Predictive modelling in the Cook Islands Exclusive Economic Zone
Kenex has completed mineral prospectivity modelling of polymetallic nodule deposits over the Cook Island Economic Exclusive Zone (CIEEZ) for the Cook Island Seabed Minerals Authority.
Polymetallic nodules, also known as manganese nodules, have been explored as a possible source for a number of metals including cobalt since the early 1970s. Recent data on the nodule composition and abundance in the CIEEZ has led to a renewed interest in the prospectivity for manganese nodules in the region. There are a number of factors that affect nodule growth and abundance:
- Manganese nodules form on the deep seafloor as concretions formed by concentric layering of iron and manganese hydroxides around a core.
- They grow at a very slow rate, on the order of millimeters per million years.
- The nodules formed by hydrogenetic processes are most abundant, these are formed by slow precipitation of metals from seawater.
- Nodules are most abundant at depths between 4,000 m and 6,000 m in areas of low sedimentation rate.
- Hydrogenous nodules generally grow on siliceous and pelagic clay sediment.
Kenex have compiled a GIS of available data over the study area, including regional scale information such as geology, geochemistry and topography datasets.
To create the manganese nodule prospectivity map predictive maps were generated using the Weights of Evidence technique. The data most relevant to manganese nodule formation has been used in order to best represent the mineral systems model. These data were combined into a single mineral prospectivity map to show the geological potential of finding a polymetallic nodule deposits within the study area. The prospectivity model has identified 72 very prospective targets and 16 highly prospective targets based on their post-probability value. This ranking can be used to prioritise follow up investigation including assessment of the current target status and collection of additional data.
The Cook Island Seabed Authority is in a position whereby the model results can be utilised in many ways. From a planning perspective, these include:
- Structuring any tender process – short, medium and long term objectives.
- Prepare acreage for tender.
- Advising on exploration block size for allocation.
- Determining areas to be set aside for economic and/or strategic and/or environmental reasons.
- Identifying appropriate work programme or expenditure requirements from explorers. Generating maps to visually aid planning requirements.
- Meaningfully valuing the exploration acreage through using probability values to constrain estimations.
Similarly, potential explorers and investors could utilise the model in a number of ways such as:
- Enabling an estimate to be made of the geological potential of a given location to host poly-metallic nodules.
- Allowing for the identification of missing data in areas of lower probability that if collected could increase the prospectivity of an area.
- Planning and budgeting exploration programmes.