Abstract The majority of Mexico’s carbonate replacement deposits were discovered in outcrop over 100 years ago and most were oxidized to significant depths. Oxidized mantos and chimneys were diligently exploited as continuous compact bodies of silver-rich cerussite and anglesite, while ignoring then-valueless underlying or surrounding irregular, high-grade (>20% Zn) bodies of mixed Fe-Mn-Zn oxides, smithsonite, hemimorphite, willemite, and hydozincite. Recent development of effective solvent-extraction metallurgy to recover zinc from zinc oxide minerals has renewed interest in these bypassed bodies, but in most cases little was recorded of their tonnage, grade, or morphology. However, an understanding of original sulfide orebody limits, composition, morphology, and leaching processes can provide a first-order indicator of the potential zinc content and mineability of a given deposit prior to mounting a full-scale exploration effort.

The low-temperature epigenetic and stratabound Pb-Zn-Cu-Ba-F-Sr–bearing ore deposits enclosed within sedimentary columns historically have been major sources of metals. Exploration companies still find these deposits to be a profitable exploration target due to their simple mineralogy as well as the large tonnage that can present, always considering the mineral districts as a whole. In northeastern México, several nonmagmatic, low-temperature Pb-Zn-F-Ba deposits have been systematically considered as magmatic-related (skarns, high-temperature replacement deposits, epithermal deposits, etc.). Recently, these deposits have been restudied and placed within a scenario of deep fluid circulation of basinal brines through the Mesozoic sedimentary series, enriched in Ba, F, and metals during fluid flow and water-rock interactions. These fluids gave rise to a series of strata-bound epigenetic ore deposits scattered throughout the whole Mesozoic carbonate platform and can be shown to be unrelated to any period of magmatism. There is no intense alteration to the host rocks. Commonly there is a close association with organic matter, either liquid hydrocarbons or bitumen; they have a very simple mineralogy of barite, celestine, fluorite, sphalerite, galena, and have low formation temperatures (90–105 °C) combined with variable salinities. These characteristics make these deposits similar to the Mississippi Valley–type deposits, possibly most similar to the Alpine-Appalachian subtype.

Abstract Downward-percolating oxidizing meteoric waters are the single most important factor in the processes that transform primary, hypogene, sulfide protore to secondary, supergene, nonsulfide ore. Faults provide the secondarily enhanced permeability pathways for these fluids and thereby exert a fundamental control over the formation of many—if not most—supergene deposits. Under the relatively low confining lithostatic pressures at or near the earth's surface, fault structures are commonly highly permeable and allow selective weathering and related supergene processes to occur more quickly and reach more deeply than local exhumation and erosion, the greatest threats to any supergene ore deposit subsequent to its formation. On encountering sulfides, meteoric waters charged with atmospheric oxygen initiate a metal fractionation process involving the liberation and acidic mobilization of soluble base metals, the residual enrichment of insoluble materials in situ, and the progressive reprecipitation of metals at some distance from their source. This fractionation process is fundamentally controlled by the differential solubility of the metals involved and by the hydrodynamic behavior of the supergene meteoric fluids. In turn, the migration of these fluids depends on the permeability of the rocks, which is predominantly fault- and fracture-controlled. Finally, precipitation and fixation of the supergene ore minerals depend on the type and reactivity of available host rocks and the surface area available for reaction. The contribution of fault and fracture zones is arguably more important to the genesis of supergene zinc deposits than for other supergene base metal deposits, such as Cu-enrichment blankets, because of zinc's particularly high solubility and mobility in the supergene environment. Several common examples of fault control can be seen in supergene zinc deposits, including the following: Faults that simply provide access for oxidizing meteoric fluids to hypogene sulfide ores and convert them into supergene ore in situ or near the fault zones. Faults that juxtapose sulfide protore source rocks and highly reactive trap rocks (e.g., carbonate rocks) in such a way that oxidation, remobilization, and reprecipitation occur in close proximity, although not in situ. Fault blocks of impermeable lithotypes can act as hydrologic barriers to supergene ore fluids transporting dissolved base metals away from their sulfide sources and cause “ponding” or diversion of these fluids away from potential reactive hosts. The first increases residence time and consequently, fluid-wall rock interaction, whereas the second can create dispersion halos or even force metal-bearing groundwaters to surface, where they can form springs. Both processes can create metal halos detectable by exploration programs. Fault systems (especially transpressive wrench systems) that fracture large volumes of rock on all scales can increase both permeability of the fractured rock and increase reactive surface area to an exceptional degree. Locally, such pervasive fracture patterns can provide the ground preparation necessary to turn relatively unreactive host rocks such as impermeable metasiliciclastic or volcaniclastic rocks into trap rocks. In some cases (e.g., Skorpion) this can make these shattered rocks more favorable than more reactive adjacent carbonates to which the fluids have more limited access. Only faults and fault breccias have the extent to allow ultradeep meteoric oxidation and supergene mineralization to penetrate more than 1,000 m below surface, in situations where this is generally considered to be well below the groundwater table.

Abstract Mexico is widely known to be a richly endowed country in both metallic and industrial mineral deposits, the exploitation of which has constituted an economic activity of paramount importance for centuries. This paper presents an analysis of the time and space distribution of over 200 mineral deposits, which is based on the available absolute and relative ages of mineralization and constitutes a modified and updated version of the analysis of Camprubí (2009). Pre-Jurassic ore deposits are relatively scarce and of subordinate economic significance. These include Ti-bearing anorthosites and rare element pegmatites in intracratonic environments, barite sedimentary-exhalative (sedex) deposits, and ultramafic-mafic Cr-Cu-Ni(-platinum group element [PGE]) deposits in oceanic environments. Since the Jurassic, the metallogenic evolution of Mexico can be understood as a product of the evolution of two major regions: the Pacific margin and the Gulf of Mexico. The Mesozoic evolution of the Pacific margin is characterized by rifting and separation of the Guerrero composite terrane from the North American continent and the initiation of arc magmatism in an extensional continental margin setting. The ore deposits emplaced in this period are mostly polymetallic volcanogenic massive sulfide (VMS) and Cr-Cu-Ni(-PGE) deposits associated with ultramafic-mafic complexes. These occur dominantly near the boundaries of the Guerrero composite terrane. Porphyry-type deposits emplaced in the mid- Cretaceous are subordinate and, apparently, small. These likely formed in island arcs that were later accreted to the mainland. A shift from extensional to compressional tectonics resulted in the accretion of the Pacific terranes, most importantly the Guerrero composite terrane, to the Mexican mainland by the Late Cretaceous. This tectonic shift gave rise to the initial stages of the Paleocene boom in porphyry-type and sulfide skarn deposits. The continental arcs in these epochs represent the earliest stages for the Sierra Madre Occidental silicic large igneous province. The earliest known examples of epithermal deposits in Mexico are Paleocene and include, besides intermediate to low sulfidation deposits, the La Caridad Antigua high sulfidation deposit, in association with the giant La Caridad porphyry copper deposit. The Late Cretaceous iron oxide copper-gold (IOCG) deposits formed in northern Baja California and along the Pacific margin in southwestern and southern Mexico, and continued forming in the latter regions into the Paleocene. Contrastingly, some Late Cretaceous IOCG deposits formed several hundreds of km inland in northwestern Mexico, and are suspected cases for emplacement in back-arc environments. The formation of orogenic Au deposits began in the Late Cretaceous, and they kept forming into the Eocene as compressional tectonics progressed. The formation of porphyry-type, sulfide skarn, and epithermal deposits continued during the Eocene, and followed the eastward progression of the magmatism of the Sierra Madre Occidental. The number of known examples of epithermal deposits relative to porphyry-type and sulfide skarn deposits increases with time. The formation of IOCG deposits along the Pacific margin seemingly dwindled during the Eocene, although they began to form close to the Chihuahua-Coahuila border, possibly in association with the earliest stages of mineralization in the Eastern Mexican alkaline province. Also, a group of U-Au vein deposits in Chihuahua, in association with felsic volcanic rocks, is apparently restricted to the Eocene. The maximum geographic extension and climactic events of the Sierra Madre Occidental (for both magmatic and ore-forming events) were attained during the Oligocene, as the arc kept migrating eastward and southward. As magmatism reached the Mesa Central, epithermal and subepithermal, sulfide skarn, Sn veins associated with F-rich rhyolites, IOCG, and Sn-W greisen deposits formed around the main reactivated fault zones, generating the highest concentration of ore deposits known in Mexico. The focus of magmatism and mineralizing processes shifted progressively southward in the Eastern Mexican alkaline province between the Oligocene and the Miocene, and intensified significantly in northern Coahuila and Chihuahua in the Oligocene. This province also includes alkaline porphyry Cu-Mo deposits, REE-bearing carbonatites, and polymetallic skarns. During the Miocene, the magmatism of the Sierra Madre Occidental retracted dramatically southward and began concentrating in an E-W arrangement that corresponds to the Trans-Mexican volcanic belt, while continental extension evolved into the opening of the Gulf of California. During this time, metallogenic processes associated with the Sierra Madre Occidental virtually ceased. From the late Miocene, the formation of epithermal deposits, sulfide skarns, and porphyry-type deposits resumed in the Trans-Mexican volcanic belt and the Eastern Mexican alkaline province, whereas IOCG deposits seem restricted to the latter. The opening of the Gulf of California represents the beginning of a new cycle in metallogenesis, with the formation of shallow analogues of sedex deposits and sedimentary phosphorites along the Baja California peninsula, epithermal deposits near the cul-de-sac of the Gulf, and recent VMS deposits in passive continental margins and mid-ocean ridges. The sedimentary-diagenetic history of the Gulf of Mexico includes the formation of Mississippi Valley-type (MVT) and associated industrial mineral, red bed-hosted U and Cu-Co-Ni, sedimentary phosphorite, and sedex deposits. The emplacement of MVT and red bed-hosted deposits was associated with the emplacement of basinal brines through reactivated faults that controlled basin inversion. These faults also played a significant role as channelways for magmas and associated magmatic-hydrothermal ore deposits of the Eastern Mexican alkaline province.