Polymetallic Nodules

The beginning : Oceanography was still an amateur science when the HMS Challenger (left) set sail in December 1872. She returned in May 1876 with vast information that laid the solid foundation of oceanography. The first discovery of Polymetallic nodules also begins with this historic voyage of Challenger; on the 7th March 1873 the dredge hauled up on its deck ‘several peculiar black oval bodies which were composed of almost pure manganese oxide’. In 1965, J.L. Mero studied the economic possibilities of manganese nodules mining and predicted that the manganese nodule mining should be a sound business proposition in about 20 years.



A conference “Ferromanganese deposits on the Ocean Floor”, was organized at  the  Lamont – Doherty Geological Observatory in January 1972, sponsored by International Decade of Ocean Exploration  that gave a considerable stimulus to the development of an incipient nodule mining industry. Subsequently, it was discovered that these nodules cover vast areas of the ocean floor and are more abundant in areas off the west coast of Mexico, known as Clarion-Clipperton fracture zone (CCZ), in the Central Indian Ocean Basin (CIOB) and in the Peru basin. 

Genesis : They are composed mainly of Mn, Fe, Silicates and hydroxides, however, it is the trace metal contents such as Ni, Cu, Co, and Mo and Rare Earth Elements (REE) that are attracting  interests to mine these deposits to meet the growing demand for these metals. The nodules vary in size from micro-nodules to about 20 cm, the common size being two to eight centimeters. They occur abundantly as 2 D deposits at the unconsolidated sediment-water interface, and sometime scantly buried in sediments at different layers.  They occur in different  sedimentary environments, in shallow waters, in lakes, however, the deposits of economic importance occur mostly at  four to six thousand meters depths in areas of  extremely low sedimentation rate. Nodules require a nucleus to start forming. This nucleus could be anything, varying from a piece of pumice, a shark tooth, old nodule piece, basalt debris or even microfossils like radiolaria and foraminifera. The enrichment of metals around the nucleus is either hydrogenetically by the precipitation of metals from the seawater or through release from the interstitial spaces between the underlying sediments, by early digenetic process or by a combination of both. Nodules from the topographically smooth areas  of abyssal plane with an abundance of > 5 kg/m2and  a combined  > 2% grade (Cu, Ni and Co) form a sound economic proposition.  Thy are found in about a dozen morphological types, such as spheroidal to discoïdal.

Present Scenario : Polymetallic nodules are no longer the domain for marine geologists and chemists, as policy makers, lawyers, entrepreneurs, engineers and investors also have become involved in their occurrences in areas beyond the national jurisdiction in common heritage of mankind, regulated by the  International seabed authority (ISA).Following the  adoption of the Regulations on Prospecting and Exploration for polymetallic nodules in the Area, in July 2000, the ISA has entered into exploration contracts with seven entities from 2001-06, and with five others after 2011.  These entities are engaged in assessing the resources in their respective license areas allocated by the ISA, besides studying the technologies for metal extraction and mining these deposits,  they are also engaged in the environmental impact assessments prior to getting clearance for mining.

Polymetallic Sulphides