Abstract The Cadia district of New South Wales contains four alkalic porphyry Au-Cu deposits (Cadia East, Ridgeway, Cadia Hill, and Cadia Quarry) and two Cu-Au-Fe skarn prospects (Big Cadia and Little Cadia), with a total of ~50 Moz Au and ~9.5 Mt Cu (reserves, resources, and past production). The ore deposits are hosted by volcaniclastic rocks of the Weemalla Formation and Forest Reefs Volcanics, which were deposited in a submarine basin on the flanks of the Macquarie Arc during the Middle to Late Ordovician. Alkalic magmatism occurred during the Benambran orogeny in the Late Ordovician to early Silurian, resulting in the emplacement of monzonite intrusive complexes and the formation of porphyry Au-Cu mineralization. Ridgeway formed synchronous with the first compressive peak of deformation and is characterized by an intrusion-centered quartz-magnetite-bornite-chalcopyrite-Au vein stockwork associated with calc-potassic alteration localized around the apex of the pencil-like Ridgeway intrusive complex. The volcanic-hosted giant Cadia East deposit and the intrusion-hosted Cadia Hill and Cadia Quarry deposits formed during a period of relaxation after the first compressive peak of the Benambran orogeny and are characterized by sheeted quartz-sulfide-carbonate vein arrays associated with subtle potassic, calc-potassic, and propylitic alteration halos.

Abstract The Reko Diq porphyry cluster in the western Chagai magmatic belt, Pakistan, contains a geologic resource of 5.9 billion tons (5.35 Bt) @ O.41% Cu and O.22 g/t Au, largely in the H14 and H15 porphyry deposits. These two deposits, located approximately 1 km apart, are related to a series of petrologically similar, middle Miocene (12.6–12.O Ma), calc-alkaline porphyry intrusions hosted by Oligocene andesitic volcanic and clastic sedimentary rocks. The porphyry intrusions are characterized by phenocrysts of plagioclase, biotite, quartz, and amphibole in a microcrystalline mafic silicate-bearing quartzofeldspathic groundmass. Potassic, sericite-chlorite, sericitic, and propylitic alteration assemblages are zoned about the porphyry intrusions. The early and intermineral porphyry intrusions are overprinted by a pervasive potassic alteration assemblage composed of hydrothermal biotite-K-feldspar-magnetite ± anhydrite with associated chalcopyrite and bornite. Chalcopyrite, bornite, and lesser pyrite are disseminated or are associated with a stockwork of quartz ± magnetite ± K-feldspar A- and B-type and less common sulfide-only veins. Bornite characterizes a distinct high-grade core to the H14 deposit, but it is less common and always subsidiary in volume to chalcopyrite in the slightly older H15 deposit. Local sulfide mineral assemblages of pyrite-covellite-bornite-chalcopyrite associated with pervasive quartz-sericite alteration assemblages in the H15 deposit form narrow, steeply dipping vein-like zones or strata-bound horizons restricted to felsic tuff or sandstone. The late porphyry intrusions are weakly altered and mineralized, lack volumetrically significant veins, and generally have low Cu and Au concentrations. Sulfide-deficient potassic alteration assemblages at greater than 1,OOO m depth are overprinted by a texturally destructive alteration assemblage of albite-epidote ± actinolite ± chlorite, inferred to represent a sodic-calcic alteration assemblage. Total sulfide contents at these depths are less than 1%. At shallow depths, a sericite-chlorite alteration assemblage overprints potassic alteration mainly along late-stage centimeter-scale chalcopy-rite-pyrite D-type veins. The sericite-chlorite assemblage is much more extensive in the H15 deposit than in the H14 deposit. An outer sericitic alteration assemblage composed of quartz-muscovite-pyrite ± chalcopyrite flanks the sericite-chlorite assemblage. An intermediate argillic alteration assemblage composed of clay minerals (illite, smectite, montmorillonite) and carbonate is common in remnants of plagioclase within the sericite-chlorite and sericitic alteration assemblages. A propylitic alteration assemblage of chlorite-epidote-albite ± pyrite-carbonate is developed in the peripheral volcanic and sedimentary host rocks surrounding the H14-H15 porphyry complex.