Περίληψη:
Boiling is a crucial process triggering ore formation in
magmatic-hydrothermal systems and controlling the enrichment of precious
and rare metal(loid)s in epithermal-porphyry mineralizations. Steep
physicochemical gradients during boiling of hydrothermal fluids at
shallow water depths caused metal(loid) precipitation along a 3 km long
Pb-Zn-Ag vein system on Milos Island in the South Aegean Volcanic Arc.
We present new trace element and Pb, Sr, and S isotope data from
sulfides providing insights into the diversity of mineralization
processes in shallow-marine hydrothermal systems. Lead and Sr isotope
compositions of sulfides and sulfates reflect the mixing of fluids that
reacted with metamorphic basement and the volcanic host rocks, whereas
some of the S were derived from seawater. Investigation of mineralized
samples along the Kondaros-Vani fault zone revealed distinct chemical
variations that represent a vertical profile through the boiling zone of
a hydrothermal system. Boiling during fluid ascent at decreasing
temperatures (230-150 degrees C) and sulfur fugacities triggered the
precipitation of sulfides rich in Zn, Pb, Fe, Cu, Ag, Sb, and As,
resulting in increasing Pb, Ag, and Sb contents with decreasing depth. A
pyrite group with high Tl/Cu and low As/Sb ratios, as well as delta
S-3(4)VCDT values reaching as low as -6 parts per thousand, is
interpreted as precipitating from high-Cl liquids that underwent
vigorous boiling at deeper crustal levels subsequent to tectonic
faulting. Condensation of vapor (high Hg, Bi, and As contents) and
mixing with seawater (high Mo contents) in the shallow-marine
subseafloor sequences at Vani caused Hg-Bi-Mo-As-rich mineralization
similar to the active hydrothermal system at Milos.
Συγγραφείς:
Schaarschmidt, Anna
Haase, Karsten M.
Klemd, Reiner
Keith,
Manuel
Voudouris, Panagiotis C.
Alfieris, Dimitrios
Strauss,
Harald
Wiedenbeck, Michael
