Probabilistic estimates of permissive areas for undiscovered seafloor massive sulfide deposits on an Arctic Mid-Ocean Ridge

Abstract

Norway explores its seabed mining potential including exploration studies on seafloor massive sulfides (SMS) at the outermost parts of its continental shelf, the Mohn's Ridge. Owing to the significant development potential and the general lack of knowledge of the SMS deposits, the evaluation of exploration targets and resource abundance are more than ever necessary. Given current exploration status, this study proposes to (1) develop a mineral prospectivity map (MPM) indicating favorable geologic environments for the occurrence of SMS deposits, and (2) estimate the number of yet-to-be found hydrothermal mineral deposits within volcanically active areas. The first part of this research focuses on the development of the MPM using a knowledge-driven approach. For this purpose, we apply the quantitative prediction framework characteristic analysis developed for terrestrial mining exploration. In this methodology, data must be captured and compiled into a relevant spatial data set that will be transformed, combined and weighted for prediction modeling. The data consist of morpho-structures and terrain attributes obtained from an interpreted bathymetric map. A multivariate analysis on the integrated data signature allow to calculate favorability values that will be projected on an exploratory grid. Each grid cell is given a likelihood of mineralization to indicate where SMS deposits might be located.The second part of the paper estimates probabilistically how many SMS deposits remain to be found within neo-volcanic zones. These volcanic areas are geologically favorable to the occurrence of SMS deposits (permissive tracts) and provide the spatial basis for the probabilistic calculations. Estimates and associated confidence limits (10 th and 90 th percentiles) on the number of undiscovered deposits are calculated using regression equations. The resulting probability distribution function presents an expected amount of 11 SMS occurrences undiscovered.

Inactive Sulfide Ecosystems in the Deep Sea: A Review

“…High-resolution bathymetric mapping by autonomous underwater vehicles (AUVs) recently has been used to discover numerous exposed inactive sulfides, even in regions that had been already been extensively explored and mapped (Jamieson et al, 2014;Petersen et al, 2017). Investment is also being made in detailed geospatial analysis of geological features to develop probabilistic maps of favorable prospective regions of mid-ocean ridges (Ren et al, 2016;Juliani and Ellefmo, 2018). New seismic (Asakawa et al, 2018) and electromagnetic (Schwalenberg et al, 2016;Müller et al, 2018;Safipour et al, 2018) tools are being developed and tested to detect sulfides in the absence of physico-chemical water column anomalies, even when buried beneath 10's of meters of sediment.…”

Resource assessment of undiscovered seafloor massive sulfide deposits on an Arctic mid-ocean ridge: Application of grade and tonnage models

“…Specifically, the Mohns Ridge has become an important subject of investigation where a few identified SMS occurrences occur in various localities (Pedersen et al, 2010). Current analysis of resource potential along this ridge (Juliani and Ellefmo, 2018) established that several mineral deposits (11 expected in neovolcanic zones) remain to be found. However, the uncertainty about their tonnages and grades is largely due to the lack of knowledge about SMS orebodies.…”

Characterisation of Mineralised Material from the Loki’s Castle Hydrothermal Vent on the Mohn’s Ridge

“…It is common knowledge that VMS deposits occur in clusters or within districts (e.g., [6]), and evidence is in place for additional, promising mineralised sites along the AMOR [26]. Despite studies suggesting that ultraslow spreading ridges should have a significantly reduced density of hydrothermal plumes due to a reduced magma budget (e.g., [53]), discoveries such as Loki's Castle and the TAG demonstrate that fast spreading ridges are not exclusively favourable for sites of mineralisation, and that exploration targets must be diversified.…”

“…The importance of long lived detachment faults for hydrothermal activity at slow spreading ridges has been stated previously [8,[23][24][25]; the normal faults which define the margin of the AVR and form the deep rifting along the AVR crest likely act as fluid pathways, therefore controlling venting occurrences [22]. A more regional setting of this section of the AMOR has been developed as a case study [26]. Location of the Loki's Castle vent, with reference to other discoveries, after data from [8,27,28].…”