A Synthetic Haematite Reference Material for LA‐ICP‐MS U‐Pb Geochronology and Application to Iron Oxide‐Cu‐Au Systems

In both nature and synthetic experiments, the common iron oxide haematite (α‐Fe₂O₃) can incorporate significant amounts of U into its crystal structure and retain radiogenic Pb over geological time. Haematite is a ubiquitous component of many ore deposit types and, therefore, represents a valuable hydrothermal mineral geochronometer, allowing direct constraints to be placed on the timing of ore formation and upgrading. However, to date, no suitable natural haematite reference material has been identified. Here, a synthetic haematite U‐Pb reference material (MR‐HFO) is characterised using LA‐ICP‐MS and ID‐TIMS. Centimetre‐scale ‘chips’ of synthesised α‐Fe₂O₃ were randomly microsampled via laser ablation‐extraction and analysed using ID‐TIMS. Reproducible U/Pb and Pb/Pb measurements were obtained across four separate chips (n = 13). Subsequently, an evaluation of the suitability MR‐HFO in constraining U‐Pb data via LA‐ICP‐MS is presented using a selection of natural samples ranging from Cenozoic to Proterozoic in age. The MR‐HFO normalised U‐Pb ratios are more concordant and ages more accurate versus the same LA‐ICP‐MS spot analyses normalised to zircon reference material, when compared with independently acquired ID‐TIMS data from the same natural haematite grains. Results establish MR‐HFO as a suitable reference material for LA‐ICP‐MS haematite U‐Pb geochronology.     

Phytoplankton functional groups: Short‐term variation in a tropical tidal‐forced estuarine system

Functional groups have become an important tool for characterizing communities of marine and estuarine environments. Their use also holds promise for a better understanding of the temporal dynamics of phytoplankton. This study aimed to evaluate the contributions of phytoplankton size fractions and functional groups characterizing short‐term variation throughout tidal cycles and between dry and rainy seasons in a tropical estuarine system. Camamu Bay is an oligotrophic estuarine system that is under strong influence from tropical shelf waters and is characterized by high salinity and low concentrations of dissolved nutrients. Surface‐water samples were collected at nine sampling sites distributed among the three hydrodynamic regions of the bay, and at a mooring, at 3‐hr intervals during tidal cycles (12 hr each) in both the rainy and the dry season. Although the abundances of the phytoplankton fractions (pico‐, nano‐, and micro‐) were higher in the rainy season and during periods of higher tide, they were not significantly higher. The phytoplankton community in the bay comprises three functional groups: GI = “colonial” (i.e., chain‐forming diatoms and filamentous cyanobacteria); GII = “GALD >40” (i.e., pennate and centric diatoms with MDL >40 µm), and GIII = “flagellates” (i.e., species with motility via flagella). Nanoflagellates were the most abundant form in the bay, while chain‐forming diatoms, in particular, contributed to the microphytoplankton fraction during both the rainy and dry seasons. Functional groups, as defined by cluster analysis, reflected ecological strategies compatible with the high hydrodynamics of Camamu Bay, which is characterized by processes of tidal‐forced intense mixing, mainly during periods of spring tides. The phytoplankton of the bay was found to possess a series of attributes (functional traits) that endow them with some resistance to sinking. Functional diversity indexes (FEve, FDiv, and FDis) indicated a stable community without significant short‐term variation due to low variability in the environmental conditions of the system during the study period.     

Influence of relative density of the granular base soil on filter performance

Perpendicular contact erosion due to poorly designed filters is a frequent hazard for water-retaining structures serving as lifeblood to the community. This phenomenon occurs when the fine particles of a base soil at the contact interface with a coarser material are detached and transported through pores formed by the coarse particles. Therefore, most filter design criteria focus on the gradation of coarse particles or the gradation of pore constrictions. Meanwhile, the parameters of the base soil, such as relative density, are often overlooked. On the one hand, some experts neglect the impact of relative density because perpendicular contact erosion occurs at the interface, where fine particles expose themselves to larger pores. On the other hand, it is a general belief that the more compacted a base soil is, the less susceptible it will be to erosion as the seepage is reduced. This paper discusses this dilemma from a mutual perspective which assesses the influence of relative density from experimental, numerical, and analytical standpoints. The experimental study reveals that there is an optimal relative density which will release the least eroded mass. The influence is crucial as it can change the status of stability to unstable. The physical essence of the phenomenon is expressed by a numerical study at the micro-scale, which investigates the redistribution of flow lines and stress resulting from a particle detachment. The discovery at the micro-scale is confirmed by an analytical evaluation at the macro-scale, which assesses the redistribution of pore constrictions.

     

The Asosa region of western Ethiopia: a golden exploration opportunity

Gold mining has a legendary history in Ethiopia, with Ethiopian mines providing gold to the ancient Egyptian empire and possibly even King Solomon's Mines and the Queen of Sheba. Today, gold occurs in the Pan‐African age schist belt and Tertiary basaltic lavas of the Asosa region of Benishangul‐Gumuz, western Ethiopia. There is widespread artisanal gold production in the Asosa region, with moderate activity by small numbers of local workers producing relatively large amounts of gold. There is a strong relationship between predominantly shear zone‐hosted gold deposits and the Kuluck shear zone, suggesting a structural control on gold accumulation. Gold is also commonly associated with secondary sulphide mineralization and magnetite alteration in Asosa rocks. The source of the gold is thought to be the sub‐volcanic intrusions generated during the subduction of the oceanic crust at the trench island‐arc system, akin to what we see today in epithermal and porphyry type gold systems. Historical workings and anomalous gold concentrations in rock, soil and stream sediments point to a potentially significant untapped gold resource in the Asosa region of western Ethiopia.     

Securing supply: governing drinking water in the Northern Territory

ABSTRACT

This article considers the spatial and material implications of drinking water regulation in the Northern Territory (NT) of Australia. Responding to water contamination and scarcity events in remote NT communities, we argue that the politico-bureaucratic edifice of uniform drinking water governance and service provision across the NT is a state-curated fiction. The article outlines the available legislative protections for drinking water supply in the NT, which include minimum quality standards, water allocation mechanisms, testing regimes, and so on. These are shown to vary significantly between geographic locations and we argue that this produces a racialised ‘archipelago’ of differentiated islands of drinking water governance (Bakker 2003. “Archipelagos and Networks: Urbanization and Water Privatization in the South.” The Geographical Journal 169 (4): 328–341). Using the Gulf country town of Borroloola as a case study, the article then examines the colonial and land rights bases of this spatial variegation, and its significance for drinking water infrastructure provision and remediation. In doing so, we consider how the entropic materialities of ageing infrastructures work to further confound effective drinking water regulations and their practical enactments. The article argues that it is crucial to understand the limits of drinking water regulation in the NT, in order to elucidate the racialised distribution of potential environmental harms, and to mitigate further toxic inheritances.     

Analysis of ground motions at Treasure Island site during the 1989 Loma Prieta earthquake

Site response analyses and coherence studies were conducted at the Treasure Island site where surface motions were recorded during the Loma Prieta earthquake. The analyses were conducted using a nonlinear dynamic effective stress method which took into account the effects of the liquefaction that occured at the site. The rock motions recorded at nearby Yerba Buena Island were used as input motions. Computed and recorded ground motions transverse to the direction of wave propagation and associated response spectra were in good agreement. Agreement was also good in the radial direction, except in certain frequency bands higher than 1·25 Hz. Coherence studies showed that some of these discrepancies may be due to low coherence between the Treasure Island and Yerba Buena motions in these same frequency bands.     

Experimental and numerical study of hygro-thermo-mechanical properties of “Schilfsandstein” from Baden-Württemberg

In the present paper the results of experimental and numerical investigations of hygro-thermo-mechanical properties of “Schilfsandstein” from Baden-Württemberg are presented and discussed. The aim of the study was to investigate the influence of extreme environmental conditions causing severe damage that can often be observed on various monuments during restoration and reconstruction process. In the experimental investigations the stone specimen was exposed to extreme hygro-thermal conditions, which caused significant damage (cracking). During the experiment the ultrasonic and acoustic emission analyses were performed. Subsequently, a 3D finite element analysis was carried out using a coupled hygro-thermo-mechanical model for stone. The experimental and numerical results indicate that wetting in combination with either decrease or increase of temperature lead to severe damage. The most critical locations for initialization of cracks are sharp spikes (notches), or acute angles that are inward or outward oriented (corners). Stiff but brittle layers, like late diagenetic iron cementations, might be a weak point for the initialization of crack. Furthermore, the bedding direction (anisotropy) seems to be a preferred direction for crack propagation. The results of the numerical analysis are in relatively good agreement with experimental observations.     

Sequential sample reservoirs for Itrax-XRF analysis of discrete samples

Geochemical analysis of sediment samples can be used to characterize between- and within-lake variability and provide insights into lake chemistry, depositional processes and contamination sources. The number of samples for geochemical studies is restricted by cost, sample volume required, and the destructive nature of inductively coupled plasma mass spectrometry, instrumental neutron activation analysis, or wavelength dispersive x-ray fluorescence. Core scanners that incorporate energy dispersive x-ray fluorescence spectrometry, such as the Cox Itrax-XRF core scanner, have high through-put and can be used to produce high-quality geochemical datasets at low cost without destroying sample material. Here we describe a new analysis vessel that enables rapid, non-destructive Itrax-XRF analysis of discrete sediment samples.     

Foraminifera and tidal notches: Dating neotectonic events at Korphos,Greece

Fossil assemblages of foraminifera and thecamoebians from three salt-marsh cores recovered at Korphos, Greece, provided evidence for five transgression events since the mid Holocene. Marsh accretion rates based on radiocarbon-dated peat and geomorphic evidence from a series of discrete, v-shaped, submerged tidal notches indicated that these transgression events were rapid and episodic. Correlation of the tidal notches with the transgression horizons in the salt-marsh stratigraphy revealed a stepwise pattern of relative sea-level change at Korphos, which is best explained by coseismic subsidence related to fault displacement (earthquakes) associated with the Hellenic subduction zone. A comparison between the Korphos data and a model of Holocene sea-level change for the Peloponnesus reinforces this interpretation as sea-level rose in a series of jumps by amounts greater than accounted for by eustatic and glacio-hydro-isostatic factors (up to ~ 2.0 m). This study illustrates that by combining microfossil, sedimentary and geomorphic records of past sea-level change, problems frequently encountered with each record individually (e.g. dating submerged notches and autocompaction of marsh sediments) may be overcome.