Silica Sand
Belmonte - BA
The area of mining process no. 871.411/2020 occupies 47.91ha and is located in the municipality of Belmonte, Bahia, Brazil.
HIGHLIGHTS
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LOCAL GEOLOGY
The geology of the siliceous sand deposit in the studied area is the same as that of the others siliceous sand deposits in the region, that is, it is inserted in the Santa Maria Formation Eterna, so called by Lima et al. (1981).
Even though they are so common in the region, coverings enriched with siliceous sand are more expressive, both in area and thickness, when located in elevated tabular terrain, with elevations close to those at the base of the Group's lithotypes Barreiras, like the Principal and Delson Araújo incidents. These deposits are considered the most preserved, true testimonies of the entire process of formation via in situ residual concentration of the sandy-clayey part of the metadolomites siliceous with quartzite intercalations, from leaching of the carbonate fraction.
GEOLOGY AND GENESIS OF SAND DEPOSITS.
The occurrence of siliceous sand within the limits of process 871.411/2020 was mapped, at an appropriate scale.
This mapped deposit is located in the area dominated by the Santa Maria formation, in the Rio Pardo Basin, consisting of siliceous metadolomites with fine intercalations of quartzites.
The research work carried out allowed some conjectures about the origin of sandy deposits. These deposits were probably formed by in situ residual concentration of the sandy-siliceous part, resulting from leaching of the fraction carbonate present in very siliceous dolomites.
The process would have started at the time when the metasediments were covered by the Barreiras Formation. Surface water, infiltrated into the sediments, percolated through the carbonate-siliceous rocks, leaching the carbonate fraction gradually, from top to bottom (as the water table was lowered regional), widening fractures and leaving the compartments partially solubilized filled with siliceous residue.
The process remains active to this day, even after removing the coverage of the Barreiras Formation. In the same way as the sedimentary cover, a substantial portion of the deposits formed was carried away by erosive action. Reinforced hypothesis due to the presence of preserved bodies, identified in the region.
Fig 1. Local geology with rolling mesh and identified lithologies.
The angular nature of the grains of sand and gravel, the occasional occurrence of small quartz crystals well formed in the middle of the sand, the absence of clay, the low compaction (high porosity) of the sand, the existence of filled sinkholes, the absence of signs of stratification in the sandy deposit, the morphology of the deposits and the verification of a “bottom” made up of “hard sand” (not disaggregated), are some of the aspects that reinforce the genetic hypothesis exposed above, eliminating the possibility of transporting grains of sand, for which only small displacements within the “gaps” of the dissolution cavities.
DESCRIPTION OF SAMPLING HOLES
GEOLOGICAL MAPPING.
Aerial photographs, satellite images and GPS were used as auxiliary tools for geological mapping, resulting in the creation of a simplified map. No pits were dug in the area because it was only pastureland. A regular square grid of 100m x 100m was used to drill the holes, establishing a maximum depth of 6.00 m.
The surface delimitation of the sandy deposit was made through direct observation in the field with the aid of GPS, adopting paths along the contacts between clean sand and the yellowish sandy-clay material, the latter considered the remainder unusable.
It is worth noting that the transition from useful white sand to yellowish clayey sand is easily identified in the field, if we take into account the following contrasts:
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Exposure of the material brought to the surface by anthills;
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Thinner and more stunted vegetation in the areas of useful sand;
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Higher terrain with typical morphology of sand trays;
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Dry, porous terrain and a deeper water table in the sand areas
Fig 2. Topogeological map and positioning of the sounding mesh and identified lithologies.
DRILLING.
The drilling work was preceded by office planning where, in light of the preliminary geological reconnaissance work, potentially promising areas were selected and points were designed for drilling holes with anchorages to the provisional markers plotted during the topographic survey phase.
The equipment used was a shell-type auger, diameter 4” (10 cm), with a set of rods capable of reaching a depth of 6.00 meters.
A square probing grid (100 x 100) m was adopted, establishing a maximum depth of 6.00 m, for operational limitations, due to the heavy rains that fell in the region at the time of the probing, although the deposit has evidence of having much greater depths. 38 holes were drilled, distributed as follows: 26 positive holes (on clean and high-purity sand), 2 holes at the contact interface between clean sand and dirty sand, while the remaining 10 holes were negative, since they intercepted gravel and dirty clayey sand.
The positive holes were those that intercepted white, clean sand - reaching a maximum depth of 6.00 m - represented on the map above in green.
The contact holes were defined as those that intercepted an intercalation (interdigitation) between clean and dirty sand, whose holes were drilled at a depth of 2.50 m - represented on the map above in blue.
The negative holes are those that intercepted dark/yellowish sand, being interrupted after reaching a depth of 3.00 m - represented on the map above in red.
The positive holes were those that intercepted white, clean sand - reaching a maximum depth of 6.00 m - represented on the map above in green.
SAMPLING.
All the holes were sampled, however, samples from 13 holes were selected to be sent to the SGS Geosol laboratory for chemical and granulometric analysis, representing 48% of the holes drilled. The counter samples were catalogued and are stored, as are the cores from the other holes, totaling 38 specimens, including samples and counter samples.
In the sample collection system, it was defined that the first meter of the profile would be discarded, as it was dark gray sand with roots and organic matter. After discarding the first meter, all the material removed from the hole was quartered, resulting in a reduction in quantity, and two 1 kg samples were taken, each duly labeled. One sample was sent to the laboratory and another counter sample was retained and stored for possible future use.
Each sample was subjected to chemical analysis for SiO2, chromogenic elements (Fe and Ti), Al, Ca and Mg. Orientation analyses for other elements indicated values of little significance.
The analyses were performed by SGS Geosol using ICP and atomic absorption spectrometry, with detection limits of 1 ppm. Each sample was subjected to dry particle size analysis using 5, 10, 14, 16, 18, 35, 80, 150 and 200 mesh sieves.
Minerametric studies (minerals constituting the sand) and determination of physical parameters (density, moisture, porosity and swelling) were performed on samples from the studied occurrence, located near Santa Maria Eterna, whose data obtained, given the similarity of results obtained in nearby areas, were accepted and considered valid, due to the extreme similarity of the deposits and their surroundings. The natural density “in situ” adopted was 1.50 t/m3, including for calculating reserves. Other “in natura” parameters are: porosity = 42% and moisture = 3.3%.
ASPECTS OF THE DEPOSIT
QUALITY.
In the description of the materials used in the auger holes, only the macroscopic visual aspect of the samples taken was taken into account, thus establishing a standard of the material to be computed as useful material in the hole profiles, in the sampling and consequently in the calculation of reserves.
Sands with a high visual index of whiteness constitute the useful material, always presenting good contrast with the so-called impure sands, located at the top of the deposit, presenting a dark gray color and generally mixed with organic matter. It was also observed that the impure sand is located in a superficial layer up to 1.0 m deep.
Useful sands have a very homogeneous appearance in terms of grain size and whiteness among the materials coming from different holes.
Surface layer excavation
Surface layer excavation
The useful sand has a fine and homogeneous grain size, with irregular and angular quartz grains, translucent to transparent (under a magnifying glass), with intervals of fine milky and angular quartz gravel (with occasional fragments of up to 4 mm). Well-formed hexagonal prisms of hyaline quartz up to 2 cm in length have rarely been sampled.
The useful sand is very white and pure, with rare presences of gray or yellowish material, and when subjected to manual washing and subsequent drying, the color differences are not noticeable. Variations in humidity or even lighting can cause different impressions of whiteness in the same sample.
"In Natura" Sand
Manually Washed Sand
"In Natura" Sand
QUALITY.
Granulometric analyses carried out revealed that 91.71% of the sampled material was predominantly in the granulometric range of (-10, +200 mesh).
CHEMICAL ANALYSIS.
The results obtained lead to the following main observations regarding the chemical nature of the sand:
Useful sands have a very homogeneous appearance in terms of grain size and whiteness among the materials coming from different holes.
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The results are relatively uniform for all samples analyzed.
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77.00% of the samples analyzed in the deposit present levels higher than 99.51% SiO2; and the main contaminants (Ti, Ca, Mg, Al, Fe, P, Na, Zr and K) do not reach, on average, 704 ppm when converted into their respective oxides. Other elements studied (Mn, Cr, Li, Co, Ni, V and B) do not individually reach 1 ppm.
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The analyzed ore presents a maximum silicon dioxide (SiO2) of 99.80%, a minimum of 98.95%, a standard deviation of 0.22 and a variance of 0.05, reflecting the homogeneity of the deposit with regard to the SiO2 content.
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Titanium is the chromogenic contaminant with the highest average content, presenting an appreciable dispersion of values (maximum/minimum and standard deviation), unlike the other elements that show much smaller dispersions.
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Fe levels are low and relatively uniform, which helps to attenuate the chromogenic impairment caused by Ti.
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Other elements (Al, Ca, Mg, P, Na, Zr and K), due to their non-chromogenic nature and relatively low and homogeneous contents, do not compromise the quality of the sand for the most common industrial uses.
MINERALOGY.
Regarding mineralogy, leucoxene is mainly responsible for the Fe and Ti contents, being dominant in the fraction smaller than 200 mesh. A discrete portion of Fe and Ti may be included or embedded in the quartz grains.
Aluminum (Al), Sodium (Na) and Potassium (K) can be constituents of clay minerals, in the form of aggregates, more abundant in the fraction passing through 200mesh.
Zirconium (Zr) probably originating from zirconite, with very fine grain and more abundant in the passing fraction at 200mesh.
Calcium (Ca), Magnesium (Mg) and Phosphorus (P) do not show preferential levels in the three granulometric bands, and must be part of minerals included in the quartz grains. The siliceous metadolomite sheets indicate the existence of tiny carbonate granules included in the recrystallized quartz grains.
The quartz grains, always angular, are milky to semi-transparent in the fraction retained in 35mesh and hyaline in the finest fractions passing through 35mesh. These grains occasionally appear grayish, due to fine inclusions (rutile, Fe oxides) or encrusted on the surface with Fe and Ti oxides.
GEOLOGICAL MODELING.
To determine the volume of available sand, several interpretations were made based on the survey data carried out by the company.
As a result of the drilling work, a map of the influence of the drill hole grid was generated, with potential depth, indicating the ore contents and contents of the main chromogenic elements iron (Fe) and titanium (Ti) present in each drill hole analyzed.
To carry out the modeling process, data from drilling holes drilled into the sand body were used to determine the geometry and thickness of the sand body.
GRANULOMETRY.
In the sample collection system, it was defined that the first meters of the drilling profiles of each hole would be discarded as they contained roots and organic matter.
Two composite samples were taken from each hole (reduced to approximately 1 kg each, by quartering) and sent to the SGS Geosol laboratory.
Each sample was subjected to dry granulometric analysis using a Tyler sieve of #20, #28, #48, #100, #200 mesh.
SURVEY MESH.
A regular 100x100m grid was planned and executed, which proved to be quite adequate, providing good spatialization of the area and demonstrating the continuity of the material.
As a result, a map of the survey carried out in the area of this research project was generated.
ANALYSES ON THE ECONOMIC FEASIBILITY OF THE DEPOSIT
The deposit in the area in question was studied, mapped and subjected to an auger drilling program, with systematic sampling, followed by granulometric analyses by the SGS Geosol laboratory, whose set of samples from the Project were sent to the laboratory after being labeled with their respective names of the holes drilled in the area of interest, allowing the quality of the sand to be assessed, adopting the market's quality criteria and requirements.
At the end of the field work and office processing, a measured reserve of 2,408,400 tons and an indicated reserve of 1,206,000 tons were reached, which together result in 3,614,400 tons of good quality useful sand.
Below is a summary of the research work carried out on and around the sand deposit, process ANM 871.411/2020.
PRELIMINARY AREA RECOGNITION.
Aiming to make geological mapping work more consistent, a bibliographic compilation of existing information about the lithologies that outcrop in the study area was made.
In the field, geological reconnaissance was carried out across the entire area, aiming to identify potentially promising targets for sand for subsequent geological detailing and definition of the survey grid.
DEFINING THE POSITIONING OF THE HOLES.
A square auger drilling grid was designed, with spacing of 100 x 100 m, covering most of the surface domain of the useful sand, as illustrated in the maps presented in this report.
Each borehole was located using GPS, with wooden markers placed for easy identification by the drilling team. The borehole opening heights were taken using GPS.
EXECUTION OF THE SURVEY.
The holes were drilled with a shell-type mechanical auger to a depth of 6.00 m. The first meter of the drilling was discarded due to contamination, with only 5 meters being considered useful sand. The sampled material was collected and placed on a clean tarpaulin for quartering, generating, at the end, two composite samples representative of the hole, each weighing approximately 1 kg.
GEOLOGICAL MAPPING.
The geology, origin, morphology and some boundaries of the sandy deposits in the research area have been well established with the regional research work described in this report.
The surface delimitation of useful sandy deposits for the research area was carried out directly in the field, with the aid of GPS, through careful walks along their contacts with yellowish clayey sandy material and white sand.
The transition from useful white sand to yellowish clayey sand is clear in the field and can be easily identified from a short distance, based on the following contrasts:
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Appearance and color of material exposed by anthills;
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Thinner and more stunted vegetation on useful sand;
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Typical morphology of trays in useful sand;
SAMPLING.
A rectangular auger drilling grid was designed, with spacing of 100 x 100 m, covering most of the surface domain of the useful sand.
Each survey point was located with GPS and identified with a wooden stake.
Every useful sand sample collected by drilling was reduced by quartering into two samples of 1 kg each, with one sample sent to the SGS Geosol laboratory and the other sample retained to meet future needs.
CHEMICAL AND GRANULOMETRICAL ANALYSIS.
Of the total number of holes drilled in the area, 13 holes, corresponding to 48% of the total, were selected for chemical and granulometric analyses at the SGS Geosol laboratory.
The samples were subjected to chemical analysis, including SiO2 (%) and Al, Fe, Ti, Ca, Mg, Na, K, Zr (ppm) by ICP spectrometry. The particle size analysis was performed dry on meshes #5, #10, #14, #16, #18, #20, #35, #50, #80, #140, #200.
SAND QUALITY.
The granulometric analysis resulted in 53.31% of the material in the range - #35 to + #200. The chemical analysis shows the average contents of SiO2 (99.51%), Al (275.46 ppm), Fe (142.15) ppm, Ti (132.62 ppm), Ca (56.54 ppm), Na (31.08 ppm), K (25.54 ppm), Zr (22.23 ppm), Mg (18.08 ppm).
The macroscopic characteristics, granulometry, chemical and mineralogical nature of the sand studied in this area are approximately equivalent to those found in the mining district of Santa Maria Eterna.
RESERVE CALCULATIONS.
Measured reserve (MR) was calculated considering the product of the useful sand interval sampled in each positive hole, by the area of influence of the hole within the mapped limits of useful sand and by the density of the dry sand base “in situ” (1.50).
From the surface area of 32.16 ha and with a useful sand thickness of 5 m, we obtained a measured reserve of 2,412,400 t. From the drilling work it was possible to measure the reserves of useful siliceous sand existing in the area.
Indicated reserve (IR) calculated by considering half the product of the average thickness of the holes, by the area of influence of the hole within the mapped limits of sand using times the density of the dry sand base “in situ” (1.50).
To calculate the indicated reserve, the area immediately below the measured reserve area was used, given that the holes were drilled using a technical option to a depth of 6 meters and, below this depth, there is still the presence of sand, a fact proven by the fact that all the holes drilled in the area did not reach the end of the sand body.
FINAL CONCLUSIONS
Brasil Mineração Ltda, aware of the potential of the silica ore deposit existing within the limits of the polygons defining the processes under its ownership, channeled technical and financial efforts with the aim of quantifying and qualifying the high-purity silica sand deposit that occurs in the rural area of Belmonte, in the vicinity of the district of Santa Maria Eterna.
The technical and financial capacity of Brasil Mineração Ltda. is also noteworthy, as it is sufficient to carry out the research work carried out in the area, as well as the studies and analyses of the substance that is the object of the research, namely, high-purity silica sand. It is worth noting that the results obtained provide positive elements that recommend the implementation of an industrial-scale mine for continued supply to the consumer market.
Intended to make good and rational use of high-purity silica sand ore in the area under study, it intends to implement a Processing Unit for the ore of interest.
The chemical and granulometric characteristics of the ore, the existing logistical conditions in the project's surroundings, the low operating cost and the growing demand for high-purity silica sand to meet the demands of the energy transition encouraged Brasil Mineração to move forward in the search for regularization and in-depth studies in the area.
The research carried out ensures reserves that support operations for 20 years with a production of 120,000 t/year in highly competitive conditions on the global scene.
