Geochemical characteristics of the Damjan iron skarn deposit, Republic of Macedonia

Abstract

Rudno ležište Damjan smješteno je 20 km južno od grada Štipa, Republika Makedonija. Pripada rudnom području Bučim-Damjan-Borov Dol smještenom u Lece- Halkidika metalogenetskoj zoni, na granici Srpsko-makedonske mase i Vardarske zone. Geneza rudnog ležišta vezana je uz prodore oligocenskih andezita u paleogensku flišnu sekvencu. Na kontaktima andezitnih tijela s vapnenačkim članovima sekvence formirani su kalcijski egzoskarnovi, a u hidrotermalnoj fazi odlagana je Fe-ruda. Formiranje skarnskih minerala i odlaganje Fe-rude vršeno je u fazama karakterističnim za postanak skarnskih ležišta. Tijekom izokemijskog metamorfizma rekristalizirane su vapnenačke sedimentne stijene. U progradnoj fazi formirani su tipični skarnski minerali: hedenbergit, andradit i grossular. Retrogradnom alteracijom progradni su minerali hidrotermalno izmijenjeni u smjesu klorita, epidota, karbonata i kvarca. Tijekom ove faze odlagana i Fe-ruda u vidu magnetita i hematita. Iako se magnetit i hematit u ukupnom sastavu ležištu javljaju u omjeru 1:1, magnetit dominira u dubljim dijelovima ležišta te bliže kontaktima s andezitnim tijelima sugerirajući njegov nastanak na višim temperaturama te nižem fugacitetu kisika. Hematit dominira u plićim dijelovima ležišta, ukazujući na pad temperature i/ili porast fugaciteta kisika. U postrudnoj fazi formirane su manje količine karbonata i kvarca.The Damjan ore deposit is situated approximately 20 km south from the town of Štip, Republic of Macedonia. It belongs to the Bučim-Damjan-Borov Dol ore district within the Lece- Chalkidiki metallogenic zone. The mineralization occurs within the Vardar zone, near its contact with the Serbo-Macedonian Massif. The genesis of the deposit, related to the penetration of the Oligocene andesite in the Paleogene flysch sequence, comprises distinctive stages typical for skarn deposits. The stage of the isochemical metamorphism resulted with the limestone recrystallization. The Ca-exoskarn occurs at the contact of andesitic bodies and limestone members of the flysch sequence. The principal prograde minerals include hedenbergite, andradite and grossular. During the retrograde stage prograde skarn minerals were hydrothermally altered into a mixture of chlorites, epidote, carbonates and quartz. The ore mineralization represented by magnetite and hematite was deposited during the retrograde stage as well. Although the bulk magnetite/hematite ratio is about 1:1, magnetite predominates in the deeper part of the deposit and near contacts with andesite bodies, suggesting its formation at a higher temperature and under a lower oxygen fugacity. In contrast, hematite prevails in the shallow portion of the deposit, indicating its deposition at the lower temperature and/or under the higher oxygen fugacity. The postore stage is characterized by the deposition of minor amounts of carbonates and quartz