Navegando por Autor "CHOQUE FERNANDEZ, Oscar Jesus"

Agora exibindo 1 - 3 de 3

Acesso aberto (Open Access)
Caracterização mineralógica e cristaloquímica da prata em sulfetos e sulfossais do centro minero San José (Ouro-Bolívia)
(Universidade Federal do Pará, 1998-03-13) CHOQUE FERNANDEZ, Oscar Jesus; COSTA, Marcondes Lima da; http://lattes.cnpq.br/1639498384851302; https://orcid.org/0000-0002-0134-0432
Centro 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 aberto (Open Access)
Microquímica e mineralogia de processos do minério de cobre de Salobo, Carajás
(Universidade Federal do Pará, 2002-03-18) CHOQUE FERNANDEZ, Oscar Jesus; COSTA, Marcondes Lima da; http://lattes.cnpq.br/1639498384851302
The Salobo deposit, located in Carajás, southeastern of Pará, is one of the largest copper reserves in Brazil. Although severa! mineralogical studies have been developed for this ore, its origin is still controversial, with severa! interpretations, such as volcanogenic copper-bearing oxide and voicanogenic massive sulfide and iron oxide (Cu-U-Au-REE). In comparison with other well-known deposits, it is a rare example of mineralization. Particular characteristics such as disseminated mineralization, fine grain and its hardness impose serious difficulties to copper concentrates production. Due to ore complexity it is difficult the metallurgical treatment, reasons why it is constantly submitted to geological and technological reevaluations. The literature on Salobo deposit is expressive but detailed works about microchemistry and technological characterization in comminution are rare or restricted to Salobo Metais S.A. company. The objectives of this work dealt with these questions. Microchemical analyses using microprobe and SEM/EDS in samples of holes and ore piles (research gallery G3) of Salobo, allowed the identification of sulfide mineralization with bornite (4%), chalcocite (2%) and chalcopyrite (0.5%), and variable proportions of molybdenite, cobaltite, safflorite, niqueline, siegenite, gold, silver, graphite, ilmenite, hematite, Te-Ag, uraninite and REE minerais. These minerais occur in schist iron formations where the deposit es found: a) magnetite and massive fayalite, eventually banded and b) banded biotite and magnetite. These groups considered as gangue (magnetite 53% and silicates 40%) contain minor amounts of gamet, amphibole, quartz, plagioclase and subordinate amounts of fluorite, greenalite, minnesotaite, stilpnomelane, apatite, monazite, allanite and occasionally siderite, goethite and malachite. Sulfides are preferentially concentrated in magnetite rich iron formations. Copper sulfides occur as crystals less than 3.0 mm and as disseminated fine grains, with fine alternated banded and/or foliated silicates, veiniets and/or long/short stringers, tiny inclusions, bornite/chalcocite and bornite/chalcopyrite mirmekitic intergrowth and bornite-chalcocite and bornite-chalcopyrite substitutions. These minerais were formed by complex processes and are characterized by compositional controls, mainly for the presence of Fe in them. Solid solutions of bomite and chalcopyrite were formed at high temperatures and gave way to those iron excesses. Atomic radios Cu/Fe of bomite (4.3-4.9) and chalcopyrite (average of 0.9) at high temperatures allowed the co-existence of bornite-chalcopyrite equilibrium and therefore of bornite/chalcopyrite. Iron contents (maximum 0.96%) in chalcocite have been incorporated at those temperatures when the structure is highly disordered. Chalcopyrite lamellaes following the { 111 } orientation in bornite as well as the bornite/chalcocite and bornite/chalcopyrite intergrowth suggest exsolution. Although those phases are associated with severa' minerais in different paragenesis, the ore features have been affected drastically by metamorphism difficulting the reconstruction of its pre-metamorphic evolution. Ore grinding produced physical changes in the grain size and according to time, long or short, of mineral comminution the pulp reologie is modified. That process originates a grain size - 270 # (53 µm), 80 % wt. passing, grounding time on 4 hours (dry) and 2 hours (humid) adapted to copper concentration. Different volumetric fractions of copper sulfides in particles were obtained through both processes: larger fraction (6 % volume) to grain sizes < 53 µm and with a prevailing fraction (7 to 15 % volume) ranging from 26.9 to 7.5 µm. Physical modification shows larger magnetite proportions than silicate ones with a clear incidence of magnetite density in the hydrocyclone classification. Mineralogically, in the comminuted products, occur the same minerals established in ROM but with chemical modifications in copper sulfides. Magnetite is the main host for sulfides and greenalite is more frequent among the silicates, fluorite being also common. Proportions of S, Fe and Cu in bornite, chalcocite and chalcopyrite are variable relative to ROM and stoichiometry, varying in function of the grain size (larger chemical variation in grain sizes of 26.9 to 7.5 pm than on the 2360 to 37µm fraction). Iron can reach up to 6.0% wt. in chalcocite. Chemical variations in S, Cu and Fe formed ternary sulfides: bornite, characterized as "complex mistures" rich in iron (Cu4.34-4.76Fe1.03-1.04S4.0) and chalcopyrite rich in Fe Cu0.93Fe1.08S2.0 (as a solid solution extension of chalcopyrite). Chalcocite oxidation and high values of Fe in its structure also contributed to the reaction of binary sulfides: djurleite and digenite Cu1.77-1.84Fe0.04-0.06S1.0. Those ternary (Cu-Fe-S) and binary (Cu-S) copper sulfides have been formed in the initial oxidation state with superficial alterations induced by temperature (25°C on) and comminution. These sulfides were formed and controlled by the phase relationships in the Cu-Fe-S system. Low copper content in sulfides leads to a slower chemical variation than there is an excess of iron. These variations favoured the appearance of oxidized surfaces on copper sulfides with different products of oxidation [M1-nS and nM(OH)2]. Chemical variations showed to be dependent on the grain size, with smaller oxidations in sizes > 53 µm and larger oxidations in sizes <53 µm, caused by a combination of surface area and ability of chalcocite to be oxidized. Iron excess mainly as highly reactive colloidal particles could have been generated by: mill material, abrasive action of particles and probable magnetite oxidation, producing chemical variation in mill atmosphere and electrochemical corrosion processes. Comminuted ore conserves the lepidoblastic textures of the silicates biotite, fayalita and greenalite and granoblastics of magnetite or bornite, chalcocite and chalcopyrite grains. Crystals of copper sulfides, liberated and mixed with high percentage of magnetite and silicates are intensively fractured and eroded and sometimes fullfilling cracks and/or fractures of greenalite. They difficult the sulfide liberation. Copper sulfide liberations increase gradually when the grain size is finer (more than 50 % in grain sizes < 29.6 µm). Only in fractions < 37 µm (Cumulative liberation yield CLY90), the copper bearing particles begin to migrate and for higher degrees of liberation though such tendency can still be insufficient for the purposes of sulfide concentration. Besides the strong metamorphic recrystallization of the schists of ore formations, its high hardness, the extremely variable grain sizes of sulfides (5 to 300 µm) and the mineralogical ore complexity (mineralogical associations, disseminations, intergrowth complexes), this microchemical investigations, in ROM and in comminution products, revealed a significant chemical variation in copper sulfides. Iron present in sulfide mineral reticules is the main contaminant to chemical modifications (Cu/Fe ratio) influencing the quality of copper concentrate in mineral processing. It has been already established that between copper sulfides and other components of pulps during grinding and flotation (water, species collectors or modifiers) occur an interaction through electrochemical mechanisms producing oxidized species, where the chemical composition of the mineral in question is very important. The technological alternative adapted to treat the copper concentrate, with basis in mineralogical and microchemical studies in run-of-mine and comminution products, seems to be the hydrometallurgy because they can take advantage the production of fine grains and to use the reground for ultrafine grains production. These can be submitted to oxidation processes of sulfides to promote copper extraction. Finally the metallic copper extraction can follow the solvent extraction/electrowinning (SX/EW) process.
Acesso aberto (Open Access)
A turquesa de Itacupim, Pará
(2004-12) COSTA, Marcondes Lima da; CHOQUE FERNANDEZ, Oscar Jesus; TOLEDO, Maria Cristina Mota de; PASSOS, Camila Maria; PEREIRA, Patrícia Freitas
Veins and veinlets of aluminum phosphates with turquoise occur at the Itacupim Island in the coastal plain northeast the state of Pará. A thick mature lateritic iron crust rich in aluminum phosphates developed an apatite-bearing alkaline-ultramafic complex which constitutes the Island. The veins and veinlets are cm-thick, usually constituted by wavellite, fibrous to radialfibrous, with bony or porcelaneous aspect, and can turquoise. Pebbles of these phosphates inside of apatite-bearing ultramafic rocks are very common at the base of the hang wall, and locally form expressive agglomerates. Turquoise forms half spheroids and is bluish-green, microcrystalline, and is intergrown with kaolinite and Mn oxy-hydroxides. The mineral identification was carried out by XRD optic microscopy, chemical analyses by wet methods and by SEM/EDS. The lower CuO values, in comparison to turquoise elsewhere, are compensated by the higher Fe2O3 and ZnO. The spheroids display countless inclusions of micrometric goyazite or svanbergite. The turquoise relation to veins and veinlets with wavellite, goyazite or svanbergite, quartz and clay minerals, its porcelaneous aspect and well-known occurrence of turquoise in hydrothermal environment indicate that the Itacupim turquoise was formed by the same mechanism. It doesn't display any clear relationship to laterite profile. The color and compact aspect of this turquoise make it suitable for use as gems.