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THE ORIGIN OF HEMATITE IN HIGH-GRADE IRON ORES BASED ON INFRARED MICROSCOPY AND FLUID INCLUSION STUDIES: THE EXAMPLE OF THE CONCEICAO MINE, QUADRILATERO FERRIFERO, BRAZIL

2004; Volume: 99; Issue: 3 Linguagem: Inglês

10.2113/gsecongeo.99.3.611

1554-0774

Carlos Alberto Rosiére, Francisco Javier Ríos,

Geological and Geochemical Analysis

Research Article| May 01, 2004 THE ORIGIN OF HEMATITE IN HIGH-GRADE IRON ORES BASED ON INFRARED MICROSCOPY AND FLUID INCLUSION STUDIES: THE EXAMPLE OF THE CONCEIÇÃO MINE, QUADRILÁTERO FERRÍFERO, BRAZIL Carlos Alberto Rosière; Carlos Alberto Rosière Instituto de Geociências, Universidade Federal de Minas Gerais, 31270-901 Belo Horizonte MG, Brazil †Corresponding author: email, crosiere@dedalus.lcc.ufmg.br Search for other works by this author on: GSW Google Scholar Francisco Javier Rios Francisco Javier Rios Fluid Inclusion and Metallogenic Laboratory (EC1), Centro de Desenvolvimento da Tecnologia Nuclear (CDTN-CNEN), Cx. Postal 941, 30123-970 Belo Horizonte MG, Brazil Search for other works by this author on: GSW Google Scholar Author and Article Information Carlos Alberto Rosière Instituto de Geociências, Universidade Federal de Minas Gerais, 31270-901 Belo Horizonte MG, Brazil Francisco Javier Rios Fluid Inclusion and Metallogenic Laboratory (EC1), Centro de Desenvolvimento da Tecnologia Nuclear (CDTN-CNEN), Cx. Postal 941, 30123-970 Belo Horizonte MG, Brazil †Corresponding author: email, crosiere@dedalus.lcc.ufmg.br Publisher: Society of Economic Geologists Received: 20 Nov 2001 Accepted: 16 Dec 2003 First Online: 02 Mar 2017 Online ISSN: 1554-0774 Print ISSN: 0361-0128 Economic Geology Economic Geology (2004) 99 (3): 611–624. https://doi.org/10.2113/gsecongeo.99.3.611 Article history Received: 20 Nov 2001 Accepted: 16 Dec 2003 First Online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn Email Permissions Search Site Citation Carlos Alberto Rosière, Francisco Javier Rios; THE ORIGIN OF HEMATITE IN HIGH-GRADE IRON ORES BASED ON INFRARED MICROSCOPY AND FLUID INCLUSION STUDIES: THE EXAMPLE OF THE CONCEIÇÃO MINE, QUADRILÁTERO FERRÍFERO, BRAZIL. Economic Geology 2004;; 99 (3): 611–624. doi: https://doi.org/10.2113/gsecongeo.99.3.611 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyEconomic Geology Search Advanced Search Abstract Petrographic and textural analysis combined with fluid inclusion studies by infrared microscopy of high-grade (>65% Fe) hematite ore samples from the Conceição deposit, in the northeastern part of the Quadrilátero Ferrífero, Brazil, indicate a complex process of oxidation and mineralization during two orogenic events, each developed under different conditions and involving distinct fluids. The earliest mineralization formed massive magnetite-rich orebodies under relatively reducing conditions in the early stages of the Transamazonian orogeny. Magnetite was oxidized (martitized) with the development of porous hematite crystals (hematite I). Possibly during this stage, new hematite crystals were also formed from low-temperature, low- to medium-salinity fluids, as indicated by two-phase fluid inclusions. The origin of these fluids is still uncertain but tentatively interpreted as being modified surface water. The fluids were transported along normal faults and fractures during post-tectonic collapse following the Transamazonian orogeny (2.1–2.0 Ga) and creation of the dome-and-keel structural pattern of the Quadrilátero Ferrífero. These solutions were also likely responsible for the initial oxidation of the iron formations and the development of hematite I. Subsequent uplifted hot basement rocks or post-tectonic plutons were probable heat sources for the regional metamorphism and development of a granoblastic fabric of hematite II grains in the iron formations and high-grade orebodies. However, the ore was only partially recrystallized, as several relics of the early magnetite, martite, and hematite are still preserved in the granular hematite II crystals. During the Brasiliano-Pan-African orogeny (0.8–0.6 Ga), high-salinity fluids, with temperatures varying from ~120° to a maximum of approximately 350°C, penetrated the iron formations along shear zones, crystallizing initially tabular and thereafter platy hematite crystals (hematite III and specularite) forming schistose orebodies. Quartz veins that cut across the ore and envelop specularite plates and ore fragments formed from late-stage, high-temperature, and low-salinity fluids containing CO2. These later fluids did not alter the ore.Each of these stages of mineralization produced orebodies with distinct features. Recurrent hydrothermal mineralization is thought to have been responsible for the development of giant, high-grade iron ore deposits in structurally favorable sites. Fold hinges with enhanced permeability and deep faults able to conduct the fluids to the surface, repeatedly over time, should be important targets for exploration of new resources. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.