A preliminary characterization of the wasted metals enriched sediments in the abandoned mining treatment plant La Poma. Salta, Argentina

CACCIABUE, LUCÍA; ARNOSIO, MARCELO; KIRSCHBAUM, ALICIA; PETTINARI, G.

Mendoza, Argentina

Congreso; 18th International Sedimentological Congress; 2010

International Association of Sedimentologists

In the northwest of Argentina, abandoned mines as well as mineral treatment plants where metals as Pb, Ag and Zn were extracted and concentrated, represent a potential risk of acid mine drainage (AMD) generation. The mineral treatment plant La Poma is located in Chorrillos, 17 km from San Antonio de los Cobres village, Los Andes department, in Salta province. The old plant concentrated the ore using a flotation chemical method. In 1986 the plant stopped working and the waste from flotation process was left exposed to weathering. Furthermore, both infrastructure and machinery were abandoned without any planning for its closure. Nowadays a huge volume of mining tailings are present surrounding the closed plant. This material has been eroded by the Tajamar River, which pass through the abandoned place. Near the river, light and yellowish salts precipitate. By X-ray diffraction, a secondary sulfate dietrichite (Zn0.6Fe2+0.3Mn2+0.1Al2(SO4)4•22(H2O)) and sulfides such as smythite  (Fe2+6.75Ni2.25S11), galene and pyrite were determinated. Tailings are composed of medium-fine grained sand, grey-yellowish and green color, with friable consistency. None sedimentary structure is observed. Quartz, feldspar and biotite were recognized as main minerals, and zircon, hornblende, hematite and pyrite are abundant accessory minerals. Some sediments deposited by the Tajamar river after crossing the tailings were described. Three leves were recognized. The upper level, 5 cm thick, is fine grained sand, gray- greenish color. The minerals identified are quartz and feldspar, hornblende, magnetite, pyroxene, zircon and tourmaline as accessories. Pyrite is absent. The second level, 6 cm thick, is fine grained sand, dark green color. Rock fragments, quartz, feldspar and altered biotite are present; the accessory minerals identified are similar to the upper level. Pyrite is poor and it is oxidized, which is coherent with the higher rate of weathering in this transported materials instead of the static sediments in the tailings. The lower level is composed of fine grained sand. Zircon, brownish hornblende with magnetite, poor altered biotite, tourmaline and pyroxene were determinated. Pyrite is absent. The occurrence of secondary minerals on tailings surface is the result of dissolution of primary sulfides, transporting and precipitation of salts due to evaporation. These soluble salts stay on the surface until next rainy season, when they are disolved again.