The results of tectono-metallogenic, geological-structural, mineralogical, isotopic, and thermobarogeochemical studies at the Alshar deposit and in the adjacent area are discussed. The data obtained show that the gold mineralization at the deposit is similar to that observed at the Carlin-type deposits in the western United States. Similar characteristics include the Au-As-Sb-Tl-Hg geochemical assemblage; low Pb, Zn, Cu, and Ag contents in ore; widespread jasperoid and argillic metasomatic alterations of host siliciclastic-carbonate sedimentary rocks; and the spatial relations to fault zones. At the same time, the Alshar deposit differs from the Carlin-type deposits by the following features: (1) Pliocene age of mineralization, (2) expansion of mineralization over younger volcanics, (3) a high Tl grade in ore, and (4) localization of the ore field in a long-lived central-type magmatic structure. The results obtained can be used as an exploration model.

During the second half of the 20th century, several dozen large and medium deposits of disseminated pyrite-marcasite ores with total gold reserves of more than 6000 t and annual gold production of ~200 t were found in the Basin and Range Province, Nevada, United States [1,2]. This unique gold district is termed as the Carlin trend. The limited development of the Carlintype mineralization in other gold districts of the world is presently a debated issue. Naturally, each Carlin-type mineralization inferred beyond Nevada requires detailed investigations. In 2004, we began to study the Alshar deposit with Carlin-type mineralization together with Macedonian geologists [3]. The Alshar deposit is a large object in terms of Tl reserves and a medium reserve in terms of inferred Au reserves [3,4].The territory of Macedonia experienced long-term geological evolution. Its majority is occupied by the Serbian-Macedonian and Pelagonia crystalline massifs, separated by the Mesozoic Vardarian riftogenic graben ( Fig. 1). Macedonia is located in the SerbianMacedonian part of the Eurasian Tethys metallogenic belt. Mineralization related to the Cenozoic activation in this area is expressed in the formation of volcanoplutonic associations in the dispersed spreading environment [4]. The activation spanned the Serbian-Macedonian Massif and part of the Vardarian riftogenic zone. Superimposed structures of this period occur as narrow NW-trending grabenlike depressions complicated by local ring structures of the chamber type.Previous joint works with Macedonian geologists showed that the present-day tectonic structure of Macedonia reflects dislocations closely related to Cenozoic magmatism and productive mineralization. These dislocations were reconstructed from tectonic elements of the present-day relief surface using morphostructural analysis and deciphering aerial and satellite photographs. Based on the dislocations, we distinguished three (Oligocene-Miocene) NW-trending metallogenic zones superimposed onto the metamorphic sequence of the Serbian-Macedonian Massif. They are mainly composed of the Cenozoic tuffogenic-sedimentary and volcanic sequences and are crosscut by granitoids and dikes of intermediate composition. The metallogenic zones compose an ore belt (Fig. 1), which extends to the northwest (Serbia) and southeast (Greece and Bulgaria).From southwest to northeast, the metallogenic zones show variation in ore type and decrease in age of magmatic complexes and ores. One can see a distinct correlation between age and ore composition. Northeastward, the mineralization evolves from high-temperature (relatively low-sulfide) to low-temperature (polysulfide) types. The directed change of ore composition can be related to differentiation of ore matter in the deep-seated chambers. The ore type changes across metallogenic zones in the following way: skarn-magnetite ores (Borov Dol deposit), porphyry copper ores (Buchim), base metal copper ores (Kratovo-Zletovo), and base metal ores (Sasa and Toranica). In the SW-NE direction, the age o...

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Para investigar la relación entre la sismicidad y la estructura tectónica de la región de Oaxaca, en el sur de México, se usó el análisis morfoestructural; éste se basa en la determinación de los elementos tectónico-estructurales por medio del estudio de las formas y características del relieve. Para determinar las características tectónicas de esta región se utilizaron mapas topográficos, mapas geológicos a la escala de 1:1, 000,000 y otros datos geológicos disponibles. Los elementos estructurales principales incluyen domos, bloques tectónicos y lineamientos de diferentes magnitudes. Además Se infieren el desarrollo y las relaciones entre estos elementos estructurales. Se diferencian formas activas, inactivas y reactivadas.Se sugiere una correspondencia entre actividad sísmica y las estructuras tectónicas encontradas para esta región de acuerdo al análisis morfoestructural; se sugiere, además, que los epicentros de los temblores fuertes podrían estar localizados, dentro de la confiabilidad de su determinación, en la intersección de las fallas activas de dirección N65° ± 5°W con las importantes fallas reactivadas de direcciones N-S y E-W. La actividad sísmica precursora y de replicas asociadas al temblor del 29 de noviembre de 1978 (Ms = 7.8) muestran una buena correlación con los detalles de la estructura tectónica de Oaxaca. La actividad sísmica precursora está probablemente relacionada a la primera estructura de dirección N65° ± 5°W en el continente, después de la trinchera mesoamericana; las replicas están presumiblemente asociadas a las estructuras continentales con direcciones N-S y E-W, las que reflejarían acomodamientos de bloques a raíz de los desplazamientos típicos de subducción generados por el temblor principal.

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