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CLOSE THIS BOOKTools for Mining: Techniques and Processes for Small Scale Mining (GTZ, 1993, 538 p.)
C. Surface mining
VIEW THE DOCUMENTC.1. Definition
VIEW THE DOCUMENTC.2. Initial conditions and problem areas
VIEW THE DOCUMENTC.3. Factors related to environment and health
VIEW THE DOCUMENTC.4. Pit and quarry industry

Tools for Mining: Techniques and Processes for Small Scale Mining (GTZ, 1993, 538 p.)

C. Surface mining

C.1. Definition

Like underground mining, surface mining involves the production of mineral raw materials. In the latter, production takes place at surface. Surface mining processes solid rock, loose rock and alluvial deposits. Production takes place on the land surface as well as in rivers and seas, free of deep sea mining. The production activities in surface mining particularly alluvial deposits with heavy and precious metals, entails mainly the processing of products although here an attempt is made to contribute to an improved system through a strict separation of areas of activities. In the areas of production and hauling, and in draining, various techniques are applied which are used as well in underground mining. A renewed discussion of these devices will not be undertaken in this section.

C.2. Initial conditions and problem areas

A number of different types of deposits are found even in the limited field of alluvial precious metal deposits. This brings about various problems in mining production, particularly in processing.

The following are the most important of those alluvial deposits which have exploitable deposits of gold, as well as tin and tungsten, zircon and sand and gravel minerals and which are appropriate for small-scale mining:

- recent fluviatile sediments in riverbed areas. This type of deposits is common in the Andes. The high morphodynamic in this mountainous region with its erosion and sedimentation, accounts for a recent genesis of rich precious metal deposits. These unconsolidated loose sediments either are exploited under water using dredges or suction dredges operating directly from the river. During the dry season, or when the riverbed is generally dry as a result of the diversion of the river, these are mined manually or mechanically with shovels, wheel loaders etc. Examples are the riverbed alluvial deposits of eastern scarp of Bolivia's Andes such as the Rio Tipuani, Rio Mapiri, and Rio Kaka. Analogous to the above mentioned gold deposits, recent fluviatile alluvial tin deposits are exploited, e.g. on the Rio Huanuni, Dept. Oruro, Bolivia. After 500 years of mining history, these deposits additionally exhibit anthropogenetic characteristics 1(natural erosions from anthropogenous forms such as waste deposits, tailing ponds).

- fluviatile fossil placers and terrace deposits. Being older geological formations, these Palo- frenches (sediment filled old V valleys) and graded terraces are often already solidified. Due to the high mobility of cementing minerals as a result of the climatic conditions of the tropics, even recent accumulations are already solidified. This causes difficulty in mining, and particularly in processing when only liberated feed may be worked upon. Fossil placers of this kind are frequently overlapped with more recent sediments which marks the transition to underground mining. Provided that sufficient quantities of water are available, these alluvial deposits are exploited either hydromechanically by monitors, manually or mechanically. Examples are the gold deposits in the Cangalli series, e.g. Molleterio, Dept. La Paz, Bolivia.

- glacial und fluvioglacial alluvial deposits, moraines and sediments in the pleistocene, that is, recent glaciation of the Andes. Being sediments which have been exposed only to a short and purely mechanical transport devoid of a natural concentration through separation or chemical re- grouping, these alluvial deposits usually contain relatively marginal tin and tungsten deposit. As a result of the negligible natural size reduction to which the material has been exposed, the ores are extensively unliberated. Accordingly, the processing of ores of this kind must also involve crushing and grinding. Otherwise the sediment is usually unconsolidated and is mined using manual or mechanized methods of open-pit mining Example: El Rodeo, Cord. Quimsa Cruz, Dept. La Paz, Bolivia.

- mineral bearing rock slides, llamperas. Inferior forms of heavy mineral alluvial deposits exhibit mineral bearing fell rocks which, analogous to glacial alluvial deposits, are unliberated and partly in huge blocks. After it is produced using a mining method (drilling and
blasting), the material is processed in a manner similar to an ore exploited underground. The tungsten bearing fell rocks of the Cerro Chicote Grande, Dept. Oruro, Bolivia, which is mined by the Cooperative Minera Taminani, provide an example.

- anthropogenous deposits such as waste stockpiles, heaps, tailing ponds originating from old production and processing plants. This group of deposits offer a huge potential not only for large scale but also for small scale mining operations.

The following are the reasons behind the wide range of valuable contents of waste deposits:

- the negligible recovery of the processing plants not only of large-scale operations e.g. the COMIBOL in Bolivia with its current output at 40% of the metals but also of small-scale operations,

- the mining of previously rich deposits for centuries for which have left behind comparatively rich waste deposits,

- the mining economy of colonial Latin America which concentrated on precious metals such as gold and silver dumped by-products such as tin, tungsten, among other base metals.

- the sophisticated improved processing techniques which today is capable of, for instance, producing precious metals out of pyrites, led to the conversion of previous waste deposits into new minable deposits.

Today the above-mentioned alluvial deposits constitute an important field of activity in small-scale mining. The significance of these reserves for the national mining industry, and with it small-scale mining, will definitely increase.

Low costs of production, previously crushed material and a reserve situation which, comparatively, can be estimated with certainty, combined with a negligible investment risk, are factors which make these deposits appear predestined for small-scale mining.

Regardless of location, water usually creates crucial problems. In the case of production from a riverbed, besides the high costs of pumping and drying, excess water creates extremely difficult and dangerous working conditions.

To dry it out, the flow of the river is redirected by constructing of flanking dams on one side of the riverbed so that the other side is left to dry and is thus made available for mining.

The yearly turnus of precipitation in the alternating dry and humid tropics characterised by a marked dry and wet season, causes huge fluctuations in the water level: special characteristics of the mesoclimatic specifications in high mountain regions and local precipitations in the catchment area may cause an extreme rise of the river's water level within a short time. The planning of mining is thus influenced significantly by this unpredictable factor.

In the case of production in a dry location, the supply of industrial water requirements of mine and processing plants is particularly a problem. This is especially so when huge quantities of water are necessitated by hydraulic mining methods using monitoring. Such hydraulic mining is often necessary in places where partly a consolidation of materials of alluvial deposits has occurred. These places are usually located high above the draining level and hence difficult to supply with industrial water.

Otherwise, the technical deficiencies of small-scale mining in open-pit mining are significantly lesser compared to those in underground mining. The bigger space requirements of modern technology is not a problem at surface. Production and loading techniques are also available in the countries along the Andes and maybe utilized for the production of raw materials at surface.

As in underground mining, the degree of mechanization of operations dictates production capacity in open-pit mining. The ratio of production of manual-primitive mining to fully mechanized loading and haulage lies at present over 1: 100. In open-pit mining, huge amounts of materials may have to be produced and hauled for negligible raw ore grades. Only through a consequential, step by step partial mechanization is it possible to progress from the subsistence mining of the individual gold digger, from the margins of the subsistence level to a secure existence.

In partial mechanization, the bottlenecks are found in the provision of an energy supply which is reasonably priced and is appropriate rather than in the availability of mining methods (the technology of mining and transport in mining of alluvial deposits is definitely simpler compared to that of the underground mining).

Although it is difficult to draw a distinction between mining and processing in the field of open-pit production, it must be emphasized that critical problems in mining of alluvial deposits in the small and in the smallest scales may be found in the processing. Hence the present work puts emphasis on processing techniques.

C.3. Factors related to environment and health

In many ways, production activities of surface mining have placed a strain on the ecosystem. Apart from the dangers to the environment posed by equipment and vehicles run by internal combustion which produces

- exhaust fumes
- waste oil, and
- noise

open-pit mining disturbs the ecological balance by destroying vegetations and pollution of rivers.

- Pollution of rivers. Huge quantities of water are contaminated with mud as a result particularly of the open-pit production of alluvial deposit materials from recent riverbeds and the hydraulic mining of alluvial deposits. Usually no purification of the water follows. The effects of the suspended sediment burden endures. In some places, this may extend up to a distance of over 300 km down the river. In irrigated agriculture, the sediment burden renders cultivation difficult. In the dry season, the sludge concentration is especially high and therefore, has serious consequences for people living in areas down the river. On one hand, the quality of drinking water, which particularly in lowlands is taken directly from rivers, suffers. Filtration procedures are generally not known. On the other hand, the river fauna is altered or is exterminated as a result of changes in the aquatic environment of the rivers. The consequences are felt not only by fishermen. It is also felt in the supply of food containing animal protein. The river system Rio Tipuani, Rio Mapiri and Rio Kaka in Bolivia presents an example. It can be seen at first glance in which river gold production is being undertaken.

- Dissappearance of vegetation. The huge space requirements of open-pit mining can mean the extensive destruction of vegetation. In the humid tropics that is the climatic region of the eastern scarp of Andes, this has led to the well-known phenomenon of soil erosion (slope sliding, soil flushing, further sediment burden of rivers).

C.4. Pit and quarry industry

Among the raw materials of pit and quarry industry are various minerals and rocks, which are found in the most varied forms of deposits, used in the most varied ways, and which among other things, have extremely differing price values. The nature of mining production, depends on these and other parameters - whether this takes place on the surface or underground - the processing method, the manner of trading, the market and particularly, whether the raw material can be transported. For instance, while highly valued refractory raw materials can pay for their transport worldwide, the construction raw materials can only be marketed within a closeby region due to their low value.

The following overview according to Schneiderhhn lists the main applications of non-metallic raw materials and indicates which raw material can be exploited mainly in open-pit mining (bold and italic):

Light metal ores

Metal ores: Aluminum, Magnesium, Cesium, Rubidium, Potassium, Sodium, Lithium, Strontium, Beryllium, Calcium, Silicon.

Precious stones, gem stones

Salts and fertilizing minerals
Mineral Salt, Potassium Salt, Leucite, Alunite, Saltpeter, Limestone, Gypsum, Anhydrite, Apatite, Phosphate.

Minerals for chemical industry
Sulphur, Halite, Potassium Salt, Limestone, Fluorite, Manganese minerals serving besides of combustibles for producing the basic materials for the large scale chemical industry (Sulphuric Acid, Nitric Acid, Hydrochloric Acid, Fluohydric Acid, Hydroxydes, Ammonia, etc.).

Mineral colors, pen minerals and textile minerals
Iron oxide and hydroxide, Manganese, Cinnabar, Gypsum, Rutile, Baryte, Mica, Graphite, Chalk, Scapstone, Greenstone, Brown Coal.

Lubrication and polished minerals
Graphite, Talc, Pyrophyllit.

Refractory minerals
Quartz, Quartz sands, Graphite, Chromite, Bauxite, Dolomite, Magnesite, Asbestos, Andalusite, Olivine, Cyanite, Dumortierite, Soapstone, Zircon.

Flux minerals
Quartz, Fluorite, Greenland Spar, Apatite, Limestone, Dolomite.

Minerals for electric and thermal insolation
Asbestos minerals, Talc, Serpentine, Sea Foam, Soapstone, Mica, Amber.

Grinding and polishinq minerals
Diamond, Corundum, Emery, Garnet, Quartz, Honestonequartzite, Grindstone-Rock, Red Iron Ore, Diatomaceous earth, Triplit.

Optical minerals
Halite or Mineral Salt, Fluorite, Double Spar, Quartz Cristalls.

Bleaching and absorbent minerals
Allophan, Bolus, Bentonite, Fullers Earth, Diatomaceous Earth.

Minerals for ceramics, cement and glass industry
Kaolin, Clay, Quartz, Feldspar, Talc, Soapstone, Boron Minerals, Rare Earth
Minerals, Chalk, Marl, Gypsum, Sand, Gravel Stone, Volcanic Sinter, Chips of Rock.

Building material
Eruptive Rock, Tuffs, Sandstone and other, Building Stone Slates, Clay Slate, Chalk, Marble, Serpentine, Alabaster, Stones for Road Construction, Auxiliary Material for Road Construction, Building Sands and Additives to Artificial Stones.

Basic minerals for building materials and their application are listed below due to their importance for regional development.

Application:

Therefore suitable stones:

Split Gravel (Ballast

Quartzporphyry, Basalt, Diabase

for roads and rail

Gabbro, Granite, Syenite, Gneiss,

tracks):

Phonolite, Quartzite, Graywacke

Pavement:

Granite, Syenite, Gabbro, Basalt, Diabase, Quartzporphyry, Graywacke

Kerb, stairs,

Granite, Syenite, Gabbro, Sand

sidewalks

stone, Graywacke, Limestone, Quartzite

Interior decoration:

Granite, Syenit, Marble, Serpentine

Monuments:

Granite, Syenit, Marble, Dolomite, Sandstone

Building

Granite, Syenit, Gabbro, Sand-

foundations:

stone, Limestone, Dolomite, Gneiss

Residence rooms:

Tuffite, Sandstone, Limestone

Roofing slate:

Slate, Platy Limestone

Basically, the technique of mining of non-metallic raw materials does not differ from that of the mining techniques described earlier. Solid rock are obtained by drilling and blasting. Only special decorative stones, e.g. marble are produced by sawing using diamond saws. The bigger the blocks to be obtained, the more protective should be the blasting during mining. This can be done by selecting the correct drilling scheme and particularly through the choice of the appropriate explosive. Through the expansion or dilution of granulated and gelatinous explosives with non explosive components or through the selection of explosive medium which are less powerful, the miner can obtain a huge heap of broken material. Thus the mining of shale for roof tiles for example, uses black powder for the production of large slate blocks. The special techniques of producing blocks of stones and their processing however should not be the concern of the present work especially because these techniques are described accurately in the following recently published work.

STONE. An Introduction. Asher Shadmon. Intermediate Technology Publications. LONDON 1989 [ISBN 0946688 08 7 (UK); ISBN 0942850 15 7 (USA)]

Relative to the mining techniques for metallic raw materials and fuel minerals (coal, lignite, peat, asphalt, bituminous shale), the specific quantities of exploited raw materials are usually greater. Surface mining of construction materials, particularly, is a mass production due to the minimal value of the product already mentioned above. The problem lies mainly in the haulage and the transport to the market. Usually, cost intensive transport systems as truck/wheel loader, etc. are required by means of which operations located on the deposits of these raw materials already land in the range of medium-scale mining. On the other hand, mining activities aiming at highly-valued products, e.g. graphite, diatomite, or other industrial minerals, or mining work which has a big share of manual work or activity which can not be mechanized easily, can definitely be undertaken by the usual small-scale operations using partially mechanized or improvised method.

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