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The technological properties of a local kaolin, considered as a potential industrial material, were correlated with the thermal behavior and sintering processes carried out through a series of thermochemical analyses. The chemical and mineralogical characterization of the material was carried out, together with a simple microstructural characterization. The used material corresponded to the kaolinized basement rocks (saprolite zone) mined at La Verónica quarry, Chillar area, Azul County, Argentina. The complete kaolinite-metakaolinite-spinel-mullite thermal series was characterized. Sintering behavior was studied; a viscous phase sintering mechanism was proposed. Apparent density and porosity of fired ceramics were measured. A light-firing color was confirmed by colorimetry. The viscous phase mechanism was possibly described thanks to the multi-technique thermal behavior analysis complemented by XRD analysis. These results permitted to establish formulation and processing strategies of ceramic materials based on the studied clay. The possible applications include: tile manufacturing, sanitary ware, tableware, kaolinitic proppants, chamotte and refractory materials.

Dawsonite, NaAlCO 3 (OH) 2 , occurs as a replacement, cement, and fracture filling in continental, zeolitized and silicified vitric tuffs and litharenites of the Cenomanian Cerro Castaño Member, Cerro Barcino Formation, Chubut Group, Patagonia, Argentina. Analcime is the only associated zeolite; it replaces the vitric masses and also fills fractures and cavities. Dawsonite and analcime display an inverse ratio. Textural relationships indicate that dawsonite is a pseudomorph after oligoclase, quartz, vitric shards, and vitric masses; it coexists with diagenetic quartz cement and postdates analcime, calcite, and hematite cements. Unaltered crystals of high sanidine postdate all other cements generated. Silicification of the tuffs is likely to have occurred in various stages during the diagenetic history of the sequence. Hypabyssal bodies of alkaline basic rocks of the El Buitre -El Canquel Formation, which intruded regionally the Cerro Castaño Member during Eocene time, are interpreted to be responsible for the introduction of CO 2 gas at high partial pressures, together with sodium, which led to dawsonite formation. Diagenetic quartz, at a late stage of silicification, is related to the transformation of oligoclase and analcime to dawsonite, also releasing Na and Ca into the system. The d 13 C (PDB) values of dawsonite, in the range -1.2 to -2.4‰, attest to alkaline igneous activity in the Cerro Castaño Member during the Eocene and, in addition, set a limit on the age of the dawsonite.

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El objetivo del presente trabajo fue dilucidar aspectos básicos y aplicados del proceso pirometalúrgico que fuera usado hace más de 100 años en la fundición Santa Florentina (Chilecito, provincia de La Rioja, Argentina) para extraer cobre a partir de minerales del yacimiento La Mejicana (Famatina). Con este propósito, formulamos las posibles reacciones que describen la obtención del metal, realizamos una exhaustiva caracterización fisicoquímica de la escoria, estimamos el desprendimiento gaseoso durante la oxidación de diversas sustancias, evaluamos el impacto de la minería en la deforestación regional y revisamos las causales que respaldaron la opinión de discontinuar el proyecto. La metodología experimental empleada comprendió: análisis químico, difracción de rayos X, microscopía electrónica de barrido, espectroscopía de energía dispersiva de rayos X, termogravimetría-análisis térmico diferencial y determinación de densidad. Los resultados aquí exhibidos nos permitieron establecer que la recuperación de cobre fue alta, recopilar detalles operativos de la tecnología implementada en aquella época, aportar evidencias sobre la contaminación ambiental producida por las actividades llevadas a cabo e identificar dos potenciales motivos que habrían impulsado a tomar la resolución de abandonar definitivamente el emprendimiento.

In the Tandilia Basin, Buenos Aires Province, Argentina, we study the genesis of mud beds and pipes in the Loma Negra Formation (limestones), Sierras Bayas area, together with the emplacement of alunite and aluminum phosphate sulfate (APS) minerals in the Las Aguilas Formation, Barker area. All these features are related to basin inversion, uplift, erosion, and injection or expulsion, or infiltration of fluids and oxidation reactions in the exhumed rocks during a telodiagenetic stage. On the basis of K-Ar dating of alunite in the Las Aguilas Formation (claystones) giving an age of 254 6 7 Ma (middle Permian), these processes are considered to be linked to a major geological event which affected these Neoproterozoic lithostratigraphic units: the folding of the Ventania System, located 150 km to the SW of the study area.

We report the occurrence of dawsonite, NaAlCO 3 (OH) 2 , in volcaniclastic rocks of the Albian hydrocarbon reservoir Castillo Formation, Golfo San Jorge Basin, neighboring the Cañadón Asfalto Basin in Patagonia; this is the first known occurrence in Argentina. Dawsonite replaces crystals pseudomorphically, and can also be found as a cement together with other carbonates, which induced a loss in the porosity of the host rock. Previous studies reported incomplete chemical reactions which suggested that oligoclase and analcime were dawsonite precursors. In the present work we document either totally achieved or incomplete chemical reactions which led to the transformation of analcime into kaolinite and dawsonite into kaolinite, respectively. These facts allowed us to deduce that the transformation of analcime into kaolinite was via dawsonite, minerals formed during different stages under a telogenetic regime. Dawsonite values of δ 13 C PDB (-0.1 to 1.5‰) are consistent with a magmatic source of CO 2 provided by hypabyssal, basic alkaline igneous rocks of regional importance starting in the Eocene. We identify both internal and external sources of Na and Al used in the formation of dawsonite.

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