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  Metal Mining

Metals have been central to the development of human civilisation from the Bronze Age to modern times, although in the past, metal mining and smelting have been the cause of serious environmental pollution with the potential to harm human health. Despite problems from artisanal mining in some developing countries, modern mining to Western standards now uses the best available mining technology combined with environmental monitoring, mitigation and remediation measures to limit emissions to the environment.

Exploration

Exploration through to new project development is a vital part of any natural resource company's business. There are many mines that have been working continuously for several decades but in all cases they are exploiting a finite asset that must ultimately be depleted. Companies must therefore find new, replacement, ore bodies and more if the business is to grow. This is the fundamental difference between the natural resources and manufacturing industries.

Until this century, all exploration relied upon finding the surface outcrop of high-grade mineral deposits. Although this will continue to be the first indication of many significant new mineral deposits the vast majority of mine production of the major metals today comes from large scale operations exploiting low grade deposits discovered and evaluated by sophisticated technology. Equipment is expensive and may be used on the ground or in airborne surveys in purpose built aircraft.

Initial indications of an exploration target might be geophysical anomalies such as areas of high gravity or electrical conductivity. Nowadays the study of satellite imagery/remote sensing can play an important role in a preliminary regional assessment. Exploration sites are frequently in remote locations, which are costly to access and operate and may necessitate the use of helicopters and fixed wing aircraft.

Surface trench sampling and shallow scout drilling have established once an exploration target it becomes necessary to employ large diamond drilling equipment to put down deep holes that recovery core samples of the rock for examination and analysis. Thereafter the deposit may have to be accessed underground from shafts or tunnels to obtain more and confirmatory geological information and bulk samples for metallurgical test work.

All this, together with other studies on the site and associated infrastructure, has to be completed before a full feasibility study of the project is possible.

Surface Mining

Most surface metal and coal mining is based on relatively low-grade shallow deposits that have to be mined continuously and on a large scale to be economic. Natural aggregates such as crushed rock, sand and gravel are produced from quarries and pits, sometimes on a large scale comparable to some metal mines.

However the largest opencast/open pit mines are orders of magnitude bigger than the largest quarries and also differ in other important respects. Quarry products are generally of low unit value and only the minimum of waste overburden can be removed economically whereas opencast/open pit mines are frequently obliged to excavate a substantial tonnage of overburden to expose the ore grade material. The stripping ratio (ratio of waste to ore mined) can be as much as ten or more and all this waste rock must be mined, loaded and transported to a waste dump.

Other surface mining methods are also described in this section.

Quarrying

The adequate supply of natural aggregates such as crushed rock, gravel, sand and clays is essential to the building and construction industries in any country. In 1996 the UK produced more than 215 million tonnes of crushed rock, sand and gravel worth over 10400 Crores from more than 1,300 quarries employing 18,534 people. A few "super" quarries each produce around 10 million tonnes a year of crushed stone. These operations use a variety of heavy mobile equipment and crushing/washing plants. Added value operations producing ready-mixed concrete, cement, coated stone or bricks are commonly an integral part of a quarrying company's activities.

Underground Mining

Underground mining, by its very nature, is high cost but has to be the method of choice when a surface operation is not feasible due to the depth or geometry of the deposit, topography or environmental considerations.

Reference has already been made to the large lateral extent of bedded sedimentary deposits such as coal. In most cases the generally consistent nature of these deposits means that exploration drilling can enable the full extent and characteristics of the deposit to be established with a high degree of confidence. This in turn means the mining engineer can prepare a detailed long-term plan for the underground layout and mining method.

By contrast however metallic mineral deposits can vary greatly in shape, size, inclination, depth and value from narrow mineralised veins to massive multiple ore bodies such as those at Mt Isa in Australia. The operation can then range between small-scale, high-grade, selective mining and large scale bulk mining in lower grade, disseminated, mineral deposits where economies of scale approaching open pit operations are possible.

Shallow

For shallow deposits underground access and ore transport is likely to be by inclined tunnels or declines. This provides flexibility and enables trucks and large mobile equipment to be used underground equipment can therefore range in size up to very large and costly units for drilling, loading and transportation..

Most shallow operations will use flexible "trackless" methods and avoid the need for an underground railway system. Dump trucks and load-haul-dump (LHD) machines have robust rubber tyres and can travel and operate in any part of the mine. The actual working places where the ore is broken are referred to as "stopes" and a wide variety of stoping methods, and variations, could be used depending on the geological conditions and physical shape and dimensions of the orebody. This is too broad a subject to be covered in this document, suffice to say that in large mines similar equipment will be used for most stoping methods likely to be employed.

Ventilation requirements (volume of air circulating) usually depend on the total engine capacity of diesel equipment operating underground because exhaust fumes must be diluted to acceptable levels (usually specified in regulations).

All mines will have to install sufficient pumping capacity to keep the workings dry and cope with peak inflows. Water entering the mine can come from a number of sources: surface water percolating through the fractures in the rock (from rainwater, rivers, lakes or the sea) and underground aquifers.

Metal Processing

Crushing & Grinding

For natural aggregates it may only be necessary to crush and screen the rock. Coal/lignite may require little or no preparation before shipment or need cleaning and sizing depending on customer requirements. Removal of shale or sandstone waste and reducing sulphur content are the main objectives and be based on gravity separation methods.

In the vast majority of metalliferous mining operations the ore will have to be crushed and milled (finely ground) to liberate the particles of the contained minerals before these can be subject to further separation and concentration.

Concentrating

This normally follows crushing and grinding the ore and flotation of the liberated minerals on bubbles generated in special agitated cells. Chemicals are used to prepare the surface of the minerals and to produce the right sort of froth. The flotation concentrate is then recovered and filtered and dried for shipping to a smelter and refinery. Many mines produce two or more different metal concentrates that require differential flotation to separate the minerals.

Hazards & Risk In Mining

The mining side of the natural resources industry is perceived to be hazardous and in the past this was routinely the case. Although conditions have improved mining will continue to experience risk and loss from a variety of causes including:

Explosions gas/coal dust; explosives; fuels and oils; chemicals; boilers and pressure vessels; air blast (from collapsed ground) Fire timber/inflammables; explosives; fuels and oils; gas; chemicals; Seismic events; sudden ground failure; rock bursts (as a result of mining operations) Collapse of Ground; failure of sidewall in surface mine; underground (note air blast could be produced); flooding inundation of workings by water or mud/tailings; Shaft Accidents variety of possible causes Human Error potential wide ranging affects Political Risk mainly in developing countries Theft and Fraud products; equipment Sabotage all assets at risk Terrorist Activity all assets at risk

What measures should a well managed natural resources company take to minimise risk in each of the above categories? In all cases anticipation is a pre-requisite as a basis for the specification of standard procedures that combine effectively with local (mining and industrial) regulations applicable to the operation. Effective implementation then becomes of paramount importance and will only be possible if the appropriate resources are applied to the task in a consistent and acceptable manner. These fall broadly into two categories: equipment to detect and respond to faults eg, smoke detectors and extinguishers and a well-trained workforce with good management.

In the developed world today safety/loss prevention/risk management standards are generally good but high fatality rates still occur in deep mines like the South African gold operations where very severe and extreme physical conditions are encountered. The worst safety record in the industry is probably held by the Chinese coal mining industry where standards are very low and disasters all too frequently occur from gas/coal dust fire and explosions and from massive falls of ground.

In terms of "All Risks", rather than personal liability, there is an important distinction to be made between conditions in South Africa and China. The average South African gold mine is a large industrial complex above and below ground and comparatively well managed. Even the more frequent major incidents: fire and seismic events (as a direct result of mining operations), tend to be relatively localised in effect and damage to physical assets, although at least partial business interruption is often experienced. Much of the Chinese coal mining industry however is in small units that suffer from low standards in all respects - old equipment, labour intensive methods and poor management. Major disasters are all too frequent with great loss of life and possibly the destruction of most, if not all, of the mine facilities underground.

This comparison illustrates the point that most major accidents in mining are potentially avoidable if there are consistently high operating and safety standards and good management that anticipate risk. Recent disasters in South African mines have resulted from lapses in set standards.

The association of accidents involving injury or death with or without damage to physical assets, almost inevitably involves some loss of production. Safety standards are often incorporated into "Loss Control" procedures that anticipate risk and the overall threat to personnel and output.

As regards theft and fraud, in at least one Latin American country it has been said "stealing from a foreign (mining) company is a patriotic act" whether it is equipment or the product. Elsewhere it may be less routine but can nevertheless be a serious problem. Gold theft in South Africa has increased considerably in recent years.

The industry is facing an increase in political risk; particularly following the opening up of Eastern Europe and the Former Soviet Union and Mongolia, China and Asian countries with dubious political regimes. Latin America will also continue to be associated with political risk. Risk of terrorist activity and/or sabotage is a recurring problem and not always easy to anticipate but some mines are obliged to employ an armed quasi-military security force.

Foreign investors/companies associated with the mining of natural resources is frequently politically sensitive and seen as the exploitation of a national resource that belongs to "the people". Business Interruption can arise for any number of reasons above and below ground. Costly replacement parts may be held on-site as contingency spares to guard against serious downtime from unusual component failure. Natural Perils are not considered in the sections that follow.

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