Polymetalic nodules or manganese nodules

Polymetallic nodules or Manganese nodules

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Define
Formation
Occurance
Polymetalic nodules program of India
Merits and challenges

 Polymetalic or manganese nodules is a rock concretion lying over the sea floor at the depth of 3500 to 6000 meters. it appear like a potato with concentric layers of manganese and iron hydroxides depositing around the core. which further crystallised turning even the core into manganese .it grows of diameter from 10-100mm

Polymetallic nodules are Fe-Mn oxides deposits,potato shape, porous,black
earthy colour with size from 2 to 10 cm in diameter. The nodules develop under calm deep water conditions such as :

1.     low sedimentation rate
2. Oxidising environment means supply of good oxygen
3. availability of nucleus around which accretion of oxides takes place.
4. bottom currents of low velocity
5. low sedimentation rate of suspended material otherwise nodules will be covered by sediments
6. Constant flow of antartic bottom water that remove fine sediments and coarser sediments of shell or other act as nuclei for metallic compound deposition.
7. aqueous sediments capable of holding pore water.

there is 3 ways/process by which manganese or polymetallic nodules formed over the core 

1. Hydrogenous process : above 4000m, over smooth surface, rich in Fe,Co,P,Pb,Ti content. the Mn/Fe ratio =1
2. Diagenetic process : below 5000m depth over rough surface, rich in Mn,Cu, Ni, and Zn content. The ratio of Mn/Fe is more than 2.5.
3. muxed type : both hydrogenous and diagenetic process is involved at depth of 4000-5000 m.

Nodules develop by the above process you can see below :-

OCCURANCE :  Manganese nodules is found in many oceanic regions . it is found in 4 regions which is economically exploitable are given below:-

1. CLARION-CLIPPERTON ZONE (CCZ): With an area of around 9 million square kilometres, approximately the size of Europe, this is the world‘s largest manganese nodule region. The CCZ is located in the Pacific, extending from the west coast of Mexico to Hawaii. The nodules are not evenly distributed over this area. At some sites they are more densely grouped. No nodules at all are found in stony areas. On the average, one square metre in the Clarion-Clipperton Zone contains around 15 kilograms of manganese nodules. Especially rich areas can have up to 75 kilograms. The total mass of manganese nodules here is calculated to be around 21 billion tonnes.
2. PERU BASIN: The Peru Basin lies about 3000 kilometres off the Peruvian coast. It is about half as large as the Clarion-Clipperton Zone. The region contains an average of 10 kilograms of manganese nodules per square metre.
3. PENRHYN BASIN: The third important manganese nodule area in the Pacific is located in the Penrhyn Basin very near the Cook Islands, a few thousand kilometres east of Australia. It has an area of around 750,000 square kilometres. Large areas in the Cook Islands coastal waters have concentrations of over 25 kilograms of manganese nodules per square metre of sea floor.
4. INDIAN OCEAN: So far only a single large area of manganese nodules has been discovered here, with an area comparable to that of the Penrhyn Basin. It is located in the central Indian Ocean. Each square metre of the sea floor here contains around 5 kilograms of manganese nodules.  Central Indian Ocean Basin (CIOB) tested successfully at 5462 depth manganese nodule.

INDIA's POLYMETALLIC NODULES PROGRAMME :-
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India recieved the licence for exploration and mining of polymetallic nodule from international seabed authority (ISA) in 2002 for a period of 15 years. the term of contract is further extended to 5 years recently in central Indian ocean Basin (CIOB).
   In the 75000sqkm area of CIOB, the estimated polymetallic nodules resource potential is 380million tonnes, containing 92.59mt of manganes, 4.7mt of nickel, 4.29mt of Cu & 0.55mt of Co. polymetallic nodule programme is oriented towards exploration and development of technologies for harnessing of nodules from the central Indian Ocean Basin (CIOB) allocated to India by international seabed authority.
    It has 4 components such as :-

1. survey & exploration
2. environmental impact assessment
3. technology development(minining), and
4. technology development (metallurgy)

after detailed survey & analysis , at this stage ,an area of 7860 square km has been identified in the CIOB for the firts generatiin mining site. EIA studies for mining of deep sea polymetallic nodules is also carried out to evaluate the possuble impacts of mining in deep-sea environment. A Remotely Operable Submersible (ROSUB 6000), capable of operating at 6000 m water depth was developed and tested successfully at a depth of 5289 m for assessing environmental condition below 5000 m.

even two pilot project to demonstrate the extraction of nodules was commissioned at 

1. A 500 kg nodules per day for extracting Cu,Ni & Co at Hindustan Zinc Limited, Udaipur
2. A 500 kg processing capacity for extracting of ferro-sillico-manganese ore from the residue obtained from HZL plant.

INDIA is pioneer in R&D ,EXPLORATION AND MINING OF MARINE RESOURCES UNDER DEEP SEABED MINING PROGRAMME . India is among top 8 countries to do deep sea mining project. Presently, such project is not commercially -economically viable due to higher cost involved in the process along with technology for mining and metullergy is at infant stage. machinery is not available now at low cost. even though India is going through its polymetallic nodule programme due  to its strategic needs of these minerals for defence,space and electronic industry , developing hi-tech industry, with the continious R&D the cost of these mineral mining will fall and in future these nodules could be potential mineral resource reserves for us. presently, all the found nodules reserves in CIOB is uneconomical and unprofitable.

Recently, INDIA was re-elected as the member of INTERNATIONAL SEABED AUTHORITY(ISA). and term for contract to explore and extract polymetallic nodules is eztended for 5 years i.e., till 2022.

For the manganese nodule areas this means that contractors apply to the ISA for an exploration area of up to 150,000 square kilometres. The individual contractor must pay a licence fee for these areas. The crucial condition is that the countries can only use half of their licence area, or a maximum of 75,000 square kilometres. After preliminary exploration, the other half is reserved for developing states. So far the ISA has awarded 12 licences for the Clarion-Clipperton Zone and one for the Indian Ocean, all to various states. The contractors are China, Germany, France, India, Japan, the Russian Federation, South Korea, and the Interoceanmetal Joint Organization, a consortium of Bulgaria, the Czech Republic, Slovakia, Poland, the Russian Federation and Cuba

all the countries experiences two problems for mining the polymetallic or manganese noduels they are follows as :-

1. machinery for deep sea mining is not fully developed so, cost of mining remains very high making deep sea mining project unviable. for example near papua new guneia projec was suspended.
2. environmental impact assessment due to deep sea mining is not done ,no detail analysis is available. no idea to environmentalist how adversely such mining project affect the marine ecology.