A method for determining deep prospecting target area of skarn polymetallic deposit by using garnet

Abstract

The application discloses a method for determining a deep prospecting target area of a skarn type polymetallic deposit by using garnet, and is based on structural alteration lithofacies mapping of a target deposit at different elevations with a scale of 1:500 or larger, and the spatial variation law of the geological characteristics of the deposit is found out. Garnet microfabric identification is carried out, especially the color, structure, structure, generation characteristics of garnet at different spatial positions. Based on the above identification results, in-situ micro-area element content testing of different types of garnet is carried out, and the element content variation law of different types of garnet is found out. The garnet precipitation mechanism is analyzed based on the content of SiO2, Al2O3, FeO, MnO, CaO, W, Sn and Mo. According to the spatial variation of characteristic elements or element combinations, the deep extension mark which can effectively indicate the ore body is extracted, the deep extension law of the polymetallic ore body is determined, and the deep prospecting direction is proposed. The method carries out deep extension and deep positioning of the skarn type polymetallic ore body through characteristic minerals, and provides mineral geochemical basis for deep prospecting of the skarn type polymetallic deposit.

Description

Technical Field

[0001] This invention relates to a method for determining deep prospecting target areas of skarn-type polymetallic deposits using garnet, belonging to the field of mineral resource exploration of skarn-type metallogenic systems. Background Technology

[0002] Skarn-type polymetallic deposits are an important global source of metals, and their mineralization is closely related to magmatic hydrothermal activity. These deposits typically form deep within the Earth's crust, and the ore bodies are characterized by great depth, wide variation, and small scale, making it difficult to capture mineralization information using traditional geophysical and geochemical methods, and hindering the identification of deep prospecting targets.

[0003] Garnet is a common skarn mineral found in skarn-type polymetallic ore bodies, often occurring alongside ore minerals. Our research has revealed that certain trace elements in garnet, such as tungsten, tin, molybdenum, copper, iron, titanium, chromium, and manganese, can serve as "fingerprints" indicating the presence of ore bodies. Through trace element analysis of garnet, we can infer the intensity, temperature, pressure, and fluid composition of skarn formation, thereby predicting the distribution and scale of the ore body. Summary of the Invention

[0004] The purpose of this invention is to provide a method for determining deep prospecting target areas in skarn-type polymetallic deposits using garnet. This method primarily relies on the variation in trace element content among different types of garnet to identify deep prospecting target areas. Based on a detailed investigation of the geological characteristics of the target deposit, the method systematically collects garnet samples. High-precision in-situ elemental analysis techniques, such as laser ablation inductively coupled plasma mass spectrometry (LASIK), are used to determine the trace element content in the garnet. Based on the trace element characteristics of garnet, combined with geological background and depth indicators, a predictive model for deep prospecting target areas is established. Finally, this model is used to guide deep prospecting work, improving prospecting efficiency and success rate.

[0005] The technical solution of the present invention is as follows:

[0006] (1): Field mapping and sample collection module; Conduct large-scale structural alteration lithofacies mapping of the target deposit at different elevations, determine the mineral symbiotic assemblage, mineralization and alteration types and zoning characteristics, identify the geological characteristics of the deposit, determine the composition of the mineralization system, and systematically collect different types of garnet.

[0007] (2): Rock and mineral processing and identification module; Select different types of garnet samples to grind thin sections, and use optical microscopes and electron microscopes to observe the microstructure of garnets, and conduct comprehensive identification of the color, structure, texture and generation of garnets.

[0008] (3): Garnet in-situ micro-area testing module; Based on the identification results, in-situ micro-area element content testing is performed on different types of garnet to obtain garnet trace element data.

[0009] (4): Test data processing module; On the one hand, based on Geokit mapping software, determine the type of garnet by analyzing the single mineral calculation software. Based on the changes in the content of characteristic elements or element combinations, identify the precipitation mechanism of different types of garnet, and analyze the temperature, pressure, and oxygen fugacity of their formation; On the other hand, conduct a comprehensive study on the variation characteristics of trace elements and rare earth elements in different types of garnet, and find out the spatial variation law of trace elements and rare earth elements in garnet.

[0010] (5): Ore body depth extension index extraction module. Based on the spatial variation of characteristic elements or element combinations, extract indicators that can effectively indicate the deep extension of the ore body and determine the deep extension pattern of the ore body.

[0011] A: Qualitative indicators: Based on steps (1) and (2), the color, structure, texture and generation of garnet identified under optical and electron microscopes are used as qualitative indicators to evaluate the deep extension of the concealed ore body.

[0012] B: Quantitative Indicators: Based on S4 analysis, the total rare earth content, europium anomaly, and cerium anomaly of different types of garnet are used as quantitative indicators to evaluate the deep extension of concealed ore bodies.

[0013] (6): Deep extension pattern of polymetallic ore bodies and target area delineation: Combine the characteristics of shallow mined middle section ore bodies, verify the rationality of the extracted qualitative and quantitative indicators, summarize the deep extension pattern of deep ore bodies, comprehensively judge the deep extension distance of polymetallic ore bodies, delineate deep prospecting target areas, and conduct engineering verification.

[0014] Preferably, the process and steps of the large-scale structural alteration facies mapping technology for different elevations of the S1 target deposit refer to the existing patent "A large-scale alteration facies positioning and prediction method for hydrothermal deposits (ZL2014 10396700.7)".

[0015] Preferably, in step (2), the spatial distribution, associated mineral assemblage, color, structure, texture, and generation of garnets at different elevations are comprehensively identified. Garnets vary in type, and specific identification should be based on macroscopic geological characteristics, including spatial location, associated mineral assemblage, relative mineral content, interpenetration relationship, color, and texture, and supplemented by the characteristics of garnets under optical and electron microscopes, including color, structure, texture, and generation, to distinguish different types of garnets.

[0016] Preferably, in step (2), different types of garnet have obvious zoning characteristics. Generally, the closer to the mineralization center, the larger the garnet particles, the better the crystal shape, and the greater the thickness. They are mainly massive structures and formed earlier. The farther away from the mineralization center, the smaller the garnet particles, the worse the crystal shape, and the more vein-like and disseminated structures they are. They formed later.

[0017] Preferably, the test method for step (3) is selected as follows: the most advanced in-situ trace element content testing technology is used to test the trace element content of garnet, such as laser ablation inductively coupled plasma mass spectrometry and electron probe microanalysis.

[0018] Preferably, the result analysis of step (4) involves inputting the contents of major elements SiO2, TiO2, Al2O3, Cr2O3, Fe2O3, FeO, MnO, MgO, CaO, Na2O, and K2O from the test data into the garnet data table in the Geokit mineral calculation module. This allows the identification of the series to which different types of garnet belong. The abbreviations for each series of garnets are: andradite - And, grossular - Gro, spessartine - Spe, pyrope - Pyr, and almandine - Alm.

[0019] Preferably, the result analysis of step (4) is as follows: based on the data obtained from the trace element test, the trace element content of different types of garnet is analyzed, mainly by using the total rare earth, europium anomaly, cerium anomaly and W / Mo and W / Sn element ratios for comprehensive analysis.

[0020] Advantages and technical effects of the method of the present invention:

[0021] The innovation of this invention lies in combining the trace element analysis technology of garnet with the prediction of deep mineral exploration target areas, providing a new technical means for deep exploration of skarn-type polymetallic deposits. This method can not only improve the accuracy of mineral exploration, but also reduce exploration costs, and has important application value and market prospects.

[0022] (1) The measurement method used in this study has the characteristics of high spatial resolution and ultra-high testing accuracy. For example, the laser beam spot size of the sample acquired by the laser ablation inductively coupled plasma mass spectrometer is 30 μm, and the detection limit is less than 1 ppb (1×10⁻⁶). -9 The electron probe electron beam spot size is 1~10μm, and the detection limit is 100ppm (100×10⁻⁶). -6 The use of this equipment has greatly improved testing accuracy and made it possible to summarize the variation patterns of element content in small spaces.

[0023] (2) A scientific and reasonable data processing method has been established to ensure that the results are objective and effective. This method innovatively uses statistical methods and machine learning algorithms to extract patterns and trends in the data, involving descriptive analysis, exploratory analysis, confirmatory analysis and predictive analysis. The results of data analysis are displayed through charts, graphs or other visual elements to help users understand and interpret the data more easily.

[0024] (3) Compared with traditional geophysical and geochemical exploration techniques, this technique is more sensitive to deep mineralization information and can better discover concealed ore bodies. The method is simple to operate, highly applicable, and can quickly evaluate the deep extension pattern of ore bodies, thereby shortening the deep mineral exploration cycle. Attached Figure Description

[0025] Figure 1 The microstructure of garnet at different stages of a skarn-type deposit in southern Hunan. Figure 1 (a) consists of massive garnet Grt1a and subhedral granular texture Grt1b, replaced by late-stage fluorite. Figure 1 (b) shows anhedral granular garnets Grt1a and Grt1b, with star-shaped Mag1 formations developed along intergranular fractures. Figure 1 The middle (c) is an euhedral granular garnet (Grt2a) with well-developed epidote alteration in the core, and star-shaped scheelite developed along the oscillating zonation zone. Figure 1 In the middle (d) section, calcite-fluorite strongly replaces euhedral granular garnets Grt2a and Grt2b along the core and intergranular fissures. Figure 1 (e) is an euhedral granular structure containing star-shaped to veinlet-like fluorite-epidote-molybdenite, which has been strongly dissolved by magnetite. Figure 1 (f) and Figure 1 The middle (h) is composed of euhedral granular Grt2a oscillating rings with star-shaped molybdenite deposits. Figure 1 The middle (g) group consists of grayish-white zonal Grt2a and grayish-black porous Grt2b, with the pores filled with fluorite and molybdenite. Figure 1 In the middle (i), Grt2a exhibits a twinned structure; Figure 1 In the middle (j), the euhedral granular Grt2b fragmentation structure is well-developed. Figure 1 The middle (k) particles exhibit an euhedral granular structure, Grt2a and Grt2b, with intergranular pores filled with calcite and scheelite. Figure 1 (l) represents the early stages of vein-like Grt3 penetration, Grt2a and Grt2b;

[0026] Figure 2 A diagram illustrating the identification of garnet at different stages of a skarn-type deposit in southern Hunan. Figure 2 (a) is a box plot showing the major element content of garnet. Figure 2 (b) is a box plot of trace elements;

[0027] Figure 3 A diagram illustrating the identification of garnet at different stages of a skarn-type deposit in southern Hunan.

[0028] Figure 4 Electron probe backscattered image and line scan results of a skarn-type deposit in southern Hunan. Figure 4 Image (a) is an electron probe microanalysis (BSE) image. Figure 4 (b) is a scan of the energy spectrum of garnet.

[0029] Figure 5 (a) shows the vertical variation of δEu content in garnet from a skarn-type deposit in southern Hunan. Figure 5 (b) is a graph showing the vertical variation of ΣREE content. Figure 5 (c) is a graph showing the vertical variation of the W / Mo ratio. Figure 5 The middle (d) graph shows the vertical variation of the W / Sn ratio;

[0030] Figure 6 This is a map showing the deep prospecting target area of ​​a skarn-type mineral deposit in southern Hunan. Detailed Implementation

[0031] The present invention will be further described in detail below through examples, but the scope of protection of the present invention is not limited to the content described. Unless otherwise specified, the methods in the examples are conventional methods. Example 1

[0032] This method was implemented in a skarn-type copper-lead-zinc polymetallic deposit in southern Hunan Province, and achieved good prospecting progress. The details are as follows:

[0033] The exposed strata of this deposit are mainly Upper Devonian and Lower Carboniferous. Among them, the Shidengzi Formation limestone of the Lower Carboniferous is the most important ore-bearing stratum in this area, followed by the Ceshui Formation. A series of complex folds and oblique thrust faults have developed in the mining area, mainly the Baoling-Guanyindazuo complex overturned anticline and the F1, F2, and F3 oblique thrust faults trending near SN-NEE, supplemented by NWW-trending F0, F6, and F9 faults, forming a "grid-like" structural framework in the mining area. Magmatism was intense, and magmatic rocks are widely distributed, but generally shallow intrusion and small in occurrence. There are about 20 small intermediate-acidic and acidic intrusive bodies in the area, occurring in the form of nodules, dendrites, and dikes. Their distribution is controlled by tectonics and shows a clustered and zonal distribution characteristic. The lithology is mainly quartz porphyry and granite porphyry. The deposit has a complete range of mineralization types, developing a skarn mineralization system consisting of porphyry-skarn (W-Sn-Bi-Mo)-hydrothermal vein (Pb-Zn-Ag) polymetallic deposits. There are numerous types and numbers of ore bodies, with more than 500 magnetite-tungsten-molybdenum and lead-zinc-copper ore bodies delineated to date. The distribution of magnetite-tungsten-molybdenum ore bodies is related to concealed granite porphyry and mainly occurs in skarn. The main metallic minerals are magnetite, scheelite, and molybdenite, followed by cassiterite, bismuthite, pyrrhotite, galena, sphalerite, chalcopyrite, and pyrite. The ore exhibits euhedral to subhedral, subhedral to anhedral, replacement residual, inclusion, and dissolution textures, with massive, nodular, disseminated, veinlet, and network vein structures.

[0034] The specific implementation steps are as follows:

[0035] I. Field Mapping and Sample Collection Module

[0036] The skarn activity is intense, with strong metasomatism at the contact zone between the rock mass and the surrounding rocks, primarily characterized by contact metasomatism. This manifests as: ① post-magmatic gas-liquid contact metasomatism forming intense skarnification; ② magmatic intrusion and thermal metamorphism forming marble, recrystallized limestone, etc. Both processes are accompanied by large-scale, multi-stage polymetallic mineralization. The study focuses on the -96m, -136m, -176m, and -256m sections. Detailed measurements using 1:200 and 1:100 scale tunnel profiles, combined with microscopic mineral identification, and based on the different alteration-mineralization types, mineral assemblages, alteration degrees, relative mineral content, and ore mineral structure characteristics of each zone, required research samples were collected from different ore bodies and at different elevations. These samples primarily include garnet-altered skarn.

[0037] II. Rock and Mineral Identification and Processing Module

[0038] Typical samples were selected as the research object. The samples were prepared into optical sections, and the tested mineral grains were identified by microscopic examination, revealing three types of garnet. Grt1 ( Figure 1 (a) Figure 1(b) : is andradite garnet, with two subclasses, Grt1a: brownish-yellow to massive, mostly without zoning, smooth to rough surface, with well-developed dissolution cavities and fractured structures, and late-stage fluorite and calcite filling the dissolution cavities ( Figure 1 (a) Garnets in contact with late-stage minerals such as fluorite recrystallize into a subhedral to euhedral granular structure (Grt1b); Figure 1 (b) granular (0.2-0.5 mm in diameter) aggregates, vein-like aggregates showing comb-like structures, often associated with pyroxene and a small amount of quartz, with obvious epidote alteration. Figure 1 In the middle (a)), no W-Sn mineralization was observed; Grt 2 ( Figure 1 Middle (c)-(k): yellowish-brown-yellowish-green-grayish-brown, euhedral-subhedral granular texture, with oscillating zoning under single-polarized light. Relatively smooth gradient Grt 2a is visible. Figure 1 (c)-(k)) and the coarser-faceted grossular Grt 2b ( Figure 1 (j)-(k)). Grt2a and Grt2b crystals grow together and often exhibit twin structures. Figure 1 (f) Figure 1 In (i), Figure 1 Medium (k)), with polygonal (e.g., rhomboid and hexagonal) outlines on the cut surface, grain size ranging from 0.5-1.5 cm, fragmentation and zoning structures are commonly developed, vesuvianite, actinolite, fluorite, and calcite replace garnet along intercrystalline fissures or cracks between zoning zones, the crystal edges and cores are strongly eroded, the eroded parts are broken into irregular shapes, and filled with grayish-white scaly molybdenite and fine-grained scheelite. Figure 1 (e)-(f), Figure 1 (h)). This type of garnet is often associated with minerals such as scheelite, vesuvianite, amphibole, and chlorite. Grt3: Grossular-andradite garnet, reddish-brown to brownish-yellow. Grt3 occurs as fine veins (0.2-0.5mm) penetrating Grt2 ( Figure 1 (l)).

[0039] III. Garnet In-situ Micro-area Analysis Module

[0040] Trace element analysis was conducted at the National Geological Experiment and Testing Center using laser ablation-inductively coupled plasma mass spectrometry (LA-ICP-MS). The results showed that garnets of different generations belong to andradite-grossular garnet, containing small amounts of spessartine, pyrope, and almandine. Figure 2As shown in Figure (a), their SiO2, Al2O3, FeO, MnO, and CaO varied from 34.83-36.58 wt%, 4.49-10.91 wt%, 35.18-40.71 wt%, 0.55-0.97 wt%, 15.63-23.80 wt%; 33.79-37.75 wt%, 0.63-17.13 wt%, 30.96-44.95 wt%, 0.30-3.36 wt%, 7.83-29.20 wt%; 29.70-45.82 wt%, 0.07-8.49 wt%, 31.40-45.46 wt%, 0.48-1.81 wt%, respectively. The content of garnet was 15.48-29.68 wt%, while the contents of TiO2, K2O, MgO and Na2O were generally low (average <0.1 wt%), ranging from 0.03-0.39 wt%, 0.00-0.06 wt%, 0.02-0.05 wt%, and 0.00-0.06 wt%, respectively. The zoning pattern of garnet in micrographs (such as BSE) showed a clear correlation with the changes in the content of its major elements. The data obtained from Geokit calculations, after being plotted to obtain end-member composition diagrams, showed that they respectively possessed Grt1:Adr... 57.43-80.77 Grs 10.50-36.12 (n=6); Grt2a: Adr 24.02-96.73 Grs 0.34-70.28 (n=42); Grt2b: Adr 43.45-99.56 Grs 1.42-55.20 (n=23); Grt3: Adr 60.85-95.78 Grs 1.54-37.53 The composition of (n=5) Figure 3 From early to late stages, there is a trend of evolution from grossular to andradite; overall, the sum of spessartine, pyrope, and almandine is <10%, while the data for sample 92-5 (Grt1, 15.02-16.64%) is relatively high; in addition, the oscillating zoning of Grt1 and Grt3 is generally well developed and their composition is homogeneous; while the oscillating zoning of Grt2a (more iron-rich) and Grt2b (more aluminum-rich) is obvious, and iron or aluminum enrichment is the main factor for their differential zoning; sample -296-4 has Adr from the core to the edge. 62.39- 67.50 Grs 26.69-35.96 (n=3, core) and Adr 26.48-31.23 Grs 69.14-64.94 (n=2, marginal) components ( Figure 3 EPMA line scan data indicate that the changes in major elements are relatively stable from the core to the edge. Figure 4 ).

[0041] Except for a few ore-forming elements which are present in relatively high amounts (such as W and Sn), trace elements... Figure 2 In (b) of the samples, almost all garnets exhibited low levels of large ion lithophile elements (LILE) and high field strength elements (HFSE), such as Ba (mean 0.17, n=76), Rb (mean 2.84, n=76), Cs (mean 0.36, n=76), and Sr (0.56, n=76) in LILE. In some samples (e.g., -296-4, HH30-3), the levels of Sc, Y, Zr, Nb, Hf, and Ta showed a negative correlation with the andradite content. All types of garnets contained certain amounts of W, Sn, and Mo, the mineralizing elements. Grt2 was the most enriched mineral, with W content ranging from 0.02 to 1532.35 ppm, Sn content from 437.76 to 13335.39 ppm, and Mo content from 0.00 to 21.53 ppm. The concentrations of W, Sn, and Mo in Grt3 were 2.42-250.40 ppm, 2110.85-9412.05 ppm, and 0.53-16.07 ppm, respectively; Grt1 had the lowest concentrations, with W, Sn, and Mo at 0.83-4.41 ppm, 1056.20-2910.14 ppm, and nd-0.31 ppm, respectively. Figure 2 (b)

[0042] IV. Test Data Processing Module

[0043] End-member component diagram ( Figure 3The data shows that the garnets in this mining area are mainly calcium aluminum-andradite series; their rare earth element distribution characteristics are related to (1) the rare earth element distribution characteristics of the hydrothermal fluids; (2) the rare earth element distribution coefficients between the hydrothermal fluids and garnets; the initial skarn composition is difficult to obtain, but the rare earth element characteristics of the hydrothermal fluids can be approximately inferred using the ore-forming rock mass; there are obvious differences in the rare earth element distribution patterns of different types of garnets, and multiple distribution patterns reflect that it has undergone a complex evolution process; experimental simulations show that the hydrothermal fluids have the characteristics of LREE enrichment and HREE depletion, so it can be known that the minerals crystallized in the hydrothermal fluids should exhibit light rare earth enrichment. The rare earth element (REE) distribution pattern is characterized by heavy REE depletion; however, this differs significantly from the distribution pattern of currently obtained garnets. Therefore, garnets do not simply inherit the REE content of skarn fluids. The andradite and grossular garnets follow certain distribution pattern characteristics, and the prevalence of oscillating zoning suggests that the REE distribution of garnets mainly depends on the distribution coefficients of REEs within the garnet. Furthermore, the lack of correlation between ΣREE and Y indicates that the distribution of REEs is not controlled by crystal chemistry but by fluid chemistry. Garnets from different generations in this deposit exhibit different structural types, including... The three types of Grta are: Grt1 (non-oscillating zoning), Grt2 (oscillating zoning), and Grt3 (vein-like). Grt1, with its relatively homogeneous composition and non-oscillating zoning structure, may have formed under relatively low water-rock reaction conditions in an early closed system. Compared to Grt2b, which exhibits anomalous interference colors and twinning, the euhedral zoning structure of Grt2a may suggest increased fluid flow and a faster growth rate in an open system. The more developed fluid inclusions within Grt2a compared to Grt2b further confirm that the rapidly growing Grt2a traps more fluid within its lattice defects. Therefore, higher water... The rock ratio and crystal chemical structure lead to variations in the partition coefficients among garnets, resulting in unique rare earth element (REE) partition patterns in Grt2a and Grt2b. Previous studies have shown that the redox environments formed by andradite and grossular are inconsistent, exhibiting differences between oxidative-weakly oxidative and weakly oxidative-weakly reducing environments. Eu anomalies depend on the salinity and redox degree of the fluid; garnet Eu anomalies can be used to explore the redox environment of hydrothermal fluids. Inclusion salinity analysis has confirmed that from the early to the late stages, the fluid salinity transitions from high salinity to medium-high salinity (i.e., the fluid contains F...). - and Cl - (Ion concentration gradually decreases over time); decreased salinity leads to a decrease in Eu in the fluid. 2+ and Cl -The decreased complexation capacity will inevitably lead to an evolutionary pattern of different types of garnets exhibiting no anomaly → weak negative anomaly → no anomaly → strong negative anomaly → weak negative anomaly. This indicates a process in which the hydrothermal fluids in the mining area gradually transitioned from relatively weakly reducing fluids to oxidizing fluids. The deposit's concealed granite body is characterized by high formation temperature, high degree of differentiation, and low oxygen fugacity. In the early stages, intense water-rock reaction between the carbonate host rocks and magmatic fluids formed high-temperature, reducing, F-rich... - and Cl - Grt1 crystallizes under fluid conditions, with the weakening of the water-rock reaction and the presence of F in the fluid. - Cl - The decrease in ions and the increase in oxidizing fluids led to the crystallization of Grt2 during this process. The chemical structure of the garnet crystal at this stage affected the elemental distribution within it. The Eu anomaly indicates that Grt1 was more reduced, Grt2a was a weakly reducing-weakly oxidizing environment, and Grt3 was an oxidizing environment. The different Eu anomaly changes between Grt2a and Grt2b also indicate that the oxygen fugacity of the fluid during garnet crystallization fluctuated.

[0044] V. Ore Body Depth Extension Index Extraction Module

[0045] (1) Qualitative indicators: The spatial variation of the characteristic indicator mineral garnet has a certain regularity. In general, from the shallow to the deep (i.e., 92-middle section → 296-middle section), the garnet in this deposit exhibits different structural patterns; (1) With the increase of depth, the grain size of the characteristic minerals is extremely uneven (<6cm), but the closer to the rock body, the larger the grain size of the minerals; the mineral types and textures tend to be more complex, including four types: oscillating zoning, no zoning, irregular shape and vein-like shape; the shallow middle section (92 to 20-middle section) is mainly developed with Grt1b and Grt2a, and the semi-euhedral to anhedral grains are mainly developed, while the -96 m middle section has Grt2a, Grt2b and Grt3 types, the -136 m middle section has Grt2a, Grt2b and Grt3 types, the -176 m middle section has Grt1a, Grt1b, Grt2a and Grt2b, and the -296 m middle section has Grt1a, Grt1b, Grt2a and Grt2b, and the -296 m middle section has Grt1b, Grt2b and Grt2b, and the -296 m middle section has Grt1b, Grt2b and Grt2b, and the -296 m middle section has Grt1b, Grt2b and Grt2b, and the -296 m middle section has Grt2 ...2b, Grt2b and Grt2b, and the -296 m middle section has Grt2b, Grt2b and Grt2b, and the -2 The middle section of the skarn is dominated by Grt2a, Grt2b, and Grt3 types, with the texture gradually evolving from subhedral to euhedral granular to euhedral to anhedral granular. This indicates that the mineralization of the deep skarn superposition was more significant than that of the shallower sections. In particular, the garnet cores with oscillating zoning crystallized before the rims; the cores are typically andradite, while the rims are grossular. The oscillating zoning was formed by variations in Fe and Al content, suggesting strong fluid convection during this stage. It also indicates that as the skarnification process progressed, the Fe content in the fluid decreased, while the degree of Al supersaturation increased, indicating a weakly reducing-weakly oxidizing, neutral-weakly acidic environment for its growth.

[0046] (2) Quantitative indicators: Observations of the δEu values ​​of different types of garnet in different sections show that, with increasing depth, the δEu value of this deposit first increases and then decreases. Figure 5 In the middle (a) region, especially in Grt2a and Grt2b, the variation of δEu is 1.64→0.16→0.43→0.51→0.63→0.87 (mean). The oxygen fugacity increases in the shallow part, is low in the middle part, and is high in the deep part.

[0047] The ΣREE content in garnet varies considerably across different sections (ranging from 1.13 ppm to 6.61 ppm, with an average of 3.20 ppm). Generally, the ΣREE content decreases gradually from the -136m section to the -256m section, but the change is relatively stable at -176m and -256m, with a clear inflection point at -176m, and the highest content at -136m. Figure 5 (b)); The content of ore-forming elements is high in the deep part; the oxygen fugacity increases with depth, and the increased oxygen fugacity is conducive to mineralization.

[0048] VI. Identification of the Deep Extension Pattern of Ore Bodies

[0049] The ore body of this deposit is controlled by multiple factors, including the rock mass and geological structure. The hydrothermal fluids are pulsating, and the geological structures are often equidistant, thus the distribution of the ore body also exhibits a certain regularity. The trace element content of garnet shows a clear transition from concave to convex in the -176m section, consistent with the concave-convex geometry of the rock mass. For garnet, the inflection point occurs at the -176m section, between the -96m and -256m sections (a height difference of 160m). The -176m section is located in the middle of these two sections. Therefore, is this 160m vertical height difference a period of change? Assuming this is a period, the next inflection point should be near the -336m section. Based on this periodicity, the approximate location of the ore body at depth can be inferred to be between -336m and -469m. The areas where the rock mass transitions from concave to convex are favorable prospecting targets. Figure 6 Based on existing geological data from the shallow middle section, it can be observed that multiple ore-forming rock bodies exhibit a "swelling-shrinking" characteristic within the 0-300m elevation range, with a vertical variation period of 100-130m. Figure 6 This is basically consistent with the periodic changes of the mineral exploration target area.

[0050] Three boreholes were drilled in the target area. The data revealed that at the designated depths, specifically at elevations of -336m and -256m, the average WO3 and Mo content in the mineralized skarn reached industrial grades. The WO3 and Mo contents at -336m in borehole 1 were higher than those in the middle section at -256m. The Mo grades at -336m in boreholes 2 and 3 were 0.05% and 0.09% respectively, significantly higher than the Mo content in the middle section at -256m. Based on this cyclical pattern, further drilling can be conducted to locate skarn-type ore bodies at deeper depths.

Claims

1. A method for determining deep prospecting target areas of skarn-type polymetallic deposits using garnet, characterized in that, Follow these steps: (1) Conduct structural alteration and lithofacies mapping of the target deposit at different elevations of 1:500 or larger, determine the mineral symbiotic assemblage, mineralization and alteration types and zoning characteristics, identify the geological characteristics of the deposit, and determine the composition of the skarn mineralization system; systematically collect different types of garnet. (2) Grind thin sections and use optical and electron microscopes to conduct microscopic identification of garnet, including the color, structure, texture and generation of garnet; establish qualitative indicators for predicting deep ore bodies using garnet. (3) Conduct in-situ micro-area element content analysis to obtain major and trace element data of garnet; (4) Based on the changes in the content of characteristic elements or element combinations, identify the depositional mechanisms of different types of garnet, analyze their evolution process, infer the source and migration pathway of ore-forming fluids, and investigate the spatial variation patterns of trace elements and rare earth elements in garnet; (5) Extract indicators that can effectively indicate the deep extension of the ore body and summarize the deep extension law of polymetallic ore bodies; (6) Verify the rationality of the extracted qualitative and quantitative indicators, summarize the deep extension law of the ore body, judge the deep extension distance of the ore body, and finally delineate the deep prospecting target area and carry out engineering verification; The indicators include qualitative and quantitative indicators. Based on steps (1) and (2), the color, structure, texture and generation of different types of garnet are identified by optical and electron microscopes as qualitative indicators for evaluating the deep extension of the concealed ore body. Based on the analysis in step (4), the total rare earth content, europium anomaly and cerium anomaly of different types of garnet are used as quantitative indicators for evaluating the deep extension of the concealed ore body.

2. The method for determining deep prospecting target areas of skarn-type polymetallic deposits using garnet according to claim 1, characterized in that: In step (1), the large scale is greater than or equal to 1:

500.

3. The method for determining deep prospecting target areas of skarn-type polymetallic deposits using garnet according to claim 1, characterized in that: In step (1), different types of garnets refer to garnets from different spatial locations, different structures, and different generations.

4. The method for determining deep prospecting target areas of skarn-type polymetallic deposits using garnet according to claim 1, characterized in that: In step (2), the specific details are as follows: Garnets vary in type, and macroscopic geological features are the main basis for identification, combined with the characteristics of garnets under optical and electron microscopes as auxiliary basis to further distinguish different types of garnets; macroscopic geological features include spatial distribution features, mineral symbiotic assemblage, relative mineral content, interpenetration relationship, color, and structure; Microscopic features include color, structure, texture, and generation.

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