Light Stable Isotopes in Aquifers Affected by Mining Activities in a Brazilian Mining Province
Abstract
Iron ore is presently a main item in the Brazilian commercial agenda. Large reserves have converted this utility into an important source of export earnings and, secondarily, of raw materials for the domestic industry. Parallel to a boom in mining activities in the last years environmental impacts and a stress on natural resources have soared. A region exhibiting pronouncedly intensive mining activities lies in the central part of the State of Minas Gerais, the third economy of the federation. Mines are sited right beside the capital and neighbor towns amounting to nearly five million inhabitants and a pronounced dependence on groundwater resources. Besides, this region is a water divide enclosing the sources of main contributors to the most strategic fluvial basins in the country. Iron ore is by large the main mineral but other metals (including gold and uranium), as well as non-metals such as limestone, quartz and granite, also occur. Given the significance of this commodity in the country's trade balance and the demand of water resources with acceptable quality for human consumption, the scale of ensuing water use conflicts caused by its exploration is wide ranging and has to be coped with well grounded environmental assessment approaches. Tracer hydrology techniques might be a valuable tool in this context. The characteristics of the area being impacted have been surveyed, including climate and pluviometry, stratigraphic litology, geological structure, use of soil, mineral resources and their exploration, surface and ground water hydrology and their sundry uses. Data to be processed have been procured at local public agencies but as regard local hydrological features, particularly isotopic compositions, ad hoc surveys and methodologies were required. One instance concerns pluviometric isotopy due to the alpine character of the surveyed region altitude and temperature effects might take place. Hence different sites were monitored; cumulative pluviometer samples collected on a monthly base had to be stored in specially designed containers to avoid fractionation due to evaporation. Meteoric and groundwater samples were collected at a monthly rate along a whole year period at a total of forty seven stations including wells, springs and drainage sources, encompassing six aquifer units. Physical-chemical parameters, major ions, and both stable and radioactive nuclides were measured in the collected samples. Stable isotope measurements comprised the 2H/1H and 18O/16O ratios. Tritium level measurements were measured to evaluate the water residence time in the aquifers; since these levels are presently so low in the southern hemisphere electrolytic enrichment was required.
- Publication:
-
AGU Spring Meeting Abstracts
- Pub Date:
- May 2013
- Bibcode:
- 2013AGUSM.H32A..04M
- Keywords:
-
- 1895 HYDROLOGY / Instruments and techniques: monitoring;
- 1829 HYDROLOGY / Groundwater hydrology;
- 1834 HYDROLOGY / Human impacts;
- 1880 HYDROLOGY / Water management