@article{RosiereSantosSilveiraBragaetal.2021, author = {Rosi{\`e}re, C. A. and Santos, J. O. S. and Silveira Braga, F. and Hensler, Ana-Sophie and Rolim, V. K. and Bekker, A.}, title = {Multiple Hydrothermal Iron-Formation Upgrading Events in Southeastern S{\~a}o Francisco Craton}, series = {The Journal of Geology}, volume = {129}, journal = {The Journal of Geology}, number = {3}, publisher = {The University of Chicago Press}, address = {Chicago}, doi = {10.1086/715242}, pages = {283 -- 296}, year = {2021}, abstract = {Large-scale, hypogene iron mineralization systems developed recurrently in the S{\~a}o Francisco craton in association with two orogenies. During the ca. 2.1-2.0 Ga Trans-Amazonian orogeny, low-temperature and low-to-moderate-salinity metamorphic fluids resulted in carbonatization-related iron enrichment of the early Paleoproterozoic Cau{\^e} Iron Formation (IF) of the Minas Supergroup (MSG) as well as short-distance iron mobilization. Monazite from the iron-oxide veins yielded a SHRIMP 232Th/208Pb date corresponding to fluid circulation coeval with the migmatization of the Archean tonalite-trondhjemite-granodiorite crust. During the Ediacaran to Cambrian Brasiliano orogeny, when the S{\~a}o Francisco craton was consolidated in its present configuration, hydrothermal fluids repeatedly mineralized the Cau{\^e} IF and the younger IFs of the lower Espinha{\c{c}}o Supergroup. Far-field hydrothermal alteration associated with distinct Fe mineralization episodes widely affected Meso- to Neoproterozoic sequences as well as Archean to Paleoproterozoic terranes of the cratonic core. Circulation of hydrothermal fluids during the Brasiliano orogeny caused desilicification, iron mobilization, and widespread alteration of the rocks. The alteration events are dated with monazite and xenotime intergrown with hematite, anatase, and recrystallized rims of detrital zircons from interlayered quartzites and of igneous zircons from pegmatites, granites, acidic volcanic rocks, and orthogneisses, yielding U-Pb dates between 542 and 493 Ma. U-Pb dates point to five Cambrian hydrothermal events from the waning stages to the aftermath of the Brasiliano orogeny. These hydrothermal fluid circulation events correspond to the emplacement ages of four granite suites and pegmatites that lasted from the final stages of the collision to the collapse of the Ara{\c{c}}ua{\´i}-West Congo orogen. Episodic circulation of fluids continued for approximately 2 billion years after IF deposition on the eastern S{\~a}o Francisco craton with the formation of high-grade iron ore deposits and resetting of the IF trace-element inventory.}, language = {en} } @incollection{HagemannHenslerFigueiredoeSilvaetal.2023, author = {Hagemann, Steffen and Hensler, Ana-Sophie and Figueiredo e Silva, Rosaline Cristina and Tsikos, Harilaos}, title = {Light Stable Isotope (O, H, C) Signatures of BIF-Hosted Iron Ore Systems: Implications for Genetic Models and Exploration Targeting}, series = {Isotopes in Economic Geology, Metallogenesis and Exploration}, booktitle = {Isotopes in Economic Geology, Metallogenesis and Exploration}, editor = {Huston, David and Gutzmer, Jens}, publisher = {Springer}, address = {Cham}, doi = {10.1007/978-3-031-27897-6_12}, publisher = {Technische Hochschule Rosenheim}, pages = {373 -- 397}, year = {2023}, abstract = {Stable isotope data from hypogene (i.e., below the line of weathering) iron oxides and gangue minerals from BIF-hosted iron ore deposits in Australia, South Africa, and Brazil have significantly assisted in constraining different hydrothermal fluid sources and fluid flow models during the upgrade of BIF to iron ore. The δ18O values on iron oxides from BIF and different paragenetic stages of enrichment display a consistent decrease from unenriched BIF (4-9 per mille) to as low as -10 per mille for high-grade iron ore. This large shift in oxygen isotope values is interpreted as evidence for enormous incursion of 'ancient' meteoric water into fault and fracture zones at the time of iron enrichment during the Archean and Paleoproterozoic time. The δ18Ofluid values of paragenetically early iron oxides of > 4 per mille suggest the involvement of magmatic fluids in greenstone belt-hosted Caraj{\´a}s-type iron ore deposits, and basinal brines in basin-hosted Hamersley-type deposits. In contrast, the paragenetically late stage iron oxides in the metamorphosed, basin hosted iron ore deposits of the Quadril{\´a}tero Ferr{\´i}fero display δ18Ofluid values > 6 per mille. This reflects the renewed deep crustal, hypogene (metamorphic or magmatic) fluid influx. Carbon and oxygen isotope data on carbonates in BIF and hydrothermally altered iron ore indicate that carbon in the latter is not derived from BIF units, but represents either magmatic carbon in the case of the Caraj{\´a}s-type deposits or carbon within the underlying basin stratigraphy as in the case of the Hamersley-type iron deposits. The systematic decrease of δ18O values in iron oxides from the early to late paragenetic stages and from the distal to proximal alteration zone, including the ore zone, may be used as a geochemical vector. In this case, oxygen isotope analyses on iron oxides provide a potential exploration tool, particularly for targeting the extension of iron ore bodies or entirely concealed high-grade iron ore deposits, in which hematite/magnetite are frequently the only mineral that can be readily analysed.}, language = {en} }