Method for judging iron-copper metallogenic potential of intermediate-acid intrusive rock based on combined identification of zircon and apatite

Abstract

This invention discloses a method for determining the iron-copper mineralization potential of intermediate-acidic intrusive rocks based on the combined use of zircon and apatite, belonging to the field of mineral exploration technology. The method includes the following steps: (1) systematically collecting samples of intermediate-acidic intrusive rocks and separating zircon and apatite; (2) conducting cathodoluminescence image analysis and major and trace element testing of zircon and apatite; (3) calculating the oxygen fugacity ΔFMQ, water content, Yb / Gd ratio of zircon, and 100*X of apatite based on the structural and compositional characteristics of zircon and apatite. Cl / X OH / X F The ratio of 1000*V / (Mn+100Ga) is used to quickly identify the mineralization potential of porphyry-skarn type iron-copper deposits. This method is simple to operate, has a short testing cycle, and high discrimination efficiency. It is suitable for the rapid screening of iron-copper ore-forming rock bodies and the delineation of prospecting target areas in the early stages of exploration, and has significant practical value and prospects for promotion.

Description

Technical Field

[0001] This invention belongs to the field of mineral exploration and evaluation, specifically relating to a method for determining the iron-copper mineralization potential of intermediate-acidic intrusive rocks based on the combined use of zircon and apatite. Background Technology

[0002] Porphyry-skarn type iron-copper deposits are typically associated with calc-alkaline to alkaline intermediate-acidic intrusive rocks in subduction or collision settings, but not all rock bodies possess mineralization potential. In this type of magma-deposit system, high oxidation state, high water content, and rich volatile matter are considered key factors for rich mineralization in magmatic rocks. Traditional discrimination methods rely on whole-rock geochemistry, alteration zoning, and mineralization indications, which suffer from problems such as long testing cycles, high costs, and delayed discrimination. Zircon and apatite, as common accessory minerals in intermediate-acidic rock bodies, have strong resistance to weathering and alteration, and are gradually becoming important carriers for judging mineralization potential. However, existing technologies mostly focus on single minerals and have not yet established a comprehensive discrimination system applicable to iron-copper mineralization systems and incorporating zircon-apatite dual-mineral phases. Therefore, a new method that is simple to operate, has a short testing cycle, and is highly efficient in discrimination is urgently needed. Summary of the Invention

[0003] This invention provides a method for determining the iron-copper mineralization potential of intermediate-acidic intrusive rocks based on the combined use of zircon and apatite. The method involves measuring the zircon and apatite composition of different intermediate-acidic rock bodies in the area to be explored, thereby determining the oxygen fugacity, water content, and volatile matter content of the intrusive rocks, and thus assessing the iron-copper mineralization potential of the porphyry-skarn rock bodies.

[0004] To achieve the above objectives, the present invention adopts the following technical solution:

[0005] A method for determining the iron-copper mineralization potential of intermediate-acidic intrusive rocks based on the combined analysis of zircon and apatite includes the following steps:

[0006] (1) Collect intermediate-acidic intrusive rock samples from the area to be explored, sort zircon and apatite, and conduct major element analysis and trace element analysis;

[0007] (2) The method for assessing the mineralization potential of intermediate-acidic rock masses is as follows:

[0008] Condition 1: Oxygen fugacity determination: Calculate the oxygen fugacity ΔFMQ of the sample corresponding to the zircon Ti thermometer. When the average ΔFMQ of zircon is ≥2 and the average 1000*V / (Mn+100Ga) of apatite is ≥2, the intrusive rock is determined to have mineralization potential; when the average oxygen fugacity ΔFMQ of zircon is <2 and the average 1000*V / (Mn+100Ga) of apatite is <2, the intrusive rock is determined to have no mineralization potential.

[0009] Condition 2: Water Content Determination: Calculate the zircon Yb / Gd ratio and water content. When the average zircon Yb / Gd ratio is ≥20 and the average H2O content is ≥4.0 wt.%, the intrusive rock is determined to have mineralization potential; when the average zircon Yb / Gd ratio is <20 and the average H2O content is <4.0 wt.%, the intrusive rock is determined to have no mineralization potential.

[0010] Condition 3: Volatile matter content determination: Calculate 100*X of apatite. Cl / X OH / X F The ratio, when the average value of apatite is 100*X Cl / X OH / X F When the value is ≥20, the intrusive rock is considered to have mineralization potential; when the average value of apatite is 100*X Cl / X OH / X F If the value is less than 20, the intrusive rock is determined to have no mineralization potential.

[0011] Condition 4: If all the conditions for mineralization potential in conditions 1 to 3 are met, the rock mass is determined to be an iron-copper ore-forming rock mass, and the prospecting target area is delineated; otherwise, it is determined to be a non-ore-forming rock mass.

[0012] Preferably, step (1) is specifically operated as follows: based on the exposure of intermediate-acidic rock bodies in the area to be explored, systematically collect unweathered and altered intermediate-acidic intrusive rock samples, sort zircon and apatite and prepare targets; obtain cathodoluminescence images of zircon and apatite targets, and select unaltered zircon and apatite with clear crystalline zoning to carry out electron probe major element analysis and LA-ICP-MS trace element analysis.

[0013] Preferably, the intermediate-acidic intrusive rock samples collected in step (1) refer to intrusive rocks with whole-rock SiO2 > 66 wt.% and LOI < 3 wt.%, and each sample contains more than 150 zircon and apatite.

[0014] Preferably, the major elements of zircon analyzed in step (1) include Zr and Si; the trace elements of zircon include Ti, Sr, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Y, Hf, Pb, Th and U.

[0015] The major elements analyzed in apatite include SiO2, FeO, MnO, MgO, CaO, Na2O, P2O5, SrO, F, Cl, and SO3; the trace elements include Ca, V, Mn, Ga, Ge, Sr, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Y, Pb, Th, and U.

[0016] Preferably, in step (2), ΔFMQ represents the difference between the oxygen fugacity of the sample and the oxygen fugacity of the fir olivine-magnetite-quartz redox buffer, and ΔFMQ is calculated based on the Geo-fO2 oxygen fugacity comprehensive analysis software of Li et al. (2019).

[0017] Preferably, in step (2), 100*X Cl / X OH / X F The ratio is a discriminant constructed from the molar fraction ratio of fluorine, chlorine and hydroxyl groups in apatite, and is used to indicate the content of volatiles in rocks.

[0018] Preferably, in step (2), V, Mn, and Ga in 1000*V / (Mn+100Ga) of apatite refer to the contents of vanadium, manganese, and gallium in apatite, respectively, in ppm.

[0019] Preferably, the mineralization potential is the mineralization potential of a porphyry-skarn type iron-copper deposit.

[0020] The beneficial effects of this invention are as follows:

[0021] This invention proposes a method for determining the iron-copper mineralization potential of intermediate-acidic intrusive rocks based on the combined analysis of zircon and apatite. Belonging to the field of mineral resource exploration technology, this method solves the problems of long testing cycles, high costs, and delayed determination in existing methods. This invention is simple to operate, has a short testing cycle, and high determination efficiency, making it of great practical value in study areas where intrusive rocks are widely developed. It also shows promising application prospects in downstream sediment source tracing and target area delineation. Based on the geochemical characteristics of zircon and apatite in intermediate-acidic intrusive rocks in the study area, this invention obtains reliable indicators of oxygen fugacity, water content, and volatile matter content, enabling rapid and effective identification of rock bodies with mineralization potential. This is of great significance for shortening the exploration cycle of porphyry-skarn type iron-copper deposits and saving development costs. Detailed Implementation

[0022] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. 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.

[0023] Example 1

[0024] A method for determining the iron-copper mineralization potential of intermediate-acidic intrusive rocks based on the combined analysis of zircon and apatite: Taking a typical rock mass in a certain region as an example, the method includes the following steps:

[0025] (1) Sample collection: Fresh, unweathered and altered samples of acidic intrusive rock bodies in six regions were collected and sample information was recorded through field geological surveys and borehole logging.

[0026] Table 1 Sample Information

[0027]

[0028] (2) Single mineral selection: Apatite and zircon grains were separated from whole-rock samples using standard heavy liquid and magnetic methods, and then manually selected under a binocular microscope. The selected zircon and apatite grains (150 grains per sample) were mounted in epoxy resin, polished to expose their interiors, and used for subsequent analysis.

[0029] (3) Microscopic photography: Before conducting trace element and isotope analysis, the morphology and internal structure of zircon and apatite particles are characterized by transmission light microscopy and cathodoluminescence (CL) to provide guidance for the selection of sites for subsequent trace element analysis.

[0030] (4) Testing and Analysis: Zircon and unaltered apatite grains with euhedral shape, no inclusions, and clear oscillatory zoning were selected for electron probe microanalysis and LA-ICP-MS analysis. In this embodiment, the major elements (SiO2, FeO, MnO, MgO, CaO, Na2O, P2O5, SrO, F, Cl, and SO3) of apatite were tested using a JEOL JXA-8230 electron probe microanalyzer at the Testing Center of China Metallurgical Geology Bureau. The accelerating voltage was 15 kV, the beam current was 20 nA, and the beam spot diameter was 2 μm. Measurements of apatite grains were preferably performed perpendicular to their c-axis to minimize element migration due to beam radiation. All data were calibrated using the ZAF method. Trace element analysis of zircon and apatite was performed by laser ablation-inductively coupled plasma mass spectrometry (LA-ICP-MS) at the State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences (Beijing). The zircon has a cluster diameter of 32 μm, and the apatite has a diameter of 60 μm. The energy density and frequency are 6 J / cm². 2 and 6 Hz. Major and trace elements analyzed in zircon included Zr, Si, Ti, Sr, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Y, Hf, Pb, Th, and U; trace elements in apatite included: Ca, V, Mn, Ga, Ge, Sr, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Y, Pb, Th, and U. 29 Si was used as the internal standard for zircon, and SRM610 as the external standard. 43Ca was used as the internal standard for apatite, and SRM612 as the external standard. Offline data correction was performed using the Excel-based ICPMSDataCal software (Liu et al., 2008).

[0031] (5) Data processing and interpretation: Based on the trace element composition of zircon and apatite, the oxygen fugacity ΔFMQ of the sample corresponding to the zircon Ti thermometer was calculated using the Geo-fO2 oxygen fugacity comprehensive analysis software developed by Li et al. (2019), and the 1000*V / (Mn+100Ga) of apatite was calculated; the Yb / Gd ratio of zircon was calculated and the water content was calculated using the spreadsheet provided by Ge et al. (2023); the measured major element composition of apatite was imported into the spreadsheet of Ketcham et al. (2015) to calculate the mole fraction (X) of fluorine, chlorine and hydroxyl groups in apatite. F X Cl and X OH And calculate 100*X Cl / X OH / X F Ratio; comprehensive assessment of the iron and copper mineralization potential of intermediate-acidic intrusive rocks.

[0032] The method for assessing the mineralization potential of intermediate-acidic rock masses is as follows:

[0033] Condition 1: Oxygen fugacity determination: Using Geo-fO2 oxygen fugacity comprehensive analysis software, the oxygen fugacity ΔFMQ of the sample corresponding to the zircon Ti thermometer is calculated. When the average ΔFMQ of zircon is ≥2 and the average 1000*V / (Mn+100Ga) of apatite is ≥2, the intrusive rock is determined to have high oxygen fugacity and mineralization potential; when the average oxygen fugacity ΔFMQ of zircon is <2 and the average 1000*V / (Mn+100Ga) of apatite is <2, the intrusive rock is determined to have low oxygen fugacity and no mineralization potential.

[0034] Condition 2: Water Content Determination: Calculate the zircon Yb / Gd ratio and water content. When the average zircon Yb / Gd ratio is ≥20 and the average H2O content is ≥4.0 wt.%, the intrusive rock is determined to have high water content and mineralization potential; when the average zircon Yb / Gd ratio is <20 and the average H2O content is <4.0 wt.%, the intrusive rock is determined to have low water content and no mineralization potential.

[0035] Condition 3: Volatile matter content determination: Calculate 100*X of apatite. Cl / X OH / X F The ratio, when 100*X Cl / X OH / X FWhen the content is ≥20, the intrusive rock is determined to have a high volatile content and mineralization potential; when 100*X Cl / X OH / X F When the content is less than 20, the intrusive rock is determined to have low volatile matter content and no mineralization potential.

[0036] Condition 4: When all the conditions for mineralization potential in conditions 1 to 3 are met, the rock mass is determined to be an iron-copper ore-forming rock mass, and the prospecting target area is delineated; when any one or more of the conditions for non-ore-forming potential in conditions 1 to 3 are met, it is determined to be a non-ore-forming rock mass.

[0037] Based on the three discrimination steps described above, the average oxygen fugacity ΔFMQ of zircon from sample 23LL-2 granodiorite porphyry is 5.34 > 2, the average Yb / Gd ratio is 25.64 > 20 (seven data points were tested for zircon from sample 23LL-2 granodiorite porphyry, one of which was invalidated due to the detection of apatite inclusions in the zircon and was not included in the calculation process), the average water content is 7.68 wt.% > 4 wt.%, the average 1000*V / (Mn+100Ga) value of apatite is 5.74 > 2, and the average 100*X Cl / X OH / X F The ratio is 40.43 > 20, therefore it is comprehensively judged as a mineralized rock mass with high oxygen fugacity, high water content and rich volatile matter, which is consistent with the actual geological conditions, and porphyry copper deposits are produced at the edge of the rock mass.

[0038] The zircon average oxygen fugacity ΔFMQ of sample 21HST-4 granodiorite is 6.41 (>2), the average Yb / Gd ratio is 24.65 (>20), and the average water content is 6.11 wt.% (>4 wt.%). The average 1000*V / (Mn+100Ga) value of apatite is 9.23 (>2), and the average 100*X... Cl / X OH / X F The ratio is 66.68 > 20, therefore it is comprehensively judged as a mineralized rock mass with high oxygen fugacity, high water content and rich volatile matter, which is consistent with the actual geological conditions. Skarn-type iron and copper deposits are produced at the edge of the rock mass.

[0039] Sample 23HL-2 granodiorite zircon has an average oxygen fugacity ΔFMQ of 6.37 (>2), an average Yb / Gd ratio of 25.93 (>20), and an average water content of 6.78 wt.% (>4 wt.%). Its apatite has an average 1000*V / (Mn+100Ga) value of 2.67 (>2), and an average 100*X... Cl / X OH / X FThe ratio is 121.46 > 20, therefore it is comprehensively judged as a mineralized rock mass with high oxygen fugacity, high water content and rich volatile matter, which is consistent with the actual geological conditions. Skarn-type iron and copper deposits are produced at the edge of the rock mass.

[0040] Sample 21WL-7, a potassium feldspar granite, has an average oxygen fugacity ΔFMQ of 1.60 < 2, an average Yb / Gd ratio of 18.14 < 20, and an average water content of 3.24 wt.% < 4 wt.%. Its apatite has an average 1000*V / (Mn+100Ga) value of 3.55 > 2 and an average 100*X Cl / X OH / X F The ratio is 2.06 < 20, therefore it is comprehensively judged as a non-ore-forming rock mass with low oxygen fugacity, low water content, and poor volatile matter, which is consistent with the actual geological conditions.

[0041] The average oxygen fugacity ΔFMQ of zircon from sample 21KLG-1 potassium feldspar granite is -1.95 < 2, the average Yb / Gd ratio is 13.77 < 20, and the average water content is 8.82 wt.% > 4 wt.%. The average 1000*V / (Mn+100Ga) value of apatite is 0.41 < 2, and the average 100*X Cl / X OH / X F The ratio is 5.46 < 20, therefore it is comprehensively judged as a non-ore-forming rock mass with low oxygen fugacity, high water content, and poor volatile matter, which is consistent with the actual geological conditions.

[0042] Several rock mass identification examples in a certain region further demonstrate the effectiveness of the mineral exploration method of this invention.

[0043] Table 2. Zircon trace element composition and related parameters of some rock masses in a certain area.

[0044]

[0045] Note: The unit for trace elements is ppm.

[0046] Table 3. Calculation results of average zircon water content in rock masses in a certain area.

[0047]

[0048] Table 4. Major element data and related parameters of apatite in a certain area's rock mass.

[0049]

[0050] Note: The unit for the content of major components is wt%.

[0051] Table 5. Trace element data and related parameters of apatite in a certain area's rock mass.

[0052]

[0053] Note: The unit for trace elements is ppm.

[0054] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0055] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for jointly determining the iron-copper mineralization potential of intermediate-acidic intrusive rocks based on zircon and apatite, characterized in that, Includes the following steps: (1) Collect intermediate-acidic intrusive rock samples from the area to be explored, sort zircon and apatite, and conduct major element analysis and trace element analysis; (2) The method for assessing the mineralization potential of intermediate-acidic rock masses is as follows: Condition 1: Oxygen fugacity determination: Calculate the oxygen fugacity ΔFMQ of the sample corresponding to the zircon Ti thermometer. When the average ΔFMQ of zircon is ≥2 and the average oxygen fugacity of apatite is 1000... When V / (Mn+100Ga)≥2, the intrusive rock is judged to have mineralization potential; when the average oxygen fugacity of zircon ΔFMQ<2 and the average oxygen fugacity of apatite is 1000 When V / (Mn+100Ga) < 2, the intrusive rock is determined to have no mineralization potential; V, Mn, and Ga refer to the contents of vanadium, manganese, and gallium, respectively, in apatite, in ppm. Condition 2: Water Content Determination: Calculate the zircon Yb / Gd ratio and water content. When the average zircon Yb / Gd ratio is ≥20 and the average H2O content is ≥4.0 wt.%, the intrusive rock is determined to have mineralization potential; when the average zircon Yb / Gd ratio is <20 and the average H2O content is <4.0 wt.%, the intrusive rock is determined to have no mineralization potential. Condition 3: Volatile matter content determination: Calculate 100% of apatite. X Cl / X OH / X F The ratio, when the average value of apatite is 100 X Cl / X OH / X F When the apatite concentration is ≥20, the intrusive rock is considered to have mineralization potential; when the average apatite concentration is 100... X Cl / X OH / X F If the value is less than 20, the intrusive rock is determined to have no mineralization potential. Condition 4: If all the conditions for mineralization potential in conditions 1 to 3 are met, the rock mass is determined to be an iron-copper ore-forming rock mass, and the prospecting target area is delineated; otherwise, it is determined to be a non-ore-forming rock mass.

2. The method for determining the iron-copper mineralization potential of intermediate-acidic intrusive rocks based on the combined use of zircon and apatite according to claim 1, characterized in that, Step (1) involves the following steps: based on the exposure of intermediate-acidic rock bodies in the area to be explored, systematically collect unweathered and altered intermediate-acidic intrusive rock samples, sort zircon and apatite, and prepare targets. Cathodoluminescence images of zircon and apatite targets were obtained. Unaltered zircon and apatite with clear crystalline zoning were selected for electron probe microanalysis and LA-ICP-MS trace element analysis.

3. The method for determining the iron-copper mineralization potential of intermediate-acidic intrusive rocks based on the combined use of zircon and apatite according to claim 1, characterized in that, In step (1), the intermediate-acidic intrusive rock samples collected refer to intrusive rocks with whole-rock SiO2 > 66 wt.% and LOI < 3 wt.%, and more than 150 zircon and apatite particles are selected for each sample.

4. The method for determining the iron-copper mineralization potential of intermediate-acidic intrusive rocks based on the combined use of zircon and apatite according to claim 1, characterized in that, The major elements of zircon analyzed in step (1) include Zr and Si; the trace elements of zircon include Ti, Sr, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Y, Hf, Pb, Th and U. The major elements analyzed in apatite include SiO2, FeO, MnO, MgO, CaO, Na2O, P2O5, SrO, F, Cl, and SO3; the trace elements include Ca, V, Mn, Ga, Ge, Sr, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Y, Pb, Th, and U.

5. The method for determining the iron-copper mineralization potential of intermediate-acidic intrusive rocks based on the combined use of zircon and apatite according to claim 1, characterized in that, In step (2), 100 X Cl / X OH / X F The ratio is a discriminant constructed from the molar fraction ratio of fluorine, chlorine and hydroxyl groups in apatite, and is used to indicate the content of volatiles in rocks.

6. The method for determining the iron-copper mineralization potential of intermediate-acidic intrusive rocks based on the combined use of zircon and apatite according to claim 1, characterized in that, The mineralization potential refers to the mineralization potential of porphyry-skarn type iron-copper deposits.

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