Mineral deposits have a heterogeneous temporal distribution, with characteristic peaks in the abundance of particular mineralisation styles at specific times in earth history. This uneven distribution can be explained by: (i) temporal changes in the processes that produce mineral deposits; and (ii) preservational potential of the environments in which the deposits form. Temporal changes in mineral-deposit forming processes can, in turn, be ascribed to: (i) the evolution of atmosphere– hydrosphere– biosphere systems; (ii) a secular decrease in global heat flow; and (iii) long-term changes in tectonic processes (e.g. Barley and Groves1). As shown below, (iii) may be a direct consequence of (ii), and these factors also affect the longterm preservational potential of terrains. Although individual lines of evidence for change in the oxidation state of the atmosphere–hydrosphere system are hotly debated, the nature of metal deposits for which transport and deposition are highly affected by redox state (e.g. Fe, Mn, U), and which formed in sedimentary environments, show marked evolutionary changes over time. A direct control on mineral deposit distribution by the secular decrease in global heat flow is the restriction of Ni–Cu deposits in high-Mg komatiite volcanic rocks to the Late Archaean and Palaeoproterozoic. In contrast, Palaeoproterozoic to Tertiary Ni–Cu–PGE deposits are associated with large intrusions and giant layered complexes that are less magnesian.
|Journal||Institution of Mining and Metallurgy. Transactions. Section B: Applied Earth Science|
|Publication status||Published - 2003|