E. E. Zakharov, 1967. "Genesis of the Lead-Zinc Mineralization of a Telethermal Type in the Southern Kazakhstan", Genesis of Stratiform Lead-Zinc-Barite-Fluorite Deposits (Mississippi Valley Type Deposits), J.S. Brown
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A hydrothermal genesis of the lead-zinc mineralization in carbonate rocks of Southern Kazakhstan is indicated. Its epigenetic nature is confirmed by its restriction to tectonic zones of northwest, northeast or submeridional strike rupturing carbonate rocks of the Middle and Upper Paleozoic and conjugate with the large ancient regional fault that later was renewed repeatedly.
Lead-zinc mineralization is localized in the carbonate rocks of the Famena and the Lower Turne but. even in the neighboring ore-bearing areas, is confined to certain stratigraphic horizons. More than fifty percent of all ore is in dolomites, twenty percent in alternate dolomite and limestone, interbedded, about thirty percent in limestones. Mineralization is practically absent in marls, argillites and terrigenous rocks. The common occurrence of mineralization in dolomites made up of fine, tightly packed oolites and pseudo-oolites is explained by their physical and mechanical properties which led to the formation of many fissures that later were filled with veinlets of galena and sphalerite.
Mineralization is represented mainly by:
1. Predominant galena with some sphalerite as streaky impregnated ores forming sheet-like deposits in heavily crumpled Famennian ribbon dolomites. Minor amounts of pyrite and copper and silver sulfides are present.
2. Galena-sphalerite-pyrite in massive form as subvertical lenses and cross veins in gently pitching Turne dolomites. The pyrite (60%-90%) is cut by veinlets of galena and sphalerite. Other sulfides are rare.
Upper Paleozoic intrusives have not been discovered near the lead-zinc ores but are present some 100 km to the northwest and about 200 km to southeast.
The following processes of hydrothermal alteration are widespread: propylitization of Permian alkaline rocks in the southeast; then marmorization and skarn alteration of carbonate rocks in the zones of direct contact between the Upper Paleozoic and intrusives; then, at some distance, silicification. barytization and sideritization localized in tectonic zones and fissures. Silicification, barytization and fluoritization have been traced along these fissures to the region of lead-zinc mineralization thus establishing a close genetic relationship.
Large samples from these intrusives contain up to 14 g of galena per ton. Galena also occurs in the skarns as well as in the quartz-barite veins at some distance from the ore-bearing areas.
Considering all the data it is possible to classify this lead-zinc mineralization as telethermal.
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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