Mineralisation of the Brothers Volcano, Kermadec Arc (IODP Expedition 376)

We here request funds to support the post-cruise Moratorium science programme of Cardiff PhD student Andrew Martin, who has been selected as a UK participant on International Ocean Discovery Program (IODP) Expedition 376 'Brothers Arc Flux' (5th May to 5th July 2018). Expedition 376 aims to investigate the fundamental processes that govern sub-seafloor hydrothermal mineralisation in submarine volcanoes by conducting a scientific drilling campaign at the Brothers Volcano, Kermadec Arc, SW Pacific. By drilling a series of scientific boreholes into the summit of the underwater volcano Expedition 376 scientists aim to: (1) characterise the transport of volatiles from the magmatic to hydrothermal system, and test whether a single-phase gas or two-phase brine-vapour system exists; (2) investigate the distribution of trace and base metals and establish the physico-chemical conditions that lead to their enrichment; (3) quantify the extent of fluid-rock interaction and establish the importance of magma-derived sulphur and carbon species in metal transport; and (4) assess the diversity and extent of microbial life in the system.

Andrew's role on board will be as a member of the Alteration Mineralogy team. He will play an integral role in characterising and logging the alteration facies associated with the Brothers hydrothermal system. For his post-cruise science programme in Cardiff, which has been approved by the Expedition 376 Sample Allocation Committee, he has committed to generating a comprehensive set of major and trace element analyses of representative whole-rock and in situ mineral samples of sulphide and silicate materials, focusing in particular on characterising their base, trace and precious metal concentrations and distributions. Cardiff's ELEMENT laboratory, under the leadership of Co-I Dr Iain McDonald, is a world leader in the analysis of such materials, by both solution and laser-ablation mass spectrometric techniques. The analyses Andrew will generate should play a vital role in helping to achieve objectives 2 and 3 of the wider Expedition 376 goals.

Andrew's selection for Expedition 376 was in recognition of his growing expertise in understanding how critical and precious elements in sulphides are transferred from the magmatic to hydrothermal environment. This process (with particular emphasis on Te and Se) forms the subject of his PhD, which focuses on the ancient analogue of the Troodos ophiolite of Cyprus. Though clearly of broad relevance to the subject of his PhD, the Expedition 376 research is not likely to form part of it; hence, on the basis of the guidance we have received, we are seeking 3 months of stipend for Andrew, over and above the analytical costs, to allow him to meet his IODP responsibilities without jeopardising his PhD research programme.

Minerals and metals underpin modern society; as consumption increases and society transitions toward the use of high-tech critical elements, the need to secure future resources has never been greater. With increasing pressure on conventional land-based mineral resources we look to the oceans for our future supply of minerals and metals. In order to better understand the future economic potential of seafloor mining we first need to understand the fundamental processes that form seafloor mineral deposits. This is especially true in arc- and subduction-related hydrothermal systems, which are enriched in critical and precious but also potentially toxic metals. It is these issues that underpin the broader justification for the International Ocean Discovery Program (IODP) Expedition 376 to the Brothers Volcano.

The drilling and exploration of modern day analogues will contribute to advancing our comprehension of ancient mineral districts currently being explored or exploited. Understanding generic mineralising processes will allow us to develop better genetic models, in turn leading to more targeted exploration and efficient mineral extraction and increase resource efficiency both on land and, ultimately, on the seafloor.

Understanding the distribution of precious and critical elements in seafloor hydrothermal systems such as the Brothers Volcano therefore has important long-term economic implications. It will also allow us to better estimate potential mineral resources in the oceans and quantify factors which lead to the enrichment of economic minerals. Once we have a fundamental understanding of this process information can be used to develop links between modern and ancient analogues, improving our exploration practice for the future. The data generated will also allow us to assess the economic and environmental advantages and disadvantages between different tectonic settings; we may, for example, find certain geological environments prove better candidates for mineral extraction than others as they contain lower concentrations of toxic trace elements.

The research we propose to conduct here on samples from Expedition 376 will generate both in situ and whole rock trace element geochemical data. These will be some of the first such data collected from an active sub-seafloor arc volcano system, and will thus be invaluable in helping develop a genetic model for sub-seafloor mineralisation which can in turn be used as a template for future seafloor mineral exploration in other arc systems. This will be useful in interpreting sub seafloor metal zonation in toxic trace metals and their potential negative environmental impact during seafloor mining.