Beyond tectonics – controlling mechanisms for ore formation in the Dinarides

The Alpine Wilson cycle in the Dinarides produced a succession of fertile belts, including Permian-Triassic Fe-Ba and Pb-Zn-Ba systems, Jurassic oceanic Cr-VMS mineralization, Late Cretaceous porphyry Cu-Au deposits, and Cenozoic Pb-Zn-Ag belt (Palinkaš et al., 2009). Individual belts contain hundreds of millions of tonnes of ore, for example up to 500 Mt in the Ljubija Fe district, 172 Mt in the Vareš Fe-Pb-Zn-Cu-Ag-Au district, 23.9 Mt of chromite ore in the Mirdita ophiolite, and at least 40 Mt Cu and 1,570 t Au within Late Cretaceous Banatite-Timok-Srednogorie belt. Their formation required very different scales of mass transfer, from approximately 1,800-2,230 km³ of basinal brines in Ljubija, through 40,000-60,000 km³ of hydrothermal fluids in Vareš, to 100-300 km³ of boninitic melts in Mirdita and >1,000 km³ of fertile arc magmas in the Banatite-Timok-Srednogorie belt. Most of these metallogenic events developed within only a few million years, and all are directly linked with large scale regional tectonics.

In contrast, the Sava Suture Zone represents one of the least productive segments of the Alpine Wilson cycle in Dinarides. Initially interpreted as a Late Cretaceous remnant-ocean/back-arc system (Schmidt et al., 2020), it occupied approximately 15% of the surface area of the Dinaridic Neotethys and remained tectonically active for about 50 My, almost a quarter the lifespan of the Dinaridic ocean. Its geodynamic setting should allow elevated heat flow and existence of SEDEX-VMS, porphyry and epithermal mineralization. Instead, magmatism is sparse, economically significant ore deposits (as well as non-economical) are absent, and evidence for fluid flow is lacking. Plausible explanation is that no true ocean existed after the Jurassic obduction, but rather an oblique subduction creating scarce bimodal magma intrusions as initially proposed by Spahić and Gaudenyi (2022).

The new cycle in Dinarides begin within the barren Sava Suture Zone, where Early-Middle Miocene post-collisional extension generated the Western Balkan Li-B metallogenic belt. The new metallogenic belt is estimated to contain at least 3.2 Mt Li and 20 Mt B (Borojević Šoštarić and Brenko, 2023). Current genetic models relate syngenetic Li-B mineralization to fault-controlled extensional lacustrine basins, arid climate and high heat and fluid flow related to exhumation of metamorphic core complexes.

It all begins with tectonics, but individual metallogenic belts will develop only where favourable tectonic structures are joined with heat and fluid flow, metal sources and geochemical barrier.

 

Borojević Šoštarić, S. & Brenko, T. (2023). The Miocene Western Balkan lithium-boron metallogenic zone. Mineralium Deposita, 58, 639-658.

Palinkaš, L.A., Borojević Šoštarić, S. & Palinkaš, S.S. (2008). Metallogeny of the Northwestern and Central Dinarides and Southern Tisia. Ore Geology Reviews, 34, 501-520.

Schmid, S.M., Fügenschuh, B., Kounov, A., Matenco, L., Nievergelt, P., Oberhänsli, R., Pleuger, J., Schefer, S., Schuster, R., Tomljenović, B., Ustaszewski, K. & van Hinsbergen, D.J.J. (2020). Tectonic units of the Alpine collision zone between Eastern Alps and western Turkey. Gondwana Research, 78, 308-374.

Spahić, D. & Gaudenyi, T. (2022). On the Sava Suture Zone: Post-Neotethyan oblique subduction and the origin of the Late Cretaceous mini-magma pools. Cretaceous Research, 131, 105062.