【引用本文】 张彦, . 40Ar/39Ar定年矿物绢云母的提纯研究[J]. 岩矿测试, 2019, 38(6): 599-608. doi: 10.15898/j.cnki.11-2131/td.201904010042
ZHANG Yan. Study on the Separation of Sericite for 40Ar/39Ar Dating[J]. Rock and Mineral Analysis, 2019, 38(6): 599-608. doi: 10.15898/j.cnki.11-2131/td.201904010042

40Ar/39Ar定年矿物绢云母的提纯研究

自然资源部深地动力学重点实验室, 中国地质科学院地质研究所, 北京 100037

收稿日期: 2019-04-01  修回日期: 2019-05-30  接受日期: 2019-07-16

基金项目: 国家自然科学基金面上项目(41573049);中国地质调查局地质矿产调查评价专项(DD20190001,DD20190004)

作者简介: 张彦, 教授级高级工程师, 主要从事40Ar/39Ar年代学研究。E-mail:yzhang737@sina.com

Study on the Separation of Sericite for 40Ar/39Ar Dating

Key Laboratory of Deep-Earth Dynamics, Ministry of Natural Recourses; Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, China

Received Date: 2019-04-01
Revised Date: 2019-05-30
Accepted Date: 2019-07-16

摘要:绢云母的40Ar/39Ar年龄是研究矿床形成年龄的重要手段,但是40Ar/39Ar定年矿物绢云母的提纯一直是一个难题。现有分离提纯方法得到的绢云母集合体中通常含有微斜长石,如本研究中常规磁选-重液法得到的微斜长石含量在0~28%,常规悬浮液法得到的微斜长石含量在3%~45%。当绢云母集合体中的微斜长石含量超过10%时,会直接影响测年的准确性。为探索一种有效的绢云母提纯方法,本文首先考察了常规磁选-重液法和常规悬浮液法的提纯效果,实验结果表明两种方法得到的绢云母纯度均不高,而且常规悬浮液法的粒度有时很细,不能满足定年要求。进而采用超声波解离-悬浮液法对磁选-重液法得到的含微斜长石的绢云母集合体进行了条件实验,绢云母的纯度从28%提高到77%,微斜长石相对于绢云母的含量从12.5%降为0。绢云母的粒度大于1μm的占比在95%以上,最小粒度大于0.356μm,大于39Ar核反冲丢失的理论估算值0.08μm,该粒度下的绢云母在接受中子照射过程中不会引起明显的核反冲丢失,对中高温阶段的40Ar/39Ar年龄影响不大。研究认为,对于采用磁选-重液法得到的绢云母集合体,当其中的微斜长石含量大于10%时,可以采用超声波解离-悬浮液法进一步富集绢云母,降低微斜长石的含量,保证测年的准确性。

关键词: 40Ar/39Ar定年, 绢云母提纯, 微斜长石, 39Ar核反冲丢失, 超声波解离, 悬浮液法

要点

(1) 提高40Ar/39Ar定年矿物绢云母提纯率的关键是去除绢云母集合体中的微斜长石。

(2) 超声波解离-悬浮液法得到的绢云母粒度不会引起明显的核反冲丢失。

(3) 超声波解离-悬浮液法可以显著提高绢云母的纯度,保证测年的准确性。

Study on the Separation of Sericite for 40Ar/39Ar Dating

ABSTRACT

BACKGROUND:

The 40Ar/39Ar dating of sericites is a very important method for constraining the age of deposits, but the purity of sericite remains a problem. The sericite aggregate acquired by the available separation and purification method commonly contains microline. For example, the content of microline obtained by the conventional magnet-heavy liquid method in this study is 0-28%, whereas the content of microline obtained by the conventional suspension method is 3%-45%. When the content of microline in the sericite aggregate exceeds 10%, it will directly affect the accuracy of dating.

OBJECTIVES:

To find a useful method to increase the content of sericite and decrease the content of microline while the grain size is not too fine to cause 39Ar recoil loss during the irradiation.

METHODS:

The purification effects of conventional magnetic separation-heavy liquid method and conventional suspension method are firstly investigated. The experimental results show that the purity of sericites obtained by the two methods are low, and the particle size of the conventional suspension method is irregular and cannot meet the requirements of dating. The ultrasonic disaggregation-suspension method was used to carry out conditional experiments on the microline-bearing sericite aggregates obtained by the magnetic separation-heavy liquid method.

RESULTS:

Using the ultrasonic disaggregation-suspension method, the content of sericite increased sharply while the content of microline decreased greatly. For example, the content of sericite for one experiment increased from 28% to 77% and the content of microline relative to sericite decreased from 12.5% to 0. The fraction of the grain size < 1μm was above 95% and the smallest grain size was >0.356μm which was larger than 0.08μm estimated for the 39Ar recoil distance. Such grain size cannot obviously cause 39Ar recoil loss and did not have obvious effects on the age of middle to high temperature steps.

CONCLUSIONS:

When the content of microline relative to sericite in the sericite-bearing aggregates concentrated by magnet-heavy liquid method is more than 10%, the ultrasonic disaggregation-suspension method can be used to further increase the content of sericite and decrease the content of microline to improve the accuracy of 40Ar/39Ar dating.

KEY WORDS: 40Ar/39Ar dating, sericite seperation, microline, 39Ar recoil loss, ultrasonic disaggregation, suspension method

HIGHLIGHTS

(1) The key to improve the purity of sericite for 40Ar/39Ar dating is to remove microcline from sericite aggregate.

(2) The grain size of sericites obtained by the ultrasonic disaggregation-suspension method cannot cause obvious 39Ar recoil loss.

(3) Using the ultrasonic disaggregation-suspension method greatly improves the purity of sericites and the accuracy of dating.

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40Ar/39Ar定年矿物绢云母的提纯研究

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