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By J. J. Carlson

Studies were carried out to determine whether filtration rate changes observed in an iron ore concentrator were due to variations in particle shape. It was confirmed that ores mined from different locations differed in filtration rates by as much as 60%. However, when image analysis was used to quantify the shapes of the individual particles in the filtration feed, it was found that the particle shapes showed almost no variation, and the shapes did not correlate with the filtration rate. It was also determined that the filtration rate variations were not caused by changes in particle size distribution. These results suggest that the differences in filtration rate are due to factors other than size and shape, such as surface chemistry.

Jan 1, 2008

By Belcher C. B

The Groote Eylandt manganese ore deposits contain mainly pyrolusite and cryptomelane with lesser amounts of the manganese minerals lithiophorite, todorokite, psilomelane, and nsutite. The major non-manganese minerals which occur are quartz, kaolinite, and goethite.Determination of the mineralogy relies mainly on x-ray diffraction analysis. Quantitative methods for the determination of pymlusite and cryptomelane in Groote Eylandt manganese ores have been developed, A large amount of isomorphous substitution may occur in the manganese minerals and a number of minor and trace element associations have been noted. A correlation has been established between the potassium and cryptomelane contents for a wide range of ore types. Anomalous calcium, magnesium, and sodium values occur in samples containing todorokite, and barium is associated with psilomelane. Groote Eylandt lithiophorite appears to contain negligible amounts of lithium (<O· 05 per cent).A relationship between the H20+ and the Al203, K20, and Fe203 contents has been estahlished indicating that much of the combined water content is due to the presence of kaolinite and goethite, and cap be removed by beneficiation of the ore.

Jan 1, 1975

The phenomena of nature cannot present themselves to any thinking wild without claiming from it some solution. The earth, as it has often been observed, is laid out like a well ordered cabinet, presenting to us, in measure, some means of judging how the laws of nature and the essential properties of matter have worked out all we see before us. "That there have been depositions of strata gradually laid down aud stocked with the remains of the living objects, vegetable and animal, that flourished when they were being imposed, is an universally acknowledged fact. It speaks of a constantly maintained series of operations whereby the globe has been brought to its present condition, and which are ever advancing it to stages that are still before it. That immeasurable ages have been consumed in effecting these developments is also conceded. We witness the very graduated rate of the existing advances and can see that the past action must have been conducted in the same slow deliberate manner. There are many questions, however, upon which inquirers are not agreed, hence they are still within the domains of fair discussion.What has led to those great climatic changes whereby the same portions of the earth have had at various times climates that were glacial, temperate, and tropical? What causes the constant contortions and dislocations of strata and the upheaval and depression of land levels, and that there is a tendency to alternation in the parallel areas undergoing opposite kinds of movement as if the sinking of one area balanced the rIsing of another? What is the reason that the centres of volcanic action are continually shifting, and that the line of greatest activity is always upon the rising areas? That portions of the earth have been subjected to intense alid long continued volcanic action, and again to long periods of repose, and that the periods of activity and repose are·recurrent at long intervals of time? What the mountain chains of the world are in broadly parallel bands? What has caused the stratified rocks to be tilted from their original?

By G. I. Gritsko

In this paper we consider the elements of a distributed information geomechanic monitoring system which is used in computerized mine planning and mining operations control. The automated system is a technical means of geomechanic monitoring, as a complex system of regulated observations, estimation and prediction of geomechanic state of rock mass and workings during underground mining of coal deposits. Geomechanic monitoring at coal mines and the automated system execute data collection, analysis and calculations of geomechanic situation in the panel during planning, development and carrying-out of mining operations for ensuring geotechnical stability of underground mining.

Jan 1, 1996

By Edward M. Dowey

The concrete lining for a long 8.05 km (5 mi) section of New York City Water Tunnel No. 3 was cast in place. The contractor, Grow-Perini-Skanska, placed over76,841 m3 (100,505 cy) of concrete, pouring 24 hours per day, 5 days per week. The concrete was dropped 204 m (670 ft) to the tunnel level, transported by rail to a concrete remixer and pump, and placed in 146.3m (480 ft) of full circle forms. Some of the many challenges include the sheer magnitude of the job, navigating through drifts, a raise and curves, dealing with ground water inflows, and placing the concrete within time limits.

Jan 1, 2001

By B. Moore, Y. J. Zhang

In today’s competitive dimensional stone business environment, use of available technology is critical to achieve and maintain a competitive advantage. Awareness of improvements in diamond cutting technology, operation planning/scheduling, and geotechnical data manipulation/implementation are the keys to success. This paper presents the modern techniques of limestone sawing and quarrying developed and adopted by Indiana Limestone Company, Inc.(ILCI).To fulfill the growing market demands, ILCI’s quarries are committed to deliver planned quantities of all type of stone blocks in a variety of different colors, sizes, and textures. This involves scheduling which quarry ledges should be mined and when in order to minimize unnecessary inventory buildup. Challenges associated with ILCI’s operation are discussed and summarized in the closing of this paper.

Jan 1, 2004

By James D. Nickerson

Thee Brightwater water treatment facilities, currently scheduled to be completed in 2010 and begin operating in 2011, will serve the northern part of King County, WA. The facility includes a new treatment plant and extensive conveyance system consisting of more than 21 km (13 miles) of influent and effluent conveyance tunnels and five portals. The majority of the conveyance system tunnels are mined by tunnel boring machines (TBM) and microtunnel boring machines (MTBM). Tunnel and portal construction is divided into three main contracts. The Ballinger Way receiving portal, constructed under the central tunnel contract, is the terminus for the BT-3 leg of the central contract and the BT-4 terminus of the west contract. The shaft has a 7.3-m (24-ft) finished inside diameter (ID) to accommodate removal of the central project TBM and the west contract TBM and extends to a depth of 66 m (216 ft) below grade through a complex and challenging soil profile characterized by multiple ground water tables. Vinci Grand Projects/Parsons/Frontier-Kemper Constructors (VCFK) was the joint venture team for the Ballinger Way portal. Frontier-Kemper was responsible for the shaft sinking. VCFK evaluated either slurry wall techniques or ground freezing for earth support during excavation of the portal and liner installation. The selection process took into account the vertical depth, cost, past practice, geology, water tables and a 9-m- (30-ft-) thick zone of contaminated soil at the top of the shaft. Ground freezing, which would also act as a hydraulic barrier, was deemed the better option for this project. The contract was awarded to New Jersey-based geotechnical contractor Moretrench. Typically, frozen walls, by design, key into an underlying cutoff. At the Ballinger Way portal, however, the [ ] freeze bottomed out in a substantially thick stratum consisting of predominantly clay, but with some inclusions of permeable soil that indicated significant ground water pressures. To ensure stable conditions at the bottom of the shaft, Moretrench, which also specializes in dewatering, designed and installed a perimeter array of deep wells to temporarily depressurize the permeable soils. The movement of ground water generated by pressure

Jan 1, 2009

By J. A. Caceres

Mining planning and mineral processing are almost two unconnected areas. The mining area builds its economical models considering the plant like a constant parameter: a constant throughput, an average recovery and a unitary cost. On the other hand, the mineral processing area assumes a mine plan with grades, ore type, work index, estimating the performances in an independent way. Previous researches have evaluated the advantage for increasing throughput by increasing the liberation size, thus sacrificing recovery. These valuables approaches have left behind the work index factor, critical variable for Recovery-Throughput capacity estimation. This study describes a method combining mineral processing and mining planning. This method incorporates the grinding and flotation performances into the mining economic models optimizing simultaneously the Throughput- Wi(Work index)- Recovery relations with mining sequence, cut-off strategies, and reserve schedules. This method has been used at Andina Mine Chile, showing 18% net present value increasing with minimum investment associated.

May 1, 2003

By H. H. Einstein

This paper reviews how uncertainty has been dealt with over the past 40 years using the decision making cycle as a frame of reference. The review of the phases of this cycle, as applied to rockmechanics and rock engineering, namely characterization, performance analysis, updating and decision making shows that in each, progress has been made over the past 40 years, although most of the basic concepts existed already in the 1960’s. Characterization is the area in which the greatest scientific steps were taken, this phase and performance analysis also gained from the tremendously expanded computational capabilities which allow one to use both more complex and more practically oriented models. The greatest practical advance is without using any doubt in risk based decision making although its acceptance shows interesting differences between different professions. Dans l’article suivant on utilise le cycle de décision pour illustrer le développement du traitement des incertitudes en mécanique des roches et en construction en roche dans les quarante années passées. La revue des phases du cycle de décision montre qu’on a fait du progrès dans chaque phase du cycle de décision, c’est à dire dans la caractérisation, dans l’analyse et la prédiction du comportement, dans l’actualisation et dans l’acte de décision, même si les concepts fondamentaux existaient déjà dans les années 1960. Les plus grands avancements scientifiques se trouvent dans le domaine de la caractérisation tandis que l’analyse prédictive profitait du développement de l’informatique qui a mené à des modèles plus complexes mais aussi plus pratiques. Le plus grand progrès est sans doute dans le domaine de l’acte de décision sur la base des risques. Ce procédé est devenu assez commun même s’il y a encore des différences d’acceptation entre différentes professions. Im vorliegenden Artikel wird der Entscheidungszyklus gebraucht, um darzustellen wie sich derUmgang mit Unsicherheiten im Felsbau während der letzen 40 Jahre entwickelt hat. DerÜberblick über die Phasen des Entscheidungsprozesses zeigt, dass bei der Anwendung in derFelsmechanik und im Felsbau, in allen Phasen d.h. bei der Charakterisierung, bei der analytischenVorhersage, beim Aktualisieren und bei der Entscheidungsfindung Fortschritte gemacht wurden,obwohl die grundlegenden Konzepte bereits in den 1960er Jahren existierten. Im Gebiet derCharakterisierung gab es wohl die grössten wissenschaftlichen Entwicklungen, während dieanalytische Vorhersage vor allem von den Fortschritten der Informatik profitierte, welchekomplexere wie auch praktischere Modelle möglich machte. Der grösste Fortschritt ist ganz sicherin der Entscheidungsfindung zu beobachten, wo Risikobetrachtungen gang und gäbe sind, obwohlhier noch einige Unterschiede zwischen verschiedenen Berufsgattungen zu finden sind.

Jan 1, 2003

By Michael Arnold, Bob Faulhaber, Joe Nichols

"Center Hill Dam is a critical part of the infrastructure controlling floods at the Caney Fork River and reducing flood levels at the Cumberland, lower Ohio and Mississippi Rivers. The Center Hill Dam Foundation Remediation Project was necessary to address Karst features in the foundation rocks and observed signs of distress of the dam. From 2011 to 2014 BAUER Foundation Corp. (BFC) performed deep foundation works for this project. The executed features of work include the installation of two walls. The first wall extends throughout the clay embankment into the underlying rock to provide encasement during the construction of the second wall. Its width of 7.4 feet makes it the widest diaphragm wall ever installed. The second wall is the actual seepage barrier and provides a continuous 2- feet wide wall. It extends through the first wall into the underlying rock and is up to 300 feet deep. The paper introduces the project, the requirements specified by United States Army Corps of Engineers (USACE) for encasement and barrier wall and the approaches taken by BFC. It discusses the ground conditions and describes the excavation equipment as well as the excavation methods used. A special focus is put on the steering capabilities of the hydrocutter equipment and the verticality performance.PROJECTBeginning in 2011, BFC was tasked by the USACE with the installation of a seepage barrier/cutoff wall at the Center Hill Dam Foundation Remediation project under a partially performance based specification. The remediation was necessary due to karst features in the foundation rocks and observed signs of distress, which led USACE to rate the dam with the most critical dam safety action classification (DSAC I). The executed features of work include the installation of two walls. The first wall, an encasement wall, extends vertically through the clay embankment and is embedded minimally into the underlying bedrock to provide embankment stability during the construction of the second wall, the barrier wall. The encasement wall is constructed of overlapping panels 7.4 feet (2.25 m) wide, which is the widest diaphragm wall ever installed, and up to 210 feet (64 m) deep. The second wall is the seepage barrier and provides a continuous 2 feet (0.6 m) wide wall consisting of overlapping panels. It extends through the encasement wall into the underlying bedrock and is up to 307 feet (93 m) deep. BAUER BC40 and BC50 hydrocutters mounted on MC96 and MC128 foundation cranes were used to perform the majority of the works (Figure 1). Excavations were performed under bentonite slurry (encasement wall) and water (barrier wall) and concrete was poured with the tremie method. Adding to the challenges, the project had to be executed in an environmentally sensitive area. Based on the high risk, a special focus was put on monitoring, quality control and geometric accuracy. The WallTracker information management system was used to share all relevant data between BFC and USACE (Roff et al. 2014)."

Jan 1, 2017

By James C. M. Li, J. Weertman

James C. M. Li (United States Steel Covp.)—The author has discovered a single analytical relation between the minimum, or the steady-state, creep rate and the applied stress confirming a statement made earlier by orn" that such relation should exist and should reduce to the power law at low-stress levels and to the exponential law at high-stress levels. However, as pointed out by the author, all the available theories of creep are not adequate to explain such a single relation. Inspired by such a statement, I have made a suggestion concerning a possible explanation13 of the new relation. This is based on the concept that the rate-controlling step is the cooperative motion of a short dislocation segment. The nature of and the reason for the cooperation have been discussed13 as well as the reason why the motion of the dislocation could be controlled by the mobility of the short segments. A natural short segment has been proposed13 to be the node formed at the intersection of two dislocations. The reason why the node may contain only a few atoms has not been discussed and the application of the proposed model to all the metals and alloys reported in this paper has not been attempted. It seems appropriate to include these in this discussion. The model was partly inspired by the substructure recently observed in the electron microscope on creep specimens. One such example is shown in Fig. 48 in Darken's Campbell Memorial Lecture. The substructure is a collection of dislocation intersections and irregular networks. No pileups have ever been observed in such specimens. A closer look at the network indicates that one set of dislocations is more straight than the other set sug- gesting that the other set may be mobile in the plane of the net. Since, for the network to survive the creep deformation, some dislocation reaction has to take place at the intersection of the two sets of dislocations, the mobile dislocation, even if it can slip in the plane of the net, will have difficulty in moving at these intersections. To illustrate, an idealized network is shown in Fig. 9. The thin lines represent the set of dislocations which are mobile and can slip in the plane of the net except at the nodes which are formed at the intersection of the two sets of dislocations. The other set of dislocations, represented by the thick lines, may have a Burgers vector which is not parallel to the plane of the net, and therefore may be immobile. Because of this nonparallel Burgers vector, the Burgers vector of the node, which is avectorial sum of the Burgers vectors of the two sets of dislocations, will also be nonparallel to the plane of the net. Therefore, the node cannot slip in the plane of the net and the set of mobile dislocations will have to drag the node along as indicated in Fig. 9. Now the problem is how many atoms could be involved in the nodes. Exact calculation of the length of the node is a difficult task especially since the length should be a steady-state length and not an equilibrium length. An estimate of the equilibrium length can be made by balancing the line tension of all the dislocations. The results would be a small fraction of the length 1 between nodes as shown in Fig. 10. In some instances such a calculation shows that the node will not be formed. But, since the calculation is only approximate, it does not rule out the possibility of the formation of a short node. In other instances the equilibrium length of the node is an appreciable fraction of I. Such a node would

Jan 1, 1963

By William C. Cooley

SUMMARY A review is presented of the state of development of high pressure water jet equipment and of large impact hammers for rock tunneling. Information from the U.S.S.R. is based on published literature and three personal visits. Applicable papers which were presented at the International Symposium on Jet Cutting Technology in Coventry, England in April 1972 are reviewed. Data are presented on continuous jet systems, pulsed water cannons, and hydraulic-powered impact hammers with respect to the specific energy of rock breakage and potential application in tunneling machines. INTRODUCTION It has been estimated that the cost of underground excavation during the period 1970-1979 in 15 countries of the Organization for Economic Cooperation and Development will be over $54 billion, an increase of 104% over the period 1960-1969. It is expected that 55% of the tunneling construction will occur in hard rock (Ref. 1). Present tunneling machines are generally limited to soft and medium-hard rock. When used in hard rock, the cost of replacing mechanical cutter bits is high. Therefore there is a need for improved rock fracture methods which can be applied economically in tunneling machines for hard rock. Water jets and mechanical hammers are two

Jan 1, 1997

By Sharpe E. J

The Triton lode is a schistose feldspar biotite chlorite rock with quartz, carbonate, pyrite and some pyrrhotite. Its more chloritic sections strongly resemble the enclosing greenstones, its more feldspathic portions are indistinguishable from the flne-grained phases of the porphyry dyke into which the southern extremity of the ore body merges. The ore body' has a length of 880 ft. and an average width of I2t ft.; in places this widens to as much as 30 ft.The average dip is 85° west and pitch of the ore shoot 75° south.METHOD OF SAMPLING.With the exception of a limited amount of channel sampling (a reference to which is made elsewhere in this paper) all the sampling is by chip sample.The samplers use a hammer weighing approximately 11 lb. and chip directly into the sample bags. Sampling is generally carried out over 3-ft. sections and portions thereof to the nearest half foot-thus a face 8t ft. wide is divided up into two sections of 3 ft. each and one section of 2 ft.-no measurements of less than 4 ft. are used and calculations are all in feet and dwt. per long ton.In the oxidised stopes wp.ere the lode is much narrower, .i.e., 6 ft., sampling is over 2-ft. sections. All borehole samples are over 2-ft. sections, this corresponding approximately to steel changes.(a) DEVELOPMENT SAMPLING.Driving.-This is done by following the east wall and each face is sampled-this corresponding to an advance of 5 ft. If the full width o,f the lode is not exposed boreholes...

Jan 1, 1938

PERSPECTIVE ?Natural resources exploration, extraction and beneficiation is complex and challenging: ?Input costs rising, complexity increasing, rising stakeholder management needs, regulatory compliance issue, etc. ?With increasing costs and complexity of managing operations are we simply getting less bang for our buck?

May 1, 2013

By M A. Lund, C D. McCullough

In Australia and worldwide, open cut mining has become increasingly common over the last few decades through changes in excavation technology and ore economics. However, such operations frequently leave a legacy of open mine pits once mining ceases. Pit lakes will then form in mine pits that extend below the water table when dewatering operations cease. Pit lake waters are typically contaminated with metals, metalloids, saline or acidic/alkaline and rarely approach natural water body chemistry. Physically, pit lakes have unique bathymetries, are often strongly wind sheltered and have very small catchments. Nevertheless, pit lake waters often constitute a vast resource but of limited beneficial use (due to water quality issues); with a potential to contaminate regional surface and ground water resources. Water in pit lakes has the potential to be useful for a range of purposes in the Australian context of characteristic hot, dry climate and relatively few natural water bodies. Consequently, pit lakes can be seen to represent either a significant liability or a water resource to mining companies and regional communities. However, the lack of knowledge on pit lakes continues to hinder their proper management. This paper summarises the limited information currently available on water quality associated with Australian pit lakes. Information on pit lake occurrence, distribution and water quantity and quality is not nationally collated and requires immediate and ongoing attention from both mining companies and regulating authorities. Lack of a readily available database for pit lake occurrence, distribution and water quality fails to realise the potential for these water resources by both mining companies and Australian communities. Lack of access to pit lake quantity and water quality data may also lead to failure to manage this significant source of mining environmental risk.

Jan 1, 2009

By K. E. Stanfield

[Asphalt ~~d road oil ar8 the principal products manufactured from Wyor.1in~ Ilblack oilo" \r,hich, beca.use of th?lir hig.~ E\.sphal t and hig} sulfur COi.1Jce~1t, .!?re difficult e':ld costly to refine into hi?;h-gra.de motor f 101s, burning oils. and lucri ants by presont mothods. Accordin~ly. the demand for truHle asphaltic renidl urn for the construction of roade aJ1.d other uses is 3. controlling factor in the quantity of crud~ oil prod ICed. The increasiilg -u.tilization of special aST>ha.lts as ine}""Pensive bonding, in-]

Jan 1, 1941

By Ali Ameli

Design loads are limited for piles relying upon toe stresses in rock due to uncertainty about the rock quality over the whole pile diameter because of rock mass properties or construction effects. The paper discusses the use of video images to evaluate rock quality at the bottom of piles socketed into graniodorite bedrock in a steel pipe pile project. Skillful interpretation was required to assess the 3D properties of the rock from video images. It is necessary to observe the rock mass characteristics near the project site for better perception of the rock features from the images. Video image interpretation skills were established by the evaluation of the cores drilled under the socket base and the results of pile loading tests. Correlations were found between rock appearance in the images and the rock socket drilling records. Rock socket acceptance criteria were developed through monitoring the drilling operations for the specific site procedures. Video images then served as one of the quality-assurance tools together with probing and pile loading test. Lessons and methods learned from video inspection in this project could be used to evaluate rock quality in similar cases.

Jan 1, 2006

By Donald Leroux, Dave Scott, Giovanni Di Prisco

"The Lady Loretta lead-zinc deposit in Northwest Queensland, Australia contains an average of 5.9% lead, 17.1% zinc and 97 g/t silver. Ore mineralization is mostly comprised of fairly complex intergrowths of pyrite, sphalerite and galena. Starting in 1998, Noranda Inc., the major joint venture partner of the project, conducted extensive metallurgical test work, which culminated in July - August 2000 in a series of Pilot Plant tests. A common thread to all the metallurgical work has been the deportment of a large portion of silver into non-payable metallurgical products. Average silver distribution from four Pilot Plants shows a distribution of silver in lead concentrate of 28%, whereas silver in zinc concentrate was 49%, and 23% in the final tails.The consistently poor silver recovery as well as the fairly unusual silver distribution, particularly in zinc concentrate, was considered an issue to be thoroughly investigated. A mineralogical plan was devised to determine if these particular metallurgical results were somewhat related to the nature and mode of occurrence of silver carriers. Work was performed to determine discrete silver-bearing minerals and/or silver contained in solid solution in a suite of commonly occurring sulphides. Ore microscopy, SEM methods, Electron Microprobe and Ion Microprobe analyses were all used to answer these questions, and to find the silver carriers, so a metallurgical plan could be devised to improve silver recovery.INTRODUCTIONPotential economic exploitation of the Lady Loretta deposit in Queensland, Australia is driven by revenue derived from zinc and lead flotation concentrates and co-product silver recovery in lead. Relatively low recoveries of payable silver to lead concentrate, and high silver distribution to zinc concentrate necessitated an investigation into the natu"

Jan 1, 2002

By Verya Nasri, Heather M. Ivory, Kevin Clarke, Eric Cole

Development of the New York City Water Supply System The New York City water supply system serves a population of almost nine million, including residents in neighboring counties. Peak day demands on the system are currently running at about 70 m3/sec (about 1,600 mgd), which is significantly lower than in the 1990s. This trend of reducing demands over the past 25 years, which has been experienced in other major urban centers in the US, is mainly the result of conservation measures and increased cost consciousness on the part of water users. In the long term, demands are expected to once again follow an increasing trend with population growth, so that by the end of the planning horizon of these studies, the year2045, the peak day demand is expected to increase to about 85 m3/sec (2,000 mgd).The system is served largely by surface water sources, regulated by a system of 19reservoirs and three controlled lakes, which are connected to the City by a series of aqueducts, the longest of which is about 87 km (54 miles). The total storage in the sys-tem amounts to about 560 billion gallons, providing a system firm yield of about1300 mgd. The Delaware system provides about 50% of the City’s water, the Catskill about 40%, with the remaining 10% provided by the Croton. The system as a whole, which is shown on Figure 1, has been built up over the past 150 years, and is truly a marvel of engineering. The Catskill and Delaware aqueducts both discharge into Kensico Reservoir, which is a daily balancing reservoir located in Westchester County about 24 km(15 miles) north of the New York City line. The two aqueducts extend south for a further 14 miles to combine again at Hillview Reservoir in the Bronx, which provides hourly balancing storage for New York City system. The Croton aqueduct runs nearby as shown on Figure 2, but does not connect into the two reservoirs. From Hillview Reservoir the water is supplied to the city via three main distribution tunnels, known as City Tunnels 1, 2, and 3. City Tunnel No.1 was developed in the 1920s as part of the Catskill system. City Tunnel No. 2 followed in the 1960s as part of the Delaware system. City Tunnel No. 3 (CT3) is partly under construction and partly in operation, and is being implemented to permit the other distribution tunnels to be taken out of operation for the first time for inspection and maintenance. Presently CT3 is supplied with water from Hillview Reservoir via a large underground valve chamber, the Van

Jan 1, 2007

THE North Mount Lyell Mine is situated on the southern side of Mount Lyell at an altitude of 1750 ft. above sea-level. The average rainfall is 117 in., and there are generally several light falls of snow during the year. Despite the heavy rainfall, which is fairly evenly distributed over each of the twelve months, the climate is equable and not unduly rigorous, and, provided that the mine employee is suitably clad, it is only on exceptional days that he experiences any discomfort by becoming wet journeying to and from the mine.The majority of employes reside at Queenstown, and are conveyed by special trains to and from the top of the haulage, which is less than a mile from the mine. The mean surface temperature at the mine is 46° F., with a maximum variation from 26° F. to 85° F., the relative humidity generally being higher than in other districts. The rock temperature is 48° F. on the 200-ft. or Main Adit level, and 54° F, on the 1200-ft. level, giving a rise of 6° F. for 1000 ft. in depth.The ventilation of the mine is natural, the downcast being served by the Crown and Blocks shafts and the Crown mullock pass, and the upcast air is carried away from the workings by the Main shaft and the Nos. 1 and 2 mullock passes. The quantity of air circulating varies from 25,000 cub. ft. to 35,000 cub. ft. per minute, the greater quantity moving in the colder weather. The downcast air in traversing the wet shafts becomes saturated and enters the level at the rock temperature of 54° F. in winter and about 56° F. in summer, while temperature readings of the outcast air indicate that it varies very little.In the southern end of the mine the Blocks shaft downcast air upcasts through the different stopes, and their mullock passes, to the level above for each level to the 700-ft. level, where it passes to one of the main uptakes. The prown shaft downcast air supplies...

Jan 1, 1927