2022-11-032022-11-031998-03-13CHOQUE FERNANDEZ, Oscar Jesus. Caracterização mineralógica e cristaloquímica da prata em sulfetos e sulfossais do centro minero San José (Ouro-Bolívia). Orientador: Marcondes Lima da Costa. 1998. 88 f. Dissertação (Mestrado em Geoquímica e Petrologia) - Programa de Pós-Graduação em Geologia e Geoquímica, Centro de Geociências, Universidade Federal do Pará, Belém, 1998. Disponível em:http://repositorio.ufpa.br:8080/jspui/handle/2011/14916 . Acesso em:.https://repositorio.ufpa.br/handle/2011/14916Centro Minero San José is located in the Bolivian Tin Belt in a group of hills known as the Serrania de Ouro, which stand alone in the central Altiplano, 8 km from the Eastern Cordillera of the Andes. The Center is made up of polymetallic deposits (Ag, Sn, Pb, Sb, Zn), which at the time of its shutdown in 1990, had a production capacity of 400t/day with average contents of 360 g of Ag/t and 2.0% of Pb, and produced concentrates of 19.10% Pb, 6275 g/t Ag, 12.80% Sb and 2.76 g/t of Au, which could no longer be marketed due to the fine imposed by the presence of Sb. Several metallurgical processes sought to obtain the Ag metal, but due to the complexity of the ore, all of them proved to be unfeasible. There are no references about mineralogical works, especially chemical microcomposition carried out on Ag in this Mining Center, for these reasons this work aimed to study the mineralogical and crystallochemical characteristics of silver in this Center, trying to identify the possible causes of the problems found in the metallurgical processes. Mineralogical studies carried out by reflected light microscopy, x-ray diffraction and scanning electron microscopy, allowed the characterization of galena and franckeite as the carriers of Ag (averages of 0.54 and 0.48% respectively). Stanite-kesterite (average of 0.33%), zinkenite (0.47%), bournonite (average of 0.43%) and sulphosalt types (a) (1.08%), (b) (1.56% ) and (c) (0.43%) are also carriers of Ag, but they occur in small amounts in the ore. Pyrite, arsenopyrite, sphalerite, wurtzite, chalcopyrite, marcasite and pyrrhotite as sulfides, boulangerite and jamesonite as sulphosalts, are associated minerals and do not contain Ag. The crystallochemical studies of galena, franckeite, zinkenite, stannite-kesterite and bournonite suggest the existence of simple ionic substitution of lead by silver in the first three (with influence of Cd, As and Sb contents not detected by SEM-EDS or the occurrence of interstitials) and Ag+=Cu+ in the last two. In galena, there must also be coupled substitution of the Ag++ type (Sb)3+ = 2Pb2+ since the concentrations of Ag are almost similar to those of Sb. The unit cell parameters of galena, franckeite and zinkenite are a (5.933±0.001 Å); a (5.86 Å), b (5.86 Å) and c (17.35 Å), and a (22.111±0.004 Å) and c (4.322±0.001 Å), respectively. Probably the parameter a of galena is influenced by the presence of Ag and Sb in its structure, since it is slightly smaller than that reported in the literature for galenas considered standard (5.936-5.94 Å). The micromorphological characteristics of galena, franckeite, zinkenite and stannite-kesterite, observed in micron scales, show absence of inclusions, suggesting that silver is found as complex solid solutions, being consistent with the ionic substitutions indicated above. Silver is also found in galena as inclusions of franckeite (as needles and straight or curved prismatic aggregates) and zinkenite (needles and polygonal). These inclusions sometimes occur with orthogonal orientation and at other times chaotically, they are even distributed homogeneously and are similar to the topaxial relationships of galena, thus showing strong evidence of exsolution. Irregular-looking stannite inclusions in galena, and bleb-shaped bournonite in stannite, are also due to exsolution. Mineralogical studies also allowed the identification of other problems that may influence the metallurgical treatment of Ag minerals, such as: - Existence of haze or coatings of anglesite and Pb-S-O mineral next to galena and franckeite, which can cause hydrophobic behavior. - Abundance of pyrite in the ore, in addition to a small amount of arsenopyrite, marcasite and exsolved pyrrhotite and other sulfides such as sphalerite, wurtzite and exsolved chalcopyrite, which can cause high consumption of reagents, inhibition of cyanidation processes, in addition to being difficult to removal in refinement. - Presence of Sb and Sb, Cd and As minerals. Next to franckeite, zinkenite and bournonite, boulangerite and jamesonite are the main minerals of Sb. Antimony is also found in the structure of galena, stannite-kesterite, pyrite, arsenopyrite and sulphosalt types (a), (b) and (c). Cadmium is usually present in galena and spharelite sulfides as well as in all identified sulfosalts. Arsenic is restricted to galena, pyrite, franckeite, boulangerite and sulfosalt complex type (a). Sb minerals and these other metals are harmful to different metallurgical processes. The cyanidation of Ag with these metals would be practically impossible and in pyrometallurgical processes they can cause problems of partial melting of the charge and capping the furnaces. In both cases they can form toxic gases. From the point of view of grain release, all minerals carrying or not carrying Ag are considered easy to release, with the exception of the exsolved and myrmekitic phases considered difficult or practically impossible to release. All these aspects allow us to conclude that: - There is a large number of mineral species identified in the ore at Centro Minero San José. Among these species, sulfides and sulfosalts represent the main source of Ag, Sb, Sn and Pb. - Ag is found as solid solutions in galena, franckeite, zirkenite and stannite-kesterite, thus being chemical locking or solid solution locking. Ag solubility limits in these solid solutions are approximately 0.5%. - Ag is also found as exsolutions of franckeite, zirkenite and stannite-kesterite in galena, and of bournonite in stannite-kesterite. - Ag extraction must be done from galena and franckeite minerals mainly, and its treatment must be like base metal minerals. - Non-Ag-bearing minerals can make Ag metallurgical treatment processes more difficult and expensive.Acesso AbertoAttribution-NonCommercial-NoDerivs 3.0 Brazilhttp://creativecommons.org/licenses/by-nc-nd/3.0/br/Sulfetos e sulfossais de AgCaracterização mineralógicaCristaloquímicaConotação metalúrgicaSan JoséBolíviaDissertaçãoCNPQ::CIENCIAS EXATAS E DA TERRA::GEOCIENCIAS::GEOLOGIAMINERALOGIA E GEOQUÍMICAGEOQUÍMICA E PETROLOGIA