Abstract The giant (>20 Moz) Telfer Au-Cu deposit is located in the Paterson Province of Western Australia and is hosted by complexly deformed marine Neoproterozoic metasedimentary siltstones and quartz arenites. The Telfer district also contains magnetite- and ilmenite-series granitoids dated between ca. 645 and 600 Ma and a world-class W skarn deposit associated with the reduced, ~604 Ma O’Callaghans granite. Based on monazite and xenotime U-Pb geochronology, Telfer is estimated to be older than O’Callaghans, forming between 645 and 620 Ma. Au-Cu mineralization at Telfer is hosted in multistage, bedding-parallel quartz-dolomite-pyrite-chalcopyrite reefs and related discordant veins and stockworks of similar composition that were emplaced into two NW-striking doubly plunging anticlines or domes. Mineralization is late orogenic in timing, with hot (≤460°C), saline (<50 wt % NaCl equiv) ore fluids channeled into preexisting domes along a series of shallow, ENE-verging thrust faults and associated fault-propagated fold corridors. A combination of fault-propagated fold corridors acting as fluid conduits below the apex of the Telfer domes and the rheology and chemical contrast between interbedded siltstone and quartz arenite units within the dome are considered key parameters in the formation of the Telfer deposit. Based on the presence of the reduced Au-Cu-W-Bi-Te-Sn-Co-As assemblage, saline and carbonic, high-temperature hydrothermal fluids in Telfer ore, and widespread ilmenite-series granites locally associated with W skarn mineralization, Telfer is considered to be a distal, intrusion-related gold deposit, the high copper content of which may be explained by the predominance of highly saline, magmatic fluids in gangue assemblages cogenetic with ore.

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 Los Bronces-Río Blanco copper-molybdenum district, located in the late Miocene to early Pliocene magmatic arc of central Chile, has been the focus of exploration and mining activities since the discovery of highgrade copper ore in 1864. From humble beginnings as a source of small tonnages of direct-shipping ore, the district has grown to be one of the world’s premier copper producers, with 2009 production exceeding 448,000 metric tons (t) of copper from open-pit and underground mines owned and operated by Anglo American (Los Bronces) and Codelco (Río Blanco). Anglo American acquired Los Bronces in 2002 as part of its purchase of Compañía Minera Disputada de Las Condes from an Exxon Mobil Corporation affiliate. Near-mine exploration conducted by Anglo American Exploration Division since the acquisition resulted in addition of at least 65 million metric tons (Mt) of copper to the district mineral inventory in two world-class porphyry deposits, Los Sulfatos and San Enrique-Monolito. Exploration activities at Los Sulfatos were undertaken by previous owners of Los Bronces in the late 1960s and early 1990s, but it was not until Anglo American’s third drilling campaign, in 2006 to 2007, that large volumes of high-grade, hypogene porphyry- and breccia-style mineralization with clear economic potential were discovered beneath a previously untested part of the prospect area. Copper-molybdenum mineralization at Los Sulfatos is related to at least two discrete porphyry centers and a large, composite magmatic-hydrothermal breccia complex. The current inferred mineral resource at Los Sulfatos is 1,200 Mt averaging 1.46 percent Cu and 0.02 percent Mo, although the overall potential is envisioned to be 4,000 to 5,000 Mt at 0.8 to 1.0 percent Cu. Location of the deposit in precipitous high Cordilleran terrain, brevity of the summer field season, and rigorous environmental restrictions combined to complicate the exploration, and mandated helicopter support for the program. Key discovery tools at Los Sulfatos are considered to have been high-quality geologic mapping, innovative geologic thinking, and deep diamond drilling. Additional important factors include the early decision to appraise and rank all district prospects prior to commencement of exploration and to assign the program to Anglo American Exploration Division rather than to the Los Bronces mine geology team, thereby ensuring that timely evaluation of Los Sulfatos was conducted by personnel unencumbered with the daily responsibilities of an operating mine.