A debate has recently unfolded around how much copper – and related metals – are present in Norway’s mid-oceanic ridge system, an area where mining could take place in the future as the search for metals needed for the electrification of society intensifies. The main players in this debate are the Geological Survey of Norway (NGU) and the Norwegian Offshore Directorate (NOD), who both have expertise in this domain. Here, we present a short summary of the main aspects of the debate, which is based on articles published in Norwegian on the GEO365 website.
Interview with Terje Bjerkgård
NOD’s response – Harald Brekke
Volumes and grades
First of all, there is the estimated amount of copper per 1,000 km2 in the deep sea. Based on comparable deposits on land, the ore geologists at NGU last year arrived at an estimate of 0.18 million tonnes of copper per 1,000 km2 when they published their resource estimate. In contrast, NOD’s resource assessment arrived at a value twice as high – 0.36 million tonnes per 1,000 km2 – based on analyses of samples taken from the area itself. This is not the only instance where the two organisations results differ though.
The NGU expects a grade of 1.47% as a median value for copper, while they claim that the NOD’s estimate median value is 2.27%. That is 35% lower.
In a response, Harald Brekke, senior geologist at the NOD, puts forward that the 2.27% represents a weighted average instead, arguing that a weighted mean must be compared to the arithmetic mean, not the median, and that their values therefore don’t differ that much as the NGU suggests.
Brekke also adds that the NGU researchers have used the same statistical methods as the NOD and NTNU. This means that they calculate the resources with Monte-Carlo simulations of distributions for occurrence size, content and number of occurrences per area.
Enough for mining?
NGU geologist Terje Bjerkgård argued that a deposit on land could be commercial given a grade of ~1,5 % Cu, if the deposit is large enough. A possible future seabed mineral industry that will operate in rough terrain at great water depths far from the mainland will very likely depend on deposits with significantly higher levels than those we find in operational mines on land in order to achieve profitability. At the same time, the deposits must have sufficient tonnage to provide a lifetime that justifies the investment costs, with calculations indicating that commerciality for prospects of around 20 million tonnes of ore require grades of approximately 5% copper.
Brekke subsequently states that one must not mix up a total estimate for a large area with the size and profitability of the individual prospects. He argues that there will be deposits that show higher concentrations than the NGU’s median, even higher than the NOD’s weighted average. And it is these prospects that need to be explored for.
Debate on databases
As stated above, NGU’s estimates are based on a large data set from onshore sites, from deposits that have been drilled or are in operation. “The challenge with estimating the resource potential based on data from the seabed is that we currently have too little data, both from the seabed mineralization and the host geology”, Bjerkgård points out.
“Many of the samples are from chimneys, the structures that are built where the minerals are deposited in contact with the seawater. These samples often have higher metal contents than what is found in the sulphide deposits otherwise, and can contribute to an overestimation of the resources. To get a full overview of the presence of the various metals and in what concentrations they occur, one has to study all parts of a given deposit through detailed mapping and, not least, drilling.”
The NGU researchers have therefore started with what they know best – volcanic massive sulphide (VMS) deposits on land. This database was reviewed and updated with the latest data on weights and tonnages so that only sulphide deposits formed in representative seabed environments remained.
As a response to this approach, Brekke states that it is impermissible to remove data only because it is perceived as uncertain. “Our perception of a good resource estimate of undiscovered resources is that we must take care of the uncertainties as best we can. It is from the range of uncertainty that opportunities emerge – both on the downside and the upside. As long as an analysis of content is correct, it can be used to assess and weigh the spread in a data set even if it is not itself representative as such. There is no guarantee that a database as a whole at this stage will become more representative by cleaning it down to only the “good” data.
“In our report”, Brekke adds, “we also show how we have compared the marine data sets with an onshore data set from NGU’s Fennoscandia database to assess which uncertainty range we should lie in, both in terms of size, content and density of occurrences. We have deliberately tried not to be too optimistic or too pessimistic and believe that our figures are scientifically very well justified and documented in the report.”
Behind the words
What is really quite interesting in this debate is the different stances these Norwegian institutions seem to take in the debate around deep-sea mining. Whilst the NOD is clearly more optimistic – is there a relation to the exploration mindset of hydrocarbon explorers? – the NGU seems to make a case for continued onshore development of mines if you read between the lines. Could there be some more at play here? It is not unthinkable that the NGU would have preferred to lead the work on deep-sea research in Norwegian waters given their expertise in ore geology and mining. Instead, a lot of this work now falls under the remit of the NOD, and some folk at NGU may not have been too pleased with that. However, if there is one thing both parties can probably agree on, it is that more exploration is needed to further prove up economic quantities of critical metals. No matter what models or datasets one uses, it is ultimately more data that will form the basis for the big decision to go ahead or not.
