SHRIMP U–Pb ages of diagenetic and hydrothermal xenotime from the Archaean Witwatersrand Supergroup of South Africa

SHRIMP dating of xenotime overgrowths on detrital zircon grains can constrain maximum durations since diagenesis and therefore provide minimum dates of sediment deposition. Thus, xenotime dating has significant economic application to Precambrian sediment-hosted ore deposits, such as Witwatersrand Au–U, for which there are no precise depositional ages. The growth history of xenotime in the Witwatersrand Supergroup is texturally complex, with several phases evident. The oldest authigenic xenotime ²⁰⁷Pb/²⁰⁶Pb age obtained in sandstone underlying the Vaal Reef is 2764 ± 5 Myr (1 σ), and most likely represents a mixture of diagenetic and hydrothermal growth. Nevertheless, this represents the oldest authigenic mineral age yet recorded in the sequence and provides a minimum age of deposition. Other xenotime data record a spread of ages that correspond to numerous post-diagenetic thermotectonic events (including a Ventersdorp event at ≈ 2720 Ma) up to the ≈2020 Ma Vredefort event.     

Anthropogenic trace metals in sediment and settling particulate matter on a high-energy continental shelf (Sydney,Australia)

The anthropogenic contribution of trace metals to settling particulate matter (SPM) and surficial sediments was determined on the high-energy continental shelf adjacent to Sydney, Australia. Settling particulate matter and surficial sediment was collected in the vicinity of a major sewage outfall and at five control sites on the middle shelf (80-100 m water depth). Sediment traps were deployed on 10 occasions for up to 2 weeks during the summer and winter of 1995 and SPM was analyzed for Ag, Co, Cr, Cu, Fe, Mn, Ni, Pb and Zn. Cobalt, Fe, Mn and Ni act conservatively in SPM and in sediments regionally and are used as normalizing elements to determine anthropogenic enrichment. Surficial sediments and SPM are enriched in Ag, Cr, Cu, Pb and Zn near a major ocean outfall and at four of the five control sites, although sewage particles contribute < 5% of trace metals in the total sample. Silver is the most sensitive trace metal tracer for establishing the presence of sewage particulate matter. Sewage particulate matter flux near the outfall was estimated using a two end-member mixing model and is below 0.5 g m(-2) day(-1) during all deployment periods. The mean sewage particulate matter flux at sampling locations 30 km and 60 km north of the outfall are <0.13 g m(-2) day(-1) and <0.01 g m(-2) day(-1), respectively, indicating an efficient dispersal of anthropogenic material on this high energy continental shelf.     

Storms and shoreline retreat in the southern Gulf of St. Lawrence

Storms play a major role in shoreline recession on transgressive coasts. In the southern Gulf of St. Lawrence (GSL), southeastern Canada, long-term relative sea-level rise off the North Shore of Prince Edward Island has averaged 0.3 m/century over the past 6000 years (>0.2 m/century over 2000 years). This has driven long-term coastal retreat at mean rates >0.5 m/a but the variance and details of coastal profile response remain poorly understood. Despite extensive sandy shores, sediment supply is limited and sand is transferred landward into multidecadal to century-scale storage in coastal dunes, barrier washover deposits, and flood-tidal delta sinks. Charlottetown tide-gauge records show mean relative sea-level rise of 3.2 mm/a (0.32 m/century) since 1911. A further rise of 0.7±0.4 m is projected over the next 100 years. When differenced from tidal predictions, the water-level data provide a 90-year record of storm-surge occurrence. Combined with wind, wave hindcast, and sea-ice data, this provides a catalogue of potentially significant coastal storms. We also document coastal impacts from three recent storms of great severity in January and October 2000 and November 2001. Digital photogrammetry (1935–1990) and shore-zone surveys (1989–2001) show large spatial and temporal variance in coastal recession rates, weakly correlated with the storm record, in part because of wave suppression or coastal protection by sea ice. Large storms cause rapid erosion from which recovery depends in part on local sand supply, but barrier volume may be conserved by washover deposition. Barrier shores with dunes show high longshore and interdecadal variance, with extensive multidecadal healing of former inlet and overwash gaps. This reflects recovery from an episode of widespread overwash prior to 1935, possibly initiated by intense storms or groups of storms in the latter half of the 19th century. With evidence from the storms of 2000–2001, this points to the importance of storm clustering on scales of weeks to years in determining erosion vulnerability, as well as the need for a long-term, large-scale perspective in assessing coastal stability. The expected acceleration in relative sea-level rise, together with projections of increasing storm intensity and greatly diminished winter ice cover in the southern GSL, implies a significant increase in coastal erosion hazards in future.     

Placing sexuality in health policies: feminist geographies and public health nursing

Despite the increasing public profile of same-sex issues, health policies are often shaped by heteronormative assumptions. The health concerns of lesbian, gay, bisexual, transsexual/transgender, two-spirit, intersex, queer and questioning (LGBTTTIQQ) people are complex and require broadening from an often exclusively sexual health and risk focus to a more holistic approach. In this context, this paper illustrates how a critical feminist geography of health, with its focus on the mutual construction of gender relations, space and place, potentially enhances and extends current understandings of public health policy and practice. Moreover, the use of a policy lens foregrounding gender and other power relations suggests that feminist research and coalitions facilitate participatory processes that address “the politics of discourse.” In particular, public health nursing practice can enhance the construction of spaces of resistance that challenge heteronormative discourse through research strategies focused on sexual minority communities’ health experiences and their visions for supportive care. In this respect, two strategies consistent with public health priorities to increase knowledge and participate in alliances are described. Ethnographic research with childbearing lesbians demonstrates that attention to institutional dynamics that foster safe spaces can facilitate access to public health services. Public health nurses’ involvement in community coalitions can enhance dissemination of community knowledges. The implications for gender inclusive and place-sensitive public health nursing practice include the development of sensitive educators, meaningful educational curriculum and related program planning, explicit policies, community partnerships and political leadership in institutional and research venues.     

Gold mining in Ghana's forest reserves: a report on the current debate

This paper examines the debate surrounding a recent decision made by the Ghanaian government to permit gold exploration – and potentially, mining – in 'protected' forest reserves. In 2001, four mining companies were awarded mineral exploration concessions in forested regions of the country, and have since put forward applications to mine for gold. Notwithstanding the sharp divide in opinion on the issue, the continued uncertainty surrounding the implications of the proposed activities makes further research on the ground imperative in the short term. Work aiming to elicit indigenous perspectives on the projects, as well as research that facilitates dialogue between and/or among stakeholder parties, should be prioritized.     

The environmental impact of small-scale gold mining in Ghana: identifying problems and possible solutions

This paper examines the environmental impacts of small-scale gold mining in Ghana, and prescribes a series of recommendations for improving environmental performance in the industry. Since the enactment of the Small Scale Gold Mining Law in 1989, which effectively legalized small-scale gold mining in the country, industrial operations, collectively, have made important contributions to national gold output, foreign exchange earnings and employment. Accompanying this pattern of socio-economic growth, however, have been increased environmental complications – namely, mercury pollution and land degradation. The Ghanaian Minerals Commission has been burdened with most of the jurisdictional responsibilities related to small-scale mining, but with a staff of only 35–40 people working with a pool of highly obsolete research resources, it is clearly incapable of facilitating sufficient environmental improvement on its own. It is concluded that marked environmental improvements can only be achieved if: (1) assistance is provided to the Minerals Commission from local governmental bodies and academic units; (2) industry-specific environmental management tools and strategies are designed and implemented; (3) concerted effort is made to prospect for deposits suitable for small-scale gold mining, a key to preventing unnecessary exploration; and (4) a nation-wide industrial mercury study is commissioned, and a mercury retorting programme is implemented.     

A statistical approach to evaluating distance metrics and analog assignments for pollen records

The modern analog technique typically uses a distance metric to determine the dissimilarity between fossil and modern biological assemblages. Despite this quantitative approach, interpretation of distance metrics is usually qualitative and rules for selection of analogs tend to be ad hoc. We present a statistical tool, the receiver operating characteristic (ROC) curve, which provides a framework for identifying analogs from distance metrics. If modern assemblages are placed into groups (e.g., biomes), this method can (1) evaluate the ability of different distance metrics to distinguish among groups, (2) objectively identify thresholds of the distance metric for determining analogs, and (3) compute a likelihood ratio and a Bayesian probability that a modern group is an analog for an unknown (fossil) assemblage. Applied to a set of 1689 modern pollen assemblages from eastern North America classified into eight biomes, ROC analysis confirmed that the squared-chord distance (SCD) outperforms most other distance metrics. The optimal threshold increased when more dissimilar biomes were compared. The probability of an analog vs no-analog result (a likelihood ratio) increased sharply when SCD decreased below the optimal threshold, indicating a nonlinear relationship between SCD and the probability of analog. Probabilities of analog computed for a postglacial pollen record at Tannersville Bog (Pennsylvania, USA) identified transitions between biomes and periods of no analog.     

Mapping the Bonanza: Geographies of Mining Investment in an Era of Neoliberal Reform*

Geographic analyses of how national policies of economic liberalization influence global patterns of economic activity often draw their conclusions from studies of the paradigmatic sectors of manufacturing and, to a lesser extent, services. There is, by contrast, relatively little work examining how neoliberal policy reforms in the developing world may be driving changes in the geography of primary sector (i.e., extractive) activities at the global scale. This article presents and analyzes new data on direct investment in the international mining industry. It reports methods and results from a research project to systematically map and evaluate changes in the commodity mix and geographical spread of mining‐related investment in the world economy since 1990. It confirms and quantifies what was hitherto anecdotal evidence of a geographic shift in investment during the 1990s away from mature targets toward a small number of “rising stars” in the developing world, following the adoption in many countries of neoliberal economic policies from the mid‐1980s onward. However, the findings challenge conventional interpretations of this shift as an investment “bonanza” in the periphery and highlight how recent investment trends are highly specific in geographical scope, concentrated within a few commodities, and how the allocation of investment between established and emerging targets is variable over both time and space.     

The estimation of shear-wave statics using in situ measurements in marine near-surface sediments

Shear‐wave statics in marine seismic exploration data are routinely too large to be estimated using conventional techniques. Near‐surface unconsolidated sediments are often characterized by low values of V_s and steep velocity gradients. Minor variations in sediment properties at these depths correspond to variations in the shear‐wave velocity and will produce significant static shifts. It is suggested that a significant proportion of the shear‐wave statics solution can be estimated by performing a separate high‐resolution survey to target near‐surface unconsolidated sediments. Love‐wave, shear‐wave refraction and geotechnical measurements were individually used to form high‐resolution near‐surface shear‐wave velocity models to estimate the shear‐wave statics for a designated survey line. Comparisons with predicted statics revealed that shear‐wave statics could not be estimated using a velocity model predicted by substituting geotechnical measurements into empirical relationships. Empirical relationships represent a vast simplification of the factors that control V_s and are therefore not sufficiently sensitive to estimate shear‐wave statics. Refraction measurements are potentially sensitive to short‐wavelength variations in sediment properties when combined with accurate navigational data. Statics estimated from Love‐wave data are less sensitive, and sometimes smoothed in appearance, since interpreted velocity values represent an average both laterally and vertically over the receiver array and the frequency–depth sensitivity range, respectively. For the survey site, statics estimated from near‐surface irregularities using shear‐wave refraction measurements represent almost half the total statics solution. More often, this proportion will be greater when bedrock relief is less.