Navegando por Assunto "Epitermal"

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Acesso aberto (Open Access)
Geologia e Metalogênese do Depósito Au-Ag (Pb-Zn) do Coringa, Sudeste Província Mineral Tapajós, Pará.
(Universidade Federal do Pará, 2020-09-16) GUIMARÃES, Stella Bijos; KLEIN, Evandro Luiz; http://lattes.cnpq.br/0464969547546706; https://orcid.org/0000-0003-4598-9249
The Tapajós Mineral Province (TMP) is located in the south-central portion of the Amazonian Craton and is considered one of the main metallogenic provinces of Brazil. A significant part of the province comprises felsic volcanic and volcanoclastic rocks and granites, which formed predominantly in two intervals, 2.02 to 1.95 Ga and 1.91 to 1.87 Ga, belonging to several stratigraphic and lithodemic units. Fieldwork, petrography, and high-resolution airborne geophysics allowed us to produce a new map at the 1:100,000 scale for the southeastern portion of the TMP, where the gold and silver (Cu-Pb-Zn) Coringa deposit is located. We identified two new geological units: (1) the volcanic and pyroclastic rocks of the Vila Riozinho Formation, previously attributed to the Iriri Group, including a facies defined here of this formation, which comprises a group of rocks with the largest magnetic content in the region (Vila Riozinho Formation - magnetic pyroclastic facies), and (2) the Serra Alkali Feldspar Granite, which intruded into the Vila Riozinho Formation (VRF). These units are the host rocks of Coringa deposit. The FVR rocks represent a magmatic arc with high K calcalkaline to shoshonitic affinities. There are similarities in the patterns of LILE and HFSE and the multielementar diagrams with the granitic rocks from Creporizão Intrusive Suite (CIS). The contemporaneousness between these units reinforce a possible petrogenetic correlation and converge to the hypothesis of similar sources, of probable remelting of arc rocks. Isotopic data revealed similar behavior between VRF, SAFG and Maloquinha Intrusive Suite expose similar behavior and present negative εNd values; however, it indicates rocks derived from enriched sources (ancient crustal rocks). Therefore these units had the same source during tectonic setting and crustal evolution of TMP. It is a transcurrent post-collisional stage that followed the collision of the Cuiú-Cuiú Magmatic Arc related to the Orosian volcano-plutonic event (2033-2005 Ma). Based on available geochronological information these units can be associated with a volcano-plutonic event that occurred in the Orosirian period, at about 1.98 Ga. The Au-Ag (Cu-Pb-Zn) Coringa deposit, occurs essentially in veins and veinlets whose match the regional trend (NNW-SSE). The host rocks are volcanic and pyroclastic rocks of the Magnetic Pyroclastic Facies (MPF) from the Vila Riozinho Formation (ignimbrites, tuffs, and breccia), and the Serra Alkali Feldspar Granite, with a predominance of the supracrustal rocks The hydrothermal processes affected all lithotypes associated with mineralization, producing distal alteration (carbonate-chlorite-epidote), intermediate-proximal alteration (sericite-pyrite) and proximal alteration (chlorite-hematite). The mineralized veins are generally composed of quartz + pyrite + chalcopyrite + galena + sphalerite + electrum + chlorite + sericite. Gold grains occur as inclusions or fractures in pyrite. The fluids presents low salinity, rich in H2O and poor in CO2, with evidence of mixing (magmatic-meteoric), and the presence of adularia and Mn-carbonate are outstanding features of this deposit. All characteristic converge to confirm an intermediate- sulfidation epithermal deposit as a genetic model to Coringa deposit.
Acesso aberto (Open Access)
Metalogênese do depósito aurífero Volta Grande, Domínio Bacajá (PA), Cráton Amazônico: aplicação de espectroscopia de infravermelho VNIR-SWIR.
(Universidade Federal do Pará, 2024-02-27) PARESQUI, Brenda Gomes Silva; FERNANDES, Carlos Marcello Dias; http://lattes.cnpq.br/0614680098407362; https://orcid.org/0000-0001-5799-2694
The world-class Volta Grande gold deposit contains measured reserves of ~6.0 Moz at 1.02 g/t, divided into north and south exploration blocks. It is inserted in the geological context of the Bacajá Domain and was affected by the Trans-Amazonian Cycle (2.26–1.95 Ga). Part of the mineralization is hosted in a group of gneisses and mylonitized granitoids in amphibolite facies of medium to high metamorphic grade of the Três Palmeiras Group (2.36 Ga). Recent research in the northern block has revealed the presence of late volcanics and plutonics, with isotropic texture and intermediate to felsic compositions, which host disseminated gold in different types and styles of hydrothermal alteration, as well as in quartz and carbonate (±sulfides) venules and veins. Thus, this Master's Thesis represents the continuity of research in the northern block of this repository with the application of the VNIR–SWIR (visible-near and short-wave infrared) infrared spectroscopy technique. This tool helps to explain in detail the configuration of the hydrothermal system, contributing to a better understanding of the genesis of the deposit. The mineralogy observed by spectroscopy in metamorphic rocks confirms the occurrence of potassic, propylitic, intermediate argillic, pervasive carbonate, and advanced argillic hydrothermal alterations types. The latter occurs associated with high levels of gold and alunite, a mineral indicative of epithermal systems with high-sulfidation. In turn, the isotropic volcanic and plutonic rocks present more developed, intense, and larger-volume hydrothermal alterations. They reveal greater diversification of hydrothermal minerals, where jarosite is the superior indicator of advanced clay alteration, which is also consistent with high-sulfidation epithermal mineralizations. In addition, the appearance of rhodochrosite, pyroxmangite, and galena, mainly related to volcanic rocks of andesitic and dacitic compositions, suggests an epithermal system of intermediate-sulfidation. The geological features present in the region and the hydrothermal alterations, especially the propylitic alteration in the rocks with allanite, clay minerals, montmorillonite, and zeolites, portray a typical epidote subzone of a low-temperature propylitic alteration that are genetically related to the medium-depth intrusions where they appear hydrated porphyry stocks. In this way, the Volta Grande gold deposit reveals characteristics compatible with rare and base metals porphyry and epithermal mineralizing systems, already identified in other regions of the Amazon Craton. The high-sulfidation conditions at the northwest portion of this repository and intermediate-sulfidation at the southeast region point to a transitional environment. The VNIR–SWIR spectroscopy method represents an important tool that identifies and characterizes hydrothermal minerals quickly and efficiently, as well as differentiating them from weathered ones. In general, it becomes a significant prospective guide when robustly analyzing minerals that are difficult to recognize by other methods such as conventional optical microscope or scanning electron microscope (SEM). The results presented here represent a remarkable contribution to the geological and metallogenetic knowledge of the Bacajá Domain, as well as the Amazonian Craton as a whole, pointing out the potential for identifying economically viable deposits of precious and base metals associated with volcanic and plutonic systems that occur in a vast area of this domain.
Acesso aberto (Open Access)
Petrografia e mineralogia das alterações hidrotermais associadas ao bloco Sul do depósito aurífero Volta Grande do Xingu, Domínio Bacajá (PA), Cráton Amazônico
(Universidade Federal do Pará, 2025-04-22) PINTO, BRENDA THAYS BARROS; FERNADES, Carlos Marcello Dias; http://lattes.cnpq.br/0614680098407362; https://orcid.org/0000-0001-5799-2694
The world-class Volta Grande gold deposit, at the Bacajá Domain, contains measured reserves of approximately 6.0 Moz at 1.02 g/t, divided into the north and south exploratory blocks. Historically, this mineralization has been classified as orogenic (lode-type) and is found within a set of mylonitized granitoids in the amphibolite facies of medium to high metamorphic degree attributed to the Três Palmeiras Group (2.41 Ga) and the Oca Granodiorite (2.16 Ga). However, recent research on the rocks of the northern block has established a late volcanic sequence with significant gold mineralization. Aiming to contribute to its metallogenetic modeling, this Master’s Dissertation focused on the southern block, involving macroscopic and microscopic petrographic descriptions and the application of VNIR–SWIR reflectance spectroscopy in core samples from the Pequi, Grande, and Itatá targets. First, the results include the petrography of metamorphic rocks, represented by amphibolite and mylonitic granodiorite, and an associated isotropic volcanic and plutonic suite. The data compilation revealed mineral paragenesis related to metamorphic and magmatic-hydrothermal processes. The metamorphic paragenesis reveals regional and dynamic-thermal metamorphisms and moderate overprinting of hydrothermal alterations typical of epithermal systems, associated with the emplacement of the isotropic rocks package. Second, in the isotropic rocks, there is an overprint of hydrothermal alterations and gold mineralization conceivably of intermediate- and high-sulfidation epithermal-type genetically linked to magmatic-hydrothermal systems, with carbonate alteration in a boiling zone and advanced argillic alteration. In conclusion, data integration from the southern block shows, similarly to the northern block, at least two genetically distinct gold mineralizing events that enhanced the grade and tonnage of the Volta Grande deposit, thus representing a new prospective model for the Bacajá Domain.