Navegando por Assunto "Ouro roxo"

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Acesso aberto (Open Access)
Evolução dos fluidos mineralizantes e modelo genético dos veios de quartzo auríferos em zona de cisalhamento do depósito Ouro Roxo, Província Tapajós, Jacareacanga (PA), Brasil
(2013-12) VELOSO, Ângela Suélem Rocha; SANTOS, Márcio Dias; JAVIER RIOS, Francisco
The Ouro Roxo gold deposit, located near Jacareacanga, Tapajós Gold Province, southwestern Para, Brazil, comprises a hydrothermal system of sulfide quartz veins that was hosted by the calc-alkaline mylonite granitoid Tropas Intrusive Suite of Paleoproterozoic age and controlled by the N-S trending ductile-brittle oblique Ouro Roxo-Canta Galo, crosscutting the granitoid Tropas. Three kinds of fluids were identified as sources of mineralization in the Ouro Roxo deposit: 1) an aqueous fluid within the H2O-NaCl-MgCl2-FeCl2 system, with low-to-middle salinity and homogenization temperature (Th) = 180-280°C; 2) Cu and Bi-bearing H2O-NaCl-CaCl2 brines, with Th = 270-400°C, genetically related to a magmatic event coeval to shearing, which underwent dilution by mixing with meteoric water; 3) gold bearing middle-salinity aquocarbonic fluid, with Th = 230-430°C, which was interpreted as ore fluid related to shearing. The T-P conditions of ore formation, estimated by chlorite geothermometer and fluid inclusion isochors, range from 315 to 388°C and 2,0 to 4,1kb. The two main mechanisms for gold deposition in transtensional sites of the shear zone were: 1) Mixing of aquocarbonic fluid and magmatic brines induced an increasing of fO2 and decrease of pH; 2) interaction between fluids and feldspars and ferromagnesian minerals of the hoster granitoid which reduced fO2 and fS2 during hydrolysis and sulfidation reactions, with precipitation of iron sulfides together with gold. The orogenic environment, the veining style, the structural control by shearing, the hydrothermal alteration (propylitic+philic+carbonatization), the metallic association (Au+Cu+Bi), the association of aquocarbonic ore fluid with magmatic brines in ore deposition, are all consistent with an orogenic model for genesis of the Ouro Roxo deposit with magmatic participation.
Acesso aberto (Open Access)
Geologia e metalogênese do depósito aurífero Ouro Roxo, Província Tapajós, Jacareacanga-PA.
(Universidade Federal do Pará, 2011-05-25) VELOSO, Ângela Suélem Rocha; SANTOS, Márcio Dias; http://lattes.cnpq.br/6977793618030488
The OuroRoxo gold deposit is located near São José Village at Pacuriver margin, far around 36 km from Jacareacanga city, western Tapajós Gold Province, SW portion of Para State. The OuroRoxo deposit comprises a hydrothermal system of sulfide quartz veins hosted by mylonitegranitoidTropas Intrusive Suitof Paleoproterozoic age. The ore bodies are controlled by a N-S trending shearing known as OuroRoxo-CantaGalo shear zone. The host granitoids are oxidized calc-alkaline granodiorite and tonalite with magnetite and sphene, characterized as magmatic arc granitoids.The OuroRoxoCantaGalo shear zone is a sinistral oblique ductile-brittle shear of low to middle angle which has turned the granitoids into protomylonites and mylonitesinterlayed with breccias zones. The protomylonites are characterized by predominance of porfiroclasts over the matrix composed by phengite, chlorite and quartz which grade into mylonites and minor ultramylonits with almost 100% of matrix. The mylonitic foliation is defined by chlorite, biotite and phengite along NNE-SSW direction dipping to ESE. Stretched quartz grains define a lineation which indicates the oblique tectonic movement to NNW. Shear features such as mica-fish,shadow pressure, tail recristalization and microboudinage are ubiquitous in theses rocks and indicate a sinistral kinematics for shearing. The ore bodies are quartz veins and pipes hosted by mylonites and breccias, surrounded by prominent alteration halos and concordant to mylonitic foliation. Besides silicification and sulfidation more concentrated in the ore bodies, three types of hydrothermal wall-rock alteration were recognized in alteration halos: 1) propilitic alteration: chlorite+phengite+carbonate. Four chlorite generations were identified, the last one being veinlets; 2) phylic alteration: phengite+quartz+carbonate+pyrite, with three phengite generations; 3) carbonatization with three generations of carbonate, the last one beingveinlets. Besides magmatic quartz and microcrystalline quartz of mylonites, five generations of hydrothermal quartz were recognized in the lodes, the last one beingveinlets.The ore shoots are mainly made up by pyrite and chalcopyrite, with minor bismutinite, native bismuth and gold. Besides the pyrite associated to gold and an earlier pyrite magmatic generation, late pyrite veinlets occur. Two generations of chalcopyrite were identified and the second one substitutes the pyrite 2 associated to ore. The main gange minerals are quartz, chlorite, phengite and carbonate. Azurite, bornite and covellite are copper supergenic minerals derived from alteration of chalcopyrite.Three kinds of fluids were identified in vein quartz of the OuroRoxo deposit: 1) low-to-middle salinity aqueous fluid within the H2O-NaCl-MgCl2-FeCl2systemwhich occurs in quartz 3, with Th=180-280°C; 2) brines within the H2O-NaCl-CaCl2 system which occur in quartz 4 and 6, with Th=270-400°C, and underwent dilution brought about by mixing with meteoric water, lowering its salinity and temperature (Th=120-380); 3) middle-salinity aquocarbonic fluid which occurs in quartz 3 and 4, with Th=230-430°C. The aquocarbonic fluid was interpreted as ore fluid related to shear zone with higher Th in ductile conditions. The brines origin was related to a magmatic event coeval to shearing, with lower Th in the end of the residual magmatic process.The temperature and pressure conditions of OuroRoxo deposit formation were estimated using the hydrothermal chlorite geothermometer and the isochors calculated from the fluid inclusion microthermometric data. Values range from 315 to 390°C and 2,0 to 4,2 k b. Two mechanisms were regarded to be the main cause for gold deposition. 1) Fluid- rock interaction brought about increasing of fO2 and reduction of fS2 during hydrolysis (propylitic and phylic alteration) and sulfidation reactions; 2) Mixing between aquocarbonic fluid and magmatic brines induced an increasing of fO2anddecreasing of pH. These two mechanisms would favor gold deposition in transtension sites of the shear zone.The age of ore formation, obtained by Pb-Pb method in pyrite, was estimated around 1858±130Ma. The large error of that age turn it as reference age only which shows a time relationship between the mineralization, the shearing and the Maloquinha granite event. The orogenic magmatic arc environment, the veining style, the structural control by the shear zone, the hydrothermal alteration (propylitic+philic+carbonatization), the metallic association (Au+Cu+Bi), the middle-salinity aquocarbonic ore fluid and the participation of magmatic brines in ore deposition, are all consistent to a hybrid model (orogenic with magmatic participation) for the genisis of the OuroRoxo gold deposit.
Acesso aberto (Open Access)
Geologia, petrografia e geocronologia das rochas do depósito aurífero Ouro Roxo, Província Tapajós, Jacareacanga (PA), Brasil
(2013-03) VELOSO, Ângela Suélem Rocha; SANTOS, Márcio Dias
The Ouro Roxo gold deposit lies near the city of Jacareacanga, Tapajós Gold Province, southwestern of Pará, Brazil. The Ouro Roxo deposit comprises a hydrothermal system of sulfide quartz veins hosted by mylonite granitoid Tropas Intrusive Suit of Paleoproterozoic age and controlled by the N-S trending Ouro Roxo-Canta Galo shear zone (OCSZ). The host granitoids are oxidized calc-alkaline granodiorite and tonalite of magmatic arc filiation. The OCSZ is a sinistral oblique ductile-brittle shear, which belongs to the third deformation event of the Tapajós Province and has turned the granitoids into protomylonites, mylonites and breccias. The NNE-SSW mylonitic foliation dipping to ESE and stretch lineation in quartz grains indicate the tectonic movement to NW. Mineralized quartz veins and pipes are hosted by mylonites and breccias and surrounded by hydrothermal alteration halos. Besides silicification and sulfidation, concentrated in the ore bodies, three types of wall-rock alteration occur: propilitization (chlorite + phengite + carbonate); phylic alteration (phengite + quartz + carbonate + pyrite); carbonatization. Besides magmatic quartz and microcrystalline quartz of mylonites, five generations of hydrothermal quartz were recognized in the lodes. The isotopic Pb-Pb data do not support a genetic relationship between the gold deposit and the Tropas granitoids, being the deposit coeval to Maloquinha granite. The orogenic environment, the veining style, the structural control, the hydrothermal alteration and the metallic association (Au + Cu + Bi), are all consistent with a mesozona-epizona orogenic model for the genisis of the Ouro Roxo deposit.