The Metals Company Inc., through its subsidiary, Nauru Ocean Resources Inc. (NORI), holds exploration rights to four areas (NORI A, B, C, and D).
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Summary:
Two major west-south-west and east-north-east trending fracture zones that run through the seafloor define the Clarion-Clipperton Zone (CCZ): the Clipperton Fracture Zone to the south and the Clarion Fracture Zone to the north. These fractures zones can be seen clearly on the bathymetric map. The eastern and western limits can be defined by the Mathematicians Seamounts or Ridge in the east and the Republic of Kiribati or Line Islands in the west.
The CCZ seafloor is part of the abyssal plain, the largest physiographic habitat type on Earth that covers approximately 70% of ocean basins and 30% of the Earth's surface (UN Division for Ocean Affairs and the Law of the Sea and the ISA, 2004). Ridges believed to have formed from the process of seafloor spreading traverse the CCZ. The ridges have a north-north-west to southsouth-east (locally ±20°) orientation with amplitudes of 50 to 300 m (maximum 1,000 m; Hoffert, 2008) and wavelengths of 1 to 10 km. The bathymetric map of NORI Area D (The whole of NORI Area D (25,439 km2 ) was surveyed. Due to swath width and vessel orientation relative to course-made-good, some data was recorded beyond the bounds of those areas.
Extinct volcanoes that rise 500 to 2,000 m above the seafloor punctuate the seafloor of the CCZ. Depth in the CCZ increases from 3,800 to 4,200 m at 115° west to 4,800 to 5,200 m at 130° west and 5,400 to 5,600 m at 145° west. The sediment types exhibit trends perpendicular to the bounding fracture zones, from predominant carbonate sediments in the south-eastern extreme to predominant siliceous red clay in the west north-west.
Sedimentation and nodule formation
Nodules comprise nuclei and concentric layers of iron and manganese hydroxides and form via the precipitation of metals from seawater and sediment pore-water. The metal accumulates slowly, and it generally takes millions of years for a nodule to form (Skowronek et al. 2021).
Nodules are abundant in abyssal areas with oxygenated bottom waters, low sedimentation rates (less than 10 cm per thousand years), and where sources of abundant nuclei occur (Hein et al., 2013). Nodules grow on 0.1 to 1 cm nuclei (e.g., pieces of pumice and older broken nodules) and generally range from about 1 to 12 cm in their longest dimension, with the low to middle-range typically the most common (1 to 5 cm).
The specific conditions of the CCZ (water depth, latitude, and seafloor sediment type) are considered to be the key controls for nodule formation along with the following factors:
• Supply of metals to the growing surface;
• Presence of a nucleus;
• The corrosive/erosive forces caused by benthic currents;
• Occurrence of a semi-liquid surface layer on the seafloor (sediment water interface);
• Bioturbation.
The highest values of metals in nodules are thought to be best developed on the seafloor in the equatorial regions away from land sources of sediments. In these regions, surface waters have high primary productivity. Tiny plants and animals concentrate the metals from seawater and, when they die, they sink to the seafloor, dissolve, and release the metals into the pore water of seafloor sediments. It is believed that the upper portion of the nodules accumulate metals that precipitate from seawater, while the lower portion of the nodules, partially buried in sediment, accumulate metals from pore water in the underlying sediments.
Sediments from the CCZ consist mostly of clays and siliceous biological casts. Sands and larger sediments are not generally found so far from land, and the commonly formed carbonate biological casts dissolve on the seafloor in these deep-water regions faster than they accumulate.
Polymetallic mineralization
The ISA completed a geological modelling project in 2009, based on data collected by contractors over the preceding 30 years (ISA, 2009, 2010a, 2010b).
Nodule grades
Nodule chemistry varies only slightly within the CCZ. The high continuity and low variability of grades across vast distances is remarkable. Copper and manganese generally increase towards the southeast, cobalt is generally higher towards the north, and nickel is generally higher towards the center and southwest of the CCZ. The reason for these very largescale trends is not clear. The German data for NORI Area D were not included in the ISA geological model.
Nodule abundance
Nodules lie on the seafloor sediment, often partly buried. Some nodules are completely buried, although the frequencies of such subsurface occurrences are very poorly defined. Kotlinski and Stoyanova (2006) document up to five discrete layers of buried nodules, although all were within 45 cm of the surface despite using sediment cores of 250 to 380 cm depth. Other images of box corers also suggest that all or most of the nodules are at the surface. Consequently, drilling is not required for defining the Mineral Resources.
During the 2018 – 2022 NORI Area D campaigns, 93% of nodules sampled were situated at surface These include nodules on the surface and nodules with their top surfaces in the upper 1 cm of sediment. At least 96% are inferred to be within the top 5 cm of sediment. A few nodules were found at depth; most of these were usually clustered around the edges of the box core and are considered to have been pushed below surface by the box coring process.
Nodules vary in abundance, in some cases touching one another and covering more than 70% of the seafloor. The highest concentrations of nodules have been found on abyssal plains between 4,000 and 6,000 m below sea level.
Nodule facies
NORI identified three broad facies of nodule distribution on the seafloor (distribution pattern with similar nodule coverage and nodule sizes), based on camera imagery.
Type 1 nodule facies is typically characterized by >50% nodules (by area of coverage). The majority of these nodules are typically medium-sized and are closely packed, with many nodules in contact with their neighbors.
Types 2 and 3 are characterized by larger nodules, and the nodules are typically separated (i.e., there are noticeable sediment gaps between individual nodules).
In high-resolution camera imagery, facies boundaries may be quite sharp (i.e., not gradational) and variable over short distances (<100 m).
Nodule distributions can be mapped by measuring the backscatter (return signal) response from multibeam echo sounding (MBES) from vessels on the ocean surface. Type 1 nodule facies correlates with moderate-amplitude backscatter areas and is the most common facies. Type 2 and 3 nodule facies typically correlate with higher-amplitude backscatter areas.
Nodule morphology and formation
A variety of nodule classification systems were used in previous studies of the CCZ (for example, Haynes et al. 1985), but the three-class system promoted by the ISA (ISA 2010) prevails today. Nodules are classified according to their morphology or texture, as:
• S-type (smooth type);
• R-type (rough type);
• S-R-type (smooth-rough mixed type).
It is postulated that the different textures are related to the position of the growing nodule, relative to the seafloor. The S-type nodules are interpreted to have grown by absorption of metals directly from seawater (hydrogenetic processes), the R-type are interpreted to have absorbed metals from the water within the seafloor sediment (diagenetic processes), and the S-R-type are interpreted to have grown as a result of both hydrogenetic and diagenetic processes. These formation mechanisms affect grade distribution and are considered in the development of estimation domains under S-K 1300.
There is a general association between this textural classification and the nodule facies observed in seafloor photographs and interpreted from backscatter response. Type 1 facies appears to be characterized by smaller S-type or S-R type nodules and Type 2 and 3 facies appear to be characterized by larger R-type or S-R -type nodules.