Introduction

Economic geology is, at heart, the most fundamental form of applied geochemistry. In essence, the industry professional is focused on understanding where accumulations of geochemical anomalies (i.e. the mineralisation) occur. Whether that be in an exploration setting or a resource evaluation context, all geologists involved in this task are trying to pinpoint where a certain element (or elements) are located. In this task a large number of tools are applied: understanding the relationship of mineralogy to structure, fluid pathways, relative timing and often the association of economic commodities with other, more common, chemical proxies.

In essence, isotopes are simply the most distinctive chemical proxy a geologist can have in the toolkit – they are (trace) elements with labels on them. These labels, when interrogated, allow us to varying degrees to investigate when and how the elements got to where they are today. However, often the information isotopes contain is not utilised effectively – the reasons for this are many, including geological and educational. Often, even the specialist needs to refer back to a source of information or reference when understanding a system they have not used for some time or may not have encountered previously, and the same is certainly true of isotopes. Sometimes perceived complexity can obscure fundamental simple understanding, and the converse can be true as well.

This contribution attempts to make the sometimes arcane world of isotopes more accessible and tractable for those who have had little or no formal background in isotope geochemistry, while maintaining a level of sophistication and detail that allows those more familiar with the issues to maximise the benefits of isotopic data sets. To this end, there is some basic background regarding nomenclature and shorthand that the reader should familiarise themselves with, but at heart it is worth remembering that although we are dealing with isotopes and often ‘nuclear’ processes, the way these are distributed in the earth is often controlled by more familiar chemical processes. From this basis, a linking of chemistry with the nucleus allows us to interrogate the geological record and apply that understanding in a huge range of situations in the minerals industry. Thus, the isotopic toolkit primarily contains methods of determining when events took place (geochronology) and fingerprinting where elements have come from (geotracing).