Gold ore prospecting prediction method based on Hg-W ratio of pyrite

Abstract

The invention discloses a gold ore prospecting prediction method based on the Hg-W ratio of pyrite, and the method comprises the steps: recognizing an internal annulus structure of pyrite through a scanning electron microscope back scattering electron imaging technology, and locking a growth edge annulus representing a main metallogenic period; performing in-situ trace element content testing on the edge girdle by adopting a laser ablation inductively coupled mass spectrometer to obtain mass concentrations of mercury and tungsten; calculating the mass concentration ratio R of mercury to tungsten in the edge annulus, and drawing an Hg-W logarithmic scatter diagram; the smaller the R value in the Hg-W logarithmic scatter diagram is, the closer the R value is to the root of the mineralization system, otherwise, the closer the R value is to the shallow part of the mineralization system. According to the method, the superimposed interference of multi-stage signals in the non-mineralization stage is effectively eliminated, and a quantitative discrimination index is established by using the geochemical differentiation law of Hg and W in fluid evolution. The method has the advantages of being high in spatial resolution, accurate in prospecting information, reliable in denudation degree evaluation and the like, and a scientific basis can be provided for accurate positioning of the deep concealed gold mine.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of mineral resource exploration and geological and geochemical prospecting, and particularly relates to a method for analyzing the decoupling relationship between mercury (Hg) and tungsten (W) contents in the main ore-forming period pyrite zonation by using laser in-situ testing technology, and further identifying the denudation degree of gold mine (especially Carlin-type gold mine) and deep prospecting potential. BACKGROUND

[0002] Carlin-type gold deposits (CTGDs) are one of the most important gold deposit types in the world, widely distributed in Nevada, USA and the "Yunnan-Guizhou-Guangxi" region of China. This type of deposit has the characteristics of large scale, stable grade, and easy scale mining, and is the key support for the gold resource reserves of various countries. However, with the discovery of easily identifiable shallow deposits almost exhausted, the detection of deep concealed deposits has become a major challenge currently faced by geological exploration. In traditional geochemical prospecting work, whole rock geochemical analysis and primary halo prospecting theory are usually used. According to the classic element vertical zoning model, the hydrothermal ore-forming system often shows a spatial sequence of As-Sb-Hg (prohalo elements), Au (halo elements) and Mo-W-Sn (tail halo elements). In theory, by analyzing the content changes of these elements, the spatial position of the ore body can be indicated, that is, in the deep or shallow part of the ore-forming system. However, in practical application, the traditional prospecting method has the following serious defects:

[0003] First, the superimposed interference of multi-period hydrothermal mineral signals (signal dilution effect). Gold deposits (especially super-large deposits) usually undergo multiple stages of tectonic-hydrothermal activity superimposition. For example, the main gold-bearing mineral pyrite often contains sedimentary pyrite, pre-ore hydrothermal pyrite, and main ore-forming period hydrothermal pyrite. The traditional whole rock analysis method or single mineral bulk chemical analysis method will mix the signals of different periods and different origins. Since the pre-ore and sedimentary minerals occupy a large part of the rock mass, the weak but key geochemical signals carried by the main ore-forming stage are seriously diluted, and even completely masked by the background value, leading to biased conclusions.

[0004] Second, the fuzziness and multi-solution of the element vertical zoning index of the ore-forming system. Although the existing prospecting indicators (such as As, Sb, Tl, etc.) are significantly enriched in the ore-forming system, due to their geochemical properties, they are often distributed in the prohalo and tail halo areas of the ore body, lacking strong vertical differentiation. In addition, affected by the modification and redistribution of multi-period hydrothermal activity, the vertical zoning sequence of elements often appears "inverted" or "disordered". For example, in some mining areas, As, which should be at the top, appears high in the deep, making it difficult for exploration personnel to accurately determine whether the current denudation surface is above or below the ore body.

[0005] Third, there is the issue of spatial heterogeneity at the deposit scale. Previous studies have often focused on isolated high-grade ore bodies, lacking a systematic comparison of gold-bearing minerals within a large-scale spatial framework. This has led to differences in geochemical characteristics at different sampling depths being attributed to mineralization complexity, rather than establishing a unified, quantitative spatial location model.

[0006] Fourth, the potential of mercury (Hg) and tungsten (W) in mineral exploration has not been fully explored. Mercury is highly volatile and tends to precipitate in large quantities in the shallow parts of the mineralization system due to decompression, degassing, and condensation. Tungsten, on the other hand, is a typical high-temperature sensitive element and tends to precipitate in the deep parts near the fluid source in the early stages of hydrothermal uplift. Although this physicochemical differentiation of Hg and W can theoretically indicate the vertical position of the mineralization system, the extremely low content of W in pyrite (usually in the μg / g range or even lower) makes it difficult to accurately determine its content at the mineralization stage using traditional methods. As a result, this highly promising "high-temperature tail halo - low-temperature front halo" coupling index has long failed to be transformed into an industrial-grade mineral exploration criterion.

[0007] Therefore, there is an urgent need for a prospecting prediction method that can effectively eliminate signal interference from multiple phases of hydrothermal activity, use high-precision in-situ testing methods to lock in fingerprint information of the main mineralization period, and provide clear and robust quantitative thresholds, so as to solve the technical bottleneck of locating deep concealed minerals and accurately assessing the degree of erosion. Summary of the Invention

[0008] The purpose of this invention is to address the technical challenges in existing gold exploration, such as the inability of whole-rock geochemical analysis to eliminate interference from multi-stage mineralization, the ambiguity of vertical zoning indicators, and the difficulty in quantitatively assessing the degree of ore body erosion. This invention provides a gold prospecting prediction method based on the Hg-W ratio of pyrite. This method utilizes the extreme differentiation characteristics of trace elements in gold-bearing pyrite from the main mineralization stage to establish a robust and quantitative "depth-erosion" discrimination model, providing a scientific basis for the accurate location of concealed ore bodies.

[0009] To achieve the above objectives, the present invention adopts the following technical solution:

[0010] A gold deposit prospecting prediction method based on the Hg-W ratio of pyrite, the specific steps of which are as follows:

[0011] Step 1: Sample collection and preparation of rock thin sections.

[0012] Based on the known structural location and elevation of the ore bodies in the mining area, ore samples were collected at different elevations.

[0013] The collected ore samples were prepared into thin rock sections with a smooth surface and a thickness of about 100 μm, and then finely polished to ensure signal stability during the laser ablation process.

[0014] Step 2: Identification and identification of pyrite zonation during the mineralization period.

[0015] The microstructure of pyrite was systematically observed using backscattered electron (BSE) imaging technology of scanning electron microscopy (SEM).

[0016] Identify the evolutionary sequence within pyrite, from sedimentary pyrite during the diagenetic period, to hydrothermal pyrite cores before mineralization, and then to the growth margin zoning zone of pyrite during the mineralization period.

[0017] The focus is on identifying the pyrite marginal zone, which represents the main mineralization stage. In BSE images, this zone appears as a grayish-white edge with significantly higher brightness than the internal pyrite core. It is usually irregularly shaped and surrounds the dark gray pyrite core, and is often associated with fine-grained arsenopyrite.

[0018] Using an energy dispersive spectroscopy (EDS) instrument paired with a SEM, preliminary qualitative analysis of the identified pyrite marginal zone was conducted, confirming that it possesses the characteristics of arsenic-rich mineralized pyrite.

[0019] The thickness of the pyrite edge ring (typically between 20 μm and 100 μm) is measured and recorded to provide a reference for the subsequent selection of laser beam spot.

[0020] Step 3: In-situ fine testing of mineralization zonation.

[0021] In-situ trace element analysis was performed on the pyrite edge zone locked in step (2) using laser ablation inductively coupled mass spectrometry (LA-ICP-MS).

[0022] The laser beam diameter is set to 15μm to 30μm to ensure that the beam spot falls completely within the edge ring of the pyrite without touching the pyrite core.

[0023] The ablation frequency was set to 4Hz to 6Hz, and the ablation depth was controlled within 30 μm. The ablation signal curve was monitored in real time to ensure that the signal range was flat and free from contamination by inclusions.

[0024] At least the mass concentration data of mercury (Hg) and tungsten (W) should be obtained. It is also recommended to obtain the mass concentration data of elements such as Au, As, Sb, and Tl to help verify whether the pyrite edge zone is pyrite from the main mineralization stage.

[0025] Step 4: Calculation of mineral exploration identification indicators.

[0026] Using the elemental quantitative data obtained in step (3), calculate the mass concentration ratio of Hg to W in the pyrite marginal zone: R = C Hg / C W And plot the logarithmic scatter plot of Hg-W mass concentration.

[0027] Step 5: Spatial location of the metallogenic system and evaluation of its prospecting potential

[0028] Based on the distribution of R-values ​​around the critical diagnostic threshold of 10, spatial positioning and mineral exploration evaluation are performed:

[0029] If R < 10, the sampling point is determined to be located in the deep part or tail region of the mineralization system. In this region, the Hg content is low (e.g., average content < 15 μg / g), while W, as a high-temperature sensitive element, is significantly enriched in the pyrite edge ring (e.g., average content > 2 μg / g). The smaller the R value in the Hg-W logarithmic scatter plot, the higher the degree of erosion at that location, and the more limited the potential for further mineral exploration at depth.

[0030] If R > 10, the sampling point is determined to be located in the shallow or pre-halo region of the ore-forming system. In this region, W has been "precipitated" earlier by deeper deposits, resulting in extremely low content (e.g., average content < 0.5 μg / g), while Hg is heavily enriched in the pyrite edge ring due to degassing (e.g., average content > 20 μg / g). The larger the R value is than 10, the greater the potential for exploration of concealed ore bodies below the sampling point.

[0031] If R≈10, the sampling point is determined to be in the middle part of the mineralization system, indicating that there is still some mineral exploration space below the sampling point.

[0032] Due to the pulsating nature of ore-forming fluids, individual measuring points may be at the threshold edge. This method recommends using multi-point averages or overall trends to determine ore-forming potential.

[0033] The potential assessment also includes: statistically analyzing the distribution of R values ​​at sampling points at different altitudes under multi-sample conditions, and constructing a model of the longitudinal erosion degree of the mining area.

[0034] The present invention also discloses an application according to any of the above methods, comprising:

[0035] The method is applied to the systematic location of Carlin-type gold deposits, orogenic gold deposits, and hydrothermal metal deposits with high-temperature-low-temperature element vertical decoupling characteristics, and to complete a comprehensive evaluation of the deposit's mining potential.

[0036] Compared with the prior art, the present invention has the following significant advantages:

[0037] This invention does not employ conventional whole-rock analysis. Instead, it utilizes scanning electron microscopy (SEM) with backscattered electron (BSE) imaging and energy dispersive spectroscopy (EDS) to pre-identify growth zonation during the mineralization period, achieving "targeted erosion." This method completely eliminates the dilution of mineralization information by signals from non-mineralization periods, amplifying the decoupled signals of Hg and W several times and improving the sensitivity of the discrimination.

[0038] The study found that although elements such as As and Sb are enriched in both the front and rear halos, Hg and W exhibit almost completely opposite vector directions. By constructing the Hg / W coupled index, the originally ambiguous qualitative patterns are transformed into clear quantitative indicators, thus solving the problem of multiple solutions in mineral exploration prediction.

[0039] This invention, through the analysis of measured data spanning a large spatial scale, determined a diagnostic threshold of 10, which is significant for the evolution of ore-forming fluids. This value is universally applicable; geological technicians can quickly determine the current degree of erosion and the potential for deep mineral exploration simply by measuring the composition of pyrite growth edges, much like looking up a table, thus greatly reducing exploration risks.

[0040] Because the distribution of Hg and W at the edge of pyrite is extremely sensitive, this method only requires the analysis of a very small number (a few) of typical samples to make an accurate evaluation of the deep prospecting potential of the entire mining area or ore body, saving a lot of blind investment for the layout of subsequent drilling projects. Attached Figure Description

[0041] Figure 1 This is a simplified geological map of the mining area and a schematic diagram of sampling profiles according to an embodiment of the present invention; wherein: a is a geological map of the mining area, showing the locations of two sampling profiles according to an embodiment of the present invention; b is a representative profile of the mining area, showing the sampling location of shallow ore bodies; and c is another representative profile of the mining area, showing the sampling location of deep ore bodies (a, b, and c are all icons in the lower left corner).

[0042] Figure 2 These are backscattered electron images of pyrite, showing the structure of pyrite in three phases, as well as the LA-ICP-MS test sites and results. Specifically: a) shows pyrite from the sedimentary diagenetic stage, including pyrite 1 (Py1) with a regular shape and uniform color, and fine-grained clustered pyrite 2 (Py2); b) and c) show banded pyrite in shallow ore bodies, where the dark gray core is pre-mineralized hydrothermal pyrite 3 (Py3), and the grayish-white growth band at the edge is mainly pre-mineralized hydrothermal pyrite 4 (Py4). The Hg / W values ​​of Py4 in b and c are 425 and 42.3, respectively; d) shows banded pyrite in deep ore bodies, with the dark gray core being Py3 and the grayish-white edge being Py4 (the Hg / W values ​​at the two analysis sites are 1.70 and 1.84, respectively).

[0043] Figure 3 Logarithmic scatter plot of W-Hg content in the marginal zone (Py4) of pyrite during the main mineralization period;

[0044] Figure 4 This is a schematic diagram of a vertical zonation prospecting model for gold deposits based on Hg / W values. Detailed Implementation

[0045] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of the embodiments of this invention will be described in more detail below with reference to the accompanying drawings. In the drawings, the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The described embodiments are some embodiments of this invention, but not all embodiments.

[0046] Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0047] The embodiments and directional terms described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0048] Example 1

[0049] This embodiment takes the Shuiyindong super-large Carlin-type gold deposit in Guizhou Province as an example. Figure 1 a) Samples were collected from two spatial locations within the deposit, at altitudes of 1100 m and 200 m. The effectiveness of the method described in this invention was verified by observing and conducting in-situ compositional analysis of the pyrite within these two sets of ore body samples.

[0050] Step 1: Sample Collection and Thin-Section Preparation

[0051] In this embodiment, ore samples were collected from two representative elevations of the deposit to construct a vertical spatial comparison framework:

[0052] The shallow samples were collected from the marl of the first member of the Triassic Yelang Formation, at an elevation of approximately 1100 m. Figure 1 b). This area represents the shallow or pre-halo environment of a metallogenic system, with great potential for deep mineral exploration.

[0053] The deep samples were collected from the silty claystone of the first section of the Longtan Formation in the Permian system, at an altitude of approximately 200m. Figure 1 c). This area is close to the deep channels of ore-forming fluids, representing the deep or tail-like environment of the ore-forming system, with little potential for further mineral exploration.

[0054] The two sets of ore samples were cut, ground, and finely polished to prepare thin rock sections. The sections were required to be free of scratches and residual polishing compound to ensure the signal-to-noise ratio of the laser ablation signal.

[0055] Step 2: Identification of pyrite growth stages and zonal structure

[0056] Pyrite was observed by backscattered electron imaging using a field emission scanning electron microscope (model JEOL JSM-7800F) under the conditions of accelerating voltage 20 kV and probe current 10 nA.

[0057] Experimental observations show that the pyrite in the Mercury Cave gold mine exhibits complex, multi-stage characteristics. Figure 2 ):

[0058] Pyrite Py1 and Py2: These are pyrites formed during the sedimentary diagenetic period. Py1 is a pyrite with a regular and homogeneous structure, while Py2 is a fine-grained, clustered pyrite. They have relatively low brightness in backscattered electron images. Figure 2 a).

[0059] Pyrite Py3: This is a pre-mineralized hydrothermal pyrite core, appearing as an irregular dark gray core in backscattered electron images. The core diameter ranges from 50 μm to 100 μm. Figure 2 bd).

[0060] Pyrite Py4: This represents the marginal growth zone of pyrite from the main mineralization period, appearing as a grayish-white growth edge enclosing the dark gray Py3 in backscattered electron imaging. The thickness of this zone ranges from 20 μm to 100 μm, exhibiting distinct micron-scale growth oscillations. Figure 2 bd).

[0061] The key to this technology is that the present invention selects only the grayish-white edge ring of pyrite Py4 as the target area for laser ablation, aiming to obtain the purest chemical information of the main mineralization stage and eliminate interference from non-mineralization signals in early pyrite such as Py1-Py3.

[0062] Step 3: In-situ trace element content testing

[0063] In-situ elemental analysis of the Py4 ring at the edge of pyrite was performed using a laser ablation inductively coupled mass spectrometer (Agilent 7900 mass spectrometer coupled with a RESOlution S155 laser ablation system). Test parameters were set as follows: beam diameter 19 μm (ensuring the beam spot was completely within the pyrite edge ring and did not overlap with the pyrite core); ablation frequency 4 Hz; energy density 4.0 J / cm²; high-purity helium (flow rate approximately 0.8 L / min). MASS-1 polymetallic sulfide standard was used as an external standard, with iron (Fe) as an internal standard for concentration correction. The ablation time at each site was approximately 40 s, and the background acquisition time was approximately 20 s. During the ablation process, the signal spectra of Hg and W were monitored in real time, and abnormal signal regions affected by fine-grained inclusions were eliminated.

[0064] Step 4: Experimental Data and R-value Calculation

[0065] The table below lists the measured contents of Hg and W in the Py4 ring at the edge of pyrite in the deep and shallow samples of this embodiment, and the calculated R values ​​(R = C). Hg / C W See Table 1 below. Figure 3 The plot shows a logarithmic scatter plot of Hg-W mass concentrations, with the horizontal axis representing the W content in pyrite and the vertical axis representing the Hg content in pyrite. The high contents of Au, As, Sb, and Tl in the pyrite analyzed indicate that it is a gold-bearing pyrite from the mineralization period.

[0066] Table 1. In-situ trace element analysis results and Hg / W values ​​of the Py4 ring at the edge of the pyrite in the Mercury Cave gold mine.

[0067]

[0068] Step 5: Results Analysis and Mineral Exploration Prediction Evaluation

[0069] Analysis of the above measured data shows that the data from the two sets of sampling points are mostly located above and below the Hg / W=10 isoline in the Hg-W mass concentration logarithmic scatter plot. Figure 3 ):

[0070] The R-value (average 1.62) of the pyrite edge zone at a depth of 200m is much less than the threshold of 10. This reflects that in the high-temperature and high-pressure deep environment, W preferentially enters the pyrite lattice, while Hg has not yet precipitated in large quantities. Mineral exploration evaluation: This location is at the root of the mineralization system, indicating that the potential for further exploration of large-scale industrial ore bodies below this sampling point is relatively limited. Figure 4 This finding is consistent with existing discoveries; no industrial ore bodies have yet been found at the depth of this sampling point.

[0071] The R-value (average 55.6) of the pyrite edge zone at a shallow elevation of 1100m is much greater than the threshold of 10. This reflects that W was pre-precipitated and consumed at deeper levels during the upward migration of fluids, while Hg precipitated at shallow levels driven by decompression and degassing. Mineral exploration evaluation: This location is at the forefront or above the metallogenic system, indicating a great potential for concealed ore bodies at depth below the sampling point. Figure 4 Subsequent drilling at the sampling point confirmed the existence of a hidden ore body at a deeper depth.

[0072] Explanation of the method's universality

[0073] This embodiment demonstrates that by utilizing the in-situ Hg / W value of the pyrite marginal zone during the main mineralization period, the "signal dilution" problem caused by multi-stage hydrothermal superposition in Carlin-type gold deposits can be successfully overcome. The Hg / W value is a sensitive indicator for distinguishing the vertical spatial location of ore bodies; the smaller the ratio, the closer it is to the root (deep part) of the mineralization system, and vice versa. This method is not only applicable to Carlin-type gold deposits but can also be analogously extended to other hydrothermal metallic deposits with "temperature-sensitive and pressure-sensitive" element coupling characteristics.

[0074] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for gold ore prospecting prediction based on Hg-W ratio of pyrite, comprising the following steps: (1) Sample collection and pretreatment: Collect ore-bearing rock samples at different spatial locations in the target mining area, and prepare rock slices with smooth surface and no contamination; (2) Targeted identification of ore-forming period zonation: Use backscattered electron imaging technology of scanning electron microscope to observe the microstructure of pyrite in the sample, identify its internal evolution period, and lock the pyrite edge zonation outside the pyrite core representing the main ore-forming period; (3) In-situ microelement testing: Use laser ablation inductively coupled plasma mass spectrometer to test the in-situ composition of the pyrite edge zonation, and obtain the mass concentration data of Hg and W in the zonation; (4) Discrimination index calculation: calculate the mass concentration ratio R of Hg and W in the edge ring belt of the pyrite, the calculation formula is: R=C Hg / C W , and draw the Hg-W logarithmic scatter plot; (5) Ore-forming system positioning and potential evaluation: According to the distribution of R value on both sides of the key diagnostic threshold of 10, evaluate the vertical spatial position of the ore body and the deep prospecting potential of the sampling point.

2. The method of claim 1, wherein: The characteristics of the pyrite edge zonation in the backscattered electron image in step (2) are: The brightness is significantly higher than that of the gray-white edge of the pre-ore pyrite core; The growth edge zonation is irregular or straight wrapped outside the dark gray pyrite core; The zonation thickness is between 20 μm and 100 μm.

3. The method of claim 1, wherein: In step (2), the identified pyrite edge zonation is also subjected to preliminary composition qualitative analysis using an energy dispersive spectrometer matched with the scanning electron microscope to confirm its characteristics of arsenic-rich ore-forming period pyrite.

4. The method of claim 1, wherein: In step (3), the parameter settings for in-situ composition testing of the pyrite edge zonation using the laser ablation inductively coupled plasma mass spectrometer are as follows: The laser beam spot diameter is set to 15 μm to 30 μm, the diameter is less than the width of the pyrite edge zone, and the beam spot does not cover the dark gray pyrite core; the laser ablation frequency is set to 4 Hz to 8 Hz; the laser energy density is set to 3.0 J / cm 2 to 5.0 J / cm 2 ; The ablation depth is controlled within 30 μm without penetrating the pyrite edge zonation.

5. The method of claim 1, wherein: In step (5), the diagnostic threshold of R includes: If R < 10, it is determined that the sampling point is in the deep or tail halo area of the ore-forming system, indicating that the spatial position has a high degree of denudation and a relatively small potential for further deep prospecting; If R > 10, it is determined that the sampling point is in the shallow or front halo area of the ore-forming system, indicating that the spatial position is above the ore-forming system and has a large potential for concealed ore body prospecting in the deep part; The smaller the R value in the Hg-W logarithmic scatter plot, the closer it is to the root of the ore-forming system, and the larger the R value in the Hg-W logarithmic scatter plot, the closer it is to the shallow part of the ore-forming system.

6. The method of claim 1, wherein: In step (5), the potential evaluation also includes: Under the condition of multiple samples, the R value distribution of sampling points at different altitudes is counted to construct a longitudinal denudation degree model of the mining area.

7. The method of claim 1, wherein: In step (3), the in-situ microelement testing also includes: Simultaneous determination of the mass concentration of gold, arsenic, antimony and thallium to assist in verifying whether the pyrite edge zonation is the pyrite of the main ore-forming stage.

8. An application of the method according to any one of claims 1-7, comprising: The method is applied to the positioning of Carlin-type gold deposits, orogenic gold deposits and hydrothermal metal deposit systems with high-low temperature element vertical decoupling characteristics, and completes the comprehensive evaluation of the ore deposit prospecting potential.

Images