoo, R. John Caulfield, D. Scott Kieffer

In 1994, the East Bay Municipal Utility District (EBMUD) commenced a system-wide Seismic Improvement Program to protect their facilities from catastrophic damage. A primary focus of this program has been on retrofitting the 75-year old Claremont Tunnel, which crosses the active Hayward Fault zone. A large earthquake on the Hayward Fault could generate enough right-lateral fault slip to effectively sever this important lifeline. The retrofit project involves construction of a new bypass tunnel through the Hayward Fault zone, together with systematic contact grouting and localized structural repair of the existing concrete liner. Several innovative design measures have been incorporated into the seismic retrofit design, including an oversized tunnel cross section, backfill concrete side drifts, seismic isolation of an internal structural pipe, and shear fuses in the final lining.

Jan 1, 2005

By Chaoxun Zhao, Daniel Tao, Craig Blue, Narendra B. Dahotre, Rick Honaker, Bhupendra K. Parekh, Hongyang Han

Equipment wear and corrosion have significant adverse impacts on the operating cost and efficiency of mineral processing plants. In this project advanced surface enhancement technologies are being investigated to decrease the wear and corrosion rate of metal surface. Enhanced metal surfaces are achieved through surface conversion, enrichment, and coating by use of advanced High-Density Infrared (HDI) and other technologies. Studies have been done to determine the effects of process parameters on surface properties and identify optimum conditions. The microstructure of the enhanced metal surfaces was characterized by SEM, EDS, and microindentation. Laboratory wear testing was carried out to investigate the wear performance and the viable coating candidate was determined.

Jan 1, 2005

By John Naughton

At the General Electric ResearchLabora-tories, we have been interested in the iron-manganese system and the effect of hydrogen on the properties of these alloys. Dr. H. H. Uhlig previously has presented some of these results.' We wish now to offer some other of the data that have a bearing on the subject of this symposium. In the determination of hydrogen in the iron-manganese system by any heating Method we are presented with the problem of the evaporation of volatile manganese and the consequent adsorption of hydrogen by this evaporated metal. It seems wise. therefore, to extract gas at as low a temperature as feasible. Consequently we chose the vacuum or hot extraction method for the analyses of these alloys. The apparatus used is shown in Fig. I. The design is a modification of the apparatus described by Holm and Thompson. To limit loss of hydrogen, samples are stored in a chamber immersed in liquid air. We recommend this procedure whenever there is a question of loss of hydrogen at room temperature. Thence they are moved to the quartz furnace by means of a small magnet, where they are heated by induction to 700' to 800°C. The extracted gas is removed by the circulating pump and placed in the known volume VI (or V2). The circulating pump has been described.3 It is so designed that in spite of the fact that the outlet portion of the pump is part of the known volume, this volume is affected neither by the speed of pumping nor by the pressure of stored gas. The pump also serves to circulate the gases for analysis. The analytical system consists of a

Jan 1, 1945

By Thomas F. Donnelly

Discussion of the paper of THOMAS F. DONNELLY, presented at the San Francisco meeting, September, 1915, and printed in Bulletin No. 104, August, 1915, pp. 1759 to 1768. F. LYNWOOD GARRISON, Philadelphia, Pa. (communication to the Secretary *).-The paper is of value in giving the public some first-hand information regarding a copper property that from various causes has attracted considerable attention, especially in Philadelphia, and which has also been the source of several fantastic flotations that had little to recommend them. Since 1906, no work has been done on this property under my direction, with the exception of a topographic survey made last winter by Mr. Donnelly, which was intended as the first step in a sound and logical system of development. From 1906 to 1915, desultory attempts were made to develop these orebodies, but as the work was not in competent hands much money was wasted and even more disappeared in ways regarding which it is perhaps not best to inquire. The result is, this interesting property has now practically no more ore developed upon it than in 1906, despite the fact that a new 100-ton mill is being erected, although, as I have intimated, it is today not much more than a prospect. Turning now to the scientific and more agreeable side of the subject, it is interesting to note that these Santo Domingo copper ores are invariably found in volcanic tuffs and that, in a geologic sense, they are all very old, for there are no evidences of recent volcanic activity in the greater Antilles, of which this island is the second largest. The existence of copper in tuffs in different parts of the world is a notable fact. Often, if not usually, it is present in mere traces, but not infrequently we find it in sufficient amount to be of economic importance. Thus, for example, chalcopyrite and bornite occur in the Tertiary tuffs of Japan, and a number of producing copper mines of that country are either actually in, or closely associated with, rocks of this character. Whether the copper minerals are original primary ores in the tuffs, or were derived from accompanying eruptive dikes, appears not yet to have been determined in any instance. In most of the Japanese cases of which I can find any record the tuffs appear to be associated with shales and limestones. These Japanese copper ores also carry some gold, especially in the upper parts of the veins; in this they resemble the Santo Domingo deposits which not infrequently carry as much as $6 or $7 per ton of gold on the outcrop. As a rule the content of gold in both the Japanese and

Jan 12, 1915

By Jens Kempken

A competitive landscape pressurizes the steel producers business, zero defect requirements from customers forces the operators for additional efforts in process control and quality management. The so called quality related cost, which include also rework, cost for downgrading or even scabbing of material is already a remarkable lever in a plants profitability breakdown. The introduction of advanced state of the art grades in the product portfolio requires already a budgeting for the expenses for R&D and quality management. PQA has been developed as a process and quality management software solution next to existing level 2 or level 3 automation systems. It is focusing on the analysis of process data, equipment information, in line quality measurement devices and trend analysis to obtain an answer whether the process is according to definition and expectation and whether the intermediate or final product can be shipped for further processing as prime material. Advanced analytics which are linked to an expert know how based configuration identifies deficiencies in the production and processing process. An intelligent, state of the art quality rating system evaluates tolerable deviations. PQA comprises the software platform including the database, data configurator and collector from the different sources in the production process and units. The core element of the platform is the knowledge based expert know how package defining process and quality determining fundamentals. The paper describes the structure of the software package, it gives insights on the expert know how package, process and quality evaluation and points out the customer benefits, cost reduction, improvement yield, customer satisfaction increase. The link to recent operational references is given.

Oct 30, 2017

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

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

Jul 10, 2012

By S. E. Phillipson

The Mine Safety and Health Administration?s (MSHA) Roof Control Division (RCD) collects a variety of geological and engineering information pertaining to mining conditions in surface and underground mines throughout the United States. Recently, lineament analyses, trends of geologic structures, and inferred stress directions based on mapping at mines with problematic ground conditions, have been integrated into a GIS. The incorporation of different kinds of information into the same geographic coordinates and map projection, placed on digital geologic maps, allows site specific data to be evaluated in a regional geospatial context, identifying trends in the orientation of horizontal stress or patterns of structural geologic features. As more information is collected, the GIS will evolve as a tool for district- and basin-wide evaluations of controls on ground instability, and may evolve into a predictive tool for some kinds of geologic hazards. In addition to the geologic and geotechnical evaluations, the GIS also serves as a searchable database of previous mine investigations. The database can be searched for a variety of criteria, and the results displayed in real geographic coordinates to find the locations of previously visited mines or to evaluate mine fatality and injury data. This not only allows old reports to be found, but also places the information in a geospatial context with respect to neighboring mines or geographic areas. The GIS also has the capability to serve as a digital mine map repository, where maps can be stored in digital, georeferenced format for display in relation to each other and various themes of interest. This allows evaluation of multiple seam mining interactions and proximity to other mines, and on a national level could serve as an abandoned mine map database.

Jan 1, 2008

By David Allen

Cable bolting is a relatively new strata reinforcement technique that has been used successfully in Australia and the United Kingdom. Jim Walter Resources, Inc. has examined the principles and can visualize its useful application in many areas, such as: a) Longwall pull-out areas, b) Roadway junctions, particularly those involving yield pillars, c) Rib reinforcement, and d) Possible replacement of cribbing in roadways, especially longwall tailgates. This paper describes the conditions which led to cable bolt testing, the results of tests conducted to date, and conclusions about the direction that Jim Walter Resources, Inc. is heading as far as testing and potential applications are concerned.

Jan 1, 1994

By V. G. c Papangelakis, M. Huang

A conductivity cell, developed previously, was employed in an effort to investigate the inter-relation between electrical conductivity and acidity of sulphuric acid - metal sulphate solutions at high temperatures. The measured solutions include the H2SO4-H2O, MgSO4-H2O, H2SO4-MgSO4-H2O, H2SO4-MgSO4-Al2(SO4)3-H2O solutions. All solutions reported in this paper were measured from 15 to 250 °C at equilibrium vapour pressure. The maximum measured concentrations of H2SO4, MgSO4 and Al2(SO4)3 were 0.45 m, 0.30 m and 0.10 m, respectively. It was found that, from 15 to 250°C, there is a linear relationship between H2SO4 concentration and electrical conductivities for acid concentration up to 0.45 m. At 250 °C and constant H2SO4 concentration, the solution conductivity drops with the increase of MgSO4 concentration. Lt is suggested that this drop is caused by a decrease in the concentration of H. Finally, an empirical model was developed based on the available measurements. This model has been tested against real laterite leach solutions where sulphuric acid and metal sulphates are dominant electrolytes. The average difference between the estimate acid concentration from this model and the one from titration was less than 5%.

Jan 1, 2004

By Witold M. Pytel

A simplified, three-dimensional, time-dependent, mechanistic model of the overburden-coal seam-floor interaction has been developed and validated at two Illinois coal mines. The model based on the thin plate theory can involve any complex layout of mine workings, time-dependent sequence of extraction and, rheological properties of immediate floor strata. The model output data consist of spatially distributed surface subsidence and its slope and curvature, as well as load acting on pillars in one or more panels. A comparison of calculated and monitored surface subsidence or in-mine convergence measurements has proven the model's effectiveness for surface subsidence and load transfer prediction.

Jan 1, 1992

By William R. Kohl, Craig B. Clemmens

"Since 2010, North Central Resources, Bridgeport, WV, has been using the sonic log to estimate the rockmechanics properties of the coal and adjacent strata in their exploration drilling program. In 68 out of the 85 boreholes they have drilled since 2010, they have conducted shear wave analysis on sonic logs run in these boreholes. By incorporating the rock mechanics logs into the geological model of the coal seam, the engineers can develop a better understanding of the support requirements for the mine.WellCAD Borehole processing software provides vastly improved efficiency in analyzing shear waves from borehole sonic data than previously available methods. The calculation of most rock mechanics parameters requires knowledge of the density and both the compressional wave velocity and the shear wave velocity. Density logs are well known and an industry standard. Sonic logging is equally well known, although less frequently used, as an accurate source of compressional wave velocity. Shear wave velocity is difficult to measure in a geophysical log, but can be estimated from digitally recorded wave form records. This is a time consuming manual procedure which requires the visual examination of thousands of individual wave forms.WellCAD allows the viewing all the wave forms on a VDL display. The observer can create a pair of false logs by manually tracing the interference points on the display for each receiver. He can check himself by observing wave forms in the traditional format. He can then create a shear wave transit time log or “Delta-S” log by subtracting the false log from the near receiver from that of the far receiver. This can be plugged into standard formulae to generate curves for most standard rock mechanic parameters, including bulk modulus, shear modulus, Young’s modulus, and Poisson’s ratio.While these parameters do not entirely substitute for destructive testing, they are extremely cost effective. An entire borehole can be analyzed for the cost of a single destructive test. This allows for a more judicious use of destructive testing while permitting the extension of test data into the rock mass with much greater confidence."

Jan 1, 2015