André Bernard Et François Foglierini, 1967. "Etude Methodologique Sur La Genese Des Gisements Stratiformes Du Plomb-Zinc En Environnement Carbonate", Genesis of Stratiform Lead-Zinc-Barite-Fluorite Deposits (Mississippi Valley Type Deposits), J.S. Brown
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Critical examination of genetic hypotheses concerning the deposits comprised under this heading leads to an historical impasse which results from a fruitless combination of fundamental ideas: telethermal (telemagmatic), hydatogene (pseudo-hydrothermal), sedimentary.
The scientific problem posed by these deposits should be approached, like all geological problems, by an analysis in time and space conducted on the various scales of observation that are imposed by the size of the subject studied, in order to understand the deposit and its geological environment.
The authors therefore examine, scale by scale, the nature of the information available on stratiform deposits of lead-zinc in a carbonate environment.
The regional scale: the geo-tectonic and paleogeographic environments.
The scale of the deposit: the sedimentary environment and sedimentary characteristics of the mineralized series.
The mineralogical scale: paragenetic sequences, study of inclusions.
The chemical scale: trace elements, isotopic composition.
The logical utilization of the information obtained on the regional scale and on the scale of the deposit leads naturally to the useful orientation of prospecting for minerals. These scales likewise supply the greatest amount of significant genetic information, especially since they permit a sensible utilization of the time factor. The mineralogical scale, carefully evaluated, is beginning to be fruitful. The chemical scale is still in a state of evaluation, and it seems premature to attempt to draw worthwhile genetic conclusions.
In sum, taking into account the state of progress of our knowledge and of the development of analytic techniques, the authors recognize the possibility of several complex solutions to the problem of the genesis of stratiform deposits of lead-zinc in a carbonate environment, especially the "telethermal-sedimentary" and "sedimentary-hydatogene."
However, as the result of a selection of geological assumptions, the authors favor the "sedimentary-hydatogene" hypothesis which they present in a tabulated summary.
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Genesis of Stratiform Lead-Zinc-Barite-Fluorite Deposits (Mississippi Valley Type Deposits)
Proponents of syngenetic theory base their interpretation largely on widespread uniform mineralization within a restricted stratigraphic interval and a consistent relationship of mineralization to sedimentary features. Proponents of epigenetic theory base their interpretation on mineralization of post-depositional structures, changes in extent and grade of ore, open space filling, district-wide lack of close control by sedimentary features, and relation of ore to tectonic structures. These and other criteria are evaluated in an attempt to define diagnostic criteria.
On the basis of the criteria defined the major lead-zinc deposits of Mid-continent United States must be considered as epigenetic.
Features of the Southeast Missouri lead district are listed. The deposits are epigenetic. The metals are believed to have been derived from nearby sedimentary basins and carried out of basins onto shelf areas in a concentrated brine. Movement of solutions was controlled by basement topography and deposition of metals occurred when solutions entered the Bonneterre formation on the flanks of and over buried knobs.
Objective.—The problem of origin of stratiform ore bodies cannot be resolved until we define, and agree upon, what constitutes diagnostic evidence for each type of deposit. This paper is an attempt to review the nature of geologic evidence; to define those features that must be regarded as unique and necessary criteria in classifying any deposit or district; and to apply the criteria to a major district, the Southeast Missouri lead deposits.
Theories of Origin.—The major elements of theories on origin of stratiform ore bodies are summarized in Table 1. A deposit is Syngcnetic if formed by processes similar to and simultaneously with the enclosing rock; epigenetic if introduced into a pre-existing rock (3). A diagenetic origin implies deposition of metals with the host sediments but with recrystallization, rearrangement, and limited migration.
The search for an acceptable theory of origin must be separated into its two component parts: (1) definition of whether the deposit has syngenetic, diagenetic, or epigenetic features and. (2) history of mineralization to explain source, transport, and deposition of metals. A statement of preferred hypothesis is meaningless until the first is answered and accounts for all geologic facts. The answer must be based solely on observed megascopic and microscopic features and on geochemical and isotopic data; it should not be biased by lack of knowledge to answer all phases of the second. In evaluating the evidence to determine type of deposit one cannot be concerned