Super Porphyry Copper & Gold Deposits - A Global Perspective

The approximately 1000 Mt @ 0.6% Cu, 0.3-0.4 g/t Au Majdanpek porphyry copper is the most northerly deposit within the Timok Magmatic Complex (TMC) which also hosts the exploited Bor and producing Veliki Krivelj deposits. Slightly older, but similar magmatic rocks southeast of the region host the significant porphyry-high sulphidation mineralisation at Elatsite and Chelopech in neighbouring Bulgaria. Similar porphyry deposits are also known in Romania, across the Danube river to the north of Majdanpek. The TMC igneous rocks show clear evidence of crustal contamination and thus likely relate to an eastward dipping subduction zone beneath a continental margin located to the west. Mineralisation is related to sparse and narrow north-south trending andesitic dykes dated at 83 Ma. These dykes intrude along a north-south trending fracture zone cutting Proterozoic and Palaeozoic metamorphic rocks, and Jurassic limestones. Extrusive facies of the TMC are rare at Majdanpek, although they are common farther to the south of the region. Mineralisation is typicaly developed as stockworks, the bulk of which are actually within the metamorphic aureole of the andesitic dykes. There are also numerous skarns and replacement bodies flanking the intrusives, while more distal replacement bodies are found in the Jurassic limestones. The highest copper grades relate to K-silicate alteration and zones of strong silicification. Mo grades are very low throughout the deposit, while the Cu%:Au g/t ratio is approximately 2:1. PGEs occur as minor phases accompanying the copper mineralisation and are recovered at the smelter. Significant supergene upgrading is recorded in an oxidation blanket that was 25 m thick in the north and covered the deposit.