Análises prospectivas em mineralizações hospedadas em depósitos orogênico e do tipo óxido de ferro-cobre-ouro-(prata) no Greenstone Belt Faina, Brasil, utilizando dados multifonte

O Greenstone Belt Faina está localizado na porção sul do Bloco Arqueano de Goiás e vem sendo pesquisado desde o século XVIII por conta dos seus depósitos auríferos. Estudos recentes revelaram o potencial polimetálico do cinturão, em razão dos valores anômalos de Ag, Cu, Fe e Co, além de Mn, Ba, Li, Ni, Cr e Zn. Este estudo foi desenvolvido por meio da caracterização de dois alvos selecionados, Cascavel e Tinteiro, utilizando dados multifonte, tais como aerogeofísica de alta resolução, geoquímica e geologia. Esses dados foram integrados para criar um mapa prospectivo final utilizando a técnica lógica fuzzy. A mineralização aurífera do alvo Cascavel está inserida em um sistema orogênico e ocorre em dois sistemas de veios de quartzo superpostos, denominados de Mestre-Cascavel e Cuca, encaixados em quartzitos e com espessura média de 50 cm e orientação N45º-60ºW/25ºSW com a presença de ouro livre em grãos de 2-3 mm até 3 cm. O mapa prospectivo criado para esse prospecto indicou quatro áreas mineralizadas com favorabilidade de primeira ordem e novos focos com média favorabilidade. O alvo Tinteiro, derivado de estudos realizados pela empresa Orinoco do Brasil Mineração Ltda., mostra uma mineralização polimetálica associada a depósito do tipo óxido de ferro-obre-ouro-(prata), posterior à mineralização do alvo Cascavel. Seu mapa prospectivo apontou 19 novos focos com alta potencialidade para mineralização de Au, Cu e Ag, sugerindo novas direções para futuros programas prospectivos.The Faina Greenstone Belt is located in the southern sector of the Goiás Archean Block and has been investigated since the 18th century because of its gold deposits. Recent studies have revealed the polymetallic potential of the belt, which is indicated by anomalous levels of Ag, Cu, Fe and Co in addition to Mn, Ba, Li, Ni, Cr and Zn. This study was developed based on a detailed analysis of two selected target sites, Cascavel and Tinteiro, and multiple data sets, such as airborne geophysics, geochemistry and geological information. These datasets were used to create a final prospectivity map using the fuzzy logic technique. The gold mineralization of Cascavel target is inserted in an orogenic system and occurs in two overlapping quartz veins systems, called Mestre-Cascavel and Cuca, embedded in quartzite with an average thickness 50 cm and guidance ­N45º-60ºW/25ºSW with free coarse gold in grains 2-3 mm to 3 cm. The prospectivity map created for this prospect generated four first-order favorable areas for mineralization and new medium-favorability foci. The Tinteiro area, derived from studies conducted by Orinoco do Brasil Mineração Ltda., shows polymetallic mineralization associated with an iron oxide-copper-gold ore deposit (IOCG) system posterior to Cascavel target mineralization. Its prospectivity map generated 19 new target sites with the potential for Au, Cu and Ag mineralization, suggesting new directions for future prospecting programs

Prospectivity analysis of gold and iron oxide copper-gold-(silver) mineralizations from the Faina Greenstone Belt, Brazil, using multiple data sets

ABSTRACT: The Faina Greenstone Belt is located in the southern sector of the Goiás Archean Block and has been investigated since the 18th century because of its gold deposits. Recent studies have revealed the polymetallic potential of the belt, which is indicated by anomalous levels of Ag, Cu, Fe and Co in addition to Mn, Ba, Li, Ni, Cr and Zn. This study was developed based on a detailed analysis of two selected target sites, Cascavel and Tinteiro, and multiple data sets, such as airborne geophysics, geochemistry and geological information. These datasets were used to create a final prospectivity map using the fuzzy logic technique. The gold mineralization of Cascavel target is inserted in an orogenic system and occurs in two overlapping quartz veins systems, called Mestre-Cascavel and Cuca, embedded in quartzite with an average thickness 50 cm and guidance N45º-60ºW/25ºSW with free coarse gold in grains 2-3 mm to 3 cm. The prospectivity map created for this prospect generated four first-order favorable areas for mineralization and new medium-favorability foci. The Tinteiro area, derived from studies conducted by Orinoco do Brasil Mineração Ltda., shows polymetallic mineralization associated with an iron oxide-copper-gold ore deposit (IOCG) system posterior to Cascavel target mineralization. Its prospectivity map generated 19 new target sites with the potential for Au, Cu and Ag mineralization, suggesting new directions for future prospecting programs

Chemostratigraphy of the Carajás banded iron formation, Brazil : a record of Neoarchean Ocean chemistry

One of the most important occurrences of banded iron formation (BIF) worldwide is situated in the Carajás Mineral Province, southeastern Amazonian Craton. The BIFs are jaspilites and are hosted in the Neoarchean ( 2.74 Ga) volcano-sedimentary sequence of the Grão-Pará Group. They are mostly composed of cm-thick intercalations of hematite, jasper, and chert. Their primary textures and structures are still preserved, which make them an ideal archive to evaluate the paleomarine environment. Low abundance of Al2O3 (<1.0 wt%) and HFSE (<1 ppm) for most BIF samples indicate an essentially detritus-free depositional environment. Overall, the rare earth elements and yttrium (REY) patterns show a weak positive lanthanum (La) anomaly, and a pronounced positive europium (Eu) anomaly (Eu/EuPAAS = 1.86 – 5.05), although the presence of true cerium (Ce) anomaly is not evident. Stratigraphic variations in iron isotope compositions, up to 0.80‰ (d56Fe = +1.10 to +1.90‰) over tens to hundreds of meters of stratigraphic section, point to relative changes in the iron isotope composition of Carajás seawater over periods of a few million years. The jaspilites show heterogeneous distribution of Nd isotopic signature throughout the BIF sequence, and rocks from near the basaltic flows/jaspilite contact (type-II) have negative eNd (t) values (–4.97 to –0.90). In contrast, predominantly positive eNd(t) values (–0.84 to +5.40) are common in the remaining samples (type-I). The strongly positive d56Fe values indicate a low degree of partial oxidation of Fe(II), which, combined with the pronounced positive Eu anomalies and the absence of Ce anomalies, hint towards that the deposition occurred mainly on a deep-sea environment with intense hydrothermal activity under anoxic and suboxic conditions, distal to continental landmasses. Locally, considerable oxygen was probably present in the ancient ocean’s water masses, which led to the precipitation of BIFs

Multi-process and multi-scale spatial predictive analysis of an orogenic Archean gold system, Rio das Velhas Greenstone Belt, Brazil

There has always been a need for new methodologies and research to improve the decision-making process at the early stages of mineral exploration. This article presents a novel approach to integrating geodata in support of a mineral systems-based spatial analysis of orogenic gold deposits in the Rio das Velhas Greenstone Belt (RVGB), Quadrilkero Ferrffero Province, Brazil. The gold mineralization in the RVGB is spatially associated with thrust faults and shear zones and mainly hosted by iron-rich rocks such as mafic-ultramafic sequences and banded iron formations. To best represent the targeting elements of this mineral system spatially, a knowledge-based fuzzy logic method was employed to map the expressions of the gold depositional processes at the province (1:500,000), district (1:100,000) and camp (1:50,000) scales. At each scale, multivariate statistical techniques served to enhance multiple geological, geophysical, and geochemical datasets and extract from these data spatial proxies of the gold depositional processes. The results of this multi-scale predictive analysis were as follows: The first, province-scale model (M1) identified the entire gold prospective tract and the areas within it that may be of greatest relevance to future exploration. The second, district-scale model (M2) identified the different gold camps within the prospective tract and mapped the areas of gold favorability in a more detailed manner. The third, camp-scale model (M3) identified areas that, based on the current knowledge and distribution of high resolution geodata, are the most favorable whilst also being small enough as to permit target testing using conventional mineral exploration tools such as geophysics, geochemistry and/or drilling. The results obtained from our predictive models were validated by comparing them against the known gold occurrences using ROC (receiver operating characteristics) curves and AUC (area under the curve) graphs. According to these validations, model Ml scored an accuracy of 93.38%, whereas models M2 and M3 scored accuracies of 88.31% and 93.38%, respectively. A key observation made in the course of this study is that the gold prospective area as predicted by models M1, M2 and M3 varies according to the scale of the analysis. A novel factor in our approach is that we aimed assess the targeting criteria and spatial datasets that underpin them according to their spatial resolution and presented the results in form of integrated maps. In addition, the tools developed in this study have the capacity to reduce the cost of direct detection technologies regarding the transition from broad regional to camp scale at the early stages of mineral exploration, where the most initial decisions in search and area reduction are critical

Prospectivity analysis of gold and iron oxide copper-gold-(silver) mineralizations from the Faina Greenstone Belt, Brazil, using multiple data sets

<div><p>ABSTRACT: The Faina Greenstone Belt is located in the southern sector of the Goiás Archean Block and has been investigated since the 18th century because of its gold deposits. Recent studies have revealed the polymetallic potential of the belt, which is indicated by anomalous levels of Ag, Cu, Fe and Co in addition to Mn, Ba, Li, Ni, Cr and Zn. This study was developed based on a detailed analysis of two selected target sites, Cascavel and Tinteiro, and multiple data sets, such as airborne geophysics, geochemistry and geological information. These datasets were used to create a final prospectivity map using the fuzzy logic technique. The gold mineralization of Cascavel target is inserted in an orogenic system and occurs in two overlapping quartz veins systems, called Mestre-Cascavel and Cuca, embedded in quartzite with an average thickness 50 cm and guidance N45º-60ºW/25ºSW with free coarse gold in grains 2-3 mm to 3 cm. The prospectivity map created for this prospect generated four first-order favorable areas for mineralization and new medium-favorability foci. The Tinteiro area, derived from studies conducted by Orinoco do Brasil Mineração Ltda., shows polymetallic mineralization associated with an iron oxide-copper-gold ore deposit (IOCG) system posterior to Cascavel target mineralization. Its prospectivity map generated 19 new target sites with the potential for Au, Cu and Ag mineralization, suggesting new directions for future prospecting programs.</p></div