The coal-bearing sequence of Oligo-Miocene age has been studied in the Pupunahue Basin, in order to establish a model type of study to be applied to other deposits of similar characteristics in the south of Chile. The following elements were analyzed in coals: B, S, Ti, V, Cr, Co, Ni, Cu, Zn, Ga, Ge, As, Cd and Pb. In shales were determined: Ti, V, Cr, Co, Ni, Cu, Zn, As, Cd and Pb. The contents of sulphur and boron indicate a moderate marine influence in cornparison with other deposits of the region (e.g. Catamutun). Elements of economic importance, such as Ge, V and Ti, display no interesting concentrations. The level of arsenic, sulphur, zinc and cadmium is not significant enough to consider them as potential contaminants. KEY WORDS. Trace elements in coals. Pupunahue. Chile.

Coal blends are increasingly utilised at power plants with significant savings and without breaking environment regulations. However, evidence of interaction among the coals requires the study of some parameters that affect combustion efficiency and related opacity of emissions.Actual plant data was available for the combustion of five families of binary blends (single coals and approximately 25%/5%, 50%/50% and 75%/25% blends) with variable contents of ash, volatiles and maceral composition. Size distribution of particles was determined for the coals fed to the plant boilers and the fly ashes, as well as for unburnt carbon in the latter.The almost homogeneously sized feed from different coals generates a size distribution in the fly ash where 250-mum particles vary up to 1.29%, while particles smaller than 38 gm vary between 21.74% and 62.41%. Unburnt carbon increases with size of ash particles from a maximum of 12.2% for fractions smaller than 38 mum up to 73.9% for the fraction bigger than 150 mum.Total content of unburnt carbon in the fly ash from combustion of coal blends show deviations from the expected weighted average of the constituent coals (K, L, T, P, F, S and N). These deviations are related to maceral composition and rank based on reflectance values. The smallest deviation is shown by the blend (T/P) with coals having low values of reflectance and homogeneity of maceral contents. Larger deviations were found for blends K/L, P/F and S/N with higher difference of rank and greater heterogeneity of maceral composition. The K/L, R/N and S/N blends show positive deviations with respect to the expected weighted average, that is, blending was detrimental to the combustion efficiency, while blend P/F showed an enhance of the combustion efficiency as measured by unburnt carbon in the fly ash.A "reactive maceral index" introduced in this work plays a useful role. If a ratio of reactive maceral index is established for a binary blend as the ratio of the respective values of the index for the single coals, then the magnitude of the deviation from the expected average is proportional to the ratio of reactive maceral index of the blend. Thus, the K/L and P/F blends, with values of 4.6 and 65.6 for the ratio of reactive maceral index, differ significantly from the expected average, while blends T/P and R/N, whose binary families have a ratio of reactive maceral index close to 1, show a behaviour (in terms of unburnt carbon) which closely approach the expected weighted average. (C) 2002 Elsevier Science B.V All rights reserved.

Although coal blends are increasingly utilized at power plants, ash slagging propensity is a non-additive property of the pure coals and hence difficult to predict. Coal ash tendency to slag is related to its bulk chemistry and ash fusion temperatures, and the present study aims to compare the results obtained from thermodynamic simulation with characterization of samples obtained as outcomes of plant-based coal-blend combustion trials at three utilities located in the Centre and North of Chile. Pulverized coal and plant residues samples from five families of binary blends tested in an experimental program were characterized for chemistry, mineralogy and maceral composition. The slagging was evaluated by determination of fusion curves using the MTDATA software and NPLOX3 database for the main coal ash oxides. The ranking obtained was approximately the same as obtained from carbon in the fly ashes and from plant residues observations. The thermodynamic modeling was a valid option to predict the fusibility during the combustion of blends.

The geology, petrography and chemical variation of the Pecket coal sequence, Magellan Region (52°57′S, 71°10′W), the only Chilean coal used for electricity generation on a large scale, has been studied in order to predict their combustion behaviour, especially in coal blends. The depositional environment of formation of the coal seams was a swamp rarely exposed to subaerial conditions and was associated with the development of the folded foreland of the Magellan basin during the Tertiary (Oligo–Miocene). The general tectonic regime of the collision of the Antarctic and South American plates is reflected by a system of joints with 40°N–50°W strike. The maceral composition of all six seams studied indicates high contents of vitrinite (>90%), minor content of liptinite (4.7%) and inertinite (<2%). Occurrence of tonstein horizons altered to kaolinite indicates a distal volcanism during peat accumulation. Coal rank varies between lignite and subbituminous (Ro=0.28–0.42%) with an average dry basis calorific value of 5450 kcal/kg, 17 wt.% moisture, 41 wt.% volatile matter, and sulphur content below 0.5 wt.%. The mineral matter (LTA) associated with the coal shows a dominance of kaolinite with quartz, smectite, and minor basanite. SiO2/Al2O3 and Fe2O3/CaO ratios of the ashes diminish towards the lower seams. With respect to the utilisation of Pecket coals in combustion, base/acid ratios (B/A) and silica ratios (SR) indicate potential fouling for seams 1, 2, 5, and 6i, with high fouling indexes (Rf) for seams 2 and 5. Pecket coal is excellent for blend combustion due to its low sulphur content.

Lithology, metamorphism, and deformation of the host rocks of chromite-bearing serpentinite bodies are described. The metasedimentary rocks and the intercalated metabasalts were metamorphosed under greenschist facies conditions. Several metamorphic and deformational phases are distinguished. The first three developed under constant strain directions with NNE–SSW to NE–SW trending fold axes. E–W trending fold axes formed in a later phase, still under ductile conditions. Only after the Carboniferous/Permian boundary were kink bands formed that indicate transition to brittle deformation. Block-stream-like arranged chromitite boulders indicate the occurrence of major chromitite layers within a large serpentinite body. The emplacement of the serpentinite body into the host rocks took place between the third and fourth folding phase. Cr/(Cr+Al) ratios of chromite ores indicate an island arc position for the chromitites, whereas data from neighbouring areas point to backarc conditions. A polyphase, more or less continuous, subduction process from the Carboniferous up to the end of the Permian is thought to be responsible for tectonically mixing up these units.

Trace element contents (Cu, Zn, Co, Ni, Ct V, Ge, B, As), vitrinite reflectance values and content of mineral matter (low temperature ash (LTA) samples characterised by XRD) have been determined in Eocene-Miocene coals from Lebu (bituminous, Concepcion-Arauco basin), Pupunahue (subbituminous, central-southern Chile) and Pecket (subbituminous, Magellan Region). Trace element concentrations do not differ between the deposits and potential recovery of those from the ash, which does not appear to be of economic interest. Boron and sulphur contents point to a moderate marine influence during deposition. Arsenic and sulphur concentrations in subbituminous coals do not exceed the standards set by the Chilean legislation Sulphur concentrations in bituminous coal are high (> 3%) and they should be blended with low sulphur coals. In the Pupunahue deposit, Pearson's correlation between ash content and Cu (r = 0.42), Zn (r = 0.84), Co (r = 0.87), Ni (r = 0.32), Cr (r = 0.84), V (r = 0.80) and As (r = 0.09) shows an inorganic affinity and an organic affinity between ash content and Ge (r = -0.32), B (r = -0.4) and S (r = -077). The same correlation and affinity are observed in the Pecket mine for Cu (r = 0.50), Zn (r = 0.91), Co (r = 0.58), Ni (r = 0.71), Cr (r = 0.13), V(r = 0.22) and As (r = 0.24); Ge(r = -0.22), B (r = -0.97) and S (r = -0.13) also show an organic affinity. In Victoria de Lebu, the tendency is the same but the data are too reduced for a formal correlation. Mineral matter changes qualitatively and quantitatively in response to the local sediment input during coal formation. Quartz and pyrite dominate at Lebu (Ro = 0.70%), a basin isolated from volcanic emerged ranges to the east (Proto Andes Mountains). Pupunahue (Ro = 0.45%) received more pelitic (illite/muscovite) and volcanoclastic sediment, the latter altering to kaolinite. Coals from the Magellan region (Ro = 0.40%) contain kaolinite group minerals and smectite, similar to the accompanying "Tonstein" horizons. LTA residues show differences in the crystallinity of the kaolinite mineral, changing from a dominantly 1 T polytype at Pupunahue to I Md polytype at Pecket. (C) 2000 Elsevier Science B.V. All rights reserved.

Las serpentinitas del area de La Cabana forman parte de la Serie Occidental del Basamento Metamorfico de la Cordillera de la Costa de la IX Region y corresponden a dunitas de grano grueso parcial a totalmente serpentinizadas. Contienen cromita como mineral accesorio, la que generalmente esta alterada en grado variable a ferricromita. En cambio, las cromitas presentes en las cromititas de Centinela Bajo, preservan su composicion original con un minimo grado de alteracion, lo que permite su uso como indicadores petrotectonicos. Sus valores de 'numero de cromo' (#Cr= Cr/Cr+Al) entre 0,65 y 0,90, de 'numero de magnesio' (#Mg=Mg/ Mg+Fe+2) entre 0,40 y 0,70, indican un ambito de arco de islas para el emplazamiento de las peridotitas estudiadas.