Mineral Deposits Found on Deep Sea Floor

Deep beneath the oceans—beyond the continental shelf and slope—lies the deep sea floor. And while it may seem dark and lifeless, this zone is actually rich in minerals of enormous economic value. Let’s explore the key types found here.

1️⃣ Marine Manganese Nodules (Polymetallic Nodules) and Crusts

What are they?

Imagine round, blackish lumps lying freely on the ocean floor—these are manganese nodules, also called polymetallic nodules. They are rich in:

• Manganese (~30%)
• Nickel (1.25–1.5%)
• Copper (~1%)
• Cobalt (~0.25%)
  And also contain iron, silicon, and aluminium in smaller amounts.

🌊 How are they formed?

• From precipitation of metals dissolved in seawater.
• From hydrothermal vents (hot springs on the ocean floor).
• Through microbial activity.

These nodules just lie on the sea bottom as loose material, making them easy to locate but hard to collect due to extreme depth.

Similarly, manganese crusts form on rocky outcrops under the sea—same materials, just a different setting.

🌍 Where are they found?

• Countries with rich potential: India, US, Brazil, Japan, South Africa, Canada, etc.
• Notably, India has exclusive rights to explore over 75,000 sq. km in the Central Indian Ocean Basin (CIOB), granted by the International Seabed Authority (ISA).

⚠️ Challenges:

• They lie 5–6 km deep, making extraction technologically and economically difficult.
• If land-based sources (like nickel) are cheap, then deep-sea mining becomes non-viable.

2️⃣ Marine Gas Hydrate Deposits

What is Gas Hydrate?

Also called fire ice, methane ice, or hydro methane, it is a crystalline solid where methane gas is trapped inside a cage of water molecules. Found in:

• Deep oceans (where pressure is high and temperature is low)
• Polar shallow waters

⚙ How does it form?

• Organic matter in marine sediment decays → methane is released
• Under high pressure and low temperature → methane gets trapped in icy structures

If this structure is disturbed (e.g. during extraction), methane is released—1 cubic metre of gas hydrate releases ~164 cubic metres of methane!

🌍 Reserves:

• Found in Atlantic and Pacific margins of both Americas
• In India:
  • Krishna-Godavari (K-G) Basin – biogenic methane hydrate
  • Bay of Bengal – large, concentrated deposits discovered by ONGC

⚠️ Challenges:

• Methane hydrates are extremely pressure and temperature sensitive.
• Extraction is risky—when brought to surface, they dissociate, releasing methane.
• Methane is a greenhouse gas 20x more potent than CO₂—so it can exacerbate global warming if mishandled.

3️⃣ Marine Polymetallic Sulphides (PMS)

What are they?

They are metal-rich deposits containing:

• Iron, copper, zinc, silver, gold, platinum
• Formed when superheated fluids from deep within the Earth (magma) rise and cool rapidly on the seafloor—especially along mid-ocean ridges

🌍 India’s Role:

• India has a 15-year contract with ISA to explore 10,000 sq. km in Central and South-West Indian Ridges (SWIR).
• Near the Galapagos Rift, PMS deposits show:
  • 48% Sulphur
  • 43% Iron
  • 11% Copper, along with zinc, tin, silver, etc.

4️⃣ Marine Evaporite Deposits

What are they?

Evaporites are minerals formed by evaporation of seawater in geological basins. They include:

• Anhydrite and gypsum (calcium sulphates)
• Sodium and magnesium salts
• Potash minerals

They often create structures like salt domes—which can trap oil and gas due to their shape and impermeability.

🤔 Are they valuable?

• Not really for marine mining, because land-based deposits of rock salt are far more accessible and abundant.

Key Takeaways:

• Deep sea floors have nodules, crusts, hydrates, sulphides, and evaporites.
• These are rich in metals, methane, and other economic minerals.
• India has made major strides, especially in the Indian Ocean.
• However, technological, environmental, and economic challenges make exploitation a tricky path forward.