Keith Atkinson

Prediction of water contamination arising from disposal of solid wastes

The dispersion of metal-bearing wastes into the natural environment has caused widespread contamination and pollution of soils. Poor regulated disposal has also put ground water quality at risk. In a world of diminishing soil and water resources, the identification and remediation of the most degraded sites has assumed a greater importance than ever before. This paper describes the extent and nature of soil contamination, its impact on ground water quality and the significance of metal contaminant partitioning between the solid and aqueous phases, and between inorganic and organic soil components.

Uranium ores of sedimentary affiliation

Uranium is used as a fuel mineral for nuclear power, and in the manufacture of nuclear weapons. In this chapter we begin by briefly reviewing the adequacy of uranium resources to supply an expanding nuclear industry and then consider the relative importance of the principal deposit types. The diversity of uranium occurrences precludes a detailed consideration of each deposit type but the reader is referred to Nash et al. (1981) for an excellent overview of the subject. We have selected unconformity and sandstone-type deposits for particular consideration. The reasons are partly because together they constitute more than 60% of World resources but also because they serve to illustrate contrasting approaches to exploration. Uranium contained in quartz—pebble conglomerates is discussed in Chapter 5.

Hydrothermal vein deposits

The term ‘hydrothermal’, when used in the context of mineral deposits, means that the minerals have formed from a hot aqueous fluid of unspecified origin. Many styles of ore deposits are considered to have been deposited from hydrothermal fluids, and in this chapter we restrict our attention to those deposits where the ore minerals are contained dominantly within veins. High- grade hydrothermal vein deposits, and their oxidation products, must have been one of the principal styles of mineralization worked by prehistoric man. Knowledge of this early activity is lost in antiquity, but the publication of De Re Metallica by Agricola in 1556 demonstrates that many of the characteristics of hydrothermal deposits were appreciated by the medieval miner. The most comprehensive review of current thinking on hydrothermal ore deposits is The Geochemistry of Hydrothermal Ore Deposits edited by Barnes (1979).

Sediment-hosted Copper—Lead—Zinc deposits

The recognition of sedimentary processes in the genesis of base-metal deposits can be traced back to Werner’s observations on the German Kupferschiefer in the late eighteenth century. Werner’s belief that all rocks and ores were of sedimentary origin led eventually to the discrediting of his views on ore genesis. In the mid- nineteenth century, Hunt (1873) expressed a more balanced and sophisticated sedimentological explanation for the genesis of some base-metal sulphides, and foreshadowed much contemporary thinking on the subject. However, during the first fifty years of this century concepts of ore genesis were strongly influenced by American geologists, who observed the proximity of many ore deposits in the USA to igneous intrusions, and considered that igneous hydrothermal solutions were of dominant importance in ore formation. Lindgren and Bateman were amongst the leading advocates of the ‘hydrothermal’ school, and in their opinion ore deposits associated with sediments were largely the products of replacement by solutions emanating from a cooling magma.

Ores formed by metamorphism

The processes of metamorphism give rise to some of the World’s major deposits of tungsten and some important copper occurrences. These processes may also result in important high-grade sources of molybdenum, lead, tin, iron and zinc as well as by-product base and precious metals. Industrial minerals are also worked from deposits formed by metamorphism. Among the industrial minerals are asbestos, wollastonite, magnesite, talc and graphite.

Iron ores of sedimentary affiliation

The bulk of the World’s production of iron ore is processed into steel, and the needs of the steel industry therefore have a profound effect on the type of ore mined. An understanding of the technology of the steel industry is useful for the geologist working on iron ore deposits, and a good introduction to the subject has been provided by Strassburger (1969). Recent changes in the mining and processing of iron ore are reviewed by Peterson (1980).

Ore deposits formed by weathering

Many types of mineral deposit form by weathering. For discussion in this chapter we have selected bauxite, nickel laterite and kaolin; we also describe supergene manganese and the supergene enrichment of sulphides. These mineral deposits are among the most important ores formed by weathering and supergene enrichment is one of the best understood aspects of weathering. The selections were made to illustrate the several different chemical processes taking place during weathering.

Magmatic hydrothermal deposits

In the previous chapter we have described some of the mineral deposits that have formed by magmatic activity, often by segregation within the magma chamber itself. In this chapter we turn our attention to other magmatic activity which results in important mineral deposits. These are not ores that have segregated during crystallization of the magma but are those that arise by hydrothermal activity associated with igneous bodies emplaced at high levels in the earth’s crust. Fluid inclusion and isotope studies indicate that magmatically derived fluids and circulating meteoric water have played varying roles in the genesis of these hydro- thermal ore bodies. The tectonic setting, primary mineralogy and alteration characteristics are very important in guiding exploration for these deposits.

The design and implementation of exploration programmes

Every mining operation begins with an exploration phase. The exploration procedure adopted varies with the finance available, the type of mineral deposit sought and the geological and geographical environment. Well-organized exploration programmes follow an established pattern beginning with a desk study and ending with the target selection. The target is then evaluated and feasibility studies on the deposit are undertaken. Some companies precede the full feasibility study with a pre-feasibility study when the geological and mining factors are drawn together to outline the likely extent of the project and the form the full feasibility study should take. If the feasibility studies are favourable and all factors are positive the project proceeds to development and eventually to production. The generalized sequence is illustrated in Fig. 11.1 and the component parts are elaborated upon in Table 11.1.