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Abstract

Recalling the idea of the type of a deposit as put forward by F. Blondel and developed by P. Routhier, the authors propose to explain the typical geologic history of deposits of the "Tri-State," "Silesian" or "Alpine" type according to the specifications of the sponsors of this Symposium. It is thus intended to encompass the entire chain of processes of metalliferous concentration.

For this purpose, the history of Les Malines district is examined in general terms, and the probable, or at least, the most plausible sequence of the processes of metalliferous concentration is deduced therefrom. Comparing the chain of geological events which appears in Les Malines district with the similar histories known in other metalliferous provinces, the authors attempt to outline a general common sequence of processes of concentration which may be considered as the genetic pattern of the type. An indecision remains between the "exhalative-sedimentary" and the "pedological-sedimentary" patterns.

To shed light on this dilemma, it is interesting to examine the nature of the basements underlying or adjacent to the mineralized cover. It appears, on one hand, that the various lithologic zones of the basement do not possess an equal capacity for enriching the cover, and, on the other hand, the variable depths of erosion of the eugeosyncline—the most favorable (zone) with respect to stratiform mineralization in the cover—have a significant effect. The weak mineralization of the cover (strata) situated above or near the areas of eugeanticlines where late orogenic vulcanism is characteristic leads the authors to reject the "exhalative-sedimentary" hypothesis, at least with respect to stratiform deposits of lead-zinc, barite and fluorite, in a carbonate environment lacking in evidences of volcanic activity contemporaneous with the sedimentation.

It is no doubt still necessary to further evaluate the "pedological-sedimentary" possibilities, but the importance of the phenomena of enrichment due to meteoric alteration (residual deposits, karsts,…) is a certainty, though it is sometimes forgotten, compared to the possible recognition of tuffs, a dubious sign of metallizing activity, since it is plain that, properly understood, not all vulcanism is metallogenic.

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