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Milpillas is a porphyry copper deposit with supergene enrichment located in the Sonora-Arizona- New Mexico metallogenic province, which is characterized by low-grade (0.1–0.15% Cu) hypogene copper mineralization associated with the emplacement of Laramide plutons. The post-Laramide extensional tectonics promoted a rapid exposure of the hypogene mineralized zones to the weathering environment. This favored the development of outstanding leached caps and formation of supergene enriched chalcocite blankets at the base of the oxidized zones. The supergene ore zone occurs at depth under a postmineral column and a leached cap, which jointly accumulate from 150 to 700 m of vertical extent. This zone was preserved due to subsidence and burial by gravels of the Cuitaca Norte semigraben, a regional basin structure typical of the Basin and Range province. The dominant supergene alteration is characterized by pervasive clays, which overprint an earlier intense hypogene alteration. The latter was initially of potassic-propylitic nature, followed by moderate to strong phyllic and argillic phases, overlapping the earlier alteration. These mineral assemblages constitute a poor or non-reactive gangue with supergene acid solutions, which facilitated the development of the thick, zoned leached cap and secondary copper concentration. The supergene mineralization is characterized by chalcocite and minor covellite, as well as their oxidized counterparts in the upper portions of the chalcocite blankets, which are typically replaced by copper sulphates and accessory copper carbonates. The leached cap is of the hematitic type, characterized by limonitic iron oxides and kaolinite. This mass balance study allowed reconstruction of the original geometry of the hypogene system, which is incomplete to the southeast because it is possibly interrupted and displaced along the Milpillas Oeste fault. The estimation of the total heights of the original leached column and the eroded leached column, were used to determine the zones where Cu was accumulated and those where it was lost. The results show a negative copper balance, which supports the possible occurrence of exotic copper concentration adjacent to the main ore deposit.

A sedimentological, petrological and geochemical research work was carried out in order to find out the origin and provenance of coastal and inland desert dunes from El Vizcaíno Desert, northwestern Mexico. Fifty four sand samples were collected from the windward, crest and slip face of coastal and desert dunes (barchan, transverse, aeolian sand sheets). Onshore winds generates fine, well sorted, near symmetrical dune sands with mesokurtic distributions in the El Vizcaíno Desert inherited from beach sands from the Vizcaíno bay. The coastal and inland dune sands are derived from nearby sand sources like the beach sands and also from alluvial deposits originated from sedimentary-volcanic and schists, granitic and granodiorite sources. This is evidenced by the presence of high quartz content, shell debris, carbonates, mica and hornblende that are constituents of the both coastal and inland dune sands and are probably derived from the action of longshore drifts and onshore winds. The El Vizcaíno coastal and inland dune sands are placed in the craton interior and recycled orogen fields in the Q-F-L diagram suggesting intrusive, sedimentary and partly metamorphosed sources in the composition of the sand. The geochemistry of the sands supports also the maturity process of the sands mainly associated with the presence of alluvial deposits and marine-aeolian action. Additionally, the El Vizcaíno dune sands are chemically related to acid rocks, felsic-plutonic detritus source rocks, which are associated to an active continental margin. The low chemical index of alteration (CIA) values in the dune sands suggest that dryness of the area plays a role in the preservation of labile minerals. The presence of volcanic, metamorphic and plutonic rock around the El Vizcaíno desert basin might contribute to the higher content of plagioclase and mica in the sands when compared to other North American deserts.

Nine taxa represent the crustacean component of the Turonian fauna from the Eagle Ford Group limestones and marls that crop out in several quarries, northwest of Múzquiz, Coahuila, Mexico. Three crustacean taxa are found in common with deposits of similar age and paleoenvironment of the San Rafael Formation of Colombia. Planktic foraminifera, ammonoids, inoceramid bivalves, fishes, marine reptiles, a pterosaur and plant remains were preserved in the Múzquiz quarries, in what has been interpreted as an anoxic, low energy bottom at a water depth of no less than 50 m. The cirriped Stramentum preserved on the ammonite Forresteria is described. Stomatopod remains of the family Pseudosculdidae are described, their incompleteness and poor preservation prevent their detailed identification. One species of scyllarid lobster is included. An indeterminant species of nephropid lobster is also part of this assemblage. Presence of Gourretia aquilae (Rathbun) new combination, confirms correlation with the Eagle Ford Group in Texas. A systematic and morphologic review is provided for Cenomanocarcinus vanstraeleni Stenzel, a species widely distributed during Turonian times, and based on morphologic features of the abdomen and its relationship with coxae, it is assigned to the Podotremata. Also, preservation of soft tissue is reported from C. vanstraeleni and the scyllarid lobster. The raninid Cretacoranina sp. cf. C. dichrous (Stenzel) is also reported. In addition, two raninid taxa are described, their poor preservation prevents more detailed identification. The flattened appendages of C. vanstraeleni and of the raninid species suggest a burrowing habit and/or active swimming.

Hoya de Estrada is one of the explosion craters (maar volcano) forming the Valle de Santiago volcanic field, (Guanajuato), México. It is located at the northeastern corner of Michoacán-Guanajuato volcanic field, within the central part of the Transmexican Volcanic Belt. The crater Hoya de Estrada is one of the few maar type volcanoes of rhyolitic composition. The Hoya de Estrada geologic evolution comprises two main stages: an explosive one forming the maar crater, which was followed by an effusive stage. The maar-forming stage includes two main units separated by a local erosive contact. The lower unit is characterized by sequences of indurated ashy surges interbedded with some massive layers of clast-supported coarse lapilli, composed predominantly of rhyolite pumice and lava, in addition to accidental lithics. The upper unit is composed of medium to coarse lapilli massive fallout layers, which are intercalated with a few thin, indurated fine ash beds. This upper unit includes a basal part with abundant rhyolitic pumice and lava clasts (SiO2 ~77 %), which exhibits small enclaves of mafic magma (basaltic- trachyandesite). The presence of these products suggests periodic injection of basaltic-trachyandesite magma (SiO2 ~55–56 %), while rhyolitic magma rises during the emplacement of this unit. Injection of mafic magma should have played an important role in reducing the water/magma ratios, and increasing the volume of magma. Therefore, it may have changed from one phreatomagmatic eruption (rhyolitic magma) to a magmatic spatter-lava eruption (basaltic-trachyandesite magma), which occurred within the crater. The preferential distribution of the pyroclastic deposits of the upper unit, as well as the spatter rocks to the west, suggest a possible migration of the eruptive locus into that direction, and this may be controlled by the regional E-W-trending structural system.

Petroleum exploration is a high risk business. In this paper, we apply several fundamental concepts of petroleum prospect probability evaluation, illustrating the topic with a case study from southern Mexico. Prospect is a small geographic area where geotechnical evidence predicts the probable economic existence of oil and/or gas. Risk assessment helps to estimate discovery probabilities before drilling. Several geologic chance factors, i.e., reservoir facies, pore volume, geologic structure, seal, source rock, migration and retention were rated to obtain prospect probabilities for the potential accumulation for zones A to D. Zone A is composed of Upper Jurassic rocks, and includes a real reservoir(s). Zones B to D are hypothetical but based on geological facts of the same geologic province. They are respectively composed of Cretaceous, Miocene and Pliocene rocks and located in the same geographic area of Zone A. Based on the prospect geological framework and its associated geologic chance factors, we defined and calculated the corresponding common factor as well as the individual probabilities, thereby allowing us to build a clear picture of discovery probabilities. Three models, representing contrasting source rock concepts generated a range of discovery probabilities for each zone (A to D). Our results show that the discovery ranking begins with Model 2, followed by Model 1, and lastly by Model 3. Using those probabilities results we defined the best geological scenario and point out what we believe are the most appropriate next steps for an improved, less risky exploratory effort.

A complete description of Vallecillichthys multivertebratum Blanco and Cavin, 2003, is provided. This ichthyodectiform fish was collected in the Vallecillo Member of the Agua Nueva Formation (Upper Cretaceous: lower Turonian) at Vallecillo, Nuevo León State, northeastern Mexico. On the basis of a comparative study, this monospecific genus is recognized as member of the suborder Ichthyodectoidei and placed with Ichthyodectes and Xiphactinus into the family Ichthyodectidae. This work provides data on Vallecillichthys for a future comprehensive phylogenetic analysis including all ichthyodectiform species.

The fossil-rich deposits of Térapa (east-central Sonora) contain more than 60 zoological taxa, many with tropical affinities such as Crocodylus (crocodylian), Hydrochaeris (capybara), and many birds. The deposits also contain the dermal ossicles (osteoderms) of two extinct xenarthrans, a glyptodont (Glyptotherium cylindricum) and a pampathere (giant armadillo; Pampatherium cf. mexicanum). Glyptodont remains are also known from other less-well studied localities in Sonora. The faunas from these localities also contain the genus Bison, which indicates that the deposits are of the Rancholabrean Land Mammal Age, late Pleistocene. The presence of Pampatherium at Térapa and the presence of Glyptotherium at Térapa and the Río Mayo/Río Yaqui sites represent the first published accounts of these species from Sonora, and greatly extends their known geographical distribution during the Rancholabrean by about 1,100 km into northwestern Mexico.

In this work we present a new methodology to evaluate the stress and strain produced during the process of subsidence within a multi-layered aquifer system with different granular materials. The hydraulic properties of the materials are such that the increase of the effective stress is assumed to be time independent and to occur simultaneously to the groundwater drop. For this purpose, we derive expressions to estimate the increase of effective stress from the volumetric and gravimetric relation for the soil mass, which allows us to estimate the strain distribution and deformations within the drained soil mass as well as below the water level. The methodology is useful to simulate the phenomenon of subsidence by means of the analysis of an equivalent system, which consist of the evaluation of the effect of an apparent increase of the volumetric weight associated with the increase of the effective stress. The model is applied to a geological section of the free aquifer of the Queretaro valley deduced from gravity measurements and calibrated with lithology logs from available wells. This led us to define the aquifer thickness and the distribution of the different material types within it. Then, by using finite elements, we made a stress and strain analysis on the section of the effect of water withdrawal of the aquifer. A boundary condition imposed to the system is the actual average level of drawdown, which is about 150 m. The results are compared with observed subsidence and soil failure along the modeled section.

In this study, geochemical methods are used to reliably analyze and understand the Simav geothermal field whose thermal water is rich in terms of Na-HCO3-SO4 and is affected by groundwater which is low in Cl. The water is of meteoric origin and belongs mostly to the immature water group. Quartz and Na-K geothermometers are used to calculate the reservoir temperatures as 70-195 ºC and 167–249 ºC, respectively, and the Na-K-Mg geothermometer indicated temperatures of approximately 230–240 ºC. The isotopic evaluation of the geothermal system indicates that the water in the Simav geothermal reservoir is 18O enriched, is fed by cold water from Nadarçam and that the age of the water is older than 50 years. The alteration mineralogy of the field points out to reservoir temperatures between 160 ºC and 250 ºC in the thermal water. The activity diagrams of the thermal water indicate the existence of fluid-rock interaction and show that the water is in equilibrium with K-feldspar, muscovite, albite (Na-feldspar), Mg-chlorite and epidote minerals at a temperature range of 150–250 ºC. The activity diagrams also point to a potential source that might be located in a deeper zone that is hotter than the reservoir currently used for production, which is consistent with the alteration mineralogy of the field and Na-K geothermometers. The mineral equilibrium diagrams yield reservoir temperature values that are in harmony with the values obtained from the production zone and silica geothermometers. According to the mineral equilibrium diagrams, it is probable that calcite precipitates at high temperatures and that silica precipitates at low temperatures.

The Lower Cretaceous Cupido Formation, a carbonate system developed in northeastern Mexico, like many ancient carbonate platforms contains numerous dolomite bodies. These diagenetic features are particularly well exposed at Bustamante Canyon (Nuevo Leon State) where the Cupido Formation crops out from base to top along 6 km. Dolomitization affected practically all facies and crosscuts bedding planes; dolomite bodies are irregular in outer and margin platform facies and tabular/subhorizontal in inner platform facies. Most dolomite is replacive and also occurs as cement in small amounts. Crystal shape of replacement dolomite varies from nonplanar, planar-s to planar-e, whereas the dolomite cement consists mostly of saddle dolomite. Dolomite is non ferroan and shows dull red luminescence, its δ18OPDB varies from -4.2 to -6.4‰ and its δ13CPDB from 1.8 to 3.4‰. 87Sr/86Sr ratios of replacement dolomite vary from 0.70754 to 0.70770. Homogenization temperatures in dolomite from fluid inclusion analysis range from 190 ºC to 200 ºC and are interpreted as the minimum temperatures for the dolomite formation. Petrographic data, geometries and distribution of dolomite bodies, microthermometric results from fluid inclusions and geochemical information suggest that the dolomitization occurred under deep-burial diagenetic conditions. Similar homogenization temperatures were determined in dolomite and post- dolomite calcite cement of the Cupido Formation from southern locations including Potrero Chico and Potrero Minas Viejas. The high temperatures recorded in the Cupido Formation dolomites are the result of a regional thermal anomaly developed probably around salt structures. 87Sr/86Sr values, oxygen stable isotopes, and trace element composition of dolomite suggest that the dolomitizing fluid was perhaps a hot mixture of formation water (modified sea water) of the Cupido Formation and brines derived from the updip La Virgen Formation, a carbonate-evaporite succession equivalent in age to the Cupido Formation. Dolomite distribution was apparently not controlled by major tectonic features (e.g., faults or fractures); the dolomitizing fluid seems to have followed subhorizontal or lateral flowing circulating patterns controlled by the former porosity and permeability of the calcareous facies.