Oxygen and carbon isotope mapping of hydrothermally altered wall rocks was applied to the blind ore prospecting of skam
Pb-Zn deposits in the Kamioka mining district, central Japan, where the wall rocks consist of heterogeneous rock units.
The results (8180sMow of -1.1 to +17.3%o and 613CPDB of -5.0 to +4.8%o for limestones, and 8180SMOW of -0.8 to +12.5%c
for silicate rocks) show isotope zonations of the wall rocks with depletions in heavy isotopes (180 and 13C) toward the
center of mineralization. The isotope zonations likely formed by interaction of migrating thermal waters with the wall
rocks during the mineralization. The heavy-isotope depleted zone, which indicates higher temperature or higher water-to- rock ratio of the system, occurs in the footwall of a fault, indicating that the fault played the role of main conduit of the
ore-forming fluids. A heavy-isotope depleted zone was also found in an area, where significant mineralization had yet to
be identified. Recent drilling in this area has intercepted a zone with a grade of 16.0% Zn, 0.8% Pb, and 35g Ag per metric
tonne at a depth of about 360m.