Geochemical Hazard Mapping
Total Page:16
File Type:pdf, Size:1020Kb
Western Cape Unit P.O. Box 572 Bellville 7535 SOUTH AFRICA c/o Oos and Reed Streets Bellville Cape Town Reception: +27 (0) 21 946 6700 Fax: +27 (0) 21 946 4190 Geochemical hazard mapping M. Maya and T. Cloete Council for Geoscience Report number: 2011-0064 © Copyright 2011. Council for Geoscience 1 Contents Contents..................................................................................................................................................2 Figures.....................................................................................................................................................2 Tables......................................................................................................................................................3 1 Introduction ....................................................................................................................................4 2 Introduction and background for Geochemical Mapping ..............................................................5 2.1 Sampling ................................................................................................................................5 2.2 Sample preparation and analytical method..........................................................................5 3 Potential geochemical hazards rising from smelters and power stations......................................6 4 Potential geochemical hazardous elements: Arsenic (As)..............................................................8 5 Potential geochemical hazardous elements: Lead (Pb)................................................................10 6 Potential geochemical hazardous elements: Zinc (Zn) .................................................................12 7 Potential geochemical hazardous elements: Copper (Cu)............................................................14 8 Potential geochemical hazardous elements: Nickel (Ni) ..............................................................16 9 Potential geochemical hazardous elements: Chrome (Cr) ...........................................................17 10 Potential geochemical hazardous elements: Vanadium (V)....................................................19 11 Potential geochemical hazardous elements: Uranium (U)......................................................21 12 Potential geochemical hazardous elements: Thorium (Th).....................................................23 13 Geochemical distribution of Sb on the 1:100 000 map Tzaneen.............................................25 14 Potential geochemical hazardous elements: Zinc (Zn) ............................................................26 15 Conclusion................................................................................................................................27 Acknowledgements ..............................................................................................................................27 References ............................................................................................................................................28 Figures Figure 1: A regional geochemical map of elements associated with power stations and smelters.......8 Figure 2: A regional geochemical map of As distribution.......................................................................9 Figure 3: A regional geochemical map of Pb distribution.....................................................................11 Figure 4: A regional geochemical map of Zn distribution.....................................................................13 2 Figure 5: A regional geochemical map of Cu distribution.....................................................................15 Figure 6: A regional geochemical map of Ni dsitribution .....................................................................17 Figure 7: A regional geochemical map of Cr distribution. ....................................................................19 Figure 8: A regional geochemical map of V distribution.......................................................................21 Figure 9: A regional geochemical map of U distribution ......................................................................23 Figure 10: A regional geochemical map of Th distribution...................................................................24 Figure 11: Geochemical distribution of Sb on the 1:100 000 map Tzaneen.........................................26 Figure 12: Geochemical distribution of Zn on the 1:100 000 map Tzaneen.........................................27 Tables Table 1: List of known geochemical anomalies ......................................................................................4 Table 2: Calibration concentration range of elements in reference materials that were used and the calculated determination limits (DL).......................................................................................................5 3 1 Introduction Potentially hazardous geochemical element-anomalies (Table 1) were identified on the existing geochemical data sets and maps of South Africa, which have been generated over the last three decades by the Geochemistry Unit of the Council for Geoscience. These anomalous element accumulations are either natural- or anthropogenic in origin and may or may not be hazardous to man and animal. Some of these anomalies have been studied due to their known negative health impacts on the environment. The natural anomalies of Pb and Zn, for example, are linked to known to pockets of mineralisation around the Bushveld Complex in the Transvaal Supergroup rocks, which are also known to impact the quality of drinking water causing high infant mortality rates and also poor fertility of cattle. Typically, anthropogenic anomalies (Cu, Ni, Cr and V) have been mapped around smelters and some power stations. Table 1: List of known geochemical anomalies Potentially hazardous Area Comments elements Cd, Hg, S, P, Se, Cu, Bi, As Iscor smelter Pretoria Anthropogenic Rustenburg smelters Anthropogenic Rooiwal power station Anthropogenic Radioactive elements Wits goldfields(mine dumps) Anthropogenic U and Th Granites (geochemical maps Natural available) Karoo basin Natural Fe-Mn Asbestos Limpopo and N Cape (Penge and Natural Griquatown formations) Arsenic anomalies Tzaneen-, Polokwane maps Natural Loeriesfontein Natural (Geochemical maps available) Cu anomalies Nababeep (Nababeep formation) Anthropogenic Cr, V anomalies Witbank Anthropogenic Pb, Zn anomalies Magaliesberg Quartzite Formation Natural Malmani Subgroup Formation Natural Sb, Zn anomalies Klein Letaba River Anthropogenic 4 2 Introduction and background for Geochemical Mapping The Council for Geoscience (CGS) of South Africa has been involved in a regional geochemical mapping program since 1972. The CGS has collected close to 400 000 stream sediment and soil samples have been collected since then. SXRF analysis for 23 elements has been done for most of these samples and nine 1:250 000 scale geochemical wall maps have been produced and are available on open file. 2.1 Sampling The study area consist of the three 1:250 000 scale map sheets of Pretoria, Rustenburg and Pietersburg and some portions of Mafikeng, Thabazimbi, Nylstroom, Tzaneen, Pilgrims Rest, Barberton and Ellisras sheets. Soil samples for the study area were taken on a grid of one sample/km 2 by helicopter supported transport. However, in the urban environment, soil samples have been taken on foot with 4X4 vehicle supported transport. Each 5 kg sample was taken from the top 20 cm of the sampling medium. A sampling density of 1 sample per km 2 was adopted from geochemical orientation studies (Labuschagne et al. 1993). A total number of 126465 samples were taken over a period of 10 years. 2.2 Sample preparation and analytical method The samples were dry sieved and were analysed on the following analytical technique: • Simultaneous X-Ray Fluorescence Spectrometer (Sim-XRF): TiO 2%, MnO%, Fe 2O3T%, Sc, V, Cr, Co, Ni, Cu, Zn, As, Rb, Sr, Y, Zr, Nb, Sn, Sb, Ba, W, Pb, Th and U; Simultaneous X-Ray Fluorescence analysis Samples were analysed on a Philips PW 1606 Simultaneous X-Ray Fluorescence Spectrometer (SXRF) for the following elements: Sc, TiO 2%, V, Cr, MnO%, Fe 2O3T%, Co, Ni, Cu, Zn, As, Rb, Sr, Y, Zr, Nb, Sn, Sb, Ba, W, Pb, Th and U. The steps to calibrate the instrument, accuracy and precision obtained and the reference materials used are described by Elsenbroek (1995 and 1996). The chemical elements analysed for, with their calibration ranges and determination limits, are displayed in Table 1. A drift correction was made after every 10th unknown sample, with the aid of an internal glass-disc monitor, to correct for any instrumental drift. The resulting stability of analyses was checked, per batch of 300 samples analysed on a daily basis, using in-house powder-briquette monitors of various concentrations. An example of the results obtained from the in-house monitors is given in Table 2. These monitors generally have a precision better than 5 % except for MnO%, Sn, Sb, W and U. Table 2: Calibration concentration range of elements in reference materials that were used and the calculated determination limits (DL) Element Range (ppm) Detection Limit ppm) Sc 1–55 1 TiO 2 0.2–3.77 % 100 V 9–526 5 Cr 10–2 900 4 MnO 0,01–0,32 % 100 Fe 2O3T 1,40–18,76 % 100 5 Co 11–210 10 Ni 10–2 380 10 Cu 19–1 230 9 Zn 10–680 3 As 18–412 10 Rb 9–860 1 Sr 25–1 100 1 Y 5–718 1 Zr 22–1 210 1 Nb 10–960 5 Sn 3–370 2 Sb 10–2