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Abstract

In the Central Asian copper province seven copper belts each host at least one large (>5 million metric tons (Mt)) Cu deposit or deposit cluster; three other copper belts each host at least one medium-size (∼4 Mt) Cu deposit, with copper resources likely to increase during ongoing exploration. Of these, eight copper belts host porphyry deposits, including four giant (>10 Mt Cu) porphyries (Oyu Tolgoi, Almalyk, Aktogai, and Erdenet); one belt contains sediment-hosted deposits (including giant Dzhezkazgan); and one belt hosts volcanogenic massive sulfide (VMS) deposits.

The deposits formed in seven periods between 510 and 240 Ma, with ∼30- to 50-m.y. intervals between porphyry emplacements occurring mostly between the major tectonic events, whereas formation of the sediment-hosted deposits was coeval with the major collisional tectonic event in the Tien Shan and Urals at 290 Ma. The greatest metal endowment and largest number of individual deposits fall into the period 320 to 340 Ma (Almalyk, Aktogai), followed by the second most important period at 385 to 370 Ma (Oyu Tolgoi and Magnitogorsk), and third most important event at 295 Ma (Dzhezkazgan).

Individual copper belts are typically several hundreds of kilometers long, dominated by a single deposit type, and commonly have only one large to giant deposit in a belt (this may partially be a function of preservation but also of exploration maturity). Most copper belts were generated under transpressional tectonic regimes in either arc or backarc settings. Local structural controls include terrane boundaries and crustal-scale arc-oblique or arc-parallel faults.

The immature arc terranes generally host deposits with 3- to 5-Mt Cu endowments in porphyry or VMS deposits. Deposits with giant, >10-Mt Cu endowments were discovered in regions of tectonic overlap; giant porphyry deposits occur in mature, overlapping magmatic arcs, and sediment-hosted deposits are present in 3- to 6-km-thick, overlapping sedimentary basins.

Plate tectonic reconstructions suggest a strong correlation of higher grade (>0.6 wt % Cu) porphyry copper deposits with peri-oceanic magmatic arcs, whereas lower grade (0.35–0.5 wt % Cu) porphyry deposits occur in magmatic arcs that formed in relationship to subduction in backarc oceanic basins. Based on distance to the respective ophiolitic sutures, which indicate the traces of the former subduction zones, we have estimated the approximate dip of the paleosubduction zone. We propose a correlation between a low (∼30°) angle dip of the reconstructed subduction zone and the larger copper endowment of related porphyry deposits.

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