ABSTRACT:Mapping methods for iron oxides and clay minerals, using Landsat-8/Operational Land Imager (OLI) and Earth Observing 1 (EO-1)/Hyperion imagery integrated with airborne geophysical data, were applied in the N4, N5, and N4WS iron deposits, Serra Norte, Carajás, Brazil. Band ratios were achieved on Landsat-8/ OLI imagery, allowing the recognition of the main minerals from iron deposits. The Landsat-8/OLI imagery showed a robust performance for iron oxide exploration, even in vegetated shrub areas. Feature extraction and Spectral Angle Mapper hyperspectral classification methods were carried out on EO-1/Hyperion imagery with good results for mapping high-grade iron ore, the hematite-goethite ratio, and clay minerals from regolith. The EO-1/Hyperion imagery proved an excellent tool for fast remote mineral mapping in openpit areas, as well as mapping waste and tailing disposal facilities. An unsupervised classification was carried out on a data set consisting of EO-1/Hyperion visible near-infrared 74 bands, Landsat-8/OLIderived Normalized Difference Vegetation Index, Laser Imaging Detection and Ranging-derived Digital Terrain Model, and high-resolution airborne geophysical data (gamma ray spectrometry, Tzz component of gradiometric gravimetry data). This multisource classification proved to be an adequate alternative for mapping iron oxides in vegetated shrub areas and to enhance the geology of the regolith and mineralized areas. KEYWORDS:Remote sensing; Multispectral and hyperspectral imagery; Iron ore. RESUMO: Métodos de mapeamento para óxidos de ferro e argilas, aplicados em imagens Landsat-8/Operational Land Imager (OLI) e Earth Observing 1 (EO-1)/Hyperion e integrados com dados aerogeofísicos, foram testados nos depósitos de ferro de N4, N5 e N4WS, Serra

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The Cerro La Mina prospect, located in the Los Menucos area, Argentina, is currently being explored for epithermal gold mineralization. Triassic-Jurassic hydrothermal activity produced intense alteration of rhyolites, andesites, ignimbrites, and tuffs of the Late Triassic Los Menucos Group, in the Somún Curá Massif. A detailed surface map of the principal alteration assemblages at Cerro La Mina was produced employing field mapping, supported by short-wave infrared (SWIR) field spectroscopy, petrography, X-ray diffraction (XRD), and scanning electron microscopy (SEM).Advanced argillic, argillic, and silicic alteration zones and their internal mineral assemblage variations were recognized at Cerro La Mina. The silicification consists of massive bodies of fine-grained quartz and minor vuggy quartz, locally containing disseminated aggregates of pyrite, and rutile. Advanced argillic alteration of magmatic-hydrothermal origin occurs adjacent to the silicic alteration zones and can be subdivided into three mineral assemblages: (1) stage 1 alunite + quartz ± dickite ± kaolinite ± pyrophyllite ± diaspore ± rutile ± pyrite ± barite; (2) dickite + kaolinite ± pyrophyllite ± diaspore ± pyrite ± barite; and (3) dickite + quartz ± diaspore. The advanced argillic and silicic alteration grades to argillic alteration, comprising three mineral assemblages:(1) kaolinite ± dickite ± quartz ± illite ± smectite; (2) kaolinite ± illite ± smectite ± ferroan clinochlore; and (3) illite ± quartz ± muscovite ± kaolinite. Supergene alteration, which locally overprints the prior alteration zones, consists of jarosite + hematite + goethite ± stage 2 alunite ± aluminum phosphate sulfate (APS) ± poorly crystalline kaolinite.Consistent discrimination of the main alteration minerals of this prospect was also achieved by means of satellite multispectral remote sensing. The application of image processing techniques, specifically designed for mineral mapping, to selected spectral bands of the Terra/ASTER multispectral sensor resulted in a detailed alteration map for the entire prospect. Comparison between the results achieved through remote sensing with field data on the Cerro La Mina confirmed the accuracy of the former.The silicification and minor vuggy quartz, the abundant dickite, and the coarse-grained hypogene alunite, among other advanced argillic alteration assemblages, suggest that Cerro La Mina corresponds to a volcanichydrothermal leached environment, possibly controlled by permeable lithological units. These characteristics led us to interpret this prospect as a possible lithocap similar to those that typically host subsequent highsulfidation mineralization.

Large gold provinces commonly show complicated mineralization histories, and the Paleoproterozoic Alta Floresta, one of Brazil's most exciting Au-Cu mineral provinces, is a good example. The current models defined four deposit types, all connected to a single (1.88-1.75 Ga) magmatic-hydrothermal event. However, long Province history, diverse geodynamic environment, and older ages of Type-1mineralisation weaken the single metallogenic event and enable the hypothesis of overprinted mineral events. By scale-integrated analyses, we revise the tectonic-geological context, structural-hydrothermal alterations, and chlorite-white mica geothermobarometer and propose the type-1 as an older, granitoid-hosted orogenic mineralisation, with subsequent overprinting by the magmatic-hydrothermal event. The older orogenic gold event developed orogenic gold deposits on WNW-trending shear zones in the Peixoto de Azevedo domain granitic-gneiss rocks. Phengite, biotite, chlorite-carbonate phyllonites (3.3-6.1 kbar, 300º-420ºC) host fault-fill quartz veins (pyrite-chalcopyrite-magnetite-pyrrhotite-gold-Bi-Ag tellurides). Mg-rich chlorite-phengite is the main alteration footprint for this mineralisation type. A younger magmatic-hydrothermal event in the Juruena magmatic-arc rocks produced Fe-rich chlorite-white mica alteration zones (0.6-4.6 kbar, 120º-380ºC) and disseminated and stockwork-breccia ore (pyrite-chalcopyrite-gold-molybdenite- Ti minerals-allanite) in porphyry-epithermal deposits. Where the younger mineralisation overprints the older, phyllic alteration destroyed the phengite orogenic gold phyllonite Sn+1 foliation. The ages of two pyrite populations (1979 and 1841 Ma) in the older fault-fill veins and molybdenite in late fractures (1805-1782 Ma) or disseminated in the ca. 1.79 Ga syenogranite porphyry suggest more than two episodes of mineralisation. These two events differ in their alteration styles, P-T conditions, and structural, mineralogical, and textural ore styles. The multi-scale approach enlightens the relationships between the various mineralisation events, allowing a new explorational potential within the province.Supplementary material at https://doi.org/10.6084/m9.figshare.c.6056324