Granite
Floresta Azul - BA
The area of mining process no. 870.935/2021 occupies 41,01ha and is located in the municipality of Sento Sé, Bahia, Brazil.
HIGHLIGHTS
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LOCATION AND LOGISTICS
The area of mining process No. 870.935/2021 covers 41.01 hectares and is located in the municipality of Itaju do Colônia, Bahia, near the municipal headquarters.
Fig 1 & 2. Geographical location of the visited mining process, highlighting access routes and other polygons of ANM processes.
The nearest city is Floresta Azul-BA, which is 25 km away, with 12 km on well-maintained asphalt and 13 km on a dirt road, also in good condition. Floresta Azul is approximately 483 km from Salvador-BA.
a) and b) illustrate the access routes to the visited area, on local dirt roads in good condition and with mountainous terrain.
The region of Floresta Azul offers good infrastructure conditions to support a mining project. Although this city is inadequate in this regard, Ibicaraí is only 10 km away and Itabuna 48 km, both offering various options for hotels/inns, specialized workshops, heavy equipment rentals, and other positive aspects (such as banks and medical services).
GEOLOGICAL CONTEXT AND REGIONAL MINERAL POTENTIAL
The visited mining process is located in the southern part of the Itabuna-Salvador-Curaçá belt, where crystalline basement rocks such as various granulites predominate. The rocks of this macro-region correspond to a very ancient stage in the geological period and evolution of the deep continental crust along the southern/southeastern coast of Bahia. Two main types of granulites stand out near the visited area: Basic and Paraderived granulites.
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Basic granulites originate from highly metamorphosed metagabbros and metabasalts, usually occurring as deformed enclaves parallel to the regional foliation. They are generally composed of pyroxenes, opaque minerals, garnet, biotite, and quartz.
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Paraderived granulites, on the other hand, are also represented by enclaves but of larger proportions, reaching kilometers in size. These rocks exhibit greater compositional diversity, ranging from quartzites associated with iron/manganese formations, calc-silicate rocks, graphitic rocks, and other aluminum-magnesian granulites.
This regional geological context limits the possibilities of various mineral substances with potential for investigation and/or exploitation. However, it increases the chances of identifying target zones for investigations of rock massifs suitable for ornamental stone extraction.
It is important to highlight that the diversity of metamorphosed rocks in the granulite facies within this southern region of the Itabuna-Salvador-Curaçá belt creates opportunities to identify various different lithotypes within the evaluated area, which is under the influence of this context and has not undergone detailed specific mapping.
Fig 5. Regional geology of the ANM process area in focus. Note that the predominant geological influence in the visited region is due to the presence of high-grade metamorphic rocks (granulites) that had different origins in their protoliths (such as volcanic rocks and sedimentary rocks).
WORK METHODOLOGY
The methodology applied in this work is divided into four stages: (1) acquisition, compilation, and analysis of pre-existing data; (2) field surveys; (3) interpretation of information and discussion; and (4) preparation of the report.
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The first stage consisted of collecting information on regional and local geology (focusing on the Itabuna-Salvador-Curaçá crystalline rock belt), where high-grade metamorphic rocks (granulites) occur, originating from a long tectonic evolution of various rock types.
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Various maps were developed after photointerpretation of satellite images and SRTM data from the Topodata project with 30m resolution. All maps were processed and georeferenced using ArcGIS 10.8 software. In the field, the surveys lasted 1 day and took place in October 2023. Outcrop points, control points, and an old deactivated quarry outside the mining process were visited. At each location with favorable physiographic characteristics, descriptions of local structural geology and strategic aspects were carried out, along with sample collection (when necessary).
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In the third stage, interpretations of field data, bibliography, and interpolations with maps were developed.
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Finally, all technical information was processed, interpreted, and discussed to support the preparation of this report and the standardization of the data.
LOCAL GEOLOGY
The field activities allowed for the identification of a single main geological compartment within the visited process, where minor variations in the observed rocks were noted but are not significant enough to be represented on the map. These variations appear to be associated with structures/deformation of the predominant lithotype in the polygon, which will be described below.
TONALITIC GRANULITES.
Several outcrops of the same type of crystalline rock from this geological unit were cataloged. It has a light to dark gray color with beige portions, a phaneritic texture with medium to fine grain size, and a typical composition of a metamorphosed tonalite, which is an igneous rock that, in this case, appears deformed and foliated along the NNW-SSE trend. The main outcrops observed are composed of pyroxene, biotite, quartz, garnet, and plagioclase.
a), b), and c) illustrate the outcrop and details of the rock found to be the most representative of the evaluated area: a gray-colored granulite with varied hues and medium to coarse grain size.
In this unit, as mentioned earlier, there are some changes in the compositional aspect of the lithotypes, which are associated with a more penetrative foliation and/or shear zones with a significant presence of iron oxides such as hematite. These are seen in considerable quantities, which clearly alter the rock's density, along with a finer grain size and the occurrence of sulfides (arsenopyrite or pyrite). Point 8 is an example where these more altered lithotypes are found.
a) Outcrop with fold marks and penetrative foliation associated with a possible shear zone or high strain zone of the regional deformation; b) and c) illustrate in detail the characteristic of the rock, which contains a large amount of iron oxides and sulfides.
Fig 5. Map of visited points, highlighting the deactivated quarry next to the visited ANM process.
PREVIOUS MINERAL POTENTIAL OF THE AREA AND ROCK SAMPLING
According to the preliminary data obtained and the macroscopic characteristics of the rocks described in this report, it is possible to state that the area has mineral potential, although not very high. In this sense, the following possibilities stand out:
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Metallic associations in rocks with sulfides and iron oxides, as the found characteristics are favorable for identifying metallic chemical elements. Despite this possibility, the apparent volume of the sheared and sulfide-rich layer is not very significant.
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Ornamental stone (block extraction) for two main aspects: the color of the rock and the existence of a quarry of the same material type just a few meters from the polygon. However, in these aspects, the following observations must be considered:
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The cited quarry is deactivated due to likely limited mining operations (highly fractured) for extracting blocks of adequate dimensions and/or market acceptance for the final product.
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The outcrops visited within the polygon of the dark-colored rock also show well-defined fracturing and foliation systems, characteristics that could hinder extraction, similar to the deactivated quarry mentioned.
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ROCK SAMPLING.
During the field visit, samples were collected, subdivided according to the purpose of each one, based on the principle of a more detailed description in the office, with cataloging for laboratory submission and specific chemical tests, as well as polishing tests to verify the aesthetic quality of the existing dark granulite.
GENERAL CONSIDERATIONS
The previous chapters make it clear that there is a positive preliminary mineral potential for certain substances, thus, the scenarios highlighted below encompass research activities aimed at advancing work in both possibilities.
METALLIC ASSOCIATIONS IN ROCKS WITH SULFIDES.
Due to the geological possibilities of various metallic anomalies in this type of rock, the most appropriate course of action is to conduct preliminary chemical tests on the collected samples to then determine the viability of proceeding with new technical research stages.
ORNAMENTAL STONE – DARK-COLORED GRANITES.
To determine the feasibility of a block production project, it is essential to understand the quality of the final product and market acceptance, as well as the volume and actual fracture index of the potential mining fronts.
FINAL CONCLUSIONS
ABOUT THE GEOLOGY AND PREVIOUS MINERAL POTENTIAL, it is concluded that:
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The study area is located in a region with occurrences of intrusive igneous and metamorphic crystalline rocks, predominantly tonalites and related rocks, as well as sporadic occurrences of volcanic rocks associated with structures that may exhibit anomalous metal contents;
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Nonetheless, the geology of the area is more suited for research aimed solely at block extraction, which represents the greatest existing preliminary mineral potential;
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Key characteristics for proper mining operations still need further investigation in order to assess volume, quality, and isotropy of the rock, as suggested in above.
ABOUT STRATEGIC POINTS, it is important to highlight that:
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The logistics for transporting a potential block extraction should be well planned, but initially, it presents good development conditions;
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It is essential that, before advancing with any research activity at any point within the areas, formal contact is made between the Holder and Surface Rights owner to clarify the research and mineral extraction intentions in the region;
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The area benefits from proximity to energy and water sources.