Fill the blanks with the necessary words: volume, proportion, value, developments, entities, cost-cutting

1. Mergers and acquisitions have been made, in order to create larger, more cost-effective and financially stronger…

2. In terms of … and … of output, it is still much alive and kicking.

3. … mined underground equates with some 16% of the total volume of ores extracted.

4. Technical … resulting in more deeply penetrating exploration methods, increase the probability of

finding new, richer, deeper ore deposits.

5. Intensive...... is now standard in all companies.

 

4) Give answers to the following questions:

1) What economic factor is now standard in all companies?

2) What is mining about?

3) What’s the difference between underground and open pit mining?

4) How much ore is produced globally each year?

5) What country is the most important in underground ore production?

 

4) Quоte the sentences in which these words and word combinations are used:

… to grow steadily, to make it possible, to have an impact, a tough fight, in terms of, on the other hand, at the other extreme, to come from, to become depleted.

 

5) Tell what you know about:

1) economic situation in world mining industry

2) improving productivity

3) underground mining

4) production distribution

5) future growth of world mining industry

Mine Development

Rock and Minerals

High temperatures and chemical reactions are some of the pro­cesses behind the concentrations of metal bearing minerals, found in the bedrock of the earth's crust.

A rough classification divides rock into sedimentary, metamorphic and igneous. Igneous rock, created by volcanic forces and high temperatures, is gener­ally compact and massive in struc­ture. Rapidly cooled lava flows harden into massive, homogenous rock. Granite, formed deep inside the earth's crust, has cooled more slowly, developing crystalline pat­terns, with aggregates of quartz, feldspar and mica.

Sedimentary rocks are created by erosion, with fragments car­ried by water streams settling at the sea bottom, and left for mil­lions of years to consolidate into a solid mass. Sedimentary rocks are identified by stratification, with younger rocks layered on top of older formations.

Metamorphic rocks were origi­nally sedimentary or igneous for­mations, and later restructured by heat and/or pressure. The origin of metamorphic rocks can be difficult to detect. Nevertheless, despite their origin, all of these rock types have to be drilled efficiently, which is where Atlas Copco experience in mechanized rock excavation really counts.

 

Ores and Orebodies

Ore is an economic concept, defined as a concentration of minerals, which can be economically exploited and turned into a saleable product.

Before a mineral prospect can be labelled as an orebody, full knowledge is required about the mineralization, proposed mining technology and pro­cessing.The feasibility study has to be undertaken to prove that the prospect can be economically developed into a mine.

Metal prices set on the London Metal Exchange (LME) determine the day-to-day value of a mine's ore.

Run-of-mine ore is treated in a dressing plant, and processed into dif­ferent concentrates. Where the ore contains more than one metal of value, separate concentrates of various min­erals are produced. The value of in-situ ore can be calculated by applying market prices to metal contents, and deducting costs for treatment and transportation of concentrates, togeth­er with the smelter's fee. The balance should cover the direct mining costs, and leave a margin for the mine opera­tor.

Metal prices fluctuate from day to day, depending on the supply-demand situation. An oversupply builds stocks of surplus metal, and the market price drops, along with the profit margin. As costs for processing, transport, smelting and refining remain constant the mine takes the squeeze of reduce income. The mine operating on narrow margin must prepare to survive periods of depressed metal prices.

One tactic is to adjust ore boundaries to a higher cut-off grade to increase the value of the run-of-mine product. Another is to increase the efficiency of mine production by modifying the mining method, possibly by introducing new, more powerful machines. The mine must remain profit generator, in an environment of increasing manpower cost and demand for better quality of life.

 

Prospecting and Exploration

The mining enterprise needs to secure satisfactory reserves, to guarantee pro­duction for the economic life of its existing mines. It also needs to locate new deposits to replace production from exhausted mines. Searching for new prospects, and investigating extensions of existing orebodies, are routines for the mining company.

The prospector looks at the surface lithology, observing irregularities. The geology may be established by pieces of coloured rock, mineralized blocks appearing in glacial drift areas, or sand in streams and waterways.

Such ocular inspection only identi­fies surface mineralization, and cannot be used in areas covered by alluvium or water. Where minerals show on sur­face, the downward extension is a matter of guesswork. Ancient miners may already have taken the most valu­able mineral.

Different geophysical methods are used to explore the bedrock, based on physical properties of rock and metal-bearing minerals. Magnetism, gravity, electrical conductivity, radioactivity, and sound velocity are used. Two or more geophysical methods are often com­bined in one survey, to acquire a more reliable database. Results from the sur­veys are compiled, and matched with geological information and records from core drilling, to decide if exploration activities are worth continuing.

Magnetic surveys measure varia­tions in the Earth's magnetic field, caused by magnetic properties of sub­surface rock formations. In prospect­ing for metallic minerals, these techniques are particularly useful for locating magnetite, pyhrrotite and ilmenite. Magnetic logging inside drill holes is also used, to obtain infor­mation for directing holes in core drilling programmes.

Electromagnetic surveys are based on variations of electrical conductivity in the rock mass. An electric conduc­tor is used to create a primary alternat­ing electromagnetic field. Induced currents produce a secondary field in the rock mass. The resultant field can be traced and measured, indicating the presence of a conductor. Electromagnetic surveys are mainly used to discover mineral deposits and to map geological structures. Sulphides containing copper and lead, magnetite, pyrite, graphite and certain manganese minerals, are examples of discoveries by electromagnetic surveys.

Electric surveys measure either the natural flow of electricity in the ground, or galvanic currents are directed into the ground, and accurate­ly controlled. Electrical surveys are used to locate mineral deposits at shal­low depth, map geological structures, determine the depth of overburden to bedrock, or identify the groundwater table. When prospecting for ore, the electric survey is often used to differ­entiate conducting zones located by electromagnetic surveys.

Gravimetric surveys detect small variations in the gravitational field caused by the pull of rock masses, which may be located several kilo­metres below the surface. The varia­tion in gravity may be caused by faults, anticlines, and salt domes that are often associated with oil-bearing formations. Gravimetric surveys are also used to detect high-density miner­als, like iron ore, pyrites and lead-zinc mineralization.

Radioactivity surveys measure the intensity of radiation of rock forma­tions containing radioactive minerals, which will be considerably higher than the normal background level. Measuring radiation levels helps locate deposits containing uranium and thorium, and other minerals associated with radioactive substances.

Seismic surveys are based on varia­tions of sound velocity experienced in different geological strata. The time is measured for sound to travel from a shock point to one or more detectors placed on the ground. The source of sound might be the blow of a sledge­hammer, a heavy falling weight, a mechanical vibrator, or an explosive charge. Seismic surveys determine the quality of bedrock, and locate the upper surface of compact mineral deposits deep in the ground, and are also used to locate oil-bearing strata.

Geochemical survey is a compara­tively recent technology, featuring several specialities. One is to investi­gate the presence of various metals in the topsoil cover. By taking numerous samples over a large surface area, and analyzing for minute traces of each metal, regions of interest are identi­fied. Areas can then be delineated for more detailed studies.

 

Exploration Drilling

 

Core drilling is carried out using spe­cial drill rigs, equipped with a tube drill string and impregnated diamond bit (IDB). The open-centre IDB cuts a cylindrical core of rock, which is stored in a core barrel inside the tube, and retrieved as a sample. For tunnelling applications, core drilling provides essential information to determine the optimum excavation method and type of rock reinforce­ment to be adopted.

 

 

Figure 1. Atlas Copco HOBIC impregnated diamond coring bit.

The core is recovered from the core barrel by pulling up the complete tube string. All tubes are then disconnected and stacked close to the drillrig. Alternatively, a wireline arrangement can be used, which recovers the core barrel by pulling a wire inside the tube string.

The core is a proof of underground geology, which can be inspected, and split in halves. Samples of special interest are sent to laboratories for analysis of metal content. Cores from exploration drilling are stored in spe­cial boxes, and kept in retrievable archives. Boxes are marked to identify in which hole, and what depth, the sample was taken.

The information gathered by core drilling is important, and represents substantial capital investment, so max­imum use is made of the information from each core. The borehole may also be used a second time, for another form of geophysical exploration.

Diamond drilling is expensive, and core drilling programmes are time-consuming undertakings. Reverse cir­culation drilling is a complementary exploration technique, faster, but less accurate. Reverse circulation drilling is carried out with standard percussion rockdrills, using a special technique where the flushing media is introduced through a casing at the hole collar. Drill cuttings are pushed up through the drill string, discharging through a pipe outlet on the front head of the rock drill. Drill cuttings are sampled to identify varia­tions in the rock mass. Exploration by reverse circulation drilling provides a comparatively fast and inexpensive way to explore rock down to 30 m depth. Results are, however, not of the same quality as for core drilling.

Reverse circulation drilling is nowadays the most common method for surface exploration of gold, espe­cially in alluvial deposits.

 

Mineral Prospect

While the geophysical survey may indicate presence of minerals, such evidence is not sufficient to identify the prospect ore. Miners need proof of what minerals are there, and the metal grades, and confirmation that volumes of mineralized rock are large enough to continue the search. The first check would be to look for an outcrop of the mineralization. Where the ground cover is only a shallow layer of allu­vial, trenches can be dug across the mineralized area, to expose the upper surface of the bedrock. A prospector will identify the discovery, measure both width and length, and assess the mineralized area. Rock samples from trenches sent to the lab for analysis may provide evidence to merit drilling some coring holes.

After outlining borders of the min­eral deposit on the ground surface, the next step is to confirm that the miner­alization continues down into the rock. The surface area multiplied by the extension at depth provides a first esti­mate of ore volume. Core drilling is used to map the geology inside a rock mass, and several thousand metres may be required.

Sets of diamond-drilled holes are laid out to intersect the mineralized zone along the strike, in parallel verti­cal sections. The geology can then be traced at different levels underground, and presented in three-dimensional models. Analysis of core samples will give further detail to the geology, and the mineralization can be divided in high- and low-grade sections.

An underground exploration pro­gramme may then be undertaken, using a temporary mine arrangement, with hoist and shaft. Strategic develop­ment of horizontal drifts will allow the diamond drillrig to core from the most promising locations. Core samples of the mineralization arc often used to establish the economics and viability of mineral dressing processes. In some cases, despite a high grade, the flota­tion process might be difficult, due to grain size after milling.

 

 

Figure 2. Samples of cores obtained from exploratory drillholes.

Before a mining company takes the decision to convert a prospect into a producing mine, the company's Board of Directors must be convinced that the mine will yield an acceptable return on capital invested. The feasibility study presents the time schedule, necessary capital, return rates and payback period.

 

Underground Mining

 

The underground mine aims for maxi­mum economic recovery of minerals contained in the bedrock. The orebody is the volume containing valuable min­erals, while the rock around it is waste.

Waste dilutes the ore, so miners try to leave it in place, wherever possible.

Ore close to the surface is mined by open pit techniques, in which the waste rock can be separated by load­ing, and trucked to the waste dump instead of the concentrator. Subsurface orebodies are exploited by under­ground mining, for which techniques are more complex.

The mining method is adapted to the rock conditions, and the shape, dimensions, strength and stability of the orebody.

In order to work the underground rock mass, infrastructure is required for access to work places, ore produc­tion, power supply, transport of ore, and maintenance of equipment.

 

 

Figure 3. Basic infrastructure required for a typical underground mine.

The shaft forms the access to the underground levels, and is the mine's main artery for anything going up or down. Shaft stations, drifts and ramps connect stopes with orepasses, tramming levels, and work­shops for movement of miners and equipment.

Efficient ore handling is important. The blasted ore is loaded from produc­tion stopes, via orepasses to a main level, and thence to the crusher at the hoisting shaft. The crushed ore is then stored in a silo before transfer by con­veyor to the measuring pocket at the skip station, from where it is hoisted to the surface stockpile.

Electric power is distributed throughout the mine, and is used to illuminate work places and to power drillrigs, pumps and other machines. A compressor plant supplies air to pneu­matic rock drills and other tools, through a network of pipes.

Water reticulation is necessary in the mine, wherever drilling, blasting and mucking takes place, for dust sup­pression and hole flushing. Both ground water and flushing water are collected in drains, which gravitate to a pump station equipped with high-lift pumps to surface.

Air quality in mine workings must be maintained at an acceptable health standard.

The mine needs a ventilation system, to remove smoke from blast­ing and exhaust gases from diesel-powered machines, and to provide fresh air for the workers. This is nor­mally provided via downcast fresh-air shafts. High-pressure fans on surface extract foul air through the upcast shafts. Ventilation doors control the underground airflow, passing fresh air through active work areas. Polluted air is collected in a system of exhaust air­ways for channelling back to the ven­tilation shaft.

 

Mine Infrastructure

 

Each mining method requires a differ­ent underground infrastructure, such as access drives to sublevels, drifts for longhole drilling, loading drawpoints, and orepasses. Together, they form an intricate network of openings, drifts, ramps, shafts and raises, each with its designated function.

The shaft is a long-lived installa­tion, and may be more than 50 years old. The hoist and cage provide access to the shaft station, which connects with a main level along which trains or conveyors may run. The skip is the most efficient way to hoist ore from underground to surface.

Materials handling may be by utility vehicles or locomotive-hauled trains. The co-ordination of train haulage with shaft hoisting, from level to level, makes the logistics of rail transport complex. Workers in a rail-track mine are required to wait for cage riding until shift changes, or scheduled hours, with material trans­port only permitted at certain periods. Ore hoisting takes priority over man-riding and material transport.

The Load Haul Dump (LHD) loader introduced mines to diesel power and rubber-tyred equipment in the 1970s. This was the birth of trackless mining, a new era in which labour was replaced by mobile equipment throughout the mine. Maintenance workshops are now located under­ground at convenient points, usually on main levels between ramp positions.

The shaft remains the mine's main artery, and downward development is by ramps to allow access for the machines. On newer mines, a decline ramp from surface may facilitate machine movements and transport of men and materials, and may also be used for ore transportation by truck or conveyor, eliminating the need for hoisting shafts

 

Mine Development

 

Mine development involves rock excavation of vertical shafts, horizon­tal drifts, inclined ramps, steep raises, crusher stations, explosives maga­zines, fuel stores, pumphouses and workshops. Drill-blast is normally used, with raise boring for ventilation, ore- and rock till passes, and slot raises.

A deep shaft may secure many years of production, until ore reserves above the skip station are exhausted. The shaft can be rectangular, circular or elliptical in profile.

Extending the shaft in an operating mine is costly and difficult, requiring both expert labour and specialized equipment.

Drifts and ramps are dimensioned to accommodate machines passing through, or operating inside.

Normal ramp grades vary between 1:10 and 1:7, with the steepest grade to 1:5. The common curve radius is 15.0 m. A typical ramp runs in loops, with grade 1:7 on straight sections, reduced to 1:10 on curves.

Raises are steeply inclined open­ings, connecting the mine's stations at different vertical elevations, used for ladderways, orepasses or ventilation. Inclination varies from 55 degrees, which is the lowest angle for gravity transport of blasted rock, to vertical, with cross-sections from 0.5 to 30 sq m.

The raiseboring machine (RUM) provides safe and efficient mechanized excavation of circular raises up to 6 m-diameter. In conventional raise boring, it drills a downward pilot hole to the target level, where the bit is removed and replaced by a reaming head. The RBM then reams back the hole to final diameter, rotating and pulling the reaming head upward. The cuttings fall to the lower level, and are removed by any convenient method.

An RBM can also be used to exca­vate raises where there is limited, or no, access to the upper level. In this box-hole boring method, the machine is set up on the lower level, and a full diameter raise is bored upward. This method is used for slot hole drilling, as well as upward raise development. The cuttings are carried by gravity down the hole, and are deflected from the machine by the use of a muck col­lector and a muck chute.

Hole opening, or downreaming, using a small-diameter reamer to enlarge an existing pilot hole, can also be carried out by an RBM. The opera­tion is similar to pilot hole drilling, except that a small reamer is used instead of a pilot bit. Hole opening is only used whena standard reaming system is either impractical or not pos­sible, for back filling purposes for instance.

The capital cost of an RBM is high, but if used methodically and consistently, the return on investment is very worthwhile. Not only will raises be constructed safer and faster, they will be longer, smoother, less dis­ruptive than blasting, and yield less overbreak. The consistently-sized rock chips produced by an RBM are easy to load.

The BorPak is a small, track-mounted machine for upward boring of inclined raises. It starts boring upwards through a launching tube. Once into rock, grippers hold the body, while the head rotates and bores the rock fullface. BorPak can bore blind raises with diameters from 1.2 m to 1.5 m, up to 300 m-long.

 

List of words

 

1. access – доступ

2. headframe – копер

3. shaft station – приствольний двір

4. drift – штрек

5. stope – вибій (забій)

6. opening – виробка

7. raise – підняттєвий

8. ladderway – сходні або людський хідник

9. orepass – рудоспуск

10. ream – розширення свердловини;

11. reamer – розширник

12. tramming level – відкотний горизонт

13. drillrig – бурова каретка

14. ramp – рампа;скат;схил

15. outline – окреслювати;оконтурювати;оконтурити

16. shaft (downcast, upcast) – ствол (низхідний;висхідний)

17. longhole drilling – буріння довгими шпурами

18. impregnated diamond bit-імпрегнована алмазна коронка

19. cut off grade – бортова місткість, мінімальна кількість цінного компоненту

 

 

Exercises:

1)Give Ukrainian equivalents of the following words and word combinations:

 

feasibility study, depressed metal prices, ore boundaries, cut-off grade, exhausted mine, search for new prospect, to acquire a more reliable database, magnetic properties of substances, at shallow depth, to identify the groundwater table.

 

2) Give English equivalents of the following words and word combinations:

пошук, детальна розвідка,оголятися (виходити на поверхню); вихід на поверхню мінералізації, електромагнітне обстеження, гірнича виробка, мінерали, що містять метал, непошкоджений (цілий) зразок; бурова штанга; життєздатність рудного штоку (родовища)

 

3)Fill the blanks with the necessary words and word combinations: