Abstract

Many of us talk today of metallogenic provinces, but nearly always with qualifications, such as the coincidence of these provinces with structural (or geodynamic) zones, the alleged necessity of distinguishing metallogenic epochs before delimiting provinces, premature terminological discussions on the hierarchy and names of mineralized areas. Few specialists, however, try to fix province limits which have a practical value, i.e., within which many deposits of reasonable size and/or viable grade occur, and outside of which such deposits are rare or absent.Among parameters which, by the interplay of their associations, give provinces such variable characteristics, the mining geologist, the metallogenist, and the geochemist are in the first instance concerned with distinguishing the metal, or metallic associations, on a regional or planetary scale. Metallogenic epochs and types of deposits are left aside at this stage.Three examples are chosen to illustrate this approach: (1) the south Iberian pyrite belt, (2) Circum-Pacific tin and tungsten, (3) lead-zinc and copper in a part of Europe. The third example shows two lead-zinc belts (there are probably others!) and a wide copper zone. These features cannot result from physiographic conditions and human history. In any case, these belts reveal obvious heterogeneities and anisotropies in the distribution of significant concentrations. Furthermore, in many places they intersect the structural alignments and isochronous "megasurfaces" shown on geological maps. They by no means coincide everywhere with easily reconstructed plate margins. Do not these facts reveal the existence of earlier metallogenic belts in a very old framework (cf. De Launay, 1913, p. 4) ? If so, global tectonics should face this challenge."Les points ou certaines categories de roches, dont les exemplaires steriles sont ailleurs abondamment representes, se sont trouvees contenir exceptionnellement des provisions si extraordinaires de metaux rares, ont du offrir tres anciennement quelque chose de special, et nous sommes logiquement autorises a chercher d'abord ce quelque chose (d'autant plus special que la concentration metallique envisagee a ete plus rare) dans les premieres phases de la consolidation planetaire, ou tout au moins dans les periodes ou les parties internes de la Terre avaient encore, avec la superficie, des communications qui ont disparu depuis." (L. De Launay, Traite de Metallogenie, 1913, v. 1, p. 4).

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