PRODUCTIVITY OF VOLCANIC-HOSTED MASSIVE SULFIDE DISTRICTS - NEW CONSTRAINTS FROM THE DELTA-O-18 OF QUARTZ PHENOCRYSTS IN COGENETIC FELSIC ROCKS

A correlation has been established between Zn productivity of volcanic -hosted massive sulfide districts and delta(18)O of quartz phenocrysts from cogenetic rhyolitic rocks, In highly productive districts, ores are associated with rhyolitic rocks, of possible S-type affinity, cont aining high delta(18)O quartz phenocrysts, In less-productive district s, ores are associated with I-type rhyolitic rocks,vith low delta(18)O phenocrysts, This correlation may be caused by (1) low-temperature is otopic alteration that produced O-18-rich overgrowths on phenocrysts, and (2) emplacement of transitional S-type intrusions at greater depth s than I-type intrusions, resulting in larger hydrothermal cells and a llowing leaching of more Zn. The latter hypothesis is favored.