Geochemie & Lagerstättenkunde

Hypozonal orogenic gold deposits

Orogenic gold deposits are hydrothermal gold-only deposits that are hosted in quartz vein or shear zone systems in metamorphic wall rocks. Such systems are responsible for approx. 30% of the known gold that was concentrated in ore deposits. Hypozonal orogenic gold deposits formed at temperatures above 450-500°C. Their origin has been debated in recent years and various models are discussed, suggesting (1) pre-peak metamorphic gold mineralization followed by prograde metamorphism and (2) hydrothermal gold mineralization during metamorphic peak or retrograde exhumation of the host terrane. This implies in addition different ideas about the source of the hydrothermal fluids and gold, being located in the metamorphic rocks of the terranes or contemporaneous granite intrusions. We currently study hypozonal orogenic gold deposits in Finland, Greenland, Australia and Zimbabwe. Previous investigations covered hypozonal orogenic gold deposits in India, Namibia and Russia. The main scientific questions are: (1) What is the timing of orogenic gold mineralization with respect to metamorphism or magmatism; (2) what are possible geochemical proxies for the source of gold and hydrothermal fluids and (3) what are the complex orogenic processes that favour orogenic gold mineralization?