Recovery of minus ten micron cassiterite by liquid-liquid extraction     

G.Z. Zambrana  R.T. Medina  G.B. Gutierrez  R.R. Vargas 《International Journal of Mineral Processing》1974,1(4):335-345

Fine-size cassiterite can be recovered by a liquid-liquid extraction process using low molecular weight petroleum derivatives and Aerosol-22 as collector. Parameters investigated in this study were pH, collector concentration, and rate of agitation. Depending on agitation rate and collector concentration, rougher concentrates can be up-graded by single cleaning to about 9% tin with a recovery of approximately 78%. After a second cleaning step, recovery decreases to about 50%, while grade increases to about 14% tin. The average tin enrichment ratios (related to the feed) are 6 and 9.4 respectively.  相似文献   

Climatic change and quasi-oscillations in central-west Argentina summer precipitation: main features and coherent behaviour with southern African region   总被引：1，自引：0，他引：1  

R. H. Compagnucci  E. A. Agosta  W. M. Vargas 《Climate Dynamics》2002,18(5):421-435

Summer rainfall variability (October to March) shows inter-annual to multi-decadal fluctuations over a vast area of subtropical Argentina between 28°S–38°S and 65°W–70°W. Statistically significant oscillations of quasi-period in the bands of 18–21, 6, 4 and 2 years can be found throughout the region and intra-regionally, though the latter are variable. The lower frequency variation produces alternating episodes of above and below normal rainfall each lasting roughly 9 years. This quasi-fluctuation appears to be shared with the summer rainfall region of South Africa and were in-phase related one another until mid-1970s. The teleconnection between both subtropical regions could be generated by an atmospheric-oceanic bridge through the global sea surface temperatures (SSTs), particularly those of the equatorial-tropical South Atlantic. From mid-1970s, the alternating wet and dry pattern has been interrupted in the Argentine region producing the longest, as yet unfinished, wet spell of the century. Thus, a significant change of the long-term variation was observed around 1977 toward lower frequencies. Since then the statistical model that explains more than 89% of the variance of the series until 1977, diverges from the observed values in the 1980s and 1990s. In addition the Yamamoto statistical index, employed to detect a climatic jump, reaches its major value in 1973 at the beginning of the current long wet spell. Therefore the change could be located between 1973 and 1977. Application of the t-student's test gives significant differences of mean values for pre-1977 and post-1977 sub-samples from both individual time series and the regional index series. The spectral analysis also shows changes in energy bands in concordance with the features of the change that occurred from mid-1970s. The change gives rise to a significant increment of more than 20% in average of normal rainfall over the region. Conversely, a drought between mid-1980s and the 1990s has been observed in the South African counterpart with severe characteristics, thereby continuing the quasi-18-year oscillation. Consequently, the low-frequency coherent behaviour between both the Argentine and South African regions is lost from the mid-1970s. The analysis of association of wet/dry spells and warm/cold, El Niño/La Niña episodes appears to be not significant at scales of year-to-year variability although at decadal to multi-decadal scales the association could be relevant. More than one process of multi-decadal variability of global SSTs could influence the Argentine summer rainfall region and the former bi-decadal teleconnection. Finally, potential hypothetical factors of change are discussed, such as the strengthening of direct and indirect mechanisms of moisture flux transport associated with global warming, low-level atmospheric circulation changes and/or to SSTs mean condition long-term variations over tropical and subtropical South Atlantic and South Pacific oceans.  相似文献   

The Appinite-Migmatite Complex of Sanabria, NW Iberian Massif, Spain   总被引：1，自引：0，他引：1  

CASTRO  ANTONIO; CORRETGE  L. GUILLERMO; DE LA ROSA  JESUS D.; FERNANDEZ  CARLOS; LOPEZ  SUSANA; GARCIA-MORENO  OLGA; CHACON  HELENA 《Journal of Petrology》2003,44(7):1309-1344

The Sanabria appinitic rocks and host migmatites form an unusual,non-peri-batholithic complex in which all the typical membersof the appinite suite are present. It differs from most appiniticcomplexes in the deeper level of emplacement and the close temporaland spatial association with migmatites. Consequently, manyin situ relationships that resulted from the invasion of maficmagma into a crustal anatectic zone are extremely well preserved.The complex shows unequivocal relations between members of theappinitic suite and between these and migmatites derived byanatexis of a gneissic formation (Ollo de Sapo gneiss). Theserelations point to derivation of monzodiorites and biotite dioritesby hydrous basalt fractionation combined with fluid-assistedmelting of the crustal rocks surrounding the appinitic intrusions.This hydrous basic magma may be derived from an enriched regionof the mantle associated with subduction. Petrogenetic modelshave been tested using a combination of field relations andgeochemical data. Despite the complexity of the processes involved,it is concluded that water played an important role in the petrogenesisof the intermediate and mafic magmas. Reaction between monzodioritemelts and the host migmatites was responsible for the generationof a range of intermediate rocks within the complex. The needfor water to facilitate magma generation in both the mantleand the crust suggests that melting is linked with subduction.This interpretation has important implications because appiniticmagmatism may be considered as indicative of subduction processesinvolved not only in the generation of the mafic end-membersof the suite, but also in the generation of batholiths withwhich the appinitic rocks are spatially and temporally associated. KEY WORDS: appinite; monzodiorite; migmatite; Variscan orogen; Iberian massif  相似文献   

Book Review: Geostatistics Rio 2000, Quantitative Geology and Geostatistics : By M. Armstrong, C. Bettini, N. Champigny, A. Galli, and A. Remacre (eds.) Kluwer Academic Publishers, Dordrecht, 2002, 235 p., $94 (U.S.), ISBN 1-4020-0470-2 (hard back)     

J. A. Vargas Guzmán 《Mathematical Geology》2004,36(6):759-760

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Hydraulic behavior of tsunami backflows: insights from their modern and ancient deposits     

J. P. Le Roux  G. Vargas 《Environmental Geology》2005,49(1):65-75

Tsunamis are unpredictable, catastrophic events, and so present enormous difficulties for direct studies in the field or laboratory. However, their sedimentary deposits yield evidence of a wide variety of hydrodynamic conditions caused by flow transformations on a spatial and temporal scale. Tsunami deposits ranging from the Miocene to modern times identified at different localities along the Chilean coast are described to provide a database of their characteristics. Among the typical features associated with tsunami deposits are well-rounded megaclasts eroded from coastal alluvial fans or beaches by very dense, competent flows. Sand injections from the base of these flows into the substrate indicate very high dynamic pressures, whereas basal shear carpets suggest hyperconcentrated, highly sheared flows. Turbulence develops in front of advancing debris flows, as indicated by megaflutes at the base of scoured channels.  相似文献   

Monitoring runoff coefficients and groundwater levels using data from GRACE,GLDAS, and hydrometeorological stations: analysis of a Colombian foreland basin     

Diana L. Ospina M.  Carlos A. Vargas J. 《Hydrogeology Journal》2018,26(8):2769-2779

The determination of space–time variation in groundwater accumulation in Colombia’s Eastern Llanos foreland basin from 2003 to 2014 was done using terrestrial water storage (TWS) anomalies identified in two versions of the Gravity Recovery and Climate Experiment (GRACE) data—from the Global Data Center for Space Research (CSR) at the University of Texas at Austin (USA) and from the Institute of Geodesy at the Graz University of Technology (ITSG, Austria)—and also soil moisture storage (SMS) data from the Global Land Data Assimilation System (GLDAS). These data were compared to changes in groundwater storage obtained using the water-budget equation, calculated based on recorded data from hydrometeorological stations. This study confirmed the viability of using satellite information to understand and monitor temporal variation in groundwater recharge in the study area. Temporal variations in TWS, SMS, and groundwater level were shown to correspond to regional rain and drought periods, which are sensitive to climate phenomena such as El Niño and La Niña. Comparing changes in TWS and groundwater level to changes in infiltration and recharge revealed correlation coefficients of 0.56 and 0.98 with CSR data and 0.71 and 0.86 with ITSG data, respectively.  相似文献   

Experimental Constraints on Hercynian Anatexis in the Iberian Massif, Spain   总被引：13，自引：4，他引：9  

CASTRO  ANTONIO; GUILLERMO CORRETGE  L.; EL-BIAD  MOHAMMED; EL-HMIDI  HASSAN; FERNANDEZ  CARLOS; PATINO DOUCE  ALBERTO E. 《Journal of Petrology》2000,41(10):1471-1488

We have studied experimentally the melting relationships ofthe Ollo de Sapo gneiss (OSG), an important crustal protolithfor the Iberian leucogranites, of possible volcanoclastic origin.The results of this study are compared with previously determinedPTt paths, allowing us to interpret the mechanisms of meltingand granitoid production during the Hercynian orogenic cycle.Phase relationships determined in fluid-absent experiments indicatethat the OSG is a fertile source for peraluminous leucogranites.The slope of the fluid-absent solidus is strongly controlledby the breakdown of Ms in the presence of Qtz, Pl and Kfs. Thissolidus curve has a positive slope ranging from dP/dT = 30 bar/°Cat low P (<6 kbar) to dP/dT = 70 bar/°C at higher P (6–15kbar). The relationships between the Ms vapour-absent solidusand the PTt metamorphic paths in different sectors of the Iberianmassif have two important implications: (1) melt productivityis strongly favoured at low P; (2) anatexis in the Iberian massifprobably took place by decompression associated with crustalthinning and extension. These results are in agreement withthe relationships between granite production and tectonic deformationphases observed in the Iberian massif. Our results emphasizethat anatexis is a process that is strongly controlled bothby the phase relationships of the crustal protoliths and bythe thermal structure of the continental crust. Consequently,one must be careful when assigning potential crustal protolithsto particular granite associations exclusively on the basisof geochemical comparisons. KEY WORDS: anatexis; Hercynian orogen; Iberian massif  相似文献   

Analyses of bottom simulating reflections offshore Arauco and Coyhaique (Chile)   总被引：1，自引：1，他引：0  

Ivan de la Cruz Vargas Cordero  Umberta Tinivella  Flavio Accaino  Maria Filomena Loreto  Francesco Fanucci  Christian Reichert 《Geo-Marine Letters》2010,30(3-4):271-281

Two seismic sections offshore Arauco and Coyhaique, Chile, have been analysed to better define the seismic character of hydrate-bearing sediments. The velocity analysis was used to estimate the gas-phase concentration, which can serve to correlate hydrate presence to the geological features. The velocity model allowed us to recognise the hydrate layer above the bottom simulating reflector (BSR), and the free gas layer below it. The velocity field is affected by strong lateral variation, showing maximum (above the BSR) and minimum (below the BSR) values in the southern sector. Here, highest gas hydrate and free gas concentrations were calculated (15% and 2.7% of total volume respectively). The estimated geothermal gradient ranges from 35 to 95°C/km. In the northern sector, the highest gas hydrate and free gas concentrations are 15% and 0.2% of total volume respectively, and the geothermal gradient is uniform and equal to about 30°C/km.  相似文献   

Internal vein texture and vein evolution of the epithermal Shila-Paula district,southern Peru     

Alain?ChauvetEmail author  Laurent?Bailly  Anne-Sylvie?André  Patrick?Monié  Daniel?Cassard  Fernando?Llosa?Tajada  Juan?Rosas?Vargas  Johann?Tuduri 《Mineralium Deposita》2006,41(4):387-410

The epithermal Shila-Paula Au–Ag district is characterized by numerous veins hosted in Tertiary volcanic rocks of the Western Cordillera (southern Peru). Field studies of the ore bodies reveal a systematic association of a main E–W vein with secondary N55–60°W veins—two directions that are also reflected by the orientation of fluid-inclusion planes in quartz crystals of the host rock. In areas where this pattern is not recognized, such as the Apacheta sector, vein emplacement seems to have been guided by regional N40°E and N40°W fractures. Two main vein-filling stages are identified. stage 1 is a quartz–adularia–pyrite–galena–sphalerite–chalcopyrite–electrum–Mn silicate–carbonate assemblage that fills the main E–W veins. stage 2, which contains most of the precious-metal mineralization, is divided into pre-bonanza and bonanza substages. The pre-bonanza substage consists of a quartz–adularia–carbonate assemblage that is observed within the secondary N45–60°W veins, in veinlets that cut the stage 1 assemblage, and in final open-space fillings. The two latter structures are finally filled by the bonanza substage characterized by a Fe-poor sphalerite–chalcopyrite–pyrite–galena–tennantite–tetrahedrite–polybasite–pearceite–electrum assemblage. The ore in the main veins is systematically brecciated, whereas the ore in the secondary veins and geodes is characteristic of open-space crystallization. Microthermometric measurements on sphalerite from both stages and on quartz and calcite from stage 2 indicate a salinity range of 0 to 15.5 wt% NaCl equivalent and homogenization temperatures bracketed between 200 and 330°C. Secondary CO₂-, N₂- and H₂S-bearing fluid inclusions are also identified. The age of vein emplacement, based on ⁴⁰Ar/³⁹Ar ages obtained on adularia of different veins, is estimated at around 11 Ma, with some overlap between adularia of stage 1 (11.4±0.4 Ma) and of stage 2 (10.8±0.3 Ma). A three-phase tectonic model has been constructed to explain the vein formation. Phase 1 corresponds to the assumed development of E–W sinistral shear zones and associated N60°W cleavages under the effects of a NE–SW shortening direction that is recognized at Andean scale. These structures contain the stage 1 ore assemblage that was brecciated during ongoing deformation. Phase 2 is a reactivation of earlier structures under a NW–SE shortening direction that allowed the reopening of the preexisting schistosity and the formation of scarce N50°E-striking S2-cleavage planes filled by the stage 2 pre-bonanza minerals. Phase 3 coincides with the bonanza ore emplacement in the secondary N45–60°W veins and also in open-space in the core of the main E–W veins. Our combined tectonic, textural, mineralogical, fluid-inclusion, and geochronological study presents a complete model of vein formation in which the reactivation of previously formed tectonic structures plays a significant role in ore formation.  相似文献   

Life inhabits rocks: clues to rock erosion from electron microscopy of pisolite at a UNESCO heritage site in Brazil     

Kazue Tazaki  Ryuji Asada  Zara Gerhardt Lindenmayer  Tatsuya Shirotori  Juliana Missiaggia Vargas  Carlos Henrique Nowatzki  Osmar Wöhl Coelho 《International Journal of Earth Sciences》2009,98(1):227-238

Rock erosion is attracting increasing attention from scientists worldwide. The area encompassing the Saint John Baptist Church, Saint John Village, XVII century ruins in Rio Grande do Sul at the UNESCO World Heritage Site is considered a Brazilian treasure. However, the risk of damage to this site from rock erosion has recently increased tremendously. Generally, the rocky construction such as fence, wall and tomb stone, seems strong but is actually extremely sensitive to erosion caused by lichens, fungi, molds and bacteria. Because of biological erosion and massive exposure, the fresh rock is dominated by clays and microorganisms. Water-adsorbing clays and microorganisms influence the mechanisms of the rock erosion. In this study, the formation of bio-clay-minerals in porous structure of pisolite was demonstrated using electron microscopy. Bacterial clay mineralization can deform the rock structure and even produce organic materials. Biological activity could easily corrode rocky constructions around the Saint John Baptist Church site. The rocks are pisolitic laterites possibly formed in Tertiary over the Kretaceous Parana flood Basalts. Samples inhabited by lichens and fungi were collected from a collapsed wall in the ancient church. The zonal reddish-brown pisolites are 4 mm in diameter in a matrix of clays associated with porous and empty spaces. Elemental distribution maps from X-ray fluorescence microscopy show iron-rich spherules of pisolite, whereas the matrix is composed of Al, Si, Mn, and Sr; thus producing goethite and kaolinite. Transmission electron microscopic observation showed that various types of bacteria inhabit the spherule and are associated with clay minerals and graphite. STEM elemental analysis confirmed the bio-clay-mineralization with Al, Si, S, and Fe, around bacterial cells. The results presented here will improve our understanding of nm-scale bio-mineralization and bio-erosion in lateritic rocks. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.  相似文献