Seabed Exploration for Massive Sulfide Deposits using Self-Potential data
This project was assigned to the student Ole Skår Jøsøk when he started his Master's program in Earth Sciences, Geophysics, Autumn 2022.
The Earth’s mid ocean ridge system, which is 65,000 km long, contains more than 500 known hydrothermal systems. At these hydrothermal systems large amounts of minerals, including metals such as iron, copper and zinc and, in some cases, also relatively large amounts of precious metals like silver and gold come to the surface. A large part of these metals ends up in plumes in the ocean and gets dispersed over large areas. Another part stays near the ridge, mainly in the form of (black) smokers. These black smokers collapse after a while, because of an earthquake or because they are unstable, and get replaced by other black smokers, which eventually also collapse. Over a long period of time these collapsed smokers thus form an area of metal deposits, called seafloor massive sulfide (SMS) deposits.
Hypothesis (scientific problem):
The SMS deposits are interesting because they contain a lot of information about the deep Earth and because they could potentially be exploited because of their metal content. However, many questions regarding SMS deposits remain. First, the deposits that have been found are believed to be only a part of the deposits near hydrothermal systems. Hydrothermal systems typically are found using measurements in the water column and this gives a bias towards the hotter hydrothermal systems (which give rise to black, as opposed to white, smokers). Moreover, many SMS deposits have moved away from the ridge system because of seafloor spreading. They are therefore separated from the axial heat source and thus in some sense extinct. These are difficult to locate, especially since many of them
also have been covered by marine sediments. It is therefore useful to be able to locate SMS deposits and accurately determine their mining potential.
A number of methods can be used to identify and locate SMS deposits. These include geophysical methods, such as seismic, gravity, magnetic, resistivity and self-potential (SP). SP has become quite popular and is used in autonomous underwater vehicles (AUVs). This allows for relatively cheap and potentially efficient data acquisition. In this thesis SP modeling will be used to synthetically create a number of different types of SP data sets and to set up an inversion method. Given the importance of uncertainty the inversion methods will both be deterministic and stochastic (i.e. uncertainties in the measurements will systematically be taken into account). If time allows, the SP modeling and inversion algorithm will be combined with other measurements, especially magnetic measurements, to further
constrain the SMS location and concentration.