A veteran geoscientist who worked with TSX-listed Nautilus Minerals’ on its journey into uncharted resource-estimation waters at the Solwara 1 multi-metal project in the Bismarck Sea suggests this may not be the case.

Ian Lipton, the qualified person (QP) for Nautilus’ NI 43-101 technical report and mineral resource estimate for Solwara 1 in Papua New Guinea territorial waters when it was issued in 2008, is now principal consultant at AMC Consultants. The original technical report was compiled when Lipton was with Golder Associates. AMC had its QP imprimatur on this week’s upgraded resource estimate announced by Nautilus for its CCZ (Clarion Clipperton Zone) project in the Central Pacific, south of Hawaii.

The increase in CCZ’s inferred mineral resource base from 410 million tonnes (wet) to 685Mt was combined with the inclusion of 68Mt (wet) in the indicated resource category, and 2.6Mt in measured.

“Interest in the exploration and mining of seafloor mineral deposits continues to grow, spurred on by a range of factors including decreasing deposit grades on land and the development of new subsea mining technology,” Lipton says in AMC’s latest client newsletter.

“Leading the race to seabed production is Nautilus Minerals, which announced in September 2015 the start of construction of the production support vessel for its Solwara 1 copper-gold project in the Bismarck Sea.”

Earlier this year the company’s three seafloor production machines arrived at Port Duqm in Oman for ‘wet’ testing.

“About a third of the world’s seafloor area is covered by Exclusive Economic Zones and other areas of continental shelf that fall under the jurisdiction of individual nations,” Lipton says. “In these areas, the reporting requirements for mineral resources and mineral reserves are set by the laws of the nations within the exploration companies operate and/or the public exchanges on which the companies are listed.”

Lipton says while “a conventional site visit to examine the geology [at projects such as Solwara 1 and CCG] is crushingly impossible … this is not a serious impediment to mineral resource assessment since a well-designed programme will provide extensive sea floor video records, detailed bathymetric data and, probably, data from a range of geophysical sensing methods”.

“Every last drop of information that can be used to support the mineral resource estimate needs to be extracted from these less conventional sources. For example, at Solwara 1, a deepwater electromagnetic survey was used very successfully to map the lateral extents of the massive sulphide deposit; and the distribution of chimneys, mapped by high-resolution bathymetry, was used to identify the main pathways for the mineralising fluids.”

Still, the biggest challenge to seafloor exploration is undoubtedly obtaining sufficient representative samples at ocean depths of 5,000m or more.

Lipton says sampling techniques will vary according to the deposit type.

“Loose mineral deposits on the seafloor can be sampled with grab-samplers with opposing jaws or box-corers which penetrate the upper part of the soft substrate under their own weight and have a mechanical plate that rotates and closes the base of the box.

“These tools are used to determine, for example, the abundance [kilograms per square metre] of nickel-copper-manganese nodules or phosphate nodules on the seafloor.

“For deposits with a significant depth extent beneath the seafloor, a variety of coring methods has been developed. Cylindrical gravity corers and piston corers, which penetrate substrate under their own weight, and vibro-corers may be used to sample soft sediments down to tens of metres and may achieve satisfactory recoveries in favourable circumstances.

“For hard rock deposits, such as the volcanic-hosted massive sulphide deposit at Solwara 1, powered rotary drilling is required to cut through the rock. Vessel-mounted drilling systems, derived from oil and gas exploration methods, have been used but are hampered by the hundreds or thousands of metres of drill pipe in the water column and by the difficulty of controlling vessel heave.”

Nautilus has pursued development of diamond core drills that sit on the seafloor and can be remotely positioned, monitored and operated from a ship via an umbilical cable. This type of rig was successfully used to define indicated and inferred mineral resources at Solwara.

Lipton says sample recovery is the key issue.

“All the data required to support the assay data must be collected at the time of drilling. Because of the extremely high cost of seafloor drilling programmes, there are no economic options for going back and trying again if the first pass data collection is flawed or incomplete.

“Unlike terrestrial drilling, one can’t simply run out to resurvey the location of a box core sample or redrill a poorly-sampled drill hole.

“Detailed planning of data acquisition programmes is absolutely critical.

“Clearly defined procedures, well-trained staff, rigorous QA/QC procedures, thorough record-keeping, and integrated independent audits help to provide maximum bang for buck and ensure that the best possible data is collected.”

Lipton says survey control for observation points is also a challenge in the deep water environment, and accurately locating the position of a remote sensing device drifting at the end of several thousand metres of cable requires sophisticated equipment and experience.

The International Seabed Authority (ISA) responsible for the administration of seabed exploration and mining rights in international waters had recently issued a standard for the reporting and classification of mineral resources and mineral reserves in such areas.

Director and principal geologist at AMC, Pat Stephenson, past co-chairman of the Committee for Mineral Reserves International Reporting Standards (CRIRSCO), chaired the working group that identified the main items that had to be addressed in an ISA reporting standard, and modified the CRIRSCO template to produce a draft standard for the ISA.

Lipton says the standard applies to reporting of estimates that are not intended for public release or for the prime purpose of informing investors or potential investors and their advisors.

“Since the standard is based on the November 2013 edition of the international reporting template of CRIRSCO, it will ensure that private reports lodged with the ISA follow the same guiding principles and use the same definitions as public reports that comply with reporting standards such as CRIRSCO, JORC, NI 43-101, SAMREC, etc,” he says.

“The new ISA reporting standard provides extensive guidelines for the reporting of seafloor mineral resources.

“The over-riding principles of materiality and transparency, and the breadth of information required to be referenced by Enclosure 1 of the reporting standard, mean that investors reading reports prepared under the standard will be provided with a similar level of information to that provided for terrestrial deposits.”

Lipton says while significant challenges remain for those aiming to discover, define and develop mineral deposits on the seafloor, technology is advancing rapidly, “driven by innovative mining and exploration companies with an eye on mineral deposits of exceptional grade and size”.