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A number of terrane reconstructions conflict with global plate histories or with data from adjacent regional studies. Paleogeographic maps have ignored terranes thus are over-simplified. This paper represents an attempt to "marry" Mesozoic global plate reconstructions and terrane analysis to produce examples of a "third generation" of global plate tectonic maps. The best approach to global terrane analysis involves intercomparison of all regional data and the evolving global model. Data conflicts within and between terranes and regions must be resolved by a system of relative data reliability "weighting." The most reliable and useful data are those which constrain "departure" (rift) and "arrival" (collision) times. Certain ad hoc decisions aid in the analysis (e.g. only one net vector allowed per plate). The maps that follow summarize Early Mesozoic global tectonic history at three critical junctures: 240 MA (Triassic); 180 MA (Jurassic); and 120 MA (Cretaceous). Due to space limitations, maps drawn at 20 m.y. intervals appear elsewhere. A preliminary Middle Triassic reconstruction is presented in Figure 1. Major plates and continental blocks are labeled; smaller blocks are marked with abbreviations. Examination of Figure 1 indicates the necessity of modeling Triassic tectonics with at least 68 blocks. Spalling- off of microcontinental slivers from Gondwanaland is active some 70 m.y. before the actual breakup of the supercontinent. In the SW sector of the Pacific, the Australian margins were embroidered with several terranes (e.g. Sumba) which eventually rifted away and crossed Tethys. The NW sector at this time included 10 microcontinental chips forming a huge archipelago along the Asian margin. All blocks inboard of Indochina collided by latest Triassic. Terranes of the NE sector include several (e.g. Arctic Alaska) along the North American margin, and at least six large blocks (e.g. Stikinia) drifting SE with the Farallon Plate. The SE sector

Jan 1, 1987

By R Gilbertson, N Freeman

Metallurgical accounting is key to the control and production planning process of any mining operation. This is even more crucial for complex operations involving mining, concentration, smelting, refining and marketing. The tracking of multiple metal product and contaminant components through the operation can improve process predictability and inventory management. Appropriate use can be made of æhigh quality dataÆ for strategic reserve utilisation, mining operations, milling operations, etc. This information enables the optimisation of all aspects of the mining and processing operations. This case study discusses a metal balance implementation for WMCÆs Olympic Dam operations; a large integrated mining, concentration and refining operation, which used an existing off the shelf statistical data reconciliation package developed for the oil industry. It was extended to track and balance the metal co-products across the entire integrated mining, mineral processing and refining plant. The key benefits discussed are tight integration with existing data collection systems, formalisation of previously informal processes, and leveraging the development and support available for a widely used package. The project provided a solution for the site metallurgical balance spanning the mine and processing plant. The solution facilitates a bridge between the planning and production worlds, using a common data model across the site.

Jan 1, 2002

Continuous improvement in environmental management assists in the achievement of sustainability goals for the mining and processing of minerals. The use of regular internal environmental audits (scored or unscored) which form an integral component of an Environmental Management System (EMS), provide demonstrable evidence of this improvement. The audits described in this paper involve working with site personnel to develop and implement major improvement projects, providing advice on how to improve environmental practices and facilities, and disseminating innovative ideas and practices across the site and to other operations within the same group. Essentially the lead auditor assumes the role of a æskills coachÆ as opposed to a æpolicemanÆ, which is quite often the case for many audits. The audit process has been developed from involvement with a number of major coal mines in the Hunter Valley, where regular internal environmental audits have been undertaken every two to three months, over periods varying from 18 months to five years and more recently, with a metalliferous mine in the Northern Territory. Examples of the benefits of improved environmental performance (driven by the audit process) to sustainable development are provided. The auditing process as described is applicable to metalliferous mines, the processing of mineral ores, coal mines, coal handling and preparation plants, quarries, and oil and gas projects.

Jan 1, 2004

By Rowena C. Duckworth

The Ocean Drilling Program (ODP) is the largest international geoscience project in the world, and the state-of-the-art drill ship, the JOIDES Resolution, is permanently at sea. Each year there are six scientific cruises (legs) which each last approximately two months. These legs are designed by geoscientists from the nineteen countries that subscribe to ODP. Australia and Canada presently share ODP membership under the banner of the AUSCAN Consortium. The benefits of Australia's involvement in ODP include internationalisation of Australian geoscience, advanced graduate training, and unique scientific investigations of the ocean floors in the Australasian region. In addition, visits to Australian ports by the ODP drill ship, the JOIDES Resolution, contribute up to $2 million per visit to the local economy. Amongst the many other aspects of ten years of scientific drilling, ODP has significantly contributed to our understanding of hydrothermal processes on the seafloor. To date, three hydrothermal sites have been drilled to date by the ODP, Snakepit (MAR), Middle Valley (Juan de Fuca Ridge) and TAG (MAR). Two more hydrothermal sites are scheduled for 1996.

Jan 1, 1995

By Murdaugh W

The application of photogeological techniques and analysis of more advanced remote sensor images can be a cost and time effective tool in the search for desert placer gold deposits. Examples are given of regional analysis using standard false color composit Landsat images and conventional black and white aerial photography. The examples include identification of sites to sample to evaluate the pathways of .alluvial gold migration and identification of potential sites of concentration. The results of these studies developed an increased number of target areas and exploration in proceeding with promising results. In addition to the development of additional target concepts and identification of specific target areas data useful to evaluation of mineability can also be obtained from photogeological investigation. Some indication at least can be obtained of the existence of duricrusts and salines that may hamper mining. Identification of possible sources of water is another important task in the desert environment. In addition indications of the clay content of the material to be worked is very important because of its economic impact on operational costs and overall recovery. The application of photogeology to these questions is discussed.

Jan 1, 1988

By Valenta R. K

A technique is presented for the integrated forward modelling of the three-dimensional structure and the geophysical response of multiply deformed terrains. This technique allows information collected by field geologists and geophysicist to be reconciled by the development of a simplified kinematic structural history of the area. The structural modelling simulates the deformation history of the area in terms of a succession of structural events, such as folds, shear zones and intrusions. The interaction of these events with a starting stratigraphy results in the prediction of the geometry of the structures. By specifying geophysical rock properties for the units in the initial stratigraphy predictions are possible for the potential field anomalies for gravity and magnetics. This approach is suited to a range of applications, and its uses in the modelling of regional structures, testing of geophysical data processing, volume balancing, multiply constrained inversion and training are discussed.

Jan 1, 1995

The Ravensworth-Liddell area is part of the Muswellbrook- Singleton Coal District of the Northern Coalfield. It lies in the Parishes of Liddell, Ravensworth, Vane and Howick, in the County of Durham, midway between Singleton and Muswellbrook, and is traversed by the Great Northern Railway, and the New England Highway.Ravensworth and Liddell railway stations are 57 miles arid 61 miles, respectively, north from Newcastle (Fig. 1).The area has been the centre of an intensive search for open cut coal during the past few years. More than 1,200 bores, of which about 10% were cored diamond drill holes, were drilled to depths of about 200ft. Portions with thicker cover have been explored by 10 diamond drill holes to depths of over 400ft. but core recovery from these deeper holes was poor, and the lack of detail in the recorded logs limits geological interpretation. The drilling has proved about 34,000,000 tons of open cut coal, and about 246,000,000 tons under deeper cover.GEOLOGYThe Ravensworth-Liddell area lies on the eastern flank and southern extremity of the Muswellbrook Dome, extending from Hebden in the north, to Jerry's Plains in the south, and the rocks under consideration belong to the Tomago Stage of the Upper Coal Measures. On the north they are truncated by the Hebden Thrust fault, which has a throw of about 4,500ft. (Raggatt, 1929). On the west they are bounded by outcrops of the Upper Marine Series, which conformably underlies the Upper Coal Measures, and...

Jan 1, 1953

By Ruschitzka C

The productivity and economic success of a German hard coal mine is attributed to the high productivity of a small number of operation points; however high rates of production are associated with increased gas emission at the working sites. Therefore modem high technology is required in order to reach the planned production rate, since high methane concentrations often cause unplanned breakdowns in operation. The optimised simulation of gas emission is a fundamental planning tool for mine design as well as for determining the potential of a coal deposit and has increased in significance over the last years. Methane-INFO enables the three-dimensional, graphical simulation of a working site taking account of different aspects such as the mine design, ventilation, production rate, geology, seam quality, gas exhaustion, etc. The following paper gives a short overview over the benefits of the discussed system.

Jan 1, 1995

By P C. J Blackney, I M. Glacken

Spotted Quoll is a massive sulfide nickel deposit located in the Forrestania greenstone belt in the Archaean Yilgarn block in Western Australia. Discovered in October 2007, mining has progressed from open pit to underground and currently uses longhole open stoping with paste fill as the primary stoping method. Immediately prior to 2019, the Mineral Resource estimate (MRE) was defined by a single grade domain of nickel greater than or equal to 0.8 per cent, irrespective of the host lithology, a legacy of the original ore wireframe being built using explicit methods. While a number of obvious structural offsets were honoured in this nickel grade domain, only one modelled fault was used to undertake domaining of arsenic. From 2019 onwards, implicit modelling in Leapfrog Geo™ was used to construct a mine-scale geological model, which triggered the definition of a high-grade core of massive/matrix nickel sulfides surrounded by a low-grade halo of stringer/disseminated nickel sulfides in the surrounding rock. As part of the evolution of the geological model and with the aid of Seequent Central™ to allow collaboration between site-based mine geologists, Perth-based resource geologists and Melbourne-based consultants, a detailed review of the structural mapping was carried out as additional information from underground development became available. This allowed numerous faults and shears to be identified – particularly in the lower half of the mine. These were used to define further structural domains and to refine the understanding of the nickel and arsenic grade distributions in the mineralised envelope. The increased definition to the domains provided by the geological model resulted in a significant improvement in the accuracy of the Mineral Resource estimate, as measured by reconciliation using voids of the mined stopes determined from the cavity monitoring survey (CMS).

Mar 22, 2022

By C D. McCullough, M Gerner

Rarely do opportunities arise allowing closure of a mine site to be planned as a key beneficial land use asset within a new urban growth area; particularly so well prior to cessation of mining.Pit lakes are common mine closure legacies for many open cut mines and may form in open cut mine voids extending below the water table upon closure. Mine closure guidelines increasingly require post-mining land uses of equivalent capacity to premining conditions and that minimise long-term post-mining liabilities and maximise benefits to stakeholders and the environment. However, risks presented by pit lakes are regularly neglected in closure planning or are not able to be addressed to allow beneficial end use of the lake or surrounding land.This paper describes strategic planning initiated by quarry owners ten years before mining ceases. In liaison with the planning agencies, the planned closure of a large 100-year-old limestone quarry pit will form a lake on mine completion, with a well-considered beneficial end use in an urban setting in mind. The quarry pit and adjoining land at Batesford South about the edge of the City of Greater Geelong, Victoria, Australia. Geelong is experiencing growth pressures that necessitate development of a new growth area from about 2025.A multidisciplinary expert team assessed the constraints, opportunities and feasibility of rehabilitating the quarry and pit lake and developing the surrounding land as Geelong’s next urban growth area.The concept is exciting and demonstrates that a former mine site could become a valued home to about 40 000–45 000 people. About 30 per cent of the land will also be developed as an ecological riverine corridor including the pit lake that will become a regionally iconic lake as the centrepiece of an urban development.Our paper outlines technical challenges and how these can be met to achieve closure and beneficial use that meets the social, economic and environmental expectations of contemporary urban planning.CITATION:Gerner, M and McCullough, C?D, 2014. Planning for the future – development of beneficial end use from a quarry pit lake, Victoria, Australia, in Proceedings Life-of-Mine 2014 , pp 99–112 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Jul 16, 2014

By D Van Doorselaere

The purpose of blasting during mining is to produce a muck pile that can be efficiently loaded and transported. There is an increasing awareness of the variation in muck pile characteristics and its economic implications. It is well known that good fragmentation by itself is not sufficient to optimise the muck loading efficiency. The swelling and configuration of the muck pile also significantly affect the productivity of the loading equipment. The characteristics of a muck pile depend upon the blast design parameters, explosive properties and rock mass geology. This study has focused on the dependence of muck pile configuration on blast design parameters, explosive properties and size distribution of the muck.The field work was done in two phases. In the first phase 12 blasts were monitored, while in the second, three blasts were monitored. The blast design parameters and explosive properties for each blast were documented and the following muck pile characteristics were measured:muck pile height and its distance from the facedistance of throwwidth of the power troughsize distribution by image analysis technique.The effects of burden, bench height, heave energy of explosive, row-to-row delay, powder factor and the mean particle size of the fragments on muck pile configuration were examined. It was observed that muck pile height and distance of throw are strongly influenced by the burden, bench height, heave energy of the explosive and the size distribution of the muck. The width of the power trough depends upon the row-to-row delay, powder factor and total burden. In addition, the effect of the fragment size distribution on the muck pile parameters has also been discussed.CITATION:Singh, S P and Van Doorselaere, D, 2015. The relationship between blasting parameters and muck pile configuration, in Proceedings 11th International Symposium on Rock Fragmentation by Blasting, pp 369–374 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Aug 24, 2015

By K J ROSENGREN

Underground rock mechanics was initiated as a formal discipline in Australia by early studies for underground structures for the Snowy Mountains Scheme in the 1950s. These techniques were quickly embraced by underground mining and there has been steady development to the present time. The paper reviews the status of current techniques for rock mechanics studies and discusses some important issues such as ground support, mine filling and caving. It concludes that a considerable degree of engineering judgement is still required for the practical application of rock mechanics to underground mine design.

Jan 1, 1992

The lignites of Otago and Southland offer a potentially viable future feedstock for electricity production and possible conversion to petrochemicals or liquid fuels. The deposits, when combined, represent New ZealandÆs largest energy inventory; equivalent to about 74 000 petajoules û or approximately 35 times current natural gas reserves. Too often dismissed as irrelevant to New ZealandÆs energy future because of adverse perceptions of the value of low rank coals, the strategic value of this resource is in fact huge.   Investigations of the lignites extend back over more than 50 years (LFTB various, CRL Energy Ltd). Whilst it is not the intention of this paper to review this work, these investigations have confirmed the suitability of the resource as a feedstock for thermochemical conversion. Current estimates of South Island lignite mining costs are NZ$1.0 - 3.0/GJ (Natusch 2005), making these resources amongst the most competitively-priced energy sources available world-wide.   This value, however, will only be captured if we as a country begin to envisage a world-scale, long-life, integrated and multi-faceted development sized to supply world markets for chemicals or fuels. Recent CAE studies (Hooper and Riddolls, 2005) have emphasised the vital importance of ensuring that any exploitation of this resource maximises their value to New Zealand. The question that thus must be applied is how might large-scale utilisation of the resource fit with New ZealandÆs primary energy supply, and its potential for the export of high-value commodities.   From the broader perspective of New ZealandÆs total energy supply equation we need to examine other supply options beyond just the generation of electricity. We face in this country a situation wherein almost all our liquid fuels feedstock has to be imported with projections for an increasing dependence on imported oil. In addition NZ has a natural gas reserves-to-production ratio of less than ten years, and dwindling supply from local production. Without further natural gas discoveries, New Zealand has only a window of approximately five years before we will need to commit to imported LNG or some other thermal fuels option.   In other words, New Zealand is facing an uncertain future unless we can restore energy inventories to cover an adequate strategic reserve capacity as well as enable long-term investment in alternative sources. Within this context the South Island lignite resources are thus deserving of more attention. The extent of the resource is well known, its suitability for conversion reasonably assessed, and its magnitude such that there is little doubt that lignite conversion could adequately meet NZÆs future energy needs for many years out.   This paper reviews coal gasification technology, its application to lignite and the possibilities for future development of the lignite resources. It is argued that the strategic imperative for this country is to secure the lignite resources as a primary energy source for this country well into the latter half of this century.

Jan 1, 2005

By L Cooper, J Sharma, M J. Hendry

Thick clay tills below potash mine tailings and brine ponds are important natural barriers protecting fresh water aquifers in Saskatchewan. Centrifuge modelling was applied to assess geochemical processes and impacts of dilute brine (0.1 M NaCl) migration through clay till core samples obtained from non saline, unoxidised clay till at a mine site. At accelerated gravity of 876 + g, during each day of centrifuge modelling, flow driven through a 52 mm length core simulated transport through a 45 m thick clay over ~2100 years. Hydraulic conductivity, monitored continuously before and during brine permeation, was low and relatively constant (8.5 + 10-12 m/s), confirming that confining stresses prevent permeability increase. Core density and porosity measurements confirmed that reactive transport occurred under realistic in situ conditions. Breakthrough (defined by C/C0 = 0.5) of non-reactive Cl- occurred at 25 days. The slight delay for Na+ breakthrough, associated with small increases in Ca2+ and Mg2+ concentrations in the effluent were attributed to ion exchange, but carbonate reactions were relatively unimportant. Cation exchange analysis of core samples was inconclusive without corrections for porewater Na+ and carbonate dissolution. Geochemical processes that were observed during centrifuge modelling were successfully simulated using the 1D geochemical transport code PHREEQC. Solute transport was dominated by diffusion with limited ion exchange to delay Na+ migration. Brine would not break through a 45 m thick clay for tens of thousands of years. Based on these findings, the thick clay till at this site, if laterally extensive and undisturbed by drilling activity, is likely to act as an effective natural barrier to vertical brine migration over the long term.

Jan 1, 2003

By T Y. Dube

In this paper current net present value (NPV) based mine valuation techniques that take into account market and private risk are discussed and analysed. Potential pitfalls that arise from the application of a portfolio, market or commodity based risk metric to a mining project are identified. An alternative non-simulative framework for quantifying and factoring market and private risk in NPV calculations is proposed and then applied to a hypothetical case study in an attempt to overcome identified pitfalls. Mathematical proof that a static discounted cash flow (DCF) calculation can underestimate or overestimate mine NPV is presented, the conditions for each are outlined and the degree of underestimation defined.CITATION:Dube, T Y, 2012. How the use of market-based risk metrics can undervalue good mining projects and overvalue poor ones, in Proceedings Project Evaluation 2012 , pp 29-34 (The Australasian Institute of Mining and Metallurgy: Melbourne).

May 24, 2012

By K Sommerville, J Parkinson

"Open pit mines today have more technology and data available. The challenge is to effectively use resources to analyse and identify mine productivity improvements. AMC Consultants Pty Ltd (AMC) has completed more than 100 benchmarking studies worldwide. In the process of gathering cost and productivity data, insights have been gained on how mines are using data to drive productivity. This paper aims to share good practice on using data, what benchmarks operations should be aiming for, where mines are currently sitting, high value areas to target, and how to best prioritise improvement to meet operational goals.A key purpose of data is to assist in managing and improving operations. Key information is used to drive meetings, decisions, budget estimates and reports. Safety, equipment productivity, available stocks, grade and spatial reconciliation are examples of where data is important for management systems. The key is to keep reporting simple whilst maintaining access to source data for troubleshooting and analysis.Some operations still have paper-based reporting systems. Some operations collect data directly off machines and instruments, use cameras and have off-site control centres. The level of technology is a fit-for-purpose choice.Comparisons of productivity assumptions commonly used in feasibility studies with good practice productivity numbers sourced from AMC’s benchmarking database will be shared in this paper. A typical activity mining cost breakdown will highlight where the high value areas for productivity improvement sit.In addition to examining the productivity of each mining step it is also important to examine the impact on the mine plan. Equipment numbers, strip ratio, grade and material hardness can impact the results of bottleneck analysis. A bottleneck example case study will highlight how productivity and other factors can be used to identify and prioritise improvement opportunities.Keep it simple. Use only the critical data for meetings, decision-making, reports and plans. Knowing and communicating the key performance indicators (KPIs) you are striving for aligns the operation and prioritises improvement plans.Citation:Parkinson, J and Sommerville, K, 2016. Getting the Most Out of Technology to Drive Mine Productivity Improvements, in Proceedings Ninth AusIMM Open Pit Operators' Conference 2016, pp 84–93 (The Australasian Institute of Mining and Metallurgy: Melbourne)."

Nov 15, 2016

By J Rose, D O’Toole, D Grant

Orepasses are a critical element in the transport of ore from the stope drawpoint to the surface ore stockpile, making them an integral part of an underground mine’s ore-handling system. Well-designed and operated orepasses improve productivity and lower operating costs over a long period of time.The Olympic Dam mine, as part of a 6 Mt/a expansion project in 1997, constructed a large network of orepasses feeding a rail haulage system to facilitate the movement of approximately 8 Mt/a to the Clark crusher and hoisting shaft. The orepass network comprises 14 orepasses and currently includes 59 individual tip points. The orepass network has been in operation for over 15 years and in excess of 110 Mt of ore has been moved through the system.Olympic Dam’s management of mine infrastructure includes a program of assessing the condition of the Clark system orepasses. A comprehensive program was initiated in 2011 and consisted of systemically performing volumetric surveys to determine the integrity of the various sections of the orepasses. The current geometrical state of the orepasses provides essential information for comparison of geotechnical and operational parameters and a baseline for understanding the key causes of orepass deterioration to assist in the planning of both usage and potential replacement options.The collection of geotechnical and operating data allowed the review of the current condition, potential longevity and associated risks with the various orepass sections. Initial studies have also reviewed options for rehabilitation and/or replacement.CITATION:Rose, J, Grant, D and O’Toole, D, 2016. Orepass monitoring and management at Olympic Dam Mine, in Proceedings Seventh International Conference and Exhibition on Mass Mining (MassMin 2016), pp 609–616 (The Australasian Institute of Mining and Metallurgy: Melbourne).

May 9, 2016

The Olympic Dam copper-uranium-gold-silver deposit, located 520 km NNW of Adelaide, S.A. was discovered by Western Mining Corporation Ltd in 1975, and is now being developed as a joint venture between WMC (5107o) and the BP Group (4907o). The discovery of this deposit resulted from the application of a conceptual model for the formation of sediment-hosted copper deposits. This model postulated that the oxidation of basaltic rocks could release significant amounts of copper into solution and that, under favourable conditions, these solutions might pass upwards along faults, and the copper be precipitated in reduced- facies sediments higher in the sequence. The Stuart Shelf province was chosen for exploration because geological interpretation suggested the presence of suitable basal- tic source rocks at depth, and favourable host sedimentary rocks in the overlying sequence. The Olympic Dam site was selected for drill-testing because of the presence of coincident gravity and aeromagnetic anomalies suggesting the presence of basalts and/or mineralisation at depth. This site also had a favourable tectonic signature, indicating the presence of deep crustal structures which might have allowed fluid migration.

Jan 1, 1988

A study was conducted to evaluate the effectiveness of the three types of sample grinders routinely used in the mining industry for the sample preparation of gold ores with particular emphasis placed on testing their capacity to produce a representative assay sample of coarse gold ores. The grinders used in this study are the Labtechnics LM5, the Mixermill 4010 ringmill and the Keegor vertical spindle pulveriser, commonly called a Keegormill. The study was based on the preparation of samples from two sources of known coarse gold ore, the Union Reefs Gold Mine and the Brocks Creek Gold Mine in the Pine Creek region of the Northern Territory of Australia, and a fine gold ore which was from the Macraes Gold Mine in New Zealand. The Union Reefs Mine contains visible coarse gold with 30 per cent to 40 per cent of the gold in the plus 75 μm fraction of milled ore. Discreet particles up to 5 mm have been recorded, Hellsten (1994). Union Reefs Gold Mine recovers 40 per cent of its bullion production through a gravity circuit, Riches (1997). Brocks Creek ore contains visible coarse gold with gravity bullion production fluctuating between 50 per cent and 65 per cent, depending on the mill feed. Average gravity bullion production from the Brocks Creek Mine is 55 per cent, Wilke (1997). The average gold grain size of Macraes Mine ore is 20 μm with 40 per cent of the gold in sub 10 μm particles. No gravity bullion is produced from the Macraes Mine, O'Keefe (1997). The testwork demonstrated conclusively that it is possible to prepare a representative sample for assay, of a coarse gold ore, when a Keegormill is used to pulverise the sample to a nominal 100 μm particle size (90 per cent passing a 100 μm screen by wet sieving). Both the Mixermill and the Labtechnics LM5 failed to prepare a representative sample, even when ground to a nominal 75 μm particle size.

Jan 1, 1998

By Bartosiewicz H

A method for the determination of the gas content of coal seams is presented which improves upon existing methods. The method makes use of a gravitational technique for measurement of the gas desorbed. The amount of lost gas is estimated by determining an empirical relationship relating the desorption of gas with time for each sample separately. This is to replace the assumption that desorp- tion follows a square root law with time. Laboratory investigations have been conducted which indicate that the square root desorption law does not hold good for carbon dioxide. Results of investigations on various factors influencing the technique are presented. It is shown that co-efficients of the empirical equation are dependent upon the elapsed time and the period of observation. Data about gas pressure measurements is presented and it is concluded that gas pressure can be approxi- mated to 0.6 times the pressure below a column of water equal to the depth of cover. This estimate is good enough for adsorption tests to evaluate desorption co-efficients. The technique for repressurisation of the sample,

Jan 1, 1982