U/Th-rich bitumen in Archean granites and Palaeoproterozoic metasediments, Rum Jungle Mineral Field, Australia: implications for mineralizing fluids

Uranium/thorium (U/Th)‐rich bitumen has been discovered within both Palaeoproterozoic black pelites and the Archean granitic basement of the Rum Jungle Mineral Field, Northern Territory, Australia. Granite‐hosted bitumen occurs as small (up to 400‐µm diameter) discrete individual nodules, which exhibit many morphological similarities to those observed in Phanerozoic siliciclastic rocks. Thorium, the dominant radioelement, occurs primarily as a hydrated Th–Y–Si–P phase. Uranium‐rich inclusions are rare, and correspond to a hydrated U–Th–Y–Si–P phase, identified as coffinite–thorogummite. Metasediment‐hosted bitumen is more variable in morphology, occurring as massive (<2 cm in width) veins that cross‐cut all foliations, as discrete individual nodules or as elongate seams (up to 500 µm in length), interpreted to represent a series of coalesced individual nodules. In all examples, uranium, the dominant radioelement in the metasediment‐hosted bitumen, is present as Th‐poor uraninite, with variable Y₂O₃ contents (up to 3.21 wt.%). Raman investigation of all types of bitumen indicates that it is a poorly organized carbonaceous matter, which has not been subjected to metamorphism. Consequently, a post‐metamorphic timing for hydrocarbon emplacement can be inferred and a magmatic origin can be precluded. Potential source rocks for the bitumen are black shales of the Whites Formation (up to 8 wt.% total organic carbon (TOC)) and the Koolpin Formation (approximately 13 wt.% TOC). Post‐metamorphic sericitization of rocks within the Whites Formation is accompanied by a near‐complete removal of organic matter. Alteration was possibly the catalyst for hydrocarbon generation. The Th–Y–Si–P phase within the granite‐hosted nodules is interpreted to be the result of the alteration of antecedent monazite. During this alteration, U, LREE and P were fractionated and removed, while Th, Y and Si remained immobile, and recombined to form a hydrated Th–Y–Si phase. This pervasive alteration within the basement U/Th‐rich granites is proposed as a genetic model for the formation of uranium deposits in the Rum Jungle Mineral Field and possibly unconformity associated uranium deposits on a global scale.     

Transient fluid flow in and around a fault

We present the results of simple numerical experiments in which we study the evolution with time of fluid flow around and within a permeable fault embedded in a less permeable porous medium. Fluid movement is driven by an imposed vertical pressure gradient. The results show that fluid flow is controlled by two timescales: τ_f = Sl²/κ_F and τ_F = Sl²/κ_M, where S is the specific storage of the porous material, l the length of the fault, and κ_M and κ_F are the hydraulic conductivities of the porous material and the fault, respectively. Fluid flow and the associated fluid pressure field evolve through three temporal stages: an early phase [t < τ_f] during which the initial fluid pressure gradient within the fault is relaxed; a second transient stage [τ_f < t < τ_F] when fluid is rapidly expelled at one end of the fault and extracted from the surrounding rocks at the other end leading to a reduction in the pressure gradient in the intact rock; a third phase [t < τ_F] characterized by a steady‐state flow. From the numerical experiments we derive an expression for the steady‐state maximum fluid velocity in the fault and the values of the two timescales, τ_f and τ_F. A comparison indicates excellent agreement of our results with existing asymptotic solutions. For km‐scale faults, the model results suggest that steady‐state is unlikely to be reached over geological timescales. Thus, the current use of parameters such as the focusing ratio defined under the assumption of steady‐state conditions should be reconsidered.     

Lost in the Mail: the Inherent Errors of Mapping Australia Post Postcodes to ABS Derived Postal Areas

It is now common practice, by users of geographic information, to link data held at the postcode level to that obtained from the national census. This paper examines the relationship between Australia Post (AP) postcodes and Australian Bureau of Statistics (ABS) derived postal areas — which are an approximation of the former based on aggregated census collection districts (CDs). A group of adjacent ABS postal areas in northwest Melbourne was compared with the true AP postcode areas they purported to represent and the discrepancies were investigated. Firstly, shape mismatches were studied and their potential impacts upon resource allocation decisions were assessed. Next, comparisons of areas were undertaken. It was found that, in established inner city urban areas, the two sets of boundaries were highly correlated. However, outer suburban neighborhoods were identified as being particularly prone to major areal discrepancies. The implications of mismatches between these two key boundary data sources may be severe, given that management decisions and the allocation of public and private resources are often based on spatial statistical analyses which use these data sets. The authors acknowledge ABS efforts in providing information at the levels of aggregation that society demands. The introduction of ABS postal areas data has undoubtedly facilitated the use of demographic data in many sectors; it has, however, also caused some problems, for instance, when users assume that ABS postal areas are identical to AP postcodes. These issues could easily be avoided with the inclusion of more comprehensive metadata documentation accompanying ABS data. Research is continuing to develop a method by which agencies may derive common boundaries for their administrative units, yet still meet their own individual data and sampling requirements.     

Geochemistry of the Bagnères-de-Bigorre thermal waters from the North Pyrenean Zone (France)

Thermal springs are poorly known in the sedimentary sites of the Pyrenees. In this paper, we describe the ‘Bagnères‐de‐Bigorre’ springs which occur in a remarkably active seismotectonic context. A chemical and isotopic study of 15 spring waters (both cold and thermal, ranging in temperature from 7.0 to 49.9°C), and continuous monitoring of a single spring allow us to characterise water–rock interactions, fluids paths and mixing processes. Three groups of waters are distinguished: (I) SO₄²⁺–Ca²⁺–Cl^– thermal waters (II) SO₄²⁺–Cl^––Ca²⁺ thermal waters and (III) HCO₃^––Ca²⁺ cold shallow waters. Their characteristics suggest interactions with Mesozoic evaporite and carbonate formations. O and D isotopes from thermal waters indicate a local meteoric origin of Atlantic signature and a recharge elevation of 800 to 1000 m, which corresponds to a single feeding area. Their δ¹³C values (?2.8 to ?9.6‰) are consistent with carbonate dissolution, slight fractionation and a surficial organic input leading to δ¹³C depletion. Sr isotopes (0.70751 to 0.70777), Na⁺/Cl^– and (Ca²⁺ + Mg²⁺)/SO₄^2– ratios as well as thermodynamic calculations show that the dissolution of anhydrite and halite‐bearing Triassic layers control the chemical composition of group‐I and ‐II waters. The contrasting trends of cation/Cl^– ratios and TDS of waters from groups I and II suggest the existence of two different circulation paths at depth as well as dilution with surficial waters similar to group III. Calculated mixing proportions show that three waters from group I are diluted from 17 to 66%, whereas all waters from group II are mixed. The aquifer temperature is estimated to be in the range 55–64°C using the retrograde and prograde solubilities of anhydrite and chalcedony, respectively. Accordingly, the mean depth of the reservoir is around 1.7 km, which allows us to constrain the depth of the Triassic layer.     

3. MENTALITY AS A SOCIAL EMERGENT: CAN THE ZEITGEIST HAVE EXPLANATORY POWER?1

This paper probes the explanatory value of mentality as a social emergent in general and of the Zeitgeist in particular. Durkheim's contention that social facts have emergent properties is open to the charge that it implies logically inconsistent “downward causation.” on the basis of an analogy with the brain‐mind dilemma and mental emergentism, the first part of the essay discusses and dismisses the notion of social emergent properties that cannot be reduced to the properties of their component parts—individuals—and their internal relations. However, ontological individualism need not compel us to methodological individualism. The second part introduces two challenges to methodological individualism. The most radical is Rajeev Bhargava's assertion that the meaning of a belief is determined not by the individual holding the belief but by the entire linguistic community. Bhargava's “contextualism” is closely related to the (post)structural demand that we focus on discourse as a communal entity instead of continuing a delusive quest for the intentions of individual speakers. a more modest alternative is Margaret Gilbert's plea for using “plural subjects”—social groups in which “participant agents” act jointly or have a jointly accepted view—in the practical syllogisms that are central to rationalizing action explanation. The notion of plural subjects lends credence to, and is reinforced by, “situationist” social psychology, which shows how people conform to peer groups, authorities, and roles. building on Wesley Salmon's and Peter Railton's ecumenical accounts of explanation, the essay argues that both individual rationalizing action explanations and explanations based on plural agents can give explanatory information: we need not choose one or the other. The third part discusses how the Zeitgeist can provide added explanatory value in an analysis of the New left. This is possible if the “spirit of the sixties” is seen as representing the values and worldviews of the “sixties generation” as a social group in Gilbert's terms. Radical youth would suspend judgment and pool their wills to conform to what they perceived were the views of the imagined “sixties community” or—rendering more explanatory force—to smaller parts of it in the guise of peer groups and organizations.     

Non-destructive chemical characterization of ceramic sherds from Shipwreck 31CR314 and Brunswick Town, North Carolina

The purpose of this study was to chemically and texturally characterize ceramic oil jar sherds from North Carolina Shipwreck 31CR314 and to explore the utility of environmental scanning electron microscopy/X-ray energy dispersive spectrometry (SEM/EDS) for that purpose. The oil jar sherds, widely dispersed about Shipwreck 31CR314, are morphologically similar to each other, which suggests they could be from a single jar, but with so few joins this could not be concluded with certainty. Therefore, an aim of this study was to investigate whether chemical or textural characterization of the sherds might reveal unique attributes that could distinguish individual jars; results of characterization perhaps could give information on their origin and possibly site formation processes, such as whether environmental forces could have scattered sherds of a single jar during and after sinking of the ship. Previous studies have indicated this shipwreck is likely the remnants of the Queen Anne's Revenge, flagship of the pirate Blackbeard. Sherds from this shipwreck were compared with similar oil jar sherds excavated from a land site, Brunswick Town, North Carolina, to explore the use of composition and texture as hallmarks. The chemical components of the artifacts were determined by SEM/EDS. This method of analysis is valuable for archaeological research because it is rapid and non-destructive to the ceramic artifacts. Both groups of lead-glazed coarse red earthenware sherds were texturally similar except for the glazed sides of all 31CR314 sherds that exhibited small tracks of unique crescent-shaped marks. These marks may be due to manufacturing effects and immersion in seawater, and the marks may serve as hallmarks for individual jars or potentially individual manufacturers. The sherds were generally similar in composition, but the two groups exhibited distinct differences. Brunswick Town sherds consistently contained more phosphate on unglazed sides, an average 1.46 wt.% P₂O₅, and also contained trace elements not detected in the Shipwreck 31CR314 sherds. These distinct differences could be due to different manufacturing origins for Shipwreck 31CR314 and Brunswick Town ceramics but also could reflect their subjection to different environments during use and loss prior to archaeological recovery.     

Sample-specific (universal) metric approaches for determining the sex of immature human skeletal remains using permanent tooth dimensions

In this paper, three approaches for developing sample-specific sex determination methods of immature skeletal remains based on permanent tooth dimensions are proposed and tested using a sample of identified skeletons. The sample comprises adult and subadult individuals selected from the Lisbon documented skeletal collection, housed at the National Museum of Natural History in Lisbon, Portugal. Faciolingual and mesiodistal diameters were the tooth dimensions utilized. In the first approach, sex-specific logistic regression formulae based on adult tooth dimensions are developed and then used to determine the sex of the subadult sample. The second and third approaches are based on the sectioning point procedure, which uses the overall mean of a measurement (tooth diameter) collected from the sample as the discriminant criteria for determining the sex of the individuals in that sample. While in the second approach the adult overall mean of each dimension is used as the discriminant criteria for determining the sex of the subadults, in the third approach it is the subadult overall mean of each dimension that comprises the discriminant criteria that is applied back to the subadults for determining sex. Results show that the canines are the teeth with the highest sexual dimorphism and methods of sex determination based on canine dimensions provide correct allocation accuracies between 58.8% and 100% depending on the diameter and the approach that is being used. Canine faciolingual dimensions provide the best overall results. Combinations of measurements from the same and different teeth do not increase significantly the accuracy of the methods and approaches. Some of the problems of subadult sex determination methods based on adult tooth dimensions result from differing levels of sexual dimorphism between the adult and subadult segment of the sample. Mortality or cultural bias may increase or decrease the sexual dimorphism of the subadults compared to the adults. Small subadult samples utilized in this study may also raise questions regarding the accuracy of the three different sample-specific approaches. However, high consistency of results using the canine and different approaches, suggests that adult and subadult canine dimensions can be reliable sex discriminators of immature skeletal remains in archaeological samples. The major advantage of the approaches presented here is that they can be used to derive sample-specific methods and, therefore, eliminate the problem of applying morphological or metric methods to individuals originating from a population that differs from the one that contributed to the development of the method.