Area selection for diamonds using magnetotellurics : examples from southern Africa

Author Posting. © Elsevier B.V., 2009. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Lithos 112 (2009): 83-92, doi:10.1016/j.lithos.2009.06.011.Southern Africa, particularly the Kaapvaal Craton, is one of the world’s best natural laboratories for studying the lithospheric mantle given the wealth of xenolith and seismic data that exist for it. The Southern African Magnetotelluric Experiment (SAMTEX) was launched to complement these databases and provide further constraints on physical parameters and conditions by obtaining information about electrical conductivity variations laterally and with depth. Initially it was planned to acquire magnetotelluric data on profiles spatially coincident with the Kaapvaal Seismic Experiment, however with the addition of seven more partners to the original four through the course of the experiment, SAMTEX was enlarged from two to four phases of acquisition, and extended to cover much of Botswana and Namibia. The complete SAMTEX dataset now comprises MT data from over 675 distinct locations in an area of over one million square kilometres, making SAMTEX the largest regional-scale MT experiment conducted to date. Preliminary images of electrical resistivity and electrical resistivity anisotropy at 100 km and 200 km, constructed through approximate one-dimensional methods, map resistive regions spatially correlated with the Kaapvaal, Zimbabwe and Angola Cratons, and more conductive regions spatially associated with the neighbouring mobile belts and the Rehoboth Terrain. Known diamondiferous kimberlites occur primarily on the boundaries between the resistive or isotropic regions and conductive or anisotropic regions. Comparisons between the resistivity image maps and seismic velocities from models constructed through surface wave and body wave tomography show spatial correlations between high velocity regions that are resistive, and low velocity regions that are conductive. In particular, the electrical resistivity of the sub-continental lithospheric mantle of the Kaapvaal Craton is determined by its bulk parameters, so is controlled by a bulk matrix property, namely temperature, and to a lesser degree by iron content and composition, and is not controlled by contributions from interconnected conducting minor phases, such as graphite, sulphides, iron oxides, hydrous minerals, etc. This makes quantitative correlations between velocity and resistivity valid, and a robust regression between the two gives an approximate relationship of Vs [m/s] = 0.045*log(resistivity [ohm.m]).We especially thank our academic funding sponsors; the Continental Dynamics programme of the U.S. National Science Foundation, the South African Department of Science and Technology, and Science Foundation Ireland

Natural Resource Knowledge and Information Management via the Victorian Resources Online Website

Since 1997, the Victorian Resources Online (VRO) website (http://www.dpi.vic.gov.au/vro) has been a key means for the dissemination of landscape-based natural resources information via the internet in Victoria, Australia. The website currently consists of approximately 11,000 web pages, including 1900 maps and 1000 downloadable documents. Information is provided at a range of scales—from statewide and regional overviews to more detailed catchment and sub-catchment levels. At all these levels of generalisation, information is arranged in an organisationally agnostic way around key knowledge “domains” (e.g., soil, landform, water). VRO represents a useful model for the effective dissemination of a wide range of natural resources information; relying on partnerships with key subject matter experts and data custodians, including a “knowledge network” of retired land resource assessment specialists. In this paper, case studies are presented that illustrate various approaches to information and knowledge management with a focus on presentation of spatially contexted soil and landscape information at different levels of generalisation. Examples are provided of adapting site-based information into clickable maps that reveal site-specific details, as well as “spatialising” data from specialist internal databases to improve accessibility to a wider audience. Legacy information sources have also been consolidated and spatially referenced. More recent incorporation of interactive visualisation products (such as landscape panoramas, videos and animations) is providing interactive rich media content. Currently the site attracts an average of 1190 user visits per day and user evaluation has indicated a wide range of users, including students, teachers, consultants, researchers and extension staff. The wide range of uses for information and, in particular, the benefits for natural resource education, research and extension has also been identified