Genesis of the Sawusi lead-zinc deposit in the eastern Maizi volcanic-sedimentary basin,southern Altay Mountains

Sawusi lead-zinc sulfide deposit is located in the eastern portion of the Maizi volcanic-sedimentary basin along the southern margin of the Altay Mountains.This study elaborates the geological and geochemical characteristics of the deposit in an attempt to tackle its genesis for the first time.Host rock of the deposit consists of stratiform garnet-biotite and grunerite skarns,meta-rhyolitic crystalloclastic tuff,rhyolite-porphyry and a small amount of impure marble within the upper section of the Early Devonian Kangbutiebao Formation.In brief,the Sawusi deposit bear dual characteristics of both volcanic-exhalative sedimentary deposit and skarn deposit.This study performed geological investigation,petrographic observation and detailed electron microprobe analyses on typical minerals.Our results show that the stratiform skarn of the Sawusi consists mainly of spessartine,almandine,grunerite,biotite,and Fe-Mn-Ca carbonate minerals,and has been formed through mutual infiltrative-metasomatism between tuff and thin,intercalated sedimentary bands of Fe-Mn calcic carbonates.The scale of metasomatism is limited to a few centimeters.Carbon,hydrogen and oxygen isotope compositions show that the ore-forming fluid involves two components of magmatic fluid and surface water.In conclusion,skarns in the Sawusi deposit occur as stratiform,strata-bounded,consist of the Mn-rich mineral assemblage,and have been formed through centimeter-scale mutual infiltrative-metasomatism.These characteristics indicate a volcanic exhalative-sedimentary genesis instead of typical contact metasomatic origin.This study has broad relevance to the massive sulfide deposits along the southern Altay Mountains in both genesis study and ore prospection.