Developing concepts for the mine planning of deep-sea polymetallic nodules

Abstract

Over the last decade, interest in deep-sea mining of Polymetallic Nodules (PN) has reignited. It is driven by an increasing demand of metals that are critical for the digital economy and modern technologies such as batteries. Methods for resource estimation of PN are known and commercially available. There is however no standard method of a planning a deep-sea mining operation. This is an essential step to define mineable reserves. To address this problem, an existing concept has been applied in this thesis. This planning concept was inspired by agriculture and subdivides a mining license area into large scale mining sites, which are in turn subdivided into smaller, continuouslymineable areas calledmining fields. The subdivision is illustrated in figure 1. The contribution of this thesis is the development of a methodology for this concept. The concept was applied to a framework based upon a license area in the Clarion-Clipperton Zone (CCZ) in the Pacific Ocean. The mining will be done using a Nodule Collector (NC), which is a self-propelled machine that continuously gathers PN on the ocean floor and transports them upwards to a vessel at the ocean surface. Certain areas are deemed constrained by slopes or nodule types. Mining sites wherein the NC will operate were outlined within the license area using those constraints and Nodule Abundance (NA).Within the mining sites, a new metric was introduced for assessing the mineability for the NC: the Straight-Line Distance (SLD). The next step down from mining sites are the mining fields. The operation of the NC within them is approximated by two different driving patterns. Different field shapes are also analyzed, along with the impact of obstacles inside the field. Different methods of creating fields inside the mining sites were considered. The procedure relied upon the SLD to define the boundaries between fields. Two sets of field are created: with elongated shape and compact shape. The best set of fields was selected using the approximation of NC operation. Lastly, a method for determining the sequence of fields is developed that uses a Genetic Algorithm (GA) as optimization method. It takes into account constraints for mining rate, operational hours, nodule targets and travelling time. The methods outlined in this thesis are flexible and can be applied in a variety of circumstances. The selection of mineable areas turns out to be the must crucial step. The subsequent delineation of mining fields and sequencing does not make or break the profitability of the operation, although they are essential steps for the definition of mineable reserves.