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By A. Sobhy

Froth flotation is a widely used, cost effective coal cleaning process. However, its high process efficiency is limited to a narrow particle size range between approximately 50 to 600 µm for coal and 10 to 100 µm for minerals. Beyond this range, the efficiency of froth flotation decreases sharply, especially for difficult-to-float coal fines of weak hydrophobicity (e.g., oxidized coal). This study was aimed at enhancing recovery of an Illinois fine coal sample using a flotation column featuring a hydrodynamic cavitation nanobubble generator. Nanobubbles that are mostly smaller than 1 µm can be formed selectively on hydrophobic coal particles from dissolved air in fine coal slurry. Results indicate that combustible recovery of a -150 µm coal was increased by 5-50% for different size fractions in presence of nanobubbles, depending on process operating conditions. Other major advantages of the nanobubble flotation process include lower collector dosage and air consumption since nanobubbles are produced from air naturally dissolved in water and they act as a secondary collector on particle surfaces, thereby resulting in considerably lower operating costs. Key words: Cavitation; coal; froth flotation; nanobubble.

Feb 27, 2013

By Remo Grandori

The Umiray Angat 13,2 km long tunnel in Philippines have been bored through extremely variable and difficult ground conditions including a number of special events. In particular the following adverse conditions were found: faults in decomposed ground, high temperature rocks, extremely rapid and important convergence phenomena, water inflows up to 800 litres per second. The special El Nino climatic conditions caused a long dry season and lower the level of the lake that was granting the access by barge to the site under the minimum navigable level. Many equipment have had therefore to be transported to site by a 10 ton capacity helicopter, after having been partially dismounted. For the same reason most of the tunnel drive have been bored servicing the site by 1 ton capacity helicopters to transport materials, spares and personnel. In order to overcome the above geological and logistic problems several innovation were introduced and tested in this project. Despite all that difficulties the 13,2 km of tunnel were bored in about 24 months, with a global average of 500 m/month.

Jan 1, 2001

By D. R. Brox, J. Levell

The Montana Tunnels Mine was mined out to a depth of 900 feet at the end of 1999. The first signs of instability were recognized in 1996 along the upper slope area of the northwest sector when the pit was mined out to a depth of approximately 500 feet. To extend the life of mining operations, it has been proposed to extend and steepen the northwest highwall to a depth of 1000 feet. Slope stability analyses were carried out using the UDEC software program to assess the stability and deformation of the proposed highwall design. Back analysis of an instability in 1997 along the upper slope section and highwall deformation to date has indicated reasonable agreement with the observed mode of failure and displacement monitoring results. The results of detailed analyses of the proposed highwall design have indicated very limited additional deformation, further development of tension cracks is unlikely and large-scale instability is not expected to occur. A total of 40% of additional mining has been completed and ongoing displacement monitoring to date has confirmed very limited additional movement and no further tension crack development.

Jan 1, 2001

By B. Mishra

This paper presents a rock mechanics investigation of the time-dependent behavior of the rock immediately surrounding the excavation in a hypothetical one-entry coal mine based on the geology of the Illinois coalfields Research in the area of time-dependency is almost nonexistent and, therefore, this research was performed to make inroads into this neglected research area. Numerical analysis of a typical one-entry coal mine in an Illinois basin was performed using the commercial finite difference program FLAC3D. The immediate roof of the coal entry was assumed to be a shale formation. Shale in other formations has shown a tendency to creep with time. Therefore, in this study the authors modeled the shale in the roof using time-dependent characteristics. The input properties were taken from laboratory creep tests performed on shale. Model runs were performed at different stages, mimicking the progressive excavation of the entry. The model results showed that stresses in the roof attained the limit of yielding. Using Mohr-Coulomb failure criteria, potential zones of failure were also predicted. The results showed that the current computational capacities are sufficient to explore this previously uncharted territory of ground control.

Mar 1, 2014

By F. Grajales Muñoz

The Ciénega project, now under construction by Peñoles group, is located in the mountains of northwest Durango, Mexico. The gold and silver deposits are found in a 4-km (2.5mile) long system of veins. An underground operation will be built. The planned 1 kt/ d (1100 stpd) process plant will contain a countercurrent cyanide circuit for oxide ore and a flotation circuit for sulfide ore. Considerable resources have been devoted to the development of infrastructure in the isolated location, as well as for the mitigation of environmental impacts. Startup is scheduled for the third quarter of 1994. Ciénega’s ore bodies consist of quartz veins containing gold, silver, lead and zinc values. The vein thicknesses vary from 2 to 10 m (6.5 to 33 ft) with a northwest trend and nearby vertical dip. Veins are hosted in Tertiary volcanic rocks. The district has intermittently been explored since 1971 by Penoles. After the third series of diamond drilling and direct development work on vein, Peñoles decided to begin project construction.

Jan 1, 1994

By Richard D. Lang

Introduction Argyle is located in the Kimberley region in northwest Australia (Fig. 1). It is a significant diamond discovery by world standards and is the first major diamond find in Australia. The deposit consists of a pipe and associated alluvial deposits. Before the 1970s, diamonds were known to exist only sporadically in Australia. They have been found occasionally in association with gold deposits in Western Australia. There is a small deposit near Copeton in New South Wales. Some alluvial occurrences have also been found in Victoria, South Australia, and New South Wales. The first indicator minerals in the Kimberley region of Western Australia were discovered in January 1973. Production from the alluvial deposits at Argyle began in 1983. A $430-million construction program to develop a mine and treatment plant capable of producing 25 million carats per year was completed in December (1 carat = 0.2 grams). Ownership and management Participants in the project are known as the Argyle Diamond Mines Joint Venture. The group consists of CRA Ltd., 56.8%; Ashton Mining Ltd., 38.2%; and the Western Australian Diamond Trust (formerly Northern Mining Corp.), 5%. The project is managed by Argyle Diamond Mines Pty. Ltd., a wholly-owned subsidiary of CRA. Marketing is undertaken separately by the Western Australian Diamond Trust and by Argyle Diamond Sales Ltd. (for CRA and Ashton Mining groups). History Ownership of the Exploration Joint Venture has changed over the last 12 years as various parties changed their shareholdings. The original Kalumburu Joint Venture was formed in 1972 with five participants, each holding a 20% interest. By 1983, a number of ownership changes had occurred. The end result is that two original participants have sold out. CRA now holds a 56.8% share and the Ashton Mining Group holds 38.2%. CRA also assumed project management in January 1977. Table 1 demonstrates the long lead times involved in developing a project.

Jan 1, 1986

By B. Law, M. Menabde, B. Baird

Blasor is a new mine planning tool which is being used in the long and medium-term optimization of multi-open-pit operations throughout BHP Billiton’s Base Metals and bulk commodities portfolio. It is not just a scheduler, nor even only a schedule optimizer—although this function lies at the heart of the tool’s functionality—but a pit development plan optimizer, used from ultimate pit design and process plant capacity sizing right through to mining phase design and optimal panel scheduling. The tool uses a mixed-integer-linear-programming optimization engine to determine when material should be excavated and where it should be sent to optimize discounted operating cash flow over the life of operation. The core software design concept of Blasor is to provide a tool which is intuitive and flexible enough so that a competent mine planner can perform a pit development plan optimization without assistance from optimization specialists. To this end, a generalized graphical user interface has been implemented which allows full configuration of the optimization problem, including the definition of all inputs and constraints, specification of the material flow topology, bin and destination class definitions and full specification of the economic model encompassing prices and costs. This paper describes the capability of Blasor and outlines the design concepts underlying its design philosophy.

Jan 1, 2007

By Jianbo Hu, Gang Han, Tao Zheng, Junfeng Jiang, Rui Su, Qihua Zhao

The rock quality designation (RQD) is a commonly used index for the classification and evaluation of rock mass quality and is widely adopted in mining and geological engineering. The traditional method of obtaining RQD still requires manual measurement of core length and calculation of RQD, which is inefficient. To address this problem, we propose a framework for drilling core image segmentation and RQD estimation from digital images of cores in core boxes based on the deep learning algorithm. The proposed framework is generated by combining the Mask Region-Based Convolutional Neural Networks (Mask R-CNN) instance segmentation algorithm, the U-Shaped Convolutional Neural Networks (U-Net) semantic segmentation algorithm, and the image processing functions of the Open Source Computer Vision Library (OpenCV). To demonstrate the accuracy of the proposed method, seven boreholes in the Xiushuihe vanadium-titanium magnetite mine, located in the Sichuan Province, China, were used as the case study. According to the comparison of the manual measurements and calculations of the cores taken from seven boreholes used to conduct this study, the framework can record the length of the drill cores and calculate RQD within an average error rate of 3.42%, while it saves about 85% of the working time. The results illustrate that the proposed framework enhances the efficiency of RQD calculation while satisfying the engineering requirements.

Jul 31, 2023

By G. ALBORNOZ, S. Utili, A. AGOSTI, C. VALDERRAMA, R. PELL, N. Morales

The steepness of the slopes of an open pit mine has a substantial influence on the financial return of the mine. The paper proposes a novel design methodology where overall steeper pitwalls are employed without compromising the safety of the mine. In current design practice pitwall profiles are often planar in crosssection and the profile in between ramps especially tend to be planar and defined by a constant inter-ramp angle. Sometimes rock layers exhibiting different strengths require the inclination of the profile to vary with depth, but the inclination across each layer is usually constant. Here instead, a new geotechnical software, OptimalSlope, is employed to determine optimal pitwall profiles of depth varying inclination. OptimalSlope seeks the solution of a mathematical optimization problem where the overall steepness of the pitwall, from crest to toe, is maximized for an assigned lithology, geotechnical properties and Factor of Safety (FoS). Bench geometries (bench height, face inclination, minimum berm width) are imposed in the optimization as constraints which bind the maximum local inclination of the sought optimal profile together with any other constraints such as geological discontinuities that may influence slope failure. The obtained optimal profiles are always steeper than their planar counterparts (i.e. the planar profiles exhibiting the same FoS) up to 8 degrees depending on rock type and severity of constraints on local inclinations. The design of a copper mine is first carried out employing planar pitwalls, secondly adopting the optimal pitwall profiles determined by OptimalSlope. The adoption of optimal slope profiles leads to a 34% higher net present value and reductions of carbon footprint and energy consumption of 0.17 Mt CO2 eq and 82.5 million MJ respectively due to a 15% reduction of rockwaste volume.

Mar 2, 2022

By Paul Eger

The use of wetlands to treat mine drainage has become increasingly common, particularly as more information is available on their operation and construction. However, the lifetime of each system is still, at best, an estimate. Treatment lifetime depends on the types of processes that provide the majority of the metal removal. Anaerobic systems (vertical flow systems) rely primarily on sulfate reducing bacteria, which reduce sulfate to sulfide and generate alkalinity. Metals can be precipitated as sulfides, and acidity is neutralized. These systems can remove over 90% of the metals and increase pH from around 4 to over 7. The bacteria will remain active as long as the system remains anaerobic and contains an adequate supply of sulfate and small chain organics. Although estimates of lifetime made on the total carbon in the system suggest that lifetime should exceed 20 years, data from field and laboratory studies show that the rate of sulfate reaction decreases with time, and that after several years rates decreased substantially. To maintain acceptable treatment, either additional organic material must be added or the total metal and acid load to the system would need to be reduced substantially. Aerobic systems (overland flow wetlands) can effectively remove metals from neutral mine drainage by reactions with organic material in the substrate. Over 90% of the copper and nickel have been removed in aerobic systems treating mine drainage in Minnesota. The primary removal processes in these systems include adsorption, ion exchange and complexation, which are finite; removal will cease unless new removal sites are generated. Two wetlands built in Minnesota have been successfully treating mine drainage for 12 years. At one of the wetlands, the annual production of new removal sites has been estimated to be equal to the annual metal input, and, as a result, metal removal should theoretically continue indefinitely.

Jan 1, 2005

By J. E. Friant

Until 1956, drill and blast was the only way to excavate rock. In that year, a tunneling machine using disc type cutters economically bored a small Toronto tunnel. Its amazing 105 ft/day set a new world record and set the stage for a new industry. The Disc Cutter Role in Excavation Mechanical excavation of hard rock is by now deeply ensconced in the heavy civil construction industry. All over the world, from the Swiss Alp Melange to Hong Kong Granite, to New York Gneiss, huge Tunneling Boring Machines (TBMs) create transportation, water and sewer tunnels. Powerful machines, boasting as much as 6000 hp, bore through rock, excavating in excess of 1400 tons per hour. The tool that makes this tunneling phenomenon possible is the single blade, rolling disc cutter. These hardened steel discs, from 15 1/2 to 19 inches diameter are arranged on a rotating cutterhead, to cut concentric circles in the rock. As the machine is propelled forward under great pressure, rock below each cutter is crushed. But the efficiency of the cutterhead is derived from the science of cutter spacing (distance between cutter paths). The majority of the rock excavated is not crushed, but flakes off in chips and chunks. No pick, tooth, or drag type cutting tool can duplicate the performance of a disc cutter. The economic use of drag type tools is limited to as low as 5,000 psi UCS rock strength in massive formations. In weakly bonded, foliated rock, drag tools do better, but are still limited to rock generally less than 15,000 psi.

Jan 1, 2002

By J. Um, B. Morin, P. H. S. W. Kulatilake

Development of a three-dimensional mine visualization model for a section of the mine is addressed first. Discontinuity orientation and location information was taken from this visualization model for use in slope stability analyses. Estimated shear strength properties of discontinuities and mechanical properties of intact rock from the rock mass samples obtained from the mine are discussed next. The paper is then focused on the calculated maximum safe slope angles based on the performed kinematic and block theory analyses using the mapped discontinuities at the mine. Finally, the effects of water that exist in the rock mass, tension cracks, slope face inclination, overall wedge height and double benching on factor of safety of wedge stability are illustrated through limit equilibrium slope stability analyses.

Jan 1, 2002

By Sarah Holtz Wilson, Kenneth Rossi, Carl R. Handford, David F. Tsztoo

The East Bay Municipal Utility District’s Claremont Tunnel is an 18,000-foot long water tunnel that crosses the Hayward Fault zone near Oakland, California. It was originally completed in 1929. This project involved the construction of a bypass tunnel through the fault zone, including an enlarged vault section designed to accommodate up to 8.5 feet of horizontal offset. Ground conditions encountered included sheared and crushed serpentinite and clayey fault gouge, and presented specific challenges for construction. A special excavation and support sequence used concrete-backfilled side drifts as foundations for the vault steel sets. It also allowed for a 20-foot-wide top heading and bench excavation in soft and squeezing ground conditions.

Jan 1, 2007

By Richard Hanke

Tunnel construction on the Brightwater Conveyance System?s East and Central contracts required ground modifications of the existing site soils, comprised of sandy alluvium to very dense glacial till, to assist with both hand-mined and TBM tunneling operations at vertical access shafts. The ground modification program was completed with a modified double fluid jet grouting system to construct continuous overlapping soilcrete columns to depths up to 94-ft below existing grade. This paper presents the sequence and methodology for the ground modification work and capabilities of jet grouting for structural support and groundwater control in the challenging soil profile present at the Brightwater Conveyance System Project.

Jan 1, 2008

By H. Lyn Bourne

This is the fifth annual tabulation of mineral royalty information. This tabulation, like the previous editions, includes all of the earlier data. There are also 60 new entries. In addition to royalty information, some entries show the cost of purchased reserves. Two articles relative to the evaluation of minerals reserves appeared in December, 1986. R.H. Paschall (In the Aggregate, ME, p 1139) wrote a good article, although it lacked specific royalty data. However, this author takes exception to two ideas in Paschall's column. Paschall contends that the royalty rate does not affect the mineral appraisal. This present author could not disagree more. Paschall also claims the location of an industrial mineral deposit is the only serious or practical caveat in comparing royalties. Comments received here from readers helped make the list of caveats that are cited each year. The readers will decide which factors influence the mineral value for their commodities of interest. Paschall's point about the relationship of the parties who are negotiating a royalty agreement is important and very well taken. The other article, written by William Vernon (Pit and Quarry, December 1986), gives a step-by-step process on how to conduct a mineral appraisal. The article cites three reasons for an appraisal: transfer rights; collateral for a loan; and taxation. A fourth reason is to establish adequate compensation for reserves lost through condemnation. This author has appeared in several court cases where compensation for loss of mineral reserves through condemnation required a mineral appraisal. Royalty rate becomes an important factor in the appraisal process, although the Pit and Quarry article refers to that part of the valuation equation as "profitability." Both articles were well written and are recommended reading for those interested in mineral valuations. The same caveats that have appeared in previous columns relative to factors that influence the value of reserves are restated. The data in the table serve as a general reference and are not intended to present an absolute scale of reserves costs. Several factors influence the value of any mineral commodity. The factors include: • location/transportation - especially significant for most industrial minerals; • market conditions both for the commodity and the company acquiring the right to mine; • quality or grade of the deposit as it reflects the amount of processing/beneficiation necessary to produce the finished product; and • legislative restrictions and conditions for mining a given material at a given site. These and other factors will significantly influence the cost of reserves. The table shows the range of royalties and the variations in the basis of computing the fees. In a few instances, it gives the cost of acquired reserves based on purchase price and quantitative estimates of the material in place. The table lists the commodity in column 1, and the subsequent columns give: • the location by state, US geographic area, or Canadian province ; • the cost - R for royalty and P for purchased cost; • the year in which the lease or purchase agreement occurred; and • comments or footnotes for more information. The cost column requires more explanation. The units may refer to cubic yards (/cu yd), cubic feet (/cu ft), short tons (/T), or acres (/A). 1 cu yd = 0.76 M2 1cuft = 0.28m3 1 st = 0.9072 t 1 acre - 0.4047 ha or m2

Jan 7, 1987

By Charles Merguerian

In medium- to high-grade metamorphic terrains such as found in New York City(NYC), rock mass texture and mineralogy are important factors in predicting TBM penetration destiny. Integration of data from over two decades of traditional field and tunnel mapping suggest that hard-rock TBM penetration in the NYC area depends upon textural, mineralogic, and structural control. The bedrock of NYC consists of many different lithologic units of varying age, composition, texture, and metamorphic grade including many varieties of intrusive rock. In addition, brittle faults of numerous orientations cut the polydeformed crystalline bedrock, producing zones of highly fractured and disturbed ground and high water inflows. Pre-bid compilation of published bedrock data, drill core analysis by geologists to establish lithologic and mineralogic trends, integrated surface geologic mapping along a proposed alignment, and targeted petrographic and geotechnical investigations to characterize the rock mass conditions together constitute an important prelude to successful subsurface bidding and tunneling. A carefully planned program of as-built geological mapping, structural analysis, fracture class mapping, and monitoring of machine performance data provide important information for adjusting to changed conditions. In complex terrains, a clear understanding of the structural geology of any proposed tunnel line is the simplest and most cost-effective method to mitigate losses encountered during TBM tunneling.

Jan 1, 2005

By Yuchen Wu, Purushotham Thkkaraja, Marek Borowski, Jie Liu, Jianwei Cheng, WANCHENG ZHENG, Yu Wang, Weidong Lu, Gang Zhao, Zhanyou Sa, Huan Yang, Yuhang Wu, Hui Wang

The abstract discusses the importance of gas drainage in coal mines for safety, environmental protection, and resource utilization. It highlights the significance of borehole sealing technology for efficient gas drainage. The study introduces a new inorganic retarding sealing material and investigates its properties, including stability, thermal stability, fluidity, and thixotropy. The material's diffusion performance in cracks is tested using a self-designed system. Field tests in a coal mine demonstrate the material's effectiveness in improving borehole sealing compared to traditional materials.

May 1, 2022

By Wayne Trudel, Lloyd McEvers, Lori Clarke, Eric Saderholm, Charles Lynn Bolin, Leroy Schutz

Newmont mine geologists in Nevada are most proficient when applying technical expertise with multi-departmental teams in three main settings. The first is value creation through near-mine discovery, development and reserve conversion. Since 1986, geologists have created substantial net asset value in developing more than 1.35 kt (43 million oz) into quality Nevada surface and underground gold reserves. The second setting is value realization by supporting mine operations with ore control, selective mining, reconciliation investigations and strategic planning. The investment of technical research on reconciliation investigations led to new concepts and practices that highlighted opportunities for large revenue and reserve gains. In 2002, more than $65 million in projected revenue was added to the Gold Quarry south layback. Kriged mine polygon construction and controlled blast heave at the Lone Tree Mine provided millions of dollars in mining efficiencies. High-quality geologic advice in selective mining at the Twin Creeks Mine helped obtain $4.3 million revenue gains throughout 2002-2003.

Jan 1, 2004

Face and pillar bursts, bumps and bounces are violent failures that occur in underground coal mines in response to a complicated interplay of face and pillar geometry, seam depth, coal properties and interactions between roof, seam and floor strata. Additional complications arise from the presence of gas, mainly methane, and associated pressure and flow that vary with time and are further influenced by the rate of face advance. Where gas plays a dominant role, the term outburst is often used; where stress concentration is primary, terms such as burst, bump or bounce may be used. Hargraves [1983] presents an often cited review of outburst phenomena with emphasis on Australian conditions. Beamish and Crosdale [1998] indicate outbursts have occurred for over a hundred years and present tabulations of outburst numbers in major coal basins throughout the world. A central consideration is the rate of depressurization that occurs in the course of mining. Outbursts are not limited to coal seams and adjacent strata; they also occur in salt and potash mines [Molinda et al 1988]. Stress concentration and gas pressure act in consort, so the combined action is important to understanding the mechanics of bursts or outbursts and to the development of measures to reduce the associated hazard. Gas flow is a complicated phenomenon associated with diffusion of gas from micro-pores and the flow of gas along cleats. Laboratory measurements indicate both are dependent on stress and pressure [Harpalani and Ouyang 1998]. Moreover, gas permeability in porous media is often many times water permeability [Klinkenberg 1941]. However, there is also evidence that gas and water permeability are similar at elevated stress and follow Darcy?s law [Dabous et al]. Gas flow is also of importance to mine ventilation. Price et al [1973] in cooperation with personnel of the former U.S. Bureau of Mines developed finite difference models to estimate methane emission in mines in the Pocahontas No. 3 and Pittsburg seams using a premining pressure of 4.69 MPa (680 psi) and Darcy's law implying laminar flow. However, the effects of stress were not taken into account. In this regard, mine measurements of permeability are usually based on Darcy?s law [Peide 1990]. Early models of gas flow with stress effects were one-dimensional in space and time (x,t) and were developed with the goal of estimating the gas pressure profile from the face into the seam as time passed [Schlanger and Paterson 1987, Zou and Yu, 1999]. A zone of high permeability adjacent to the mining face was recognized in these early models. Later models based on the popular finite element method allowed two spatial dimensions (x,y) and variation in time (t) and for coal seam heterogeneity [Tang et al, 2002]. Zhu et al [2007] formulated a set of nonlinear equations involving a complicated stress-pressure-permeability relationship for application to coal seam gas flow and concluded the coupling was important but failure of coal should also be considered. Wold et al [2008] used a hybrid finite difference - finite element model interleaved with a reservoir simulation model to study outbursts based on extensive mine and laboratory measurements. An important feature of the modeling was the use of spatially variable material properties and Monte Carlo simulation to obtain quantitative estimates of outburst conditions and probabilities. Connell [2009] used the same reservoir simulation model as Wold but used the popular finite difference code FLAC3D for hydro-mechanical responses to evaluate two permeability relationships, one depending on porosity and the other on stress, and concluded that permeability changes with gas production were more complex than computed by either permeability model. Gadde [2010] in an integrated laboratory and field study of coal pillar strength explored the effect of spatial variability and concluded that design based on average strength was acceptable in some circumstances, although gas pressure was not an issue. Liu et al [2011] also applied a FLAC code to analyze two-dimensional gas flow and deformation of layered but homogeneous strata in a Chinese coal mine using a strain-softening model and concluded that damage and gas pressure were important to strata safety relative to the case without gas.

Feb 27, 2013

By D. E. Poole

Injury Prevention: Dependent, Independent and Interdependent In recent years, management-directed (dependent)safety programs have lost ground to the more successful self-directed (independent) programs, where employees take responsibility for their own safety. Today, with the growth of the team concept in industry, a mutual-caring (interdependent) approach to workplace safety is gaining wide acceptance. This presentation compares characteristics and results of the three progressive levels of safety responsibility and explains how to develop a successful interdependent program. The presentation will also detail the common principals that are necessary for safety excellence under any of the management styles.

Jan 1, 2000