1,721,075 research outputs found
Fluid-rock interaction and gold deposition within a late archaean shear zone, Dalny Mine, Zimbabwe
No full textGold mineralisation at the Dalny Mine, Zimbabwe, is restricted to a brittle-ductile shear zone which transects a sequence of late Archaean (2.7 Ga) Fe-rich tholeiitic basalts and minor intercalated sediments. The lithological associations, together with some preliminary geochemical analyses suggest that the sequence was probably deposited in a marginal basin above a subduction zone. The Dalny shear zone, which extends NE-SW for approximately 10km, was initiated as a Reidel structure associated with dextral strike-slip displacement along the crustal-scale Lily fault zone interpreted here as a late Archaean terrane boundary. Subsequent regional deformation within the Chegutu-Kadoma greenstone belt resulted in upright folding and reverse compressional reactivation of the Dalny shear zone which dips 70o towards the north-east. The introduction of gold-bearing fluids during this deformational event resulted in a complex sequence of vein emplacement terminating in the development of widespread carbonate veins. Gold is restricted to three characteristic vein types at Dalny and is associated with abundant pyrite and arsenopyrite, together with accessory chalcopyrite, pyrrhotite, tetrahedrite, sphalerite, galena, bornite, tourmaline and scheelite. Gold primarily occurs as inclusions (up to 60μm diameter) within pyrite but also resides as native grains within fractures, and on the surface of pyrite. Gold was deposited from H_2O-CO_2 fluids (5-10 mole % CO_2) of low salinity (averaging 6.74 wt.% NaCl equiv.) and moderate density 0.97 ± 0.05g cm-3 under P-T conditions of 3.6 ±0.3 kbars and 390 ±20oC. Similar fluids have been identified from the adjacent Dawn and Arlandzer deposits implying that the auriferous fluids were of regional extent. The δ18O composition of the fluids estimated from δ18O chlorite analyses was 8.18 to 8.69% o δD compositions ranged from -12.3 to -17.7% _o. The δ34S composition of H_2S within the gold-bearing fluid probably ranged from 3.85 to 4.15% _o. The peak metamorphic timing of fluid introduction and the absence of associated magmatic intrusions combine with the stable isotope data to suggest a source for the fluids involving regional metamorphic dehydration of the mafic volcanic sequence at depth. Extensive fluid-rock disequilibrium at Dalny resulted in the formation of a zoned alteration assemblage distinguished by the extensive development of pyrite immediately adjacent to quartz vein margins, and an ankerite-muscovite assemblage which extends up to 3m from the mineralised zone. Muscovite-chlorite, and calcite-chlorite mineral assemblages are evident with increasing distance from the mineralised zone, the former being characterised by significant enrichments in K_2O, CaO, Ba and Rb together with a consequent depletion of Na_2O. The pH of the gold bearing fluid is estimated at 5.35 ± 0.55 whilst the log fO2 of the fluid has been constrained at -26.7 (at 390oC). The log fH2S of the fluid was 0.093 which is equivalent to 457ppm H2S assuming 6.7 mole% CO2. Gold deposition resulted from destabilisation of the AuHSo complex due to a decrease in the fS2 of the fluid accompanying sulphide precipitation. The widespread occurrence of later aqueous inclusions within quartz-carbonate veins at Dalny, indicates the occurrence of a late fluid of moderate salinity (9.33 wt.% NaCl equiv.) which was trapped at 275oC and 1.9 kbars. This fluid may have resulted from the protracted evolution of the earlier gold-bearing H2O-CO2 fluid.</p
An integrated packing-moisture control approach in bitumen-stabilized materials (BSM) design
Full text linkThe mechanical performance of bitumen-stabilized materials (BSM) hinges on two interrelated factors, including aggregate packing and moisture control. However, current design practices offer little guidance on how to systematically balance these variables. This study, therefore, proposes an integrated volumetric framework that couples the Bailey packing principles with a liquid-filled-voids (VFL) criterion to identify the optimum aggregate gradation and total water content for mixtures composed entirely of reclaimed asphalt pavement (RAP). Four gradations were manufactured by blending coarse and fine RAP to represent 60 %, 80 %, 90 %, and 100 % of their loose-unit-weight (LUW) packing states. Each blend was stabilized with a 3 % residual bitumen emulsion and total water dosages ranging from 3 % to 6 %. Compaction behaviour was captured through the dry density, voids filled with liquid (VFL), and voids in the mixture (Vm), which were monitored for up to 100 gyrations. In contrast, water loss due to compaction, long-term evaporation, and 56-day indirect tensile strength (ITS) were also assessed. Results indicate that the 80LUW gradation, combined with a total water dosage of 4 %-4.5 %, produced the densest internal structure (Vm ≈ 8.4 %) and maintained VFL at the 85 % threshold that prevents liquid seepage. In contrast, finer (60 %LUW) and coarser (90–100 %LUW) gradations exhibited excessive voids at comparable moisture levels. The proposed framework thus offers a practical way for selecting gradation–moisture combinations, reducing experimental repetition and advancing the sustainable use of BSMs
A multiple regression model for developing a rap binder blending chart for stiffness prediction
No full textThe increase in the use of Reclaimed Asphalt Pavement (RAP) makes it necessary to focus on the interaction between the old and the virgin binders represented by the so-called blending chart. Different types of linear binder blending chart are currently available to predict the characteristics of the final blend. This study constitutes part of a wider research campaign whose aim it is to provide prediction models for the rheological properties of RAP, taking into account a selection of variables that cause its heterogeneity. The objective of this paper is to provide a multiple regression model at medium and high temperatures for the prediction of the complex modulus and phase angle of binder blends. The models consider more than one variable at the same time: the type of virgin and aged binders, the percentage of aged binder, the loading frequency and the temperature. Thus, within a specific validity range based on the extreme values defined by the experimental domain, it is possible to predict the rheological properties of the binder blends, and to carry out a sensitivity analysis on the effects of each parameter
Impact of different ageing levels on binder rheology
No full textThis paper evaluates the variability of binder rheology for different ageing levels and the influence of ageing at different testing temperatures. Three different ageing levels were applied on a single type of bitumen with a penetration grade of 70/100.The artificial ageing of the binder was performed using the rolling thin-film oven test and the pressure ageing vessel. The rheological behaviour was investigated at low temperatures with the bending beam rheometer (BBR) and at medium and high temperatures with the dynamic shear rheometer (DSR). Several experiments were conducted to determine the range of stiffness and complex modulus results, the type of distribution comparing real and theoretical models, and the effects of ageing on the variability of the rheological behaviour. It was shown that not only the mean results from BBR and DSR tests change with ageing, but also the variability of the results changes with ageing. This would have an impact on mechanistic-empirical pavement design because it would influence the calculated stresses and strains as well as the calculated reliability
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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