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By C. Patel, George H. Hope

"INTRODUCTIONThe Hemlo area is located in Northern Ontario, some 350 km east of Thunder Bay along highway 17. Hemlo is Canada's largest, recent discovery of gold ore. Three companies, Lac, Noranda, and Teck are currently developing mines and processing facilities in the area. A combined milling capacity of approximately 10,000 tonnes per day will ultimately be available in the area. The gold yield will be between 750,000 to 1,000,000 ozs. per year. This will slightly more than double Ontario's gold production but only represents 2.5% of the total world gold production.Lac Minerals Ltd. is substantially committed to the gold mining business. Lac currently operates four (4) gold mines and mills and produces 300,000 ozs. per year. Lac's Hemlo development will put the company in the position of number one gold producer in Canada.The Lac Hemlo ore body has an estimated reserve of 37 million tonnes at 6.2 g/t. The mining will take place at an initial rate of 3,000 t/d commencing in the first quarter of 1986. The mine and plant will be expanded to 6,000 t/d in 1988. At this capacity, Lac will be the largest producer in the Hemlo area.1. GEOLOGYThe orebody is divided into two (2) zones for mining purposes. The 'A' Zone is to the east and dips to the Northeast from surface to 300 m below surface. This zone has a strike length of 250 m to 300 m at an average width of 20 m. The upperpart of the zone will be mined by open pit and the remainder from underground. The 'B' Zone, to the north west of the 'A' Zone, although lined up is not necessarily an extension of 'A' Zone. 'B' Zone has a known strike length of 600 m and is open to depth and along the strike. It is over 70 m wide in the core. This zone holds most of the property's known reserves. 'C' Zone with narrow gold zones is under exploration in the south west portion of the property."

Jan 1, 1985

By Bernard Dallaire, Jean Cayouette, Sylvain Duchesne

"Louvicourt Mine's concentrator, located near Val d'Or, Quebec, treats an average of 4,300 tonnes of ore per day composed mainly of copper, zinc, gold and silver. An analysis of concentrator revenues and metallurgical losses shows a potential for additional gain, particularly in regards to precious metals (kustelite) where recovery is usually around 67 -70 %. The planning, installation and trial operational period of two Outokumpu SK-240 flash cells at the underflow of the primary cyclones took two years. The use of (( flash flotation )) technology has made it possible to exploit the favourable conditions at the underflow of the primary cyclones such as precious metal concentration and the presence of liberated coarse chalcopyrite. These conditions permit early flotation (fresh surfaces) of the kustelite and the liberated copper. Since the start-up of the flash cells, the metallurgical gains have turned out to be very positive with increases in metal recovery reflected in appreciable NSR gains. Also, significant savings in reagent consumption and a coarser copper concentrate have made it possible to reduce the drying cycle of the Larox filter presses since the cells were put into operation.BACKGROUNDLouvicourt Mine is operated by Aur Resources Inc. (30% ownership) on behalf of its partners Novicourt Inc. (45%, subsidiary of Noranda Inc.) and Teck Corp. (25%). The mine is located in northwestern Quebec about 600 km north of Montreal and about 25 km east of the mining town of Val d'Or. The mine commenced commercial production in July 1994.The massive sulphide ore deposit lies at depths varying between 450 m and 900 m. Mining reserves (2% Cu equi. cut-off) as of Jan. Is', 2000 are estimated at 7.5 million tonnes of ore averaging 3.4% Cu, 1.8% Zn, 28.0 g/t Ag and 0.9 g/t Au. Delineated ore reserves permit the use of a mechanized transverse blasthole mining method. The extraction order is a typical 1.3.5 mining sequence. Primary and secondary stopes are 15 m wide, 15 to 70 m long (25 m long average) and 30 m high. Backfilling for pillar recovery and regional stability is required."

Jan 1, 2001

By Christina Dahnér, Kristina Jonsson, Savka Dineva

The iron-ore underground Kiirunavaara mine (Sweden) has been seismically active since 2008. In 2021 the production is on levels 1079 and 1108 m, at the deepest. The seismic activity has changed in character over time with one step change in 2015 when the number of large (ML>2) seismic events increased, and another one when the mine experienced a seismic event with Mw 4.2 in 2020. In 2017, the mine evaluated Hydraulic Fracturing (HF) as a possible mitigation technique for larger seismic events and a one-hole trial was performed. The trial proved promising, and it was decided to go forward with a large-scale trial covering an entire production area in the mine. The large-scale trial consists of 25 fracturing holes, 50 – 100 m long, running along 500 m out of the ~4500 m long orebody and spanning between production levels 1108 m and 1252 m. The fracturing process continued for a year, resulting in ~38,000 seismic events with −3.3<ML<1.4. The breakdown pressure varied between fractures in the same hole as well as between holes in the same area. Average breakdown pressure per hole was between 12 MPa and 50 MPa. The seismic response to HF in 2021 varied greatly from hole to hole and between fractures in the same hole. The variation in response could be related to the geological conditions and the infrastructure, such as large caving ore passes. In this paper some details about the experiments and broad preliminary analysis of the effect of the HF by using seismic source parameters of the induced seismic events are presented: 1) Distribution of seismic activity, 2) the ‘equivalent’ magnitudes for each hole calculated from the cumulative seismic energy and seismic potency released during the fracturing, compared with the local geological conditions; 3) the predominant failure mechanism of the seismic events caused by HF was defined. A difference in the behaviour between larger and smaller events was noticed, as ML>0 events seem to be compression type failures and ML<0 events seem to be related to slip on pre-existing structures. No seismic events related to creation of a new fracture have been identified yet.

Apr 26, 2022

By Fernando O. L. Xavier

"The Barro Branco coal mine was located in the southern region of Brazil, in the state of Santa Catarina. In 2002, an incident occurred at the mine, leading to a violent, massive pillar failure, resulting in almost 100 failed pillars in less than 3 hours, totaling nearly 700 collapsed pillars after a period of 6 weeks. The paper outlines the geological and operational conditions before the accident and analyzes the primary factors leading up to the event. This paper also discusses and examines the unusual characteristic of violent, uncontrolled pillar bursts that occur over a longer timespan, in comparison to other equally violent but rapid events, such as those that occurred at the Crandall Canyon Mine, at a Book Cliffs District mine, and at the Solvay Mine. INTRODUCTION The southern region of Brazil holds 100% of the coal reserves for the country, and half of it is located within the state of Santa Catarina. Almost the entire Brazil’s coal production, around 8 million tonnes/year, is consumed for electricity generation. Most of the coal mines in Santa Catarina are underground room-and-pillar mines, and most are shallow mines, with depths of cover ranging from 20 to 400 m. The Barro Branco mine, near the city of Criciuma, experienced a violent mine collapse at the end of March 2003, which was analyzed and discussed by Zingano, Koppe, and Costa (2004). The event consisted of violent failure of 100 pillars in less than 3 hours, and a subsequent failure of approximately 700 additional pillars over the next 6 weeks. After the panel collapsed, the mine was closed due to unsafe conditions as a consequence of the seismic event. A map of the collapsed area is shown in Figure 1. GEOLOGY AND MINING METHOD There are two coal seams mined at Barro Branco mine. The first is the 1.5 m to 2.3 m thick Barro Branco Seam, under about 75 m of cover. The second is the Bonito Seam, where the collapse occurred. The Bonito Seam is 2.5 to 5.5 m thick located at a depth of approximately 80 m, with an average dip of 0° to 15°. Various major faults and inherent joints are present in the area."

Jan 1, 2017

By Robert S. Ondrey, Robert A. Haney, Kenneth G. Fields

As part of an MSHA program to assess the effectiveness of dust control parameters for longwall mining operations, respirable dust studies were conducted on six longwall sections. The purpose of these studies was to evaluate the influence of airflow and production on longwall dust control. The sections were sampled for 3 to 35 shifts. In addition to dust, ventilation and production measurements, other dust control and operational parameters were measured. The water spray system at each operation conformed with generally recommended practices. Therefore, improvements to the dust control system would be most appropriately achieved through improvements to ventilation along the face. Two methods of assessing the influence of ventilation and production were used. For two of the six mines where extensive sampling (22 and 35 shifts) was conducted, multiple linear regressions were used to relate the dust concentration versus airflow and production data. For these two mines, statistically significant correlations existed between concentration and both production and airflow. The multiple regressions fit to the data indicated that for every 0.47 m3/s (1,000 cfm) increase in airflow, there would be approximately 0.04 to 0.07 mg/m3 reduction in dust concentration; and, for every 1,000 ton increase in production, there would be approximately 0.15 to 0.50 mg/m3 increase in dust concentration. For the four mines with limited data (3 to 10 shifts), as well as for the two mines with extensive sampling, an average ratio of airflow per ton of coal mined was calculated by proportioning the airflow to production and the designated occupation personal respirable dust exposure to a 2.0 mg/m3 concentration. The airflow-to-tons ratio required to maintain a 2.0 mg/m3 dust concentration ranged from 0.0038 0.0071 m3/s per ton (8 to 15 cfm/ton). Both of these data treatments were used to calculate airflow requirements based on normal production rates. For the two mines where both the regression and airflow-to-tons ratio were calculated, results from the two methods agreed within 25 percent.

Jan 1, 1993

By Leon Maday, Dan L. Pecha, Jeremy Johnson, Daniel N. Adams

The Brightwater conveyance system includes 26 km of tunnels, a 130 mgd pump station, 2 km of micro tunnels, and a 2.4 km outfall. The tunnels extend from Woodinville to Puget Sound through varying soils in 1 to 7 bars of hydrostatic pressure and depths to 185 m. The tunnel diameters range from 4 to 6 m and include numerous lining systems. This paper highlights major shaft and tunnel design, including dual cellshafts, multiple pipe configuration tunnels, polymer concrete segments, and the use of a one pass lining designed to convey high pressure effluent.

Jan 1, 2005

By J. A. Finch, Zhenghe Xu, Z. A. Zhou

A particle-bubble collision model was used to investigate the minimum recovery zone height, H(r,min) required for flotation columns. The criterion used to define H(r,min) is that height which gives unit collision probability. It is shown that H(r,min) is determined by particle and bubble size, gas hold-up and bubble-bubble interaction. Under typical operating conditions, for flotation of particles less that 10 micrometres in size H(r,min) is greater than 10 m, but it reduces to less than 1 m for particles greater than 100 micrometres

Aug 1, 1995

By Ricardo Oliveira Gallart de Menezes, Claudio Gerheim Porto, Reiner Neumann

The Jiboia heavy mineral sands deposit is a new discovery associated with the São Francisco River delta on the northern coast of Sergipe state. The identified resources are part of the much larger mineralized trend. Mineralization is hosted in paleodunes deposited on Holocene marine terraces (Fig. 1). The dunes are up to 30 m above sea level, and mineralization occur from 6 m above sea level upward. The main ore minerals constitute pseudorutile, ilmenite, zircon, rutile and monazite. This work presents a thorough characterization of the mineralogy and granulometric distribution of the Jiboia orebody.

Apr 1, 2024

By Baczynski NR, Fagan MJ

A 3050m long section of a 1.65m internal diameter tunnel is presently under construction in the Brisbane area by means of the pipe-jacking method. The soils along the alignment had been deposited in a deltaic/estaurine environment and rapid changes in soil type occur. The tunnel passes beneath several extensive bodies of surface water. Groundwater problems have been experienced with tunnelling through alluvial sands and gravels. Details of the ground conditions, the pipe-jacking method used and tunnelling experience are discussed in this Paper.

Jan 1, 1987

By Shamsuz Zaman, Barry Hansen

The major development in the evolution of the conventional subaeration flotation machine has been the steady increase in the size of the individual units. In 1950, large machines were of 1.35 m3 (48 ft3) volume capacity. In 1989 the largest volume capacity operating is 85 m3 (3,000 ft3 ) These improvements have enabled the mining industry to operate successfully in the face of declining ore grades and adverse metal prices. This paper describes the design features and performance characteristics of a number of significant flotation machine designs.

Jan 1, 1989

By Carlos León

El proceso de recuperación de cobre es una de las actividades más importantes para la empresa minera Antamina. En ese sentido, el presente texto señala la optimización de este proceso como uno de los objetivos de la empresa Antamina. Por ello, se realizaron estudios en la etapa de molienda y flotación orientados a mejorar la recuperación de cobre en minerales M1 y M4A y así determinar cuáles han sido los controles o cambios implementados en dichas etapas que han permitido obtener una mejora en la recuperación de este metal.

Sep 21, 2013

1-Iron and Steel JOHN A MATHEWS, Chairman RALPH H SWEETER, Vice-Chairman WILLIAM CAMPBELL, Vice-Chairman MAX ROESLER, Secretary Iron Ore CHARLES B MURRAY, Chairman R C ALLEN W O HOTCHKISS MAX ROESLER ERNEST F BURCHARD WILLIAM KELLY DWIGHT E WOODBRIDGE M M DUNCAN CHARLES F RAND CARL ZAPFFE C T FAIRBAIRN THOMAS T READ Blast Furnace WALTER MATHESIUS, Chairman WILLIAM H BLAUVELT P KINNEY C SNELLING ROBINSON A J BOYNTON DORSEY A LYON H SWEETSEP D T CROXTON RICHARD MCCAFFERY R J WYSOR THOMAS L JOSEPH CHARLES P PERIN

Jan 1, 1923

[1-Iron and Steel JOHN A. MATHEWS, Chairman RALPH H, SWEETSER, Vice-chairman WILLIAM CAMPBELL, Vice-chairman MAX ROESLER, Secretary Iron Ore CHARLES B. MURRAY, Chairman R. C, ALLEN W. 0, HOTCHKISS MAX ROESLER ERNEST F, BURCHARD WILLIAM KELLY DWIGHT E, WOODBRIDGE M. M, DUNCAN CHARLES F. RAND CARL ZAPFFE C, T, FAIRBAIRN THOMAS T, READ Blast Furnace WALTER MATHESIUS, Chairman WILLIAM H. BLAUVELT S. P, KINNEY C. SNELLING ROBINSON A. J. BOYNTON DORSEY A. LYON R. H. SWEETSER D. T. CROXTON RICHARD MCCAFFERY R. J, WYSOR THOMAS L, JOSEPH CHARLES P, PERIN]

Jan 1, 1928

By Siegmund Babendererde

1. Introduction In Sayreville, New Jersey, the Middlesex County Utilities Authority put the construction of a 1041 m long sewer outlet to tender in June 1989. It had an internal diameter of 3,36 m and was part of a sewage treatment works project for county Middlesex. The contract was awarded to the Lodigiani Company, USA, who employed Hochtief Incorporated as subcontractor to drive the sewer outfall. 2. Ground Conditions According to the preliminary geological site investigation, carried out by the consultants Metcalf & Eddy, the tunnel passed through marine deposits.

Jan 1, 1991

By Edward Thomas

Yucca Mountain Overview The U.S. Department of Energy?s Yucca Mountain Project is a geologic repository project designed to receive, handle, package, transport, and emplace spent nuclear fuel and high level radioactive waste. The planned repository would be located in Yucca Mountain on the western edge of the Nevada Test Site, about 90 miles northwest of Las Vegas, Nevada, and would include both surface and subsurface areas. Yucca Mountain rock formations consist of successive layers of volcanic rocks (called tuffs) approximately 14 to 11.5 million years old, formed by eruptions of volcanic calderas to the north. With the volcanic rock the potential for methane emission is not an issue and the subsurface repository is a non-gassy (methane) classification. This paper will provide a summary of the development ventilation system design that provides fresh air for subsurface construction activities, and the emplacement ventilation system design that removes heat generated by the waste packages. The subsurface layout, illustrated in Figure 1, contains 108 emplacement drifts, one Performance Confirmation(PC) observation drift, nine intake/exhaust shafts, and three access ramps. The existing Yucca Mountain facilities, shown in bold lines in Figure 1, include a 7.8 km long, 7.62 m (25 ft) diameter U shaped tunnel that is formed by the North and South Ramps at both ends of the Exploratory Studies Facility (ESF) drift and a 1.5 km long, 5.0 m (16.4 ft) diameter Enhanced Characterization of the Repository Block drift (ECRB) that were constructed from 1994 through 1998. These drifts were used for site characterization activities and have been incorporated into the subsurface repository configuration. The unexcavated perimeter access main and exhaust main drifts are typically 7.62 m (25 ft) diameter TBM excavations and the emplacement drifts are 5.5 m (18 ft) diameter TBM excavations. The turnouts leading into the emplacement drifts are to be excavated by either mechanical, or drill and blast methods and serve as the launch chambers for the emplacement drift TBM excavations.

Enhancement of Energy Efficiency in Fine Grinding of Copper Sulfide Minerals Using a Pilot-Scale Stirred Media Mill - IsaMill The mineral liberation size of run of mine ores has dramatically reduced over recent years. As a result, the demand for fine grinding which is the most energy-intensive form of grinding has markedly increased in the minerals industry. Furthermore, the fine grinding costs increase exponentially with decreasing product particle size. As a result of the increased energy requirement for fine grinding, it is desirable to optimise fine grinding processes such as stirred media milling (ie IsaMill) to enhance energy efficiency, throughput and the product fineness. In the present study, the influence of slurry rheology, grinding media type and grinding media-to-feed size ratio on energy efficiency in a pilot-scale IsaMill was investigated under certain industrially relevant pulp processing conditions. It was shown that a critical rheological state existed, below which the energy required to achieve an 80 per cent passing (ie P80) 20 ¦m product size was unaffected by shear rheology (ie apparent viscosity and shear yield stress) whilst above which the grinding energy required increased dramatically with increasing shear rheology. Colorado River sand (3.35 mm) showed higher energy efficiency than MT1 ceramic media (2.5 mm) for a target P80 of 20 ¦m in the solids concentration range of 38 to 55 per cent by weight, but the former experienced more than four times the wear rate of the later. The high wear rate of the Colorado River sand may be due to its much lower hardness. For feeds with an 80 per cent passing (ie F80) 70 to 110 ¦m, 2.0 or 2.5 mm MT1 media appeared to be more energy efficient than 3.5 mm MT1 media whilst a media-to-feed size ratio of 41 to 53 is applicable for ~50 ¦m (ie F80) feeds for efficient grinding.

Sep 13, 2010

By Gurupraveen Ramanathan

Shallow-dipping orebodies (45°–60° dip) present significant challenges for underground longhole stoping, particularly due to limited gravity flow, drill misalignment near the footwall, increased potential for dilution from hanging wall overbreak, and deviation from drill string sagging at shallow angles. These geometrical and operational constraints often lead to unblasted ore wedges and excessive overbreak when standard practices are applied. This study develops a structured, data-driven framework to optimize longhole stoping in such conditions by integrating five key focus areas: (1) mining method selection, (2) stope and drift design, (3) drill and blast optimization, (4) equipment selection, and (5) performance evaluation. The suitability of longitudinal longhole stoping was validated for narrow vein geometries using orebody analytics and prior case studies. Geometric modeling was employed to determine optimal stope height (15–20 m) and stope width (1.5–2.5 m), with drift widths adjusted based on orebody dip to maintain drill access and minimize unbroken ore. Drill and blast design emphasized sequential blasting over multi-ring methods to improve void control, reduce wall damage, and enhance fragmentation. Specific burden and spacing guidelines (e.g., 1.8–2.3 m burden; 2.5–3.0 m spacing) were applied based on stope width and dip angle, and patterns were selected based on geometry—dice-5 for narrow stopes, and 3-hole rows for wider stopes. Drill rigs—including top hammer and ITH models from Sandvik, Epiroc, Boart Longyear and CMAC-Thyssen—were evaluated for compatibility with drift dimensions and alignment accuracy. Equipment was matched based on dip, drift width, and the ability to access the footwall at shallow angles. Sensitivity analysis quantified how changes in geometry, drilling accuracy, and blast design affect ore recovery, dilution, and operating cash flow. Results show that tailored drift and stope geometries, combined with proper blasting and rig selection, can boost ore recovery to over 95% and reduce dilution to below 5% in optimal conditions. This methodology offers a practical and economically optimized solution for shallow-dip mining scenarios.

May 4, 2025

By Brian V. Roulston

Potash is Canada&apos;s leading industrial mineral in terms of value of production, with 11.1 M tonnes of muriate of potash produced in 1992 for a value in excess of $1 billion U.S. Each tonne of potash produced generates about 2 tonnes of waste salt, together with slimes and brine. The disposal of these waste products, particularly the salt and slimes which are discharged on the surface, has recently become an environmental concern. This concern is forcing companies and regulatory authorities to review disposal practices. In New Brunswick, on Canada&apos;s east coast, Potash Company of America operates a mine at which 2 M tonnes of potash ore and 0.5 M tonnes of rock salt are mined each year. The mine is situated in an environmentally sensitive area, noted for its dairy farming and salmon angling. In such an area it was recognized that the storage of waste on surface would be unacceptable, and the mine was designed around this principle. Three main waste streams - salt, slimes, and brine - must be managed as an integral part of the mining system. Around 1.5 M tonnes of fine salt tailings from the milling process and the rock salt screening operation, are sent directly to the active cut-and-fill potash stopes to be used as backfill. Slimes and excess brine from the mill are piped underground as a slurry to be discharged into one of the basin shaped stopes created by mining of the rock salt. While the slimes settle out, the clarified brine is withdrawn from part of the stope to be pumped to surface as a feedstock for the evaporator - a process which recovers the contained potash values in the brine. By designing a system which integrates the mining, processing and disposal of all product streams, and by careful production planning, it has been shown that zero effluent potash mining is possible and points the way for the industry in the future.

Jan 1, 1995

By William D. Gallant, Thomas M. Barczak, Carol Tasillo

"This paper describes the results of full-scale testing of several multi-layered wood crib configurations that were tested in the Bureau of Mines mine roof simulator in cooperation with the Cape Breton Coal Research Laboratory and Cape Breton Development Corporation of Sydney, Nova Scotia. Nine different crib configurations currently being used as wood packwall supports for advancing longwall applications in Canada were evaluated. Configuration parameters understudy included the aspect ratio (height-to-width relationship) and percentage of solid material used in the crib construction. Test results and generalized wood crib behaviour are discussed in detail. Recommendations are made concerning crib constructions to maximize strength and stability. A cost benefit analysis of multi-layered wood crib configurations is made. A comparison of laboratory results and underground observations of several wood packwall supports in the Sydney coalfield suggest in situ load capacity is less than that measured in laboratory testing. Reasons for the apparent decrease of in situ load bearing capability are described.IntroductionA cooperative effort was undertaken by the U.S. Bureau of Mines with the Cape Breton Development Corporation (CBDC) and the Cape Breton Coal Research Laboratory (CBCRL) to evaluate the behaviour of gateside packing materials used in advancing longwall mining applications in the Sydney coalfield. As part of this effort, full-scale tests were conducted on wood packwall supports in the Bureau&apos;s 3-million pound (13.3 MN) active load frame.Nine different pack configurations were evaluated as part of this study. The wood packwall supports were multi-layered crib constructions from 6 in. (0.15 m) by 6 in. (0.15 m) cross section timbers using timber s 30 in. (0.75 m) and 60 in. (1.5 m) in length . The percentage of solid material in the crib constructions varied as illustrated in Figures 1 and 2. A summary of crib constructions is provided in Table 1."

Jan 1, 1991

By Charles Bohdanowicz

Production of crude in 1937 decreased (Tables 1 and 5) by about 2 per cent, while gas production for that period increased by about 6 per cent after a slight decrease in 1936 (0.4 per cent).&apos; As in preceding years, drilling operations were confined principally to extensions of old oil fields in the Jaslo district (fields 1 and 7) and to some extent to such extensions in the Stanislawbw district (field 27). Deepening of old wells to horizons reached more recently by new wells gave on the average better results per well than those attained by new wells (Table 3). Reserves of proved lands have increased some by new oil fields discovered, Targowiska (field 8) and Czarna (field 19) both of which, however, have only small production. The Daszawa gas field (field 25) has not been extended, but two new gas fields were located instead— Opary, distant 25 km. (151/2 miles) northwest of Daszawa, Balicze at 12 km. (7 1/4 miles) southeast of Daszawa, and Kalusz (TESP Company exploiting potassium salts) in the vicinity of the town of that name (field 33). Drilling upon the gas area near Tarnbw and Debica, while gas-bearing sandstone had been found at depths of from 300 to 512 meters (984 to 1680 ft.) (Zdziary No. 2) and at 220 m. (722 ft.) [pressure 11 atmospheres, flow 24 cu. m. per min. (847 cu. ft.)] (Przyborbw No. l), has not as yet ascertained horizons qualified for permanent exploitation. The exploring well near Kos6w remained for the last seven months at the depth of 1420 m. because of the collapse of rotary drilling pipe. Below the 300-m. level no gas sands have been encountered at this well. Gas Reserves In connection with the broad plan of developing industrially the sector of Poland lying between the Vistula and the San Rivers, and extending farther north as far as the city of Radom, there arose the necessity of a more accurate calculation of gas reserves for the fields of

Jan 1, 1938