摘要:
为了探究Rb、Sr在闪锌矿中的赋存状态及其Rb-Sr定年机理,对挑纯闪锌矿开展了矿物、稀盐酸提取相和硫化物相(王水溶解相)的Rb、Sr、Pb、Zn、Fe、Ca、Mg和Al含量分析.结果表明,挑纯闪锌矿中,79.19%-97.61%(平均90.47%)的Rb与Pb、Zn、Fe主要分布在硫化物相中,而70.30%-98.12%(平均82.92%)的Sr与Ca、Mg主要分布在稀盐酸提取相中,且其中的Sr与Ca+Mg含量之和大致呈正相关,指示硫化物相较之全矿物的Rb/Sr比值变化范围增大和Rb-Sr定年成功率得以提高,是因为通过稀盐酸提取过程去除了方解石、白云石等包裹体中的普通Sr对硫化物相中少量(2.34%-9.79%)放射成因Sr的掩饰作用.上述结果表明,闪锌矿Rb-Sr同位素定年可能是基于硫化物相而非所含流体包裹体和碳酸盐包裹体中的Rb和Sr,从原理上初步证实该定年方法是有意义的.通过条件实验,检验了稀盐酸提取过程可将碳酸盐包裹体中的Sr完全提取出来,且提取酸浓度和浸泡时间对等时线年龄没有影响,验证了闪锌矿分相Rb-Sr体系定年分析流程稳定可靠.
Abstract:
Rb-Sr dating of sphalerites has been shown a promising and effective technique for the direct dating of Pb-Zn deposits.However,this technique is still questioned by some scholars due to the divergent opinions about the occurrence of Rb and Sr and the dating mechanism.Therefore,This study analyzed the contents of Rb,Sr,Pb, Zn,Fe,Ca,Mg and Al in the hand-picked sphalerites,diluted HCl acid leachates and sulfide residues(Aqua regia dissolving phases),respectively.The analytical data shows that 79.19%-97.61%(averaged 90.47%)Rb is dis-tributed in the sulfide residues with Pb,Zn and Fe,while 70.30%-98.12%(averaged 82.92%)Sr is concentrated in the diluted HCl leachates with Ca and Mg,and there is an approximately positive correlation between the con-tents of Sr and those of Ca and Mg,which indicates that the common Sr in carbonate inclusions demonstrated by Electron Microprobe analysis can be eliminated through the diluted HCl leachating,so the radioactive Sr(2.34%-9.79%)in minerals can't be masked by the high common Sr in the carbonate inclusions,then the Rb/Sr ratios and their variation range of the sulfide residues become bigger,which is of great significance for the successful Rb-Sr dating of sphalerites.Meanwhile,these results show the Rb-Sr dating of sphalerites is probably based on the Rb and Sr in the sulfide residues not on those in the fluid or carbonate inclusions,which preliminarily con-firms this dating method is of geological significance in principle.What's more,through several condition experi-ments,it's verified that the common Sr in the carbonate inclusions can be removed thoroughly by the diluted HCl leachating,and that all Rb-Sr isotope data points are distributed along the same Rb-Sr isochrones no matter what the leachating acid concentration or soaking time is. That is, the Rb-Sr isochrone age is reliable, showing the analysis process of the Rb-Sr dating of sphalerites is stable and reliabale.
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