Jože Duhovnik, 1967. "Facts for and Against a Syngenetic Origin of the Stratiform Ore Deposits of Lead and Zinc", Genesis of Stratiform Lead-Zinc-Barite-Fluorite Deposits (Mississippi Valley Type Deposits), J.S. Brown
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For the strata-bound lead and zinc ore deposits of Mežica and Bleiberg the following origin can be accepted: hydrothermal, syngenetic or hydatogene in the meaning of the word according to syngeneticists. The following facts favor a syngenetic origin: the ores occur in horizons at certain distances from a characteristic bed; they have a regional extent; mineral composition differs strongly from that of normal hydrothermal deposits; geopetal fabrics suggest a syngenetic origin. The geopetal fabric can be observed in fossils (syngenetic) and in vugs, occurring generally in carbonate rocks (epigenetic). Lead is isotopically older than the enclosing rocks.
Arguments against a syngenetic origin are the lenticular form of the ore bodies and the zonal arrangement of individual minerals in some deposits (Topla). There is also a problem in the co-existence of carbonates and sulfides at the same EH and pH. There are regional differences in the Pb: Zn ratio which increases from west to east. The relation of marcasite towards the economic minerals is not favorable (Kherzet Youssef, Algeria). Faults along the ore bodies contain mineralization with the same texture as the strata-bound ores. Aureoles of metals surround the ore bodies. The hydatogene origin of the deposits is very doubtful, as a selective solution of sulfides should take place with respect to carbonates. Secondary dolomite never shows a bedded structure; hence it does not replace the primary stratiform sulfide ores but rather forms irregular vein systems following fissures parallel to the main faults. The absolute age of the lead speaks for regenerated ore deposits as proposed by the late Professor Schneiderhöhn (11). The rhythmic fabric could be observed not only in the strata-bound mineralization but in fragments of the ore in the fault ore bodies posing a question whether this is a true geopetal texture or only a replacement of rhythmic carbonate beds. So more of the facts favor a hydrothermal origin for these two deposits.
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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