Teses em Geologia e Geoquímica (Doutorado) - PPGG/IG
URI Permanente para esta coleçãohttps://repositorio.ufpa.br/handle/2011/6341
O Doutorado Acadêmico pertence ao Programa de Pós-Graduação em Geologia e Geoquímica (PPGG) do Instituto de Geociências (IG) da Universidade Federal do Pará (UFPA).
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Tese Acesso aberto (Open Access) Evolução supergênica do depósito cuprífero Alvo 118 - Província Mineral de Carajás(Universidade Federal do Pará, 2022-12-15) SANTOS, Pabllo Henrique Costa dos; COSTA, Marcondes Lima da; http://lattes.cnpq.br/1639498384851302; https://orcid.org/0000-0002-0134-0432The Carajás Mineral Province is home to one of the most extensive cupriferous belts in the world, where hypogene mineralizations were partially transformed into gossans, later lateritized and/or truncated during landscape evolution. These covers represent an information source for mineral exploration and, in some cases, can be mined together with parental hypogene mineralizations. The plateaus of the South American Surface host complete and lateritized gossans, while the surrounding denuded areas, typical of the Velhas Surface, exhibit incomplete or immature gossans, with the Alvo 118 deposit as an example. In this orebody, the hypogene mineralization was converted into an immature gossan located at depth, while the host rocks were weathered near the surface, forming a mineralized saprolite. The gossan comprises an oxidation zone, which includes goethite, malachite, pseudomalachite, cuprite, tenorite, native copper, ramsbeckite, chrysocolla, and libethenite, with relics of a secondary sulfide zone, represented by chalcocite. These minerals are distributed in the goethite, malachite, cuprite, and libethenite zones, with their mineral successions reflecting the transition of mineralizing solutions from acidic to slightly alkaline conditions and an increase in oxidation potential. This environment was established from the interaction of acid solutions, derived from chalcopyrite dissolution, with the gangue minerals (calcite and apatite) and the host rocks, granodiorites and, secondarily, chloritites, which acted in buffering the system, favoring the formation of new copper-bearing minerals. The strong correlations of CuO with Ag, Te, Pb, Se, Bi, Au, In, Y, U, and Sn in the hypogene mineralization reflect the inclusions of petzite, altaite, galena, uraninite, cassiterite, and stannite in chalcopyrite. In the gossan, Ag, Te, Pb, Se, and Bi remained associated and were incorporated into neoformed copper minerals. On the other hand, Au, In, Y, U, and Sn exhibit greater affinity with iron oxyhydroxides, as well as Zn, As, Be, Ga, Mo and Ni. The δ65Cu values reinforce that the investigated gossan is immature and was not intensely affected by leaching processes. The main mineral phases identified in the saprolite are kaolinite (predominant), associated with chlorite, smectite, vermiculite, quartz, and iron oxyhydroxides. Iron oxyhydroxides are strongly correlated with Ga, Sc, Sn, V, Mn, Co, and Cr, partly derived from the weathering of parent rocks. Additionally, Mössbauer spectroscopy data point to the important role of ferrihydrite and goethite as copper-bearing phases. There is no evidence of copper incorporation by clay minerals. The δ56Fe values indicate a little contribution of primary mineralization to the Fe content of the saprolite, which is more influenced by chlorite weathering. The association Al2O3, Hf, Zr, Th, TiO2, Ce, La, Ba, and Sr represents the geochemical signature of the host rocks, which influence the chemical composition of the three types of mineralization. On the other hand, the association In, Y, Te, Pb, Bi, and Se comprise the main pathfinder elements of the hypogene mineralization. Detailed knowledge of the supergene mineral and geochemical fractionation makes the Alvo 118 deposit a reference guide for investigating immature gossans and mineralized saprolites in denuded areas of the Carajás Mineral Province or equivalent terrains.Tese Acesso aberto (Open Access) Geocronologia e geoquímica isotópica dos depósitos de Cu-Au Igarapé Bahia e Gameleira, Província Mineral de Carajás (PA), Brasil(Universidade Federal do Pará, 2002-05-10) GALARZA TORO, Marco Antonio; MACAMBIRA, Moacir José Buenano; http://lattes.cnpq.br/8489178778254136Copper sulfide + Au ore deposits are common in the Carajás Mineral Province and systematically occur in Archean metavolcano-sedimentary sequences associated or not with granitoid intrusions. Two of these deposits, Igarapé Bahia and Gameleira, have been chosen for a geochronological and isotopic study with the purpose of not only determining their ages, origin and relationships with the host rocks, but also the formation and evolution of the crustal segments within which both deposits are located. The Igarapé Bahia Group hosts the Igarapé Bahia deposit and is composed of mafic metavolcanic (MVR), metapyroclastic (MPR) and meta sedimentary rocks (MSR), besides banded iron-formations and hydrothermally altered breccias zone (HBZ). The whole rock pile is crosscut by mafic dikes (MIR). The Cu-Au ore forms disseminations to massive bodies, mostly occurring in the HBZ which marks the contacts between the MVR and the MSR/MPR rock units. Petrographic and geochemical data about the MVR (basaltic meta-andesites), MPR (laminated and lapilli metatuffs) and MIR (quartz diorites) show them all to be derived from mafic magmas of tholeiitic affiliation, in spite of the alteration evidence. These rocks also show geochemical similarities (major and trace elements, including REE) with the coeval Grão Pará Group volcanic rocks. Chloritization (dominant), carbonation, sulfidation and magnetitization are the most important types of hydrothermal alteration. The ore is chiefly composed of chalcopyrite with variable amounts of pyrite, bornite and chalcocite. Chrorite, magnetite, siderite are abundant as gangue minerals, whereas tourmaline, molybdenite, fluorite and biotite are subordinate. Pb-Pb dating on zircon yield crystallization ages of 2745±1 Ma and 2747±1 Ma for the MVR and MPR, respectively. Similar whole-rock ages were obtained for the MVR (Pb-Pb / 2776±12 Ma and Sm-Nd / 2758±75 Ma) and the MPR (Pb-Pb / 2758±36 Ma). A Pb-Pb age of 2764±22 Ma for the chalcopyrite and gold suggests the mineralization to be contemporaneous with the host Igarapé Bahia Group. Similar Pb-Pb ages are recorded on chalcopyrite from the HBZ (2772±46 Ma), MVR (2756±24 Ma), MPR (2754±36 Ma) and MIR (2777±22 Ma), and in gold from the MVR (2778 Ma). All these geochronological data support a syngenetic to late syngenetic origin of the Igarapé Bahia Cu-sulfide + Au ores. Pb-Pb ages of 2385±122 and 2417±120 Ma obtained by leaching of the BHZ chalcopyrite may indicate a period of remobilization probably related to tectonic reactivations of the Carajás-Cinzento Strike-Slip System. δS18 values of +0.1 to +4.2%0 in ZBH sulfides (mostly chalcopyrite) corroborate both the involvement of magmatic hydrothermal fluids and exhalative deposition, whereas δC13PDB values of -7.28 to -15.78‰ in ZBH siderite suggest the mantle as a likely source for the homogeneous CO2- rich fluids responsible for the carbonate precipitation (carbonatic source) although, if it does not have evidences of the existence of this type of rock in the Carajás region. In turn, δO18PDB values of -15.51 to -20.96%0 in the same siderite indicate some contribution of meteoric waters to the fluids that altered the breccias. The Gameleira ore deposit is hosted by the Archean Igarapé Pojuca Group which consists of mafic metavolcanic rocks (MVR), amphibolites, schists, banded iron-formations and hydrothermalites. Neoarchaean mafic intrusive rocks (MIR), Paleoproterozoic quartz-feldspathic apophyses and granitoids crosscut all the Igarapé Pojuca rocks. Petrographical and geochemical data allow the MVR and MIR to be classed, respectively, as basaltic meta-andesites and quartz diorites of tholeiitic affiliation. The schistose rocks can be classified as plagioclase-quartz-biotite schist. Biotitization, chloritization, sulfidation, tourmalinization and silicification are the most remarkable types of hydrothermal alteration. The ore occurs chiefly in veins and veinlets and is characterized by selvages of chalcopyrite, pyrite, pirrhotite, bornite, molybdenite, rare cubanite, besides quartz, tourmaline, fluorite, chlorite and biotite. The MVR seem to be contemporaneous with those of the Grão Pará, Igarapé Bahia and Igarapé Salobo groups, adopting the age of the Grão Pará Group as the age of formation of these rocks. Dating of the MIR (Pb-Pb on zircon) yields a value of 2705±2 Ma interpreted as the crystallization age of these rocks and similar to those found for the mafic sills (2.70 to 2.65 Ga) that occur in the neighboring Águas Claras deposit. Pb-Pb ages of 2615±10 and 2683±7 Ma on zircon from a saprolith of the Igarapé Pojuca Group domain probably represent rocks coeval with those sills. Pb-Pb ages of 2646±30 Ma (MVR / whole-rock), 2422±12 Ma (vero sulfides) and 2218±14 Ma (leaching of chalcopyrite) are indicative of a superimposed event on the Igarapé Pojuca metamorphic rocks, either the emplacement of granitoid intrusions (1.87-1.53 Ga) or the reactivation of the Caraj ás-Cinzento Strike-Slip System. This event probably caused remobilization of pre-existing ore as well as (partial or total) resetting of the Pb isotopic system. Both the Igarapé Bahia and the Igarapé Pojuca groups, and other greenstone-like metavolcano-sedimentary sequences of Carajás, overlie a basement made up of rocks that are contemporaneous with the Xingu and Pium complexes as well as with the Arco Verde tonalite, which are the likely sources of the inherited zircon found in the MVR and MIR of the Igarapé Bahia Group and dated at 3.03-2.86 Ga. Therefore, the ranges of 3.03-2.86 and 2.76-2.74 Ga represent, respectively, well-defined periods of crust formation and expressive volcanism in the northern portion of the Carajás Mineral Province. Sm-Nd model ages (TDM) of 3.17-2.99 Ga, obtained for the rocks of both the Igarapé Bahia and Gameleira deposits are consistent with those determined for the basement rocks and granitoids that occur in the Carajás Mineral Province. ΕNd(t) values for these rocks (-0.36 to -2.12) indicate nor only participation of older crust material in the parental magmas but also that magmas were generated in a continental rift environment. This supports the current hypotheses about the tectonic environment of formation of the Itacaiunas Supergroup to which belong both the Igarapé Bahia and the Igarapé Pojuca groups. In conclusion, both studied deposits seem to have a similar primary genesis, but distinct further history in the Neoarchaean and Paleoproterozoic times, which certainly affected their mineralizations.Tese 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/1639498384851302The 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.