ABSTRACT Comparative characteristics of PGE, noble-metal and sulphide mineralization in phoscorites and carbonatites from the Kovdor and Phalaborwa deposits are given. Four typical sulphide-rich samples from Kovdor and Phalaborwa (phoscorites and carbonatites from both deposits, as well as sulphide concentrate from the Kovdor Concentrating Mill and a flotation sulphide concentrate from the Palabora Mining Company) were studied. In Kovdor, mainly in calcite-rich areas of the phoscorites, small, drop-shaped isolated sulphide (pyrrhotite, chalcopyrite ± pentlandite) inclusions occur in calcite, as well as similar calcite inclusions in sulphide aggregates. Besides these and other rare sulphides, six Pt-bearing minerals, nine Pd-bearing minerals and four Au minerals were identified in the ‘heavy concentrates’ of the Kovdor samples. Copper-bearing minerals - bornite, chalcopyrite, minerals of the chalcosine group and cubanite - dominate within sulphides of the samples from the Loolekop deposit, Phalaborwa. Typical exsolution textures of chalcopyrite-bornite solid solution, as well as myrmekitic intergrowths of bornite and chalcosine-group minerals are usually observed. Besides these sulphides and other scarcer ore minerals, one Pt-bearing mineral, eight Pd minerals, four Au-bearing minerals, and five Ag-bearing minerals were identified in the ‘heavy concentrates’ of the Phalaborwa samples. At Kovdor, pyrrhotite sulphide mineralization crystallized from a high-temperature sulphide-rich fluid phase, separated from the carbonatitic (or phoscoritic) magma. In contrast, the crystallization temperature of the dominant copper sulphide mineralization at Phalaborwa is considered to be medium to low. Thus, sulphide mineralization in the Kovdor Complex occurred at a higher temperature than at Loolekop, and was essentially richer in S and poorer in Cu than the Phalaborwa Complex.

Abstract Carbonatite-associated deposits include a variety of mineral deposits that occur both within and in close spatial association with carbonatites and related alkalic silicate rocks. Carbonatite-associated deposits are mined for rare- earth elements (REEs), niobium, iron, copper, apatite, Vermiculite, and fluorite. Byproducts include barite, zircon or baddeleyite, tantalum, uranium, and in the unique Palabora carbonatite of South Africa, platinum group elements, silver, and gold. In some complexes, calcite-rich carbonatite is mined as a source of lime to produce Portland cement, and in Europe, carbonatites have provided lime and iron for hundreds of years (Dawson, 1974; Deans, 1978; Bowden, 1985). Carbonatites are igneous rocks which contain at least 50% modal carbonate minerals, mainly calcite, dolomite, ankerite, or sodium- and potassium-bearing carbonates (nyerereite and gregoryite). Other minerals commonly present include diopside (in early carbonatites – e.g., Bond zone, Oka, Quebec), sodic pyroxenes or amphiboles, phlo- gopite, apatite, and olivine. A large number of rare or exotic minerals also occur in carbonatites. Definitions of rock names used in describing carbonatite-associated deposits are provided in Table 24-1 and chemical formulae of some less common minerals are given in Table 24-2. Carbonatites occur mainly as intrusive bodies of generally modest dimensions (as much as a few tens of square kilometres), and to a lesser extent as volcanic rocks (flows and derived deposits), which are associated with a wide range of alkali silicate rocks (syenites, nepheline syenites, nephelinites, ijolites, urtites, pyroxenites, etc.) (Bowden, 1985; Barker, 1989). Although carbonatites are invariably associated with alkalic rocks, the inverse relationship does not necessarily hold (Möller, 1989b). Carbonatites are generally surrounded by an aureole of metasomatically altered rocks called fenites produced by reaction of country rock with peralkaline fluids released from the carbonatite complex (Morogan, 1994).

Abstract Alkaline igneous rocks and carbonatites are compositionally and mineralogically the most diverse of all igneous rocks and, apart from their scientific interest, are of major, and growing, economic importance. They are valuable repositories of certain metals and commodities – the only significant sources of some of them – and include Nb, the rare earths, Cu, V, diamond, phosphate, vermiculite, bauxite, raw materials for the manufacture of ceramics, and potentially Th and U. The economic potential of these rocks is now widely appreciated, particularly since the commencement of the mining of the Palabora carbonatite for copper and a host of valuable by-products. Similarly, the crucial economic dominance of rare earth production from carbonatite-related occurrences in China has stimulated the world-wide hunt for related deposits. This volume describes and provides ready access to the literature for all known occurrences of alkaline igneous rocks and carbonatites of Antarctica, Asia and Europe (excluding the former USSR), Australasia and the oceanic islands. More than 1200 occurrences from 59 countries are outlined, together with those of 57 oceanic islands and island groups. The descriptions include geographical coordinates and information on general geology, rock types, petrography, mineralogy, age and economic aspects, with the principal references cited. A brief description is also given of alkaline minerals in meteorites and of alkaline rocks on Mars and Venus. There are 429 geological and distribution maps and a locality index. As has been demonstrated by the three earlier volumes, Alkaline Rocks Part 4 is likely to be of considerable interest to mineral exploration companies, as there are no comprehensive published reviews of the economic aspects of the alkaline rocks. It will also interest research scientists in the fields of igneous petrology and volcanology, and geologists concerned with the regional distribution of igneous rocks and their geodynamic relationships.