Polymetallic nodules

Also called: Manganese nodules, Polymetallic nodules of the Central Indian Ocean Basin · Topic: Mineral Resources of India: Distribution and Conservation · NCERT: Class 11, Ch 1 "Geography as a Discipline"

Meaning

Polymetallic nodules (also called manganese nodules) are potato-sized lumps that lie on the deep ocean floor and are rich in manganese, nickel, copper and cobalt. "Polymetallic" means "containing many metals".

They matter because cobalt, nickel and copper are critical minerals (minerals a country needs for clean energy, electronics and defence, but whose supply is at risk). India depends on imports for these metals. India also has a special early claim to explore nodules in the Central Indian Ocean Basin (CIOB).

Explanation

How nodules form (cause → process → result)

• Cause: metals are dissolved in seawater and seabed mud.

• Seawater and the mud on the ocean floor hold tiny amounts of dissolved metals.

• Process: the metals settle in layers around a small core.

• The core can be a shark tooth or a small bit of rock.

• The metals build up in thin layers, one around another, like the layers of an onion.

• Result: very old lumps that cannot be replaced.

• Nodules grow only a few millimetres in a million years.
• So a nodule field is very old. Once mined, it cannot be replaced in human time. This makes nodules a non-renewable resource.

What they contain

• Main metals: manganese, nickel, copper, cobalt and iron.
• NCERT Class 10 calls them manganese nodules on ocean beds, because manganese is a major part of them.
• Some nodules are cobalt-rich. An example is the Andaman Sea nodules [2].

Conditions they need

• Setting: the abyssal plain. This is the flat, deep floor of the open ocean, about 4,000–6,000 m deep.
• A quiet, stable seabed. Growth is very slow, so the nodules need a calm floor that stays the same for millions of years.
• Nodules are not found only in very deep water. Over 100 kg of cobalt-rich polymetallic nodules were collected from 1,173 m depth in the Andaman Sea [2].

Nodules among the three deep-sea deposits

Deposit	Relief where it forms	Main metals
Polymetallic nodules	Abyssal plains	Manganese, nickel, copper, cobalt, iron
Polymetallic sulphides	Mid-ocean ridges (underwater mountain chains where plates move apart), near hydrothermal vents	Copper, zinc, lead, gold, silver
Cobalt-rich ferromanganese crusts	Slopes and tops of seamounts (underwater volcanic mountains)	Cobalt, manganese, nickel, rare metals

Where it occurs

• World: the abyssal plains of the Pacific, Indian and Atlantic Oceans.
• India: the Central Indian Ocean Basin (CIOB). This is a deep basin in the Indian Ocean, far south of the Indian peninsula.
• It lies in the "Area". Under UNCLOS (United Nations Convention on the Law of the Sea, 1982), the Area is the seabed beyond national limits. Its minerals are the common heritage of mankind, which means no single country owns them.
• 1987: India became the first country to get pioneer investor status. A pioneer investor is a country that spent money on seabed exploration early, so it got a reserved area before the full system began.
• 2002: India got an International Seabed Authority (ISA) exploration contract over 75,000 sq km in the CIOB. The ISA is the UN body that controls mining in the Area. Its headquarters is in Kingston, Jamaica.

• December 2022: India's autonomous underwater vehicle Ocean Mineral Explorer (OMe 6000) surveyed the CIOB nodule site at 5,271 m. It worked from the research vessel Sagar Nidhi. It surveyed 14 sq km and mapped a 1 km × 0.5 km patch in detail. The aim was to study how the nodules are spread out and what lives there [2].

• Andaman and Nicobar Islands (Andaman Sea):

• Cobalt-rich nodules were found at 1,173 m [2].

• Blocks for polymetallic nodules and crusts were in the first offshore auction tranche (November 2024, 13 blocks). This auction was held under the Offshore Areas Mineral (Development and Regulation) Act, 2002, as amended in 2023.

• Deep Ocean Mission (DOM): a Ministry of Earth Sciences (MoES) mission. The Cabinet approved it in June 2021, at a cost of ₹4,077 crore over five years [2].

• Its first component builds an Integrated Mining System to lift nodules from the Central Indian Ocean. It also builds a crewed submersible to reach 6,000 m [2].
• That submersible is Matsya-6000, under the Samudrayaan project. It carries 3 people and is built by NIOT with VSSC, ISRO [2].

Don't confuse with

• Polymetallic sulphides: these form at mid-ocean ridges near hot-water vents, not on abyssal plains. India's sulphide contract (2016) is for the Central and South-West Indian Ridges, not the CIOB.
• Cobalt-rich ferromanganese crusts: these are a hard coating on bare rock of seamounts, not loose lumps on the mud. India's crust application (2024) is for the Afanasy-Nikitin seamount.
• Clarion-Clipperton Zone: this is a nodule area in the Pacific. India's nodule contract is in the Central Indian Ocean Basin.
• Andaman nodule blocks vs CIOB nodules: the Andaman blocks are inside India's own sea zone, so India auctions them under the Offshore Areas Act. The CIOB lies in the Area, so India needs an ISA contract.

Prelims Hooks

• India was the first country to get pioneer investor status (1987) for seabed nodules.
• India's ISA nodule contract (2002) covers 75,000 sq km in the Central Indian Ocean Basin.
• Match the deposit to its setting: nodules → abyssal plains; sulphides → mid-ocean ridges; cobalt crusts → seamounts.
• OMe 6000 surveyed the CIOB nodule site at 5,271 m in December 2022, working from Sagar Nidhi [2].
• Trap: an ISA exploration contract allows only survey, sampling and testing. Commercial mining needs the ISA mining code (the rules for mining, royalties and environmental protection), and this code is still not settled.
• Trap: the ISA does not license blocks inside India's EEZ (Exclusive Economic Zone, up to 200 nautical miles). The Andaman nodule blocks are auctioned under the Offshore Areas Mineral (Development and Regulation) Act, 2002 (amended 2023), not under the MMDR Act, 1957.

Mains Points

• Strategic need (GS-III): India imports cobalt, nickel and copper, and it needs them for batteries and the energy transition.
• CIOB nodules are a long-term strategic source of these metals.

• The DOM (₹4,077 crore) and Matsya-6000 build the technology to reach and lift them [2].

• Environmental cost: nodules take millions of years to form, so mining destroys habitats that cannot recover.

• Mining machines scrape the seabed. Sediment plumes (clouds of stirred-up mud) spread and smother life.

• Deep-sea species grow slowly, and many are still unknown. This is why many countries want a moratorium (a temporary stop) or a "precautionary pause". Answers should call for baseline environmental studies and an environmental impact assessment before any mining.

• Governance and resource planning: under the NCERT split, minerals inside the EEZ are national resources, and minerals beyond it are international resources.

• This explains why India explores the CIOB under an ISA contract but auctions blocks near the Andamans.
• India's commercial nodule mining is meant to start only "once global rules are set by the International Seabed Authority" [2]. Using these minerals with care, planning and recycling is part of conserving non-renewable minerals.

Related concepts

• Deep Ocean Mission
• Offshore mineral blocks auction

Read more

• Ocean minerals: polymetallic nodules, the Deep Ocean Mission and offshore blocks