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Mineralogy and genesis of rare metal, noble metal, PGE and REE mineralisation in carbonatite complexes, and its petrogenetic significance

Ziel

Carbonatites are rare igneous rocks consisting predominantly of mantle-derived carbonate. They have extreme trace element compositions, with characteristic enrichment in REE, Nb, Ta and Zr, and occasionally also noble metals and PGE. Some carbonatites are major economic sources of these elements. However, despite the importance of carbonatites to mantle processes, and their economic value, fundamental questions about the mechanisms by which they are produced, their relationships to associated silicate rocks, and the processes of mineralisation remain to be answered.

This project proposes a comprehensive and carefully coordinated approach to understanding the diverse processes of mineralisation in carbonatites, particularly by study of mineral chemistry, whole rock geochemistry, isotope geochemistry and fluid inclusions. It combines NIS and INTAS teams with expertise in various aspects of the mineralogy of carbonatites and links these with INTAS teams experienced in isotope systematics and whole rock geochemistry. It aims for a new classification scheme for carbonatite mineralisation, of use to researchers and exploration geologists, and also aims to apply the results to the fundamental problems of carbonatite petrogenesis.

The specific objectives are
(a) To determine the mineral chemistry and paragenesis of primary Nb,Zr, Ta and REE mineralisation associated with carbonatites and related rocks;
(b) to characterise fully the secondary mineralisation, which has yielded many new minerals, formed during sub-solidus alteration of carbonatites;
(c) to acquire major and trace element chemical data of the host rocks, in order to constrain their genetic relationships;
(d) to characterize the sulphides, PGE and noble metal phases;
(e) to measure S and Pb isotopic compositions of the sulphides in order to establish the conditions of formation and source of the ore metals;
(f) to use stable and radiogenic isotope signatures of carbonatite mineral fractions, chosen from the mineral chemical and geochemical studies, so as to determine their origin and crust-mantle relationships and place the carbonatites within a detailed time frame, and;
(g) to undertake a fluid inclusion study of rock forming minerals in selected examples to constrain better the conditions of various stages of mineralisation.

The project concentrates on carbonatites of the Baltic Shield, Russia because they provide examples of all of the main varieties of mineralisation, including PGE minerals which have recently been described for the first time in carbonatites. Good material is available from drill core and working mines, and all project partners will carry out fieldwork together. A second fieldtrip to the Ural Mountains, and collections at The Natural History Museum, London, and in Russia, will enable comparison with other carbonatites to ensure that the results are generally applicable. State of the art electron microprobe, ICPMS, CL, whole rock geochemistry, isotopic and fluid inclusion analysis techniques and procedures are available at the INTAS institutions and will be used by the NIS partners, including 7 young scientists, during their visits. Preliminary analytical work will be done in Russia.

The project will result in a number of publications in international scientific journals, arising from each of the specific objectives, as well the overall aims, and is the most comprehensive study of carbonatite mineralisation thus far attempted.

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Koordinator

Natural History Museum
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Adresse
Cromwell Road
SW7 5BD London
Vereinigtes Königreich

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Beteiligte (5)