Method for delineating deep prospecting target area of magmatic hydrothermal polymetallic deposit by using magnetite

Abstract

The application discloses a method for delineating deep prospecting target area of magmatic hydrothermal polymetallic deposit by using magnetite, and mainly comprises the following steps: carrying out 1:500 or larger scale structural alteration lithofacies mapping of a target deposit, finding out spatial variation law of geological features of the magmatic hydrothermal polymetallic deposit, and systematically collecting related samples. Color, structure, structure and generation of different types of magnetite are identified by using an optical microscope and an electron microscope. Based on the identification results, the variation law of element content of different types of magnetite is found out by testing micro-area in-situ element content of different types of magnetite. According to the spatial variation of characteristic elements or element combination, the deep extension indicator of the polymetallic ore body is extracted, the deep extension law of the polymetallic ore body is determined, and the deep prospecting direction is proposed. The method can carry out deep positioning of the magmatic hydrothermal polymetallic ore body by using characteristic minerals, provide a theoretical basis for delineating the deep target area of the magmatic hydrothermal polymetallic deposit, and save exploration cost.

Description

Technical Field

[0001] This invention relates to a method for delineating deep prospecting target areas of magmatic hydrothermal polymetallic deposits using magnetite, belonging to the field of mineral resource exploration of magmatic hydrothermal mineralization systems. Background Technology

[0002] Magmatic-hydrothermal polymetallic deposits are mineral deposits rich in various metallic elements, formed by magmatic-hydrothermal activity. They are widely distributed across all continents and possess immense economic value.

[0003] In deep prospecting of magmatic hydrothermal polymetallic deposits, identifying deep prospecting target areas is a crucial technical task. Traditional prospecting methods rely primarily on geological, geophysical, and surface geochemical anomalies for deep prospecting prediction. However, as mining depths increase and exploration depths grow greater (greater than 1000m), geological conditions become increasingly complex, and traditional methods often fail to capture mineralization information, resulting in unsatisfactory prospecting outcomes. Summary of the Invention

[0004] The technical problem this invention aims to solve is the difficulty in capturing weak deep mineralization information. The purpose of this invention is to provide a method for determining the direction of deep mineral exploration in magmatic hydrothermal polymetallic deposits using magnetite, specifically including the following steps:

[0005] S1: Field mapping and sample collection module: Based on existing geological maps and data of the target deposit, conduct large-scale tectonic alteration lithofacies mapping at different elevations, determine mineralization and alteration types, mineral assemblages and mineralization and alteration zoning characteristics, investigate the spatial variation of geological characteristics of magmatic hydrothermal deposits, and determine the composition of magmatic hydrothermal mineralization systems; systematically collect magnetite of different spatial locations and types.

[0006] S2: Rock and Ore Processing and Identification Module: Conduct macroscopic and microscopic textural observations of magnetite, select magnetite samples from different locations and with different mineral associations to grind thin sections; use optical and electron microscopes to comprehensively identify the color, structure, texture, generation, and mineral association of different types of magnetite; establish qualitative indicators for predicting deep ore bodies using magnetite;

[0007] S3: Magnetite Element Content Analysis Module: Based on the identification results of optical microscopy, in-situ micro-area analysis technology is used to obtain major element, trace element and rare earth element data of different types of magnetite;

[0008] S4: Test Data Processing Module: Based on the corresponding templates in existing Geokit and Corelkit mapping software, the precipitation mechanism of different types of magnetite is determined based on the total rare earth element content, europium anomaly, cerium anomaly, and changes in the content of Ti, V, Ni, Cr, and Mn elements. The temperature-pressure-oxygen fugacity conditions for magnetite formation are analyzed. A comprehensive study on the variation characteristics of trace elements and rare earth elements in different types of magnetite is conducted to clarify the spatial variation law of trace element and rare earth element content in magnetite.

[0009] S5: Ore body depth extension index extraction module, based on the spatial variation of characteristic elements or element combinations, extracts indicators that can effectively indicate the extension of polymetallic ore bodies into deep unknown areas, and determines the depth extension law of polymetallic ore bodies; establishes quantitative indicators for deep ore body prediction using magnetite.

[0010] S6: Combining the spatial distribution patterns of shallow, mined ore bodies in the middle section, verify the rationality of the extracted qualitative and quantitative indicators, summarize the deep extension patterns of deep ore bodies, and comprehensively assess the deep extension distance of polymetallic concealed ore bodies and prospecting target areas.

[0011] Preferably, the process and steps of the S1 target deposit structural alteration facies mapping technology at different elevations of 1:500 or larger in this invention refer to the existing patent "A large-scale alteration facies positioning and prediction method for hydrothermal deposits (ZL2014 1 0396700.7)".

[0012] Preferably, the specific process of S2 in this invention is as follows: using macroscopic geological features as the main criterion and combining them with the characteristics of magnetite under optical and electron microscopes as auxiliary criteria, different types of magnetite are distinguished and represented by codes such as MagⅠ, MagⅡ, MagⅢ, MagⅣ...; the macroscopic geological features are: spatial distribution characteristics, mineral symbiotic assemblage, relative mineral content, interpenetration relationship, color, and structure; the microscopic features are: color, structure, generation, and mineral symbiotic assemblage.

[0013] Furthermore, in S2, the magnetite particles near the ore-forming center are large and have good crystal shape, mainly with massive structure, and formed earlier; while the magnetite particles far from the ore-forming center are small and have poor crystal shape, mainly with vein-like and disseminated structure, and formed later.

[0014] Furthermore, in S2, the qualitative indicators for predicting deep ore bodies using magnetite are established as follows: macroscopically, from the ore-forming center to the surrounding rocks, extracting the mineral assemblages, relative mineral content, interpenetration relationships, color, and texture of different magnetite deposits; microscopically, based on the identification results of optical and electron microscopy, extracting the changes in color, structure, texture, generation, and mineral assemblages of different magnetite deposits. This is used as a qualitative indicator for evaluating the deep extension of concealed ore bodies.

[0015] Preferably, the S3 in-situ micro-area analysis technology of the present invention is selected as follows: the micro-area trace element content testing technology method is laser ablation plasma mass spectrometry, and the micro-area major element content testing method is electron probe microanalysis.

[0016] Furthermore, the S4 result analysis described in this invention involves mapping the elemental content of different types of magnetite based on the test data. This is primarily achieved through a comprehensive analysis of the content and elemental ratios of V, Ti, Ni, Co, Ga, Sn, Cr, and Ni, including Ti / V, Ni / Co, and Ni / Cr. This analysis aims to determine whether the magnetite's genesis is magmatic-hydrothermal and to identify the magnetite's formation environment.

[0017] Preferably, the quantitative index of S5 in this invention is based on the comprehensive analysis of the data in S4, and encourages the variation of rare earth elements, Ti, V, Ni, Cr and Mn elements in different types of magnetite as a quantitative index for evaluating the deep extension of concealed ore bodies.

[0018] Compared with the prior art, the advantages and technical effects of the method of the present invention are as follows:

[0019] (1) This invention takes magnetite in magmatic hydrothermal deposits as the research object, effectively extracts qualitative and quantitative evaluation indicators that indicate the extension of deep ore bodies, and quickly guides the delineation of deep ore bodies in crisis mines.

[0020] (2) Compared with traditional geophysical and geochemical exploration techniques, this technique can quickly capture deep mineralization information, determine the location of deep hidden rich ore bodies, and delineate deep prospecting target areas.

[0021] (3) This method utilizes modern high-precision analysis and testing technology, and features low detection limit, high analysis accuracy, and simple operation process; it is highly applicable and can quickly evaluate the deep extension law of the ore body, thereby shortening the deep mineral exploration cycle. Attached Figure Description

[0022] Figure 1 Microstructures of different types of magnetite in a magmatic hydrothermal deposit in southeastern Yunnan;

[0023] Figure 2 LA-ICP-MS time-resolution profile of a magnetite sample from a magmatic hydrothermal deposit in southeastern Yunnan.

[0024] Figure 3 A diagram illustrating the genetic identification of magnetite in a magmatic hydrothermal deposit in southeastern Yunnan.

[0025] Figure 4 A diagram illustrating the formation environment of magnetite in a magmatic hydrothermal deposit in southeastern Yunnan. Figure 4 (a) Cr-V, Figure 4 (b) Ga-Mg, Figure 4 (c) Ga-Sn, Figure 4 (d) (Ti + V)-(Al + Mn);

[0026] Figure 5 Figure showing the average contents of ΣREE, δCe, and δEu in magnetite from different sections of a magmatic hydrothermal deposit in southeastern Yunnan.

[0027] Figure 6 This indicates the direction for deep mineral exploration in a magmatic hydrothermal deposit in southeastern Yunnan. Detailed Implementation

[0028] 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

[0029] This method was implemented in a magmatic hydrothermal tin-zinc polymetallic deposit in southeastern Yunnan Province, and achieved good prospecting progress. Details are as follows:

[0030] The deposit is located on the southern edge of the Laojunshan granite body in southeastern Yunnan Province, comprising five mining sections from north to south: Tongjie, Manjiazhai, Lazizhai, Wukoudong, and Nandangchang. The surrounding sedimentary rocks are mainly the Neoproterozoic Xinzai Formation and the Middle Cambrian Tianpeng Formation. The Neoproterozoic Xinzai Formation consists of three sections: the lower section is mainly composed of quartz schist and mica schist, interspersed with marble lenses; the middle section is mainly composed of quartz mica schist and marble, which is the main ore-bearing stratum and has a significant impact on the formation of the deposit; the upper section is mainly composed of sericite schist. The Middle Cambrian Tianpeng Formation, mainly composed of phyllite, dolomite, and limestone, overlies the Xinzai Formation and is only exposed in the western part of the mining area. The deposit exhibits significant tectonic activity, and the spatial distribution of the ore bodies is clearly controlled by tectonic activity. The magmatic activity closely related to tin-zinc mineralization in the mining area is mainly Yanshanian granite. This granite body occurs along or across bedding planes, often in the form of dendritic or vein-like structures, reaching a maximum thickness of 70m. Vein-like to nodular mineralization is frequently observed within the rock body, while malachite and limonite are commonly found on the surface.

[0031] The specific implementation steps are as follows:

[0032] I. Field Mapping and Sample Collection Module

[0033] The area exhibits intense magmatic-hydrothermal activity, with strong metasomatism, primarily contact metamorphism, occurring at the contact zone between the intrusive body and the surrounding rocks. This is manifested in two ways: ① post-magmatic hydrothermal metasomatism of the surrounding rocks; ② magmatic intrusive thermal metamorphism forming marble, recrystallized limestone, etc. Both processes are accompanied by large-scale, multi-stage polymetallic mineralization. Focusing on the 1260m, 1200m, 1140m, 1080m, 1040m, and 1000m sections, detailed measurements using 1:200 and 1:100 scale tunnel profiles reveal that the main metasomatism / alteration processes in the mining area include dry skarnification, wet skarnification, chloritization, sericitization, silicification, and calcite alteration. The superposition of various metasomatic / alteration processes is quite evident. Based on the mineral characteristics revealed by open-pit mines and boreholes, the different phases of magmatic hydrothermal fluids in this deposit exhibit distinct mineralization and alteration zoning at the deposit scale. Garnet-dominated skarn occurs at relatively deeper levels compared to pyroxene or actinolite-dominated skarn. However, due to the superposition of actinolite from the wet skarn stage onto pyroxene skarn from the dry skarn stage, the boundary between pyroxene skarn and actinolite is indistinct. The ore bodies are mainly banded, layered, and lenticular in the Neoproterozoic Xinzhai Formation. The ores can be classified into magmatic hydrothermal type, marble type, and schist type ores. Magnetite is present in all types of ores. Skarn-type ores are widely distributed within the mining area and are closely related to mineralization. Based on different mineral assemblages, the mineralization zones are divided into: actinolite-chlorite-magnetite zone, pyroxene-chlorite-actinolite-magnetite type, and pyroxene-actinolite-magnetite-pyrrhotite-sphalerite zone. Combining mineral occurrence characteristics, early skarn stage, late skarn stage, oxide stage, sulfide stage, and carbonate stage were identified. Magnetite content was relatively low in the early and late magmatic hydrothermal stages, significantly increased in the oxide stage, and no magnetite was found in the sulfide and carbonate stages. Cassiterite is usually associated with magnetite, which is unevenly distributed, with more exposure in the southern part of the Manjiazai mining area and the northern part of the Tongjie surface outcrops, closely associated with cassiterite and sphalerite. Based on different alteration-mineralization types, mineral assemblages, alteration degrees, relative mineral content, and ore mineral structure characteristics in each zone, the required research samples were collected according to different ore bodies and elevations.

[0034] II. Rock and Ore Processing and Identification Module

[0035] Based on the comprehensive identification of magnetite from different mid-sections, macroscopically, shallow-region magmatic hydrothermal ore exhibits euhedral to subhedral crystal structures, anhedral crystal structures, zonal structures, and replacement veinlet structures, as well as dense massive and banded textures. In deeper regions, the ore structures of magmatic hydrothermal cassiterite sulfide ores mainly include dense massive structures, dense disseminated structures, scattered-spotted structures, brecciated structures, and lamellar structures. Microscopically, based on mineral assemblage and interpenetration relationships, this invention classifies magnetite into two types: Mag-I (…) in massive ores… Figure 1 (a) Figure 1 (b) , in granular or broken form ( Figure 1 The fissures are filled with chlorite and actinolite. Figure 1 (e) Figure 1 (f) in the middle, or partially encased in sphalerite. Figure 1 (g)). Mag-II is spatially closely related to sulfides. Figure 1 (c) Figure 1 (h) Figure 1 (i)).

[0036] Qualitative indicators for predicting deep concealed ore bodies: The mineral association, type, structure, and occurrence of magnetite exhibit certain regularities in spatial variation; Mag-I is developed in the shallow and middle sections, while Mag-II is dominant in the deep sections; the core of Mag-I generally develops microporous structures, and microscopic observation shows that the interior of the micropores is mostly composed of silicate minerals, thus the Si, Ca, Mg, and Ti contents of Mag-II show an increasing trend.

[0037] III. Magnetite In-situ Micro-area Analysis Module

[0038] Major and trace element analysis was conducted at the National Geological Experiment and Testing Center using laser ablation-inductively coupled plasma mass spectrometry (LASIK) and electron probe microanalysis. The major element results showed that magnetite is a typical hydrothermal magnetite, with relatively low contents of Al₂O₃ (average 0.02 wt%) and CaO (average 0.01 wt%). Mag-I exhibited higher contents of SnO₂ (0.01–0.52 wt%) and SiO₂ (0.03–4.90 wt%), and lower contents of TiO₂ (below the detection limit), MnO (0.01–0.15 wt%), and MgO (0.05–1.13 wt%). Mag-II has high contents of TiO2 (0.01-0.14 wt%), MnO (0.25-0.35 wt%), and MgO (0.77-0.91 wt%), and low contents of SnO2 (0.08-0.16 wt%) and SiO2 (0.19-0.38 wt%). Trace element analysis of magnetite showed that the overall magnetite in the deposit was poor in Co (0.03-0.42 ppm), Ni (0.43-14.2 ppm), and Cu (0.01-9.13 ppm), and rich in Zn (22.3-2687 ppm). Mag-I had higher contents of Ga (5.76-31.3 ppm), Al (46.8-439 ppm), Si (1319-28082 ppm), and Ca (0.01-498 ppm) than Mag-II (Ga=0.66-2.19 ppm, Al=21.0-322 ppm, Si=1940-3697 ppm, Ca=14.0-251 ppm). Mag-I had Ti content of 0.28-260 ppm, V content of 0.09-16.8 ppm, and Mn content of 200-873 ppm. The Ti content of Mag-II is 11.2-4264 ppm, the V content is 0.56-64.5 ppm, and the Mn content is 506-1321 ppm. Other trace elements are as follows: Mag-I has In content of 1.56-17.2 ppm, Sn content of 354-2716 ppm, and Pb content of 0.01-278 ppm; Mag-II has In content of 2.04-6.46 ppm, Sn content of 489-1504 ppm, and Pb content of 0.01-0.06 ppm. Figure 2 ).

[0039] IV. Test Data Processing Module

[0040] Magnetite Genetic Types: The major elemental data of magnetite are plotted on the TiO2-Al2O3-(MgO+MnO) magnetite genetic discrimination diagram. Figure 3From (a), it can be seen that most of the magnetite data points fall into the magmatic-hydrothermal type region, and a few fall into the metamorphic sedimentary type region, indicating that the magnetite in this deposit is magmatic-hydrothermal magnetite; when the obtained data is plotted onto the Ni / Cr-Ti magnetite genetic discrimination diagram, most of the data points fall into the hydrothermal type magnetite. Figure 3 (b)); The magnetite deposit contains numerous silicate inclusions, in which Ca, Al, and Mn are enriched, leading to the depletion of Ca, Al, and Mn elements in the host magnetite. This is reflected in the (Ti + V)-Ni / (Cr + Mn) diagram. Figure 3 In the middle (d), Ti + V has a low concentration, and all data points fall in the magmatic hydrothermal region, which is a common feature of some magmatic hydrothermal deposits at home and abroad. Combined with field observations, the ore samples collected all contain diopside, garnet and actinolite, further proving that the deposit should be a magmatic hydrothermal type.

[0041] Environmental analysis: Plotting the data points of this invention reveals ( Figure 4 In (a): the contents of Cr and V show an approximately linear relationship, especially the V content, which shows a significant increasing trend, indicating that the oxygen fugacity of the ore-forming fluid generally decreases from Mag-I to Mag-II. Considering that Mag-I is usually associated with silicate minerals and Mag-II is usually associated with sulfides, we judge that the oxygen fugacity gradually decreases from the Mag-I to Mag-II stage. Plotting the obtained data onto the Ni / Cr-Ti magnetite genetic discrimination diagram, most data points fall on hydrothermal magnetite. Figure 4 (b)). Furthermore, the Ni / Cr ratio in magnetite varies considerably (0.03-8.18), which is related to the strong mobility of Cr in fluids or the water-rock reaction between the ore-forming fluids and the rock mass. In the Ga-Sn and Ga-Mg diagrams of magnetite ( Figure 4 (b) Figure 4 In (c), there is a good linear relationship between the elements. The temperature of the ore-forming fluid decreases from Mag-I to Mag-II. Combined with the (Ti+V)-(Al+Mn) diagram, Figure 4 The analysis of (d) shows that the overall temperature is approximately 300°C.

[0042] V. Ore Body Depth Extension Index Extraction Module

[0043] (1) Quantitative Indicators: The ΣREE content in magnetite varies considerably across different sections, ranging from 1.13 to 6.61, with an average of 3.20. From the 1080m (shallow) section to the 1000m (deep) section, the ΣREE content generally shows a gradual decreasing trend. However, the ΣREE content is relatively stable at 1040m and 1000m, with a clear inflection point at 1040m, and the content is lowest at 1000m. The average δEu value varies relatively widely across different sections of magnetite, ranging from 0.74 to 3.87, with an average of 2.1. The δCe value varies less, ranging from 0.38 to 0.93, with an average of 0.7. The δEu value shows a trend of first increasing and then decreasing from shallow to deep, with a clear inflection point at 1040m. The δCe value varies less across different sections (…). Figure 5 The magnetite data points from this study were plotted using a (Ti+V)-(Al+Mn) model. The results show that the vast majority of Mag-I data are not located within magmatic, hydrothermal, or magmatic-hydrothermal superposition regions, with only some Mag-II data falling within magmatic-hydrothermal + magmatic rock type regions. Figure 4 (d) Mag-I from this deposit has very low Ti+V and Al+Mn contents, and is located above the BIF-type region on the graph. This may be related to the large number of silicate inclusions in Mag-I, which leads to a decrease in its Ti, V, and Al contents, coupled with the reduced ability of multivalent element V to enter magnetite under low oxygen fugacity conditions; Ti is relatively enriched in the Mag-II stage after large-scale water-rock reaction (median value increases from 188 ppm to 372 ppm). The temperature of the ore-forming fluids decreases from Mag-I to Mag-II.

[0044] (2) Determination of the deep extension pattern of the ore body

[0045] Hydrothermal fluids are pulsating and their tectonic distribution is often equidistant; therefore, the distribution of ore bodies also exhibits certain regularities. In this invention, the trace element content of magnetite shows a clear transition from concave to convex at the 1040m level, consistent with the concave-convex geometry of the rock mass. For magnetite, from the 1080m level (shallow) to the 1000m level (deep, 80m elevation difference), an inflection point appears at the 1040m level, which is precisely in the middle of the two. Therefore, is the 80m vertical elevation difference a period of change? Assuming this change is a period, the next inflection point should be near the 920m level. Based on this periodicity, the approximate locations of the ore body at depths of 920m, 840m, and 760m can be inferred. The areas where the rock mass transitions from concave to convex are favorable prospecting targets. Figure 6 ).

Claims

1. A method for delineating deep prospecting target areas of magmatic hydrothermal polymetallic deposits using magnetite, characterized in that, Specifically, the following steps are included: S1: Field mapping and sample collection module: Based on existing geological maps and data of the target deposit, conduct large-scale tectonic alteration and lithofacies mapping at different elevations, determine mineralization and alteration types, mineral assemblages and mineralization and alteration zoning characteristics, investigate the spatial variation of geological characteristics of magmatic hydrothermal deposits, and determine the composition of magmatic hydrothermal mineralization systems; systematically collect magnetite of different spatial locations and types. S2: Rock and Ore Processing and Identification Module: Conduct macroscopic and microscopic textural observations of magnetite, select magnetite samples from different locations and of different types for processing, and then use optical and electron microscopes to comprehensively identify the color, structure, texture, generation, and mineral association of magnetite from different locations and of different types; establish qualitative indicators for predicting deep concealed ore bodies using magnetite. S3: Magnetite Element Content Analysis Module: Based on the identification results of optical microscopy, micro-area in-situ analysis technology is used to obtain major element, trace element and rare earth element data of different types of magnetite; S4: Test Data Processing Module: Based on existing mapping software and templates, determine the precipitation mechanism of different types of magnetite based on the changes in the content of characteristic elements or element combinations, analyze the geological environment in which they are formed, and identify the spatial variation patterns of magnetite with different geochemical characteristics. S5: Ore body depth extension index extraction module, based on the spatial variation of characteristic elements or element combinations, extracts indicators that can effectively indicate the extension of polymetallic ore bodies into deep unknown areas, and determines the depth extension law of polymetallic ore bodies; establishes quantitative indicators for deep ore body prediction using magnetite. S6: Combining the spatial distribution pattern of the shallow mined middle section ore body, verify the rationality of the extracted qualitative and quantitative indicators, summarize the deep extension pattern of the ore body, and comprehensively judge the deep extension distance of the polymetallic concealed ore body and the prospecting target area. Qualitative and quantitative indicators in steps S2 and S5: The color, structure, mineral association, and generational variation of magnetite identified under optical and electron microscopes are used as qualitative indicators to evaluate the deep extension of concealed ore bodies; Based on the comprehensive analysis of the data in S4, the total rare earth content, europium anomaly, cerium anomaly, and the variation trends of Ti, V, Ni, Cr, and Mn elements in different types of magnetite are used as quantitative indicators to evaluate the deep extension of concealed ore bodies.

2. The method for delineating deep prospecting target areas of magmatic hydrothermal polymetallic deposits using magnetite as described in claim 1, characterized in that: In S1, the large scale is 1:500 or larger.

3. The method for delineating deep prospecting target areas of magmatic hydrothermal polymetallic deposits using magnetite as described in claim 1, characterized in that: The specific process of S2 is as follows: using macroscopic geological features as the main basis for judgment, and combining the microscopic features of magnetite under optical and electron microscopes as auxiliary basis, different types of magnetite are distinguished. Macroscopic geological features include: spatial distribution features, mineral symbiotic assemblage, relative mineral content, interpenetration relationship, color, and texture; microscopic features include: color, structure, mineral symbiotic assemblage, and generation.

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