The sulfur isotope composition of sulfide ore minerals of the Drau Range
varies considerably, down to centimeter-scale variations, both on a
regional and a local scale. Broadly scattering delta(34)S values,
ranging between +2 and -25 per mil with a mean around -17 per mil. are
probably related to both local bacteriogenic and thermal reduction of
Late Triassic marine sulfate. The S-34 is typically more depleted in ore
deposited in subtidal carbonate rocks than in the economic Zn and Pb
ore, preferably deposited within intratidal carbonate host rock, The
S-34/S-32 ratio increases on the order of FeS2 < PbS < Zn, which
reflects disequilibrium and low-temperature formation. The strong
depletion of S-34 in botryoidal sphalerite, ranging between -24 and -32
per mil, appears to be correlated with the crystal mode
(wurtzite-sphalerite fibers) and the enrichment of the trace elements
Fe, As, Tl, and Ge, Sphalerite generations of specific
cathodoluminescense, color, and closely related trace element
composition are correlated district-wide. A decrease of the trace
elements Fe, As, Tl, and Ge in the sphalerite generations is coeval with
a minor depletion of S-34 in the range of -3 and -12 per mil for
delta(34)S values in several hand specimens, Variations in delta(34)S
values and trace element zonation on a regional to local scale indicates
mixing of local sulfur sources with a regional metal-rich brine,
However, distinct peaks in some ore deposits and more positive
delta(34)S values of between -5 and -10 per mil are also compatible with
derivation of the sulfur from basement rocks. The enrichment of the
trace element Cu in orange-luminescing sphalerite negatively correlated
with Fe, As, Tl, and Ge and, therefore, strongly suggests leaching of
copper from Late Permian to Early Triassic continental red beds.
Frequent evaporites in this stratigraphic section might have supplied
sulfur of relatively heavy isotopic composition to the brine. Hence,
some sulfur may also have been transported with a metal-rich brine.