The Schellgaden mining district, central Austria: A strata-bound Au-W deposit in the central Alps

The Schellgaden gold mining district is located in central Austria, south of
Salzburg, partly both in Salzburg and Carinthia provinces. It is an example of the
scheelite-type of strata-bound deposits classified by Höll and Maucher (1976), as one
of several syngenetic, metalliferous systems in the Eastern Alps that formed in the
early Paleozoic. It was mined principally for gold as early as the fourteenth century
and intermittently after that into the early nineteen hundreds. The district covers an
area of approximately 30 km north-south and 4 km east-west. Many ancient and
recently active gold mines occur throughout the district, but the two most recently
active and largest mines are located in the northernmost part.
The host rocks at Schellgaden are part of the early Paleozoic Penninic basement
rocks exposed in the Tauern Window. The structural setting is much simpler than that
of the overriding Permo-Mesozoic nappes, although there is considerable faulting.
The host rocks are a thousand meter thick sequence of metamorphosed volcanic and
volcanoclastic rocks that are now greenschist, black carbonaceous schist, calcareous
schist, mica schist, gneiss and amphibolite. Gabbro and serpentinite are also present.
The host rocks contain two types of ore deposits. The most common type is stratabound,
sheet-like to lensoid layers of fine to medium grained, granular quartz up to
three meters in thickness. These occur as multiple layers in schistose sequences that
form continuous horizons, formerly termed “Lagers” that are parallel to bedding of
the host rocks. These horizons are 10 to 25 meters thick and continuous along strike
and dip. A less common type of ore is present in the form of discordant quartz veins
that are similar in their mineralogy to the strata-bound quartz layers.
The Schellgaden-type quartz ores contain gold, pyrite, galena, and chalcopyrite
or bornite in bands or layers. Scheelite is present in some ore layers/horizons, but not
in others. Tourmaline may also be present in the quartz, but does not co-exist with
scheelite. Gold is free milling and associated with pyrite and galena. The ore contains
Au, Ag, Pb, Cu and in some ore horizons W. Zinc, As and Sb are low.