alteration and petrology of intrusive rocks associated with gold mineralization at kuh-e-zar gold deposit, torbat-e-heydaryeh

kuh- e -zar gold deposit located 35 km west of torbat-e-heydaryeh, (khorassan e- razavi province), east of iran. this deposit is a specularite-rich iron oxide type (iocg). this mine is situated within khaf-bardascan volcanic plutonic belt. based on recent exploration along this belt, several iocg type system plus kuh-e-zar deposit are discovered. in the study area, several type of tuff and lava having acid to intermediate composition are identified (upper eocene). oligo-miocene granite, granodiorite, synogranite and monzonite intruded upper eocene andesite-dacite-rhyolite. intrusive rocks are meta-aluminous, medium to high-k series i-type. based on spider diagram, intrusive rocks show enrichment in lile = k, th, rb and depletion in hfse = nb, sr, ti. based geochemistry of igneous rock, they formed in continental margin subduction zone. propylitic (chlorite) alteration is dominated and covers large area. silicification is restricted only to mineralized zones. argillic and albitization is found in certain location and cover small areas. the style of mineralization was controlled by the type and geometry of fault zones. mineralization is found as vein, stockwork and breccias. hypogene mineral paragenesis include: specularite-quartz-gold-chlorite ± chalcopyrite ± pyrite ± galena ± barite. secondary minerals formed due to oxidation are: goethite, limonite, lepidocrucite, malachite, azurite, covelite, cerucite, hydrocerucite, pyrolusite and smitsonite. in a few localities, chalcopyrite and minor pyrite and galena are found. based on sem analysis gold is present as electrum. mineralization appeared in different type such as vein, stockwork and hydrothermal breccia in strike sleep fault zone which are hidden inside volcano plutonic rocks. the average gold grade is between 3.02 ppm and ore reserve is estimated more than 3 million tons (cut off grade = 0.7 ppm).