information brochure 11 cook islands deep-sea minerals...

1

The Cook Islands consists of fifteen islands, all islands between 8oS and 23oS and 156oW and 167oW. It is geographically divided into two groups a Northern Group comprising Penrhyn, Rakahanga, Manihiki, Suwarrow, Nassau and Pukapuka. All are atolls except Nassau. The Southern Group comprises Palmerston, Rarotonga, Mangaia, Mauke and Atiu as high islands; Aitutaki a part atoll with a volcanic peak and a large lagoon; Mitiaro an elevated coral island and Manuae and Palmerston atolls. Tukutea is a small island near Atiu. However, submarine topographic features divide the Exclusive Economic Zone (EEZ) of the Cook Islands into four regions: the Penrhyn Basin in the northeast, the Manihiki Plateau in the northwest, the Samoa Basin to the west, and the Cook Islands seamount line in the south (Figure 1).

Seabed minerals explorations within the EEZ of the Cook Islands were reported to have been first carried out by the US and USSR research vessels in the 1960s. These surveys were later picked up by other companies and consortia in the early 1970s and continued until the late 1980s that resulted in the discovery of significant manganese nodule resources. These early seabed mineral investigations were mainly focused on identifying mineral occurrences and understanding their mode of occurrence and the geological setting in which they occur. Apart from efforts to identify other mineral types such as metalliferous sediments, cobalt-rich crusts, phosphate, and precious coral, manganese nodules was the chief target of seabed mineral prospecting in the offshore areas of the Cook Islands.

SPC-EU EDF10 Deep Sea Minerals (DSM) Project

Information Brochure 11Cook Islands Deep-sea Minerals Potential

1

Figure 1. Seafloor topography of the Cook Islands waters showing major features.

Manihiki Plateau

Samoa Basin

Southern Seamounts

Penrhyn Basin

Deep Sea Minerals in the Pacific Islands Region Brochure 11.indd 1 9/30/13 11:51 AM

SPC-EU EDF10 Deep Sea Minerals Project2 SPC-EU EDF10 Deep Sea Minerals Project SPC-EU EDF10 Deep Sea Minerals Project

Early surveys were not carried out in a reasonably detailed and systematic manner hence manganese nodule resources could not be quantified. It was not until the twenty-one year Japan-SOPAC Cooperative Study that commenced in 1985 that any serious attempt was made to estimate the manganese nodule resources within the Cook Islands’ EEZ. Four exploration cruises (i.e. in 1985, 1986, 1990 and 2000) were carried out in the Cook Islands as part of this programme and the sea areas surveyed in the first three cruises are shown in Figure 2. The 2000 survey was conducted in the central eastern part of the country’s EEZ.

Figure 2. Japan-SOPAC 1985, 1986 and 1990 survey areas within the EEZ of the Cook Islands.


SPC-EU EDF10 Deep Sea Minerals ProjectSPC-EU EDF10 Deep Sea Minerals Project 3SPC-EU EDF10 Deep Sea Minerals Project

7 The data and results of the 2007 RV Sonne survey are being included in this information brochure with the permission of Professor Peter Halbach of the Free University, Berlin Germany.

Figure 3. Sampling sites where nodule and crust samples were collected during the research cruise SO 193. Samples that were taken for further studies are underlined and station TVG 71 is marked by an arrow (from Halbach, 2010).

Additionally, a survey was conducted by the RV Sonne (i.e. research cruise SO 193) in the Manihiki Plateau in 20071. This submarine Plateau is considered to be a large Igneous Province and was formed by several Hot Spot centres. The main objective of the cruise was to study the petrological and geological development of the plateau. During the 2007 survey, a flat top seamount (i.e. guyot) was visited and sampled by TV grab stations (Figure 3). TVG 71 was carried out on a platform that has an average water depth of 1220 m, and the sample locality is shown on Figure 3 below.



Exploration History A summary of offshore research and seabed mineral investigations that were undertaken in the Cook Islands’ waters are given in Table 1 below.

Table 1: Summary of previous offshore research and minerals exploration in the Cook Islands.

Research Vessel & Year of Survey Survey Area Surveyed Commodity

RV Tangaroa (1974) Rarotonga, Cook Islands Manganese Nodules

MV Ravakai (1976) Area between Rarotonga and Penrhyn Manganese Nodules, Metalliferous Sediment and Phosphate

RV Acheron (1977) Southern Group, Cook Islands Precious Coral, Manganese Nodules

RV Coriolis (1977) Selected areas within the EEZ of the Cook Islands

Manganese Nodules

RV Machias (1978) Penrhyn and Samoa Basins, Nearshore waters of the Cook Islands

Manganese Nodules and Precious Coral

RV Sonne (1978) West of Rarotonga and Aitutaki Passage Manganese Nodules

RV Machias (1980) Northern Cook Islands Manganese Nodules, Phosphate, Precious Coral

RV Machias (1980) East of Penrhyn Island, Penrhyn Basin, Penrhyn, Manihiki, Nassau Islands

Manganese Nodules, Precious Coral, Phosphate

RV Sonne (1980) Aitutaki Passage Manganese Nodules

RV Hakurei Maru (1980) South Penrhyn Basin Manganese Nodules

MV Ravakai (1983) Slopes of Rakahaga and Manihiki Atoll Precious Coral

RV Hakurei Maru (1983) South Penrhyn Basin Manganese Nodules

RV Hakurei Maru 2 (1985) Western Penhryn Basin, eastern margin of the Manihiki plateau and the North of Penrhyn Island.

Manganese Nodules

HMNZS Tui (1986) Manihiki Plateau and adjacent Southwest sea areas

Cobalt-rich Crust, Manganese Nodules

RV Hakurei Maru 2 (1986) Western edge of the southern Penhryn Basin (to the east of the Manihiki plateau)

Manganese Nodules

RV Moana Wave (1987) Cook Islands: Suwarrow trough, eastern Manihiki Plateau, Rakahaga-Manihiki island area

Cobalt-rich Crust and Metalliferous sediments

RV Thomas Washington (1987) Northern Cook Islands and adj acent High Seas

Manganese Nodules, Cobalt-rich Crust, Deep Sea Sediment

RV Sonne (1990) North-east edge of Manihiki Plateau Complex of Volcanic Cones and mineral resources

RV Hakurei Maru 2 (1990) Southern Cook Islands Manganese Nodules

RV Hakurei Maru 2 (2000) Central Cook Islands (i.e. Southern Penrhyn Basin)

Manganese Nodules

RV Sonne (2007) Manihiki Plateau Petrological and geological plateau development, Manganese Nodules

Survey ResultsSummary of Pre-Japan-SOPAC Survey Findings

• Duringthe1976survey(Figure4),alargefieldofmanganesenoduleswasdiscoveredtoextendfurtherto the south than previously reported. The deposit is thought to cover most of the South Penrhyn Basin between Aitutaki and Penrhyn. Manganese nodules were recovered at 9 of the 12 sampling stations occupied, and bottom photographs at 6 of these 9 stations indicate about 90% nodule coverage.

• DeepseasedimentscollectedinthevicinityofthesouthernCookIslandsduringthe1977expeditionarebrown clay with a surface layer of ferromanganese nodules.


SPC-EU EDF10 Deep Sea Minerals Project 5SPC-EU EDF10 Deep Sea Minerals Project SPC-EU EDF10 Deep Sea Minerals Project

• Out of the five sampling stations surveyedin the northern Penrhyn Basin in 1978, high density of manganese nodules per unit area was recovered from three sites. The survey results show two distinct areas: the western part has an undulating seafloor and nodules are irregularly distributed, rarely occurring densely. The eastern part is flat floored and is covered by a layer, probably continuous of densely distributed nodules. In the Samoa Basin, moderate numbers of small to medium sized nodules were collected at two of the three stations occupied.

• During the 1980 survey (Figure 5), noduleconcentrations varied from insignificant to dense, with the highest concentrations of 23.7kg/m2 occurring to the southeast of Penrhyn Island – just outside the Cook Island waters, but significant concentrations occur within Cook Island waters in this same area (Figure 5).

• Manganesenodulesoccurtothesoutheastof Penrhyn Island in sufficient abundance to have potential as an economic deposit. However, the trend in general based on the March 1980 survey indicates that nodule abundances in the Penrhyn Basin itself are very low.

• Only one manganese nodule sample wascollected during the April 1980 cruise in the Penrhyn Basin between Manihiki and Penrhyn consisting of 5.75kg of nodules.

• Basedonthe1983survey, themineral resourcepotentialof theManihikiPlateauandadjacentareasappears to be minimal. The manganese crust collected are relatively thin, and the manganese nodules for the most part resemble those of the Cook Island facies, characterised by low Nickel, Copper and Cobalt contents.

Figure 4. Cruise track of the RV Ravakai during the 1976 survey in the Cook Islands.

Figure 5. The 1980 survey track-lines highlighting nodule abundance at selected sampling sites.

0.3kg/m2

24kg/m211kg/m2

1.5kg/m2



1985 Japan-SOPAC Survey• Distributionofthemanganesenodulesinthe1985surveyareawasascertainedtobehighertothewest

ofthe158°Wlongitudinallineandlowertotheeast.Smallsizedmanganesenodules(0–2cm,2-4cm)arethemajorityfromthecentertoeasternpartinthesurveyedareas.Middlesized(>4cm)aredistributedin the surroundings of sea knolls in the western part of the area.

• CogradeincreaseswithabundancewhileNiandCugradesdecrease.

1986 HMNZS Tui Survey• High nodule abundances were confirmed in the area of the 1986 HMNZS Tui cruise and dredged

sediments of the eastern escarpment of the Manihiki Plateau, revealed 0.5 to 2cm of crust. Two samples haveverywelldevelopedcrustsupto4.5cmthick;

• The1986surveyof theManihiki-Rakahagaarea revealedaseriesofconicalprotrusions thatcanbeinterpreted as that of mud volcanoes. Such edifices could have been constructed by gas and fluid escaping from over-pressured, organic-rich horizons within the sedimentary section.

1986 Japan-SOPAC Survey• Theabundanceandcontinuityofmanganesenodulesdistributioninthe1986surveyareaarehigh,with

high abundance zone (i.e. more than 7.5 kg/m2) of about 50% of the whole survey area. In all of the 180 sampling points, the abundance exceeded 20 kg/m2 in 97 points, 30 kg/m2in32points,and40kg/m2 in 2 points.

• Themanganesenodulesgradedistributioninthewhole1986surveyareais:highNi-CogradeandlowCo grade in the north area, and high Co grade and low Ni-Cu grade in the south area.

• Samplesofnoduletypesthatoccurinthe1986surveyareaareshowninFigure6below.

1990 RV Sonne Survey• During the 1990 survey of the NE Manihiki Plateau volcanic cone complex, it was revealed that the

cones and main edifice bear thick manganese crusts, and may therefore have mineral resource potential. Dredging has shown that these crusts are commonly 6 cm thick; at one site manganese crust 10 cm thick was recovered.

Figure 6. Manganese nodules that occur in the 1986 survey area: (A) Spheloidal manganese nodules; (B) Platy manganese nodules.

A B


SPC-EU EDF10 Deep Sea Minerals Project

Figure 7. Variation in manganese nodules abundance in the EEZ of the Cook Islands.

Figure 8. Cobalt content of manganese nodules in the EEZ of the Cook Islands.

7SPC-EU EDF10 Deep Sea Minerals Project SPC-EU EDF10 Deep Sea Minerals Project

1990 Japan-SOPAC Survey• The1990 resultsof theanalysisof the fiveprincipalelements reveal thatNi-Cu-MnandCo-Fehave

positive correlations respectively and that the two types are in negative correlation. Small sized manganese nodules have a tendency to have higher grades of Ni, Cu and Mn, and large sized ones have a tendency to have higher grades of Co and Fe. Furthermore, the Ni-Cu-Mn type occur in lesser abundance and the Co-Fe type occur in higher abundance.

• Amonga totalof146stationssampledduring the1985,1986and1990Japan-SOPACsurveys,62stations indicated average nodule abundance higher than 10 kg/m2, while two stations had no nodules. Thenoduleabundanceatthestationsrangedfromnilto34.57kg/m2. Latitudinal variations in nodule abundance can be discerned from Figure 7. The data show that nodules are most abundant in the central-eastern part of the EEZ (Figure 7), between 10oS and 18oS, where they exceed the widely proposed economic abundance of 10 kg/m2.

2000 Japan-SOPAC Survey• The2000surveyrevealedthefollowing:(i)CentralArea:2~6cm-diametermanganesenodulesconstitute

85% (weight ratio) of the area. High-abundance zones exceeding 30kg/m2 extend in the flat parts deeper than5,000mandoccupy42%(7,021km2) of the area; (ii) South Area: Most (about 65%) of the manganese nodulesare2~6cm.Thesizevariesconsiderablyandtherearearound10%of8~16cmnodules.Theexistence of high-abundance zones with more than 30kg/m2 of manganese nodules, and the zone with more than 20kg/m2 nodules extend for about 40,000km2. (iii) North Area: 2~6cm nodules are mostabundant and constitute about 65%. Nodules larger than 8cm were not observed.


8 SPC-EU EDF10 Deep Sea Minerals Project SPC-EU EDF10 Deep Sea Minerals Project

Figure 7. Variation in manganese nodules abundance in the EEZ of the Cook Islands.

Figure 8. Cobalt content of manganese nodules in the EEZ of the Cook Islands.

• Further (i) the nodulesof theCenter andSouthAreashave lowerNi,Cu, andMnaveragecontentscompared to those of the North Area while the Co and Fe contents are higher; (ii) Co grade of manganese nodules is higher than Clarion-Clipperton Zone (CCZ), but Ni and Cu contents are lower, and Ni+Cu+Co content is around 1%; and (iii) nodule abundance is high, and thus the metal quantity per unit area is higher in Ni and Cu for Center and South Areas combined. The amount of Co is fourfold higher than the value of the CCZ.

Metal Grades and DistributionFigures 8, 9 and 10 show the distribution of Co, Ni and Cu respectively in nodules from the Cook Islands’ waters. Generally, cobalt was present in nodules with content below 0.3 % north of 8oS, and between 0.3% and 0.6% south of 8oS. The highest contents of cobalt are observed between 15oS and 16oS, where they often exceed 0.5 %. Both the Ni and Cu contents in nodules show higher values, generally above 0.5%, in a zone north of 9oS, than the rest of the study, though a few sampling stations show high values in the western and southern margins of the area.

2007 Manihiki Plateau SurveyTV grab station 71 was extremely successful by recovering a huge amount of large hydrogenetic manganese nodules (up to 20 cm in diameter). The local abundance of hydrogenetic ferromanganese crust is very high and averages at least 20 kg/m². The nodule layer is occasionally interrupted by outcropping ferromanganese crusts. Some unconsolidated calcareous sediment covers the crusts and underlies the nodules.




The nodules that were taken for investigations have spherical shapes with diameters of 6 to 10 cm. The principle setup of the nodules (Fig. 12) is marked by an outer layer of younger generation, a transitional layer which already shows some apatite impregnation and a central part of older generation consisting of hydrogenetic material strongly impregnated with carbonate-fluorapatite and more or less identical in composition with older generation manganese crusts from similar water depth in the same area.

The maximum content in carbonate-fluorapatite of the central nodule parts is up to 31%. The nodules often have a small nucleus consisting of consolidated sediment of fine-grained altered lava ash or of an older nodule fragment.

Because of the relatively shallow water depth, the nodule composition shows a very good metal quality with regard to Mn, Co, Ni, Mo, W and Pt. The maximum values of these economically interesting elements are: 23.5%Mn,0.98%Co,0.87%Ni,686ppmMo,416ppmWand1299ppbPt.TheFeconcentrationisfairlylowandhasamaximumvalueof8.0%,therespectiveMn/Feratioamountsto4.2.Theaveragegradesofthese elements are: Mn 21.69%, Fe 6.63%, Co 0.77%, Ni 0.77%, Mo 568 ppm, W 178 ppm and Pt 1080 ppb). These metal concentrations are distinctly higher than those calculated for manganese crusts from the Manihiki Plateau of the depth range of 1000 to 2600 m.

Figure 11. Seafloor image of research cruise SO193 from the seamount platform of station TVG71 (courtesy of Prof Peter Halbach, Free University Berlin Germany).

Figure 12. Two cut hydrogenetic nodule samples from station TVG 71. The cut faces show the layered setup of the nodules with an outer young layer, an apatite -impregnated central part and a small core of consolidated sediment.




Summary ResultsThe 1985, 1986, 1990 and 2000 Japan-SOPAC survey results in the Cook Islands are summarised in Table 2 below.

Table 2. Summary results of the Japan-SOPAC deep sea minerals survey in the Cook Islands.

Year of survey 1985 1986 1990 2000Area surveyed (km2) 85,000 237,700 1,037,000 431,000

Depth range (m) 4,500–6,100 5,100 – 5,600 5,000 – 6,000 4,600–5,600

Nodule shape Pebble thin with minor ellipsoidal fat

Spheroidal with minor massive and

gravel types

Spheroidal and pebble types with minor plate

type

Spheroidal and minor pebble

Abundance (kg/m2) Moderate - Low Centre: 33.56 South:10.94

Total average: 17.1

8.84 Centre:24.00South:16.34

Continuity Moderate Extremely high Moderate High

Average Grade (%) Ni 0.74 0.24 0.39 Centre: 0.25; South: 0.32; North: 0.61

Cu 0.51 0.14 0.22 Centre:0.14;South:0.19; North: 0.38

Co 0.28 0.47 0.42 Centre: 0.50; South: 0.46;North:0.35

Metal Quantity (tonnes)

Ni 219,000 (in area where Ni is more than 20g/m2)

9,755,208 2,920,000 (in area where Ni is more than 20g/m2)

4,110,000

Cu 14,616(inareawhereCu is more than 20g/m2)

5,690,538 1,363,500 (in area where Cu is more than 20g/m2)

2,390,000

Co 241,860(inareawhereCo is more than 20g/m2)

19,103,949 4,300,000(inareawhereCo is more than 20g/m2)

7,510,000

Grade variation Co increases with abundance while Ni &

Cu decrease

Low in Ni & Cu and high in Co




Resource EstimationThe polygon method was used to estimate the Cook Islands manganese nodule resources. An illustration of the use of the polygon method for resource estimation is shown in Figure 13. The distribution and abundance of manganese nodules is based on the sampling data, the photos collected by an underwater camera and the images gathered by the acoustic instruments. Due to the limited ground truthing data over a huge area, the distribution and abundance of manganese nodules are subjected to certain degree of assumption hence geological confidence is generally low. As a result, the estimated manganese nodule resources is categorised as “inferred”.

A summary of the inferred manganese nodule resources in the Cook Islands is given in Table 3. Above the assumed cut-off nodule abundance of 5 kg/m2 (ondrybasis),anoduleresourceof4,461milliontonnes isexpected in an area of 360,000 km2. Cobalt, nickel and copper resources in the nodule deposits of over 5 kg/m2 were calculated to be 21.2 million tonnes, 13.0 million tonnes and 7.6 million tonnes respectively.

Table 3. Estimation of resource of nodules and metals of the study area in the Cook Islands (Kojima, 2001).

NoduleAbundance (dry)

Area(km2)

Total resources (in million tonnes)Nodules (dry) Co Ni Cu

Over 20 kg/m2 33,000 723 3.54 1.75 1.02

15-20 kg/m2 99,400 1763 8.47 4.93 2.91

10-15 kg/m2 92,200 1080 5.20 3.13 2.91

5-10 kg/m2 135,100 894 4.04 3.20 1.86

Cut off 5 kg/m2 359,700 4461 21.25 13.01 7.64

Total 765,100 5139 23.84 15.94 9.36



Siebold (1978) listed the following three points as the necessary conditions for mining manganese nodules: (a) abundance of more than 10kg/m2; (b) grade of Ni+Cu+Co higher than 2%; and (c) the manganese nodule distribution in an area of at least 20,000–30,000km2, and bedrocks are not exposed and covered by unconsolidated sediments.

Based on the requirements of Seibold’s (1978), the Ni+Cu+Co quantity of the 2000 survey of the South Penrhyn Basin(i.e.combinedCenterandSouthArea)wouldamountto14.01milliontonnes.


Cronan 2013 Resource EstimationThe most recent resource estimation of nodules and metal within the Cook Islands’ EEZ combining the nodule tonnages for the four regions was conducted by Cronan in early 2013 (Cronan, 2013). A total of 10.26 billion metrictonsofnodulesisestimatedtooccurwithintheCookIslands’EEZ(Table4).

Table 4. Cronan 2013 resource estimation of nodules and metals within the Cook Islands’ EEZ (Cronan, 2013).

NoduleAbundance (dry)

Total Resource (in million tonnes)Total Nodule Cobalt Manganese Nickel Copper Titanium

North Penrhyn Basin 616.075 1.663 123.215 3.388 1.909 6.9

South Penrhyn Basin 2,831.95 13.593 424.792 7.929 4.531 32.284

Manihiki Plateau 691.6 2.282 117.572 2.697 1.452 7.4

Southern Cook Islands 6,126.55 25.731 1,225.31 22.055 9.802 117.629

Total 10,266.175 43.269 1,890.889 36.069 17.694 164.213

The average REEcontent ofCook Islands’EEZnodules is 0.17%,deriving a figureof 17,452,000 metrictonnes REE in nodules of the Cook Islands’ EEZ.

A

B

Figure 13. (A) Manganese nodules abundance map of the Cook Islands; (B) An illustration of the polygon method of resource estimation that has been used to estimate manganese nodule resources in the Cook Islands.


12 SPC-EU EDF10 Deep Sea Minerals Project SPC-EU EDF10 Deep Sea Minerals ProjectSPC-EU EDF10 Deep Sea Minerals Project

Contact for more information: Applied Geoscience and Technology Division (SOPAC), Secretariat of the Pacific Community,Mead Road, Nabua, Fiji Islands. Tel. (+679) 3381377 / Fax. (+679) 3370040/3384461

Website: www.sopac.org / email: [email protected]

Comparison of Manganese Nodule Metal Composition in the Manihiki Plateau and the Clarion-Clipperton Zone (CCZ)The Table 4 below shows a comparison of the mean metal composition of the manganese nodules thatoccur in the Manihiki Plateau and the Clarion Clipperton Zone. It has become obvious that some metals such as Cobalt, Titanium and Platinum have higher grades in the Manihiki Plateau nodules whilst in the CCZ the concentration of metals such as Nickel and Copper are higher.

Table 4. Comparison of mean metal composition of the Manganese Nodules that occur in the Manihiki Plateau and the Clarion-Clipperton Zone.

Metals Manihiki Plateau: Metal Content* in Manganese Nodules (g/t)

Clarion-Clipperton Zone: Metal Content* in Manganese Nodules (g/t)

Cobalt (Co) 7700 2000

Nickel (Ni) 7700 12000

Copper (Cu) 953 11000

Titanium (Ti) 6000 3000

Molybdenum (Mo) 568 500

Platinum (Pt) 1080 0.25

Cerium (Ce) 609 240

Tungsten (W) 199 140

*dried material (Courtesy of Prof Peter Halbach, Free University Berlin Germany).

ConclusionEarly deep sea mineral reconnaissance surveys within the Cook Islands sea area are characterised by low number of samples that were collected over huge study areas. The four Japan-SOPAC surveys represent reasonably detailed assessment of manganese nodules to date in the Cook Islands. Significant amount of manganese nodules have been discovered in the sea area of the Cook Islands over the last fourty years but nodule abundance is highly variable.

Nodules with metal grade exceeding 2% (Ni+Cu+Co) occur in the South Penrhyn Basin with abundance of more than 30kg/m2 in some parts hence the South Penrhyn Basin is the most promising within the Cook Island sea area. The Japan-SOPAC surveys confirmed that zones of high abundance of manganese nodules occur in the western margins of the South Penrhyn Basin. It has been determined that the Cobalt grade of manganese nodules in the Cook Islands is higher than Clarion-Clipperton Zone (CCZ), but the Nickel and Copper contents are lower.

With the results of the 2007 Manihiki Plateau survey made available, it presents an exciting opportunity to conduct further investigations for manganese nodules and crusts on similar guyot structures within the plateau. With the exception of nickel and copper, the metal grades are higher than the CCZ hence the market value is mostly likely to be higher.

Based on existing offshore exploration data, the Cook Islands’ EEZ offers the best potential for commercial manganese nodules mining in the region. Apart from manganese nodules abundance, other factors such as size, continuity and metal grades as well as engineering and environmental considerations need to be assessed for any commercial extraction.


information brochure 11 cook islands deep-sea minerals...

Documents