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Isotopes

Characterisation of geological events

Radiogenic isotopes are used for dating minerals and rocks, but they can also be used for petrogenesis studies. As magmatic rocks inherit their radiogenic isotopic ratios from the source region, these ratios can be used to differentiate source and identify mixing during formation. Stable isotopes are also useful for fingerprinting hydrothermal fluid interaction with wall rocks and have been shown to be an effective exploration vectoring tool.

Isótopos

Radiogenic isotopes

These methods provide insight into provenance and character of hydrothermal fluids and rock genesis, helping unravel geological events for a more sophisticated understanding of ore bodies and regional geology.

Methods available

ALS's partners offer Sm/Nd isotopes for whole rock samples (submitted as pulps). Lead isotopic methods are also available for whole rock or specific minerals. For most isotopic methods that involve column separation of the elements to be measured, the laboratory must first measure the element concentration in the sample.

Stable isotopes

Many important parameters of mineralising fluids may be determined from stable isotope ratios. The isotopic alteration halo may extend beyond visible mineralogy changes, creating a larger deposit footprint for easier exploration vectoring.

Methods available

ALS provides a range of stable isotope methods through partner institutions. Methods include C and O isotopic composition of carbonate minerals which is performed at the Mineral Deposits Research Unit (MDRU) at the University of British Columbia on pulverised samples. Carbon and oxygen isotopes can also be performed on mineral separates at Queen's Facility for Isotopic Research at Queens University. Other methods available include O and H isotopes in silicate minerals, and sulphur isotopes in sulphide or sulphate minerals.

Downloads

pdf

ALS Pb Isotope Ratios

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Sulphur Isotopes

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Isotope Submission Guide

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Isotopes in Carbonate Minerals Technical Note 2012

Pb isotope ratios for exploration

As a vectoring tool, Pb isotopes are useful for two kinds of mineral deposit; sulphide-rich and U-rich. For sulphide deposits, the Pb isotope ratio of the ore does not change with time, as U and Th are excluded from sulphide minerals. In this case, host rocks become more radiogenic (higher Pb isotope ratios) with time, and therefore increasingly different from the sulphide ore. For U mineralisation, the opposite is true - the ore becomes more radiogenic than the host rocks with time because of the elevated U and Th in the ore.

Routine Pb isotope measurement

Challenges to successful Pb isotope determination via ICP-MS include ²⁰⁴Pb mass overlap with ²⁰⁴Hg. Traditionally, this mass overlap has been overcome through time-consuming column separations to isolate Pb. The method at ALS circumvents this separation step through unique sample preparation and instrument introduction approaches. For mineral exploration purposes, the level of precision required is lower than is required for age dating. ALS provides a fit for purpose method with careful tuning of the ICP-MS instrument to rapidly scan the isotopes of interest and provide a level of precision that is suitable for mineral exploration.

Frequently asked questions

Related Topics

Geochronology

Radiogenic isotopes for dating

The dating of geological events can use a variety of radiogenic isotopic systems. The appropriate system will depend on the minerals available.

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Sample preparation quality

Sample preparation

Some isotopic analysis require preparation before submitting the samples to external institutions. Preparation methods can be performed by ALS.

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