Porphyry Cu mineralization related to the small Tertiary volcanic intrusions in the Bučim ore deposit, Eastern Macedonia

Abstract

The paper presents data about the geology, geochemistry, structure, genesis and specific features of the Bučim porphyry Cu deposit which is actively mined in Macedonia. The porphyry mineralization (0.3 % Cu, 0.3-0.5 ppm Au) is spatially and temporarily associated with Tertiary subvolcanic intrusions of latitic and latitic-andesitic composition. The intrusions occurred during Oligo-Miocene time (24 to 27 Ma), a period of intensive tectono-magmatic and ore-forming processes.. The latest results of this study identify an array of major ore (hypogen) minerals such chalcopyrite, pyrite, magnetite, haematite, cubanite, valleriite, native Au and bornite and secondary enrichment zone minerals (within Čukar ore body) including chalcocite, covellite, tenorite, native Cu, malachite, azurite etc. Added minerals such as calaverite, krennerite, electrum, petzite and bismuth±selenium minerals (bismuthinite, galenobismutite, krupkaite, friedrichite, emplectite, cosalite, laitakarite and native bismuth) are also present. Variations of the δ34S values for the whole Bučim ore deposit ranged from +0.2 ‰ to +2.5 ‰ while δ13C‰ and δ18O‰ isotope values ranged from -10.8 to -3.8‰ and from +14.0 to +22.7 ‰, respectively. With regard to fluid inclusions, it was confirmed that beside the pre-dominant gas-liquid, two-phase inclusions, there are also three-phase fluid inclusions (gas + liquid + solid phase). Also, recent Sr and Nd isotope ratios (87Sr/86Sr 0.70666-0.70741 and 143Nd/144Nd 0.512487–0.512489) indicate slight contamination of the magmatic products by continental crust material, due to partial melting of the deep parts of continental crust underthrust by collision of continental blocks. The REE data show results that are comparable with high contents of large ion lithophile elements (LILE), high Ba/Nb ratio (116.72-190.72) and depletion in high field strength elements (HFSE) and Europium negative anomaly (0.68893-0.91251).