Dating geologic gold deposits and authenticating a Greek gold tiara, an ancient gold chalice, and swimming dragon artifacts of the Chinese Han dynasty

Otto Eugster

doi:10.1007/s13404-018-0238-z

Abstract

In this work, we present the application of the uranium, thorium–helium (U,Th–He) dating method to two different types of gold objects: geologic gold deposits and archeological gold objects. Direct dating of geologic gold deposits is difficult without assuming contemporaneity between gold and datable hydrothermal minerals. We show that our results indicate that the applied dating method opens a new perspective for the dating of gold deposits without assuming contemporaneity between gold and datable hydrothermal minerals. The second application of our dating method is authenticating archeological gold objects. This is a major problem, as gold is probably the most difficult material in terms of detecting modern forgeries. The feasibility of this application was mentioned in 1996 in an earlier article in Gold Bulletin, Eugster (Gold Bull 29:101–104, 1996). In the past two decades, we applied the U,Th–He dating method to numerous gold antiquities in order to determine the time of their formation or their latest melting process, respectively. Gold always contains traces of uranium and thorium that produce alpha particles by radioactive decay which transform to helium. When gold is molten to manufacture an art object, the helium is lost, but gets stored again when the gold cools down. Thus, the radioactive clock starts anew. Here, we present the results for direct dating of gold deposits and for the authentication of some of the most remarkable artifacts and describe their history.

Highlights

The time when gold present in a gold mine or a gold nugget found in a gold deposit was formed can be determined using a dating method based on the radioactive decay of uranium and thorium into helium
When gold crystals are formed in a cooling hydrothermal fluid in the Earth’s interior, uranium and thorium atoms are included in the crystal lattice
If an art object is manufactured by melting of gold, the helium produced by the decay of uranium and thorium since the gold existed is degassed

Summary

Introduction

The time when gold present in a gold mine or a gold nugget found in a gold deposit was formed can be determined using a dating method based on the radioactive decay of uranium and thorium into helium. When gold crystals are formed in a cooling hydrothermal fluid in the Earth’s interior, uranium and thorium atoms are included in the crystal lattice. These elements are radioactive and decay by emitting alpha particles. They capture two electrons and become helium atoms. If an art object is manufactured by melting of gold, the helium produced by the decay of uranium and thorium since the gold existed is degassed. Because the decay constants of uranium and thorium are known, the time of the last melting process for the gold can be determined by measuring the uranium, thorium, and helium concentrations

Methods

Results

Conclusion