Darhand copper occurrence:An example of Michigan-type native copper deposits in central Iran

Abstract

The Darhand copper occurrence consists of disseminated. veinlet and pocket-shaped native copper mineralization in Late to Mid-Ecocene basalt located 200 km south of Tehran, in the middle of the Orumieh-Dokhtar metallogenic belt, in central Iran. The submarine amygdalo idal spilitic basalt, which hosts the mineralization has undergone a propylitic alteration (chloritic, epidotic) as well as a low-grade metamorphism resulting in zeolites and prehnite-pumpellyite-quartz. The pockets, veinlets and amygdales of prehnite, epidote, chlorite and laumonite (zeolite), which fill the open spaces of basalt, ost most of the copper mineralization. The Cu mineralization in veinlets, pockets and amygdales is composed of cuprite > native copper_> malachite_> tenorite_> chrysocolla. The round and ellipsoidal grains of native copper and cuprite range up to 2cm in size. With the exception of rare scattered pyrite grains, in the host rock, no sulfide minerals were observed in the mineralization. The Cu content of the ore reaches 3.5% with rather high values of silver (6 ppm). Also the copper concentration in the submarine basalt is anomalously high with 250 ppm. The mineralization is bound to a definite basalt layer underlying the Oligo-Miocene limestone.