V. I. Smirnov, 1967. "Problem of the Origin of Stratiform Lead and Zinc Deposits in the USSR", Genesis of Stratiform Lead-Zinc-Barite-Fluorite Deposits (Mississippi Valley Type Deposits), J.S. Brown
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[Professor Smirnov's paper is available only in this abbreviated form. Editor]
Classical deposits of the type under consideration are well known inside the territory of the Soviet Union in the Russian Platform, in Siberia, Kazakhstan, Middle Asia and the Caucasus.
In the broad regional geological plan three groups can be recognized, among them:
Formation on ancient platforms;
Formation on younger platforms;
Formation in the folded regions in the later stages of the geosynclinal cycle.
In the sedimentary rocks of the upper structural stage of the Russian and Siberian platforms stratiform deposits of fluorite, sphalerite and galena are well known among carbonate beds of different ages from Lower Cambrian to the Triassic.
On the superimposed molds of the post-Caledonian platform in Central Kazakhstan, stratiform deposits of lead and zinc are well known among Upper Devonian strata of dolomitized limestone.
In the sedimentary rocks of the folded regions belonging to the Hercynian cycle these deposits are well known in the carbonate beds of Devonian and Carboniferous age in Middle Asia and Western Kazakhstan; in the similar rocks belonging to the Alpine cycle, they are found in Georgia in the Caucasus.All the deposits have distinctive traits typical of similar deposits all over the world and so, as everywhere, their genesis is disputable.In favor of the syngenetic sedimentary origin of these deposits the following
Figures & Tables
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