SEG Lecture: “Subsea Mining: The Nautilus Experience”

Seventy-one percent of the Earth’s crust is covered by ocean. According to NOAA, “more than 95 percent of the underwater world remains unexplored.” In other words, seventy percent of the planet could hold vast, untapped mineral resources. As technology improves, humankind’s ability to access these resources increases as well. Soon, the majority of mining may be done, not on land as today, but far below the sea.

On March 6, Mr Tony O’Sullivan (now with OPX Mining) came to the Mines student chapter of the Society of Exploration Geologists (SEG) to talk about his experiences working for Nautilus Minerals, a company which seeks to exploit these undersea resources. Nautilus was started in 2005 to buy copper leases off of Papua New Guinea, Tonga, New Zealand, and so on. While offshore mining already occurs for diamonds in Namibia, gems in India, and tin in Malaysia, Nautilus was the first company to obtain an environmental permit for deep-sea mining.

Nautilus takes its inspiration from the oil and gas industry. Terrestrial mineral deposits are becoming increasingly hard to find and more difficult to permit. Those that are found tend to be of lower grade, as the high grade deposits are discovered and mined out, and removal of the minerals tends to be detrimental to the environment. A mobile, ocean-surface mining platform, on the other hand, would leave a small footprint, since the infrastructure involved would be minimal.

With very little exploration having been done, over three hundred massive sulfide deposits are known on the seafloor. A massive sulfide deposit forms when an undersea volcanic vent, or “black smoker”, releases hot metallic gases into the water. The metals fall in a sort of particulate rain, down current from the smoker, leaving incredibly rich deposits of copper, gold, silver, zinc, iron, and many other useful minerals. They also form a chimney over the hydrothermal vent, which collapses once the vent goes cold, leaving a mound of high-grade ore. Some of the richest terrestrial mineral deposits that have been mined are ancient black smokers; Nautilus proposes to mine them while the sulfides are still fresh – a few years (or even months) old instead of a few million years old.

In 1996, the first deep-sea title was granted to the people who would later go on to found Nautilus. The title is for an area of the seafloor the size of Spain; Nautilus wishes to snap up as much land as they can now, while such properties are still cheap. The deposit they wish to mine, Solwara 1, is off the coast of Papua New Guinea, near an island called New Ireland. It is a modern, active massive sulfide, with fifteen-meter-high chimneys, strongly fault-controlled, and relatively small but easily accessible. The mineralogy is simple, consisting of mainly chalcopyrite, a copper ore mineral. Best of all, the ore grade is 7.2% copper. To put this in perspective, the average grade of copper ore currently being produced from is less than 0.6%.
Despite the attraction of such an impressive ore, the operating lease for the property was not granted until 2011, following extensive investigations into available technologies, environmental studies, geophysical surveys and so on. The overlying water allows for sonar mapping of the substrate, which is helpful because the vent plumes can be tens of kilometers across and can interfere with mapping efforts. Geochemical sampling of the plume itself was conducted, and drill cores were taken, but the cores were pulverized by the rig. In order to circumvent this problem, in a mere fourteen months Nautilus developed a drill mounted on an ROV (remotely operated vehicle), an underwater robot controlled from the ship. The new drill took core recovery from ten to seventy percent. Another new technology Nautilus created, going from concept to practice in less than two years, is an electromagnetic survey of the seafloor, which shows useful ores but not pyrite, giving an excellent picture of copper mineralization at the site.

As it turned out, Nautilus had to invent a number of technologies to make seafloor mining feasible and efficient. They based their production machinery on pipeline building/burying ROVs developed for oil and gas, and the mechanism to bring ore to the surface was modified from a Chevron machine that pumps drilling mud out of offshore drillholes. There are three types of ROV, two rock cutters and a collector. The machines are quite large, about four meters by ten meters (~12’x30′). The first cutter makes a bench in the sea floor, the second cutter mines the bench, leaving piles which the collector chews up. The ore sizing is done on-site by the collector, which sucks up the material into the pump. The pump carries the ore to the ship, where it is dewatered; the water is used to power the pump, and the pump is designed in such a way that waste material from the seafloor returns to where it came from, rather than being dumped. The ore is then offloaded onto another, larger ship, which takes it to the mainland to be sold to China. The mine should be productive for about three years before the mine ship must be moved to a new location.

In order to ensure peak efficiency, a detailed model of the deposit and a mining plan were created, taking into account the rock hardness, the ore grade and so on. This plan – and the unique character of the site – ensures there will be almost no waste of resources on unproductive rock or “overburden”. Because the facilities are mobile, they can be reused again and again, reducing environmental impact and cost. Finally, the stratification of the ocean and the existing hostility of the environment mean that the ecological impacts of the mine will be minimal.

The mine is not yet producing, O’Sullivan noted, though it was supposed to begin this year, thanks to a governmental crisis going on in Papua New Guinea. Once production can begin, however, it will surely herald a sea-change in the mining world… literally.

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