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Because of its small interburden thickness, concentrated stress distributions, high coal seam metamorphism, and complex geological conditions, mining the five coal seams (Nos. 5, 7, 8, 9 and 12) of Kaiping coalfield is difficult. Kaiping coalfield is located within 80 m in the Kailuan Group. The overburden caving caused by mining the five coals seams was measured using ZTR12 geological penetration radar (GPR) survey combined with borehole observations. The development characteristics of full-cover rock fractures after mining were obtained from the GPR scan, which provides a measurement basis for the control of rock strata in close multiple-seam coal mining. For the first time, it was found that the overburden caving pattern shows a periodic triangular caved characteristic. Furthermore, it is proposed that an upright triangular collapsed rock pile and an inverted triangular area with larger fragments piled up alternately appear in the lower gob. The research results show that the roof structure formed in the gob area can support the key overlying strata, which is beneficial to ensure the integrity and stability of the upper coal seams in multiple-seam mining of close-coal seams.

Jan 7, 2020

By Emily Sarver

"Across all sectors and commodities, a common theme is driving progress in raw resource supply: sustainable development (SD). Over the past few decades, the mining and minerals industries for their part have undertaken significant and intentional changes at every level to become more responsible — no longer to just their shareholders, but also to the environment, to the communities in which they operate and to society at-large. Led by some of the global majors, these industries have indeed helped to define and operationalize the basic principles of sustainable development. Now in the midst of a full-on cultural shift, they are also key players in the continual effort to re-examine and calibrate practices to meet dynamic and increasingly complex objectives.SME’s technical position statementAs a home for so many technical experts and practitioners, SME has long recognized the importance of a commitment to sustainable development by the mining and minerals industries. In April 2016, the Society formally adopted a technical position on the topic following years of participation in, and support for, related activities. The full position statement appears below. It was drafted, revised and presented for approval to the board of directors by SME’s Sustainable Development Committee.Statement of Technical Position on The Mining Industry and Sustainable Development:• The National Environmental Policy Act of 1969 (NEPA) and the Surface Mining Control and Reclamation Act of 1977 (SMCRA) imposed considerable environmental restrictions on the mining industry; SME has always reinforced strict adherence to the laws.• In 2002, SME established a Sustainable Development Committee to lead its efforts in this area and to propel the organization into global prominence.• SME is a signatory to the Milos Statement of 2003 on Sustainable Development, so it is committed to providing scientific, technical, educational, and research skills in minerals, metals and fuels.• SME recognizes that SD programs adopted by the industry have a tangible return on investment through brand recognition and loyalty, facilitation of permitting, reduced occurrence of community protests and vandalism and diminished political risks.• SME actively promotes educational programs that encourage professional growth and interaction with the engineering professional community through books, articles, symposia, short courses and/or conferences on sustainable development in the mining and minerals industries.• SME has developed abundant expertise to provide balanced advice to government bodies, congressional staff and other interested organizations."

Jan 12, 2017

By C. G. Anderson

In some parts of the world, silver chloride occurs naturally in deposits of cerargyrite (1) (i.e. horn silver). In other cases, silver chloride is produced and exploited for its well- known photographic or electrochemical properties. In this case, it is a valuable commodity needing no further refinement. However, silver chloride is frequently encountered in precious metals refining. In most cases, it is a by-product that occurs in small amounts. For example, it is a common occurrence in gold refining when using the Miller and Wohlwill refining processes or when parting fire assay beads. As such, the mode of reduction to elemental silver is of little impact on the overall refining economics. Thus, a variety of reduction methods are employed all enjoying varying degrees of popularity (2). On the other hand, silver chloride serves as a key intermediate in the production of fine silver by nitrogen species catalyzed acid pressure leaching of refractory silver concentrates. This has most recently been practiced at the Sunshine Mining & Refining plant located in Kellogg, Idaho. Thus, efficient methods of reduction, precipitation and materials handling on an industrial scale are of the utmost importance. In this presentation, the evolution of these methods will be detailed.

Jan 1, 1997

By Thomas Novak, Sampurna Arya, Joseph Sottile

Dust generation and its dispersion in a longwall mine pose significant health and safety issues. The concern is prominent at both the working face, where coal excavation exposes workers to high dust concentrations, and also in the return, where float dust accumulates. To address this issue, researchers at theUniversity of Kentucky designed and fabricated a flooded-bed dust scrubber integrated into a full-scale physical model of a longwall shearer. This mock-up was installed in the longwall test gallery at the Pittsburgh Research Laboratory (PRL) of the National Institute for Occupational Safety and Health (NIOSH). A full-factorial experiment was designed to measure the effectiveness of the scrubber on dust capture. Test results indicated dust reduction of up to 57% in the return airways. This paper presents the development of a computational fluid dynamics (CFD) model and its validation by comparing the simulation results against the experimental results. The CFD simulations show good agreement with experimental results with differences between + 6.9 and − 9.7%. The validated CFD model was used further to predict the scrubber performance under additional operating conditions, resulting in a dust reduction of up to 66.5%. With this level of success, the scrubber concept can be a game changer for the mining industry, and it can be utilized to improve health and safety in longwall mines.

May 26, 2020

By K. Fountain

In Novemeber of last year I visited a mica mine in Hunan Province, China. For nine months , we had been trying to sell Chinese mica to a customer in Belgium. Talking to the customer was like negotitating with a stone wall. The buyer refused to communicate any -thing other than his steadfast refusal to consider Chinese mica. He would not advise us what he wanted, what specifications or grades. He would give no indication if our price at market, or reasonable, or totally out to lunch. He would not even accept samples. It took no genius to guess that the mica buyer had at some time in the past bought a shipment of Chinese mica and had received a disaster. I invited the mica mine in Hunan in order to see for myself what could be done - without massive investment in equipment and instruments - to upgrade the quality of the mica for export. We had seen this type of customer reaction before. One disgruntled customer who had pur¬chased pigment grade barites direct from China ranted and raved about unreliable and inconsistent quality. It did no good to explain to him that China is a big country, with hundreds of mines scattered throughout many areas, each producing a different product. Our further explanation that Chinese export organizations also varied in degree and efficiency of customer service fell on deaf ears. Samples had no effect on his perception. Eventually we showed him photoraphs of two mountains of pigment grade barites. One lot was our sales of pigment barites to a major European minerals processor. Our Chinese barites stood proudly white and beautiful next to a hill of other material which now appeared at best mediocre and dull by comparison, and which the buyer had decided to reject after he received our Chinese barites. Finally the customer was sufficiently impressed to look seriously at our guaranteed specification and the outturn analysis performed by our other customer.

Jan 1, 1987

By William Gleason

"Ed Rapp is among those who believe in the saying that necessity is the mother of all invention. Rapp is the president of Caterpillar’s mining group. As such, he is tasked with leading the world’s largest mining equipment maker, and its customers, through this time of lower commodity prices, while also positioning his company to be prepared for better days that lie ahead.The decade-long mining boom fueled by growth in emerging markets and demand for commodities that led to record prices for some metals paused in 2008 with the global financial crisis. However, according to Rapp, thanks to stimulus packages around the world, and in particular the stimulus from China that was focused on infrastructure, the mining sector recovered fairly quickly, and from 2010 to 2012, mining was strong.And then the stimulus stopped. Credit dried up and global growth began to slow down and, in the three years since, commodity prices have declined by an average of 60 percent. Caterpillar expanded during the boom, acquiring Bucyrus, and investing billions into the mining sector. It has felt the pinch of the slowdown as much as any mining company in the world. These pages, and those of other mining publications as well as mainstream media, have been filled with stories of doom and gloom about the industry. But Rapp, while acknowledging that the difficult times have been painful, also said Caterpillar sees opportunity in the slow down and reaffirmed his company’s commitment to the mining industry as absolute."

Jan 1, 2014

By Charles F. Coleman

Kinetics studies and other rate measurements are reviewed in the amine extraction of uranium and of some other related and associated metal ions. Equilibration' is relatively fast in the uranium sulfate systems most important to uranium-hydrometallurgy. Significantly slow; equilibration-has ' been encountered' in some other systems. Most of the recorded rate information, both qualitative and quantitative; has come from exploratory and, process-development development work, while some kinetics studies have been directed specifically toward elucidation of, extraction mechanisms. In contrast to some other extraction systems, relatively little attention has been given to the kinetics of uranium extraction by amines. This is because investigators have not been troubled by slow extractions. Instead, when rate limitations have been of concern in amine extraction (Amex) process developments, they have been mainly from slow phase disengagement rather than from slow equilibration. Nevertheless, taking uranium together with several other elements that are closely related to it or associated with it in typical processes, a considerable body of rate information has been recorded.

Jan 1, 1979

By Steinar L. Ellefmo, Fredrik Søreide

"The Norwegian University of Science and Technology (NTNU) and Nordic Ocean Resources AS, with support from Statoil ASA have carried out a project reviewing the knowledge about seabed mineral resources in Norway to identify and prioritize needs for further research and development.A special focus area in the project has been to increase the knowledge of possible massive sulfide mineralizations along the Mid-Atlantic Ridge. This Ridge is a subsea mountain range which separates the Eurasian and the North American continental plates. In this area, seafloor massive sulphides (SMS) are formed from the volcanic and hydrothermal activities along the Ridge. A large part of the North-Atlantic Mid-Atlantic Ridge between Jan Mayen and Spitsbergen is located on the Norwegian shelf.Analysis and interpretations of multibeam data have been carried out by NTNU in cooperation with the Russian Institute for Geology and Mineral Resources of the Oceans in order to disclose relevant areas for the formation of SMS deposits. This analysis has identified several promising areas."

Sep 1, 2014

By J. Bertisen, G. Davis

Previous analyses of small samples of mining projects have found that feasibility studies tend to well under-estimate the actual capital costs of the project. Our review of 63 mining and smelting projects completed over 4 decades confirms that as-built capital costs are, on average, 25% higher than as estimated at the bankable feasibility study stage. There appears to be little attenuation over time of this bias in capital cost estimation, at first appearing to reflect an absence of learning on the part of the consulting engineer. We instead argue that this persistence of bias is intentional, driven by a scarcity of project financing and the need to inflate the project economics in a bid to secure financing. Around this intentional bias is a considerable amount of scatter. Roughly half of all projects’ as-built capita costs fall outside of the expected ±15% of the feasibility study capital cost estimate, even after allowing for intentional estimation bias. Cost overruns of 100% or more happen in roughly 1 out of 13 projects. The data reveal that a shifted lognormal probability distribution should be used when modeling mining project capital costs in a Monte Carlo analysis.

Jan 1, 2007

By Juan Ares, Enrique Fernández, Alejandro Sanz, Francisco González

"INTRODUCTION Crossrail is a subsidiary company of Transport for London created for the construction of a new transverse train line 118 km long between Maidenhead and Heathrow in the West, and Shenfield and Abbey Wood in the East, including 21 km underground below London. Crossrail C305 Eastern Running Tunnels project is the biggest contract within Crossrail Project and involved boring 11.8 km of twin tunnels through London’s city center. Crossrail C305 Project interfaced with different contracts along its alignment and therefore logistics and solutions had to be developed to minimize disruptions or interferences with other contractors and the neighborhood. The paper describes this innovative approach. C305 CONTRACT APPROACH C305 contract was split into three drives, to be excavated by four EPB TBMs 7.1m diameter, as shown in Figure 1. •,Drive Y: 8.2km long between Limmo Peninsula and Farringdon Station in the city center •,Drive Z: 2.7km long between Pudding Mill Lane and Stepney Green Junction •,Drive G: 0.9km long between Limmo Peninsula and Victoria Dock Portal in the East. Crossrail C305 Project scope of works included the excavation of TBM tunnels and shafts at Limmo Peninsula and Stepney Green (including 17m span turnout caverns), along with the requirement to traverse station and shaft structures of other Crossrail contracts. Limmo Peninsula Site was a strategic element as it was the only access point on the tunnel alignment with sufficient available area at the surface for tunnelling logistics and also connected to the Lea River, tributary of the River Thames which facilitated marine operations for segment supply and muck removal. These were the reasons for operating Drive Y & Drive G TBMs from that location. Drive Z TBMs were originally planned to be launched from Stepney Green to Pudding Mill Lane, supplying the TBMs during Drive Z excavation from Limmo Peninsula site through the excavated section of Drive Y between Limmo and Stepney Green. During the early stages of the project, a value engineering proposal with a new tunneling strategy was agreed wherein the Pudding Mill Lane contractor would provide space for TBM assembly and operation in their portal, allowing for reversing Drive Z excavation and launching the two TBMs from Pudding Mill Lane. This optimization reduced some of the shaft requirements at Stepney Green which were contingent upon critical enabling works and provided program certainty and cost savings for the full Crossrail Project. It allowed for the reuse of both the Drive Z TBMs for Drive G excavation from Limmo to Victoria Dock Portal thereby saving on the procurement of two TBMs, in addition to easier logistics for both Drives Y&Z, therefore de-risking the TBM excavation process and the C305 Project program completion."

Jan 1, 2016

By T. E. Wayland

Bentonites are clay materials composed principally of minerals in the montmorillonite group. Distinctive physical properties of the montmorillonite minerals are responsible for selected bentonite deposits having become the raw materials source of industrial clay products which are virtually essential to the maintenance of high production standards in the petroleum, foundry, taconite and other basic industries. These versatile materials have no suitable substitutes in either their major applications or in hundreds of speciality products, The economics of the bentonite mining industry follows closely the established pattern of other non-metallic raw materials. Aggressive competition, advanced technologies, progressive marketing techniques, substantial reserves, and vast unmeasured resources insure the continued supply of high quality bentonite to industry at bargain prices. The purpose of this paper is to discuss the geology and economics of bentonite deposits, summarize both major domestic mining districts and foreign deposits, and report significant results of research and development.

Jan 1, 1970

By J. Pereyra, M. DeMarco

"INTRODUCTION It can be vital that bolted joints holding subassemblies together remain secure. Bolts should resist the loosening effects of vibrations and dynamic loads yet need to be easily removable during maintenance. When a threaded fastener is subjected to vibration, the rapid movement causes a lowering of friction against the threads and a subsequent loss of preload. The loss of preload allows the fastener to vibrate loose and possibly fall out. As the diameter of fasteners increase desired preload becomes increasingly more difficult to achieve. Input torque requirements for achieving proper bolt preload is exponentially related to any given fasteners diameter. This means that specialized tooling or bolting practices are usually required to attempt the tightening of fasteners to reach their required preload. Traditional methods can cause problems with joint integrity and do not provide consistent bolt load across the bolted surface. BOLTED CONNECTIONS A failed critical bolted joint can lead to high maintenance costs, machine downtime, and risk to worker safety. Control of the clamp load in a bolted joint is vital. However, when faced with a problem joint, it is not surprising that the design engineer will not have an answer if asked about the clamp load. Torque calculations must always be based on the existing conditions that often are vague. Unless all parameters are correct, the calculation will be unreliable. Examples of parameters are: • Thread condition of the fasteners • Hardness of contact surface • Material (steel, aluminium, copper, etc.) • Extra friction from a locking fastener • Extra friction from an adhesive • Lubricant on the thread • Type of bolt head (flanged, regular or serrated) • Surface coating of the bolt • New or reused fastener During tightening, bolts are subjected to both tensile and torsional stress. The total stress in a bolt can be calculated using the formula: Total stress = vsx2 + 3txy2 In order to maximize the desired tensile stress (sx) it is vital to minimize the torsional stress (txy). Tensile stress (clamp load) is achieved when the bolt is axially elongated. Unwanted torsional stress (twisting) in bolts arises during tightening due to thread friction. High thread friction increases torsional stress and causes yielding at lower clamp load levels than normal. A lubricant is necessary to minimize the malign torsional stress. However, many commonly used bolt-locking systems are based on increased thread friction (deformed nuts, adhesives, etc). To minimize thread friction and concurrently safely secure the joint has often incorrectly been considered impossible. The use of locking systems that increase thread friction is the single most common reason why the full capacity of bolted joints is not utilized. The following example illustrates the problem."

Jan 1, 2015

By John E. Caffrey

United States Steel Corporation began mining coal in southern West Virginia at the turn of the century, and until the late 40's production was confined to underground mines. Surface mining was initiated in our southern West Virginia -holdings as a means of recovering coal that could not be obtained by underground mining methods. After observing and evaluating surface mining methods employed by other companies, some of which operated on lands of U. S. Steel on a lease basis, we undertook the establishment of a surface mining operation. Our method, as, initiated in the early 50's, remains basically the same today. Variations have come about primarily by equipment modifications. The method consists' of a pioneer cut to establish the coal outcrop, a drill bench for drilling, blasting, and removal of the overburden from the top of the coal. The land is rugged except for the flood plains of some of the larger streams. The mountains have steep slopes, averaging 30 degrees, with relatively sharp ridges and very narrow valleys,. Geologically, the coals_ lie in the Pocahontas formation of the Pottsville group in the Pennsylvanian system. This means that the coals in our area of operation lie at the base of. The coal measures in the Appalachian range. The coal that we have mined is primarily the Pocahontas nos. 3 and 4 seams. We have mined negligible amounts of other seams in the Pocahontas groups above the no. 4 seam. The Pocahontas no. 3 seam, which is the lowest mineable seam geologically in this area, lies anywhere from 700 feet below: the valley floor up to 400 feet above the floor. This is occasioned by the Anticlinal formation which gives us grades Of about 9% at the anticline, decreasing to about 1 to 1-1/2% on the extreme flanks. We have the opportunity to engage in surface mining where the coal seams intercept the surface above the valley floors.

Jan 1, 1972

By Valerie Kollonitsch

Functional mineral pigments are used in large quantities in paint, paper, plastics, rubber, textiles, agriculture, and several other industries. U.S. consumption in 1969 is estimated at over 5 million tons a year, valued at nearly $150 million, as shown in Table 1. Originally extender pigments were employed only to lower cost. They were thought of merely as adulterants to replace more expensive prime pigments and binders. However, over the years their role has become better understood, and today their main functions are: - Increasing strength, stability, and service life. - Improving surface properties. - Enhancing application and processing properties. - Extending prime pigments. - Controlling viscosity and package stability - Lowering overall costs of the finished product. The principal minerals used as functional pigments are kaolin, ground calcium carbonate, talc, and asbestos. Other minerals include barytes, attapulgite, diatomite, mica, ground silica, wollastonite, and nepheline syenite. Several synthetic products, including precipitated calcium carbonate; precipitated, gel, and fumed silica; alumina trihydrate; and barium sulfate, compete with mineral products. They are more expensive, but often have more closely controlled particle size or other properties because they can be tailor-made according to the requirements. This paper covers only natural products selling for $10 or more a ton, approximately the lower limit for pigment grades. Data refer only to consumption in pigment applications. For example, such applications as filter aids for diatomite are not included. Key properties of the major mineral pigments are given in Table 2. It is important to note that these properties are primarily physical rather than chemical. In general, these products are sold to performance specifications for what they can do rather than on chemical composition specifications on what they contain.

Jan 1, 1969

By William Gleason

"Speakers and attendees of the 2016 Cutting Edge Conference could not be faulted for keeping one eye on the presentations taking place at the Hyatt Regency at LAX in Los Angeles, CA on Nov. 7 and 8 and another on the results of the historic election in the United States that took place on Nov 8. While there was certainly interest in the presidential campaign, there was also a great deal of interest in Measure M on the California ballot. Measure M, which passed easily, is a half-cent sales tax increase that will fund the most ambitious transit expansion in Los Angeles County history.In the coming years, the ballot measure will transform a traffic-choked region by funding the construction of nearly a dozen new rail lines with an estimated $120 billion raised in four decades. Among the projects that could come to fruition are a twin-rail tunnels project through the Sepulveda Pass and new connections in the city.During the update on West Coast projects, Bill Hansmire summed things up with a slide asking “How much work is there on the West Coast,” and his answer was “Billions.”From Seattle, WA south to Los Angeles, there is already a lot of work for tunneling and underground construction experts, and Measure M ensures that there will be plenty of work for decades to come.Currently, The Los Angeles County Metropolitan Transportation Authority (Metro) has three rail projects underway that were funded by Measure R in 2008 — the Regional Connector, the Purple Line subway extension and the Crenshaw/LAX Line that are designed to alleviate the traffic pressure with an eye to more solutions.Measure M is the fourth sales tax increase to fund transportation in L.A. County, bringing the base sales tax rate to 9.25 percent. In some cities, which already levy their own sales tax, the rate would be higher, The Los Angeles Times reported.About 35 percent of the revenue will fund major new transit projects, such as the subway under the Sepulveda Pass, extension of the Gold Line to Claremont, extension of the Crenshaw Line to West Hollywood and acceleration of the Purple Line Subway construction along Wilshire Boulevard to finish in 2024, 10 years earlier than scheduled.About 17 percent would fund a dozen highway improvement projects, such as widening parts of I-5 in the Antelope Valley and southeastern county, adding bus lanes to the Sepulveda Pass section of the 405 freeway and adding truck-only lanes to a section of the 710 freeway."

Dec 1, 2016

By Juan J. Monsalve, AMAN SONI, ALEX PFREUNDSCHUH, Nino Ripepi

Ground control failures are one of the main causes of accidents in the underground stone mining industry. Some of the fundamental tools for rockfall hazard identification are related to rock mass characterization and geotechnical discontinuity mapping. Recent technological advances in these methods are related to remote sensing techniques and pointcloud processing software for automated discontinuity mapping. Remote sensing techniques, such as LiDAR and photogrammetry, generate multimillion-point clouds with millimetric precision, capturing the structure of the rock mass. The automated point-cloud processing tools offer alternative algorithm-based methods to characterize and map these discontinuities. However, their applicability is constrained by multiple factors, such as site-specific conditions of the rock mass and the parameters used within the mapping algorithms. This paper evaluates the performance of automated discontinuity extraction software compared with manual virtual discontinuity mapping. Sampling windows from laser-scanned sections in an underground limestone mine are defined and mapped using the Discontinuity Set Extractor (DSE) opensource software. Results from the virtual discontinuity software are compared with manually extracted fractures from I-Site based on reviewing orientation, trace length, spacing, number of extracted discontinuities, and processing time.

By C. M. Jones

The training program developed at Sierrita over the last twelve months has led to several significant improvements in both safety performance and productivity. Our most easily quantified results have been in truck productivity, where we have also experienced a 6% decrease in truck cycle times. We feel this is due to increased skill levels and awareness on the part of our operators due to our new training effort. The cycle time improvement has resulted in an increase in Truck productivity of 6%. Costs associated with productivity training have been $160,300. This includes program development and execution costs, as well as lost productivity during the training itself. These costs are offset by $1,400,000 in savings directly attributable to the increased skill levels of our technicians due to our training effort. As such, this represents a solid, high return investment at Sierrita.

Jan 1, 1998

By W. G. Pariseau

Reliable stress measurement using hollow inclusion gauges and monitoring stress change using borehole stress meters and borehole deformation gauges in anisotropic rock remains a challenge for the rock mechanics community. In this regard, the complex variable method advanced in 1983 for deducing stress in anisotropic rock is flawed and software is privileged. Fortunately, advances in computer hardware and software now enable fast, reliable reduction of hollow inclusion stress measurement data for determining stress in anisotropic rock. Monitoring stress change in anisotropic rock poses a different challenge but is also subject to numerical analysis. Stress measurement using a hollow inclusion (HI) gauge such as the triaxial Australian HI is done in four steps: 1) drilling a measurement hole, 2) installation of an HI, 3) stress relief of the HI by overcoring, and 4) data reduction. The last step, data reduction, is the focus of this work. The process is well-known in linearly elastic, isotropic rock (Worotniki and Walton 1976, Duncan Fama and Pender 1980). However, in case of linearly elastic, anisotropic rock the requisite technology is not readily available. This situation is somewhat surprising because anisotropy is more often the rule rather than the exception, especially in the neighborhood of ore bodies. Rahn (1984) has pointed out the potential for significant errors with neglect of anisotropy and the adverse consequences for engineering design. Amadei (1984) has also pointed out the potential for errors with neglect of anisotropic rock properties in stress measurement. Worotniki (1993) cites other studies that indicate potential for serious errors when doing measurements in anisotropic rock. In both theoretical cases (isotropy and anisotropy), data reduction is essentially a composite of solutions to boundary value problems in linear elasticity. In the finite element approach, the analysis is a simulation of gauge hole drilling, installation and overcoring. Two important advantages with the finite element approach are a more faithful representation of the conditions of HI stress measurement than approximated in theory and the capability for handling rock whether isotropic, transversely isotropic or fully anisotropic

Mar 2, 2022

By John Reilly

Traditional methods of project procurement of have remained virtually unchanged in the U.S. infrastructure construction industry for more than 50 years. The traditional method, Design-Bid-Build (DBB), uses a two-step process that separates planning and design from construction. Design is generally done by the public agency and their consultants and the subsequent construction contract is procured from the private sector, almost always by a “low-bid” approach. This method has worked well for many projects, delivering quality work for the lowest bid price. This is particularly true for those projects where the work, and the public agency’s management procedures, are well understood by the contracting community and there is relatively low uncertainty in the work or conditions, particularly geotechnical conditions for underground construction. However, concerns exist with the DBB process. It is time consuming because all planning and design work must be completed prior to beginning any construction work and it is of concern for complex or large projects, plus those with significant risk, where the separation of design and construction, in conjunction with pressures resulting from the low-bid environment, often result in substantial cost and schedule increases. Frequently, these increases occur in a non-productive, inefficient, adversarial work environment leading to claims, disputes and costly litigation (Quick 2002).

Jan 1, 2007

By Charles Banks Belt

In 1925, Niggli (1925, pp, 1-69), formulated a physico-chemical, explanation for the origin of hydrothermal ore deposits, from a concept that had appeared earlier in the literature in the writings of Von Groddeck, Stelzner, Beck, de Launay, Kemp, and Lindgren. Niggli proposed that pressure at depth could force volatiles from deep-seated magmas. The volatiles would In turn form pegmatites and then ore deposits as the fluids cooled. This is one view of a general theory of ore genesis that gained secondancy for years among such prominent geologists as Fenner (1926, p, 697) and Emmons (1936, pp. 29-70). It was, proposed that ore deposits were precipitated from solutions or fluids that had escaped or been separated from a deep-seated magma by means of liquid immiscibility or crystallization or gas transfer. This theory is based on the presence of igneous rocks close in space and age to hydrothermal ore deposits in many mining districts of the world. As is well known, there are many ore deposits apparently of hydrothermal origin that are neither spatially nor chronologically related to igneous rocks, In still other localities where there are no hydrothermal ore deposits, igneous rocks occur that are similar in composition to those in mining districts. In view of such facts, the applicability of the Niggli theory to all hydrothermal ore deposits may well be questioned. The chief purpose of this paper is to test the Niggli theory by studying the primary petrology, hydrothermal alteration, and distribution of copper and zinc in silicic igneous plutons supposedly genetically related (in the Niggli sense) to nearby hydrothermal ore deposits, Silicic Tertiary plutons in three New Mexico mining districts were chosen, the Hanover-Fierro intrusive at Hanover and Fierro, the Granite Mountain pluton at Magdalena, and the four outliers of the Lordsburg stock at Lordsburg. First, it had to be established whether the observed plutons were or were not the source of the adjacent ore deposits. This was done by studying the relation between the copper or zinc distribution-and the primary or secondary features in the plutons studied, and the time relations between instrusion and ore deposition. Primary igneous features of a pluton are defined as the minerals, texture, shape, and character of the pluton which were formed prior to the complete solidification of the rock, secondary features include all changes that took place in a pluton after solidification. They are identified by their cross cutting nature or as replacing primary minerals, Under the Niggli concept, it is proved that the ore ions did not originate from the parts of the pluton now visible as immediately adjacent to the ore deposits; it must then be established, if possible', that the ore ions were separated from deeper parts of the intrusive, Some idea as to whether the copper or zinc ions originated from a related magma at depth may be gained by a comparison between the primary (that is, pre-alteration) zinc and copper abundances found in ore localizing intrusive studied and the average abundances for copper and zinc in silicic igneous rocks most recently given in the literature. Finally, the relation between ore deposition and hydrothermal alteration was studied on a regional as well as on a local scale.

Jan 1, 1958