information brochure 9 kiribati deep-sea minerals potentialkiribati has a vast exclusive economic...

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Kiribati has a vast Exclusive Economic Zone (EEZ), one of the biggest in the region. It has three separate and distinct island groups, each with its own separate EEZ: the Gilbert Islands Group, the Phoenix Islands Group and the Line Islands Group. Early marine minerals exploration in Kiribati waters was undertaken as part of the Pacific Ocean expedition in the 1960s and early 1970s. The first reported survey in the Kiribati area was during the 1979 CCOP/SOPAC investigations for potential manganese nodules and crust resources. This was followed by two years (1980 – 1981) of relatively intensive exploration for manganese nodules and crust, and precious coral and phosphate. Investigations for cobalt rich crusts and metalliferous sediments were not carried out in Kiribati until 1987 during the ‘RV Moana Wave’ and ‘RV Hakurei Maru 2’ exploratory cruises in the region.

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Information Brochure 9Kiribati Deep-sea Minerals Potential

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Figure 1: The Japan-SOPAC 1987, 1989 and 1991 survey areas within the EEZ of Kiribati.

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Exploration HistoryThe highlights of seabed mineral investigations in Kiribati are given in Table 1 below.

Table 1: Summary of previous offshore minerals exploration in Kiribati.

Research Vessel and Year of Survey

Survey Area Surveyed Commodity

RV Machias (1979) Southeast of the Gilbert Islands chain, principally the Nova Canton Trough

Manganese Nodules and Crust

RV Machias (1980) East of the Line Islands, Kiribati Manganese Nodules

RV Machias (1980) Eastern part of the Phoenix Island group Manganese Nodules, Cobalt-rich Crusts, Phosphate, Precious Coral

RV Machias (1980) Southern Line Islands (Vosok, Flint and Caroline Islands)

Manganese Nodules, Precious Coral, Phosphorites

RV Machias (1981) Southwest area of the Gilbert Islands chain Manganese Nodules

RV Machias (1981) Southern Gilbert Islands (Abemama, Aranuka, Nonouti, Tabiteuea , Beru Islands)

Phosphate

RV Machias (1981) Phoenix Islands (west and north of the northern Tokelau Islands)

Manganese Nodules and Crusts

RV Moana Wave (1987) Line Islands area Cobalt-rich Crusts and Metalliferous sediments

RV Thomas Washington (1987)

Central Line Islands and adjacent High Seas Manganese Nodules, Cobalt-rich Crusts, Deep Sea Sediment

R. V. Hakurei Maru 2 (1987) The Nova Canton Trough in the Phoenix Islands and the associated central mountainous area

Manganese Nodules, Cobalt-rich Crusts

RV Nei Tewenei (1988) Islands of the Gilbert Group Precious Coral

R. V. Hakurei Maru 2 (1989) Seamounts and troughs in the Line Islands Manganese Nodules, Cobalt-rich Crusts

R. V. Hakurei Maru 2 (1991) Sea area (including 5 seamounts) of the Gilbert Islands

Manganese Nodules, Cobalt-rich Crusts

R. V. Hakurei Maru 2 (2003) SE01 Seamount, Gilbert Islands Cobalt-rich Crusts

Survey ResultsSummary Results of Earlier Surveys • Duringthe1979manganesenodulesandcrustsurvey intheNovaCantonTroughregion(south-eastof

Tarawa), nodules recovered from three stations (stations 4, 6 and 10) ranged in size from 3 mm to 30 mm diameter. Crusts were recovered at station 8 at a depth of 5,200 m and ranged up to 16 mm in diameter. The 1979 survey track lines are shown in Figure 2.

• ResultsoftheFebruary1980cruiseindicatedthatmanganesenodulesexistedintheeasternbasinofthePhoenix Group in sufficient quantities to have potential as an economic deposit provided that sufficient

These early prospecting efforts within the EEZ of Kiribati were aimed at identifying mineral occurrences, particularly manganese nodules and crusts. In the later surveys, the focus was shifted to the assessment of manganese nodules and cobalt rich crust resources. A major part of this was the three Japan-SOPAC Cooperative Study research cruises that were carried out in Kiribati in 1987, 1989 and 1991. The survey areas are shown in Figure 1. These later surveys were a significant milestone as they confirmed the mineral resources potential within Kiribati’s EEZ.

This information brochure highlights previous exploration efforts, survey results and potential areas in the three island groups of Kiribati.

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concentration of metals exist. Results of analyses of the samples collected during this cruise indicate, however, that grades of the principal economic minerals (Cu, Ni and Co) are well below those generally quoted as being the cut-off limit for economic exploitation.

• ComparisonofthesamplingresultswiththeechosoundingrecordsoftheFebruary1980surveysuggesteda strong negative correlation between nodule abundance and the thickness of the mud layer occurring on the seabed. Nodules are also generally smaller where a transparent mud layer occurs.

• TheMarch1980surveyconfirmedthatabundantmanganesenodulesexistedabout200milestothewestof the Southern Line Islands. No manganese nodules were found to exist in the immediate vicinity of the Southern Line Islands or to the south between the Southern Line Islands and Tahiti.

Figure 2. The 1979 survey track-lines in the Nova Canton Trough of south-eastern Kiribati.

Figure 3. General occurrence of Cobalt-rich crust on seamounts.


• The reconnaissancesurveyalong theeasternmarginof theLine Islands from7°S to7°N inMay1980suggested that manganese nodules are not abundant in the area. The greatest abundances occurred east of the Southern Line Islands.

• ThegenerallylowabundanceofnodulesfoundintheFebruary1981surveyofthesouth-westernregionofthe Gilbert Islands chain, probably due to high sedimentation rates, clearly indicates that the area has no economic potential.

• During the1987surveyof thesouthernLine Islands, rockscoatedwith2-5cmcobalt-richcrustswerecollected from the summit of a seamount. The survey reveals slight accumulations on the summit with little or no sediment on the flanks of the edifice.

• DredgesamplesfromanotherseamountinthesouthernLineIslandsrevealthatcobalt-richcrustsaccountfor about a third (1/3) of the samples and some range from 1 to 6cm in thickness. The remaining two thirds (2/3) of the sample are weathered basalts covered with Fe-Mn-oxide stains or crusts less than 1cm thick. A schematic cross section of a cobalt-rich crusts bearing seamount is given in Figure 3.

• ThethirdseamountsurveyedinthesouthernLineIslandsin1987ischaracterisedwithbrecciatedvolcaniccobbles and several large boulders. None was encrusted with significant thicknesses of Fe-Mn oxide. The steep slopes of the seamount, the rounded shape of the specimens and the lack of crust growth all suggest that this edifice is too unstable for crust formation.

• Manganese nodules in the Southern Lines Islands are found generally to decrease in abundance withdecreasing latitude. Dredging of crusts in the Line Islands yielded moderate to thick crusts at several locations.

Summary Results of the Japan-SOPAC Survey

Figure 4. Bird’s eye view of seamounts in the Line Islands Group.


Figure 5. Variation in manganese nodules abundance in the EEZ of the Phoenix Islands Group.

• Thedistributionandcontinuityofmanganesenoduleswerefoundinthe1987Japan-SOPACsurveyinthePhoenix Group to be generally poor with only a 6,600km2 area of higher abundance.

• Thebearingsituationofcobalt-richcrustsbythissurveycouldbedescribedasfollows:bearingdepthisaround 1,000m – 3,200m and the bearing zone would extend further, crust shapes are mainly crust type, and crusts in the deeper zone have more compact characteristics.

• ThewesternpartoftheLineIslands(surveyedin1989)belongstotheNorthPenrhynBasinandiscomposedof knolls including seamount SC06, while the eastern part belongs to the Northeast Pacific Basin and consists of mountains. Seamounts SC01-SC04 are part of the eastern mountain series and seamount SC05 is included in the western series (Figure 4).

• SeamountsSC02andSC06haveexcellentgrade.Thesummitandtheupperpartofslopesofseamountsin depths of 1,000m – 1,500m have the highest grade. Co grade decreases as the depth deepens. Analysis of sectional samples shows that the outer-shell that directly touches the sea water is high grade, decreasing in the order of mid-shell, inner-shell. Analysis data show that the Co grade and the Ni, Mn grade are in positive correlation while the Co grade is in negative correlation with Fe.

• Theanalysisresultsofthe1991surveyformanganesenodulesrevealedthatthereishighpositivecorrelationamong Mn, Ni and Cu and between Fe and Co and high negative correlation between these two types.

• Basedon the1991analysisofcobalt-richcrusts,highpositivecorrelationamongMn,NiandCo,highnegative correlation Fe versus Mn, Ni and Co, and lower correlation between Cu and the other four elements are recognized. The higher grade of Mn, Ni and Co, is found under shallower conditions and reversed for Fe.

• Based on the 2003 survey, the occurrence of cobalt-rich crusts on the SE01 Seamount seems to belocalised and not widespread over the whole area.

Metal Concentration and DistributionManganese Nodules


Phoenix Islands

In the study area of the Phoenix Islands waters, manganese nodules occur discontinuously in general. The high-abundance area (>10 kg/m2) is limited to the south-eastern part of the survey area, which covers approximately 6,600 km2 (Figure 5). The nodule abundance at the stations ranges from nil to 34.74 kg/m2 and the average abundance of the 57 stations is 4.45 kg/m2. Altogether 194 nodule samples were analysed. The average values of Co, Ni and Cu were 0.22 %, 0.66 % and 0.60 % respectively.

Figure 6. Variation in manganese nodules abundance in the EEZ of the Line Islands Group.

Line Islands

It was found that the eastern region has higher nodule abundance than the western area in the Line Islands waters: the average abundance of the eastern area is 6.56 kg/m2, while that of the western area is 2.94 kg/m2. Only three of the 33 stations occupied during the survey showed abundance of more than 10 kg/m2, and 13 stations were barren or have abundance of less than 2.5 kg/m2. The average abundance of all the stations is 4.37 kg/m2. Altogether 205 nodule samples were analysed. The average values of Co, Ni and Cu were 0.20 %, 0.84 % and 0.57 %, respectively.


Gilbert Islands

The survey results showed that almost all the stations have abundance of less than 5 kg/m2 in the Gilbert Islands’ waters. The average abundance of the 46 stations is 1.54 kg/m2, much lower than those of the other parts of Kiribati’s EEZ: 4.37 kg/m2 in the Line Islands and 4.45 kg/m2 in the Phoenix Islands. The average values of Co, Ni and Cu were 0.23 %, 0.96 % and 0.96 %, respectively.

Figure 8. Thickness and metal contents of cobalt-rich crust at each seamount in the Phoenix Islands.

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

Phoenix Islands

The bathymetric survey conducted on and around the five seamounts revealed that three of them are peaked seamounts and the other two are atolls. The cobalt-rich crusts were found to be well developed at all the surveyed seamounts except SA02, where distribution of crusts is quite limited. The crusts generally occur at the top and along the slope of the seamounts. The crusts tend to become inferior at the lower part of the slope.

Cobalt-rich Crusts

The average crust thickness of the five seamounts is 17 mm. Sampled crusts vary in thickness from a patina to 80 mm. The average chemical composition was: Co 0.78 %, Ni 0.66 %, Cu 0.11 %, Mn 25.38 % and Fe 14.48 %.

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Line Islands

Four seamounts on the Line Island Ridge (SC01-04), a seamount west of Vostok Island (SC06) and the slopes of Flint Island (SC05) were surveyed in 1989.

The bathymetric survey conducted on these six seamounts revealed that all the seamounts except for SC05 (table reef) were peaked seamounts.

The results of the Continuous Deep-sea Camera with Finder (FDC) survey revealed that crusts occur from the summits to the middle slope of the seamounts at water depths ranging from 990 m to 3270 m. High crust coverage was identified on the summits of the seamounts.

The average crust thickness of the six surveyed seamounts is 19.5 mm. Sampled crusts vary in thickness from a patina to 200 mm. Thick crusts were found at the summits and upper part of slopes in water depths below 1500 m and on substrates of sedimentary rocks, pyroclastics, phosphorite and hyaloclastite. Substrates of basalt and limestone had thin crusts. The average chemical composition was: Co 0.62 %, Ni 0.60 %, Cu 0.12 %, Mn 20.59 % and Fe 13.99 %.

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Figure 9. Thickness and metal contents of cobalt-rich crust at each seamount in the Line Islands.

Figure 10. Thickness and metal contents of cobalt-rich crust at each seamount in the Gilbert Islands.

Gilbert Islands

The survey was carried out on three seamounts (SE01, SE03, SE05) in the Gilbert Islands chain and two seamounts located approximately 120 miles and 240 miles east of Tarawa. The bathymetric survey conducted on the five seamounts revealed that four seamounts are peaked and the other (SE01) is a guyot (seamount with a flat top).

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From the results of the FDC survey, distribution of the crusts was identified. SE01 and SE02 are predominantly overlain by unconsolidated sediments. Exposed rocks with limited distribution are coated with Mn-oxide film. No crusts were observed on these two seamounts. At SE03, SE04 and SE05 unconsolidated sediments are widely distributed and the crusts occur on pinnacles and steep slopes.

The average crust thickness of the five surveyed seamounts is 12 mm. Sampled crusts vary in thickness from a patina to 65 mm. The thickness of crusts generally increases with water depth and is thickest at depth of 3000–3500 m. The average chemical composition of the five seamounts was: Co 0.69 %, Ni 0.58 %, Cu 0.10 %, Mn 22.87 % and Fe 17.95 %.

Summary of ResultsThe summary of the Japan-SOPAC survey results in Kiribati are tabulated in Tables 2 and 3 below.

Table 2. Summary results of the manganese nodules survey within the EEZ of Kiribati.

Manganese Nodules Survey

Phoenix Group Line Group Gilbert Group

Year of Survey 1987 1989 1991

Area Survey (km2) 320,000 520,000 1,300,000

Depth range (m) 5,000 – 5,400 4,700 – 5,400 West: 3,000 – 4,500mEast: 5,000 – 6,000m

Nodule shapeNorth area: predominantly roughSouth area: predominantly smooth

Predominantly pebble and massive with minor pebble thin type

Predominantly spheroidal and massive with minor pebble

Average Abundance (kg/m2)

<1 4.37 1.55

High Abundance zone

>10kg/m2 occurs in a 6,600km2

area>10kg/m2 occurs at the eastern part

>8kg/m2 occurs at two locations in the east central plain area

Continuity Poor Poor – Moderate Poor

Average Grade (%)

Ni 0.66 0.84 0.96

Cu 0.60 0.57 0.96

Co 0.22 0.20 0.23

Metal Quantity (tonnes)

Ni 1,300,050 (in 40,500 km2 area where Ni is more than 20g/m2)

3,960,000 (in 116,607 km2 area where Ni is more than 20g/m2)

1,758,100 (in 95,860 km2 area where Ni is more than 20g/m2)

Cu 1,066,050 (in 34,500 km2 area where Cu is more than 20g/m2)

1,563,000 (in 55,426 km2 area where Cu is more than 20g/m2)

1,487,710 (in 86,950 km2 area where Cu is more than 20g/m2)

Co 477,360 (in 11,700 km2 area where Co is more than 20g/m2)

360,300 (in 14,126 km2 area where Co is more than 20g/m2)

296,616 (in 30,962 km2 area where Co is more than 20g/m2)

Grade variation trend

High abundance zones are observed in sea-knoll and hilly province below the CCD of 5,200m.

The abundance is comparatively low in the survey area, but parts of the eastern sea have abundance zones.

Correlation between grade of Co and abundance is positive, but negative between the grade of Ni and abundance.

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Table 3. Summary results of the cobalt-rich crusts survey within the EEZ of Kiribati.

Phoenix Group 1987

Seamount SA01 SA02 SA03 SA04 SA05

Type of Seamount Peaked Atoll An atoll and a

peaked seamount Peaked Peaked

Dimension (km x km) 37 x 15 21 x 19 Atoll: 24 x 19

Peaked: 14 x 9 18 x 13 13 x 13

Height (m) 3,600 5,000 Atoll: 5,000Peaked: 4,170 4,360 4,230

Water depth to summit (m) 1,640 0 Atoll: 0

Peaked: 1,030 1,040 1,170

Occurrence * C, B, M, N, S, single layer

Mostly thin coating

Prominent crust, S, M, B, with two layer

Prominent crust, B

Only crust, one – three layers

Coverage (%) Flat top: 0Gentle slope: 10 – 70Steep slope: 10 – 100

Eastern slope: <50Other slope: 0 or thin coating

Atoll: 10 – 70Peaked: 10 – 90

Unable to estimate Unable to estimate

Average Thickness (mm) 17 2 Atoll: 1.0

Peaked: 2.0 1.8 1.9

Average grade (%)

Co 0.79 0.36 0.78 0.71 1.05

Ni 0.67 0.47 0.70 0.68 0.57

Cu 0.13 0.12 0.10 0.09 0.07


There is a positive correlation among the content of Co, Ni and Mn, and there is a negative correlation between the water depth and the content of Co, Ni, and Mn. There is also a positive correlation between the water depth and the content of Fe and Cu.

Line Group 1989

Seamount SC01 SC02 SC03 SC04 SC05 SC06

Type Peaked Peaked Peaked Peaked Table reef Peaked

Dimension (km x km) 16 x 47 10 x 24 15 x 15 18 x 15 28 x 10 15 x 12

Height (m) 3,410 2,960 3,360 3,695 4,500 3,570

Water depth to summit (m) 1,590 1,040 1,140 805 0 1,130

Occurrence Prominent B, with S, C

Prominent C, with S, B, N

Prominent C, with N, B

Prominent C, with N, B, S

Poor crust development, coating predominates

Prominent C, with S

Coverage (%) FDC not operated

Upper slope: 30Middle slope: 10

Top: 0-5Upper slope: 50Middle slope: 45

Top: 60Upper slope: 25Middle slope: 20


FDC not operated

Average Thickness (mm) 35.4 21.7 15.6 19.0 6.5 18.9

Average grade (%)

Co 0.56 0.78 0.54 0.42 0.66 0.76

Ni 0.65 0.64 0.56 0.59 0.53 0.60

Cu 0.11 0.11 0.13 0.13 0.10 0.11


Thickness of crust is good in depths below 1,500m, and the average of six seamounts is 19.5mm. Based on grade and thickness of crust, seamounts SC01, SC02 and SC06 have excellent potential.

* Crust Type: C – Crust; B – Cobble; M – Massive; N – Nodule; S – Slab.

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Gilbert Group 1991

Seamount SE01 SE02 SE03 SE04 SE05

Type Guyot Peaked Peaked Peaked Peaked

Dimension (km x km) 56 x 21 Diameter: 12 5 x 5 8 x 2.5 7 x 5

Height (m) 3,225 4,630 3,120 3,490 3,015

Water depth to summit (m) 1,275 370 1,577 2,012 1,685

Occurrence No sample Predominantly C Prominent C and B

Prominent C and B

Prominent C, B and pebble

Coverage (%) Top: 3Upper slope: 2Middle slope: 5

Top: 50Upper slope: 10Middle slope: 1Lower slope: 10


Top: 25Upper slope: 10


Average Thickness (mm) - 16.3 9.9 7.2 13.1

Average grade (%)

Co - 0.78 0.84 0.52 0.62

Ni - 0.69 0.68 0.47 0.53

Cu - 0.09 0.11 0.08 0.13


High positive correlation among Mn, Ni and Co, high negative correlation Fe versus Mn, Ni and Co, lower correlation between Cu and other four elements

Resource EstimationManganese NodulesThe inferred manganese nodule resources in Kiribati are summarised in Tables 4, 5 and 6. Above the assumed cut-off nodule abundance of 5 kg/m2 (on dry basis), a nodule resource of 1,392 million tonnes is expected in an area of 163,000 km2 within the EEZ of Kiribati. Cobalt, nickel and copper resources in the nodule deposits of over 5 kg/m2 were calculated to be 4.0 million tonnes, 6.6 million tonnes and 5.0 million tonnes respectively.

Table 4. Estimation of resource of nodules and metals in the study area in the Phoenix Islands.

Noduleabundance (dry)

Area(km2)

Total Resources (in million tonnes)

Nodules (dry) Co Ni Cu

Over 15 kg/m2 3,800 87 0.35 0.22 0.12

10-15 kg/m2 13,200 148 0.46 0.53 0.38

5-10 kg/m2 32,200 225 0.51 1.29 1.11

Cut off 5 kg/m2 49,200 460 1.31 2.04 1.61

Total 227,600 584 1.49 3.18 2.76

Table 5. Estimation of resource of nodules and metals in the study area in the Line Islands.


Area(km2)



Over 10 kg/m2 12,200 126 0.34 0.63 0.39

5-10 kg/m2 73,000 537 1.40 3.16 1.84

Cut off 5 kg/m2 85,300 663 1.74 3.79 2.23

Total 407,700 1267 2.91 8.95 5.80

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Table 6. Estimation of resource of nodules and metals in the study area in the Gilbert Islands.


Area(km2)



Over 10 kg/m2 16,600 202 24 0.11 0.06

5-10 kg/m2 12,300 67 317 0.83 1.15

Cut off 5 kg/m2 28,900 269 341 0.93 1.20

Total 367,700 352 579 1.51 2.27

Cobalt-rich CrustsThe resource estimates indicate a total inferred resource of 43.9 million tonnes of crust within the EEZ of Kiribati. Cobalt, nickel and copper resources were estimated to be 285,200 tonnes, 281,600 tonnes and 48,000 tonnes respectively. The details are shown in Table 7 below.

Table 7. Estimation of crust and metal resources within the EEZ of Kiribati.

Island Group SeamountsInferred

Resources (tonnes)

Metal Resources (tonnes)

Co Ni Cu

Phoenix SA01 2,821,000 22,288 18,902 3,668

SA02 461,000 1,659 2,167 553

SA03 5,228,000 40,779 36,596 5,228

SA04 1,980,000 14,056 13,462 1,782

SA05 1,400,000 14,703 7,982 980

Sub-total 11,890,000 93,485 79, 109 12,211

Line SC01 19,164,000 107,319 124,556 21,080

SC02 3,984,000 31,073 25,496 4,382

SC03 2,843,000 15,352 15,920 3,696

SC04 1,935,000 8,127 11,416 2,515

SC05 793,000 5,231 4,201 793

SC06 962,000 7,314 5,774 1,059

Sub-total 29,681,000 174,416 187,363 33,525

Gilbert SE01 - - - -

SE02 1,484,000 11,428 10,389 1,336

SE03 300,000 2,551 1,921 270

SE04 169,000 862 760 135

SE05 398,000 2,465 2,107 517

Sub-total 2,351,000 17,306 15,177 2,258

Total 43,922,000 285,207 281,649 47,994

ConclusionIn general, the manganese nodules that occur within the Kiribati EEZ are variable in terms of abundance, size and mineral contents. Although significant occurrences of manganese nodule and cobalt-rich crust resources have been confirmed, additional exploratory work is required to increase the level of knowledge in regard to the nature of occurrence and distribution of these mineral deposits, the oceanographic conditions, and other related issues that need to be considered during the feasibility study stage of any offshore mining operations.

information brochure 9 kiribati deep-sea minerals potentialkiribati has a vast exclusive economic...

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