An integrated accessory mineral approach to understanding post-subduction magmas and mineralisation

Economically important elements, such as gold, tellurium, and selenium are commonly associated with magmas that post-date active subduction. These so-called 'post-subduction magmas' regularly coincide with episodes of extension and are often rich in alkali elements. The link between this style of magmatism and mineralisation is, at present, poorly understood. One suggestion is that older, hydrous magmas formed during earlier episodes of subduction leave a residue of sulphide-bearing and metal-rich cumulates deep in the crust. During post-subduction extension, these fertile residues redissolve, thereby liberating elements such as gold, tellurium and selenium.

In contrast to many previous studies, we will use state-of-the art analytical techniques (textural and composition analysis using LA-ICP-MS, XRF, SIMS) in collaboration with Zeiss to analyse and map the chemistry of robust accessory minerals. These chemical composition of these minerals fingerprint many critical ore-forming processes over what can be long and complex magmatic histories. Critically, these minerals can withstand re-melting events may often be derived from much deeper and unexposed parts of magmatic system. This project will use zircon, apatite, titanite, and magnetite to develop a petrogenetic model for post-subduction magmatism and mineralisation. These four minerals may also carry with them inclusions of less-robust minerals, including sulphides that are thought to host many key metals.