Evidence for metre-scale variations in hematite composition within the Palaeoproterozoic Itabira Iron Formation, Minas Gerais, Brazil

2006 ◽  
Vol 70 (5) ◽  
pp. 591-602 ◽  
Author(s):  
A. R. Cabral ◽  
B. Lehmann ◽  
H. F. Galbiatti ◽  
O. G. Rocha Filho
Keyword(s):  
Chemical Composition ◽  
Spatial Relationship ◽  
Mineral Chemistry ◽  
Minas Gerais ◽  
Ore Deposits ◽  
Iron Formation ◽  
Quadrilátero Ferrífero ◽  
Iron Ore Deposits ◽  
Iron Formations ◽  
Gold Bearing

AbstractHematite is a mineral the chemical composition of which rarely differs significantly from stoichiometric Fe2O3. As such, little attention has been paid to the mineral chemistry of hematite in Precambrian iron formations, where hematite forms monomineralic high-grade orebodies. Electron microprobe analysis of hematite from two iron-ore deposits, Cauê (Itabira district) and Gongo Soco, in the Palaeoproterozoic Itabira Iron Formation, Quadrilátero Ferrífero of Minas Gerais, Brazil, has revealed distinct variations in chemical composition with respect to Ti and Cr. Hematite containing Ti and/or Cr is of very local occurrence in the itabirite unit and shows a spatial relationship to hematitic, palladiferous gold-bearing veins (known as ‘jacutinga’), occurring either within the veins (adjacent to, or included in, palladiferous gold grains) or in their vicinity. Where present, titaniferous hematite (to ∼1.3 wt.% TiO2) is lepidoblastic and defines a pervasive tectonic foliation (S1). In contrast, Ti-free, chromiferous hematite (to ∼6.4 wt.% Cr2O3) characteristically occurs as inclusions in palladiferous gold within S1-truncating ‘jacutinga’. Replacement of granoblastic, Ti-free, chromiferous martite with relicts of magnetite by lepidoblastic, Cr-depleted, titaniferous hematite proves that Cr and Ti were mobile during metamorphism. Chromium was ultimately fractionated into the hematite found in auriferous aggregates within cross-cutting ‘jacutinga’. A positive correlation between Cr and Pt in bulk-rock samples from the Itabira district suggests that Cr is a potential prospective guide for Au-Pd-Pt-bearing hematitic veins (‘jacutinga’).

INDEX AND PROBABILITY MAPS OF OCCURRENCE OF IRON ORE DEPOSITS: A PROPOSED GEOPHYSICAL APPROACH DEVELOPED IN CURRAL NOVO DO PIAUÍ (PI) STATE – BRAZIL

2013 ◽  
Vol 31 (3) ◽  
pp. 365
Author(s):  
Enos Nobuo Sato ◽  
Teodoro Isnard Ribeiro De Almeida ◽  
Vilson Marques Dias ◽  
Jorge Kazuo Yamamoto ◽  
Francisco De Assis Cavallaro ◽  
...  
Keyword(s):  
Iron Ore ◽  
Target Selection ◽  
Ore Deposits ◽  
Geological Mapping ◽  
Iron Formation ◽  
Probability Of Occurrence ◽  
Iron Ore Deposits ◽  
Exploration Area ◽  
Host Rocks ◽  
Iron Formations

ABSTRACT. This article shows the results of the development of a procedure called TC-ASA index which is based on the contrast of magnetic and radiometric properties between host rocks and the mineralization, being interpreted as the probability of occurrence and defining ambience where iron formation to occur. It consists in subtracting the values of total count (TC) from the analytic signal (ASA), which are products of gammaspectrometry and magnetic methods, respectively. This index was applied to the actual data referring to the iron formations of Curral Novo do Piau´ı, where the main mineral is magnetite, thus characterized by high magnetic susceptibility and often associated with metabasic rocks. These rocks often present low concentration of radioactive elements, enabling the identification of geological environment with potential for occurrence of iron ore. The use of this procedure allowed for the reduction of the exploration area, providing a fast target selection for geological mapping, geochemistry and ground geophysics. In addition, it supplies with important elements that will assist mining companies in setting strategic priorities.Keywords: iron ore exploration, probability of occurrence maps, gammaspectrometry, magnetometry. RESUMO. Este trabalho mostra os resultados do desenvolvimento de um procedimento aqui denominado Índice TC-ASA que tem por base o contraste de propriedades magnéticas e radiométricas entre as rochas encaixantes e a mineralização, sendo interpretado como probabilidade de ocorrência e delimitando ambiências propícias a ocorrências de formações ferríferas. Tal procedimento consiste na subtração dos valores de contagem total (CT) dos valores do sinal analítico (ASA), que são produtos dos métodos geofísicos gamaespectrométrico e magnetométrico, respectivamente. Este índice foi aplicado a dados reais coletados nas formações ferríferas de Curral Novo do Piauí, cujo principal mineral é a magnetita, caracterizada pela suscetibilidade alta e frequentemente associada à metabásicas. Estas rochas normalmente têm baixa concentração de elementos radioativos, possibilitando a identificação de ambiências geológicas potenciais para ocorrencia deste tipo de minério. A utilização deste procedimento permitiu a diminuição da área de pesquisa em estudo de reconaissance proporcionando uma rápida seleção de alvos para mapeamento geológico, geoquímica e geofísica terrestre. Além disto, proporciona elementos importantes que auxiliam as empresas de exploração mineral na definição de suas prioridades estratégicas.Palavras-chave: prospecção de minério de ferro, mapas de probabilidade de ocorrência, gamaespectrometria, magnetometria.

scholarly journals A structural model of the Fábrica Nova region, Santa Rita syncline, Quadrilátero Ferrífero: flanking folds as a folding mechanism

2015 ◽  
Vol 68 (2) ◽  
pp. 153-162 ◽  
Author(s):  
Daniel Quinaud Rossi ◽  
Issamu Endo
Keyword(s):  
Structural Model ◽  
Axial Direction ◽  
Ore Deposits ◽  
Tectonic Deformation ◽  
Folding Mechanism ◽  
Structural Framework ◽  
Deformation Phase ◽  
Proposed Model ◽  
Quadrilátero Ferrífero ◽  
Iron Ore Deposits

AbstractThis study focuses on the eastern flank of the Santa Rita syncline (Dorr 1969), with specific emphasis on the region known as Fábrica Nova. Important iron ore deposits are located on the flanks of this structure, such as Timbopeba, Alegria, São Luiz, Tamanduá, Almas and Fábrica Nova. The Santa Rita syncline is a fold with N-S axial direction and of subregional scale, with roots in the adjacent basement of the Santa Bárbara Complex and sectioned by the Água Quente thrust fault. The hypothesis of this study is that the structural framework of the region resulted from the superposition of at least three deformation phases on the Ouro Preto nappe. The Fábrica Nova mine, located in the central portion of the study area, is embedded in a synformal structure with a 100/20 trending axis named Fábrica Nova synform. The proposed model to explain the particular structural geometry of this region is based on the flanking folding mechanism (Passchier 2001). This mechanism may have been developed by E-W crustal shortening during the F4 tectonic deformation phase.

scholarly journals A paleotoca da Serra do Gandarela e seu potencial como geossítio do Geoparque Quadrilátero Ferrífero, Minas Gerais / The paleoburrow of the Gandarela Mountains and its potential as a geosite of the QF Geopark, MG

2014 ◽  
Vol 24 (42) ◽  
pp. 249-263
Author(s):  
Úrsula Azevedo Ruchkys ◽  
Jonathas De Souza Bittencourt ◽  
Francisco Sekiguchi de Carvalho e Buchmann
Keyword(s):  
Preliminary Analysis ◽  
Minas Gerais ◽  
Quadrilátero Ferrífero ◽  
Paleontological Heritage ◽  
Iron Formations

A paleotoca registrada na Serra do Gandarela, Quadrilátero Ferrífero (MG), constitui um importante registro paleontológico da megafauna extinta de mamíferos, semelhante às ocorrências prévias em formações ferríferas no norte de Minas Gerais e em litologias diversas de outras regiões do país. Destaca-se pelas dimensões de 340m de comprimento, o que faz dela a maior paleotoca encontrada até o momento. Este trabalho, realizado sob os auspícios do Ministério Público de Minas Gerais, tem como objetivo avaliar o valor científico, pedagógico e educacional associado a esta ocorrência, visando sua inserção como geossítio do Geoparque Quadrilátero Ferrífero. Esta análise preliminar sugere que a paleotoca da Serra do Gandarela é um exemplo de patrimônio paleontológico com valores que legitimam plenamente sua proposição como sítio paleontológico/geológico do Geoparque Quadrilátero Ferrífero.Palavras-Chave: Paleotoca, megafauna extinta, Serra do Gandarela, Geoparque Quadrilátero Ferrífero. ABSTRACTThe paleoburrow in the Gandarela Mountains, Quadrilátero Ferrífero (MG) is an important record of the extinct megafauna of mammals. This is similar to previous occurrences in iron formations in northern Minas Gerais and in several rocks in other regions of Brazil, but stands out for the dimensions of length 340m, making it the largest paleoburrow found so far. This work has been carried out under the sponsorship of the Minas Gerais Public Prosecutor's Office. The scientific and educational significance of this fossil occurrence is assessed, aiming at its inclusion as a geosite of the Quadrilátero Ferrífero Geopark. This preliminary analysis suggests that this paleoburrow is a valuable example of paleontological heritage, what fully legitimates its proposition as a paleontological/geological site of Quadrilátero Ferrífero Geopark.Keywords: Paleoburrow, extinct megafauna, Gandarela Mountains, Quadrilátero Ferrífero Geopark. 

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