A comprehensive exploration method for concealed sedimentary bauxite

Abstract

The application discloses a kind of concealed sedimentary bauxite comprehensive exploration methods, comprising: according to regional geological data, delimiting ore-prospecting favorable area;In favorable area, carry out geological mapping and arrange audio magnetotelluric measuring line to measure;Based on the resistivity difference of different strata, potential bauxite mineralization depression is circled on AMT measuring line;Verification drill hole is arranged in mineralization depression to carry out drilling, sampling and chemical analysis, and subsequent exploration work is determined according to the analysis result.The present application can accurately locate the bauxite body concealed in the ancient karst interface by combining geological comprehensive research, AMT measurement and drilling verification, significantly improve the drilling ore rate, reduce the exploration cost, shorten the exploration period, and is suitable for ore-prospecting exploration in Qianzhong area and similar concealed sedimentary bauxite.

Description

Technical Field

[0001] This invention relates to the field of mineral exploration technology, specifically to a prospecting and exploration technique for concealed sedimentary bauxite deposits. Background Technology

[0002] Sedimentary bauxite is an important type of aluminum resource. Its mineralization process mainly involves the deposition and alteration of aluminum-rich detrital material in low-lying areas along paleokarst interfaces after transportation. Therefore, the spatial distribution of bauxite bodies is strictly controlled by multiple factors, including paleokarst interface morphology, sedimentary environment, geological structure, and subsequent leaching alteration. In practical mineral exploration, accurately predicting the location of bauxite bodies and rationally arranging exploration projects are crucial for improving exploration success rates and reducing exploration costs.

[0003] Currently, the conventional exploration techniques for sedimentary bauxite deposits are as follows: First, based on information about exposed ore-bearing rock formations, known deposits, or mineralization points, and combined with the regional geological background, favorable mineralization areas are preliminarily identified. Then, following the exploration principle of proceeding from shallow to deep and from known to unknown, the corresponding exploration grid is determined according to the exploration type of the deposit (e.g., Class I, II, III), and boreholes are arranged at certain intervals to verify and discover deep bauxite bodies through drilling. This method is well-suited for semi-hidden bauxite bodies or those with surface mineralization.

[0004] However, for fully concealed sedimentary bauxite bodies, especially those buried above paleokarst interfaces, the prospecting direction is extremely unclear due to the lack of any known surface deposit information or outcrops of ore-bearing rock strata. Traditional exploration approaches relying on surface mineralization clues are ineffective, leading to significant blind spots in exploration work. In such cases, directly arranging boreholes according to a fixed grid often results in low drilling success rates, with many boreholes failing to find mineralization, leading to a substantial waste of exploration funds and time. Furthermore, the location of concealed bauxite bodies is controlled by paleogeography, exhibiting a discontinuous depression distribution. Conventional geological mapping cannot directly delineate these favorable mineralization depressions, necessitating a geophysical exploration method that can effectively detect deep electrical structures and identify paleokarst depressions in conjunction with these methods.

[0005] Therefore, there is an urgent need to develop a comprehensive exploration method specifically for concealed sedimentary bauxite deposits, capable of effectively narrowing down the prospecting target area and improving the success rate of drilling verification under conditions of lack of surface mineralization information. This invention is proposed based on the aforementioned technical challenges, providing a systematic and efficient technical solution for the prospecting and exploration of concealed sedimentary bauxite deposits through a technical approach that combines comprehensive geological research, audio-frequency magnetotelluric surveys, and drilling verification.

[0006] To address the aforementioned issues, the applicant proposes a comprehensive exploration method for concealed sedimentary bauxite deposits. Summary of the Invention

[0007] The purpose of this invention is to provide a comprehensive exploration method for concealed sedimentary bauxite deposits to solve the problems in the prior art.

[0008] To achieve the above objectives, the present invention provides the following technical solution: a comprehensive exploration method for concealed sedimentary bauxite deposits, comprising the following steps:

[0009] Step 1: Obtain regional geological data of the target area, determine the stratigraphy, structure and mineral distribution information, so as to delineate an area with a certain area, mineral-bearing rock series buried at a depth less than the preset depth, geological structure complexity lower than the preset threshold and not overlapping with the restricted area, as a favorable area for mineral exploration;

[0010] Step 2: Conduct geological mapping in the favorable area, identify fault information, and set up an audio-frequency magnetotelluric survey line to obtain audio-frequency magnetotelluric measurement data;

[0011] Step 3: Perform a comprehensive interpretation of the audio magnetotelluric measurement data, and delineate potential bauxite mineralization depressions along the audio magnetotelluric survey line based on the resistivity differences of different strata.

[0012] Step 4: Select a location within the delineated mineralized depression to lay a verification borehole for drilling verification. Sample and chemically analyze the ore-bearing rock series revealed by the verification borehole, and determine subsequent exploration work based on the analysis results.

[0013] Optionally, in step one, the regional geological data includes a 1:50,000 regional geological map, a 1:50,000 regional mineral map, and a 1:50,000 hydrogeological map; the restricted area includes the mining rights area, the construction project area, and the urban development boundary area.

[0014] Optionally, in step one, the area of ​​the favorable zone is greater than or equal to 10 km², and the maximum burial depth of the ore-bearing rock series is less than 800 m.

[0015] Optionally, in step two, the geological mapping is a 1:10000 scale geological mapping (revision survey), and the tracing method is used to determine the nature, combination relationship, formation and evolution of the main faults and their destructive or controlling effects on the ore-bearing rock series.

[0016] Optionally, the spacing between geological observation points in the geological mapping is 300-500 m.

[0017] Optionally, in step two, the measurement frequency range of the audio magnetotelluric survey line is 0.125~8192Hz, and the distance between measurement points is 50~100 m.

[0018] Optionally, in step two, if the distribution direction of the bauxite body can be determined through surrounding exploration data, the audio-frequency magnetotelluric survey lines are arranged perpendicular to the long axis of the ore body and pass through the already implemented ore-bearing boreholes; if the distribution direction of the ore body cannot be determined, the audio-frequency magnetotelluric survey lines are arranged perpendicular to the main structural direction within the area.

[0019] Optionally, in step three, the step of delineating potential bauxite mineralization depressions on audio-frequency magnetotelluric survey lines based on the resistivity differences of different strata includes: identifying the electrical structural characteristics of an upper high-resistivity layer, a middle low-resistivity layer, and a lower high-resistivity layer on the audio-frequency magnetotelluric profile, and delineating the middle low-resistivity layer as a potential bauxite mineralization depression.

[0020] Optionally, in step four, the chemical analysis includes five basic analyses: Al2O3, SiO2, TFe, TiO2, and loss on ignition; the determination of subsequent exploration work based on the analysis results specifically includes:

[0021] If the thickness of the bauxite body in the borehole is verified to be ≥0.8 m, and the Al2O3 content is ≥55%, and the aluminum-silicon ratio Al2O3 / SiO2 is ≥3.8, it is determined that the mineral has been found and is mineable. The favorable area is then optimized and adjusted to form a prospecting target area, and a target area report is submitted to enter the bauxite exploration stage.

[0022] If the thickness of the bauxite body in the borehole is verified to be <0.8 m, or the Al2O3 content is 40%~50%, or the Al2O3 / SiO2 ratio is 1.8~3.8, then it is determined to be mineralized, and the mineralization potential of the favorable area is reassessed.

[0023] If the Al2O3 content in the borehole is verified to be <40% or the Al2O3 / SiO2 ratio is <1.8, it is determined that no minerals are found and the favorable area is abandoned.

[0024] Optionally, the method is used to explore sedimentary bauxite deposits hidden on ancient karst interfaces, the target area being the central Guizhou region, and the ore-bearing rock system being the Jiujialu Formation of the Lower Carboniferous.

[0025] Beneficial effects: Significantly improves the success rate of drilling verification.

[0026] This invention overcomes the shortcomings of traditional methods, such as lack of surface mineralization information and blind drilling layout, through a systematic process of "favorable area delineation → geological mapping → audio-frequency magnetotelluric (AMT) measurement → delineation of mineralized depressions → verification boreholes." In an example, targeting the concealed bauxite deposits of the Lower Carboniferous Jiujialu Formation in central Guizhou, seven favorable areas were selected. After surface mapping, AMT survey lines were laid out in four of these favorable areas. Comprehensive interpretation delineated three mineralized depressions, and three verification boreholes were drilled. Two of these boreholes yielded mineable mineralization (mineralization rate of 66.7%), and two prospecting target areas were submitted. This mineralization rate is significantly higher than that of traditional empirical borehole layout methods, effectively reducing ineffective drilling work.

[0027] Precisely locate mineralized depressions on ancient karst interfaces

[0028] This invention fully utilizes the significant resistivity differences between different strata (high resistivity of carbonate rocks and low resistivity of clastic rocks) to obtain deep electrical structures through AMT measurements. It identifies a "high resistivity-low resistivity-high resistivity" pattern on the geological profile, accurately delineating bauxite mineralization depressions hidden on paleokarst interfaces. This method overcomes the limitation of conventional geological mapping in directly probing deep paleogeography, providing clear target locations for drilling verification.

[0029] Significantly reduce exploration costs and shorten exploration cycle

[0030] Compared to the traditional method of drilling according to a fixed grid system, this invention only deploys a small number of verification boreholes (usually only one) within the limited mineralized depressions delineated by AMT, avoiding blind construction in large favorable areas. In the embodiment, only 3 verification boreholes were used to obtain 2 prospecting target areas for further exploration. Among them, "Prospecting Target Area No. 1" has been directly transferred to the general exploration stage and successfully applied for the Guizhou Province 2026 New Round of Prospecting Breakthrough Strategic Action Project ("Prospecting the Jinjiaba Bauxite Mine in Qingzhen City, Guizhou Province"). This saved a lot of drilling and geophysical exploration costs in the intermediate links of preliminary and detailed exploration, and shortened the exploration cycle by more than 40%.

[0031] It is highly operable and applicable to similar concealed sedimentary mineral deposits.

[0032] This invention provides clearly defined technical parameters (such as AMT frequency range of 0.125~8192 Hz, measuring point spacing of 50~100m, geological observation point spacing of 300~500m, sampling and analysis standards, etc.), forming a standardized and streamlined technical solution for the exploration of concealed bauxite deposits. This method is not only applicable to the Jiujialu Formation bauxite deposit in central Guizhou, but can also be extended to other concealed sedimentary mineral deposits controlled by paleokarst interfaces (such as phosphate and manganese deposits), showing broad application prospects.

[0033] To provide a reliable target area for subsequent exploration phases

[0034] This invention verifies the quantitative analysis results of boreholes (thickness ≥ 0.8 m, Al2O3 ≥ 55%, aluminum-silicon ratio ≥ 3.8 indicates mineralization), scientifically optimizing and upgrading "favorable areas" into "mineral exploration target areas," and directly submitting a "Target Area Report," seamlessly connecting subsequent general survey, detailed survey, and exploration stages, achieving an integrated and rapid breakthrough from regional prediction to target area verification of concealed bauxite deposits. Attached Figure Description

[0035] Figure 1 This is a schematic diagram of the process of an embodiment of the present invention. Detailed Implementation

[0036] The preferred embodiments of the present invention are described below with reference to the accompanying drawings to make the technical content clearer and easier to understand. The present invention can be embodied in many different forms, and the scope of protection of the present invention is not limited to the embodiments mentioned herein.

[0037] This invention provides a comprehensive exploration method for concealed sedimentary bauxite deposits. The technical solution of this invention will be described in detail below with specific implementation examples and related drawings. It should be noted that this specific embodiment is only for explaining the invention and does not constitute a limitation on the scope of protection of this invention. Any equivalent substitutions or modifications made based on the technical concept of this invention are within the scope of protection of this invention. The method described in this invention is mainly aimed at sedimentary bauxite deposits concealed on paleokarst interfaces, especially those completely concealed bauxite areas where there are few outcrops of ore-bearing rock strata on the surface and traditional prospecting methods are ineffective. To more clearly demonstrate the operability and technical effects of this invention, the following uses the exploration work of sedimentary bauxite deposits in the Jiujialu Formation of the Lower Carboniferous in the central Guizhou region as an example to describe in detail the entire process from basic geological data collection, favorable area delineation, geological mapping and audio-frequency magnetotelluric survey line layout, data comprehensive interpretation, delineation of ore-forming depressions, to verification drilling implementation, sample collection and analysis, and target area submission.

[0038] Before implementing this invention, it is necessary to collect various basic geological data of the target area. These data mainly include 1:50,000 regional geological maps, 1:50,000 regional mineral maps, and 1:50,000 hydrogeological maps. These maps can provide key information such as regional stratigraphic distribution, structural framework, known mineral types and their occurrence strata, and hydrogeological conditions. Taking the central Guizhou region as an example, through systematic collection and research of the aforementioned data, it can be determined that the stratigraphic sequence of this area is complete. From bottom to top, it consists of the following formations: Cambrian II Qingxudong Formation dolomite, Cambrian Furong Formation Loushanguan Formation dolomite, Lower Carboniferous Jiujialu Formation aluminous rock series, Lower Carboniferous Baizuo Formation dolomite, Permian Yangxin Formation Liangshan Formation claystone and sandstone, Permian Yangxin Formation Qixia Formation limestone and dolomitic limestone, Permian Yangxin Formation Maokou Formation limestone, Permian Emeishan basalt, and Permian Leping Formation Longtan Formation claystone, siltstone, and coal-bearing strata. Bauxite is mainly found in the Lower Carboniferous Jiujialu Formation, which has a thickness ranging from 0 to 25 meters and an average apparent resistivity of 114.31 ohms-meters, classifying it as a low-resistivity layer. The adjacent Baizuo Formation dolomite and Liangshan Formation claystone and sandstone also exhibit different resistivity characteristics. Understanding the differences in the physical properties of these strata is the physical basis for the effective identification of mineralized depressions by subsequent audio-frequency magnetotelluric surveys. After mastering the regional stratigraphic sequence and ore-bearing strata, it is necessary to further delineate the "favorable areas" for mineral exploration. The delineation of favorable areas needs to meet the following conditions: First, the area should not be too small, generally requiring no less than 10 square kilometers, to ensure sufficient space for mineralization; second, the burial depth of the ore-bearing rock series should be moderate, with the maximum burial depth controlled within 800 meters, because 800 meters is the exploration depth determined by the bauxite geological exploration specifications, and the geophysical resolution decreases beyond 800 meters; third, the complexity of the geological structure should be simple to moderate, as areas with overly complex fault development will disrupt the continuity of the ore-bearing rock series, which is not conducive to the formation of large-scale bauxite bodies; finally, the favorable area should not overlap with existing mining rights, urban development boundaries, important construction projects, etc., to avoid subsequent exploration work being hindered by policies or ownership issues. In practice in the central Guizhou region, seven favorable areas were initially delineated based on the above standards. These favorable areas are all located on the periphery or deep within the known bauxite metallogenic belt, with no exposed nine-furnace group on the surface, and belong to typical fully concealed bauxite prospecting potential areas.

[0039] After delineating favorable areas, 1:10,000 scale geological mapping (revision) work needs to be carried out in these areas first. The main purpose of geological mapping is to clarify the nature, combination relationship, formation and evolution history of the main faults in the area, as well as their destructive or controlling effects on the ore-bearing rock series. Since the target deposit of this invention is concealed and the ore-bearing rock series cannot be directly seen on the surface, the mapping work pays more attention to the detailed depiction of faults and folds. The mapping process adopts the "tracing method", that is, tracing observation along the fault strike or stratigraphic boundary. The spacing of geological observation points is generally controlled between 300 and 500 meters, and there is no rigid requirement for the point density, with the aim of accurately controlling the geological boundary and clarifying the structural features. In a favorable area in central Guizhou, a near-north-south trending reverse fault was discovered through 1:10,000 scale geological mapping (revision). The fault dips eastward at an angle of about 60 degrees, and the fault fracture band is about 5 to 8 meters wide. The strata on both sides of the fault are obviously discontinuous. Further investigation revealed that the fault had a destructive effect on the ore-bearing rock strata of the Jiujialu Formation. The ore-bearing rock strata on the hanging wall of the fault were uplifted and eroded, while the footwall was buried. Therefore, verification boreholes should be arranged on the footwall side of the fault. After completing the geological mapping, an audio-frequency magnetotelluric (AFM) survey line needs to be laid out and implemented. AFM is a geophysical method that uses natural alternating electromagnetic fields to detect underground electrical structures. It has a large detection depth and high resolution, and is particularly suitable for the exploration of concealed sedimentary bauxite deposits. The length of the AFM survey line used in this method depends on the extent of the favorable area and should generally span the entire potential ore-forming zone. The spacing between measuring points is set to 50 to 100 meters, and the frequency range covers 0.125 to 8192 Hz. This frequency band can effectively detect electrical changes from the surface to a depth of 1000 meters underground. When the orientation of bauxite bodies can be determined using surrounding exploration data, audio-frequency magnetotelluric (AFM) survey lines should be laid out perpendicular to the long axis of the ore body, and preferably through existing ore-bearing boreholes, to establish a correlation between electrical properties and the ore body. When surrounding exploration data is lacking and the orientation of the ore body cannot be determined, the survey lines should be laid out perpendicular to the main structural direction of the area. This is because the distribution of most sedimentary bauxite bodies is controlled by paleotectonic and paleogeographical features, and a perpendicular orientation maximizes the probability of traversing potential mineralization depressions. In a favorable area in central Guizhou, due to a lack of detailed exploration data from adjacent mining areas, a north-south AFM survey line was laid out perpendicular to the near-east-west main fault direction of the area. The line is 3.2 kilometers long, with a survey point spacing of 50 meters, and a total of 65 survey points. During data acquisition, the recording time at each survey point was no less than 20 minutes to ensure the signal-to-noise ratio of the low-frequency data. The acquired raw time-series data underwent Fourier transform, far reference channel processing, and impedance tensor estimation to obtain the apparent resistivity and phase curves for each measurement point. Subsequently, static effect correction, skin depth correction, and two-dimensional inversion were performed on the data to finally generate a resistivity depth profile.The nonlinear conjugate gradient method was used in the inversion process. The initial model was set as a uniform half space. After 30 iterations, the root mean square error was less than 5%, indicating that the inversion results were reliable.

[0040] Next, the audio-frequency magnetotelluric data were comprehensively interpreted to delineate paleokarst depressions associated with bauxite mineralization. The comprehensive interpretation was based on the significant resistivity differences between different strata. In the bauxite deposit area of ​​central Guizhou, based on measured and collected physical property data, the average apparent resistivity of each stratum is as follows: the Permian Yangxin Formation Qixia Formation limestone has an average resistivity of 3376.8 ohms·m, and the Permian Yangxin Formation Maokou Formation limestone is also high resistivity. The two are in conformable contact, forming a high-resistivity layer in the profile; the average apparent resistivity of the Permian Yangxin Formation Liangshan Formation claystone and sandstone is only 81.42 ohms·m, which is low resistivity; although the resistivity of the Lower Carboniferous Baizuo Formation dolomite is not listed in the table, its average value is in the hundreds of ohms·m according to actual measurements, which is relatively low compared to the limestone; the average apparent resistivity of the Lower Carboniferous Jiujialu Formation bauxite, bauxite, and aluminous claystone is 114.31 ohms·m, which is also low resistivity; the average apparent resistivity of the Cambrian Furong Formation Loushanguan Formation and the Cambrian Second Formation Qingxudong Formation dolomite is as high as 4698.91 ohms·m and even higher, respectively, which are high resistivity. Therefore, an ideal audio-frequency magnetotelluric (AMT) profile should exhibit a three-layer electrical structure from top to bottom: high resistivity – low resistivity – high resistivity. The upper high resistivity corresponds to the limestone of the Permian Qixia and Maokou Formations; the middle low resistivity corresponds to the clastic rocks and bauxite of the Liangshan, Baizuo, and Jiujialu Formations; and the lower high resistivity corresponds to the Cambrian dolomite. The thickness variation and morphology of the middle low resistivity layer can reflect the undulations of the paleokarst interface: when a depression exists at the paleokarst interface, the thickness of the overlying clastic rocks will increase significantly, appearing as a downward bulge of the low resistivity layer on the resistivity profile. This morphology is interpreted as a potential bauxite "mineralization depression." In the actual AMT profile interpretation in the central Guizhou region, the inverted resistivity profile clearly shows a near-north-south trending banded low resistivity anomaly. This anomaly is located between station 800 and 1500 meters along the survey line, with the burial depth gradually increasing from 300 meters to 550 meters, before uplifting again to form a distinct "groove" shape. The resistivity of this low-resistivity anomaly zone ranges from 80 to 150 ohm-meters, highly consistent with the known physical properties of the Jiujialu Formation and Liangshan Formation. Below the anomaly zone, the resistivity rises sharply to over 4000 ohm-meters, corresponding to Cambrian dolomite. Therefore, a relatively large mineralized depression was delineated along this AMT survey line, approximately 700 meters wide and with a maximum depth of 550 meters. Additionally, a smaller depression was discovered at the northern end of the survey line, but it is smaller in scale and shallower, suggesting limited mineralization potential. If no mineralized depression can be delineated along a particular AMT survey line, it indicates that the favorable area lacks the paleogeographic conditions for sedimentary bauxite formation, and the area should be abandoned, with exploration resources redirected to other areas with greater potential.

[0041] After successfully delineating the mineralized depression using the AMT survey line, a field reconnaissance is required. A verification borehole should be drilled at a location with minimal fault influence and favorable surface conditions. The verification borehole should ideally be located near the deepest part of the mineralized depression, as this is where thicker bauxite bodies are most likely to be preserved. Simultaneously, active fault fracture zones should be avoided to prevent borehole collapse or water inrush. In this favorable area of ​​central Guizhou, a location approximately 100 meters south of the center of the mineralized depression is selected as the verification borehole location. This location has flat terrain, is accessible by a simple road, and is approximately 200 meters from the nearest active fault, providing favorable construction conditions. Then, a survey line should be laid perpendicular to the main structural direction of the area, extending through the verification borehole. The survey line should cover the entire mineralized depression, typically 1 to 2 kilometers in length. Based on the AMT inversion profile and geological mapping results, a survey line profile map should be drawn at a scale of 1:5000. The map should clearly indicate stratigraphic boundaries, fault locations, and predicted ore-bearing strata and depths. Simultaneously, based on the geologically predicted borehole depth (e.g., predicted depth of 580 meters), a draft borehole columnar section should be prepared at a scale of 1:500. The columnar section should indicate the predicted thickness, lithology, and expected mineralization depth of different strata. Following this, a "Drilling Construction Organization Design" should be prepared, including borehole structure, drilling technology, flushing fluid type, core sampling requirements, hydrological observation, borehole inclination measurement, end-of-hole standards, and sealing requirements. A qualified drilling team should be selected, and an XY-5 core drilling rig equipped with Φ75 mm or Φ95 mm diamond core bits should be used for full-hole core drilling. During drilling, the advance per cycle should be strictly controlled, generally not exceeding 2 meters, ensuring a core recovery rate of no less than 80%, and a core recovery rate of no less than 85% within 5 meters of the ore layer and its top and bottom plates. During the verification drilling in the central Guizhou region, the actual final drilling depth was 602.3 meters. The exposed strata, from top to bottom, were: Quaternary overburden, Permian Longtan Formation coal-bearing strata, Permian Emeishan basalt, Permian Maokou Formation limestone, Permian Qixia Formation limestone, Permian Liangshan Formation claystone, Carboniferous Baizuo Formation dolomite, Carboniferous Jiujialu Formation aluminous rock series, and Cambrian Loushanguan Formation dolomite. The Jiujialu Formation, with a thickness of 2.8 meters, is located at depths of 548.2 to 551.0 meters. Its lithology is mainly grayish-white to dark gray dense massive bauxite, locally interbedded with bauxite and aluminous claystone. After the verification drilling was completed, geological logging was immediately carried out, recording in detail the lithology, color, structure, texture, fracture development, and mineralization characteristics of each drilling run. For the ore-bearing strata of the nine furnace groups, it is necessary to describe them in layers according to differences in lithology, natural ore type, color, etc., and determine the sampling locations.

[0042] Sampling was performed using the 1 / 2 splitting method, where the core was cut in half axially. One half was sent to the laboratory for analysis, while the other half was retained in the core box as raw geological data. The length of a single sample generally did not exceed 1 meter. If the thickness of a single lithology was greater than 1 meter, it was sampled continuously at 1-meter intervals; if a layer was less than 1 meter thick, it was treated as a separate sample. In the verification borehole in the central Guizhou region, the total thickness of the nine furnace groups was 2.8 meters, which was divided into three samples: the first sample was bauxite, 0.9 meters thick, sample number ZK001-H1; the second sample was bauxite, 1.0 meter thick, sample number ZK001-H2; and the third sample was bauxite claystone, 0.9 meters thick, sample number ZK001-H3. All samples were placed in clean cloth bags, double-labeled, and promptly sent to the laboratory for chemical analysis. The analysis included five basic parameters: Al2O3, SiO2, TFe (total iron), TiO2, and loss on ignition. These indicators are the most critical parameters for evaluating bauxite quality. Al₂O₃ content determines the ore grade, SiO₂ content affects alkali consumption during smelting, the Al₂O₃ / SiO₂ ratio is the core indicator for determining the industrial value of the ore, TFe and TiO₂ are common impurities, and loss on ignition reflects the content of clay minerals and organic matter. Laboratory analysis methods typically employ X-ray fluorescence spectrometry or chemical titration, and the analytical error must meet relevant national standards (such as GB / T 3257 series). After obtaining the analytical results, a weighted average calculation is needed for the analysis results of the verification borehole samples to determine the average thickness, average Al₂O₃ grade, and average Al₂O₃ ratio of the bauxite body. In the weighted average calculation, the thickness of each sample is used as the weight, and the calculation formula is: Weighted average grade = Σ(single sample thickness × single sample grade) / Σsingle sample thickness. In the example from the central Guizhou region, ZK001-H1 has an Al2O3 content of 58.2%, SiO2 of 12.5%, and a thickness of 0.9 meters; ZK001-H2 has an Al2O3 content of 61.5%, SiO2 of 9.8%, and a thickness of 1.0 meter; ZK001-H3 has an Al2O3 content of 35.6%, SiO2 of 28.4%, and a thickness of 0.9 meters. When calculating bauxite ore bodies (only counting samples reaching the boundary grade), samples with Al2O3 ≥ 40% and an aluminum-silicon ratio ≥ 1.8 are usually included in the ore body. In this example, H1 and H2 meet the conditions, while H3 does not. Therefore, the ore body thickness is 0.9 + 1.0 = 1.9 meters, the weighted average Al2O3 is (0.9 × 58.2 + 1.0 × 61.5) / 1.9 = 59.9%, the weighted average SiO2 is (0.9 × 12.5 + 1.0 × 9.8) / 1.9 = 11.1%, and the aluminum-silicon ratio is 59.9 / 11.1 = 5.4. This result meets the industrially mineable standards of thickness ≥ 0.8 meters, Al2O3 ≥ 55%, and aluminum-silicon ratio ≥ 3.8. Therefore, the verification borehole is deemed minable.

[0043] Based on the results of the verification boreholes showing mineable mineralization, the originally delineated favorable area needs to be optimized and adjusted to form a more precise "mineralization target area." The principle of optimization and adjustment is to comprehensively determine the boundary of the mineralization target area by taking the mineralized boreholes as the center and combining geological factors such as the morphology of the mineralized depressions delineated by AMT, the distribution of planar stratigraphy, and the distribution of faults. Areas with obvious mineralization deficiencies, such as fault uplift erosion zones and ancient highlands, should be excluded from the target area. Then, a "Target Area Report" is prepared, which includes the favorable area selection process, geological mapping results, AMT measurement and interpretation results, verification borehole construction and sampling analysis results, resource estimation, and recommendations for the next steps in exploration. After submitting the target area report, the formal exploration phase of bauxite deposits begins, and general surveys, detailed surveys, and explorations are carried out sequentially according to the prepared design. In practice in the central Guizhou region, this prospecting target area was named "Prospecting Target Area No. 1". Subsequently, it successfully applied for the "Prospecting Breakthrough Strategic Action Project of Guizhou Province in 2026" and received financial support. It is currently in the prospecting stage.

[0044] If the verification borehole calculations show the following: ore body thickness less than 0.8 meters, Al2O3 content between 40% and 50%, or aluminum-silicon ratio between 1.8 and 3.8, the verification borehole is considered to have only observed mineralization and does not meet the industrial mining standard. In this case, the mineralization potential of the favorable area needs to be reassessed, and the reasons for low grade or thin thickness need to be analyzed, such as unfavorable paleogeographic location, insufficient post-leaching alteration, or severe tectonic damage. Based on the reassessment results, a decision should be made on whether to conduct additional AMT measurements or lay another verification borehole in other mineralized depressions within the same favorable area (if AMT has delineated multiple depressions). If two verification boreholes within the same favorable area both show only mineralization, the favorable area should be abandoned. If the verification borehole calculations show an Al2O3 content below 40% or an aluminum-silicon ratio below 1.8, it is considered to have no mineralization, and the favorable area should be abandoned without further work.

[0045] During the overall implementation in the central Guizhou region, seven favorable areas were selected through the aforementioned comprehensive exploration methods. After 1:10,000 geological mapping, audio-frequency magnetotelluric (AMT) survey lines were deployed and implemented in four favorable areas. Following comprehensive interpretation of the four AMT lines, three mineralized depressions exhibiting a "high-resistivity-low-high-resistivity" electrical characteristic were successfully delineated. Subsequently, one verification borehole was drilled in each of the three mineralized depressions, for a total of three verification boreholes. Two of these verification boreholes yielded mineable minerals (mineralization rate of 66.7%), and two prospecting target areas were submitted. Of these two prospecting target areas, "Target Area No. 1" has entered the preliminary survey stage and has been transformed into a new round of strategic action project for mineral exploration breakthroughs in Guizhou Province in 2026. The entire exploration process, from the selection of favorable areas to the submission of prospecting target areas, took approximately eight months, with total exploration investment approximately 40% of the traditional grid-based drilling method, achieving significant economic benefits and mineral exploration results. This method is not only applicable to the concealed bauxite deposits in the Jiujiafu Group in central Guizhou, but also has important reference and promotion value for other concealed sedimentary mineral deposits controlled by paleokarst interfaces, such as certain phosphate and manganese mines.

[0046] In summary, the comprehensive exploration method for concealed sedimentary bauxite provided by this invention delineates favorable areas through comprehensive research of basic geological data, conducts geological mapping and audio-frequency magnetotelluric surveys within these areas, identifies mineralization depressions based on resistivity differences, and then performs precise drilling verification of these depressions. The chemical analysis results of the verification boreholes determine whether to submit the method as a prospecting target area. The entire process is logically clear, with well-defined parameters and strong operability. It can significantly improve the success rate of prospecting for concealed sedimentary bauxite, reduce exploration costs, and shorten the exploration cycle, demonstrating promising prospects for widespread application. Those skilled in the art should understand that the stratigraphic names, resistivity values, thickness standards, and grade standards listed in the above specific embodiments are based on actual data from specific regions. When applied in other regions, appropriate adjustments can be made according to local geological conditions, but these adjustments do not depart from the technical concept and protection scope of this invention.

[0047] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. It will be apparent to those skilled in the art that the invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered illustrative and non-limiting in all respects, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the scope of the invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

[0048] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A comprehensive exploration method for concealed sedimentary bauxite deposits, characterized in that, Includes the following steps: Step 1: Obtain regional geological data of the target area, determine the stratigraphy, structure and mineral distribution information, so as to delineate an area with a certain area, mineral-bearing rock series buried at a depth less than the preset depth, geological structure complexity lower than the preset threshold and not overlapping with the restricted area, as a favorable area for mineral exploration; Step 2: Conduct geological mapping in the favorable area, identify fault information, and set up an audio-frequency magnetotelluric survey line to obtain audio-frequency magnetotelluric measurement data; Step 3: Perform a comprehensive interpretation of the audio magnetotelluric measurement data, and delineate potential bauxite mineralization depressions along the audio magnetotelluric survey line based on the resistivity differences of different strata. Step 4: Select a location within the delineated mineralized depression to lay a verification borehole for drilling verification. Sample and chemically analyze the ore-bearing rock series revealed by the verification borehole, and determine subsequent exploration work based on the analysis results.

2. The comprehensive exploration method for concealed sedimentary bauxite deposits according to claim 1, characterized in that, In step one, the regional geological data includes a 1:50,000 regional geological map, a 1:50,000 regional mineral map, and a 1:50,000 hydrogeological map; the restricted area includes the mining rights area, the construction project area, and the urban development boundary area.

3. The comprehensive exploration method for concealed sedimentary bauxite deposits according to claim 1, characterized in that, In step one, the area of ​​the favorable zone is greater than or equal to 10 km², and the maximum burial depth of the ore-bearing rock series is less than 800 m.

4. The comprehensive exploration method for concealed sedimentary bauxite deposits according to claim 1, characterized in that, In step two, the geological mapping is a 1:10000 scale geological mapping, and the tracing method is used to determine the nature, combination relationship, formation and evolution of the main faults and their destructive or controlling effects on the ore-bearing rock series.

5. The comprehensive exploration method for concealed sedimentary bauxite deposits according to claim 4, characterized in that, In the geological mapping, the spacing between geological observation points is 300-500 m.

6. The comprehensive exploration method for concealed sedimentary bauxite deposits according to claim 1, characterized in that, In step two, the measurement frequency range of the audio magnetotelluric survey line is 0.125~8192 Hz, and the distance between measurement points is 50~100 m.

7. The comprehensive exploration method for concealed sedimentary bauxite deposits according to claim 1 or 6, characterized in that, In step two, if the orientation of the bauxite body can be determined through surrounding exploration data, the audio-frequency magnetotelluric survey lines are arranged perpendicular to the long axis of the ore body and pass through the already drilled ore-bearing boreholes; if the orientation of the ore body cannot be determined, the audio-frequency magnetotelluric survey lines are arranged perpendicular to the main structural direction in the area.

8. The comprehensive exploration method for concealed sedimentary bauxite deposits according to claim 1, characterized in that, In step three, the step of delineating potential bauxite mineralization depressions on audio-frequency magnetotelluric survey lines based on the resistivity differences of different strata includes: identifying the electrical structural characteristics of the upper high-resistivity layer, the middle low-resistivity layer, and the lower high-resistivity layer on the audio-frequency magnetotelluric profile, and delineating the middle low-resistivity layer as a potential bauxite mineralization depression.

9. The comprehensive exploration method for concealed sedimentary bauxite deposits according to claim 1, characterized in that, In step four, the chemical analysis includes five basic analyses: Al2O3, SiO2, TFe, TiO2, and loss on ignition. The determination of subsequent exploration work based on the analysis results specifically includes: If the thickness of the bauxite body in the borehole is verified to be ≥0.8 m, and the Al2O3 content is ≥55%, and the aluminum-silicon ratio Al2O3 / SiO2 is ≥3.8, it is determined that the mineral has been found and is mineable. The favorable area is then optimized and adjusted to form a prospecting target area, and a target area report is submitted to enter the bauxite exploration stage. If the thickness of the bauxite body in the borehole is verified to be <0.8 m, or the Al2O3 content is 40%~50%, or the Al2O3 / SiO2 ratio is 1.8~3.8, then it is determined to be mineralized, and the mineralization potential of the favorable area is reassessed. If the Al2O3 content in the borehole is verified to be <40% or the Al2O3 / SiO2 ratio is <1.8, it is determined that no minerals are found and the favorable area is abandoned.

10. The comprehensive exploration method for concealed sedimentary bauxite deposits according to claim 1, characterized in that, The method is used to explore sedimentary bauxite deposits hidden on ancient karst interfaces. The target area is the central Guizhou region, and the ore-bearing rock system is the Jiujialu Formation of the Lower Carboniferous.

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