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By A Webster, T Murphy

Block cave mining, in its broadest sense, has transitioned from an orebody/rock mass determined method of extraction, to a low-cost and high production mining method that may be applied to any large ore deposit. This inherently means that caving is now required in more complex rock mass conditions where assistive damage, through preconditioning, may be necessary. This requires comprehensive understanding of the geology, and its interwoven relationship with geotechnical parameters, and is made more challenging due to limited exposure in block cave mines. Limited mine development throughout the cave volume equates to a heavy reliance on drilling data in terms of observations, modelling of the mine geology, and collection of geotechnical data. This translates as increased uncertainty of geological and geotechnical models and has potential to impact significantly on the ability to make informed decisions in the design and operation of the cave mine.Modelling of cave propagation behaviour requires a complex, coupled system of draw of material, flow of material through the cave stocks, and propagation of the cave-back assisted by autogenic stress-related breakage of the rock mass, manifested as seismicity. The role of geological features in the process of cave propagation is not well understood and requires evaluation on a mine-specific basis, given the diversity of geological controls/settings of ore deposits and local variability of stress fields.Seismic monitoring systems can elucidate key geological features and domains, as heterogeneous seismogenic activity is observed ahead of the advancing cave-back. The observations made from analysis of seismic monitoring data may have potential to be used as a validation tool for numerical modelling of predicted cave behaviour in similar geological settings (eg next lift/panel).Understanding of the geological structure, at all scales, is critical to optimise the design and operating decisions made in a block cave operation. At present, intermediate-scale structure, anisotropy, mineralogy and model uncertainty may be neglected or under-represented despite their likely significant role in the mechanisms of cave propagation.Insights from an analysis of the Ridgeway Deeps block cave mine are discussed in this paper.CITATION:Murphy, T, Webster, A and Chitombo, G, 2016. Beyond rock mass characterisation – the impact of geology on block cave mining, in Proceedings Seventh International Conference and Exhibition on Mass Mining (MassMin 2016), pp 861–872 (The Australasian Institute of Mining and Metallurgy: Melbourne).

May 9, 2016

By Joan T. May

The Bureau of Mines conducted laboratory tests to evaluate the production of high-purity H3P04 by HCl digestion and solvent extraction. Both batch and bench-scale continuous tests were made. Western phosphate rock concentrates were acidulated with HCI, and the digestion liquors were processed by solvent extraction. Phosphoric acid was extracted with isoamyl alcohol and recovered from the organic extract by contact with an NH4F solution. This solution was fractionally distilled to yield high-purity H3P04. The raffinate from solvent extraction was treated with lime to precipitate CaF2, which was subjected to steam pyrolysis to generate HF. This method was successful in recovering 95 pet of the phosphate and 80 pct of the fluoride contained in the concentrates.

Jan 1, 1976

In most mines using presplitting the final excavated wall shows a zone of damage just below the crest and well defined presplit half barrels. The crest damage (surface dilation) zone varies and is added to by subsequent adjacent perimeter blasting operations. Keeping the preconditioning to a minimum is possible using the methods described in this paper, developed on several diverse and geographically distant mining operations to control crest dilation and preconditioning by presplitting in advance - not just laterally but vertically in advance. The first documented case (Delbridge, Marton and McSweeney, 2004) in the development of the concept was undertaken at AngloGold Australia Pty Ltd's Sunrise Dam Gold Mine (SDGM), located beside Lake Carey, some 730 km northeast of Perth, Western Australia. The mine had been developed in a series of cutbacks to a depth of over 300 m and began underground mining during the latter stages of open cut operations. This mine is fairly unique in that it utilised a single pass vertical presplit which initially extended over three bench heights and after the failure mechanisms were understood, over four benches. The presplit drilling for the three stacked benches started on the floor of the second bench so that any dilation was confined to the surface one bench above the crest and modified perimeter blasting was then developed to curtail damage from blasting adjacent to the new crest. The second case is based on a South African coal mine in the Witbank Coal Measures, 140 km northeast of Johannesburg, Republic of South Africa (RSA). It was important that blasting for optimal wall stability and minimal scaling was developed in advance. A dragline is scheduled to excavate the #2 seam midburden which is the lowest of the economically viable coal seams in the five seam Witbank Coal Measures. Mining of the overburden, coal and partings above the dragline midburden pass are by excavator and truck and each mining layer is individually blasted. The results of presplitting the midburden through the overlying coal seams and partings have provided a presplit with no surface dilation of the midburden crest and ensures any subsequent crest loss is solely due to blasting adjacent to the vertical presplit. Typical of all coal mines in South Africa only vertical presplits are used. Wall control is most commonly delivered by presplit blasting and one common sight after the dust clears is a ridge of broken blocks along the presplit row, usually with a main crack running between the presplit blastholes and often parallel cracks either side of the perimeter line. The surface rock strata or block structures have been dilated by the venting gases and shock waves. Decoupled, fully coupled, single or double deck charges are used depending on a variety of factors, anecdotal practices and perceived benefits. Preconditioning of the crest rock by blasting from above may not be visible to the naked eye (or non-existent in overburden in strip coal mines) but the high speed venting of explosives gases (and often the water in the presplits) preferentially follow existing cracks and structures because there is no developed presplit crack near the surface. This nearly always lifts, shifts and separates the surface structures and geological layers. Stopping the dilation by 'sacrificial' or 'in advance' presplitting has been shown to reduce the crest loss at both metal and coal mines. Drilling and presplit blasting through an upper level of bench or layer provides a degree of restraint to the target layer where the crest must be maintained and any damage caused by the venting gases will not cause concern as it is removed as planned, leaving a stable crest.

May 1, 2010

By A. P. Squelch

The high incidence of accidents and fatalities in the South African mining industry, in particular those associated with falls of ground, is often attributed to ineffective and/or inappropriate training methods and material. Recently introduced mine health and safety legislation in South Africa also requires that all mine workers receive appropriate and effective training to enable them to operate safely in their given mining environment. There can, therefore, be no doubt that methods to provide effective training, in particular safety related training, are urgently required in the South African mining industry. In the search for alternative and improved training approaches, attention has fallen on virtual reality (VR) technology as a possible solution. VR has found acceptance in a number of industries as an effective method of training for a variety of work place activities, including those of a safety related nature. VR has successfully been applied in a number of industries to improve the effectiveness of safety and hazard awareness training. The CSIR: Division of Mining Technology (CSIR Miningtek), in conjunction with the Safety in Mines Research Advisory Committee (SIMRAC), therefore evaluated the potential of VR to be used as a training medium in the South African gold and platinum mining industry. Aspects of the evaluation included an assessment of the technical capability of VR to represent a typical underground mining environment with sufficient realism and the relevance of the VR training concept for a largely illiterate workforce. For these purposes, a prototype PC-based VR hazard awareness training simulator has been developed by CSIR Miningtek, and a series of evaluation sessions conducted at a typical deep level gold mine. The conclusion from this evaluation work is that virtual reality technology has the potential to provide effective training systems that are relevant to the South African mining industry. Keywords: Virtual reality, mine training, safety training.

Jan 1, 2001

By Thomas M. Barczak

The initial Support Technology Optimization Program (STOP),Version 1.0, was released at the 19th Ground Control Conference. This original program has since been updated to Version 2.3 which was released in May, 2001. This paper describes the additional features of Version 2.3, focusing primarily on the following three aspects: (1) including uncontrolled convergence into the design requirements for standing roof supports, (2) the addition of design procedures for cable bolts as an alternative secondary roof support, and (3) the addition of new standing roof support technologies. Another new feature which should facilitate the development of design criteria for standing roof support is the capability to define ground reaction curves through convergence measurements alone without having to make support loading measurements. There are several other new features provided in Version 2.3 which are only briefly addressed in the paper. These include: (1) additional graphics capabilities to facilitate rapid assessment of support comparisons, (2)an East-West designation for support selection to more accurately provide cost and support availability data, (3) additional safety measures including a safety factor to identify support design near the peak support capacity, checks to see if the support dimensions comply with aspect ratio requirements, and a measure of roof coverage for the design layout of the support system. These new features of STOP provide more capabilities to design and analyze secondary roof support systems for conditions which could not be fully analyzed in the original version of the program.

By N. McEwan

Keywords: refractories, chromite, Marico This paper examines the role of refractory-grade chromite in refractories. The chromite deposit at Verref?s Marico Chrome mine is described. The refractory properties of chromite and their role in basic refractories are described. The properties and metallurgical applications of chrome-containing refractories are described and finally environmental issues associated with chrome-containing refractories are discussed.

Jan 1, 2011

By K. Woodward

"SynopsisSeismically active mines generally experience an increase in seismic hazard due to rock mass instability following blasting. Re-entry protocols commonly include measures to limit the spatial and temporal exposure of personnel to increased seismic hazard induced by blasting. The management of periods of increased seismic hazard requires the development of re-entry protocols for a unique mining environment. Identifying mining conditions that may result in significant seismicity following blasting relies on retrospective analysis, which is often focused on seismicity occurring within a certain period after blasting and within a certain radius of the blast in the broader context of site-specific experience.The analysis of seismicity without considering blasting times and locations allows for the relationship between seismicity and blasting to be investigated without prior assumptions concerning dependency. To achieve independent analysis, seismicity that is clustered in space and time (referred to as a seismic sequence) must be identified by assessment utilizing only seismic parameters. An automated algorithm is implemented that assesses the timing, location, and quantity of seismicity to identify seismic sequences, represented by the time of the first event and mean location of all events in the sequence.The relationship between sequences and blasts is assessed by calculating the distance and time from each sequence to the closest blast in space and time. Establishing an independent classification between sequences and blasting provides insight into the unique cases where seismic sequences are remote and/or delayed with respect to blasts and identifies cases when sequences exhibit a weak relation to blasting. The nature of seismic responses to blasting has direct implications for the management of the increased seismic hazard associated with seismic sequences.The approach presented in this study contributes to the management of seismic hazard by providing empirical support for the relationship between seismic sequences and blasting. These relationships indicate the portions of sequences that can and cannot be practically managed using tactical approaches. Furthermore, the analysis of sequences reveals the nature and evolution of rock mass responses to blasting. These results have implications for the extent of spatial or temporal re-entry restrictions required for the optimal management of time-dependent rock mass response to mining."

Jan 1, 2015

By D. M. Fraser

"Brunswick Mining and Smelting Corporation Limited operates two mines; one open pit (No. 6) and one underground (No. 12), approximately 20 miles south-west of Bathurst, New Brunswick. Both are massive sulphide deposits containing copper, lead, zinc and silver. The No. 12 property began operation in 1963 and is presently being mined at a rate of 3600 tons per day underground and is in the completion stages of an expansion to achieve 11,000 tons per day underground by the end of 1930.Originally at Brunswick Mining, acid mine drainage was added to tailings and neutralized by an excess of lime in the tailings. A conventional recycle system was established with a biostabilization pond for the treatment of thiosalts, a liming station and sludge settling area for neutralization of acidic water and a final reclaim pond with a pumping station for reclaim water.We found that not more than one third of the reclaim water could be used as it upset the flotation circuit every time it was used. It was established that the mine water and surface drainage were the cause due to oils and detergents in the water. It was also found that the biostabilization pond method Cf thiosalt treatment was not efficient for year round operation in our climate.In 1974, we reviewed the problems and began a 3 phase program to control effluents from the property:"

Jan 1, 1980

New Zealand China Clays produces a unique halloysite clay product at Matauri Bay, Northland.   The company has licences over four deposits that were derived from the weathering of rhyodacite domes. Clay is mined and processed from two of the four deposits and is refined using a complex process based on gravity separation.   The product is almost entirely exported to niche markets in 24 countries. The main market is the fine ceramic industry where the product is used as a component in the manufacture of high quality porcelain and bone china bodies. The use of halloysite in these bodies gives the manufacturer the ability to achieve high whiteness and translucency. The other major market is for use in technical ceramics, where the product is sought after due to its high purity, fine particle size and stability at high temperatures.

Jan 1, 1997

By U. Weber

The effect of grinding media performance on milling and operational behaviour was demonstrated under different selected conditions of calcium carbonate slurry milling. A variety of grinding media materials and bead sizes, along with two different stirrer tip speeds, were used in the grinding process to generate a particle size reduction of the calcium carbonate (CaCO3). To determine the optimum milling parameters the collected test data were used to calculate and evaluate specific energy as well as stress intensity under different milling conditions. Keywords: Grinding, mill media, high energy mills, industrial minerals, precious metals.

Jan 1, 2010

During August, 1926, with the consent of Mr. Schell, mine manager, the writer conducted a mill test on this company's concentrators. Mr. Schell not only gave him his permission, but rendered all possible assistance. Although it was impossible to take all the samples one could have wished to obtain, yet the salient points of the mill flow-sheet were sampled for a continuous period of eight hours, and from these samples and separate data supplied by the manager, valuable information was collected.THE MINEThis is a true vein-type of mine; the lode formations, striking almost due north-south, cut the large porphyritic intrusion at right angles. There are three distinct veins on this property - parallel, persistent, and dipping at an angle varying between 40° - 50° to the horizontal.The country rock is very sound, and timber, save for the small amount required for ore chutes, is entirely absent from all mine workings.The lode varies from a width of 1 in. to 8 in., but the stopes are carried forward with a minimurn width of about 30 in.The mine is particularly dry for a West Coast property, and conditions underground are very favourable. Air drills are used...

Jan 1, 1928

Ore from the Hill 50 Gold Mine, consists essentially of pyrrhotite, with minor amounts of pyrite, chalcopyrite, galena and gold, replacing "jaspilite." The gold is associated with the sulphides as shotty particles. About 8 per cent. of the particles are less than '0.010'mm.The Hill 50 Gold Mine, at Boogardie in the Murchison goldfield, about 300 miles north-west of Kalgoorlie, was first operated in 1898. From 1898 to 1917 it yielded 20,000 short tons of ore for a recovery of 6,225' fine oz. gold, equivalent to a recovery grade of 6.22 dwt. gold per ton.The present company since the beginning of its operations in September 1936 to June 30, 1954, produced 811,081 short tons of ore for a recovery of 242,554 fine oz. of gold, equivalent to a recovery grade of 5.98 dwt. gold per ton.The grade of ore (recovery grade) has shown a remarkable variation with depth. From the 120 ft. Ievel to the 300 ft. level, it averaged about 7.5 dwt. Au per ton. Below the 300 ft. level it declined, and from 300 ft. to 400 ft. averaged 4.9 dwt. per ton, falling further with increasing depth to about 4.5 dwt. per ton at the '600 ft. level.On the 820 ft. level the grade improved sharply to about 14 dwt: per ton, and this grade has persisted down to and on the 1060 ft. level.The orebody has been described by Finucane (1953) as a series of lenses of finely banded jaspilite conformably enclosed by greenstones. The jaspilite is tightly folded and faulted and intruded by dykes of felspar porpnyry.Mineralization is practically restricted to the jaspilite.

Jan 1, 1955

By Eiji Kojima

In this research, dynamic and static load tests were performed on permanent foundation piles which had a pile length of 30 m, 800 mm in outer diameter and 15 mm in wall thickness. In this site the dynamic horizontal load test on a smaller test pile, 12 m in length, 500 mm in outer diameter and 12 mm in wall thickness, was also carried out. The static horizontal load versus horizontal displacement derived from the dynamic load test conformed well to that measured in the conventional static horizontal load test of the pile with 800 mm diameter. Then an attempt was made to predict the horizontal load displacement of the pile with 800 mm diameter based on the results of the dynamic horizontal load test of the pile with smaller diameter of 500 mm.

Jan 1, 2006

By Mehmet Canbazoglu, Kaarlo Haavanlammi, Hannu Laitala

Cobalt is currently a critical metal because of the increasing number of electrical vehicles forecast for production. Copper and zinc are base metals that are used in many everyday applications, including vehicle production. Eti Bakir Co. Mazidagi Phosphate Plants in the Mazidagi district of Mardin, Turkey is a multi-product facility that produces cobalt, copper, and zinc, as well as fertilizers, from the roaster calcine. Roaster off gas is treated in a sulfuric acid plant (SAP) and the acid itself is utilized in fertilizer production. The comminution circuit, roaster, SAP, and calcine leaching process were developed by Outotec and integrated with the fertilizer production process implemented by Eti Bakir A.Ş. This paper describes the hydrometallurgical calcine leaching process used at the plant, with a focus on the oxidative pressure leaching of the cobalt, zinc, and copper-containing calcine. The cold and hot commissioning phases of the pressure leaching autoclave start-up are discussed together with experiences from the ramp-up period. The production processes of the copper cathode and cobalt and zinc-containing salts are also presented together with some of the plant’s operating parameters. INTRODUCTION The ETI Bakir A.S. fertilizer plant, Turkey, is located in Mardin Province near the border with Syria, (Figure 1). The leaching plant project was started in 2012. The purpose of the plant is to separate the valuable metals from the calcine produced by the pyrite roasters, which are used to produce a SO2 containing gas for the new sulfuric acid plant. Fertilizer production requires sulfuric acid, and for this reason a sulfuric acid plant was built; customer already had access to pyrite concentrate, which is used as the roaster feed. During the engineering phase of the roaster and acid plants it was noticed that the roasted calcine contained considerable amounts of valuable metals like cobalt, copper, and zinc. To recover these metals, a calcine leaching process was developed at the Outotec Research Center in Pori, Finland. The main process connections of the Mazidagi site are shown in Figure 2.

Jan 1, 2019

By Jean-Sébastien Lambert, Joseph Kabuya, Richard Simon

Managing a highwall failure risk in an open pit mine by controlling and mitigating the impact of vibrations produced by blasting operations is key to achieving safe and cost-effective operations. The impetus behind this study was the risk of multiple bench failures in an open pit mine that was detected by Slope Stability Radar (SSR) following blasting at the foot of a highwall. The unstable high wall was over 140 meters(459.3 ft)high and 200 meters(656.2 ft)wide. The quantity of associated material was estimated at 3,000,000 metric tons(3,306,934 US tons). The overall slope angle was 44 degrees. In order to continue mining without causing the highwall to fail, this study was initiated as part of a risk management plan to mitigate this major risk by identifying mitigation measures related to blasting operations and assessing the response of the rock mass to each blast. Identifying blasting mitigation measures consisted of optimizing blasting parameters to avoid failure of the highwall. First, a signature hole operation was carried out to obtain seismic records that were georeferenced and associated with known single charges. The method used made it possible to determine the propagation velocity of the P-waves associated with the various lithologies studied and to calculate, from the geomechanical properties of the rock masses, the maximum peak particle velocities to be respected. Subsequently, the targeted area of operation was modelled with the I-Blast software in order to optimize the firing sequences to be used according to the different lithologies present. The model also made it possible to optimally predict the particle velocities associated with each blast and ensure compliance with the previously determined peak particle velocity limits. The assessment of the rock mass’s response using SSR consisted of defining alarm thresholds and an intervention plan for various possible alarms as well as quantifying the damage to the highwall from blasting. Controlling the impact of blast vibrations on the highwall’s stability was successful, as the mitigation measures used during mining did not accelerate the highwall’s movement. No upward trend in the stabilization time of the rock mass was observed by the SSR after each blast. Post-blast geotechnical inspections and analysis of post-blast deformations in the highwall also did not reveal significant damage to the highwall as a direct consequence of the blasting.

By D Johnston

Within the first full year of BarrickÆs Cowal Gold Mine operation, the Lake Cowal Foundation Limited (LCF) has already been delivering results consistent with its goal to protect and enhance the natural environment of Lake Cowal and its catchment area. The LCF is a non-profit Environmental Trust established in June 2000 in conjunction with the development consent process for the construction of BarrickÆs Cowal Gold Mine. Its primary goal is to protect and enhance Lake Cowal, a nationally significant ephemeral wetland located 350 km west of Sydney, New South Wales, Australia. Significant concentrations of water birds visit the lake and the Australian Heritage Commission listed Lake Cowal on the Register of the National Estate in 1992. The LCF is managed by a Board of Directors from representative member organisations including the Total Environment Centre, National Parks Association, Nature Conservation Council and Barrick Australia Limited. Although largely funded by Barrick, the Foundation also attracts external funding and works in partnership with a diverse range of other groups and organisations, beyond the mine fence. The total value of currently approved projects is estimated to be in excess of $7.1 million, which includes æin-kindÆ contributions made by the local community and in particular the Lachlan Catchment Management Authority (LCMA) and local farmers. To date, LCF has been involved with the development and implementation of 30 projects with a total of 34 project partners. LCF has worked with over 60 landholders to improve Lake Cowal and its catchment, with 6180 ha of land now being managed for conservation or sustainable farming in the local area. Many landholders have been, or are involved in property planning or participating in other training opportunities. Sustainability of LCF programs and outcomes will be assured by commitments to projects within four key themes: conservation, research and research support, sustainable farming and community education and training. The LCF works independently from the mining company and has no responsibility for the environmental management within the mining lease. It is about capitalising resources generated by the mine to enhance environmental outcomes in the wider Lake Cowal catchment area by working collaboratively with the local community, industry and government authorities to ensure the long-term protection of a unique wetland ecosystem affected by landscape scale degradation.

Jan 1, 2007

By Dennis R. Dolinar, John L. Ellenberger, Gabriel S. Esterhuizen, Anthony T. Iannacchione

A survey of pillar conditions was carried out at 21 operating limestone mines that use the room-and-pillar method. The surveyed pillars were all located in rock that was classified as “Good” to “Very Good” using the RMR rock mass classification system. The average pillar width was 14.5m and the width to height ratio varied between 0.53 and 3.52. Pillar conditions were rated using a visual rating system that accounts for the effect of geological structures as well as stress related fracturing. Nine cases of pillar instability were recorded. Pillar instabilities were typically limited to individual pillars or small groups of pillars within an otherwise stable layout. Local geological structures such as inclined discontinuities or weak bedding planes contributed to instability in seven of nine cases that were observed. Elevated pillar stresses contributed to instability in the two remaining cases. All the unstable pillars observed had width-to-height ratios of less than 1.5. It is concluded that pillar instability is most likely to be caused by unfavorable geological structures in pillars with width to height ratios of less than 1.5. Stress related instability such as rib spalling becomes more prevalent when the average pillar stress approaches approximately 20 MPa.

By R. A. Ixer, R. A. Lord, H. M. Prichard, A. J. Boyce, P. McConville, C. T. Pillinger, I. P. Wright, J. Maynard

Analysis of 62 samples show that the sulphides throughout the igneous stratigraphy have a magmatic signature, with the exception of the uppermost gabbros and the lowermost basal thrust talc-carbonate lithologies. Mean delta-34S values for whole-rock samples from harzburgites, dunite pods in harzburgite, crustal dunites and wehrlites, the main and high-level pyroxenites and gabbros suggest that the primary sulphides derived their sulphur from a magmatic source enriched in 34S. This finding is compatible with the proposed origin of the ophiolite above a subduction zone. Values for pyrite mineralisation in the uppermost part of the gabbros are thought to result from precipitation from a seawater-derived fluid, while isotopically light sulphur in the basal thrust could have been introduced from underlying metasediments. The replacement of pentlandite by heazlewoodite has not led to sulphur fractionation

Jun 19, 1905

By Both R. A, Daily B

The Patawarta Diapir, located in the northern Flinders Ranges (South Australia), has intruded into late Proterozoic Wilpena Group sedimentary rocks. The diapir contains disrupted blocks of a wide variety of rock types, most of which can be correlated with the Lower Callanna Beds of Willouran age, in a matrix of predominantly carbonate and siltstone breccia. Mafic rocks in the diapir appear to predate intrusion of the diapir. As with many other diapirs in the Flinders Ranges, copper mineralization is present in the diapir and occurs as narrow veins consisting essentially of carbonate with chalcopyrite and pyrite that formed after diapiric intrusion.Fluid inclusion studies demonstrate that the mineralizing fluid was a Na-Ca-K-Cl brine; probably derived by expulsion of interstitial water following emplacement of the diapir, with dissolution of evaporites within the Callanna Beds sediments and enrichment in copper by reaction with these sediments and associated basic igneous rocks. Mineral assemblages combined with fluid inclusion and geochemical data indicate a possible environment of vein formation of T ÿ 165°C, pH ÿ 4.3 ± 0.9 and log fO2 ÿ -47.3 ± 0.5. Sulphur isotope analyses indicate d34Sfluid ÿ 10 per mil, suggesting evaporites in the Proterozoic sediments as the major source of the sulphur but with some additional sulphur from an igneous source, possibly leached from the malic rocks of the diapir.

Jan 1, 1986

By James P. Rider, Charles D. Taylor, Edward D. Thimons

Research was conducted to investigate how ventilation of a mining face is affected when scrubber flow is greater or less than intake flow. Tests were conducted in a full-scale surface test gallery built to simulate a mining entry with a continuous mining ma- chine at the face. Methane gas was released at constant flow at the mining face. Gas measurements taken at six locations near the face were used to evaluate how well the face was being ventilated. Increasing scrubber flow resulted in lower methane levels even when scrubber flow was much greater than intake flow.