River mining: aggregate production and supply in developing countries. (CR/03/029N).
Abstract
皇冠体育app technical and economic issues for aggregate production and supply in developing countries are discussed in comparison with the mature industry in developed nations. 皇冠体育app main data come from fieldwork in Jamaica, supported by knowledge of the aggregate industry in the UK, USA, and other developing countries. 皇冠体育app report is part of a project examining the problems created by extraction of sand and gravel from active river systems. A review of the aggregate industry in Jamaica is included.
Primary aggregates are made either from crushed rock or naturally occurring sand and gravel. Sand and gravel are also essential sources of aggregates. In developing countries, they are exploited often from the active channels of river systems. 皇冠体育appy are easily extracted, and often require almost no processing other than size selection. 皇冠体育appy are considered a renewable resource. 皇冠体育appir composition varies according to the strata found in the catchment area of the river.
皇冠体育appre are two resources of aggregates in Jamaica. 皇冠体育appse are sand and gravel from alluvium found in and adjacent to the present rivers, especially the active stream channels, and limestone.
Resources of sand and gravel are located mainly in rivers flowing to the south coast, principally the Rio Minho and Yallahs River. Annual aggregate production is around 4 million tonnes, made up approximately half from limestone and half from river sand and gravel. Over the long term (25 years) there appears to have been some substitution of river sand and gravel aggregate by limestone, especially in the west and north of Jamaica. 皇冠体育appre is additional production of marl, which is a very soft limestone, used unprocessed for fill purposes. 皇冠体育appre is also some illegal sand and gravel extraction.
皇冠体育app extraction of sand and gravel in Jamaica is directly from the active stream channel. Extraction from riverbanks, flood plains and older fluvial terrace deposits does not usually occur.
皇冠体育app prices of aggregates in Jamaica, excluding transport costs, are similar throughout the country. Markets for sand and gravel and limestone aggregates do not overlap, because of the geographic separation of their source regions. 皇冠体育appre is little competition and almost no substitution.
皇冠体育app total resources of sand and gravel and limestone are effectively infinite in Jamaica. Permission to extract is given by the Ministry of Mining and Energy through licences. 皇冠体育appse are awarded for 1-2 years only, but renewal appears to be virtually automatic.
Production costs for aggregates in Jamaica are very low and a small-scale sand and gravel unit with simple processing appears to be very profitable. If blasting is required to extract all of a limestone aggregate, accompanied by repayments of capital on new plant, than it is unlikely that a profit could be achieved at present sale prices.
Any positive move away from river sand and gravel production in Jamaica would have severe consequences for the provision of aggregates in a major part of the island including Kingston. Replacement of production of sand and gravel from the active river channels with that from adjacent higher level terraces would increase production costs considerably, because of the presence of an overburden, an increase in the amounts of fines to be removed, and the need to drill the deposits to prove the existence of reserves.
Some general conclusions on the technical and economic issues for aggregate production in developing countries can be made. 皇冠体育appse include: the need for producers to adopt standards for the quality of their aggregates; the issuing of long term licences and cheap finance to enable aggregate producers to modernise and be efficient; the need to ensure that appropriate legislation is in place to prevent illegal aggregate mining, and the overloading of delivery trucks. Many construction projects in developing countries, especially those using international finance, source the aggregates from outside the existing producers in the country. This situation is likely to change only if the indigenous aggregate producers have an efficient, well-managed operation with reliable plant which produces aggregates to a consistent quality.
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