minerals Article Aspects of Estimation and Reporting of Mineral Resources of Seabed Polymetallic Nodules: A Contemporaneous Case Study John Parianos 1, *, Ian Lipton 2 and Matthew Nimmo 2   Citation: Parianos, J.; Lipton, I.; Nimmo, M. Aspects of Estimation and Reporting of Mineral Resources of Seabed Polymetallic Nodules: A Contemporaneous Case Study. Minerals 2021, 11, 200. https:// doi.org/10.3390/min11020200 Academic Editor: Pedro Madureira Received: 8 January 2021 Accepted: 10 February 2021 Published: 14 February 2021 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). 1 Nautilus Minerals Pacific Ltd., East Brisbane, QLD 4169, Australia 2 AMC Consultants, Brisbane, QLD 4000, Australia; ilipton@amcconsultants.com (I.L.); mnimmo@amcconsultants.com (M.N.) * Correspondence: jmp@nautilusminerals.com Abstract: Exploration of seabed polymetallic nodules identifies the Clarion Clipperton Zone and the Indian Ocean Nodule Field to be of economic interest. Mineral resource estimation is important to the owner of the resource (all of mankind; and managed by the International Seabed Authority; ISA) and to developers (commercial and government groups holding contracts with the ISA). The Committee for Mineral Reserves International Reporting Standards was developed for the land- based minerals industry and adapted in 2015 for ISA-managed nodules. Nodules can be sampled in a meaningful manner using mechanical devices, albeit with minor issues of bias. Grade and moisture content are measured using the established methodology for land-based minerals. Tonnage of resource is determined via the abundance of nodules in kilograms per square metre of seabed. This can be estimated from physical samples and, in some cases, from photographs. Contemporary resource reporting for nodules classify the level of confidence in the estimate, by considering deposit geology, sample geostatistics, etc. The reporting of estimates also addresses reasonable prospects for eventual economic extraction, including factors such as mining technology, the marine environment, metallurgical processing, and metals markets. Other requirements are qualified persons responsible for estimation and reporting, site inspection, and sample chain of custody. Keywords: polymetallic nodules; mineral resource estimation; mineral resource reporting; CRIRSCO; seabed geology; geostatistics 1. Introduction The estimation and reporting of mineral resources and their exploitable subsets, e.g., mineral/ore reserves, provide important information for the owners of the minerals, the owners of groups with development rights, and other stakeholders. We report here on aspects that we found important in producing some of the first contemporary mineral resource estimates for polymetallic nodules. There are extensive deposits of high-grade polymetallic nodules resting on the seabed within the Clarion Clipperton Zone (CCZ) in the Pacific Ocean and the Indian Ocean Nod- ule Field (IONF) (Figure 1; International Seabed Authority [1], Mukhopadhyay et al. [2]). Recent interest in developing these resources has resulted in efforts to advance questions of mineral rights (e.g., Watzel et al. [3], Toro et al. [4], Hein et al. [5]). Minerals 2021, 11, 200. https://doi.org/10.3390/min11020200 https://www.mdpi.com/journal/minerals