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.

Abstract The continental interior of Mexico is characterized by a Late Cretaceous prominent fold-thrust belt that shows characteristics of an eastward-tapering orogenic wedge. According to structural data and geothermometry of the deformation, this wedge is the result of horizontal stresses directed from the west (Pacific domain). The orogenic wedge is bounded to the west by the Guerrero Terrane, which is the second largest juvenile terrane accreted to the North American Cordillera. The possible linkage between the accretion of the Guerrero Terrane and the regional shortening in the Mexican interior is examined in detail in the region comprised between the Sierra de Guanajuato and the Peña de Bernal—Tamazunchale areas. In order to test the accretion hypothesis, we present key stratigraphic, structural, and geochronologic data from the Mexican Cordillera in central Mexico, and discuss the problems that exist in connecting the accretion of the Guerrero Terrane to the orogenic deformation of the Mexican continental interior.

Abstract Mesa Central is an elevated plateau that can be divided into two regions. In the southern region, the topography is higher than 2000 masl, except for the Aguascalientes valley. This region is mostly covered by Cenozoic volcanic rocks. The northern region shows an advanced degree of erosion, and is below 2000 masl. The crust in Mesa Central is ∼32 km thick, and it is bordered by the Sierra Madre Oriental, which has an average crustal thickness of ∼37 km, and the Sierra Madre Occidental, which has an average crustal thickness of ∼40 km. The presence of magmas below the crust is inferred, suggesting an underplating process. The oldest rocks are Triassic marine facies underlain by Jurassic continental rocks. Marine environment prevailed between the Oxfordian and the Cretaceous, forming three distinctive lithological sequences, from E to W: the Valles–San Luis Potosí Platform, the Mesozoic Basin of Central México, and marine volcanosedimentary Mesozoic rocks. All of the above rocks have plicative deformation and inverse faulting, which was produced during the Laramide orogeny. An angular unconformity separates these lithological sequences from the continental Cenozoic rocks. The bottom of the Cenozoic sequence consists of conglomerate with andesitic and rhyolitic volcanic rocks. These were followed by Oligocene topaz-bearing rhyolites, and the uppermost part of the Cenozoic sequence is Miocene-Quaternary alkaline basalt. The boundaries of Mesa Central are the Sector Transversal de Parras and major fault systems active during the Cenozoic to the E, W, and S. A major structure, the San Luis–Tepehuanes fault system, separates the northern and southern regions of Mesa Central. The majority of the mineral deposits found in Mesa Central or in its vicinities, especially epithermal deposits, is located on the traces of the major fault systems described above. The data available suggests that the structures associated with the major fault systems controlled the emplacement of both volcanic-hypabyssal rocks and mineral deposits.

Abstract The Temascaltepec district is located in the southernmost part of the Mexican silver belt. It is made up of three major vein deposits. La Guitarra is the most outstanding and it is composed of six main veins. The veins trend from 120° to 90°, dipping steeply to the southwest and south, with a strike length of more than 3.5 km and a maximum vein thickness of about 15 m (avg 5 m). The veins are hosted by a late Laramide stock, which consists of monzogranite and dikes of leucogranite and granitic porphyry. Mining has been developed on six main underground levels, exposing mineralization for 400 m vertically and 1,200 m horizontally. Vein stratigraphy is divided into three main mineralization stages. Stage I occurs in a brecciated body which contains the highest concentration of base metal mineralization within the deposit, and whose mineral assemblages are gold free and silver poor. Stage II consists of four substages (A, B, C, and D), is characterized by repetitive silica banding and brecciation, and also contains the greatest volume of precious metal mineralization. Stage III is displayed as centimeter-wide veinlets, and is the highest grade stage in terms of precious metal mineralization. The stage I silver-mineral assemblage is scarce and is directly associated with the occurrence of bladed calcite. Pseudomorphic replacements by quartz of rhombohedral adularia crystals and bladed calcite are widespread in stages IIA and IIB. Evidence of boiling coincides with both high FeS content in stage I sphalerites (up to 0.25 mole fraction) and silver mineralization. Stages IIB and III show lower FeS content in sphalerites (up to 0.16 and 0.12 mole fraction, respectively). As sphalerite grain cores are usually iron free, and iron content grows toward the rim displaying oscillatory banding, it is inferred that a repetitive sequence of an a S2 increase culminated with silver mineral precipitation. A close association between electrum and Ag-Cu sulfosalts exists. The Ag content in electrum increases with elevation in stages IIB and III, from the crystal core to the border, and it is higher in stage III than in stage IIB. The Ag-bearing tetrahedrite-tennantites have strong compositional zonations between Ag-Cu, Zn-Fe, and Sb-As. Ag and Sb content increases with height, from the crystal core to the border, and from stage IIB to stage III. Such features similarly occur in Ag-Cu and Ag-Pb sulfosalts at any stage. Mineral pairs and compositions may be used as geothermometers, considering: (1) arsenic solubility in miargyrite, (2) stephanite-arsenostephanite breakdown at high temperatures, (3) proustite-xantho-conite and pyrargyrite-pyrostilpnite dimorphic changes, and (4) opal and chalcedony occurrence. The combinations of sulfide-sulfosalt geothermometers indicate a temperature decrease with elevation and time, within each stage: from >197° to ≥170°C in stage I, from 197° to ≥120°C in stage IIB, and from ≥240° to ≥180°C in stage III. Since opal and chalcedony were deposited before the mineralized bands in stage IIB, it is thought that the metallic mineral assemblage was associated with hotter fluids than those associated with the previous bands. The main ore stages (I, IIB, and III) display a similar evolving trend in mineral deposition, starting with the deposition of base metal sulfides and ending with the deposition of Ag-Au minerals. After base metal sulfide deposition, ore associations point to an a S2 increase with time in each stage. This is marked, for instance, in the thickest ore bands of stage IIB where enargite occurs as the latest mineral. However, the a S2 conditions for each stage, determined using mineral geother-mometers, comprise similar value ranges. The Sb/(Sb + As) ratio distribution in stage IIB Ag tetra-hedrites indicates the main direction of fluid flow to be southeast to northwest, and from the lowest levels to the upper. The Ag/Pb ratio suggests the existence of several feeder channels for hydrothermal fluids during stages IIA and IIB. The paragenetic sequence and mineral zonation in La Guitarra are similar to those described in some of the large low-sulfidation epithermal deposits in Mexico, especially Fres-nillo and Guanajuato in terms of the vein stratigraphy and complex depositional history. The most abundant silver-bearing minerals in La Guitarra are Ag tetrahedrites and proustite-pyragyrite.

Abstract La Guitarra (Temascaltepec, Mexico) is a polymetallic low-sulfidation epithermal deposit. There are three main stages of mineralization. Stage I contains the most of the base-metal mineralization of the deposit. Stage II consists of four substages (A, B, C, and D), is characterized by repetitive silica banding and brecciation, and contains the most precious-metal mineralization in terms of volume. Stage III has the highest Ag-Au grade but is volumetrically minor. Fluid inclusions and stable isotopes were analyzed in the base-metal sulfide and silver mineral assemblages of stage I, pre- and post-brecciation quartz bands of stages IIA and IIB, amethyst lined vugs of stage IIC, early quartz of stage IID, and stage III veinlets. Temperature and salinity of mineralizing fluids range from 80° to 266°C and 0.8 to 14.4 wt percent NaCl equiv, respectively. Paragenetic constraints demonstrate that the temperature and composition of the solutions decrease with time. Base-metal sulfides deposited from solutions of 6 to 14 wt percent NaCl equiv whereas precious-metal mineralization and quartz deposited from solutions of 1 to 9 wt percent NaCl equiv. δ 18 O water , δD water and δ 34 S values span compositional ranges of <–1.5 to >7.3 per mil, −103 to −20 per mil, and −36.6 to −0.5 per mil, respectively. Most of the δD water values from La Guitarra are the highest found in an epithermal deposit in Mexico, whereas δ 34 S values are comparable to those reported in other sedimentary- or metasedimentary-hosted epithermal deposits in Mexico. Boiling, indicated by the occurrence of bladed calcite and adularia is the main mechanism to produce mineral precipitation of precious metals in stages I, IIA, and IIB. Mixing between magmatic brines and sur-ficial meteoric waters may be the main cause of stage I base metal ore assemblage precipitation. Mineral precipitation in stage IIA resulted from boiling and mixing between deep fluids and surficial meteoric waters. Stage III lacks evidence of boiling and mixing and thus conductive heat loss is invoked to be the main precipitation mechanism. The evidence of magmatic contributions is more conspicuous in the metallic mineral assemblages, suggesting that the occurrence of metallic mineralization in La Guitarra low-sulfidation epithermal deposit depends on the pulses of metal-carrying magmatic fluids into the deposit. As the possible presence from evaporites or connate waters does not follow from the regional geology, the occurrence of magmatic and meteoric fluids is inferrable at any stage. The magmatic fluids are characterized by an initially Na-Ca-rich brine. Salinities of 6 to 14 wt percent NaCl equiv and isotopic values of δ 18 O water up to 5.8 per mil and δD water up to −32 per mil in fluids associated to stage I point to a predominance of the magmatic component. On the contrary, in stage IID the lowest δD water (–103‰) and δ 34 S of sulfides (–36.6‰) values have been found, indicating the presence of meteoric fluids that underwent extensive water-rock interaction and bacteriogenic reduction of dissolved sulfate during a lull of the hydrothermal activity. The high calculated δ 18 O water values in the precious-metal associations of stages IIB (up to 6.9‰) and III (7.3‰) indicate a higher contribution of magmatic fluids than in the barren sections of the deposit (stages IIA, IIC). However, this magmatic fluid has lower salinity (up to 6.2 wt % NaCl equiv) than that of the fluid involved in stage I. δ 34 S data of sulfides, between −0.5 and −36.6 per mil, also point to both magmatic and crustal sources for sulfur.