METHOD FOR DISCRIMINATING ORE PROSPECTING TYPES BASED ON COMPOSITIONAL CHANGE OF EPIDOTE

Disclosed is a method for discriminating ore prospecting types based on compositional change of epidote, in particular including the following steps: metallogenic zone delineation; sample collection and analysis: collecting bedrock samples containing epidote from the metallogenic zone according to certain sampling units; trace element analysis and testing; data processing and interpretation: processing obtained initial recorded data using LADRlib software; and ore prospecting type discrimination. The method has the advantages that the description of epidote altered minerals in a magma-hydrothermal metallogenic system is improved from macroscopic characterization to microscopic quantitative interpretation of trace element change in the epidote altered minerals by using an LA-ICP-MS in-situ analysis technology, and the trace element change is linked with the response of the ore prospecting type at an ore concentration area scale, thus overcoming the difficulties of low efficiency, long period and high cost in the traditional method for discriminating the ore prospecting type.

FIELD OF TECHNOLOGY

The present invention relates to the technical field of ore prospecting in geological exploration, and in particular to a method for discriminating ore prospecting types based on compositional change of epidote.

BACKGROUND

With the comprehensive coverage of geological exploration in recent decades, the degree of mineral exploration has gradually increased, the discovery of new deposits has become increasingly difficult, and there is an urgent need to carry out new ore prospecting technical methods to guide the ore prospecting breakthrough, of which the primary task is to quickly discriminate the ore prospecting types.

The traditional discrimination of ore prospecting types has the following shortcomings: comprehensive research, such as large-scale mapping and systematic sampling analysis, is required before exploration and evaluation to clarify the orebody occurrence, the relationship with wall rocks, metallogenesis, ore-forming materials and ore-forming fluid sources, etc., so as to determine the genesis of deposits or ore prospecting types, resulting in long period and high cost, which cannot meet the urgent need for rapid exploration and evaluation at the ore concentration area scale.

SUMMARY

To solve the technical problem above, the present invention provides a method for discriminating ore prospecting types based on compositional change of epidote. The method provided by the present invention has the advantages that the description of epidote altered minerals in a magma-hydrothermal metallogenic system is improved from macroscopic characterization to microscopic quantitative interpretation of trace element change in the epidote altered minerals by using an advanced LA-ICP-MS (laser ablation inductively coupled plasma mass spectrometry) in-situ analysis technology, and the trace element change is linked with the response of the ore prospecting type at an ore concentration area scale, thus overcoming the difficulties of low efficiency, long period and high cost in the traditional method for discriminating the ore prospecting types.

The present invention is achieved through the following technical solutions: a method for discriminating ore prospecting types based on compositional change of epidote specifically includes the following steps:metallogenic zone delineation: conducting data collection according to a selected research area, and comprehensively analyzing metallogenic potential to delineate a metallogenic favorable zone;sample collection and analysis: collecting bedrock samples containing epidote from the metallogenic zone according to certain sampling units in step (1), where the density of sample points collected in the research area is 1-3 samples/Km2;trace element analysis and testing: grinding the samples collected in step (2) into a probe sheet and a laser in-situ target, firstly observing corresponding epidote alteration characteristics of the probe sheet and the laser in-situ target under a microscope, and recording epidote alteration types in detail; then performing electron probe compositional analysis to determine the chemical composition and type of the epidote, and marking the chemical composition and type of the epidote; and carrying out in-situ microdomain element analysis of laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS) on the mineral which is confirmed as the epidote by the electron probe composition, so as to obtain recorded data of each test point;data processing and interpretation: processing the initial recorded data obtained in step (3) by using LADRlib software;(5) ore prospecting type discrimination: processing data obtained in step (4) by using Excel, defining the contents of La, Y, Gd, Yb, Sr and As elements in the obtained epidote as V(La), V(Y), V(Gd), V(Yb), V(Sr)and V(As), respectively, and substituting the content of La element in the obtained epidote into the following formula (1):C1=0.28493059*lgVLa+0.5762992calculating a discriminant factor C1, when C1 is greater than lg(V(Y)), discriminating that a deposit to which the epidote belongs is a porphyry type deposit; and when C1 is less than 1 g(V(Y)), discriminating that a deposit to which the epidote belongs is an epithermal type deposit; andsubstituting the contents of Gd and Yb elements in the obtained epidote into the following formula (2):C2=lgVGd+Yb+1.5calculating a discriminant factor C2, when C2 is less than lg(V(Sr/As)), discriminating that a deposit to which the epidote belongs is a porphyry type deposit; and when C2 is greater than lg(V(Sr/As)), discriminating that a deposit to which the epidote belongs is an epithermal type deposit.

Through the technical solution above, geochemical characteristics of the epidote are introduced into the discrimination of ore prospecting types, which effectively makes up for the defect that there is no quantitative discrimination method at present, and the calculation method is more novel. Further, in step (5), the formula (1) is to perform logarithm transformation on the contents of La and Y elements in the epidote to obtain lg(V(La)) and lg(V(y)), to plot with lg(V(La)) as the abscissa and lg(V(Y)) as the ordinate, respectively, and to obtain a demarcation line between the porphyry type deposit and epithermal type deposit based on the plotting range.

Further in step (5), the formula (2) is to perform logarithm transformation on the contents of Gd, Yb, Sr and As elements in the epidote to obtain lg(V(Gd+Yb)) and lg(V(Sr/As)), to plot with lg(V(Gd+Yb)) as the abscissa and lg(V(Sr/As)) as the ordinate, respectively, and to obtain a demarcation line between the porphyry type deposit and epithermal type deposit based on the plotting range.

Further, step (2) includes the following steps: positioning each sample point by using a GPS positioning system, collecting coordinate data X and Y, taking field photos, and making detailed field records to describe lithology, alteration and mineralization characteristics of each sample.

Further, in step (4), the specific process is as follows:(1) data import: importing the recorded data in a csv format obtained from an in-situ microdomain test point of each epidote sample into the LADRlib software in batches;(2) data interpretation: obtaining a microdomain element integral curve of the sample at each observation point, and adjusting start time and end time of the integral curve of each observation point one by one according to the principle of ensuring the flattest and widest signal range of the selected element integral curve;(3) data filtration: rejecting invalid data therein according to anomaly peaks of the element integral curve; and(4) data export: summarizing interpreted and filtered data of each single-point microdomain, and then exporting the data in batch as a file in a csv format.

Through the technical solution above, the influence of other auxiliary minerals on the calculation of the discriminant factors of trace elements in the epidote mineral can be eliminated, and the method may be suitable for the processing of trace element data of the epidote in different types of deposits.

Preferably, the research area is Zhunuo ore concentration area.

In addition, application of a method for discriminating ore prospecting types based on compositional change of epidote for the discrimination of an epithermal type Ag-Au deposit is provided. Quantitative indexes of trace elements in the epidote are as follows: calculating discriminant factors C1=0.28493059*lg(V(La))+0.5762992 and C2=lg(V(Gd+Yb))+ 1.5, respectively, according to the formula (1) and the formula (2); and when C1 is less than lg(V(Y)) and C2 is greater than lg(V(Sr+As)), discriminating that a deposit to which the epidote belongs is an epithermal type deposit.

Application of a method for discriminating ore prospecting types based on compositional change of epidote for the discrimination of a porphyry type Cu deposit is provided. Quantitative indexes of trace elements in the epidote are as follows: calculating discriminant factors C1=0.28493059*lg(V(La))+0.5762992 and C2=lg(V(Gd+Yb))+ 1.5, respectively, according to the formula (1) and the formula (2); and when C1 is greater than lg(V(Y)) and C2 is less than lg(V(Sr+As)), discriminating that a deposit to which the epidote belongs is a porphyry type deposit.

Through the technical solution above, the present invention belongs to a microscopic quantitative discrimination method, which is more scientific, reasonable and accurate in comparison with the traditional macroscopic qualitative discrimination method.

(1) The description of epidote altered minerals in a magma-hydrothermal mineralization system is improved from macroscopic characterization to microscopic quantitative interpretation of trace element changes by using an advanced LA-ICP-MS in-situ analysis technology, and the trace element change is linked with the response of the ore prospecting types in an ore concentration area scale, which effectively makes up for the defect that there is no quantitative discrimination method at present, and overcomes the difficulties of low efficiency, long period and high cost in the traditional method for discriminating the ore prospecting types.

(2) It is proposed to use epidote as a characteristic mineral for discrimination, which has good connectivity and wide physical and chemical conditions, is sensitive to the changes of physical and chemical conditions, can be formed at high temperature, medium temperature and low temperature, is uniform in spatial distribution, develops in different alteration zones, and thus is more conducive to the distinction of different mineralization types.

(3) The characteristic elements, such as La, Y, Sr, As, Gd and Yb, in the epidote are sensitive to the changes of temperature, pH and redox conditions.

(4) An optimal discriminant factor is provided, which may be used for accurately distinguishing different types of deposits, and can provide a theoretical basis for the optimization and selection of further ore prospecting and exploration methods in the ore deposit scale and reduce the exploration risk.

DESCRIPTION OF THE EMBODIMENTS

The present invention is further described below with reference to the accompanying drawings.

A method for discriminating ore prospecting types based on compositional change of epidote specifically includes the following steps:(1) Metallogenic zone delineation: data is collected according to a selected research area, and metallogenic potential is comprehensively analyzed, so as to delineate a metallogenic favorable zone.(2) Sample collection and analysis: bedrock samples containing epidote are collected from the metallogenic zone according to certain sampling units in step (1), where the density of sample points collected in the research area is 1-3 samples/Km2.(3) Trace element analysis and testing: the samples collected in step (2) are ground into a probe sheet and a laser in-situ target, corresponding epidote alteration characteristics of the probe sheet and the laser in-situ target are firstly observed under a microscope, and epidote alteration types are recorded in detail. Then, electron probe compositional analysis is performed to determine the chemical composition and type of the epidote, and the chemical composition and type of the epidote are marked; and the mineral which is confirmed as the epidote by the electron probe composition is subjected to in-situ microdomain element analysis of laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS), so as to obtain recorded data of each test point.(4) Data processing and interpretation: the initial recorded data obtained in step (3) are processed by using LADRlib software, with specific process as follows:(1) data import: importing the recorded data in a csv format obtained from an in-situ microdomain test point of each epidote sample into the LADRlib software in batches;(2) data interpretation: obtaining a microdomain element integral curve of the sample at each observation point, and adjusting start time and end time of the integral curve of each observation point one by one according to the principle of ensuring the flattest and widest signal range of the selected element integral curve;(3) data filtration: rejecting invalid data therein according to anomaly peaks of the element integral curve; and(4) data export: summarizing interpreted and filtered data of each single-point microdomain, and then exporting the data in batch as a file in a csv format.(5) Ore prospecting type discrimination: data obtained in step (4) are processed by using Excel, the contents of La, Y, Gd, Yb, Sr and As elements in the obtained epidote are defined as V(La), V(Y), V(Gd), V(Yb), V(Sr)and V(As), respectively, and the content of La element in the obtained epidote is substituted into the following formula (1):C1=0.28493059*lgVLa+0.5762992a discriminant factor C1 is calculated, when C1 is greater than lg(V(Y)), it is discriminated that a deposit to which the epidote belongs is a porphyry type deposit; and when C1 is less than lg(V(Y)), it is discriminated that a deposit to which the epidote belongs is an epithermal type deposit;the contents of Gd and Yb elements in the obtained epidote are substituted into the following formula (2):C2=lgVGd+Yb+1.5a discriminant factor C2 is calculated, when C2 is less than lg(V(Sr/As)), it is discriminated that a deposit to which the epidote belongs is a porphyry type deposit; and when C2 is greater than lg(V(Sr/As)), it is discriminated that a deposit to which the epidote belongs is an epithermal type deposit.

The specific steps are as follows:step one, calculation of the discriminant factor C1performing logarithm transformation on the contents of La and Y elements in the obtained epidote to obtain lg(V(La)) and lg(V(Y)), plotting with lg(V(La)) as the abscissa and lg(V(Y)) as the ordinate, respectively, obtaining a demarcation line between the porphyry type deposit and the epithermal type deposit based on the plotting range, and calculating the discriminant factor C1 by using the following formula:C1=0.28493059*lgVLa+0.5762992step two, calculation of the discriminant factor C2performing logarithm transformation on the contents of Gd, Yb, Sr and As elements in the obtained epidote to obtain lg(V(Gd+Yb)) and lg(V(Sr/As)); plotting with the lg(V(Gd+Yb)) as the abscissa and the lg(V(Sr/As)) as the ordinate, obtaining a demarcation line between the porphyry type deposit and the epithermal type deposit based on the plotting range, and calculating the discriminant factor C2 using the following formula:C2=lgVGd+Yb+1.5step three, discrimination of the ore prospecting typesubstituting the content of La element in the obtained epidote into the formula above to calculate the discriminant factor C1, when C1 is greater than lg(V(Y)), discriminating that a deposit to which the epidote belongs is a porphyry type deposit; and when C1 is less than lg(V(Y)), discriminating that a deposit to which the epidote belongs is an epithermal type deposit (FIG.1); andsubstituting the contents of Gd and Yb elements in the obtained epidote into the formula above to calculating the discriminant factor C2, when C2 is less than lg(V(Sr/As)), discriminating that a deposit to which the epidote belongs is a porphyry type deposit; and when C2 is greater than lg(V(Sr/As)), discriminating that a deposit to which the epidote belongs is an epithermal type deposit (FIG.1).

On the basis of the above solution, step (2) includes the following steps: positioning each sample point by using a GPS positioning system, collecting coordinate data X and Y, taking field photos, and making detailed field records to describe lithology, alteration and mineralization characteristics of each sample.

On the basis of the above solution, preferably, the research area is the Zhunuo ore concentration area, specifically as follows:a. The existing geological, geophysical, geochemical and remote sensing data in the Zhunuo ore concentration area are collected systematically, the metallogenic potential is analyzed comprehensively, metallogenic favorable zones A and B are delineated, and sampling cells are marked off, where the spacing between the cells is 1 km×1 km, and the area is 1 km2(FIG.2).b. Field sample collection:The metallogenic favorable zones A and B are selected for the collection of epidote samples on the earth surface. During sampling, the sample number, sampling coordinates (X and Y), lithology category, alteration category, mineralization category and sampling site are recorded in detail, specifically as shown in the following table:

c. Sample test:The collected samples are ground into a probe sheet and a laser in-situ target, corresponding epidote alternation characteristics of the probe sheet and the laser in-situ target are observed under a microscope, and epidote alternation types (hydrothermal vein type or disseminated type) of the probe sheet and the laser in-situ target are recorded in detail. Electron probe compositional analysis is performed to determine the chemical composition and type of the epidote, and the chemical composition and type are marked by using a marking pen. The mineral with the composition confirmed as the epidote by the electron probe testing is subjected to in-situ microdomain element analysis of laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS) (FIG.3).d. Data processing: the LADRlib software is used for data processing, including four steps: (1) data import: importing the recorded data in a csv format obtained from an in-situ microdomain test point of each epidote sample into the LADRlib software in batches; (2) data interpretation: obtaining a microdomain element integral curve of the sample at each observation point, and adjusting start time and end time of the integral curve of each observation point one by one according to the principle of ensuring the flattest and widest signal range of the selected element integral curve; (3) data filtration: rejecting invalid data therein according to anomaly peaks of the element integral curve, e.g., the data such as hitting inclusions (Ti, Ag, As elements anomaly peaks) or hitting through epidote minerals (K, Mg elements anomaly peaks); and (4) data export: summarizing interpreted and filtered data of each single-point microdomain, and then exporting the data in batch as a file in a csv format.e. Ore prospecting type discrimination:Final data (Table 1) processed by using Excel is used to discriminate that an ore prospecting zone B is an ore prospecting type of a porphyry type Cu deposit and an ore prospecting zone A is an ore prospecting type of an epithermal type Ag-Au deposit (FIG.1) according to calculation results of the discriminant factors C1 and C2.

The ore prospecting method provided by the present invention has the advantages of short test time, low cost, convenience and efficiency, environmental protection, and capability of effectively shortening the mineral exploration period without damaging the environment, greatly improving the accuracy of rapid discrimination and target prediction of the ore prospecting type at the ore concentration area scale and reducing the exploration risk, which is a new and indispensable exploration means and method, and has an important promotion and popularization value.

In addition, application of a method for discriminating ore prospecting types based on compositional change of epidote above for the discrimination of an epithermal type Ag-Au deposit is provided, where the contents of La, Y, Gd, Yb, Sr and As elements in the obtained epidote are defined as V(La), V(Y), V(Gd), V(Yb), V(Sr)and V(As), respectively.

(1) Calculation of a discriminant factor C1 is as follows:

performing logarithm transformation on the contents of La and Y elements in the obtained epidote to obtain lg(V(La)) and lg(V(y)), plotting with lg(V(La)) as the abscissa and lg(V(Y)) as the ordinate, respectively, obtaining a demarcation line between a porphyry type deposit and an epithermal type deposit based on the plotting range, and calculating the discriminant factor C1 by using the following formula:

(2) Calculation of a discriminant factor C2 is as follows:

performing logarithm transformation on the contents of Gd, Yb, Sr and As elements in the obtained epidote to obtain lg(V(Gd+Yb)) and lg(V(Sr/As)); plotting with the lg(V(Gd+Yb)) as the abscissa and the lg(V(Sr/As)) as the ordinate, obtaining a demarcation line between a porphyry type deposit and an epithermal type deposit based on the plotting range, and calculating the discriminant factor C2 by using the following formula:

(3) Discrimination of ore prospecting type is as follows:

substituting the content of La element in the obtained epidote into the formula above to calculate the discriminant factor C1, when C1 is less than lg(V(Y)) and C2 is greater than lg(V(Sr/As)), discriminating that a deposit to which the epidote belongs is the epithermal type deposit.

Application of a method for discriminating ore prospecting types based on compositional change of epidote above for the discrimination of a porphyry type Cu deposit is provided, where the contents of La, Y, Gd, Yb, Sr and As elements in the obtained epidote are defined as V(La), V(Y), V(Gd), V(Yb), V(Sr)and Y(As), respectively.

(1) Calculation of a discriminant factor C1 is as follows:

performing logarithm transformation on the contents of La and Y elements in the obtained epidote to obtain lg(V(La)) and lg(V(Y)), plotting with lg(V(La)) as the abscissa and lg(V(Y)) as the ordinate, respectively, obtaining a demarcation line between a porphyry type deposit and an epithermal type deposit based on the plotting range, and calculating the discriminant factor C1 by using the following formula:

(2) Calculation of a discriminant factor C2 is as follows:

performing logarithm transformation on the contents of Gd, Yb, Sr and As elements in the obtained epidote to obtain lg(V(Gd+Yb)) and lg(V(Sr/As)); plotting with the lg(V(Gd+Yb)) as the abscissa and the lg(V(Sr/As)) as the ordinate, obtaining a demarcation line between a porphyry type deposit and an epithermal type deposit based on the plotting range, and calculating the discriminant factor C2 by using the following formula:

(3) Discrimination of an ore prospecting type is as follows:

substituting the content of La element in the obtained epidote into the formula above to calculate the discriminant factor C1, when C1 is greater than lg(V(Y)) and C2 is less than lg(V(Sr/As)), discriminating that a deposit to which the epidote belongs is the porphyry type deposit.

The foregoing embodiments merely express one or several embodiments of the present invention, the description is relatively specific and detailed, but cannot be construed as a limitation to the scope of the present invention. It should be pointed out that those of ordinary skilled in the art can make several transformations and improvements without departing from the concept of the present invention, which all belong to the scope of protection of the present invention.