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By Steve Kral

The Prospectors and Developers Association of Canada (PDAC) was established in 1932 in response to proposed regulations that would have threatened prospectors in Ontario. From there, the association grew to represent the interests of Canada?s mineral exploration and development industry. The PDAC?s mission statement reads: ?The PDAC exists to protect and promote the interests of the Canadian mineral exploration sector and to ensure a robust mining industry in Canada. The PDAC will encourage the highest standards of technical, environment, safety and social practices in Canada and internationally. ?Today, the PDAC?s 6,000 individual members include prospectors, developers, geoscientists, consultants, mining executives and students. In addition, the association?s membership includes 950 corporate members, representing senior, mid-sized and junior mining companies in addition to organizations that provide services and equipment to the mining industry. In 2010, the PDAC adopted its e3 Plus principles, a framework to guide its membership in responsible exploration.

Jan 1, 2011

By Roland Trunk, Marcel Imbach, Yves Boissonnas, Jan Vesely

"INTRODUCTION The expansion of the Suez Canal, which runs between the Mediterranean and Red Sea, is at the top of Egypt’s economic agenda. The £8 billion development plan includes a new channel alongside the existing one which will double the number of ships able to pass each day and several tunnels to connect the Sinai peninsula to the main part of Egypt. The Egyptian government ordered three new tunnels under the Suez Canal in the area of Port Said as part of the Canal Region Development Plan. The three tunnels will contribute to the North Sinai expansion, helping to create a vast industrial zone and completing the coastal road extension from Rafah to Nuewiba. Two of these three tunnels will be allocated for roads and the third for railway traffic. A further part of the Suez Canal development mega project are an additional six tunnels in the area of Ismailia and Suez. The focus of this paper is on the two road tunnels in Port Said and will give an overview of the project and the challenges encountered regarding the technical complexity and tight time schedule both in its design and execution. PROJECT OVERVIEW The tunnels will be built in the area of Port Said (see Figure 1) which is the most northern part of the Suez Canal.The road alignment connects the Port Fuad Road in the east bank of the Suez Canal to the Port Said-Ismailia highway in the west bank with a dual carriageway section. Each of the carriageways has two lanes. The bored diameter of the 2.8 km long road tunnels is 13.050 m and will be driven with two Mix-Shield TBMs. The distance between the two tunnel axes is planned with 42.5 m (discussion about a reduction are ongoing). The width of the Suez Canal is around 340 m at upper level and around 170 m at the bottom. During the TBM drive, three main geological layers are expected. Below a depth of around 40 m in a very soft clay layer, a dense to silty sand layer is predicted. Within the sand layer another silty hard clay is expected in different depths with variable thickness. After finishing the excavation of the road tunnels, the same TBM will be used for the railway tunnel. The lowest points of the road tunnels will be located 59 m below the surface (tunnel invert to surface) and only 18 m of ground cover exists between the tunnel crown and the Suez Canal invert. Minimum ground cover over the tunnel crown is approximately nine meters at the tunnel portals."

Jan 1, 2016

One of the critical challenges facing the mining industry ? and not just in the United States ? is the looming labor shortage. A significant percentage of the industry?s professional workforce is, well, getting old, and many will be retiring in the next 10 years or so. This is not a new issue to the industry. It has been discussed at various industry meetings and conferences for many years. How does mining, with its largely negative public image, attract young people to mining schools? And, equally important, who is going to teach them? Mining schools, what?s left of them in the United States, are beginning to lose qualified faculty to retirements, and no one is available to replace them. SME addressed this issue during the keynote session at its annual meeting in February in Denver, CO. This year?s theme was ?Mining: It?s About the People.? Despite a blizzard that blanketed the city on the day most attendees were to have arrived, the meeting still attracted a record 7,202 people. And the accompanying exhibit sold 822 booths, also a record. The U.S. Department of Energy?s National Energy Technology Laboratory contracted with the National Academies? National Research Council to complete a study concerning the availability of skilled workers to meet the energy and mineral security requirements for the United States. The National Research Council, in turn, asked SME to collect and analyze workforce trends in these industries. The result of SME?s analysis is the report ?Emerging Workforce Trends in the U.S. Energy and Minerals Industries.? It is available on the SME website, www.smenet.org. Click on Government Affairs. While the report did not paint a completely dismal picture, there were some disturbing results. It concluded that within 20 years there will not be a sufficient number of skilled professionals to satisfy the labor demand. That said, the report said that most of those positions would likely be filled. However, the U.S. mining will go through a period of time when the workforce will be made up of very young and senior workers.

Jun 1, 2013

By Mikael Ramström, Mark Board, Clayr Alexander, Wes Johnson

"The Coeur d’Alene mining district in northern Idaho was first discovered more than 130 years ago and has been the most prolific silver producer in the United States. The Lucky Friday Mine of Hecla Mining Co. (Fig. 1) is the oldest (76 years) and deepest mine in the district, producing approximately 725 t/day (800 stpd) from narrow, vertical lead-zinc-silver veins. Cut-and-fill stoping is currently employed at depths to about 2.3 km (7,500 ft) below ground surface, making it one of the three deepest mines in the western hemisphere. The #4 Shaft, a winze collared at approximately 1.8 km (5,900 ft) below surface and extending to a depth of nearly 2.9 km (9,600 ft), was recently completed to exploit the high-grade 30 Vein, whose resource has been identified to at least 3 km (9,700 ft) in depth.As with other deep mines worldwide, a number of challenging engineering issues occur, including: high in situ rock stress, squeezing ground, seismicity, high in situ rock temperature that requires refrigeration, diesel equipment that generates diesel particulate matter (DPM) requiring high ventilation airflow rates and long travel times for worker transport to mining areas.This article describes the methods that Hecla Mining Co. has employed during the past 50 years to combat these issues, with emphasis on the current efforts to implement continuous, mechanical mining with automated or teleremote operation and to introduce electric and battery-powered equipment to minimize refrigeration and ventilation requirements for the removal of DPMs.Geology and in situ stressThe host rock mass is an extremely thick sedimentary sequence (the Belt Series) that has been tilted vertically by mountain building. The rock mass in the current section of the mine consists of weak, heavily foliated argillites and stronger, bedded silty-argillites termed siltite. The vertical veins (80° to 85° dip) are parallel to the foliation with an approximate width of around 3 m (10 ft). There are two regional, vertical faults that parallel the vein; one forming the hangingwall of the orebody and one approximately 90 m (300 ft) in the footwall. Additionally, there are several thin, rough northdipping faults that occur in the footwall of the vein which terminate on the major vertical faults.Both the argillite and vein package rock have moderate strength, with uniaxial compressive strength averaging about 100 MPa (14,700 psi with a range from about 70 to 125 MPa), and are moderately abrasive, with CERCHAR abrasivity index of 2 to 3. The major in situ stress is horizontal and oriented in a northwest direction with magnitude about 1.5 times the vertical stress. Consequently, the Lucky Friday stress magnitude at depth is analogous to significantly deeper South African gold operations."

Jan 12, 2017

By J. -B. C. Varnier, J. A. Cremeens, D. D. Overton

"Slope failures that occurred in 2008 and 2009 at the Pikeview Quarry in El Paso County in Colorado in the United States were investigated using three-dimensional discrete element modeling methods. Large-scale block sliding failures occurred along weak bedding planes that dip steeply into an excavation located at the toe of the slope. Several mining sequences at the toe of the slope were simulated to evaluate the effects of various degrees of extraction and backfill on slope stability. Slope stability back-analysis was conducted using prefailure and post-failure conditions to determine the joint shear strength properties. Laboratory testing was also conducted to determine intact rock properties. Three-dimensional discrete element analysis was uniquely applicable to this evaluation because it allowed representation of shear stress of the basal sliding surface and afforded evaluation of several scenarios of extraction and backfill at the toe of the slope. IntroductionThe Pikeview Quarry is an aggregate quarry located approximately 8 km (5 miles) northwest of Colorado Springs in El Paso County, CO, USA. The quarry has been operated by several owners since the early 1900s. According to the U.S. Mine Safety and Health Administration (MSHA, 1986), the quarry has been a major source of construction aggregate for the Colorado Springs area for many years. In the 1950s, the site was mined by Peter Kiewit and Sons to provide limestone for the construction of the nearby Air Force Academy.A large-scale slope failure occurred on Dec. 2, 2008, which stopped mining activity at the Pikeview Quarry. A second, related slope failure occurred on Sept. 13, 2009. The second slope failure was located immediately adjacent to the initial December 2008 failure.The objective of this paper is to discuss the three-dimensional slope stability evaluation. The causal relationships of slope instability are not within the scope of this publication. However, omitting the precursors to slope failure would limit understanding of the nature of the slope stability evaluation. The regional and local geology and the history of slope instability at the Pikeview Quarry aid in understanding these precursors. Two main failure mechanisms were hypothesized during the failure investigation to explain the triggering of the 2008 and 2009 large slope failures at the Pikeview Quarry, and both of these mechanisms were given equal credence in the present study. Quarry excavation and backfilling was a key factor in the slope instability for both failure mechanisms. The excavation was backfilled in stages in an effort to provide slope support. The objective of the three-dimensional model was to evaluate the effects of extraction and backfill at the toe of the slope with respect to slope stability."

Jan 3, 2018

By R. Xiong, A. K. Fallaw, G. Wang, L. R. Moore, S. Dobson, J. Gu

"INTRODUCTION The Central District of the Florida phosphate industry is located in southwest Polk and southeast Hillsborough Counties, with the Southern Extension lying in western Hardee, eastern Manatee and northwest De Soto Counties. (Lawver, 1983) Figure 1 shows the major phosphate formations in Florida. Almost all Florida phosphate production has been in the Central district with additional production from a mine in the Northern District. The Central District is comprised of the Bone Valley Deposit, a relatively thin layer of high grade ore which has been the main source of phosphate mining for decades, and the Hawthorn formation, a thick but low grade formation which covers most of peninsular Florida. (Lawver, 1983) Florida phosphate producers use the Crago process where calcium phosphate is floated with anionic, fatty acid type collectors followed by cationic reverse flotation of silica with amine type collectors. The phosphate matrix is put through various size separation techniques to obtain a typical -28 Mesh (< 700 µm) particle size for fine flotation and a -16 mesh (< 1190 µm) to +28 mesh (> 700 µm) particle size for coarse flotation. In some cases this coarse fraction can be sent to shipping as an intermediate product. The +16 mesh (>1190 µm) to – ¾“ (19 mm) fraction is sent to shipping as a final product called pebble. Figure 2 demonstrates a simplified diagram of the mining and processing of calcium phosphate (matrix) through a Central Florida mine. Particle size and mineralogy are important considerations in the Crago process for two main reasons, the mass of the particle and the particle surface area. Both of which are dependent on the coordination of the anionic collector to available Ca2+ sites on the minerals’ surface. The increased surface area, and available Ca2+, of the smaller apatite particles will allow for more fatty acid molecules to coordinate than the larger particles, with a lower availability of Ca2+. So, the larger particle would require more collector to be introduced in the system to sufficiently cover the apatite particles to produce a surface sufficiently hydrophobic to attach to air bubbles allowing flotation to occur. (Guan, 2009) The Bone Valley deposit has very favorable flotation characteristics when compared to other mining ores around the world. The matrix of the Bone Valley is relatively high grade, BPL (Bone Phosphate in Lime) values typically range from 6-18%, BPL recoveries, from such a matrix, can often be achieved above 85+% with fatty acid based collectors dosed below 1 #/ton. As mentioned, the sizing is an important step as there is also high grade apatite in the +16 mesh (1mm) that is screened to a final product grade, 60-65% BPL. The lack of quartz in the larger size fraction has allowed the Central District to produce high quality, low cost phosphate product, called pebble, through effective screening with no further beneficiation. (Guan, 2009)"

Jan 1, 2015

By D. Nutakor

This paper presents the results of a study conducted on a slope failure that occurred in the Q7 mining cut at Rio Tinto&apos;s Bingham Canyon Mine. The slope failure occurred in a weak rock mass with an estimated rock mass rating of 25%. The failure mechanism was of the circular type, involving ten 15-m (50-ft) benches and covered a total width of 152 m (500 ft). The analysis used Adam Technology&apos;s photogrammetric method with a two-dimensional rock fall simulation program (RocFall software) to design a 3-m- (1 0-ft-) high berm located 7 m (24 ft) from the toe of the failed mass. Back and predictive analyses were performed on a cross-section through the slide using Slope/W software, resulting in flattening the interramp angle (IRA) from 44° to 38°. This design modification produced a factor of safety (FOS) of 1.14. Sensitivity analysis involving FOS vs. pore water pressure showed that FOS is sensitive to water saturation. A dewatering system using a series of horizontal holes drilled below the slide and dewatering holes drilled from a drainage gallery has since been established to improve the stability of the slope. Throughout the one-year period since this investigation, no significant slope movement has been detected by the slope stability radar, and mining is in progress below the failure.

Jan 1, 2012

By R. C. Freas

The physical and chemical properties of mica are unique relative to most other industrial minerals. As such, mica is suitable for a variety of functional applications in new and emerging markets. This paper examines some of these applications and particularly the contribution mica makes in end product performance.

Jan 1, 1997

By S. S. Klima, J. A. Organiscak

Researchers at the National Institute for Occupational Safety and Health (NIOSH) performed laboratory testing to examine and improve airborne dust capture and methane removal performance of flooded-bed scrubbers on continuous mining machines using a blowing face ventilation configuration to reduce respirable dust exposure to shuttle car operators. Several testing conditions were examined to minimize shuttle car operator dust exposure without adversely affecting continuous miner performance and production. Curtain-to-face setback distance of 9.1 m versus 15.2 m (30 ft versus 50 ft), face ventilation airflow of 226.5 m3/min versus 339.8 m3/min (8,000 ft3/min versus 12,000 ft3/min), and the use of side-body-mounted blocking sprays (on versus off) were the three primary parameters compared. Scrubber airflow was set and maintained at 198.2 m3/min (7,000 ft3/min) throughout testing. An examination of slab cuts versus box cuts and the location of the shuttle car (present behind the continuous miner versus not present in the entry) was also performed to demonstrate the effects of these constantly changing scenarios on scrubber performance. Results show that the best blowing face ventilation setup for minimizing shuttle car operator dust exposure for the tested parameters uses a 15.2-m (50-ft) curtain-to-face setback with 339.8 m3/min (12,000 ft3/min) face ventilation while operating the side-body-mounted blocking sprays. INTRODUCTION Coal mine worker overexposure to respirable coal dust continues to be a problem in U.S. underground coal mining operations, potentially leading to coal workers’ pneumoconiosis (black lung). The U.S. Mine Safety and Health Administration (MSHA) requires that respirable dust exposure to coal mine workers does not exceed a 1.5 mg/m3 average over the actual working shift (79 Fed. Reg. 24814 (2014)). Although using a blowing face ventilation configuration on continuous miner (CM) sections is beneficial for removing methane emissions from the mining face, it can be detrimental for dust control for shuttle car (or ram car) operators and any other workers on the return ventilation side of the CM when compared to exhausting ventilation. Even with machine-mounted scrubbers on CMs, shuttle car operators still have some of the higher dust exposures with blowing face ventilation systems (NIOSH 2011, Beck et al. 2015). Although scrubber discharge air is not completely clean, dust being blown around the scrubber inlet and therefore not being captured by the scrubber can further increase these dust exposures (Goodman 2000). Dust control problems are also caused by inadequate face ventilation quantities causing scrubber face airflow recirculation issues (Schultz et al. 2010). In order to minimize respirable dust exposures on blowing face ventilation sections, ventilation, water spray, and scrubber parameters were experimentally examined to improve operating ranges for both dust and gas control. Several blowing face ventilation factors were examined with respect to CM spray systems and scrubber operation. Curtain-to-face setback distance and side-body-mounted blocking sprays were previously examined in the laboratory for dust control on a full-scale CM model using a scrubber on a blowing face ventilation system (Goodman 2000). The blocking sprays produced larger dust reductions at the CM’s rear corners and return for a 6.1-m (20-ft) curtain setback distance as compared to a 12.2-m (40-ft) curtain setback distance with equal face and scrubber airflows of 169.9 m3/min (6,000 ft3/min). Because face ventilation airflow quantities, shuttle car operator locations, and tracer gas concentration gradients were not previously examined during these experiments, additional research was required to determine improved operating parameters for blowing face ventilation systems.

Jan 1, 2019

By W. Ghyoot, J. Boonstra, H. Dijkman, C. Buisman, M. Picavet

Paques and Umicore have demonstrated the feasibility of biological treatment of the highly complex Hoboken wastewaters in a1 m3/h pilot plant at Umicore Precious Metals, Hoboken, Belgium. In the first step arsenic was precipitated from copper smelter effluent as As2S3using biogenic produced H2S. Other metals such as copper, lead and cadmium were also removed as MeS to concentrations well below the discharge levels. Subsequently, sulfate and nitrate were removed to low concentrations (<300 mg/l and < 5 mg/l respectively) in high rate engineered bioreactors. Sulfide produced in the sulfate reduction process was recycled to step 1 for metals precipitation. Selenite/selenate was partly removed in the sulfide precipitation step, whereas the excess was biologically reduced and removed as selenium to concentrations <0.2 mg/l.

Jan 1, 2003

By V. M. Torres

An empirical correlation to detennine laboratory mill grinding time has been developed. Grinding samples to 90 ± 5# below 147 micrometers was required for a flotation testwork at Companhia Vale do Rio Doce (CVRD) Research Center. The initial samples were all below 1 mm in size with different size distributions and work indices (Wi) ranging from 13 to 23 kWh/st. Grinding curves were determined for some initial samples. A correlation was developed between percent retained on 147 micrometers at a standard time and the time required to grind each sample to the required size. This correlation was then used to grind all samples, based on the preliminary grinding model. Finally, a statistical analysis with the size distribution of all samples was performed. The success of using the correlation was confirmed and an equation was determined using the data set.

Jan 1, 1996

By R. Robertson

Dense medium cyclones are the preferred means for cleaning 112 in. x 14 Mesh to 28 Mesh (12.7 mm x 1.0 mm to 0.6 mm) raw coal and are becoming a common choice for cleaning raw coal from a nominal top size of 2-1/2 in. to 3 in. (63.5 mm to 76.2 mm) down to 14 Mesh to 28 Mesh (1.0 mm to 0.6 mm). During the last ten years, dense medium cyclone circuitry design has undergone changes which have combined to improve process efficiency. This paper describes these improvements and compares present day design with the design used prior to the mid 1980&apos;s. Improvements in the following areas are described: Raw coal desliming, cyclone configuration, drain and rinse applications, dilute medium circuitry, and instrumentation and control.

Jan 1, 1997

By M. N. Herrera

The bioleaching of mineral sulfide pulps in a bench-scale rotating drum reactor has been studied. The reactor includes horizontal paddles in the inner wall for lifting of the mineral pulp. The performance of the reactor was tested in the bioleaching of a refractory pyritic gold concentrate in the presence of pure Thiobacillus ferrooxidans strain (ATCC 19859). The concentrate was efficiently bioleached at 50% pulp density with the drum operating at 0.5 -1.0 rpm Attempts of bioleaching the concentrate at the same pulp density in conventional stirred reactor showed severe inhibition of bacterial activity. The results demonstrated that the drum reactor allows to operate at much higher pulp densities than the conventional stirred tank reactor. This behavior is explained in terms of an improvement of the bacterial activity due to a better control of the attrition of the mineral particles.

Jan 1, 1997

By Carl Hansen

Sonora Mining Corporation (SMC) operates the 6,000 tonne per day Jamestown open pit gold mine in the Mother Lode district of California. The mine has been in operation since January, 1987, and has produced approximately 7,800 kilograms of gold since start-up. The property consists of five ore bodies lying along a five kilometer stretch of the famous Mother Lode vein system. At present, only the Harvard ore body is being mined. The Harvard pit is centered around a historic underground mine of the same name that was operated from 1896 to 1916. The present ore body averages 2.5 grams gold per tonne as free milling gold and auriferous pyrite. The project consists of the open pit mine and concentrator complex in Tuolumne County, California, and a carbon-in-pulp leach plant located near Yerington, Nevada.

Jan 1, 1990

By G. C. Kachel

Significant effort has been expended and considerable success has been realized m the application of instrumentation and automatic control equipment in the mining and ore processing industries. This effort has been applied principally to process equipment with the objective of increasing throughput, minimizing labor requirements and/or improving grade or product quality. Less spectacular, but quite rewarding has been the successful application of instrumentation and automatic control equipment to a wide variety of material handling equipments. This paper describes some of this work including: (1) automatic weighment of load-haul-dump units and trams underground; (2) automation of skip loading; (3) instrumentation applied in feeders and conveyors; (4) level measurement in bins, silos, vessels and sumps; (5) automatic blending of sized materials; (6) automatic loading of ships, trains and trucks; (7) automatic control of tailings disposal facilities

Jan 1, 1973

By Thomas Schultheis, William Heron, Paul Watson, Colin Warren

This paper describes the geology and geotechnics associated with construction of the Thames Tunnel, part of the UK’s Channel Tunnel Rail Link (CTRL). The 2.5km long twin tunnels run beneath the river Thames at depths of up to 40m and are currently under construction. They pass through varying geology comprising alluvium, terrace gravels and chalk with flints and are currently being bored using Herrenknecht mixshield slurry tunnel boring machines (TBM’s). This paper outlines the lithology and engineering properties of each geological formation and describes the geotechnical processes, potential hazards and difficulties experienced in the works. A summary is given into the extent of the investigative work in terms of route selection, tunnel design, TBM optimisation and further details are provided on the geotechnical aspects associated with the construction of the tunnel approach structures and the tunnels.

Jan 1, 2003

By J. G. Pippenger

The Coteau Properties Company&apos;s Freedom Mine is a surface lignite mining operation located near Beulah, North Dakota. Coteau, a wholly owned subsidiary of The North American Coal Corporation, produces more than 13.5 million tonnes per year, ranking it among the largest mines in North America. In 1993, Coteau ranked seventh in terms of annual coal sales, becoming the largest mine outside the Powder River Basin of northeastern Wyoming. However, for the Freedom Mine to stand among these Powder River heavyweights, Coteau over-came several obstacles, including a coal seam with three quarters the heating value and overburden to coal ratios three times higher than the Powder River mines. Coteau&apos;s ability to compete has been built around a program of continuous productivity improvement, cost efficiency, and innovation. This report highlights a few of the major improvements implemented in recent years.

Jan 1, 1995

By C. E. Ekburg

Gold Quarry is a sediment-hosted, epithermal disseminated gold deposit located along the Carlin Trend. Gold, hosted by allochthonous Ordovician siltstones and cherts, is localized at the intersection of structures sympathetic to the major Good Hope and Gold Quarry faults. The magnitude of Gold Quarry was discovered in 1979 by surface exploration and by percussion holes drilled near the Maggie Creek orebody. Four years of development drilling delineated an open pit mineable gold deposit that contains 130 Mt (144 million st) of ore at an average 1.68 g/t (0.049 oz per st) of gold and includes a high-grade core of 46 Mt (51 million st) that average 2.64 g/t (0.077 oz per st) gold. Milling of the higher-grade portion began in 1985.

Jan 1, 1987

By Carl-Henrik Knudsen, Rolf Tore Arnesen, Eigil R. Iversen

Recovery of iron and copper from acid mine drainage was studied in pilot scale at a continuous treatment plant at the mine site of the King&apos;s mine in Roeros, Norway. The average load on the plant was 1 m3/h. The process tested in this project is a three-step process consisting of: 1) Fe(OH)3 precipitation at pH 3.5, dewatering of iron sludge and transport to ferric chloride plant; 2) after filtration precipitation of residual metals at pH 9, concentration of metal sludge by flotation; 3) extraction of metals from the sludge with sulphuric acid followed by recovery of copper by electrolysis. The copper could be used for local production of different crafts, but this condition needs a further evaluation. The process economy at a full scale plant is evaluated.

Jan 1, 2000

By A. Cecala, J. Noll, J. Organiscak

Many underground metal/nonmetal mines are using enclosed cabs on mining equipment to reduce the exposure of miners to diesel particulate matter (DPM). However, some enclosed cab systems may not be meeting their expected efficiency in capturing DPM, which could be a result of inappropriate filter use, cab leaks or insufficient pressurization. NIOSH investigated several types of filters for reducing DPM to determine which type had the best capture efficiency. The laboratory results indicated that a MERV 8 (minimum efficiency reporting value, as defined by the American Society of Heating, Refrigerating and Air- Conditioning Engineers) filter captured about 50% of the DPM, a MERV 16 filter collected 96-98% of the DPM and two HEPA (high efficiency particulate air) grade filters captured over 99% of the DPM. NIOSH also performed a field study to measure the efficiency of two cabs at a limestone mine. The cab filtration systems of a loader and haul truck were found to be over 90% effective in removing DPM, except under certain operating conditions when the efficiency was as low as 41%. A possible reason for the low efficiencies is an open window in the cab, but more studies need performed to obtain a better understanding of the cause and solution of the problem.

Jan 1, 2011