Studies of the metallogeny of northwestern Mexico (Baja California to Chihuahua to Durango) at the mining district, geologic province, and regional scale, show that deposit formation and preservation is an intricate interrelationship between magmatism, tectonism, and hydrothermal activity. These are not only complicated by superimposed factors including erosion, enrichment, and cover, but in northern Mexico, tectonic translation as well. Using palinspastic reconstructions the relative positions of geologic units are restored to their pre-extensional configuration. Metallic "belts" are heterogeneous with numerous metal associations and deposit types superimposed in the same area. The reconstructions show that magmatism and mineralization were coeval and coincident. Superimposed environments and processes cover, erode, enrich, and preserve mineralization thus substantially affecting perceived metal distribution. Cover sequences including mid-Tertiary ignimbrites and late Tertiary clastic sediments preserve and commonly conceal mineralization. Mid-Tertiary and older extensional events preserve near surface deposit types (e.g, supergene blankets, Jurassic rift-related deposits). At the Sierra Madre Occidental (SMO) province scale, ore deposit types exhibit enormous variation from adularia sericite-dominated to advanced argillic to closely pluton related. The advanced argillic alteration with gold+/-copper+/-silver deposit types appears related to magmatic centers occurring in both the older (pre-Oligocene) and younger (Oligocene) volcanic sections and is a major focus of this dissertation. Acidic alteration-related deposits make up some of the largest Au occurrences including the Mulatos >2 million ounce gold district. Extensive kaolinitic alteration halos (>8 km²) zoned around a core of vuggy silica and quartz+/-pyrophyllite host enargite-pyrite ores. Sulfide isotopes are near zero δ³⁴S(pyrite) = -5 to -3%; δ³⁴S(enargite) = -6 to -4%) with corresponding barite (δ³⁴S = +18-22%). Phase equilibria and isotopes indicate early pyrophyllite-pyrite ores formed at ∼ 300°C with later barite-pyrite-dickite ores deposited at T = ∼ 260°C. Oxygen and hydrogen isotopes show possible mixing between magmatic and meteoric waters with a late (shallow) meteoric (heavier D, lighter δ¹⁸O) overprint. District tilting (∼ 25°NE) exposes >1.5 km altered section containing two separate centers. Alunite occurs late, rarely and is above pyrophyllite, suggesting a vertical transition in acid sulfate systems.

The Tarahumara are one of the most isolated and intact indigenous groups in Mexico. Their agriculture has traditionally been practiced within the steep canyons and uplands of the Sierra Madre Occidental in southwestern Chihuahua. Adapting to these rugged conditions, the Tarahumara developed a variety of agricultural techniques that allowed them to be self-sufficient in food production and independent of external inputs. As varied and ingenious as their techniques are, they share one main objective -- to overcome the lack of organic matter in the stony mountain soils. Since the arrival of the Spaniards, the addition of organic matter has involved large amounts of animal manure to increase organic matter in the soil and maintain fertility. The focus of this study is to investigate new agricultural techniques that the Tarahumara are adopting due to the pressures of globalization and alleged climate change. These new technologies may still include many traditional agricultural methods, but they are increasingly using commercially available fertilizers and other modern agricultural additions, thereby losing self-sufficiency. This study includes in depth interviews with 28 Tarahumara farmers to better understand the modern agricultural techniques, their motivations, and overall sustainability. Soil samples determined the viability of Tarahumara agricultural techniques on soil fertility by examining the visual description, organic matter content, soil texture, and a chemical analysis. The analyses showed that traditional Tarahumara agricultural practices are efficient and sustainable, while modern additions are often ill-suited for their environment and are disruptive to Tarahumara culture. / text

Magíster en Ciencias, Mención Geología / En este trabajo de tesis se presentan los resultados de estudio geológico de exploración minera de la zona El Refugio, estos en función de la posible mineralización epitermal de metales preciosos. En esta zona de estudio existen evidencias de alteración hidrotermal (argílica y fílica), donde se ha identificado mineralización aurífera de baja ley en vetas con valores de 0,3 a 0,6 g/t Au. El área de estudio El Refugio se localiza en el flanco oriental de las montañas de la Sierra Madre Occidental, muy cerca del borde con la Mesa Central y dentro de la prolífica faja de mineralización de plata de México. Localmente se ubica en la porción centro-norte del estado de Durango dentro de terrenos de la jurisdicción de los municipios de Rodeo e Indé, y a 150 km al norte en línea recta de la ciudad de Durango. Con el mapeo geológico estructural realizado, a escalas 1:20.000 y 1:2.000, se definieron las estructuras y vetas relacionadas al sistema de fallas San Luis - Tepehuanes con dirección NW-SE y a la distensión que generaron las fosas y pilares donde se localiza el semi-graben de Rodeo. Con las edades U-Pb en circones obtenidas durante el presente trabajo, de 47,8 ± 0,2 y 49,5 ± 0,2 Ma, se interpretan dos edades de cristalización de los cuerpos hipabisales, ubicando a estos en el Eoceno temprano a medio, relacionado regionalmente a las estructuras del sistema de falla San Luis - Tepehuanes y al semi-graben de Rodeo como contemporáneos a estos eventos. Por medio de las dataciones U-Pb realizadas en este trabajo y los emplazamientos de estos cuerpos relacionados a las estructuras mencionadas, se postula que la mineralización del área El Refugio podría estar asociada al emplazamiento de los cuerpos datados Eoceno temprano a medio. La mineralización encontrada en el área El Refugio permite postular un potencial exploratorio por Au-Ag, asociado a ambientes epitermales de metales preciosos. La aseveración anterior es confirmada por estudios de inclusiones fluidas que permiten clasificar los sistemas de vetas en el área de estudio en depósitos epitermales de baja a intermedia sulfuración. Por medio de los estudios geoquímicos mediante ICP-óptico para 31 elementos más oro (Au), por ensaye al fuego, se determinó que el único elemento blanco de exploración es el Au, relacionado a los elementos As y Sb como trazadores. A través de un análisis de factores de estos datos geoquímicos se determinaron los principales factores con más alta implicancia y los cuales agrupan ciertos elementos según su ocurrencia natural. Se determinaron cinco factores. Los factores 1 a 3 reflejan aspectos litológicos y los factores 4 y 5 son representativos de una mineralización de tipo Au-Sb-As. Si bien no existe buena correlación estadística entre Au y Sb-As, estos elementos presentan una relación especial y de ambiente similar, principalmente en vetas y cuerpos hipabisales. El análisis de dispersión del elemento Au, con interés económico, se relaciona directamente al emplazamiento de las vetas del área de estudio con valores que representan anomalías del orden de 0,09 a 0,236 ppm. Además, antecedentes geoquímicos de otros estudios recientes indican que en algunas vetas del área a 0,50 m de profundidad existen leyes del orden de 0,1 a 10,0 g/t de Au y entre 18 y 77 g/t de Ag. Esto permitirá proponer esta zona de estudio, como un potencial prospecto de exploración y programar trabajos de obra directa en los lugares donde las anomalías de contraste positivo presentadas son evidentes. Se recomiendan estudios geológicos de detalle con realización de muestreo en trincheras o zanjas en las vetas.

The Sierra Madre Occidental and neighboring Madrean Sky Islands span a large and biologically diverse region of northwest Mexico and portions of the southwestern United States. Little is known about the abundance and habitat use of breeding birds in this region of Mexico, but such information is important for guiding conservation and management. We assessed densities and habitat relationships of breeding birds across Sky Island mountain ranges in Mexico and adjacent portions of the Sierra Madre from 2009 to 2012. We estimated densities at multiple spatial scales, assessed variation in densities among all major montane vegetation communities, and identified and estimated the effects of important habitat attributes on local densities. Regional density estimates of 65% of 72 focal species varied significantly among eight montane vegetation communities that ranged from oak savannah and woodland at low elevations to pine and mixed-conifer forest at high elevations. Greater proportions of species occurred at peak densities or were relatively restricted to mixed-conifer forest and montane riparian vegetation likely because of higher levels of structural or floristic diversity in those communities, but those species were typically rare or uncommon in the Sky Islands. Fewer species had peak densities in oak and pine-oak woodland, and species associated with those communities were often more abundant across the region. Habitat models often included the effects of broadleaf deciduous vegetation cover (30% of species), which, together with tree density and fire severity, had positive effects on densities and suggest ways for managers to augment and conserve populations. Such patterns combined with greater threats to high-elevation conifer forest and riparian areas underscore their value for conservation. Significant populations of many breeding bird species, including some that are of concern or were not known to occur regionally or in mountain ranges we surveyed, highlight the importance of conservation efforts in this area of Mexico.