Abstract The Río Blanco-Los Bronces copper-molybdenum porphyry district in the late Miocene to early Pliocene magmatic arc of central Chile is currently being mined by state mining company CODELCO (Río Blanco) and Anglo American Sur (Los Bronces). Combined annual production in 2011 was nearly 450,000 metric tons (t) of copper plus by-product molybdenum. With Anglo American's recent high-grade discoveries in the district (3.7 billion tons (Bt) grading 0.7% Cu at San Enrique-Monolito, and 4.5 Bt grading 0.9% Cu at Los Sulfatos) adding more than 65 Mt of fine copper to the mineral inventory, the district now ranks as the world's largest by contained metal, with more than 200 Mt of copper. Volcanic and volcaniclastic rocks of the Abanico and Farellones Formations represent premineralization host rocks ranging in age between 22.7 ± 0.4 and 16.8 ± 0.3 Ma (U-Pb dating of zircons). The bulk of the copper-molybdenum porphyry endowment is related to evolution of the San Francisco batholith, a large (200 km 2 ) granodiorite-dominated complex with U-Pb zircon ages between 16.4 ± 0.2 to 8.4 ± 0.2 Ma. Three geologic domains are defined in the district on the basis of rock types, structural breaks, and age determinations: the Los Piches-Ortiga block in the west, the San Manuel-El Plomo block in the center, and the Río Blanco-Los Bronces-Los Sulfatos block in the east. These geologic domains are younger progressively to the east, with most of the known copper endowment on the easternmost (Río Blanco-Los Bronces-Los Sulfatos) block. Intrusive and hydrothermal activity in the Los Piches-Ortiga block spanned ∼ 2.5 m.y., from 14.8 ± 0.1 to 12.3 ± 0.1 Ma. Although these events apparently did not produce high-grade copper deposits, silver-bearing veins associated with a high sulfidation hydrothermal system are present in the block. To the east, in the San Manuel-El Plomo block, a series of magmatic-hydrothermal systems developed during a ∼ 3-m.y. period between 10.8 ± 0.1 and 7.7 ± 0.1 Ma. These events also apparently failed to generate high-grade copper systems. Magmatic-hydrothermal activity in the eastern Río Blanco-Los Bronces-Los Sulfatos block, hosting virtually all of the copper endowment recognized in the district, spanned a ∼ 4-m.y. period from 8.2 ± 0.5 to 4.31 ± 0.05 Ma. Copper endowment in the district is associated with vertically continuous breccia bodies and quartz-veinstockworked porphyries. Hydrothermal assemblages follow a characteristic vertical and lateral zonation pattern. Remnants of high sulfidation and/or advanced argillic assemblages (quartz-enargite-tennantite-galenasphalerite-gypsum-anhydrite with dumortierite-pyrophyllite-alunite) and peripheral sericite-illite reflect preservation of shallow levels, whereas K-silicate alteration assemblages (biotite-K-feldspar-albite) are present in association with chalcopyrite-bornite and chalcopyrite-pyrite at depth. Between the mineralized bodies, a distal assemblage of hydrothermal chlorite-epidote-specularite-pyrite predominates. At Río Blanco-Los Bronces, igneous and/or hydrothermal- and hydrothermal-cemented breccias developed in intimate association with porphyry phases. At shallow depths, the hydrothermal breccia cement generally comprises quartz-sericitetourmaline, and contains pyrite > chalcopyrite/molybdenite. At deeper levels the breccia cement is predominantly biotite-K-feldspar containing bornite-chalcopyrite-molybdenite. These progressively grade outward into chalcopyrite-pyrite-dominated zones and ultimately to pyrite-dominated zones. Within the Río Blanco-Los Bronces-Los Sulfatos block, the upper presence of the K-silicate assemblage varies from ∼ 3,000 m above sea level (a.s.l.) in the poorly telescoped northern area (Río Blanco), to ∼ 4,000 m a.s.l in the highly telescoped southern area (Los Sulfatos). These differences may reflect varying rates of synmineral structural exhumation, or varying depth of porphyry emplacement along the Río Blanco-Los Bronces-Los Sulfatos structural corridor. Key factors contributing to the copper productivity in the district are considered to reflect both far-field tectonic conditions, and district-scale structural controls. Following the last significant phase of volcanism documented in the district (∼ 16.8 Ma), a temporally discrete period of peak compression and rapid exhumation, between ∼ 6 to 3 Ma, affected the central Chilean Andes. This period of uplift relates to flat-slab subduction of sea floor containing the Juan Fernandez Ridge into the Chile Trench and overlaps part of the emplacement history of the Río Blanco-Los Bronces-Los Sulfatos block (8.2–4.31 Ma). The lack of contemporaneous volcanism and concomitant tectonic uplift are interpreted to reflect a state of increased horizontal crustal compression due to shear coupling of the downgoing slab. By suppressing volcanism, these conditions are considered to promote the retention of magma in the deep crustal environment, where higher pressures promote greater solubility of magmatic volatiles and higher temperatures may promote longer lived magma chambers by slowing fractionation processes. Under such conditions, the potential is enhanced for increased amounts of metals and volatiles by addition of fresh batches of magma to the deep magma chamber. At the district scale, closely spaced (2 km) structures that control the position of the porphyry and breccia bodies in the Río Blanco-Los Bronces-Los Sulfatos block appear to have focused long-lived, multistage magmatic-hydrothermal activity within a narrow structural corridor, contributing to the development of large, high-grade porphyry/breccia systems.

Coal deposits in the state of Sonora are distributed mainly in two regions. One is the Cabullona region, in the northeast, where the coal is contained in the Cintura Formation of Early Cretaceous age; its physical and chemical characteristics place it in the hypo-bituminous rank. The other region is in La Barranca, east-central Sonora, where the coal is contained in the Santa Clara Formation of Triassic-Jurassic age; there the coal ranks as anthracite. This region has been divided into the San Marcial, San Javier, Santa Clara, and San Enrique areas. The Cabullona region is currently in the regional exploration stage, whereas in the La Barranca region, although there has been previous exploitation, exploration has not been completed. Therefore, the coal potential of Sonora has not yet been fully determined.

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.