Title: Exploration for deep sea mineral resources

Vision :

To explore the strategic minerals for the 21st Century

INTRODUCTION

MANGANESE (OR POLYMETALLIC) NODULES: Increasing global population, demand for metals and dwindling land resources, has come to such a pass that the next alternative source for the metals could be in the world oceans. Oceans are considered as a 'warehouse' for minerals, amongst others, polymetallic nodules (Ferromanganese nodules), phosphorites, hydrothermal sulphides, placer deposits and sand. The first discovery of polymetallic nodules was made by scientists onboard the research vessel "H M S Challenger" during 1873. In comparison, India (by the efforts of the National Institute of Oceanography, Goa) recovered nodules in the Arabian Sea during 1981 onboard "R.V.Gaveshani." In 1982, India was recognised as a Pioneer Investor in deep seabed mining, by the United Nations Convention on the Law of Sea.

Subsequently, a massive effort was put in by India for exploration of polymetallic nodules in the Central Indian Ocean Basin (CIOB) by using a number of research vessels. This national programme (running into crores of rupees) is being funded by Department of Ocean Development, New Delhi.

To-date, India has surveyed an area of nearly 4 million sq km in the CIOB. This resulted in the identification of two mine sites, each 150,000 sq km area with equal commercial grade (Cu+Ni+Co wt%) and abundance (kg/sq m) of nodules. In 1984, India filed her claim with the Preparatory Commission (PRECOM) for the International Sea Bed Authority (ISBA). In 1987, India became the first country in the world to be allocated exclusive rights for further exploration.

Team Members:
Banerjee, R.
Chakraborty, B
Gupta, S.M.
Iyer, S.D.
Khadge, N.H.
Mislankar, P.G.
Nath, B.N.
Pattan, J.N.
Rao, V.P. Valsangkar, A.B.

Gaonkar, S.S.
Jai Sankar, S.
Khedekar, V.D.
Marathe, P.
Parthiban, G.
Pattanshetti, S.S.
VijayKumar, B.

What are polymetallic nodules and the criteria for their formation?

Polymetallic nodules are Fe-Mn oxide deposits, potato shape, porous, black
earthy colour with size ranging from 2 to 10 cm in diameter.

Different shapes of polymetallic nodules .

Nodules occur at nearly 4 to 5 km depth in the deep oceans and they take one
million year to grow to one millimeter.

Under the microscope, the cross section of a nodule shows
alternative layers of iron (dark colour) and manganese (light grey colour).

Under water camera, attached to various sampling devices, reveals a dense carpet of
nodules overlying the sedimented seafloor.

Thick carpet of polymetallic nodules on the CIOB seafloor		Occurrence of polymetallic nodules in the Indian Ocean

In the Indian Ocean, nodules occur in different basins such as CIOB Wharton Basin,
Crozet Basin, Madgascar Basin, Somali Basin, South Australian Basin and Arabian sea.

The prerequisite conditions to form the nodules are:

Low sedimentation rate
Availability of nucleus around which accretion of oxides takes place
Oxidising environment
Bottom currents of low velocity

How are nodules collected from the seafloor?

Boomerang grabs or free fall grabs are used for collection of the nodules. The recovery of nodules helps to estimate the abundance (kg.sq m). The abundance of nodules varies from traces up to 25 kg/sq m.

A free fall grab being lowered.

Associated nodules and sediments can be collected with grabs such as Petterson, Van Veen and Petterson. Bulk nodules for metallurgical purpose and rocks are recovered by Dredges.

Pettersson grab being lowered for sediment sampling

What is the chemical composition of nodules?

To determine the chemical composition of nodules the samples need to be dried, powdered in an agate mortar, digested in mixture of Hydroflouric, Perchloric and Nitric acids. The digested solutions are analysed by using various analytical instruments. The average composition of nodules from the CIOB is as follows. (Source: Jauhari & Pattan 2000).

Average Chemical Composition of Nodules

Which are the minerals present in nodules?

Todorokite and delta MnO₂ are the two main minerals present in the nodules. Generally , nodules rich in manganese have todorokite and those rich in iron have delta MnO₂.

How are polymetallic nodules formed?

There are three processes for the formation of nodules.

• Hydrogenous process whereby metals are supplied from the water column and these accrete on a suitable nuceli. Hydrogenous nodules have smooth surface texture and are rich in Fe, Co, Ti, P and Pb content. The Mn/Fe ratio of these nodules is ~1.
• Diagenetic process supplies metals from the underlying sediment through the pore water by remobilisation. Diagenetic nodules have rough surface texture and are rich in Mn, Cu, Ni and Zn content. The Mn/Fe ratio is more than 2.5.
• Mixed type which is a combination of hydrogenous and diagenetic types.

The following are some significant scientific results:

• Nodule grade (Cu+Ni+Co %) is inversely related to abundance (kg/sq m).
• Manganese and iron show inverse relation suggesting their different source.
• Nodules with 2 to 6 cm size have high Mn, Cu, Ni and Zn concentration.
• Nodules grow with 1-2 mm per million year.
• Rare earth elements are supplied to nodules in association with Fe, Ti and P from the seawater.
  

Nodules of the CIOB

The formation of ferromanganese nodules on the ocean floor requires a nucleus, low sedimentation rate, oxidising conditions and low velocity bottom currents.

Bottom topography also plays an important role in the distribution of manganese nodules. The highest manganese concentration are generally found in nodules collected from high relief areas like valleys, followed by hilltops and slopes. Nodule abundance is least in the plains but have the highest content of Mn, Cu, Ni.

In contrast, nodules from hilltop have lowest concentrations of these metals. The size of nodule ranges between 2 and 10 cm in diameter, with a majority of them lying between 2 and 4 cm size range. Nodules in the CIOB are associated with practically all types of sediment and the nodule abundance varies from traces to 20 kg/m.

Nodules from siliceous sediment are smaller in size, rough surface texture, with todorokite as a dominant mineral enriched in Mn, Cu, Ni and Zn suggesting their supply through early digenetic process.

Ferromanganese nodules from red clay area are enriched in Fe, Co, Ti and P suggesting their supply mainly by hydrogenetic process. Rare earth elements are highly enriched in these nodules (~800 ppm) and are generally carried by a single authigenic phase consisting of Fe-Ti-P suggestive of their supply by seawater.

Ferromanganese nodules from the CIOB consist of ~75 % Mn as Mn (IV) and traces of Mn (III) was detected by electron spin resonance spectra. These nodules are formed under less oxic conditions compared to Pacific Ocean nodules. Mossbauer spectra of nodules exhibit a well-resolved doublet suggesting presence of paramagnetic Fe (III).

The first deep sea venture of the Institute, the exploration for nodules has started with the launching of a mega poject in 1982. The following table lists the milestones achieved:

• January, 1981: First nodule sample collected
• July, 1981: Formation of the Department of Ocean Development
• April, 1982: India recognised as a "Pioneer Investor"
• January, 1984: Application for the registration as a "Pioneer Investor"
• August, 1987: Exclusive rights allocated to the "Pioneer Investor"
• July, 1994: India relinquished 20% of the Pioneer Area as part of the obligation to the UNCLOS
• June, 1995: India ratifies the UNCLOS III convention
• July, 1995: India elected as the council member of the International Seabed Authority
• October, 1996: Relinquishment of 10 % of the Pioneer Area as a part of the obligation to the UNCLOS
• 2001-2002: Relinquishment of the final 20% of the allocated area to the ISBA
  

Sampling Data of the manganese nodule exploration programme (as on Dec. 2005)

Sampling Details

International Presence:

Out of the 114 countries who ratified the UNCLOS (United Nations Conference for the Law of the Sea), India is an important member in the group of seven Pioneer Investors. The others are France, Japan, InterOcean Metal, the Russian Federation, Korea and China. India was elected as a council member of the International Seabed Authority in 1995.

We form an important part of the global decision making groups on polymetallic nodule exploration. The scientists of the project have been participating as experts in the ISBA group meetings.

India was invited to explore the Exclusive Economic Zones (EEZ) of Indian Ocean island countries such as Mauritius and Seychelles for their resource potential.

Benefits of knowledge gained :

A) Several spin offs of the exploration have lead to R & D work resulting in over 250 publications and international patents. The following areas of science have been introduced to the Institute/country where our scientists have carved out niches:

• Deep sea sedimentary processes
• Origin and evolution of monsoon
• Tectonics and intraplate volcanic activity
• Long-term paleoceanography
• Planetology: meteorite impact products, cosmic dust
• Deep sea biogeochemistry, benthic life studies
• Seafloor mapping, marine acoustics and backscatter studies

B) The expertise gained in the deep sea exploration enabled the scientists to initiate or be key participants in several national/network programmes such as the Environmental Impact Assessment (EIA) of offshore mining, Mid-Ocean Ridge Exploration, Exploration for Gas Hydrates, EEZ Mapping, Hydrothermal sulphide deposits, Cobalt-rich crust exploration, etc.

C) Large industries and corporate houses are approaching us for our expertise in backscatter studies, EIA etc. An MOU is being finalised with a U.S. manufacturing company.

CURRENT WORK OF THE PROJECT

Current Target :

Identification of a first generation mine site for nodules in the Central Indian Ocean Basin (CIOB)

Having identified the Pioneer Area and after 50 % relinquishment of the area to the UN Seabed Authority, we are now left with 75000 km2 of nodule-rich area in the CIOB. The task of the Project Team is to identify the best chunk out this area which could form the First Generation Mine Site (FGMS). From the data generated, based on nodule abundance, consistently high grades (metal content i.e., Ni + Co + Cu ) and contiguity of the area to enable smoother navigation of the mining system, an area of about 17,500 has been earmarked for detailed investigations. This area forms the nucleus for the FGMS.

The following tasks are outlined in order to achieve the identification of FGMS:

• Close-grid sampling in the given area
• Detailed, swath mapping of the area
• Continuous resource evaluation

MAPPING THE DESIGNATED AREA IN THE CIOB:The hydrographic multi-beam system
(Hydrosweep) DS-II, is used to survey the seafloor topographic features in the First Generation Mine Site (FGMS) area. The main characteristic of the Hydrosweep system is the coverage angle of 120°-90° in which the seafloor is surveyed with high resolution beams. The area was surveyed with 90° coverage mode which is twice the center depth. The DS-II system is an improvement of the hydrosweep system having 59 hard beams with coverage angle of 90°.

The hydrosweep system can cover a water depth range from 10 m to full ocean depth and operates at 15.5 kHz. The system displays the isoline and geomorphological features on thescreen to help monitor online the data collection.

The equipment consists of two identical arrays mounted at right angles to each other at the forepart of the ship. Each array is a combination of three sub-arrays each consisting of 96 elements, making a total of 288 elements. Since the arrays are identical these can be used either in transmission or in receiving mode. For deep ocean operation, the beams are transmitted with a beam width of 45°. Hence, the coverage of this system is around 90°, varying from -45° to +45° angles.

92 blocks of 0.125° x 0.125° grid size were identified, from the FGMS, which have high nodule abundance and grade. The survey area is close to 22,000 km2 in the (CIOB) lying between 11.45ºS and 13ºS latitudes and 74.7ºE and 76.5ºE longitudes.

The line spacing for swath survey is planned based on the depth of operation to obtain full coverage of the area. In order to form hardware based 59 beams in the receiving mode 72 channels are pre-amplified, attenuation corrected and thereafter beam forming is performed using appropriate delays. The beams are 1.5° apart with an average width of 2.3° for deep-water surveys. The beam-formed outputs are tracked at bottom echo module to determine the exact depth from different directions with the help of algorithms of bottom tracking. However, preformed beam analyses combined with the new ATLAS High Directional Bearing Estimation (HDBE) allows sorting the information up to 240 small pencil-like beams (soft beams which is 240 depth values for each transmission ping). The use of such resolution beam formation will provide precise bottom bathymetry and seafloor angular backscatter analyses. The processing of raw bathymetry data are done online Hydromap system and collected as SURF data of 240 beams. Subsequently, the data are grided-using spline- interpolation with grid cell size 100m to plot contour maps and to extract depth profiles using GMT.

RESEARCH FROM THE PROJECT : Over the years, scientists in the project have developed expertise in different areas (please check out the publications against each of the Project Members). Some of which are given below, interested persons may contact the concerned scientist.

Manganese Micronodules

Manganese micronodules are small counterparts of manganese nodules and occur both in the surface and subsurface sediments. The large difference in size between micronodules (<1 mm) and macronodules (2-10 cm) suggests that the former cannot grow into later.

Micronodules also have nucleus similar to macronodules around which concentric growth structure with alternative iron and manganese oxides occurs. Micronodules have high Mn (35 %), Cu (1.6 %), Ni (1.4 %) and Zn (0.4 %) and Mn/Fe ratio of 5-101. These characteristics suggest their formation under early digenetic conditions. In general, micronodule chemical composition, mineralogy, internal and external features appear to be similar to macronodules. Micronodule abundance (number of micronodules per gm of dried sediment), size and chemical composition depends on the redox
characteristics of the sedimentary environment and can therefore be used as an indicator of the sedimentary environment.

Buried Nodules

The occurrence of buried nodules is rare compared to surface nodules. Ferromanganese nodules grow at the sediment-water interface despite the slower growth rates (few mm/Ma) than the accumulation rate of associated sediment (few mm/Ka). The possible mechanism for retaining the nodules at the sediment-water interface still remains an enigma. In CIOB buried nodules were recovered up to 5.4 m below the seafloor. The buried nodules are elliptical, elongated, rounded, sub- rounded, irregular and
polynucleated. A majority of the buried nodules are ~2 cm in diameter and exhibit both smooth and rough surface textures. Buried nodules from siliceous ooze have high Mn (27.4 %), Cu (1 %), and Cu (1 %) whereas, from red clay area they are rich in Fe (8.4 %) and Co (0.18 %).

Buried nodules from siliceous ooze are formed by hydrogenetic, diagenetic and early diagenetic processes whereas those from red clay area are only hydrogenetic in nature. However, chemical composition, morphology and surface texture of buried nodules are similar to surface nodules. This suggests that buried nodules stop their growth once they are buried within the sediment column. Contact : Dr. J.N. Pattan

VOLCANICS

• Volcanism is a dominant process in the oceans and is directly related, amongst others, to the morpho-tectonic features, creation of new oceanic crust, crustal plate movements, formation of new rock types, ore mineral formation and hydrothermal activities. The CIOB too has had it share of volcanic activities in the geological past because of which a variety of rocks have been recovered from the basin. These rocks include Normal-Mid-Ocean Ridge Basalts (N-MORB), Ferrobasalts (FeTi-rich), Spilites (Albitised basalts), Pumice (a silicic rock transported either from the 1883 Krakatoa eruption at Indonesia and/or from in situ eruptions), volcanogenic hydrothermal-materials (Si-Fe enriched sediments, Volcanic Magnetite spherules) and silicic glass shards (derived either from the 75,000 year ago Toba eruption at Indonesia and/or from in situ eruptions).
  

Photomicrograph of an oceanic basalt depicting well-formed olivine crystals in a matrix of fresh volcanic glass.

Electron micrograph of volcanic spherules. The image on the left shows entrapped spherules in metalliferous sediment, while the image on the right shows a magnified view of a spherule with well-developed magnetite crystals.

The volcanics are invariably associated with the bottom features such as seamounts, abyssal hills, fracture zones, faults etc. This indicates that in the CIOB, volcanic and tectonic activities complemented one another. For the growth of manganese nodules and crusts, a suitable nucleus is a prerequisite.The nucleus could either be a rock fragment, rock outcrop, older nodule, shark tooth, etc. In this respect, the abundant volcanics in the CIOB have acted as potential nuclei for the manganese nodules and crusts. A close correspondence between the fields of siliceous sediments, volcanics and manganese nodules is noted. This observation is similar to that existing in the Equatorial Pacific Ocean manganese nodule belt.

One of the largest and well crystallised phillipsite obtained on breaking a manganese nodule. This feature suggests a process of intranodule diagenesis for the formation of phillipsite

The constant interaction between the basalts (glass and the whole rock) with the seawater has resulted in the alteration and formation of clay minerals, palagonite and zeolites (phillipsite). Authigenic minerals tend to influence the geochemical cycle since they are sources or sinks for various elements.

Photomicrograph of a rock with fine fibre-like crystals of phillipsite crystals in a matrix of glass.

Considering a host of parameters (volcanics, morpho-tectonics, sediment types, manganese nodule characteristics etc.) a model has been developed to explain the formation and abundance of nodule deposits in the CIOB. It is important to know the distribution of the rock outcrops in the CIOB because once mining for nodule commences the underwater collecting device has to be deftly maneuvered for a better recovery of nodules, avoid damages and loss of collecting time. Contact : Dr. S.D. Iyer

PLANETARY GEOLOGY

Tektites and Microtektites

Tektites are meteorite impact generated glassy ejecta. They are distributed in large geographic domains called "strewn fields." Four such strewn fields are known, the largest and the youngest of them is the Australasian tektite strewn field spread over 10% of theearth's surface (~ 50 million km2).

We have been investigating Australasian tektites and microtektites from the Central Indian Oean for a while now, our main findings:

Discovery of minitektites which have a bearing on the age-paradox problem of the strewn field and point towards a unified, single strewn field.

Impact microcraters on Australasian microtektites and tektites reveal collisional processes in the ejecta plumes generated by large meteorite impacts and also have a bearing on the interpretation of the Lunar surface processes.

Electron micrographs of Microcraters in the Australasian Microtektites.

There is a possibility of two layers of Australasian impact ejecta in the Indian Ocean Ongoing work: 1) We have found Australasian microtektites in 16 sediment cores in the CIOB - systematic and detailed chemical composition of the microtektites is ongoing. 2) Our microtektite data are being integrated with the total available data to predict the location of the crater which generated the Australasian strewn field.

Cosmic Dust We have collected large quantities of cosmic dust by magnetic methods from the sediments of the CIOB. We call this experiment MACDUC (Magnetic Cosmic Dust collector experiment). Preliminary investigation shows us that the experiment has been successful in retrieving cosmic dust. Isolation and detailed investigation are ongoing. Contact Dr.M.Shyam Prasad Electron micrograph of a Cosmic dust

Authigenic minerals from the continental margins:

Marine phosphorites have been studied for more than a hundred years both because of their commercial value and because of their importance in the bio-geochemical processes. Phosphorus is one of the basic plant nutrients. Despite extensive studies the genesis of phosphorites is still a matter of debate. Detailed investigations were carried out on phosphate grains, phosphatised limestones and phosphorites from the upwelling regions off western India and Oman Margin and phosphorites from the non-upwelling regions (southeast coast of India) and phosphorites from Seamounts. The studies demonstrate the role of microbial organisms in assimilation and precipitation of phosphate both from
interstitial waters and water column. We have also demonstrated the occurrence of phosphate stromatolites from the continental margin off Chennai, which serve as Quaternary analogs for ancient phosphorites. Similarly extensive studies were carried out on dolomites from the carbonate platform off western India and identified the microbial role in their formation. These dolomites were formed in hypersaline sulfate reducing conditions during the late Pleistocene low stands of sea level.

Authigenic Fe-rich alumino clays consisting of verdine and glaucony facies were identified along the continental shelf and slop between Ratnagiri and Cochin. The existence of contemporary verdine, glaucony and phosphate facies at successive depths over the SW portion of the western continental margin was brought out. Lithogenic flux is an important component to the continental margin of both east and west coast of India. The sources of lithogenic material and climatic conditions prevailed on land can be investigated using rock-magnetic properties of the sediments deposited through
time. Fifteen gravity cores collected along the western margin of India at depths between 31 and
1950 m were investigated using parameters such as magnetic concentrations, magnetic grain size and magnetic mineralogy. It is evident that during the Last Glacial Maximum(LGM) the northwestern margin of India received abundant continental supply leading to the prominence of eolian sedimentation. In the SW region the influence of hinterland flux is less evident during this period, but convective mixing associated with the NE monsoon resulted in increased productivity. During the early Holocene the intense SW monsoon conditions resulted in high precipitation on land, which in turn contributed increased magnetic susceptibility. The late Holocene organic-rich sediments were however, subjected to early diagenesis and therefore caution is needed when interpreting regional climatic
change from down-core changes using sediment magnetic properties. With the help of mineralogy and Sr-Nd isotopes of the fine-grained sediments, provenance of the sediments along the eastern and western margin of India and factors controlling their distribution were identified.

Continental margins of India are regarded as passive Atlantic-type margins and one would expect documentation of glacio-eustatic sea level changes from these margins. Sixty four relict sediment samples (limestones, corals, shells, sediments and beach rocks) collected along the western margin of India were investigated for their petrology and radiocarbon ages and compared their positions on glaciao-eustatic sea level curve. In this process we have discovered the Halimeda bioherms on the carbonate platform, terrestrial limestones (caliche pisolites, calcretes and rhizoliths) as paleoshore line indicators extending at water depths of 50 m along the western shelf of India from Ratnagiri to Cochin, vadose diagenetic limestones and several evidences documenting late Quaternary neo- tectonic activity and subsidence along the northwestern margin of India.

The Bengal Fan, known to be the world's largest delta, has acquired its enormous size as a result of huge sediment flux largely from the Himalayas and Indian / Sri Lankan peninsula, and mostly transported by turbidity currents. Discussions on the composition, sources and extent of turbidites in the Bengal Fan are related to the Himalayan upliftment and eustatic changes in sea level. Several scholars do not show recent evidence of turbidite sediment accumulation in the lower Bengal Fan and suggested that the sediments are largely being trapped in the lower deltaic plain and shelf region. Others, however, demonstrated that some material bypassed the canyon and active gowth of the fan during the most recent sea level rise and highstand with turbidites deposited right on the surface. We
have studied down core variations in different sedimentological parameters and radiogenic isotopes from two gravity cores recovered from the lower and the distal Bengal Fan. The cores exhibit two distinct units, the lower unit 2 and upper unit 1 sediments. The unit 2 sediments are predominantly olive black/grey in colour with abundant finer silt-size fractions, low organic carbon and CaCO₃, quartz and mica in the coarse fraction, dominant illite and chlorite in the <2 m fraction and uniform rock-magnetic properties. Biogenic constituents are extremely rare or restricted to the lower part of unit 2. The unit 1 sediments, on the other hand, are moderate brown / yellowish brown in colour with intermittent thin dark-coloured sediment layers. Higher clay, organic carbon, CaCO₃, and biogenic constituents in the coarse fraction, and enriched smectite and kaolinite in the <2 m fraction are typical.