Genesis and Classification of Triassic Alpine Lead-Zinc Deposits in the Austrian Region
L. Kostelka, W. E. Petrascheck, 1967. "Genesis and Classification of Triassic Alpine Lead-Zinc Deposits in the Austrian Region", Genesis of Stratiform Lead-Zinc-Barite-Fluorite Deposits (Mississippi Valley Type Deposits), J.S. Brown
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It cannot be expected that all observations made on stratiform lead-zinc deposits should point entirely to one genetic pattern. In this case, there would be no problem to discuss. But if we find features which can only be explained by syngenesis, or even better by genesis synchronous with the host rock, we can assume that the ores must, at least partly, have originated contemporaneously with the surrounding rock.
After the first appearance of the stimulating publications (8, 12, 17), asserting a syngenetic-sedimentary origin of the lead-zinc deposits in the Northern Limestone Alps instead of the generally accepted epigenetic-telethermal theory, agitated opposition arose among most Austrian geologists. Several symposia took place as a result (Munich 1956, Bleiberg 1959, Mezica 1964). The second of the present authors advocated an epigenetic mineralization at the conference in Munich. But since that time detailed and critical investigations were extended to the Southern Limestone Alps and particularly to the ore district of Bleiberg-Kreuth.
O. Schulz (14) found evidence of syngenetic-sedimentary ore structures in a few places in Kreuth. The first of the present authors (5) paid special attention to the comparison of the numerous lead-zinc deposits in the Austrian Limestone Alps with regard to their stratigraphic position and their morphological features.
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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