Abstract The Bou Azzer mining district in the central part of the Anti-Atlas belt, Morocco, is renowned worldwide for its serpentinized Neoproterozoic ophiolitic complex that hosts peculiar cobalt-dominated and nickel-rich Co–Ni–Fe arsenide and sulfarsenide deposits with significant credits of gold and copper. The Bou Azzer central mine and its satellite deposits, which are spatially associated with serpentinite bodies and tectonically controlled, generally form breccias at the contact between serpentinites and more competent rock types (e.g. diorite) but may also comprise anastomosing vein and tension gashes networks rooted in the serpentinites and breaching into the competent rocks. A consensus on a genetic model for Bou Azzer has not been reached given the most controversial and still highly debated topics dealing with the absolute age of mineralization, and the identification of the source(s) of metals and arsenic. Here, within the geological framework of the Bou Azzer window and the geodynamic history in the Anti-Atlas, we summarize the key features of ore mineralogy, textures, paragenetic sequence and district-scale metal zonation. Using knowledge based on the current state of research – until high-precision and robust geochronological data are produced and permit a refinement of the genetic model – the key parameters for the origin of the Bou Azzer ores are: (1) arsenides of Ni and Co, which are followed by Co–Ni-sulfarsenides and Cu-sulfides, initiating a sequence of mineralization with precipitation controlled by the parameters mentioned in (2)–(4); (2) hydrothermal high salinity fluids (>30 wt% total salt eq.) fostering leaching of Co and Ni from debated source rocks and their transport as highly soluble chloride complexes; (3) dilution and cooling of those fluids from <320 to <200°C; (4) variable redox conditions that would control the progressive oxidation of As from the arsenide stage (As 1− ) to the sulfarsenide stage (As 3+ ); (5) unlike Neoproterozoic metalliferous and As-rich black shales, serpentinites fail to convincingly stand as a robust source of As despite being a reasonable source rock for Ni and Co; (6) the controversial U–Pb and Sm–Nd dates of brannerite and carbonate, respectively, although arguing in favour of an Hercynian timing of mineralization, do not preclude the possibility of a primary Pan-African mineralization (<615 Ma) and/or at c. 540 Ma, followed by remobilization of a pre-existing mineralization during Hercynian events.

Abstract Tenke-Fungurume is one of the world's premier copper deposits with almost 17 billion pounds (7.7 million metric tons, Mt) of contained copper as reserves and mineralized material at a combined average grade exceeding 3 wt % Cu identified by Freeport McMoRan Copper and Gold, Inc. (Freeport). It is also the world's largest known resource of potentially mineable cobalt. Tenke-Fungurume lies within the Central African Copperbelt, which straddles the border between the Democratic Republic of Congo (DRC) and Zambia. The Central African Copperbelt is the largest copper- and cobalt-producing belt in Africa and one of the three most important copper regions in the world. The belt also contains half of the world's cobalt reserves. The Tenke-Fungurume district consists of over 120 separate mineralized tectonic blocks, 30 of which have been drilled by Freeport to resource definition level with mineable reserves defined within 14 of those. Since 2006, Freeport has drilled approximately 350,000 m in over 2,000 diamond drill holes defining recoverable proven and probable reserves of 141 Mt at 3.00% Cu + 0.32% Co (8.4 billion lbs Cu and 860 million lbs Co) with an additional 105 Mt at 3.31% Cu and 0.307% Co as mineralized material adding a further 7.6 billion lbs of contained copper. Production is by open-pit mining and agitated leach processing at a current rate of 281 million lbs copper and 25 million lbs cobalt per year. Tenke-Fungurume is the third largest copper mine in Africa and the largest cobalt mine in the world. All current production and reserves are from oxide ores with oxidation typically extending to depths of 80 to 150 m. Main oxide ore minerals include up to 91% malachite and up to 9% pseudomalachite and libethenite; oxide cobalt is mainly heterogenite. The oxide zone is underlain by a 50- to 200-m-thick zone of mixed ore characterized by pink cobaltoan dolomite, chrysocolla, and chalcocite. Sulfide mineralization below the mixed ore has been drilled to a 1,900-m depth. Sulfide minerals are chalcocite, bornite, carrollite, chalcopyrite, and scant pyrite. The Central African Copperbelt coincides with the Neoproterozoic Lufilian arc, a platform sedimentary sequence of the Katanga Supergroup deposited between 880 and 570 Ma. Extension was followed by the 560 to 500 Ma compressional Lufilian orogeny that folded and thrust the ore-hosting sediments to the northeast. The large majority of the copper-cobalt ores in Tenke-Fungurume are strata bound, hosted in the Mines Series of the Roan Group. The bulk of the ore occurs directly above a regional stratigraphic contact between red, oxidized hematitic beds below, and gray, reduced carbonate beds above. The former are reddish Roches Argileuses Talqueuses (RAT) lilas, the latter are gray algal dolomites of the Mines Series. This major redox boundary underlies copper-cobalt mineralization everywhere in the Central African Copperbelt. Field and petrographic observations indicate that hypogene copper-cobalt mineralization took place in two main phases; an initial diagenetic event formed strata-bound, disseminated to fine laminated copper sulfides, and a second overprinting sulfide event generated crosscutting epigenetic veins related to the Lufilian orogeny. Deep supergene oxidation during the Tertiary formed the oxide orebodies.