Geochemical dispersion in wallrocks associated with the Norbec deposit, Noranda, Quebec

Increasing emphasis is being given to the search for blind mineral deposits and the presence of geochemical dispersion halos in wallrocks may significantly enhance the chances of exploration success. Accordingly, the nature of wallrock dispersion associated with the Lake Dufault Cu-Zn-Au-Ag massive sulphide deposit, Noranda, Quebec, was examined to see if any such patterns existed. On the basis of relatively well defined geology, the area offered an opportunity to establish the relation between geochemical alteration and metallogeny, texture, structure and mineralogy.Anomalous element contents spatially related to mineralization are confined to the stratigraphic footwall (Waite Rhyolite) where Na₂O, SiO₂ and possibly CaO depletions and total Fe₁ Mn and MgO enrichments can be related to the hydrothermal vent. Dispersion halos 150–500 m in diameter are at least twice as wide as the obvious mineralogical alteration halo. Cu, Zn, Ag and S distributions show roughly similar patterns which are not obviously related to the main alteration pipe but do reveal broad enrichment zones in the general area of mineralization.The dispersion appears to be partly controlled by texture. Because of greater primary permeability, the halos produced in rhyolite breccia are wider and better defined than those in more massive rhyolites. On a wider scale (10 km²) dispersion patterns are related to the fault and fracture systems of the area.As many as five stages of metamorphism have affected the area, altering all rocks to some extent. Samples can be classified petrographically into alteration groups, both related and unrelated to mineralization. Comparison of these groups reveals the inadequacy of certain elements for outlining alteration related to mineralization. For example, the range of K₂O in relatively unaltered rhyolite overlaps the composition of all other groups, including those related to mineralization. Similarly apparent is that the distribution of certain elements, e.g., Na₂O, may adequately define one part of an alteration zone such as the sericite-rich zone, but not another.It is concluded that careful use of lithogeochemistry in conjunction with detailed geological mapping and core logging can provide information otherwise obtainable only by time-consuming petrographic analysis. Thus it can be a potent weapon in the search for blind ore deposits.     

Seasonal,hydrological, and land management factors controlling dissolved organic carbon concentrations in the loch fleet catchments,Southwest Scotland

Dissolved organic carbon (DOC) was measured at hourly or two-hourly intervals during more than 30 events in one forested and two moorland subcatchments of the Loch Fleet catchment in southwest Scotland. The dominantly peaty soils in the catchments resulted in small discharge-related DOC variations within individual events, with a maximum range of about 2 mg 1^?1. Seasonal variations were larger with an amplitude of 8-9 mg 1^?1 and maximum concentrations in the summer months. The forested stream had the highest mean DOC, twice as large as the comparable moorland stream in the preliming phase. Applications of lime to the catchments increased stream DOC concentrations, with the largest increases in the moorland catchments.     

Depositional environments of the Hart coal zone (Paleocene), Willow Bunch Coalfield, southern Saskatchewan, Canada from petrographic, palynological, paleobotanical, mineral and trace element studies

Coal petrology, palynology, paleobotany and mineralogy of the Hart coal indicate deposition under wet, warm-temperate to subtropical climatic conditions in low-lying backswamps with fluvial channels and locally ponded areas. The coal is dominated by mixed xylitic/attrital lithotypes and by huminite macerals with secondary inertinite macerals and minor liptinite macerals. Good correlation exists between lithotypes and maceral composition. Local and vertical variations in proportions of huminites and inertinites reflect frequent fluctuations in water levels, periodic flooding, desiccation and burning of the peat. Swamps were dominated by Glyptostrobus-Taxodium forest with Betula-Myrica-Alnus communities and, locally, Laevigatosporites, which are the dominant contributors to the xylite-rich lithotypes. Attrital lithotypes with abundant Pandanus, Typha and Azolla are consistent with wetter areas of a fluvial environment, including ponds and channels. Trace elements Cr, Cu, Mo, Ni, Si, Ti, U, Se, V, W, K and Th, typically associated with synergetic minerals kaolinite, calcite and quartz, may have a volcanic source. High concentrations of Na, Ba and Ca found in organic complexes are of secondary origin and probably originate in deep source brines rather than marine surface waters.     

Timing of advance and basal condition of the Laurentide Ice Sheet during the last glacial maximum in the Richardson Mountains,NWT

This study presents new ages for the northwest section of the Laurentide Ice Sheet (LIS) glacial chronology from material recovered from two retrogressive thaw slumps exposed in the Richardson Mountains, Northwest Territories, Canada. One study site, located at the maximum glacial limit of the LIS in the Richardson Mountains, had calcite concretions recovered from aufeis buried by glacial till that were dated by U/Th disequilibrium to 18,500 cal yr BP. The second site, located on the Peel Plateau to the east yielded a fossil horse (Equus) mandible that was radiocarbon dated to ca. 19,700 cal yr BP. These ages indicate that the Peel Plateau on the eastern flanks of the Richardson Mountains was glaciated only after 18,500 cal yr BP, which is later than previous models for the global last glacial maximum (LGM). As the LIS retreated the Peel Plateau around 15,000 cal yr BP, following the age of the Tutsieta phase, we conclude that the presence of the northwestern margin of the LIS at its maximum limit was a very short event in the western Canadian Arctic.     

Is irrigated agriculture in the Murray Darling Basin well prepared to deal with reductions in water availability?

The “Big Dry”, a prolonged dry period in Australia from 1997 to 2009, dried out much of the Murray-Darling Basin (MDB) and resulted in large agricultural losses and degraded river ecosystems. Climate projections are that dry conditions in the MDB are likely to be more regular and severe than ever before, and recent policy initiatives are likely to reduce consumptive water use and redirect water to ecosystem management. This paper aims to develop an understanding of the interactions between water policy and irrigation practices by deriving lessons from drought management in irrigated agriculture of the MDB during the Big Dry, and furthermore, to draw out lessons to enhance the preparedness of irrigated agriculture for a future drier climate and reduced water availability. Reviews of irrigation farmers’ practices, attitudes and capacity to manage during prolonged droughts in the MDB, and the evolution of agricultural water policy in Australia since 1990 were made. It is clear that farmers could be better prepared to deal with a drier climate if their water management practices, e.g. irrigation methods and soil moisture measuring tools are improved, if the impediments to the uncertainty of water allocation and low water availability could be overcome, and if well-targeted research and extension could assist farmers to use water more wisely. It is also clear that Australian water policy could be better prepared in terms of assisting irrigated agriculture to deal with a drier climate. Key areas are reduction of barriers and distortions to water trading, optimizing the environmental water allocation, and seeking mutual benefits between environmental water allocation and irrigated agriculture, improvement of the cost-effectiveness of investments in water supply infrastructure, facilitating carryover and capacity sharing at larger scales, and provision of accurate, accessible and useful water information at different scales. An approach to irrigation practice and water policy is proposed based on past experience and potential opportunities. The approach is a set of linked strategies for more robust agricultural production and a more sustainable environment under a drier climate and reduced water availability.     

Settlement over peat on the A5 at Pant Dedwydd near Cerrigydrudion, North Wales

The A5 London to Holyhead trunk road suffers from large and varied settlements at Pant Dedwydd where it crosses a geotrophic peat bog developed on the glacial drift that overlies bedrock of Silurian Denbigh Grits Group. Recent carriageway settlements have created an undulating profile over a 100 m stretch, restricting forward visibility and posing recurring and persistent difficulties for highway maintenance. The highly compressible peat underlies almost 400 m of highway, ranges up to 7 m deep and a typical profile consists of an upper sphagnum peat layer and a basal reedy, woody and sedge grass peat. The highway was originally constructed by Thomas Telford in 1819 as a low floating embankment over the organic terrain. Increases in traffic over the intervening period together with successive asphalt overlays have resulted in a history of major repairs and although records are incomplete it is likely that the carriageway is now over 2 m thick over parts of the bog. Comprehensive geological investigations carried out to characterize the peat deposit included dynamic probe holes, boreholes and a trial pit. No unusual subsurface conditions were identified. However, scrub willow or grey sallow (Salix cinerea) was observed growing in spiraea thickets alongside the deepest hollows in the highway. The willows may contribute to the road subsidence by extraction of water from the peat beneath the carriageway. Accordingly, removal of the scrub willow and conventional re-grading of the carriageway have been recommended to correct the existing problem.     

The Spatial and Temporal Characteristics of Pc3 Geomagnetic Activity over Canada in 2000, as a Guide to Planning the Times of Aeromagnetic Surveys

Geomagnetic activity affects aeromagnetic surveys. Geomagnetic variations are quite complex and can be quantified in different ways. A measure of geomagnetic activity that is useful for planning aeromagnetic surveys is the Pc3 pulsation index developed by the Australian Space Weather Agency. Purposeful to developing guidelines for planning aeromagnetic surveys in Canada, we study the variations in Pc3 index amplitude over Canada in 2000. This study shows distinct patterns associated with the sub-auroral zone, the auroral zone, and the polar cap. Average Pc3 index activity is higher during the months of February, July, September, and November in the auroral and sub-auroral zones. The station in the polar cap exhibits maximum activity near midday during the summer months. Detailed analysis of a magnetic storm shows that Pc3 index amplitude during the beginning of the solar storm is least important at the polar cap. The mean Pc3 index also relates to solar wind parameters such as the solar wind velocity and the vertical polarity of the interplanetary magnetic field. Analysis of the morning maximum of the Pc3 index observed in the auroral zone can be used to develop guidelines for planning aeromagnetic surveys in Canada and other areas of the world affected by auroral zones.