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Abstract

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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