Upper Cretaceous Magmatic Series and Associated Mineralisation in the Carpathian – Balkan Orogen

Abstract: The Alpine Orogen contains in South East Europe, from the Carpathians to the Balkans–Srednogorie, an Upper Cretaceous, ore bearing igneous belt: a narrow elongated body which runs discontinously from the Apuseni Mountains in the North, to the western part of the South Carpathians (Banat) in Romania, and further South to the Carpathians of East Serbia and still further East to Srednogorie (Bulgaria). This results in a belt of 750 km/30–70 km, bending from N‐S in Romania and Serbia, to E‐W in Bulgaria. Using the well established century‐old terminology of this region, we describe it in this paper as the Banatitic Magmatic and Metallogenetic Belt (BMMB). Plate tectonics models of the Alpine evolution of South East Europe involve Mesozoic rifting, spreading and thinning of the continental crust or formation of oceanic crust in the Tethian trench system, followed by Cretaceous‐Tertiary convergence of Africa with Europe and opening of Eastern Mediterranean and Black Sea troughs. The result of successive stages in the collision process is not only the continental growth of Europe from N to S by the docking of several microplates formerly separated from it by Mesozoic palaeo–oceans, but also the rise of mountain belts by overthickening of the crust, followed by orogenic collapse, lateral extrusion, exhumation of metamorphic core complexes and post‐collisional magmatism connected to strike‐slip or normal faulting. The BMMB of the Carpathian‐Balkan fold belt is rich in ore deposits related to plutons and/or volcano‐plutonic complexes. Serbian authors have proposed an Upper Cretaceous Paleorift in Eastern Serbia for the Timok zone and some Bulgarian geologists have furnished geologic, petrological and metallogenetic support for this extensional model along the entire BMMB. The existence and importance of previous westwards directed subductions of Transilvanides (=South Apuseni = Mureş Zone) and Severin‐Krajina palaeo–oceans, popular in Roman ian literature, seems to have little relevance to BMMB generation, but the well documented northwards directed subduction of the Vardar‐Axios palaeo–ocean during Jurassic and Lower Cretaceous is a good pre‐condition for the generation, during the Upper Cretaceous, of banatitic magmas in extensional regime, by mantle delamination due to slab break–off. Four magmatic trends are found: a tholeiitic trend, a calc‐alkaline trend, a calc‐alkaline high–K to shoshonitic trend and, restricted to East Srednogorie, a peralkaline trend. For acid intrusives, the typology is clearly I‐type and magnetite–series, pointing to sources in the deep crust or the mantle; however, some high 87 Sr/ 86 Sr ratios recorded in banatites prove important contamination from the upper crust. The calc‐alkaline hydrated magmas, most common for banatitic plutons, can be considered as recording three stages of evolution: more primitive – the monzodioritic, dioritic to granodioritic trend (S Apuseni, S Ba–nat, Timok, C and W Srednogorie); more evolved – the granodioritic‐granitic trend (N Apuseni, N Banat, Ridanj–Krepoljin); the alkaline trend (E and W Srednogorie, western part of N Banat). Correlating the composition of the host plutons with the types of mineralisation, several environments can be found in the BMMB, function of timing of fluid separation (porphyry versus non‐porphyry environments), depth of emplacement, size of intrusion and geology of intruded rock pile, biotite versus hornblende crystallisation, involving the evolution of K/Na ratio in fluids, i. e. development of potassic and phyllic alteration zones: a) non‐porphyry environment with granodioritic to granitic magmas, plutonic level, skarn mineralisation prevails; b) porphyry environment with monzodioritic or dioritic to granodioritic magmas, subvolcanic–hypabyssal–plutonic level; porphyry Cu with skarn halo at hypabyssal‐subvolcanic level; c) porphyry environment with monzodioritic or dioritic to granodioritic magmas, volcano‐plutonic complexes with porphyry copper plus massive sulfide mineralisation at subvolcanic‐volcanic level; d) non‐porphyry environment with magmas of alkaline tendency, volcanic level, vein (“mesothermal” and “epithermal”) mineralisation.