Cement-Stratigraphy of Upper Wetterstein Limestone (Triassic, Austria): Clue to Timing of Lead-Zinc Mineralization

Stefan Zeeh, Bernhard Maul, Thilo Bechstadt, Judith A. McKenzie, Peter J. Kindle

Inner parts of the Triassic Wetterstein carbonate platforms of the eastern Alps contain Lofer-type cyclic sediments. Most of the Alpine lead-zinc ores are situated in this type of facies. According to many workers, these mineralizations of the "Bleiberg" type are synsedimentary to early diagenetic and differ from Mississippi Valley lead-zinc deposits.

Diagenetic evolution of the host rocks, unknown so far, is as follows: (1) early cements such as dripstone cement, mamillary crusts, botryoidal aragonite, (2) radiaxial fibrous calcite, (3) dogtooth calcite, (4) epigenetic dolomite crystals and dolomitization, (5) saddle dolomite I, (6) dedolomitization of parts of the rock, blocky calcite I with distinct zonations, (7) saddle dolomite II, and (8) blocky calcite II.

Internal sediments occur from very early to late stages of diagenesis. With progressive burial and temperature increase, oxygen isotopes become strongly negative. First results of fluid inclusion studies of late diagenetic stages reveal homogenization temperatures (T_h) between 90° and 250°C (stages 7 and 8).

According to our data, ore mineralization started after the change to an overall reducing pore-water environment--that is, after the precipitation of dogtooth cements--and continued until stage 7 (saddle dolomite II). Ore mineralization took place during shallow to deep burial conditions. The Alpine lead-zinc ore deposits therefore belong to the normal Mississippi Valley type.

AAPG Search and Discovery Article #91022©1989 AAPG Annual Convention, April 23-26, 1989, San Antonio, Texas.