BRE 211: Principles of Agriculture and Forestry LECTURE 11 MINERALS LANDS
Definition • Mineral Resources may be broadly defined as • Potentially usable concentrations of elements, chemical-compounds, mineral or rocks in a particular location or on the earth. • These resources are technically reasonable expectations of quantities of mineralized rocks that will be developed by exploitation.
Definition • A mineral deposit is referred to as a motoresource if it is expected to become an economic resource at some point in the future. • A mineral that once had value may become valueless as a result of new discoveries. • Such a resource is referred to as a paleoresource.
Definition • Mineral resources include reserves plus all other mineral deposits either not yet discovered or unobtainable due to technological or economic reasons.
Valuation of Mineral Resources • The valuation of precious minerals is normally carried out by Mining Engineers and Geologists. • There are however, a number of non-precious surface minerals such as sand and gravel, chalk and limestone etc, which often fall within the practice of the valuer. • Valuers may be called upon to assess for various purposes clay deposits, gravel deposits, sand deposits, or stone quarries. • A valuer may also be called upon to value the assets of a mining company for various purposes.
Classification of Minerals • Minerals can be classified into two groups, namely: • Precious minerals including metalliferous deposits (iron, copper, tin), fossil fuels (coal, petroleum, gas) etc. • Non-precious minerals including structural materials such as building stone, gravel, sand etc. • These are minerals other than precious metal or precious stones.
Mineral Exploitation • A mine is an excavation made in the earth to extract minerals. • The activity, occupation and industry concerned with extraction of minerals is called mining. • The art and science applied to the processes of mining and the operations of the mine is called Mining Engineering.
Mineral Exploitation • The essence of mining is to drive or construct an excavation (a means of entry) from the existing surface to the mineral deposit. • If the excavation is entirely open to or operated from the surface, it is called surface mine. • If the excavation consists of openings for human entry driven below the surface, then it is an underground mine.
Mineral Exploitation • The specific details of the procedure, layout, and equipment used distinguish the mining method is uniquely determined by: • Physical • Geological • Environmental • Economic and • Legal circumstances that prevail.
Mineral Exploitation • Mining is preceded by geological investigations that locate the deposit and economic analysis that prove it financially viable. • When deposits have been determined, extraction takes place
Mineral Exploitation • After extraction mineral processing takes place. • The processed products undergo further concentration, refinement or fabrication during conversion, smelting or refining to provide consumer products. • The mining methods basically include: • Surface Mining. • Underground Mining. • Novel methods.
Surface Mining • This is the most common method of exploitation world - wide. • It includes mechanical excavation methods such as open cast, open pit and aqueous excavation. • Open cast and open pit mining are used to exploit a deposit near the surface e.g. sand or stone quarrying.
Surface Mining • Aqueous extraction • Uniquely reliant on water. • Includes: • Dredging • Solution mining.
Surface Mining • In dredging • Unconsolidated earth, sand and gravel are excavated from beneath water by a large hydraulic machine, which usually floats on water. • Valuable minerals are extracted and earth discarded.
Surface Mining • Solution mining involves • Injection of a special solvent into an ore bed and pumping the solution back to the surface for the extraction of the solute. • Water is the solvent injected into the ore. • Minerals produced in this manner include common salt.
Underground Mining • Underground mining methods are differentiated, by the type of wall and roof supports used, the configuration of production opening, and the dimension into which mining operations progress. • Methods include: • Unsupported • Supported • Caving.
Underground Mining • Unsupported methods • Used to extract mineral deposits that are roughly tabular, flat or steeply dripping, and generally in contact with strong rock. • Supported methods • The ore is drilled selectively so that roof support is provided by natural pillars of ore that are left standing in a systematic pattern, and rooms are cut from access entries to provide working faces.
Underground Mining • Supported methods • When necessary, additional support is supplied by roof bolts or timbers. • The pillars are composed of good ores that cannot be retrieved. • The percentage that must be left for support varies with the depth of the Ore bed and strength of overlying rocks. • Ordinarily 40% - 60% of the Ore can be mined.
Underground Mining: Caving • A large block of ore, several meters to a side, is undercut and thereby caused to cave. • As the block fragments and collapses, the ore is drawn off through chutes or loading points into haulage drifts. • Alternatively, when mineral bed underlies weak ground, headings are driven to the limit of the ore zone and most distant ore is mined first.
Underground Mining: Caving • Temporary support is provided beyond the face, and as the ore retreats towards the surface, the supports are moved closer to the working zone. • As a result the marked out area collapses.
Novel Methods • These are new methods applicable to unusual deposits or employ unusual techniques or equipment. • They include • Automation • Rapid excavation in hard rock • Underground gasification • Clean mining.
Mining Method • Method selected for exploitation is determined mainly by: • The characteristics of mineral deposit • Limits imposed by safety, technology and economics. • Geological conditions such as deposit depth, and shape and strength of the ore and wall rock
Stages in the Life of a Mine • The overall sequence of activities involved in modern mining is often compared to the stages in the life of a mine. • The stages include: • Prospecting • Exploration • Development • Exploitation.
Stages in the Life of a Mine • Prospecting and exploration, precursors to actual mining, are linked and sometimes combined. • Geologists and mining engineers share responsibilities for these two stages, geologists more for the former and engineers more for the latter. • Likewise development and exploitation are closely related stages • Usually considered to constitute mining proper and are the main province of mining engineer.
Prospecting (Mineral Deposit) • Procedure: • Search for ore • Locate favourable and choosing appropriate prospecting methods. • Spot anomaly, analyze and evaluate. • Time • 1–3 years
Exploration (Ore body) • Procedure • Define extent and value of ore. • Sample drilling/excavation. • Estimate tonnage/grade. • Evaluate deposit using discounting method e.g. PV=income-cost. • Viability appraisal i.e. • Make decision to abandon or develop. • Time • 2-5 years
Development • Procedure • Opening up ore deposit for production. • Acquire mining rights. • File environmental impact statement. • Construct access roads. • Locate and construct facilities. • Excavate deposit. • Time • 2-5- years
Exploitation • Procedure • Large scale production of ore. • Factors in choice of method of extraction. • Types of mining methods. • Monitors cost and economic pay back. • Time • 10-30 years
Factors Affecting Mineral Exploitation • Physical Characteristics of the ore body. • Size, shape and type of ore body • Nature and thickness of the underlying and overlying rocks • Structure of the ore including dip, strike, folding, jointing and fault • Probability of underground water may affect safety.
Factors Affecting Mineral Exploitation • External factors • Arise due to the physical location of the ore body. • Accessibility • Transportation to market. • Labour availability. • Environmental concerns i.e. environmental impact of mineral extraction and processing. • Topography, which influences a mine or quarry planning.
Environmental Impact of Mineral Exploitation • The environment of the life layer is affected adversely in many varied ways by removal of mineral deposits and by processing these substances. • There are also direct threats upon man’s safety and health as he engages in these activities.
Environmental Impact of Mineral Exploitation • Some of important environmental effects include the following:- • Scarification of the land i.e. excavation and other land disturbances produced for purposes of extracting mineral resources, including concomitant accumulation of waste matter e.g. scarification arising from strip mines, quarries etc.
Environmental Impact of Mineral Exploitation • Mass movements of rock and overburden caused by subsidence of land surface due to collapse of mines or groundwater in excess; sliding and flowage of soil and bedrock due to removal of support in mining operations and to instability of soil accumulations. • Land subsidence i.e. Sinking of the ground following the removal of mineral matter from the rock beneath.
Environmental Impact of Mineral Exploitation • Aggravation and sedimentation i.e. mining operations that produce large volumes of sediment may cause drastic increases in bed load, which in turn cause channel aggravation close to the source and also increase the suspended load of the same streams. • Suspended load travels down the stream and is eventually deposited in lakes, reservoirs, and estuaries far from the source areas. • The sediment is particularly damaging to the bottom environments of acquatic life.
Environmental Impact of Mineral Exploitation • Air pollution caused by smelting and treatment of ores, especially sulfide ores (copper, lead, zinc etc) result n the release of SO2 into the air in enormous amounts. • Fall-out over the surrounding area is destructive to both human health and vegetation. • Mining and quarrying operations send mineral dusts into the air. • Combustion of fossil fuels resulting in formation of oxides of carbon and hydrogen and of any impurities within these fuels.
Environmental Impact of Mineral Exploitation • Ocean Pollution • Development of offshore oil and gas fields involves drilling wells on land or beneath the sea; transporting oil by tanker, pipelines, or other methods to refineries, and converting the crude oil into useful products. • All along the way, the possibility of environmental disruption resulting from accidental oil spills, shipwreck of tankers, air pollution at refineries, and other impacts are well known.
Health Hazards associated with mining • Death and injury within mines due to accidents from explosions, fires and caving-inns. • Respiratory disorders and diseases related to mining and mineral process. • There is Noise and vibration due to blasting and transportation of the products.
Minimizing the Impact of Mining on the Environment • The adverse impacts of the mining and processing of minerals whether on land or below the sea call for further research directed towards reducing them. • Accumulation of large waste heaps can often be avoided by returning the waste rock to the excavation, whether this is at the surface of underground.
Minimizing the Impact of Mining on the Environment • Subsidence of the surface can be controlled so that it causes little or no permanent damage to buildings by using appropriate mining techniques, or by filling the mined-out space with waste material.
Minimizing the Impact of Mining on the Environment • Potentially serious interference with ground water including lowering the water table by pumping to drain mines can be avoided for example by introducing a barrier to limit the affected areas. • Modern blasting practices minimize one source of noise, while intelligent siting of crushing and other processing plants can help to reduce another. • Good maintenance and thoughtful planning can reduce the noise from vehicles.