Navegando por Autor "CRAVEIRO, Gustavo Souza"

Agora exibindo 1 - 3 de 3

Acesso aberto (Open Access)
Depósito Cu-Au Visconde, Carajás (PA): geologia e alteração hidrotermal das rochas encaixantes
(2012-09) CRAVEIRO, Gustavo Souza; VILLAS, Raimundo Netuno Nobre; SILVA, Antonia Railine da Costa
Visconde Cu-Au deposit, Carajás (PA): geology and hydrothermal alteration of the host rocks. The Cu-Au Visconde deposit is located 15 km east of the Sossego mine (Canaã de Carajás, in the State of Pará) and it lies in the contact zone between the Itacaiúnas Supergroup (2.76 Ga) and the basement (> 3.0 Ga). The main rocks present in the deposit are the Serra Dourada granite, gabbros/quartzdiorites and rhyodacites, all variably altered and deformed. The Planalto Intrusive Suite has also been identified in the neighborhood, but it shows distinct alteration features. Mafic and felsic dikes crosscut the whole rock pile. The hydrothermal alteration has evolved, under rheological conditions that changed from ductile-brittle to brittle, from an early and pervasive calcic-sodic type (albite, scapolite or amphiboles) to a potassic one (K-feldspar and Cl-biotite), restoring, though locally, the sodic-calcic characteristics (albite, epidote, apatite, tourmaline and fluorite) to finally acquire a calcium-magnesium signature (clinochlore, actinolite, carbonates, and subordinate talc). In the Serra Dourada granite, albitization, epidotization, and tourmalinization were dominant in contrast with scapolitization, biotitization, amphibolitization and magnetitization in gabbros/quartzdiorites or K-feldspatization in rhyodacites. The main ore bodies are represented by chalcopyrite- and bornite-rich breccias and veins, besides chalcopyrite + pyrite ± molybdenite ± pentlandite disseminations. The basic metal suite is Fe-Cu-Au ± REE. Abundant sulfide was precipitated in the transition from potassic to calcic-magnesian alteration, along with different proportions of apatite, scapolite, actinolite, epidote, magnetite, tourmaline, calcite, gypsum, and fluorite. Metals were transported by hydrothermal fluids enriched in Na, Ca, K, Fe, and Mg, in addition to P, B, F, and S species. The similarities overcome the differences, so that the Visconde and Sossego deposits can be considered co-genetic.
Acesso aberto (Open Access)
Geologia, alteração hidrotermal e gênese do depósito IOGG Cristalino, Província Mineral de Carajás, Brasil.
(Universidade Federal do Pará, 2018-10-22) CRAVEIRO, Gustavo Souza; XAVIER, Roberto Perez; http://lattes.cnpq.br/6388495537140928; 6388495537140928; VILLAS, Raimundo Netuno Nobre; http://lattes.cnpq.br/1406458719432983; 1406458719432983
The Archean Cu-Au Cristalino deposit is located 40 km east from Sossego mine in the eastern end of the regional WNW-ESW Carajás shear zone, in the Serra do Rabo region. Its host rocks are mainly the mafic volcanic rocks of the Parauapebas Formation, and subordinately the BIF of the Carajás Formation. Field-work, petrographic data seconded by SEM-EDS, in addition to microprobe analysis and fluid inclusion and stable isotope (O, H, C and S) systematics, allowed characterizing a hydrothermal system that was responsible for the development of successive alteration zones in the wall rocks. Sodic metasomatism (650°C ≥ T > 400°C, and P > 1.8 Kbar) formed near pure albite, schorlitic tourmaline, REE-rich minerals (allanite-Ce, monazite) and minor calcite and quartz. It was followed by a more pervasive calcic-ferric alteration which produced abundant actinolite (XMg = 0.9-0.7 and up to 0.6 wt. % Cl), allanite-Ce (up to 0.6 wt. % Cl) and magnetite, associated with sulfide disseminations and replacement breccia-like bodies composed of chalcopyrite-pyrite-magnetite-Au (early ore association). Locally, Fe-edenite (XMg=0.7-0.4, Cl up to 2.9 wt. %) replaced calcic-ferric assemblages within restrict sodic-calcic alteration halos. From 410o down to 220o C and 1.8 Kbar > P > 0.6 Kbar, the previous alteration assemblages were overprinted by potassic (Kfeldspar, minor biotite) and propylitic/carbonatic (epidote, chlorite, calcite) alterations, in this order. K-feldspar is practically stoichiometric, but with high contents of BaO (up to 1.2 wt. %). Chlorite shows the greatest compositional variation among all minerals and seems to have been controlled by the type of host rock, chemistry of the hydrothermal fluid and temperature. Both chamosite and clinochlore (XFe=0.4-0.8) are present, the former being more common. Chlorine contents are in general < 0.02 wt. % and a little more significant in chlorites that replaced chessboard albite (up to 0.06 wt. %). The late ore association (chalcopyrite±Au±pyrite±hematite) is contemporaneous with the potassic and propylitic alterations and bears evidence that the Cristalino system evolved to the final stages with increase in oxygen fugacity. The ore fluid was hot (> 550°C), hypersaline and chemically approached by the system H2O-NaCl-CaCl2-CO2±MgCl2±FeCl2. Salinity exceeded 55.1 wt. % NaCl equiv. in the early stages but decreased progressively to 7.9 wt. % NaCl equiv. from 250o C on, after incursion of surficial water into the system. Initially 18O-enriched/D-depleted (δ18Ovsmow =+9.7 to +6.5 ‰; δDvsmow= -30.8 to -40.2 ‰) and most likely derived from magmatic sources, the fluid became relatively 18O-depleted/D-enriched (δ18Ovsmow =+5.57 to - 0.28‰; δDvsmow= -19.15 to -22.24‰) as result of dilution caused by mixing with meteoric water. δ13CVPDB values for vein and breccia calcite (-6.5 to -3.8‰) are consistent with a deep source for CO2, which was probably released from an underlying magma chamber. The δ34SVCDT values for chalcopyrite show narrow variation (+1.6 to +3.5 ‰) and indicate a homogeneous reservoir for sulfur, which was likely of igneous origin. Although most data point to a magmatic affiliation, a few samples reveal significant influence of sedimentary rocks on their isotope composition. Mostly transported as chloride complexes (>350oC), Cu and Au precipitated in response to decrease in temperature and Cl- activity and increase in pH. An aqueous, colder (200-150o C) and less saline (21-3.1 wt. % NaCl equiv.) fluid appears to have circulated in the Cristalino deposit area, being trapped as secondary fluid inclusions. The origin is unknown, but it could be related to a nearby Paleoproterozoic granitic intrusion. The data presented here support previous interpretations that consider Cristalino as of IOCG typology. In comparison with other Archean Carajás IOCG deposits, particularly those that lie in the southern sector of the Carajás Domain, the Cristalino deposit shows many similarities regarding ore fluid composition and evolution, as well as the isotopic signature of sulfides and carbonates.
Acesso aberto (Open Access)
Geologia, fluidos hidrotermais e origem do depósito cupro-aurífero Visconde, Província Mineral de Carajás.
(Universidade Federal do Pará, 2011-08-24) CRAVEIRO, Gustavo Souza; VILLAS, Raimundo Netuno Nobre; http://lattes.cnpq.br/1406458719432983
The Cu-Au Visconde deposit lies at the contact zone between the basement (>3.0Ga) and the Grão Pará Group (2.76 Ga) within the so-called Transition Domain of the Mineral Carajás Province. It is located at about 15 km east of the Cu-Au Sossego mine in the county of Canaã de Carajás, Pará state. Felsic metavolcanic rocks, probably belonging to that group, as well as granitic and mafic intrusions, dominate in the deposit and neighboring area. Subordinate ultramafic bodies occur within the mafic units. All these rocks are moderately to strongly hydrothermally altered and show varying degrees of deformation. Mafic dikes and a granitoid isotropic body, the latter probably related to the granitogenesis of 1.88 Ga, represent the last igneous activity in the area and cut the pre-existing rock package. Despite the mineralogical and textural changes, it was possible to infer a monzogranitic to granodioritic composition to the original granitoids largely based on the amounts of chess-board albite. Moreover, the scarcity of primary mafic minerals makes these granitoids similar to the Planalto Granite, which crops out approximately 7 km east of the deposit area. The mineral content and the partially preserved subophitic texture are suggestive that gabros and/or quartz diorites were potential protoliths of the mafic intrusions. On the other hand, the recognition of plagioclase, quartz and K-feldspar primary phenocrysts and the use of trace elements with limited mobility in the hydrothermal environment allowed discriminating a riodacitic composition for the protolith of the felsic volcanic rocks. Grading from ductile to brittle regimes, the hydrothermal alteration changed from early sodic-calcic assemblages, characterized by ubiquitous albitization, scapolitization or amphibolitization, to late potassic assemblages, in which the K-feldspar and Cl-biotite are the diagnostic minerals. Then the alteration restored its sodic-calcic character as indicated by albite, epidote, apatite, tourmaline and fluorite that replaced pre-existing minerals or filled open spaces. At last, it is recorded a calcic-magnesian stage during which clinochlore/Fe-clinochlore, actinolite, carbonate and subordinate talc were equilibrated. In the granitoids, albitization, epidotization and tourmalinization were the most prominent alteration processes, whereas scapolitization, biotitization, amphibolitization and magnetization were more remarkable in gabros/quartz diorites and K-feldspatization in the felsic metavolcanic rocks. The ore, whose formation began at the final stages of the potassic alteration, was essentially controlled by brittle structures. Initially represented by weak chalcopyrite, molybdenite and pyrite disseminations in the zones altered to tremoliteactinolite, scapolite, albite and magnetite, the mineralization evolved to sulfide concentrations in veins and breccias. Among the sulfides chalcopyrite, bornite, molybdenite are dominant, but pyrite and pentlandite also occur together with apatite, scapolite, actinolite, epidote, magnetite, martite, hematite, calcite, and gypsum or fluorite as the main gangue minerals. The typical metallic suite of the sulfide breccia is Fe–Cu–Ni–ETR±Au±Zn±Y±Co±Se, with ƩETR as high as 1030 ppm. Fluid inclusions trapped in quartz, scapolite, apatite and calcite crystals unraveled at least three aqueous fluids. Fluid 1, simplified by the system H2O-NaCl-CaCl2±MgCl2 and present in all host minerals, was hot (450–500ºC) and very saline (up to 58 wt% equivalent NaCl). The alteration and mineralization haloes should have resulted from the interaction of the host rocks with this fluid, which might have experienced cooling and dilution probably due to mixing with surficial waters. After the mineralization event, the deposit recorded the successive inflow of fluid 2 (H2O-NaCl-FeCl2±MgCl2, up to 30 wt % equiv. NaCl) and fluid 3 (H2O-NaCl±KCl, up to 18 wt % equiv. NaCl), both cooler than fluid 1. With a restrict circulation and preserved only in quartz and apatite crystals, fluid 2 might have been related to the intrusion of the late mafic dikes, whereas fluid 3 migration would have taken place in response to the emplacement of the alkali granite (1.88 Ga?), being trapped, similarly to fluid 1, in all host minerals, but as secondary IF. The high salinity and no evidence of boiling, coupled with the presence of Cl-rich minerals, suggest that a purely magmatic source is unlike for fluid 1. As an alternative, it is assumed a mixed source, involving the migration of magmatic or metamorphic fluids throughout carbonatic-evaporitic sequences from which Na, Ca and Cl have been largely leached. The mineralogical, chemical and microthermometric data allowed to characterize the mineralizing fluid as an aqueous solution consisting of NaCl, CaCl2, KCl, FeCl2 and MgCl2(?) that also carried P, B, F, Y, Ba, Sr, Rb and ETR, Cu, Ni and Co, besides S species. The Sossego and the Visconde deposits present similarities in terms of (1) the nature of the host rocks (felsic metavolcanics, granitoids, and mafic intrusions), (2) the types of alteration, highlighting the intense and widespread sodic-calcic metassomatism, (3) the occurrence of the major ore bodies in brecciated zones and (4) the Fe-Cu-Ni-ETR±Au±Co as the metallic signature of the ore. Regarding the main differences, the sub-economic sulfide accumulations and the smaller amounts of massive magnetitites of the Visconde deposit could be listed.