Navegando por Orientadores "KOTSCHOUBEY, Basile"

Agora exibindo 1 - 20 de 20

Acesso aberto (Open Access)
Caracterização e origem das formações ferríferas e xistos grafitosos do Grupo Estrondo na Região de Xambioá/Araguanã-TO
(Universidade Federal do Pará, 2005) SOUSA, Wiverson do Socorro Pantoja de; KOTSCHOUBEY, Basile; http://lattes.cnpq.br/0096549701457340
In the Xambioá/Araguanã region, located in the northern Neoproterozoic Araguaia Belt, iron-formations and graphite schists of the Estrondo Group are tightly associated with amphibolites and fine to medium-grained metagabbros, which are, respectively, interbedded in and intrusive into the metasedimentary essentially siliciclastic rocks of the cited unit. In this study, these different formations are described and compared with similar rocks and lithological associations from other regions in the world. Also, the origin and the depositional environment of the iron-formations and graphite schists, as well as their relationship with the basic rocks are discussed. The iron-formations are exposed in two principal zones, up to 5 km long, that are located along the northeastern border of the Lontra dome structure and the northern border of the Xambioá structure. These zones are discontinuous and consist of lenticular bodies, 200 to 1,500m long and 50 to 800m wide. Several more discrete iron-formations were recently identified in the study area. The iron-formations display a fine and fairly regular banding and are essentially composed of variably martitized magnetite and quartz, with highly subordinate pyrite and pyrrhotite. The studied samples are, as a rule, very rich in iron (mean Fe2O3tot=83.71%; maximum Fe2O3tot=96.77%) and revealed Pb, Zn, Cu and Co contents moderately higher than those detected in Carajás, Maru, Superior-type and Algoma-type banded ironformations. A prominent positive Eu anomaly (Eu* with mean=7.57 and maximum=15.54), the REE distribution pattern displaying LREE>HREE (mean La/Yb=18.54, maximum=82.83) and high ΣREE (mean=229 ppm, maximum= 371 ppm) suggest that the Xambioá/Araguanã iron formations are derived from chemical sediments of hydrothermalexhalative origin, in main part proximal. The graphite schists are interbedded in the micaschists of the Xambioá Formation and generally make up lenticular bodies tens to hundreds of meters long. However, to the west of the Lontra structure, graphite schists crop out for several kilometers north-south. These rocks are essentially composed of muscovite, quartz and graphite. Chemically, these schists are quite similar to other carbonaceous formations described in the litterature. Only vanadium and chromium contents are somewhat higher than those normally found in comparable rocks. Carbon, the content of which have mean=5,15% and maximum=9,41%, is likely of organic origin. The amphibolites and metagabbros are mainly hosted by micaschists and graphite schists. The former are often foliated, occasionally banded or microporphyritic, while the latter are normally isotropic or incipiently foliated and, frequently, display a porphyritic texture. These rocks are composed of hornblende-actinolite and plagioclase (labradorite and localling andesine in intrusive metamafics), with subordinate quartz, biotite, magnetite and hematite. In places, scapolite phenocrysts are fairly abundant. Sulphides (pyrite, chalcopyrite, chalcocite, and covellite, sphalerite and pentlandite) occur in traces. These metabasites are tholeiitic, sub-alkaline to slightly alkaline. Their REE distribution pattern suggest that, chemically, these rocks are similar to E-MORB. The association of iron-formations, graphite schists and basic rocks likely represents a sub-marine hydrothermal setting, developed during the distensive stage of the Araguaia basin evolution. In different sectors of the eastern part of the basin, basaltic flows and cogenetic gabbroic intrusions allowed the formation of convective systems. Percolating sea-water was progressively heated and evolved to hydrothermal fluids able to remove significant amounts of iron, silica and other metals from the basic volcanics and shallow intrusives. Chemical sediments rich in iron, resulting from this exhalative hydrothermalism were deposited in restricted sub-basins, close to venting zones. Diagenesis later transformed these metalliferous sediments into iron formations. The nutrient supply by the hydrothermal fluids and appropriate physico-chemical conditions close to these zones led to the proliferation of planctons. The organic matter accumulated in these sectors resulted in carbon enrichment of the siliciclastic sediments. During the metamorphic event that marked the late stage of the Araguaia Belt evolution, abundant aqueous solutions percolated the rocks of the Estrondo Group, removing most part of the silica from the iron-formations. Iron, almost insoluble in these probably oxidizing conditions, underwent a strong relative enrichment. At that same time, the carbonaceous matter was transformed into graphite.
Acesso aberto (Open Access)
Caulim do Morro do Felipe, baixo Rio Jari, estado do Amapá, contexto geológico e gênese
(Universidade Federal do Pará, 1995-12-04) DUARTE, Adalciléo Lúcio de Souza; KOTSCHOUBEY, Basile; http://lattes.cnpq.br/0096549701457340
The kaolin district of Morro do Felipe, located in the northwestem part ofthe State of Amapá close to the Jari river, contains abaut 366.000 metric tons of high quality ore - This arca is composed ofseveral plateaus up to 250 m, dissected by narrow valleys. The weathenng mantle which covers the plateaus consists of six, well individualized horizons, that is, firom bottom to top: a) clayey sandstones of the Alter do Chão Formation ( upper Cretaceous ); b) a thick kaolin horizon; c) a ferrugmous duricrust; d) a nodular lateritic levd; e) a gravelly bauxitic levei and f) a clayey overburden or Belterra Clay. Such stmcture and the composition of the difíerent horizons suggest, for the alteration cover, a complex and polyphasic evolution which would include the following phases: 1) Ferrugmization of Alter do Chão sediments and formation of a ferruginous duricrustin depressions. 2) Degradation ofthe upper part ofthe duricrust 3) Desilication of the Alter do Chão sediments in the topographically higher situated zones and ofthe degradation products ofthe duricrust in the lower ones. Bauxitization. Aluminization in the depressions as the result of the partial dissoludon ofpreviously formed gibbsite. 4) Dismantling ofthe upper part of the profile and formation of eluvial (nodular levei) and coluviáL (gravelly levei) deposits. Demidalion in places of altered Alter do Chão sediments. 4 5) Reworking of the weathered Alter do Chão sedimente, transport as mass flows and deposition as a severa! meters thick cover. 6) Slow regional uplift , relative lowering of the watertable and progressive alteration ofthe sedimente that overlie the lateritic - bauxitic duricrust. Desilication ofthe sandy-clayey overbnrden and gradual transformation into thick, homogeneous and gLbbsite-nch latosol, the Belterra Clay. 7) In limited zones, accumulation of oiganic matter at surface. Due to acidic and reducing conditions, local deferrification of the Belterra Clay and concentraüon ofthe mobilized iron as thin lithified fiingès. 8) Later lowering ofthe water table and alteration at depth of the Alter do Chão sedimente The Morro do Felipe kaolin was formed "in situ", at the expense of clayey sedimente of the Alter do Chão Formation, after the overlying lateritic profile was formed and the proto- Belterra Clay sedimente were deposited. The low permeablility of the clayey sedimente seems to have been decisive in this process. Due to the limited water discharge, slightly acidic and weakly oxidizing to reducing conditions installed, that caused deferrification of those sedimente and degradation ofthe constiluenl minerais. The diminute size of the kaolinite crystallites, their disordered distríbuition, the lithification ofthe upper part ofthe kaolin and the pronounced structural disorder detected in the kaolinite suggest (re) crystallization of an amorphous silico-aluminous phase. Kaolinisation, which probably started in Upper Tertiary time, was a slow, highly depending on climatic variations and tectonic factors process. It is possible thatitis stül active nowadays. 5
Acesso aberto (Open Access)
Estudo da cobertura laterítica ferro-aluminosa da aba norte da Serra dos Carajás (PA)
(Universidade Federal do Pará, 1993-03-24) SOUZA, Carlos Isaias de Jesus; KOTSCHOUBEY, Basile; http://lattes.cnpq.br/0096549701457340
Acesso aberto (Open Access)
Estudo das ocorrências auríferas da área de Natividade-GO.
(Universidade Federal do Pará, 1987-06-26) SILVA, Evaldo Raimundo Pinto da; KOTSCHOUBEY, Basile; http://lattes.cnpq.br/0096549701457340
Acesso aberto (Open Access)
Estudo do comportamento do ouro nas formações supergênicas da área Cachoeira, nordeste do Pará
(Universidade Federal do Pará, 1993-07-20) TARBACH, Milton; KOTSCHOUBEY, Basile; http://lattes.cnpq.br/0096549701457340
In the Cachoeira area, Gurupi region, northeast of Pará, there is a volcano-sedimentary sequence composed predominantly of strongly mylonitized dacites and rhyodacites, cut by bundles of quartz veins and venules from NS to NNE-SSW direction. In this sequence, gold is present in the form of fine “free” particles, disseminated both in the veins and in the heavily carbonated host rocks, as well as associated with a sulfide paragenesis consisting of pyrite, arsenopyrite, chalcopyrite and sphalerite. Over geological time, several surfaces marked by an old phosphate laterite, an immature ferruginous laterite and a level of ferruginous sandstone, respectively, developed. Furthermore, restricted-range gossans were formed early in this supergenic framework. In this work, only the most recent lateritic cover and the gossanic bodies were studied. Laterite comprises a thick saprolithic horizon, a mottled zone and a 3-meter-thick crust composed of hematite, goethite, kaolinite and generally subordinate quartz. In this alteration mantle, both gold and silver, although “invisible”, show an enrichment in the upper part of the profile and in particular in the crust. The trace elements Zn, Mn, Ni, Co, Cr, Cu and As, in turn, show higher contents in the mottled zone or at the top of the saprolite. The gossanic bodies, which mark the zones most enriched in sulphides, are composed essentially of goethite with microcrystalline quartz, kaolinite and sericite subordinated. In addition to fragments of veins. Gold, silver and arsenic show a tendency to enrich themselves in depth. In areas with higher levels of gold, it usually appears in fine visible particles or even tiny nuggets. On the other hand, the contents of Mn, Co, Zn and Pb suffer little variation in the studied profiles, while Ni and Cr show an enrichment at the top of the latter. It is assumed that during the formation of the lateritic cover, gold and silver suffered an incipient molybization, probably in the form of chlorides and/or organic complexes, whereas in the gossanic medium these elements migrated preferentially in the form of thiosulfates. In both cases the gold and silver would have been fixed by the iron hydroxide by adsorption and/or coprecipitation. Regarding the other trace elements, it is believed that their mobilization occurred mainly in the form of sulfates and according to the physical-chemical conditions of the medium. Its redistribution and fixation in the alteration products was probably controlled by its retention by poorly crystallized iron hydroxide.
Acesso aberto (Open Access)
Estudo geológico das lateritas aluminosas da Serra de Trucarã (Tucuruí, Estado do Pará)
(Universidade Federal do Pará, 1989-05-24) SOUZA, Eliene Lopes de; KOTSCHOUBEY, Basile; http://lattes.cnpq.br/0096549701457340
Acesso aberto (Open Access)
Estudo geológico e aspectos econômicos de um depósito de esmeralda clássico, Socotó-BA
(Universidade Federal do Pará, 1990-12-17) COLLYER, Taylor Araújo; KOTSCHOUBEY, Basile; http://lattes.cnpq.br/0096549701457340
The world trade in gemstones, which today involves values of around 80 billion dollars/year, dates back to millennia, having had a great influence on the development of human civilization. Emerald occupies a prominent place in this trade, and Brazil, with large gemological provinces, is an important source of this mineral. The Brazilian production, with approximately 80 tons/year of raw emerald, is favored by the relative political and social stability of the country, which constitutes an advantage in relation to other producing countries. On the other hand, the export of raw gemstones, the absence of a mineral and research policy in this sector, prevent the generation of greater resources, benefiting only small groups, usually foreigners. The present work aims to show that the Socotó emerald deposit, due to its classical characteristics, can serve as a model in view of prospecting in other areas with a similar geological environment, as well as to allow the clarification of some questions related to the formation of this mineral. The geological framework of Socotó mainly consists of an intensely fractured/failed basal-ultrabasic rock body, corresponding to a "roof pendant" or a mega-enclave embedded in the Campo Formoso granite batholith. The intrusive magma of granitic composition, rich in molybdenum, volatile elements and beryllium, reacted with the meta-ultrabasic rocks; suppliers of the chromophore elements Cr, Fe and V, which resulted, along dikes and veins, in abundant emerald mineralization controlled by geochemical, physical and structural factors. An intense metasomatism allowed the development of at least three concentric zones in the contact aureole, characterized by specific mineral associations, namely: an external zone, an intermediate zone and a more internal zone in the enclave. Through geophysical survey by scintillometry and magnetometry, the shape and the following dimensions were defined for this enclave: 2,150 meters long, 180 to 335 meters wide and a thickness of up to 161 meters. The analysis of the remaining magnetization showed the thermal evolution of the granitoids, from their placement 1973 ± 24 m.a ago (Torquato et al, 1978), to the closing of the mineralizing cycle 1784 ± 47 m.a., age obtained by the Rb/Sr method in phlogopites associated with emerald. Finally, the recognition of the different types of inclusions and the large amount of growth tubes and channels along the C axis of emerald crystals, whether or not filled with minerals, allowed the prediction, with economic objectives, of conventional or complex chemical treatment, involving the application of a laser beam and the displacement of atoms along these natural filaments.
Acesso aberto (Open Access)
Estudo petrológico e das mineralizações de granitoides Santa Luzia na região de Paraíso do Tocantins-TO
(Universidade Federal do Pará, 1996-03-24) LAMARÃO, Cláudio Nery; KOTSCHOUBEY, Basile; http://lattes.cnpq.br/0096549701457340
Acesso aberto (Open Access)
Evolução geológica no cenozóico da região norte entre Açailândia (MA) e Ligação (PA)
(Universidade Federal do Pará, 2000-06-14) CALAF, José Maria Calaf; KOTSCHOUBEY, Basile; http://lattes.cnpq.br/0096549701457340
The studied area is located along the BR-010 Highway (Belém-Brasília) between the cities of Açailândia (MA) and Ligação do Pará (PA), in the southern part of the Bauxiti-bearing Province of Paragominas and has an extension of about 115 km. In it, two surfaces were distinguished, each one supported by a specific alteritic-sedimentary sequence. The highest surface corresponds to the tops of vast residual plateaus from 360 to 220 m in altitude and presents a slight slope to the north. The other surface, embedded in the first, culminates between 210 m, to the south, and 150 m, to the north, and shows a slight swell. The old lateritic-bauxitic cover that supports the higher surface is constituted by a saprolitic horizon originating from the alteration of clayey or archosean sandstones and claystones from the “Itapecurú Deposits” of the Upper Cretaceous. On the saprolite rests a powerful armor, essentially ferruginous in the extreme south, which, towards the north, is progressively enriched in gibbsite. The first signs of bauxitic levels, still diffuse, are found about 40 km north of Açailândia. This trend is confirmed to the north with the presence of increasingly clear and consistent bauxitic horizons, above and at the base of the ferruginous horizon. Superimposed on this cover and in extremely sharp contact, there is a thick clay capping, the Belterra Clay. The lateritic-bauxitic cover developed in three phases. During the first phase, the ferruginous armor was formed through the ferruginization of the Itapecurú sediments, during the Lower Tertiary. Afterwards, the armor was affected by partial degradation and physical reworking of its products. Remains of older alterites may have also been involved in this process that resulted in deposition of nodular to pseudopisolithic gravel and sandy clay. The third phase, essentially chemical, consisted of the generation of bauxite in areas that presented more favorable climatic and geomorphological conditions. This event probably occurred at the end of the Eocene. The exclusively ferruginous lateritic armor that supports the lower surface has as substrate a reddish clayey sandstone containing small lateritic fragments and quartz pebbles. The cuirass itself has a massive, columnar or nodular structure, and the degraded stone-layer can be found in several places. Its cap is formed by a yellowish clayey-sandy material, rich in quartz grains and disseminated letheritic fragments. This laterite probably formed in the late Pliocene – early Pleistocene. Its substrate can be correlated with the Barreiras Group, while its capping would correspond to the unit called Post-Barreiras further north, in the Ipixuna-Aurora region. The stone-layers quite frequent in the area are located in the same stratigraphic position as the more recent lateritic armor and resulted from in situ degradation of this armor, without significant physical rework. However, locally, colluvial deposits of the glacis type or pediments composed of fragments of ancient armor were identified. The following stages characterized the evolution of the two alteritic-sedimentary sequences: 1- formation of a ferruginous armor from the Itapecurú Deposits; 2- partial degradation of the armor; 3- Bauxitization in the Paleogene; 4- deposition of sediments that later change to Argila de Belterra; 5- major erosive phase and individualization of vast plateaus; 6- filling of the valleys and lowered areas separating the plateaus by sandy-clay sediments correlated with the Barreiras Group and degradation products of the old armor; 7- ferruginization of the sediments from step 6; 8- more or less accentuated degradation of the ferruginous crust from stage 7, giving rise to stone-layers; 9- deposition of clayey-sandy sediments correlated with the Post-Barreiras on the armoring of stage 7 and the stone-layers; 10- dissection and establishment of the current drainage network. Climatic variations and periodic tectonic (epirogenetic) reactivations throughout the Cenozoic were the main factors responsible for this evolution.
Acesso aberto (Open Access)
Evolução recente da cobertura de alteração no platô N1-Serra dos Carajás.
(Universidade Federal do Pará, 1995-04-26) MAURITY, Clovis Wagner; KOTSCHOUBEY, Basile; http://lattes.cnpq.br/0096549701457340
Acesso aberto (Open Access)
Geologia e aspectos metalogenéticos dos elementos do Grupo da Platina no complexo máfico-ultramáfico da Serra da Onça – Sul do Pará
(Universidade Federal do Pará, 1997-08-12) MACAMBIRA, Edesio Maria Buenano; KOTSCHOUBEY, Basile; http://lattes.cnpq.br/0096549701457340
Acesso aberto (Open Access)
Geologia e gênese do veio de cristal de rocha do Garimpo da Lagoa, Xambioá – TO.
(Universidade Federal do Pará, 2000-08-31) FERREIRA, Iêda de Oliveira; KOTSCHOUBEY, Basile; http://lattes.cnpq.br/0096549701457340
The crystal rock occurrences from Xambioá region, situated in the northem part of the Araguaia Belt, are associated with quartzites of the base of the Morro do Campo Formation and schists of the Xambioá Formation, both of the Upper Proterozoic Estrondo Group. The crystal rock occurs mainly as irregular pockets within milky to grayish translucent quartz veins. The “Garimpo da Lagoa” crystal rock vein is hosted by biotite - schists of the Xambioá Formation, displays a general sub-meridian direction and is up to 5 m thick. Petrography and microthermometry of vein samples revealed the presence of two distinct fluids types: 1) oversaturated aqua - carbonic fluids in pseudo - secondary inclusions, containing up to 4 solid phases and 2) aqueous fluids of low to high salinity in secondary inclusions. The aqua — carbonic fluid inclusions contain almost pure CO», with traces of N; due probably due to the presence of carbonatic rocks and graphite in the area. Most fluid inclusions underwent crepitation before they reached Th. Even so, the minimum trapping temperature for these fluids was estimated in 550 to 600º C. It is believed that fluids are basically of deep metamorphic origin, though they also show significant contribution of magma derived solutions. The aqueous fluids were found in three-phase oversaturated, two-phase and monophase inclusions. The solutions contained in the three-phase inclusions revealed a salinity from 30 to 40% in weight of NaCl and a minimum trapping temperature between + 182 and + 321ºC. K is believed that these fluids were injected after the aqua — carbonic ones and were essentially of magmatic origin. Concemning the fluids contained in the two-phase inclusions, were distinguished solutions of low salinity (1,23 to 11,81% in weight of NaCl) and a minimum trapping temperature from + 123,8 to + 150,9ºC, and solutions of high salinity, sub-divided in two categories (a) and (b), mainly based on their morphology. The (a) type revealed a salinity of about 23% in weight of NaCl and a minimum trapping temperature between +130 and 210%, more frequently at + 160ºC, while the (b) type indicated a salinity ffom 20 to 25% in weight of NaCl and a minimum trapping temperature from + 65 to + 114,Sth C, more frequently at + 70ºC. The fluids contained in the monophase inclusions displayed a salinity of 1.91% to 18.22% in weight of NaCl. The solutions trapped in two-phase and monophase inclusions would represent late injections of hydrothermal fluids of magmatic origin, which underwent progressive cooling and composition modifications in agreement with the importance of the contribution of more superficial (meteoric, conate, etc.) waters. During the final phase of the Araguaia Belt evolution, in predominantly distensive conditions, at first aqua — carbonic fluids were injected, that resulted, in formation of a hyaline quartz vein, poor in fluid inclusions. Later on, the vein suffered multiple fracturing phases and aqueous solutions were injected showing a progressive lowering of the temperature and, in a less systematic and less regular way, of the salinity. These late injections were responsible in variable degree for the transformation of the original hyaline quartz into translucent or milky quartz. Pockets which were not affected by these late hydrothermal displays remained as crystal rock. Crystal rock, mainly as third quality chips is used as raw material for production of synthetic crystal. Prismatic, well developped quartz crystals and first quality chips are used in mineral craft for production of adornment pieces, balls, key rings and cut stones. Crystal rock is mainly exported to Belo Horizonte, Sete Lagoas, Governador Valadares, where already cut stones are commercialized , and to São Paulo and Rio de Janeiro, where raw crystals are mainly appreciated.
Acesso aberto (Open Access)
Geologia e geoquímica das mineralizações supergênicas de ouro das áreas Salobo e Pojuca-Leste, Serra dos Carajás
(Universidade Federal do Pará, 1996-11-29) SILVA, Evaldo Raimundo Pinto da; KOTSCHOUBEY, Basile; http://lattes.cnpq.br/0096549701457340
In Salobo sector, the primary gold and copper mineralization occurs in two types of iron formations, both of the silicate facies: Type I composed of magnetite>50% + fayallite + grunerite and Type II constituted of magnetite<50% + biotite + grunerite + almandine, which occurs interlayered in barren metagraywacks. In iron formations gold is present as: i) microscopic (5-14m) and submicroscopic (<0,1 µm) inclusions in magnetite; ii) microscopic and submicroscopic inclusions in primary copper sulphides (mainly chalcopyrite; subordinatelly bornite and chalcosine); and iii) as rare visible gold particles in quartz-carbonate-clorite veins which cut the Type II iron formation. Magnetite is the major gold-bearing mineral at Salobo. In the veins, gold is rich in silver and copper (16,5% and 8,4%, respectively) and exhibits increasing fineness from the border to the center of the particles. In these latter, a negative correlation between silver and copper contents, and exsolution textures suggest a separation between Au-Cu and Au-Ag during gold deposition in veins. The Salobo weathering profile is truncated and developed upon a thick metagraywacke sequence with interlayered iron formations lenses. From bottom to top, the weathering profile consists of a transition zone, a saprolitic zone and a colluvium horizon. The transition zone and the saprolite exhibit textural and mineralogical variations that reflect the heterogeneous composition of the bedrock. Weathering of metagraywacke resulted in a clay-mineral rich saprolite -hidrobiotite, smectite, kaolinite- derived principally from biotite. On the other hand, the alteration of mineralized rocks resulted, from bottom to top of the profile, in a supergene sulphide zone, an oxidized zone and a ferruginous saprolite. The most important supergene sulphides are digenite and covelline, while in the oxidized zone occur minerals such as cuprite, malaquite, azurite, native copper and native silver. In the ferruginous saprolite copper is enriched in clay-minerais (smectite) and in iron oxi-hydroxides. The secundary gold mineralization at Salobo occurs only in the oxidation products of iron formations. Gold exhibits enrichment in two levels of the weathering profile: in the supergene sulphide and oxidized copper minerals zones, and in the intermediate zone of the ferruginous saprolite. In these alteration products, gold occurs as: i) tiny inclusions (7-30m) in refractory magnetite crystals and in fratures of this mineral; ii) as submicroscopic particles inclosed in martitized magnetite crystals; and iii) as submicroscopic particles adsorbed ("invisible gold") in goethite. At Pojuca-Leste the primary gold mineralization is present in quartz-tourmaline-flurite-copper sulphides veins which cut a thick quartz-biotite-schists sequence and in iron formations lenses interlayered in these rocks. Gold occurs as: i) submicroscopic inclusions in chalcopyrite of veins, schists and iron formations; ii) as submicroscopic inclusions in magnetite of iron formation; and iii) as rare microscopic inclusions in quartz of veins. In the veins gold particles shows low fineness 809). The weathering profile at Pojuca-Leste consists of a thick saprolitic horizon and a ferro-aluminous duricrust. The saprolite exhibits compositional variations related to the nature of the parent rocks. It is generally composed of kaolinite, goethite and hematite and its iron contents are higher when derived from iron formations and sulphide veins. The secundary gold mineralization at Pojuca-Leste occurs in alteration products of sulphide veins, in the ferruginous saprolite derived from iron formations and in ferro-aluminous duricrust. In these secondary products, gold is present as: i) rare particles in relict quartz-tourmaline±sulphide veins; ii) as submicroscopic inclusions in martitized cristais of magnetite; iii) as submicroscopic particles adsorbed in goethite from the veins; and as iv) submicroscopic particles adsorbed in Fe-Al oxi-hydroxides of the duricrust. The supergene concentration of gold in Salobo and Pojuca-Leste sectors, envolved principally relative enrichment, and only subordinatelly absolute enrichment. In these areal, gold enclosed in refratary cristais of magnetite and quartz, favoured a relative enrichment during alteration of the primary mineralization. On the other hand, a minar amount of gold enclosed in copper sulphides (mainly chalcopyrite) was released, mobilized and reprecipited in the sulphide oxidation zone during several phases of the lowering of water table. Such evolution resulted in individualization of several enrichment levels, which shows variable lateral extension in the weathering profile. The main factor which controlled the secondary concentration of gold in Salobo and Pojuca-Leste areas was the forro of gold occurrence in the primary ore. In these sectors, gold armoured as tiny inclusions in magnetite and quartz crystals, dificulted the supergene remobilization process and resulted in a high relative enrichment.
Acesso aberto (Open Access)
Geologia e mineralização aurífera da área de Chapada-TO
(Universidade Federal do Pará, 2001-10-10) QUEIROZ, Joedy Patrícia Cruz; KOTSCHOUBEY, Basile; http://lattes.cnpq.br/0096549701457340
The Chapada gold deposit is located in the extreme north of the outer zone of the Brasília Belt, in the central part of the Tocantins Province. The geological framework of the area consists of an orthogneissic basement of tonalitic to granodiorite composition or Manoel Alves Complex, in the Água Suja metavolcanosedimentary Sequence metamorphosed in the high greenschist facies and comprising acidic and basic metavolcanic rocks, and metasedimentary rocks of clastic and chemical origin (older than 2172±5 Ma), in the Xobó intrusive granitic Suite (minimum age of crystallization: 2012±3 Ma) and a folded cover consisting predominantly of quartzites, corresponding to the Natividade Group. In the Chapada Garimpo, there are essentially quartz-biotite schists and metadacites of the Água Suja Sequence cut by veins and pockets of pegmatoid to aplitic, leucocratic granite, belonging to the Xobó Suite. These rocks were affected by intense transcurrent movements of general direction N30E that resulted in a shear zone hosting a complex and anastomosed system of quartz veins. The host rocks of the veins show strong signs of mylonization, eventually cataclase. The biotite shales were, in particular, transformed into muscovite-biotite mylonites. Finely disseminated metallic minerals are found in both quartz veins and mylonites in the contact zones, with pyrrhotite and pyrite being the earliest, followed by chalcopyrite and sphalerite, and finally by arsenopyrite and free gold or included in the latter, all formed at the end of the deformational/hydrothermal event. The main types of alteration observed are muscovitization, epidotization and silicification. The hydrothermal process involved several phases and was initially marked by the formation of very hot aqua-carbon solutions (<330°C). Subsequently, with the increasing participation of shallower waters, essentially lower temperature aqueous fluids acted (from 300/250 °C to about 150 °C), basically belonging to the systems CaCl2-NaCl-H2O and KCl-NaCl-H2O. The mineralized quartz and sulphide + gold vein system of the Chapada area fits into the category of orogenic lode type deposits. The isotopic analysis by the Rb-Sr method of the micas of the host mylonites of the veins allowed to determine at 517±40 Ma the age of the regional shear and, consequently, of the gold mineralization, which would be, therefore, directly related to the formation of the intracontinental megastructure referred to as Lineament. Late Neoproterozoic Transbrasilian.
Acesso aberto (Open Access)
Geologia e mineralizações auríferas da área do Garimpo do Manelão, região do Bacajá (Pa)
(Universidade Federal do Pará, 1995-03-14) SOUZA, Valmir da Silva; KOTSCHOUBEY, Basile; http://lattes.cnpq.br/0096549701457340
The Manelão area is part of the Itacaiunas Shear Belt located in the center-west of the State of Pará. The Archean-Proterozoic lithostratigraphic units recognized in this area are Xingu Complex granites and gneisses, amphibolites, micaschists and quartzites from the São Manoel volcano-sedimentary sequence and the Felicio Turvo intrusive stratoid monzogranite. Mesozoic gabbro and diabase dykes, Cenozoic laterites and recent colluvial and alluvial deposits complete the lithostratigraphic picture. The main structures identified in the area were originated by a sinistral transcurrent deformation of a ductile to ductile-ruptile nature that involved a rock mass transport from ESE to WNW. Such tectonism caused low to medium easy amphibolite metamorphism, although locally more intense hydrothermalism caused alteration of high greenschist facies. Gold occurs both in veins lodged in amphibolites and schists of the São Manoel volcano-sedimentary sequence, as well as in lateritic cover and in alluvial/colluvial deposits. Two systems of veins were identified, one with direction N70E and dip of 80° to NW, the other with direction N23E and dip equal to the previous one. In these bodies the gold is essentially in the free form, in particles of low purity (about 870) that fill fractures in the quartz or quartz-albitic gangue. Furthermore, it is believed that the pyrite disseminated both in the veins and in the mylonitized and heavily altered host rocks also contains sub-microscopic gold. The hydrothermal alteration resulted in a rough zoning in the host rocks. Upon contact with the veins, a philic alteration is normally observed, while the intermediate zone exhibits propylitization. The outer zone is marked above all by an intense epidotization of the rocks. The metallic minerals, pyrite (two generations), pyrrhotite, chalcopyrite, ilmenite and rutile are found in the form of crystals or small scattered aggregates and are more abundant in the host rocks than in the veins themselves. The fluid inclusion study revealed that the mineralizing fluids were essentially low-temperature (minimum temperature 160-180°C) aqueous solutions of low to moderate salinity (probably H2O-KCl-CaCl2 and H2O-NaCl-CaCl2) and low density. (0.9 - 1.1 g/cm 3 ). Rare three-phase inclusions suggest, however, that high temperature and high salinity solutions equally participated in the mineralizing process. Although CO2 was not detected in this preliminary assessment, its presence in subordinate amounts cannot be ruled out. Considering the predominance in the sulfide system and low temperatures of fluid trapping, the gold seems to have migrated mainly in the form of thio-complexes. In the lateritic cover developed over the São Manoel sequence, gold occurs in fine particles or small nuggets of high purity (about 985) with frequencies intergrown with iron oxyhydroxide both in the mottled zone and in relict fragments of the ferruginous crust. The high degree of purity of lateritic gold suggests that the mobilization of the metal occurred mainly after complexation with organic and thiosulfate ligands. Silver leaching into primary gold particles may also have accounted for the significant difference in purity. Gold particles and nuggets are also dispersed in the clayey matrix of colluvial deposits. Finally, gold forms concentrations of relevant economic value in the lower gravel horizon of alluvial accumulations.
Acesso aberto (Open Access)
Geologia e ocorrências auríferas da área do Morro do Lajeado, Porto Nacional – TO
(Universidade Federal do Pará, 1995-06-26) MEIRELES, Henrile Pinheiro; KOTSCHOUBEY, Basile; http://lattes.cnpq.br/0096549701457340
The gelogical setting of the Morro do Lajeado region includes Precambrian and Phanerozoic formations. The first ones comprise 1- a gneissic basement of tonalitic to granodioritic composition; a volcano-sedimentary sequence (Morro do Aquiles Formation) made up of quartz-amphibolites, mylonitic schists, metapelites and gondites, and tonalitic bodies (Torre granitoid) intrusive into the former units. Folded metapsammites of the Natividade Group occur locally. Ductile-brittle NE-SW striking shear zones crosscut all these units and constitute an anastomosing system which encloses preserved, undeformed or weakly mylonitized cores of tonalitic bodies. Paleozoic sediments of the Serra Grande and Pimenteiras formations belonging to the Parnaiba Basin, Mesozoic doleritic dykes and silis, Cenozoic laterites and recent colluvial and alluvial deposits complete the lithostratigrafic framework of the area. Quartz veins, concordant and sub-concordant with the regional foliation, occur within the shear zones. They are massive and lenticular in shape (boudin-like) and are up to several meters thick. All veins are oriented N30E, except the Torre vein whose direction is N75W, and crop out over a few meters up to 200 m along the strike. The mineralization consists of native gold and pyrite aggregates. Gold occurs as sub-millimetric particles concentrated in dimimite geodes and druses or disseminated in frature planes close to the ends of the quartz lenses. Microprobe analyses of'these particles revealed a fineness of approximately 908. Chemical analyses showed that the inner parts of the veins are barren or contain only traces of gold, whereas their borders are enriched in this metal, mainly in the extremities of the mega- boudins and at the contact with the host rocks. Microthermometric study evidenced the presence both, of aqueous salihe solutions (4-15 equiv. wt % NaCl) containing NaCl and MgClh,, and CO; - rich solutions, the latter confirmed by Raman microprobe spectroscopy. Minimum trapping temperatures of 219ºC to 260ºC were obtained for the aqueous solutions, while a temperature of approximately 350ºC was determined for the carbonic ones. The intensely mylonitized host rocks belonging either to the Morro do Aquiles Formation or to the Torre granitoid exhibit a pervasive hydrothermal alteretion. Sericitization and/or epidotization of plagioclase, chloritization of biotite and amphibole, kaolinization of K-feldspar and neoformation of cabonate are the principal alteration processes. The geological evolution of the Morro do Lajeado area, after the formation of the gneissic basement, recorded the accumulation of clastic and chemical sedimentas associated to volcanic flows, as well as the later emplacement of tonalitic intrusive bodies. All these rocks underwent a high greenschist facies regional metomorphism followed by an intense shearing and hydrothermalism. Low- to middle greenschist facies transformations affected the highly deformed rocks in the shear zones while the mobilized fluids caused leaching of gold probably out of the volcano-sedimentary pile. The mineralizing fluids are believed to have been mainly of metamorphic origin though magmatic and/or meteoric contributions should not be ruled out. Thus, the precipitation of gold together with quartz and pyrite most likely was caused by the reaction between fluids of different sources.
Acesso aberto (Open Access)
Geologia e ocorrências minerais da branquianticlinal de Xambioá - Goiás
(Universidade Federal do Pará, 1983-08-29) SANTOS, Márcio Dias; KOTSCHOUBEY, Basile; http://lattes.cnpq.br/0096549701457340
Acesso aberto (Open Access)
Geologia e ocorrências minerais da branquianticlinal do Lontra - GO
(Universidade Federal do Pará, 1983-08-29) MACAMBIRA, Joel Buenano; KOTSCHOUBEY, Basile; http://lattes.cnpq.br/0096549701457340
Acesso aberto (Open Access)
O Magmatismo granítico e os seus efeitos na região de Xambioá/Araguanã, To
(Universidade Federal do Pará, 2009-05-22) POINSIGNON, Janaina Reis; KOTSCHOUBEY, Basile; http://lattes.cnpq.br/0096549701457340
The Xambioá region is located in the eastern part of Arguaia belt, in the northern portion of the domain of Estrondo Group (northwest of the State of Tocantins). The granites of Ramal do Lontra and Serra da Ametista, intrusive in the rocks of Estrondo Group, were until recently, the only felsic bodies known in the region. More recent geological observations, during detailed geological mapping, identified several intrusive granitic bodies, generally small, as well as in many sectors, unequivocal signs of albitization, greisenization and caulinization in both granitic bodies and host rocks. Quartz vein systems, host of hyaline quartz and eventually amethyst are commonly associated with granitic intrusions and/or with altered host rocks. The felsic magmatism expressed by the emplacement of alkali-granites (Ramal do Lontra and Serra da Ametista granites and occurrences of Fazenda Novo Horizonte, Fazenda Bela Vista, Fazenda Belém, Morro das Antenas and adjacency) and of albite-granites (Araguaci and sector of Pedra Preta granites). Fine to medium-grained alkali-granites, are usually deformed. These bodies have been considered late-tectonic and correspond most likely to apical zones of larger granitic intrusions, not yet exposed. Fine to medium-grained albite-granites consist essentially of albite, like euhedral crystals, and quartz do not show deformation. It has been interpreted as products of extreme granitic magma differentiation, which originated the alkali-granite. The postmagmatic context had a complex development, resulting in the formation of quartz vein systems and marked alteration of both the intrusive garnitic rocks and host rocks of Estrondo Group formations and the Archean basement. Based on fluid inclusions studies of vein quartz, two types of fluids have been recognized: aqueous- carbonic and aqueous. The first, with high salinity (38 to 53% eq of NaCl) and temperature (340 to 500°C) of metamorphic origin with important magmatic contribution, may have caused the formation of the early milky quartz, and probably the metasomatic alterations at high temperature, namely the albitization and greisenization of both granitic intrusions and host rocks. The second type, of moderate to low temperature and salinity (to 120 from 200°C and 1 to 18% eq of NaCl), is interpreted as having a magmatic origin and after mixing with meteoric waters caused its temperature and salinity decrease. It is possible that the drops in temperature and salinity may have been, in part, resulted from the natural cooling of hydrothermal process. These fluids were responsible for the formation of hyaline quartz, in distensive context of decreasing pressure. They also caused the alteration of igneous rocks and host rocks at low temperature, essentially kaolinization. The albitization was the earliest metasomatic alteration. At high temperature and alkaline conditions, it affected both alkali-granites and albite-granites, and the nearby host formations. Albitite with riebeckite and aegirine resulted also from this process. Strong signs of albitization were also detected in the Estrondo Group rocks and Complexo Colméia, regardless of any magmatic influence, what suggests the possibility of this process not be local but regional and related to the regional metamorphism or dynamometamorphism that acted during the structural evolution of Araguaia belt. The greisenization, even more local, succeeds to albitization, at high temperature but in acidic conditions. It is restricted to immediately host rocks of the intrusive granitic bodies and probably to their marginal portions. At last, at lower temperatures and acidic conditions, kaolinization occurred and their effects have been observed only in the host schists, although this alteration may have also affected the intrusive bodies. The total destruction of all primary minerals but not quartz, resulted in the formation of pure kaolin consisting of kaolinite of high crystallinity.The geochemical data reveal coherence between several processes, like the concentration of trace elements (Th, U, Hf, Nb, Zr, V and W) very common in granitic environment.The results obtained in this study suggest that magmatic/ hydrothermal manifestations have been more intense that believed before, being recommended the continuation of investigations, in more meridian zones of the Estrondo Group domain.
Acesso aberto (Open Access)
Mineralizações de caráter gemológico (opala, ametista, quartzo tricolor, quartzo rutilado e com clorita) da região de São Geraldo do Araguaia (PA) - Xambioá (TO): caracterização e gênese
(Universidade Federal do Pará, 1999-06-16) COLLYER, Taylor Araújo; KOTSCHOUBEY, Basile; http://lattes.cnpq.br/0096549701457340
In the Xambioá-São Geraldo do Araguaia region, located in the northern segment of the Araguaia belt, pegmatitic and hydrothermal quartz veins with opal, amethyst, three colored quartz, and with rutile and chlorite occur. The genesis of these veins has been investigated due to their gemmological interest. The most important opal — bearing quartz vein is hosted by metasedimentary rocks of the Xambioá Formation, and presents a rough zoning in addition to a brecciated texture. The outer zone of the vein consists of milky quartz, while the inner zone is composed of onyx, jasper opal (C-T) cut by small veins of C-T opa! and A opal. High salinity fluids of H2O-0O2-NaCl and H20-KCl-NaCl systems (> 26 wt% of NaCl equiv.) have been found in the outer zone quartz, while in the intermediate zone low salinity fluids of the system H20-FeCl2-NaCl (0,88 to 3,71 wt% o NaCl equiv.) were observed. Th ranges from 232 to 310°C and from 110 to 145°C for the quartz of the outer and intermediate portions, respectively. These data, along with the opal metastability suggest that the quartz of the outer zone may be related to the regional metamorphism of Brasiliano age that affected the Araguaia belt. They also suggest a contribution of meteoric water to the formation to both the jasper opal and the C-T opal, as well as a supergenic origin to the A opal. The inner portions of these veins may have been formed by the reactivation of older fractures during the Paleozoic and/or Mesozoic. The vein with amethyst in emplaced into the granitoid body of Serra da Ametista. It is pegmatitic in nature and is composed of quartz, amethyst, microcline, oligoclase, muscovite, and biotite. Fluids of the system F120- KC1-NaCl are found in both quartz and amethyst. In quartz, the salinity of these fluids ranges from 18,95 to 20,75 wt°/.9 of NaCl equiv., and in amethyst from 12,73 to 18,00 wt% NaCl equiv. Th ranges from 190 to 248,5°C in quartz, and from 155 to 200°C in amethyst. These fluids might have had a magmatic origin and be related to the late cooling phase of the Serra da Ametista granitic body. Rb-Sr ages in pairs of minerais (muscovite-microchne and muscovite-oligoclase) range between 390 and 430 Ma. These ages are younger than the probable Brasiliano age of the vein and suggest a partial resetting of the Rb-Sr system due to subsequent tectonic reactivations. The three colored quartz occurs as zoned crystals in the inner parts of quartz veins emplaced into metarkoses and metasandstones of the Pequizeiro Formation. Inclusivas ofred rutile,pyrite and melanterite in the upper parts of the quartz crystals give them the light red to yellowish brown color. In the lower portion, the purple-yellow dual coloration is given by the presence of iron, aluminum, potassium and sodium. In the outer portion of the studied veie, the quartz presents high salinity fluids of the system H20-CaC12-NaCl (20,60 to higher than 23,18 wt°/0 of NaCl), and Th ranging from 488 to 492°C. Fluids of the systems H20- CaC12-NaCl and H20-FeC12-NaCl were identified in the lower portion of the three colored quartz crystals, and of the system H20-FeCl2-NaCl in the upper portions. The salinity of the fluids in the lower portions ranges from 13,83 to 17,34 and from 17,96 to higher than 23,18 wt% of NaCl, respectively. In the upper portions of the crystals, the salinity decreases. Th, which is higher than 485°C in the lower portions decreases to values between 272 and 305°C in the upper portions. A MEV study in the three colored quartz showed inclusions of thorite, metallic mercury in the basal portion; pyrite, cinnabar, and zircon in the intermediate portion; and pyrite, melanterite, anhydrite, and barite in the upper portion. The origin of these veins may be related to the regional magmatism in the Araguaia belt, but a possible influence of the final phases of the regional metamorphism cannot be ruled out. Contribution of meteoric water, mainly to the upper portions of the three colored quartz crystals, has also to be considered. The quartz veins with rutile and chlorite are hosted by the mica schists and quartzite of the Estrondo Group. They are composed by hyaline quartz crystals, rutile, chlorite, specular hematite, and magnetite. Fluids of the system H20-1CCI-NaCl, were identified in the quartz of the outer parts of the veie, as well as in the quartz with rutile and chlorite of the inner parts. However, the salinity of these fluids is higher in the quartz of the outer parts (18.80 to higher than 23.18 wt% of NaCl) than in the quartz with rutile and chlorite (4.34 a 5.26 wt% of NaCl). Th ranges from 293 to 345°C in the quartz of the outer zone, and from 136.54 to 198.9°C in the quartz with rutile and chlorite. The outer parts of the veie were possibly generated by fluids of magmatic and/or metamorphic origin. However, a considerai* contribution of meteoric waters is considered for the formation of the inner parts of the veins. The data suggest that the quartz veins systems are related to extensional tectonic and to hydrothermal events which took place in the late stages of structural development of the Araguaia belt, following the regional metamorphism and the consequent granitogenesis. In spite of the nature of the aqueous system, the magmatic and/or deep metamorphic fluids that generated the quartz veias show, initially, high salinity and medium to high temperature. Probably due to the increasing contribution of meteoric waters, both the salinity and temperatures (lower than 200° C) decreased. Later, tectonic reactivations during the Paleozoic and/or Mesozoic were responsible for migration and injection of silica bearing solutions, generated at depth, and by precipitation of silica as onix, jasper opal and opal C-T. More recently, opal A was formed in supergenic conditions.