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Numerous Pb-Zn deposits formed during the Proterozoic, in contrast with the situation in the Archean. The largest examples, which are reviewed here, are McArthur, Mount Isa-Hilton, Sullivan, Gamsberg, and Broken Hill.

These huge stratiform deposits occur well above the bases of thick, predominantly sedimentary sequences which accumulated in major ensialic troughs. The sequences are dominated by carbonates or clastics, but the mineralization is localized within distinctive chemo-clastic facies which were deposited in basins of restricted extent. There is commonly evidence for synsedimentary faulting and for distal igneous activity. Biogenic sulfide was probably incorporated into some of the pyrite but is unlikely to have precipitated the bulk of the Pb and Zn. The base metals are of crustal derivation; they could have been supplied by ascending basinal brines and/or hydrothermal fluids migrating from distant centres of igneous activity.

There is active debate, focussed on the relatively pristine McArthur deposit, as to whether the mineralization formed at or beneath the sediment-water interface. It is maintained here that all features are consistent with syngenetic accumulation of the great bulk of the sphalerite, galena, and some of the pyrite, complemented by growth of biogenic pyrite and other diagenetic minerals within the sulfidic muds.

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