Abstract
The Sambo Pb-Zn-barite mine is composed of fissure-filling quartz-barite veins within Proterozoic biotite schist which are related genetically to Jurassic granitic intrusions. Ore mineralization consists of three distinct stages of quartzbarite veins which were separated by tectonic fracturing and brecciation events. Ore textures of stage II indicate rhythmic deposition, containing five successive mineralization cycles, each with up to seven nearly monomineralic bands. Detailed oxygen isotope studies of stage II rhythmic mineralization reveals patterns both among and within cycles which can be interpreted in terms of two processes: (1) increasing involvement of unexchanged meteoric waters in the ore fluids, resulting in an overall decrease in δ 18Owate, values (from +0.9 to -6.8‰) among cycles; and (2) periodic boiling, resulting in small positive changes in δ 18Owater values within cycles. Hydrogen and oxygen isotope compositions of the Sambo ore fluids may represent mixing of magmatic or highly exchanged meteoric water with less exchanged meteoric water, or exchange of meteoric water with granitic or gneissic rocks at elevated temperatures and moderate to high water/rock atom ratios (0.1 to 0.5). Using either a mixing or exchange model, it is evident that the hydrogen and oxygen isotopic compositions of fluids in the Sambo hydrothermal system were controlled predominantly by local meteoric waters.
