CN105548339B - A kind of method of the thorium lead age of the measure bastnaesite sample based on ion microprobe - Google Patents
A kind of method of the thorium lead age of the measure bastnaesite sample based on ion microprobe Download PDFInfo
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Abstract
The invention discloses a kind of method of the thorium lead age of the measure bastnaesite sample based on ion microprobe, including：Sample target will be made in bastnaesite sample and bastnaesite standard substance insertion epoxy resin, and the sample target is put into the sample cavity of ion microprobe；Oxygen gas plasma ion gun and the bastnaesite sample focused in directional light mode on the sample target are used, to produce the secondary ion of the bastnaesite sample；Make electric field and magnetic field that the secondary ion of the bastnaesite sample passes through in the ion microprobe, to realize angle and speed double focusing and reach ion signal detecting system；The primeval lead thorium ratio in the secondary ion of the bastnaesite sample is detected using the ion signal detecting system, the primeval lead thorium ratio is corrected with the lead thorium ratio after being corrected；The thorium lead age of the bastnaesite sample is calculated using the lead thorium ratio after correction.
Description
Technical field
The present invention relates to a kind of geochemical field, more particularly to a kind of measure fluorine carbon cerium based on ion microprobe
The method of the thorium lead age of sample ore product.
Background technology
Bastnaesite REE (CO3)F.CaCO3It is a kind of light rare earth carbonate mineral, it is a kind of important rare earth resources,
In order to preferably develop this resource, it is necessary to there is deep understanding to its geologic origin.And its Formed age is exactly
One important origin cause of formation key element.The accurate ore -forming age that obtains is research Mineralizing setting, the precondition of the known geologic event of contrast.
The year method of determining to bastnaesite has had isotopic dilution Thermal Ionization Mass Spectrometry (ID-TIMS) (document in the world
1：Sal’nikova et al.,Bastnaesite:A Promising U–Pb Geochronological Tool,2010)
With laser ablation Inductively coupled plasma-mass spectrometry (LA-ICPMS) (document 2：Yang et al.,In situ U–Pb
Dating of bastnaesite by LA-ICP-MS, 2014), both, which determine year method, respectively advantage and disadvantage.
Isotopic dilution Thermal Ionization Mass Spectrometry (ID-TIMS) is most accurately to determine year method, because bastnaesite is a kind of
The mineral of solid granular, thus can whole particle with acid be dissolved into solution at high temperature, then measure solution in uranium and
Lead content, then the age is calculated, the uranium and the ratio of lead so obtained is whole particle (particle about 10-5G to 10-3G) letter
Breath, because the sample size of collection is big, so obtained age accuracy is very high, and generally less than 0.1%, such as it can obtain fluorine carbon
The cerium ore deposit age is 200 ± 0.2Ma (1000000 years).
But isotopic dilution Thermal Ionization Mass Spectrometry need whole bastnaesite particle is dissolved, therefore obtain be
The average age of whole bastnaesite, and in fact, due to alteration, therefore fluorine carbon may be undergone in the growth course of bastnaesite
Cerium ore deposit is on big yardstick and without the identical age, if measuring fluorine carbon only with isotopic dilution Thermal Ionization Mass Spectrometry
Cerium ore deposit age, the average age measured by it can not reflect real age of the bastnaesite on big yardstick.
Laser ablation Inductively coupled plasma-mass spectrometry (LA-ICPMS) can make up above shortcoming, and it can be at 50 microns
Yardstick in determine bastnaesite real age.For example, bastnaesite is grown since very small nucleus, if raw
It is long that tens microns to several millimeters can be grown in a geologic event slowly, such as it is long in 500 1000000 years (500Ma) left and right
Three millimeters, if after 200 1000000 years, and on original crystal grow new crystal, what this grew later
Several millimeters (300Ma) and several millimeters (500Ma) growing at first age information are simultaneously differed, if using isotope
Thermal Ionization Mass Spectrometry is diluted, then the annual bearing of determining being likely to be obtained is 400Ma, but this is not consistent (real with truth
Situation is to grow up in two times, a 300Ma, a 500Ma), and if using laser ablation Inductively coupled plasma-mass spectrometry, then
500 ± 15Ma can be measured in the core portion yardstick of bastnaesite, edge yardstick obtains 300 ± 9Ma (laser ablation inductives etc.
The accuracy of ion mass spectrometry is about 3%).
But the method that existing laser ablation Inductively coupled plasma-mass spectrometry determines the bastnaesite age is to determine fluorine
The uranium lead age of carbon cerium ore deposit, can be due to that bastnaesite contains higher thorium (Th), and the uranium (U) contained is than relatively low, therefore, existing
The method that some use laser ablation Inductively coupled plasma-mass spectrometries determine the bastnaesite age has very big error.This be because
For in bastnaesite, lead can be decayed into by calculating uranium206Pb=238U(eλ238t- 1) uranium lead age t is obtained, can also
Lead is decayed into thorium208Pb=232Th(eλ232t- 1) thorium lead age t is obtained, here, uranium (238U) decay into lead (206Pb), thorium
(232Th) decay into lead (208Pb), it is two independent decay serieses, accurately measures any one and can be obtained by t.Laser is shelled
Erosion Inductively coupled plasma-mass spectrometry uses measurement uranium lead age, and its problem is, thorium contains two isotopes232Th
With230Th, wherein, utilize232Th can calculate thorium lead age, and230Th can but be decayed into206Pb, if this resulted in using
It is existing that uranium lead age is measured with laser ablation Inductively coupled plasma-mass spectrometry, then measure206Pb some be230Th
What decay came, rather than uranium (238U) decay what is come, therefore which part is existing method be difficult to differentiate between206Pb is230Th decays come
, which part206Pb be uranium (238U) decay what is come, now, can be all if thorium content is low206Pb regards uranium as
(238U) decay come, and by thorium decay Lai it is seldom, the influence to uranium lead age is also little.But, if thorium content is higher,
Also all206Pb regard as uranium (238U) decay what is come, that result is exactly206Pb=238U(eλ238t- 1) in206Pb is than true
By uranium (238U) decay what is come206Pb is bigger, and the age t now calculated also can be bigger than normal.So the problem of, shows document above 2
Occur in some laser ablation Inductively coupled plasma-mass spectrometries, wherein DLC43 real age should be 12Ma, but used
Existing method, that calculate is 20Ma.Therefore existing laser ablation Inductively coupled plasma-mass spectrometry (namely is determined
The uranium lead age of bastnaesite) although the age of bastnaesite can be determined on small yardstick, it is due to that bastnaesite contains
There is a higher thorium (Th), and the uranium (U) contained is than relatively low, therefore the bigger error at the age of existing method measurement bastnaesite.
The content of the invention
The individual embodiment of the present invention there is provided a kind of thorium of the measure bastnaesite sample based on ion microprobe
The method of lead age.
According to an aspect of this disclosure, there is provided a kind of measure bastnaesite sample based on ion microprobe
The method of thorium lead age, it is characterised in that including：
Sample target will be made in bastnaesite sample and bastnaesite standard substance insertion epoxy resin, and by the sample
Target is put into the sample cavity of ion microprobe；
Use oxygen gas plasma ion gun and the bastnaesite focused in directional light mode on the sample target
Sample, to produce the secondary ion of the bastnaesite sample；
Make electric field and magnetic field that the secondary ion of the bastnaesite sample passes through in the ion microprobe, with reality
Existing angle and speed double focusing simultaneously reach ion signal detecting system；
The primeval lead thorium ratio in the secondary ion of the bastnaesite sample is detected using the ion signal detecting system
ValueAnd according to the primeval lead thorium ratio and the ratio in the secondary ion of the bastnaesite sample
Between positive correlation, the primeval lead thorium ratio is corrected with the lead thorium ratio after being correctedWherein u
Represent unknown；
Using the lead thorium ratio after correctionAnd according to formulaTo calculate the fluorine carbon
The thorium lead age t of cerium sample ore productu, wherein λ232It is decay coefficient.
According to one embodiment of the disclosure, the surface of the sample target is also polished and gold-plated processing, the ion
Signal detection system is electron multiplier；The magnetic field intensity in the magnetic field is adjusted so that the secondary of the bastnaesite sample
In ion204Pb+,206Pb+,207Pb+,208Pb+,140Ce16O2 19F2 +,232Th+,238U+,232Th 16O+,238U16O+With232Th16O2 +
Pass sequentially through magnetic field and reach the ion signal detecting system.
According to one embodiment of the disclosure, the parameter of the ion microprobe includes：Parallel light focusing O2 -It is strong
Spend for 8nA to 10nA, primary ions beam diameter is about 20*30 μm, primary ions accelerating potential is -13KV, secondary ion accelerates
Voltage is+10KV, and entrance slit is 60 μm, and contrast diaphragm is 400 μm, and energy slit is 60eV, and exit slit is 180 μm,
Measurement group number is 7, and single-node analysis precision is 2.8%-3.5%, and single-node analysis total time is about 15min, the secondary ion matter
The mass resolution of spectrometer is about 8000.
According to one embodiment of the disclosure, in the secondary ion of the primeval lead thorium ratio and the bastnaesite sample
RatioBetween positive correlation meet power function relationship represented by equation 2 below, wherein A and E are normal
Number：
Formula 2.
It is described that the primeval lead thorium ratio is corrected with the lead after being corrected according to one embodiment of the disclosure
Thorium ratio, including：
The institute at known age is detected using with detecting the bastnaesite sample identical mode on the sample target
Bastnaesite standard substance is stated, to obtain multigroup standard substance measurement data；According in multigroup standard substance measurement data
'sWithAnd be fitted according to the power function relationship of formula 2, so as to obtain constant A and constant E value.
It is described that the primeval lead thorium ratio is corrected with the lead after being corrected according to one embodiment of the disclosure
Thorium ratio, including：
By the ratio in the secondary ion of the bastnaesite sample at unknown ageSubstitute into the power of formula 2
Functional relation, and calculated using the value for being fitted obtained A and E shown in equation 5 below
Formula 5.
It is described that the primeval lead thorium ratio is corrected with the lead after being corrected according to one embodiment of the disclosure
Thorium ratio, including：
By the bastnaesite standard substance at the known ageRecommendation withIt
Be used for the correction coefficient K shown in formula 6, wherein st represent, it is known that
Formula 6.
It is described that the primeval lead thorium ratio is corrected with the lead after being corrected according to one embodiment of the disclosure
Thorium ratio, including：
The primeval lead thorium ratio is multiplied by using the correction coefficient KObtain the bastnaesite at unknown age
Lead thorium ratio after the correction of sample
It is described according to formula according to one embodiment of the disclosureTo calculate the fluorine carbon cerium
The thorium lead age t of sample ore productu, including：
Using the lead thorium ratio after the correctionAnd according to formulaIt is described to calculate
The thorium lead age t of bastnaesite sampleu, wherein decay coefficient λ232=4.9475*10-11。
According to one embodiment of the disclosure, it is known that the bastnaesite standard substance at age includes bastnaesite standard
Material K-9, the bastnaesite sample at unknown age includes bastnaesite sample LiZ and DLC016.
Compared with prior art, the present invention has advantages below：Utilize the survey based on ion microprobe of the disclosure
Determine the thorium lead age of bastnaesite sample, can accurately obtain the age of bastnaesite sample so that bastnaesite sample
The error at age is smaller, and can reflect real age of the bastnaesite sample on small yardstick.
Brief description of the drawings
For clearer explanation technical scheme, the accompanying drawing used required in being described below to embodiment
It is briefly described, it is clear that, drawings in the following description are only some embodiments of the present invention, general for this area
For logical technical staff, on the premise of not paying creative work, other accompanying drawings can also be obtained according to these accompanying drawings.
Fig. 1 is a kind of thorium lead age of measure bastnaesite sample based on ion microprobe of the embodiment of the present invention
Method schematic flow sheet；
Fig. 2 is the structural representation of the ion microprobe of the embodiment of the present invention；And
Fig. 3 shows the bastnaesite of all ages and classesWithPositive correlation schematic diagram.
Embodiment
Below in conjunction with the accompanying drawing in the embodiment of the present invention, the technical scheme in the embodiment of the present invention is carried out clear, complete
Whole description, it is clear that described embodiment is only a part of embodiment of the present invention, the embodiment being not all of, based on this hair
Embodiment in bright, the every other implementation that those of ordinary skill in the art are obtained under the premise of creative work is not paid
Example, belongs to the scope of protection of the invention.
In order to avoid isotopic dilution Thermal Ionization Mass Spectrometry (ID-TIMS) and laser ablation Inductively coupled plasma-mass spectrometry
(LA-ICPMS) shortcoming, so as to which the method in the age of less yardstick Accurate Determining bastnaesite, the disclosure is
A kind of method for the measure bastnaesite thorium lead age based on ion microprobe developed based on ion microprobe.
As shown in figure 1, present disclose provides a kind of thorium D of the measure bastnaesite sample based on ion microprobe
The method at age, it is characterised in that including：
Sample target will be made in bastnaesite sample and bastnaesite standard substance insertion epoxy resin, and by the sample
Target is put into the sample cavity of ion microprobe；
Use oxygen gas plasma ion gun and the bastnaesite focused in directional light mode on the sample target
Sample, to produce the secondary ion of the bastnaesite sample；
Make electric field and magnetic field that the secondary ion of the bastnaesite sample passes through in the ion microprobe, with reality
Existing angle and speed double focusing simultaneously reach ion signal detecting system；
The primeval lead thorium ratio in the secondary ion of the bastnaesite sample is detected using the ion signal detecting system
ValueAnd according to the primeval lead thorium ratio and the ratio in the secondary ion of the bastnaesite sample
Between positive correlation, the primeval lead thorium ratio is corrected with the lead thorium ratio after being correctedWherein u
Represent unknown；
Using the lead thorium ratio after correctionAnd according to formulaTo calculate the fluorine carbon
The thorium lead age t of cerium sample ore productu, wherein λ232It is decay coefficient.
For example, the thorium lead age in the disclosure, is the term in an isotopic geochronology.In geology, we
The age for calculating geological sample was calculated using the half-life period of radioactive element.Such as, if contained in geological sample
Thorium232Th, by the decay t of certain time, can be changed into lead208Pb, we are according to decay formula208Pb=232Th(eλ232t- 1),
For example, as it is known that decay coefficient λ232=4.9475*10-11, then according to the thorium D ratio measured208Pb/232Th, can be calculated
Go out time t, here it is thorium lead age.Thorium lead age in disclosure measurement sample, can accurately obtain bastnaesite sample
Age so that the error at the age of bastnaesite sample is smaller, and can reflect bastnaesite sample on small yardstick
Real age.For example, in the disclosure suitable sample can be selected so that acquisition when detecting bastnaesite sample
Lead208Pb is by thorium232What Th decayed and come, it now can more accurately calculate the thorium lead age of bastnaesite sample.
For example, as shown in Fig. 2 the ion microprobe in the disclosure (is called ion probe, detection is used as using ion
Instrument), as other mass spectrographs, it is made up of three parts：Ion gun, mass spectrograph and ion signal detecting system.Different
It is that ion gun in ion microprobe is to bombard sample surfaces by the focusing primary ions beam of high-energy in a vacuum
Sputtering phenomenon and produce ion, these are referred to as secondary ion with ions of sample signal, wherein+represent it is ionic condition,
The signal that can be measured all is the signal of ionic condition.
For example, in the disclosure by bastnaesite sample and bastnaesite standard substance be embedded in epoxy resin (its act on be by
Sample and bastnaesite standard substance are embedded being put into sample cavity), it is made a diameter of 1 inch (2.54cm)
The sample target (being for example put into the disk of sample cavity, referred to as target) of (diameter is determined by the size of sample cavity), and by sample surfaces
Polishing, gold-plated (such as polishing is that, in order to which sample surfaces are smooth, gold-plated is in order to which sample surfaces are conductive), prepare analysis to obtain
Thorium lead age.
For example, the particle of bastnaesite sample and bastnaesite standard substance is very small, about 100 microns, can be by these
The little particle of the bastnaesite sample at unknown age is arranged in a row, and the little particle of bastnaesite standard substance is lined up into another row,
All it is embedded on such as 1 inch of sample target.Then, when test, it can be detected or be measured with about 30 microns of beam spot,
An automatic cycle tests can be for example used to test multiple samples or standard substance particle respectively.Such as first, five, ten, 15,
20 grades are every five sample tests, one standard substance particle, and such as second, three, four, six, seven, the unknown samples of measurement such as eight, nine
Product.So, even if instrument (such as ion microprobe) condition has the state of small change, standard substance and unknown sample
It is also similar, unknown sample can be corrected by standard substance, survey year structure is more accurate.And if respectively by test sample
It is made with standard substance for two separated targets (such as on the standard substance first tested on a target, another target of re-test
Sample), then when instrument state changes (such as primary ions beam intensity diminishes), detect the result meeting of the thorium lead age of sample
It is inaccurate.
According to one embodiment of the disclosure, the surface of the sample target is also polished and gold-plated processing, the ion
Signal detection system is electron multiplier；The magnetic field intensity in the magnetic field is adjusted so that the secondary of the bastnaesite sample
In ion204Pb+,206Pb+,207Pb+,208Pb+,140Ce16O2 19F2 +,232Th+,238U+,232Th 16O+,238U16O+With232Th16O2 +
Pass sequentially through magnetic field and reach the ion signal detecting system.
For example, as shown in table 1, magnetic field intensity can be adjusted so that204Pb+,206Pb+,207Pb+,208Pb+,140Ce16O2 19F2 +,232Th+,238U+,232Th 16O+,238U16O+With232Th16O2 +Magnetic field arrival ion signal detecting system is passed sequentially through (for example to connect
Receive device, such as electron multiplier).Pass through such mode, it is possible to use obtain respectively204Pb+,206Pb+,207Pb+,208Pb+,140Ce16O2 19F2 +,232Th+,238U+,232Th16O+,238U16O+With232Th16O2 +Measurement data, it is convenient that subsequently these data are entered
Row processing.
Th-Pb dating signals measuring sequence the tables of the bastnaesite of table 1
According to one embodiment of the disclosure, the parameter of the ion microprobe includes：Parallel light focusing O2 -It is strong
Spend for 8nA to 10nA, primary ions beam diameter is about 20*30 μm, primary ions accelerating potential is -13KV, secondary ion accelerates
Voltage is+10KV, and entrance slit is 60 μm, and contrast diaphragm is 400 μm, and energy slit is 60eV, and exit slit is 180 μm,
Measurement group number is 7, and single-node analysis precision is 2.8%-3.5%, and single-node analysis total time is about 15min, the secondary ion matter
The mass resolution of spectrometer is about 8000.
For example, to obtain higher lead ion yield (because needing to use208Pb=232Th(eλ232t- 1) year is calculated
In age, if the yield of lead is high, the age error calculated will be small), thorium D Analysis of age can be used such as oxygen
Gas ions ion gun (the ion gun price is low, easy to maintenance, can Reusability, long lifespan) does primary ion source.At this point it is possible to
Make purity oxygen formation plasmoid, by O2 -Accelerate to draw, in directional light mode, (also referred to as Uniform Illumination pattern, is ion
Beam focuses on the mode of sample surfaces, and beam spot is than larger, it is adaptable to conventional sample) focus to sample surfaces, beam spot size
For 10*15 μm to 30*50 μm, e.g., about 20*30 μm (for conventional sample, such as the particle of bastnaesite, beam spot size
If greater than 20*30 μm, it is possible to measure).Can be according to ion signal detecting system (such as receiver, such as electronics times
Increase device) signal intensity be corrected that (process of correction is for example detailed later to measurement result using corresponding standard substance
Discuss), so as to calculate thorium lead age.Single-point in the disclosure (namely will be measured during an a series of measurement point, such as analyses
Many points, such as 30 points) analysis precision is about 2.8%-3.5% (such as 3%).
For example, accelerating the O drawn2 -The energy for hitting sample surfaces is 23keV, can now produce such as neutral particle and two
Secondary ion.Secondary ion realizes that angle, speed double focusing (are referred to as double focusing type fly mass spectrograph, are characterized in by electric field and magnetic field
The efficiency of transmission of secondary ion is high), and reach electron multiplier (a kind of ion signal detecting system is also a kind of receiver).
Ion gun in the ion microprobe of the disclosure for example selects O2 -Oxygen gas plasma ion gun, the secondary ion of the disclosure
Mass spectrograph in mass spectrograph is for example selected in electric field and the double focusing type fly mass spectrograph in magnetic field, the ion microprobe of the disclosure
Ion signal detecting system is, for example, electron multiplier.The mass resolution of disclosure Instrumental (such as ion microprobe)
About 8000 (50% peak heights, 50% is the place for describing signal peak height), to avoid molecular ion from interfering object ion.
For example, the design parameter of the ion microprobe of the disclosure is：Parallel light focusing O2 -, intensity is about 8nA—
10nA, primary ions beam diameter is about 20*30 μm, primary ions accelerating potential be -13KV, secondary ion accelerating potential for+
10KV, it is 23KeV, sample cavity vacuum 1E-5Torr, 60 μm of entrance slit, contrast light that primary ions, which hit sample gross energy,
400 μm of door screen, energy slit 60eV, 180 μm of exit slit, resolution ratio is about 8000 (50% peak heights), and receiver is electron multiplication
Device, measurement group number 7, single-node analysis total time is about 15min.
According to one embodiment of the disclosure, in the secondary ion of the primeval lead thorium ratio and the bastnaesite sample
RatioBetween positive correlation meet power function relationship represented by equation 2 below, wherein A and E are normal
Number：
Formula 2.
It is described that the primeval lead thorium ratio is corrected with the lead after being corrected according to one embodiment of the disclosure
Thorium ratio, including：
The institute at known age is detected using with detecting the bastnaesite sample identical mode on the sample target
Bastnaesite standard substance is stated, to obtain multigroup standard substance measurement data；According in multigroup standard substance measurement data
'sWithAnd be fitted according to the power function relationship of formula 2, so as to obtain constant A and constant E value.
It is described that the primeval lead thorium ratio is corrected with the lead after being corrected according to one embodiment of the disclosure
Thorium ratio, including：
By the ratio in the secondary ion of the bastnaesite sample at unknown ageSubstitute into the power of formula 2
Functional relation, and calculated using the value for being fitted obtained A and E shown in equation 5 below
Formula 5.
It is described that the primeval lead thorium ratio is corrected with the lead after being corrected according to one embodiment of the disclosure
Thorium ratio, including：
By the bastnaesite standard substance at the known ageRecommendation withIt
Be used for the correction coefficient K shown in formula 6, wherein st represent, it is known that
Formula 6.
It is described that the primeval lead thorium ratio is corrected with the lead after being corrected according to one embodiment of the disclosure
Thorium ratio, including：
The primeval lead thorium ratio is multiplied by using the correction coefficient KObtain the bastnaesite at unknown age
Lead thorium ratio after the correction of sample
It is described according to formula according to one embodiment of the disclosureTo calculate the fluorine carbon cerium
The thorium lead age t of sample ore productu, including：
Using the lead thorium ratio after the correctionAnd according to formulaIt is described to calculate
The thorium lead age t of bastnaesite sampleu, wherein decay coefficient λ232=4.9475*10-11。
According to one embodiment of the disclosure, it is known that the bastnaesite standard substance at age includes bastnaesite standard
Material K-9, the bastnaesite sample at unknown age includes bastnaesite sample LiZ and DLC016.
By above example, lead thorium ratio after the primeval lead thorium ratio is corrected and corrected
Process has carried out exemplary illustration.
Following content, describes the lead thorium ratio after the primeval lead thorium ratio is corrected and corrected in detail
Principle.
Formula is used in the disclosure208Pb=232Th(eλ232t- 1) calculate thorium lead age t when, it is necessary to using208Pb/232Th's
Ratio, still, it has been found that the Pb measured+/Th+With it is real208Pb/232Th be it is different, this be due to ought once from
Sub- O2 -When bombarding sample surfaces, the secondary ion Pb that sample is sputtered out+And Th+Yield is different to be caused, therefore is made
Carried out with ion microprobe when bastnaesite thorium D is determined to measure in year, it is necessary to the yield of thorium and lead be corrected, to obtain fluorine carbon
The accurate thorium lead age of cerium sample ore product.
The problem of to solve such, it has been investigated that, the Pb of bastnaesite+/Th+With ThO2 +/Th+Between exist it is good
Positive correlation, as shown in figure 3, showing the Pb of the bastnaesite of all ages and classes+/Th+With ThO2 +/Th+Positive correlation
(namely the bastnaesite of all ages and classesWithPositive correlation schematic diagram), illustrated therein is three
The measurement result of the bastnaesite of individual all ages and classes.It can be divided according to the ratio measurement of the bastnaesite of three all ages and classes
Three straight lines are not fitted, and the intercept difference of three straight lines represents the age difference of the bastnaesite of three all ages and classes.
The Pb of bastnaesite+/Th+With ThO2 +/Th+Between the positive correlation that exists can be expressed as with formula：
Formula 1
Transformation for mula 1 can obtain following formula 2：
Formula 2
Illustrate the process being corrected to lead thorium ratio with specific example below, here, from the known age
The bastnaesite standard substance K-9 of (118Ma) is illustrated, and bastnaesite standard substance K-9 is to use isotope in document 1
The age criterion material of the bastnaesite of Thermal Ionization Mass Spectrometry (ID-TIMS) research and development is diluted, standard substance is used as using K-9 here
To correct bastnaesite the sample LiZ and DLC016 at two unknown ages from Sichuan in document 2, detailed process is as follows.
(1) the bastnaesite sample and the bastnaesite mark at known age at unknown age are represented using following formula 3
The relation of quasi- material, wherein u represent unknown, and st represents known.
Formula 3
Formula 3 is transformed to formula 4, is expressed as follows.
Formula 4
(2) 20 groups of data of acquisition are measured to the bastnaesite standard substance K-9 at known age, and by obtained measurement
ArrayWithIt is fitted according to the power function relationship of formula 2, so as to obtain A and E value.
(3) by bastnaesite the sample LiZ and DLC016 at unknown age measurement dataSubstitute into formula 2
Power function relationship, using A and E value, calculates oneHere it can for example be entered using equation 5 below
Row is calculated：
Formula 5
(4) by bastnaesite standard substance K-9's(such as 0.00588, it is according to the known age to recommendation
What 118Ma was calculated) withBe used for correction coefficient K, its formula is as follows：
Formula 6
(5) line translation is entered to formula 4, obtains formula 7 as shown below：
Formula 7
The bastnaesite sample at unknown age is multiplied by using KIt can obtain the bastnaesite sample at unknown age
Thorium D ratio after the correction of product (such as LiZ and DLC016)
Finally, according to formulaThe fluorine carbon at unknown age can be calculated using equation 8 below
Thorium the lead age t, wherein λ of cerium sample ore product232It is decay coefficient.
Formula 8
According to the derivation of above formula, the specific process being corrected to lead thorium ratio is for example including following in the disclosure
Step：(1) by the array of measured standard substanceWithObtain A's and E according to power function relationship fitting
Value；(2) by institute's test sample productPower function relationship is substituted into, using A and E value, one is calculated(3) by standard substanceRecommendation withThe ratio between as correction coefficient K；(4) make
Sample is multiplied by with KLead thorium ratio after being corrected(5) useWith decline
Become constant λ232, calculate the thorium lead age t of institute's test sample productu。
Through the above description of the embodiments, those skilled in the art can be understood that the present invention can be with
Realized by other structures, feature of the invention is not limited to above-mentioned preferred embodiment.It is any to be familiar with this technology
Personnel are in the technical field of the present invention, the change or modification that can be readily occurred in, and should all cover the patent protection model in the present invention
Within enclosing.
Claims (5)
1. a kind of method of the thorium lead age of the measure bastnaesite sample based on ion microprobe, it is characterised in that bag
Include：
Sample target will be made in bastnaesite sample and bastnaesite standard substance insertion epoxy resin, and the sample target is put
In the sample cavity for entering ion microprobe；
Oxygen gas plasma ion gun and the bastnaesite sample focused in directional light mode on the sample target are used,
To produce the secondary ion of the bastnaesite sample；
Make electric field and magnetic field that the secondary ion of the bastnaesite sample passes through in the ion microprobe, to realize angle
Degree and speed double focusing simultaneously reach ion signal detecting system；
The primeval lead thorium ratio in the secondary ion of the bastnaesite sample is detected using the ion signal detecting systemAnd according to the primeval lead thorium ratio and the ratio in the secondary ion of the bastnaesite sampleIt
Between positive correlation, the primeval lead thorium ratio is corrected with the lead thorium ratio after being correctedWherein u tables
Show unknown；And
Using the lead thorium ratio after correctionAnd according to formulaTo calculate the bastnaesite sample
The thorium lead age t of productu, wherein λ232It is decay coefficient；
Wherein, the primeval lead thorium ratio and the ratio in the secondary ion of the bastnaesite sampleBetween
Positive correlation meets the power function relationship represented by equation 2 below, and wherein A and E are constants：
Wherein, it is described the primeval lead thorium ratio to be corrected with the lead thorium ratio after being corrected, including：
The fluorine at known age is detected using with detecting the bastnaesite sample identical mode on the sample target
Carbon cerium ore deposit standard substance, to obtain multigroup standard substance measurement data；According in multigroup standard substance measurement dataWithAnd be fitted according to the power function relationship of formula 2, so as to obtain constant A and constant E value；
By the ratio in the secondary ion of the bastnaesite sample at unknown ageSubstitute into the power function of formula 2
Relation, and calculated using the value for being fitted obtained A and E shown in equation 5 below
By the bastnaesite standard substance at the known ageRecommendation withBe used for
Correction coefficient K shown in formula 6, wherein st represent, it is known that
And, it is multiplied by the primeval lead thorium ratio using the correction coefficient KObtain the fluorine carbon cerium at unknown age
Lead thorium ratio after the correction of sample ore product
2. according to the method described in claim 1, it is characterised in that the surface of the sample target is also polished and gold-plated place
Reason, the ion signal detecting system is electron multiplier；The magnetic field intensity in the magnetic field is adjusted so that the fluorine carbon cerium
In the secondary ion of sample ore product204Pb+,206Pb+,207Pb+,208Pb+,140Ce16O2 19F2 +,232Th+,238U+,232Th 16O+,238U16O+With232Th16O2 +Pass sequentially through magnetic field and reach the ion signal detecting system.
3. according to the method described in claim 1, it is characterised in that the parameter of the ion microprobe includes：Directional light
Focus on O2 -Intensity be 8nA to 10nA, primary ions beam diameter is about 20*30 μm, primary ions accelerating potential be -13KV, two
Secondary ion accelerating potential is+10KV, and entrance slit is 60 μm, and contrast diaphragm is 400 μm, and energy slit is 60eV, is exported narrow
Stitch as 180 μm, measurement group number is 7, and single-node analysis precision is 2.8%-3.5%, and single-node analysis total time is about 15min, described
The mass resolution of ion microprobe is about 8000.
4. according to the method described in claim 1, it is characterised in that described according to formulaTo calculate
The thorium lead age t of the bastnaesite sampleu, including：
Using the lead thorium ratio after the correctionAnd according to formulaTo calculate the fluorine carbon cerium
The thorium lead age t of sample ore productu, wherein decay coefficient λ232=4.9475*10-11。
5. method according to claim 4, it is characterised in that the bastnaesite standard substance at known age includes fluorine
Carbon cerium ore deposit standard substance K-9, the bastnaesite sample at unknown age includes bastnaesite sample LiZ and DLC016.
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| CN106908510B (en) * | 2017-03-03 | 2019-06-18 | 中国科学院地质与地球物理研究所 | A method of the uranium lead age of measurement zircon sample |
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| CN108956747B (en) * | 2018-04-18 | 2020-02-14 | 中国地质大学（武汉） | Water vapor assisted laser ablation non-matrix matching accessory mineral U-Pb dating method |
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| US11101126B2 (en) * | 2018-12-04 | 2021-08-24 | Institute Of Geology And Geophysics, Chinese Academy Of Sciences | Method and system for measuring inert gas by ion probe |
| CN111044545A (en) * | 2019-12-30 | 2020-04-21 | 核工业北京地质研究院 | Method for effectively obtaining thorium-lead isotope age of thorium deposit |
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| CN111398403B (en) * | 2020-05-13 | 2021-04-09 | 中国科学院地质与地球物理研究所 | Method for simultaneously determining forsterite value and trace elements in olivine |
| CN115407416B (en) * | 2022-09-05 | 2024-09-17 | 核工业北京化工冶金研究院 | Space positioning method and system for ultramicro uranium minerals in uranium ores based on light-emitting |
| CN116413327B (en) * | 2023-05-05 | 2024-03-22 | 中国科学院地质与地球物理研究所 | Method for correcting age of niobium-tantalum iron ore by adopting double-standard sample navigation method |
| CN116559273B (en) * | 2023-05-05 | 2024-05-03 | 中国科学院地质与地球物理研究所 | Thorium lead age test method for niobium-tantalum iron ore |
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