Limestone & Marble
Itapebí - BA
The area of mining process no. 872.297/2021 occupies 557,15ha and is located in the municipality of Sento Sé, Bahia, Brazil.
HIGHLIGHTS
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GEOLOGICAL CONTEXT AND REGIONAL MINERAL POTENTIAL
The visited mining area is part of the regional context of the "Araçuaí Belt," a Brasiliano fold belt that borders the São Francisco Craton through large zones of complex tectonic structures formed during its Neoproterozoic evolution. The Araçuaí Belt is extensive and covers a significant portion of southeastern Bahia and northeastern Minas Gerais.
The visited area, more specifically, is located within the Rio Pardo Group, in a region close to the contacts between crystalline basement rocks and more recent sedimentary cover rocks.
RIO DO PARDO GROUP.
The Rio Pardo Group comprises metasedimentary rocks formed in continental, restricted marine, and open marine depositional environments. Within the group, there are two sub-basins: a northern one and a southern one, with the latter being of greater interest in this evaluation.
The southern sub-basin of the Rio Pardo Group consists of three distinct rock formations: the Panelinha Formation, Serra do Paraíso Formation (where the evaluated area is located), Água Preta Formation, and Camacan Formation.
Of all the formations mentioned, the Serra do Paraíso Formation is the most recent, having been the last to be deposited in the sedimentary basin of origin. It is composed mainly of various types of carbonates (with varying degrees of metamorphism) and quartzites, precisely as observed during the field visit for the area’s assessment.
Fig 2. Regional geology of the area of the ANM process in focus. Note that the entire polygon is under the influence of the Serra do Paraíso Formation, composed of carbonates and quartzites.
REGIONAL POTENTIAL FOR CARBONATE PRODUCTS.
As mentioned in the "Rio do Pardo Group" section, the area has a regional context favorable to the presence of carbonate and quartzitic rocks, with the former being major sources of marble or limestone occurrences, for example.
The macro-region of the referenced ANM process contains various active mineral extraction sites for marble and limestone, which already suggests some minimum geological potential nearby. Figure 3 below illustrates the location of the mining operations within the region of polygon 872.297/2021.
Fig 3. Active ANM processes under mining application or concession, highlighting three operations that produce marble and limestone very close to the evaluated ANM process.
WORK METHODOLOGY
The methodology applied in this work is divided into four stages: (1) data acquisition, compilation, and analysis of existing data; (2) field surveys; (3) interpretation of information and discussion; and (4) report preparation.
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The first stage consisted of gathering information on the regional and local geology (focusing on the Rio Pardo Group and Serra do Paraíso Formation, which are part of the regional context of the Araçuaí Belt), where metasedimentary rocks are found, associated with basin closure structure and rock deformation/metamorphism;
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Various maps were developed after the photointerpretation of satellite images and SRTM data from the Topodata project with 30m resolution. All maps were processed and georeferenced in ArcGIS 10.8 software. The field surveys lasted 2 days and took place in October 2023. Outcrops and control points within and outside the mining process were visited. In each location with favorable physiographic features, descriptions of local structural geology and strategic aspects were made, along with sample collection (when necessary);
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In the third stage, interpretations of field data, bibliography, and interpolation 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 identification of the predominant rocks in the ANM process was made easier after subdividing the area into two sectors: West and East. This was due to the distinct differences in relief, soil, and land use, as well as the mineral potential of each, which shows varying levels. Therefore, the local geology will be described considering the two polygons, which can be more clearly seen in Figure 5.
Fig 5. Map of the location of the subdivided sectors in the visited ANM process.
GEOLOGY OF THE WEST SECTOR.
Considering the west and east sectors, the geology of the visited ANM process can be characterized as a single unit, where the lithotypes vary according to their mineral composition but maintain the same metasedimentary origin. However, the major difference between the sectors outlined here is the degree of exposure of the outcropping rocks, as in the west sector, there are virtually no exposed rocks due to the topography and large eucalyptus plantations of Veracel Celulose.
Points P12 and P14 were the only ones that allowed for the observation of rock within the survey conducted in this west sector, and they showed that the rocks present are basically:
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Foliated limestones, gray in color with very fine granularity, making it difficult to define their degree of purity, but apparently showing to be impure limestone with the presence of silica. Samples showed little reaction to hydrochloric acid, making it an inconclusive test for interpreting its composition.
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Iron-rich concretions in lateritic rocks, with iron oxides present, giving cohesion to the brownish-colored sand-silt matrix. Fragments of angular quartz are also common, likely originating from superficial fragments of quartz veins in the region.
a) Outcrop of impure limestone at point P12, and b) Large boulder on the side of a hill with lateritic concretion, point P14.
Correlation of map data and bibliography with field observations allowed us to infer that the geological pattern below the surface/soil in the west sector remains similar, even without many directly observed data.
GEOLOGY OF THE EAST SECTOR.
Unlike the previous sector, the eastern region of the visited ANM process is characterized by land use focused solely on livestock farming, with a landscape of extensive pastures, hills, and valleys (Figure 3).
Fig 3. Overview of the physiographic aspects of the terrain in the East sector, viewed towards N200° from point P28.
The physiographic characteristics of this sector allowed for the identification of a substantially greater number of outcrops, from which it was possible to interpret that they are rocks from the same micro-regional context, with varied metasediments, quartz veins, and varying degrees of metamorphism.
In this regard, it is worth highlighting:
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Limestones: similar to those described in the west sector; however, they occur here with a greater variation in purity, tending towards calcarenite with fine granularity.
a) and b) illustrate outcrops of impure limestone tending towards calcarenite, light in color and heavily fractured. Point P15.
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Metarenites: they occur friable and weathered, but certainly contribute a large volume to the metasediment package in the area, being in gradual contact with the limestone layers. They are light-colored (white to beige), with fine granularity and a composition mainly composed of sub-rounded quartz grains.
a) and b) illustrate outcrops of friable metarenite at point P16.
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Quartz veins: these are common near the occurrences of metarenites, which are likely correlated. These veins were observed in outcrops up to 2 meters thick and/or boulders of small and large dimensions at various points. The physical characteristics of the material stand out here, showing a high degree of purity due to its crystallinity and white/transparent color.
a) and b) illustrate outcrops of quartz veins, common in the eastern sector of the visited process. Points P13.
PREVIOUS MINERAL POTENTIAL OF THE AREA AND ROCK SAMPLING
Based on the data obtained, field data, literature, and mining history, it was possible to define that only the Eastern sector of the visited process deserves attention regarding the advancement of exploratory research.
The rocks identified in this sector and described in item 5.2 can be a mineral source for the substances: dolomitic limestone or calcite limestone and high-purity quartz, and based on these informations, the following interpretations are made for each possibility:
CALCIUM CARBONATE OR DOLOMITE AND MARBLE.
The presence of carbonate rocks in the area allows for the possibility of anomalous levels of magnesium and/or calcium, giving rise to calcium carbonate minerals for soil correction and still zones of greater degree of metamorphism that allow for the formation of massive marble deposits.
The occurrence of these rocks in various points also allows for the interpretation that there may be volumes beneath the surface that could enable some type of production, however, this type of mining tends to be more profitable and less costly when of the positive type, and the terrain of the eastern sector tends to provide a negative front.
Another factor of great relevance for evaluating the viability of this type of undertaking is the logistics and local market, which in this case, does not show a very favorable disposition due to the poor conditions of access, a distance superior to 7km to asphalt and proximity of large quarries in operation, which present better logistics and excellent deposits for extraction/production of the mine.
Finally, it is primordial to understand the chemical characteristics of the samples/rocks collected, these results are what can define the path to be followed in the course of a possible mining project of calcium carbonate.
HIGH-PURITY QUARTZ.
Veins of high-purity quartz were visualized in various points of the eastern sector of the ANM process visited, and in some of them it was possible to observe macroscopically a high purity, given the crystallinity and coloration of the material.
For example, point P13 illustrates a vein of large proportions found, while point P17 illustrates the chemical quality of the rock, which appears to have a high silica content (see Figure 6).
Preliminary information is not sufficient to understand the potential volume of these veins, however, the analysis and chemical characterization of these veins is fundamental for determining whether to advance or not with the idea of more detailed research on this substance.
ROCK SAMPLING.
During the field visit, 8 samples were collected and subdivided according to the purpose of each one, based on the principle of providing a more detailed description in the office, with cataloging for laboratory submission and specific chemical tests for limestone and quartz.
GENERAL CONSIDERATIONS
The previous chapters make it clear that there is a positive preliminary mineral potential for limestone and quartz. Therefore, the scenarios outlined below encompass research activities designed to advance work on both possibilities.
LIMESTONE.
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.
QUARTZ.
As outlined in the items above, the quartz occurrences in the eastern sector deserve attention from the perspective of a more detailed assessment of their potential, as the initial visit already indicated its presence in different areas, all with good physical characteristics.
Based on these observations, target definition will be essential to understand the feasibility of considering a mineral production project involving this substance.
FINAL CONCLUSIONS
ON THE GEOLOGY, it is concluded that:
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The study area is located in a region with limited geological variety, predominantly featuring metamorphosed metasediments of varying degrees, resulting in formations such as limestones, metarenites, and associated quartz veins;
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The eastern sector of the ANM process visited is the one that provides the most geological information regarding its mineral potential and possible product types.
ON THE CURRENT MINERAL POTENTIAL, it is noted that:
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Based on reconnaissance data, only two types of substances have been identified as having potential economic value, depending on laboratory results: high-purity quartz and limestone;
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Despite its promise, the actual mineral potential of the visited ANM process will be determined after further research activities and the presentation of results, at which point the best strategy for continuation, production, or discontinuation of the projects will be defined.
ON STRATEGIC POINTS, it is important to highlight that:
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The logistics of transporting potential limestone extraction should be carefully planned due to the distance from the asphalt and the quality of the existing access routes;
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There is a large quarry in operation near the area, managed by the company "Calcário BR-101," which operates approximately 2 km from the asphalt with productive and high-volume mining fronts. This could impact market competition for any potential product to be mined in the visited area;
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It is essential that, before proceeding with any research activities in any part of the areas, a formal agreement between the Titleholder and Surface Owners be established to clarify the intentions regarding mineral research and extraction in the region, considering the promising initial contact with the field team;
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The area has access to nearby energy sources, while water will likely need to be sourced locally, probably through tubular wells.
