Module vii mine closure: case studies

MODULE VII
Mine Closure: Case Studies

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CLOSURE AND REMEDIATION OF THE POLIMETALLEC ORE DEPOSIT MINA ANGELA CHUBUT PROVINCE- ARGENTINA Lic. Guillermo E. HughesDirección Gral. de Minas y Geología-Provinicia del Chubut-Argentina INTRODUCTION The present reports pretends to show the evolution and closure of Mina Angela, a Au-Ag–Cu–Pb-Zn mine,located in the Chubut Province (Argentina). The description will be done in chronological way, as there are several dates that are very important, especially from the legal point of view. LOCATION An Argentinian Company called Cerro Castillo S.A. (CCSA) owns the mine. Lonmin Plc (Lonmin) from Great Britain and by Garovaglio and Zorraquin S.A. (G y Z) from Argentina.owns CCSA The Mina Angela mine islocated at Latitude 42° S, and Longitude 69° W in the Gastre Department, close to the border with the Rio Negro Province. The Mine is at an elevation1400 mosl. A very low population density characterizes the district, and the main activity is the livestock farming. Mina Angela is at 45 km North of Gastre (a small town of 400 inhabitant) by gravel roads, and at 116km south of Ing. Jacobacci (6500inhabitant). The closest railway station is at Ing. Jacobacci, from where it possible to access to the port of San Antonio Oeste, and Port Madryn. The access by plane is through Bariloche.

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ENVIRONMENT Geology and Geomorphology Mina Angela is located in the Somouncura Plateau. The geology comprisesJurassic breccias, tuffs and andesites (Taquetren formation). Comagmatic riodacite dikes intruded this volcanic complex. Small mountains characterize the landscape. The land has been cut by an important drainage system from SW to NE. The highest mountains reach 1700 m. over sea level. The structural characteristics, mineralization, and alteration indicate a low sulphidation ore deposit. There arevery little indications of a high sulphidation deposit, and there are very little chances of a porphyry type mineralization. Climate Winds: Frequency, intensity. The regional winds have SW-NE prevailing directions. We can say that they persist during the whole year, with an average speed of 40km/h, and a maximum speed of 120 km/h. Rains, Humidity and temperatures The annual average temperature is9°C, with extreme temperatures between – 30°C and 25°C during June and January. The rainfalls are very rare, and vary from 125 mm and 300 mm per year. Snowfalls are very frequent in winter. Hydrology a Hydrogeology: General Features The project is located close to where the drainage flows to the Maquinchao River, north of the property. The general features of the hydrogeology are controlled bygeological structure and by the stratifigraphy. The mine is located in the Clara Natividad cachtment and La Minas stream catchment (Fig. 2). The Clara Natividad catchment has an area of 8.6km2. The Las Minas catchment has an area of 2km2, and the streams finish in the Clara Natividad Stream, upstream of the tailing deposit. Downstream of the mine site and the tailing facilities, the Clara Natividadstream discharges into the Zarate stream, which discharges in the Caliente Grande River, and this one into the Maquinchao River. The underground water is limited to the areas with a high density of secondary fractures. Regional water tables have not been identified. Potential and actual uses: Due to its remote location, and to the low population density, the water use is limited to the livestockfarming. It is important to say that only 21 persons live in a 50km range, downstream of the mine site.

Villas Bôas & Maria Laura Barreto, Editors

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Water Quality The pH of the streams shows an average of 6,5. The quality of the waters is relatively good, and meets the Argentinean standard for drinking water. Soils Soils in the area tend to be...