Abstract

Major Au and Cu deposits in the Western Tethyan magmatic belt formed during two main periods of Cretaceous and Cenozoic magmatism. The Cretaceous deposits are dominantly Cu-Au porphyry, high-sulfidation epithermal, and volcanic massive sulfide deposits, whereas in the Cenozoic Cu is significant only in porphyry systems. However, the Cenozoic contains approximately three times greater total Au endowment (for Au deposits >0.5 million ounces), and also has a greater deposit diversity, including porphyry Au-Cu and Au-only deposits, high-, intermediate-, and low-sulfidation epithermal Au systems, and Au-rich carbonate replacement and sediment-hosted styles. The differences in endowment and deposit styles likely reflect regional-scale tectono-magmatic processes as well as local preservation and emplacement levels. The Cu ± Au endowment of the Cretaceous is consistent with typical subduction-related arc environments and generation of calc-alkaline porphyry to high-sulfidation epithermal systems, whereas Au enrichment related to Cenozoic magmatism appears to be related to high-K calc-alkalic to shoshonitic compositions. In many of the Au-rich Cenozoic magmatic belts, there is geochemical evidence for sourcing subcontinental lithospheric mantle that was previously enriched by Cretaceous subduction-related metasomatism. Additional differences in Au endowment may reflect the preservation of shallow-level systems in the Cenozoic, particularly for the Au-rich Miocene porphyry deposits such as Kışladağ and Bierly Vrch and the Apuseni porphyry Au-Cu deposits. However, in both the Cretaceous and Cenozoic, crustal exposure levels vary across the belt and cannot explain all the differences in Cu and Au endowment.

A compilation of exploration discovery methods highlights the importance of historic workings in addition to geochemistry and geology as an initial vector, whereas geophysics has had limited involvement in direct discovery, primarily due to its limited application historically. Geologic models for well-understood systems such as porphyry and proximal epithermal systems provide excellent guides for explorers; however, more distal deposits such as Au-rich carbonate replacement deposits and deposits with poorly constrained models such as sedimentary rock-hosted and intermediate-sulfidation deposits are more challenging for exploration.

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