Figure 1:
The main steps of the mineral exploration model. This diagram is based in the method suggested by Pan and Harris (2000Pan G., & Harris D.P. 2000. Information Synthesis for Mineral Exploration. New York, Oxford University Press, 461 p.) and Harris and Sanborn-Barrie (2006Harris J.R., Sanborn-Barrie M. 2006. Mineral potential mapping: examples from the Red Lake Greenstone Belt, Northwest Ontario. In: Harris J.R. (ed.) GIS for the Earth Sciences. Geological Association of Canada, Special Publication, 44, p. 1-21.) and adapted from Nykänen (2008Nykänen V. 2008. Spatial data analysis as a tool for mineral prospectivity mapping: Espoo, Geological Survey of Finland, 27 p.) and Silva et al. (2012Silva E.C., Silva A.M., Toledo C.L.B., Mol A.G., Otterman D.W., Souza S.R.C. 2012. Mineral potencial mapping for orogenic gold deposits in the Rio Maria Granite Greenstone Terrane, Southeastern Pará State, Brazil. Economic Geology, 107(7):1387-1402.).
Figure 2:
Simplified geologic map of the Archean-Paleoproterozoic Terrane in Goiás (Pimentel et al. 2000Pimentel M.M., Fuck R.A., Jost H., Ferreira Filho C.F., Araújo S.M. 2000. The basement of the Brasília Fold Belt and the Goiás Magmatic Arc. In: Tectonic Evolution of South America. 31st International Geological Congress Special Publication, Rio de Janeiro, p. 195-229.).
Figure 3:
Simplified regional geologic map of the Faina Greenstone Belt produced by Toledo et al. (2014Toledo C.L.B., Silva A.M., Chemale Jr. F., Almeida T., Garnier J., Araujo Filho J.O., Hauser N., Botelho N.F., Jost H., Bernardi G.B., Paiva R.G., Magaldi T.T., Ferreira V.H.C.S., Magalhães H.V.B., Araujo B.V.B., Silva L.B.C., Bastos Y.M.M., Teixeira C.D., Vieira H.A., Moraes F.G.M., Neiva Jr. F.B., Mansur E.T., Soares T.M., Valle R.S.C., Silva S.P., Oliveira A.L., Martins P.L.G., Franco G.S., Lamblém H.S., Leite A.M., Fazio G., Topan J.G.O., Daldegan L.C.B., Cassemiro R.B. 2014. Projeto Faina-Goiás - Mapeamento Geológico na escala 1:25.000. Trabalho de Formatura da Universidade de Brasília.). The black polygon indicates the study area mapped at the 1:10,000 scale.
Figure 4:
ETM+/Landsat 7 band 4, 5, 3 (RGB) color composite, partially covering the Faina Greenstone Belt. Sertão Mine and Cascavel, North, Central, South and Southeast Tinteiro prospects are indicated by yellow polygons.
Figure 5:
Main aeromagnetic products: (A) TMI; (B) ASA; (C) Dx; (D) Dy; and (E) Dz. The black outline indicates the main sites analyzed in this study: A - Cascavel, B - North Tinteiro, C - Central Tinteiro, D - Southeast Tinteiro and E - South Tinteiro.
Figure 6:
(A) K (%); (B) eU (ppm); (C) eTh (ppm) concentrations used to identify the hydrothermal alteration zones; and (D) RGB image, which is essential for the geologic mapping and the black outlines indicate the target sites (A - Cascavel, B - North Tinteiro, C - Central Tinteiro, D - Southeast Tinteiro and E - South Tinteiro).
Figure 7:
Map showing the first vertical derivative (Dz) of the TMI in the study area and identifying the main geologic structures interpreted based on the Dz, Dy, and RGB 453 image of the Landsat 7 ETM+ sensor. The boreholes conducted by the Orinoco do Brasil Mineração Ltda. are indicated by the green marker.
Figure 8:
Geologic map of the study area at the 1:10,000 scale covering the Cascavel and Tinteiro target sites; the map was produced by integrating the geologic map created by Toledo et al. (2014Toledo C.L.B., Silva A.M., Chemale Jr. F., Almeida T., Garnier J., Araujo Filho J.O., Hauser N., Botelho N.F., Jost H., Bernardi G.B., Paiva R.G., Magaldi T.T., Ferreira V.H.C.S., Magalhães H.V.B., Araujo B.V.B., Silva L.B.C., Bastos Y.M.M., Teixeira C.D., Vieira H.A., Moraes F.G.M., Neiva Jr. F.B., Mansur E.T., Soares T.M., Valle R.S.C., Silva S.P., Oliveira A.L., Martins P.L.G., Franco G.S., Lamblém H.S., Leite A.M., Fazio G., Topan J.G.O., Daldegan L.C.B., Cassemiro R.B. 2014. Projeto Faina-Goiás - Mapeamento Geológico na escala 1:25.000. Trabalho de Formatura da Universidade de Brasília.) at the 1:25,000 scale, the geologic map from Orinoco do Brasil Mineração Ltda. and data obtained in this study. Boundaries of the hydrothermal alteration halos are also indicated.
Figure 9:
Main rocks found in Cascavel: (A) quartzite; (B) feldspathic quartzite; (C) weathered metapelite; (D) intercalated carbonaceous schists in metarhythmite packages. Photos of the Cascavel site gallery: (E) fine pinkish quartz vein (marked in yellow) from 10 to 50 cm thick and hosted in quartzite with green muscovite; (F), (G) and (H) spots of free gold in the quartz vein or at the contact of the vein with the host rock. Photos e, f, g and h: Orinoco do Brasil Mineração Ltda.
Figure 10:
(A) Description of the borehole CDP-04 showing mineralized layers. Photomicrography: a) S-C foliation marked by muscovite in quartz-muscovite schist; and b) deformed potassium feldspar, showing pressure shadows filled with biotite. The muscovite is older than the biotite. (B) Description of the borehole CDP-09 showing mineralized layers. Photomicrography: c) hydrothermal muscovite (1) formed from biotite (2); d) feldspathic quartzite with muscovite; and e) late euhedral pyrite.
Figure 11:
Distribution of the elements Au, Cu, Zn, Ni, Co, Cr, Pb and W (in ppm) along the boreholes CDP-04 and CDP-09, and possible correlations (red circles).
Figure 12:
Photos of the rocks found in Tinteiro prospect: (A) massive and gray quartzite with muscovite; (B) weathered and folded quartz-muscovite schist; (C) greenish quartz-chlorite-muscovite schist; (D) massive metachert is composed mainly by quartz; (E) finely laminated metachert showing bands rich in quartz alternated with bands rich in muscovite and biotite.
Figure 13:
(A) Hydrothermal alteration of the Tinteiro site, which shows solid portions of goethite/hematite in metachert, consisting of hematite breccia; (B) hematite breccia is highly weathered and contains green muscovite; (C) photomicrography of the metallic gray cement of the hematite breccia; (D) detail of the breccia formed by irregular fragments of metachert cemented by metallic bluish gray material; (E) and (F) backscatter images of the manganiferous breccia cement showing that (E) 1, 2 and 3 are hollandite (lighter) and 4, 5 and 6 are lithiophorite (darker); (F) 1 is hollandite, 2, 3 and 4 are lithiophorite, and 5 and 6 are muscovite.
Figure 14:
Chemical analyses of the borehole TIN-1A, highlighting the layer intercepting the manganiferous breccia and showing anomalous concentrations of Ag, Ba, Pb and V in addition to Co, Cu, Mn, Ni, Zn and Li, which occur in the lithiophorite structure.
Figure 15:
Flowchart representing the steps of the fuzzy logic method for: (A) Cascavel; (B) North Tinteiro; (C) Central Tinteiro; (D) Southeast Tinteiro, and (E) South Tinteiro.
Figure 16:
Prospectivity map for the Cascavel site integrated with the soil grid, mineralized quartz veins associated with the Cascavel deposit, and the main lineaments identified from aeromagnetic images. The soil grid refinement over the area showing the highest favorability indicates an anomalous concentration of gold in this region. The concentration of the radioelement K (%) indicates that the region of highest favorability is associated with high K concentration.
Figure 17:
Prospectivity map for the Tinteiro site: (A) North Tinteiro; and (B) Central Tinteiro. The integration of the prospectivity maps with the results from the chemical analyses on the rock and soil samples and the cores validated certain high-favorability zones. These zones are intersected by lineaments and associated with high magnetic amplitudes.
Figure 18:
Prospectivity map for the Tinteiro site: (A) Southeast Tinteiro; and (B) South Tinteiro. The integration of the prospectivity maps with the results from the chemical analyses on the rock and soil samples and cores validate some high-favorability zones. These zones are intersected by lineaments and are associated with high magnetic amplitudes.
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