IBIGEO   22622
INSTITUTO DE BIO Y GEOCIENCIAS DEL NOA
Unidad Ejecutora - UE
congresos y reuniones científicas
Título:
Stratigraphy and Mineralogy of the First Abandoned Mine Tailing of the Concordia Mine, Salta, Argentina
Autor/es:
TONDA, ROMINA; KIRSCHBAUM, ALICIA; ARNOSIO, MARCELO; PETTINARI, G.
Lugar:
Mendoza
Reunión:
Congreso; 18th International Sedimentological Congress; 2010
Institución organizadora:
International Sedimentology Association
Resumen:
<!-- /* Style Definitions */ p.MsoNormal, li.MsoNormal, div.MsoNormal {mso-style-parent:""; margin:0cm; margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:12.0pt; font-family:"Times New Roman"; mso-fareast-font-family:"Times New Roman"; mso-ansi-language:ES; mso-fareast-language:ES;} p {mso-margin-top-alt:auto; margin-right:0cm; mso-margin-bottom-alt:auto; margin-left:0cm; mso-pagination:widow-orphan; font-size:12.0pt; font-family:"Times New Roman"; mso-fareast-font-family:"Times New Roman"; mso-ansi-language:ES-AR; mso-fareast-language:ES-AR;} span.hw {mso-style-name:hw;} @page Section1 {size:612.0pt 792.0pt; margin:70.85pt 3.0cm 70.85pt 3.0cm; mso-header-margin:36.0pt; mso-footer-margin:36.0pt; mso-paper-source:0;} div.Section1 {page:Section1;} --> The Concordia mine (Pb, Ag, Zn) is located at the western portion of Salta province, 3,770 m above sea level in the Puna region, where the climate is arid. The mine is located 15 km from San Antonio de Los Cobres village, and it was abandoned in 1986 without any planning for its closure. Hence, the waste dumps, tailings and mine machinery were abandoned in situ and are exposed to weathering since that moment. Nowadays the mine is water-filled and the groundwater is in contact with the sulfide minerals generating acid mine drainage (AMD). The Concordia river heading is located within the mine, where the water pH is low (3-4). However, the pH of the stream during their pathway changes to neutral values until reaching the San Antonio River. Then, this river crosses the San Antonio town and finally flows into the Salinas Grandes closed basin. During the mining activity the wasted material was stored in four tailings. These tailings, with a thick of around 3-5 m, cover an estimated total area of 20000m2. After the mine activity finished, the Concordia stream passed through the tailings eroding some of the sediments and metallic minerals deposited there. This study focuses on the stratigraphy and mineralogy of the first tailing. The volume of wasted material acumulated is around 4500 m3. In this tailing three levels were identified.  The upper level, 68 cm thick, is medium - fine grained sand, grayish yellow color. In this level rock fragments and the following minerals were identified: quartz, pyrite, Fe oxides and scarce zircon. Also nordstrandite (Al(OH)3) and szomolnokite (Fe2+(SO4)•(H2O)) were identified by X-ray diffraction. The second level, 49 cm thick, is composed by medium grained sand, grayish green color. The mineralogy is similar to the level A. The lower level, 38 cm thick, is composed of medium fine-grained sand, gray color.  In this level, quartz, pyrite and rock fragments were identified. Romboclasa (HFe3+(SO4)2•4(H2O)), rozenite (Fe2+(SO4)•4(H2O)), szomolnokite (Fe2+(SO4)•(H2O)) and anglesite (Pb(SO4)) were recognized  by X-ray diffractometry.The percentage of pyrite present in the first tailing is between 0,9 and 2,2 %. The only clay mineral found on the whole samples is illite.  Preliminary obtained data indicate that secondary minerals are the result of precipitation from tailings pore-water oversaturated on SO42-, Fe2+ and other heavy metals. Oxidization generated by surface conditions transforms pyrite into melanterite, then melanterite is transformed into rozenite, by decreasing humidity, and then into szomolnokite. The absence of melanterite on the obtained data agrees with arid conditions in this zone.