ISSN.OII0-O408

SOUTH PACIFICMARl NE GEOLOGICAL NOTES

TECHNICAL SECRETARIAT Vol. 2 No.4

cCOP-SOPAC ESCAP June 1981

SUVA

MANGANESE NODULES IN THE COOK ISLANDS REGION,

SOUTHWEST PACIFIC

N.F. Exon

UN Offshore Mineral Prospecting

c/o tviineral Resources Department

Private Mail Bag,

G.P .0. Suva

Fiji

ABSTRACT

Manganese nodules have been recovered from about the highest grade is 1.34~o in the South Penrhyn130 localities in an area of about 2,500,000 km2in Basin and 1.15~o in the North Penrhyn Basin. In thethe Cook Islands region, where they rest largely on two basins all grades exceeding 1% lie b.etweenred clay, and this paper relates their charac- 5000m and 560Om. In the South Penrhyn Basln allteristics to their location. concentrations exceeding lOkg/m2 lie between 480Om

and 530Om. There is a direct relationship betweenNodules from the Manihiki Plateau have an aver- the grade and the Mn/Fe ratio.

age grade (Ni+Cu+Co) of O,98~o, but their abundanceis unknown. Nodules from the Samoan Passage have Planktonic organisms are widely believed toan average grade of 0.88%, and unknown abundance. provide much of the Ni and Cu in deep-sea nodules.Nodules from the Samoa Basin have an average grade Metals are concentrated in their tissues and skele-of 0.67~o and variable abundance. Nodules from the tons and released during dissolution. The releasedSouthwest Pacific Basin have an average grade of metals may then be incorporated into nodules. Thus1.07%, and variable abundance; maximum nodule the relatively low Ni and Cu grades of Cook Islandsconcentration is 35.2kg/m2. Nodules from the South nodules, as compared to the nodules of the easternPenrhyn Basin have an average grade of 0.99~o, and equatorial Pacific, may result from the relativelyvariable abundance; maximum concentration exceeds low organic productivity of the surface waters.35kg/m2, Nodules from the North Penrhyn Basin have However higher grades may be present locally ifan average grade of 1.18% and a low abundance; metal-rich solutions have been escaping from activemaximum concentration is 10.7kg/m2. fracture zones.

In no case were nodules of potentially economicgrade (>2% Ni+Cu+Co) found in potentially economic Future nodule prospecting should concentrate. onconcentrations (>lOkg wet nodules per m 2), The the Penrhyn Basin, in water depths of 5000m tomost prospective basins appear to be the South 5600m, where high nodule concentrations and gradesPenrhyn Basin (maximum grade 2.02%), and the North may occur together. Other possible prospectingPenrhyn Basin (maximum grade 2.10~o). In both ba- guides include proximity to fracture zones, andsins the highest grades correspond to low concen- proximity to bottom currents which are importanttrations. For concentrations exceeding 10kg/m2, for a variety of reasons.

47

INTRODUCTION & &. 1976). Bottom photographs from 6 of thesestations showed nodules covering 90~Q of the seafloor. 2The greatest concentration of nodules was

The Cook Islands (Figs. 1 and 2) rest on the 30.6kg/m , and the highest grade was 0.88~Q Ni+Cu+southwestern part of the Pacific Plate, which con- Co. Glasby (1978) discussed the surface texture,sists of Early Cretaceous oceanic crust overlain by internal structure and mineralogy of these nodules,predominantly pelagic sediments. The submarine and showed that o-Mn02 is the major ferromanganeseManihiki Plateau (Heezen et al. 1965) has an area oxide mineral present. Ir. 1977 the Office de laof 500,000km 2, lies above 4O0om, and rises to with- Recherche Scientifique et Technique"Outre-Mer (ORS-in 2400m of the surface. It formed by voluminous TOM), Noumea, carried out two cruises in the Southeruptions of basalt at the time when the plateau Penrhyn Basin, during which 23 stations were occu-was at or near the Neocomian triple junction be- pied; nodules were obtained from 18 of them (Mon-tween the Pacific, Antarctic, and Farallon plates zier and Missegue, 1977; Recy & &. 1977). The(Winterer & ~. 1974; Schlanger, Jackson et al. greatest concentration of nodules was 22.5kg/m2,1974). Oceanic basalt is overlain by 900m or-more and the highest grade was 2.02~Q Ni+Cu+Co.

of sediment laid down in ever-increasing water

depths. In 1976 NZOI carried out a TANGAROA cruise toNorthwest of the plateau is the North Tokelau the Samoa Basin, during which nodules were recover-

Basin, which is connected to the Samoa Basin to the ed from the central part of the basin, but not itssouth by the Samoan Passage. A chain of volcanic margins (Meylan et al. 1978). Nodules wereislands and seamounts separates the Samoa Basin abundant in places:-but;the highest grade recordedfrom the Southwest Pacific Basin, which lies south was 0.68~Q Nl+Cu+Co.

and west of the southern Cook Islands. The PenrhynBasirl lies east of the Manihiki Plateau, and north In 1977 CCOP/SOPAC used the R.V. MACHIAS onof the southern Cook Islands; it is separated into cruise CK-77(1) to recover nodules from two sta-northern and southern parts by the Penrhyn Island tions northeast of Rarotonga, where they were ofchain. Maximum water depths are about 5500m in the low to high abundance (Eade, 1977). The followingNorth Tokelau, Samoa and Southwest Pacific Basins, year on cruise CK-78(2) (Eade, 1978), the MACHIAS510Om in the South Penrhyn Basin, and 530Om in the recovered scattered nodules from three stations inNorth Penrhyn Basin (Mammerickx ~&. 1973). the Samoa Basin (maximum grade 1.08~Q Ni+Cu+Co), and

abundant nodules from five stations in the SouthThe history of the volcanic islands and sea- Penrhyn Basin (maximum grade 1.4~Q).

mounts of the Cook Islands region (Figs. 1 and 2)has been discussed by Wood and Hay (1970). The Irl 1980 there were two CCOP/SOPAC surveys in theislands generally appear to occur as chains extend- Penrhyn Basin, using the MACHIAS. On cruiseing northwest, such as that involving Aitutaki, CK-80(1) nodules were recovered from 10 stations inManuae, Miniaro, and Mauke Islands. The age of the the North Penrhyn Basin (Gauss and Moreton, 1980).volcanic pedestals of most of the islands is not Concentrations ranged up to 10.7kg/m2 and gradesknown, but they probably formed over hot spots as to 2.10~Q Ni+Cu+Co, but the higher grades were asso-the Pacific Plate moved northwestward during the ciated with low concentrations. On cruise CK-80(2)Cainozoic. According to Wood and Hay (1970) much abundant nodules were recovered from one station inof the volcanism is of Palaeogene age, but the the northern South Penrhyn Basin, and the grade was

youngest eruptions on Rarotonga are earliest 0.93~~ Ni+Cu+Co (Lewis, 1980).

Pleistocene.

Oceanographic cruises by Scripps Institution of " .Oceanography (SIO), Lamont Doherty Geological A maJ~r c,ontr,~but~on to the un,der,standing ofObservatory (Lamont), Woods Hole Oceanographic nodule d~str~but~,on, an,d cha,racter~st~cs in theInstitute (Woods Hole), and the Soviet research cen~ral South Pac~f~c, ~nclud~ng the South Penrhynvessel VITYAZ in the 1960's had shown that there Bas~n, W,8S made by Pau~ot and Melguen (1976, 1979).were abundant' manganese nodules in the surface For the~r more extens~ve (1979) paper, they used

, data accumulated by ORSTOM, CNEXO, CCOP/SOPACsed~ments of the deep ocean floor near the Cook (L d t 1 1976) d AFERNOD (A ' t ' an messer ea. an ssoc~a ~on

Islands (e.g. Skornyakova and Andruschenko, 1974; Francaise pour iiEtude et la Recherche des NodulesGlasby and Lawrence, 1974). Therefore, at the Polymetalliques).Second Session of CCOP/SOPAC in 1972 (ECAFE, 1974),it was decided that, "sea b,ed investi,g~t~ons for Their main conclusions (Pautot and Melguen,mangane~e nodules ~n o,cean~c, a~eas adJo~n~ng Cook 1979), for an area which included the Marquesas andIslands should be of h~gh pr~or~ty. Tuamotu regions, the Tiki, Tapu and South Penrhyn

, ' Basins, and an area east of the Tonga Trench, wereIn 1974, the New Zealand Oceanograph~c lnst~- summarized as follows:

tute's (NZOI) vessel TANGAROA made a cruise to theSouthwest Pacific Basin, and rec~vered nodules withconcentrations of up to 20.5kg/m , and grades of upto 1.22% Ni+Cu+Co, so,pth and west of Rarotonga "Analyses of PC?l'):'metallic nodules from the(Meylan &&. 1975; Backer ~&. 1976). cen~ral So~th. Pac~f~c and from the underlying

sed~ments ~nd~cate that nodule abundance is atleast partly related to the degree of carbonate

In 1976 CCOP/SOPAC used the, Cook Islands govern- dissolution, which, itself, is stronglyment vessel RAVAK~I for ?ru~se ,CK-76(1) in the influenced by the flow of the Antarctic BottomSouth Penrhyn B.as~n, dur~ng wh~c~ nodules were Water. The greatest nodule abundance is gener-recovered from nlne out of 12 stat~ons (Landmesser ally encountered in a 300 to 400 meter thick

48

water lay.er situated between the lysocline and For ,this purpose data dealing with nodule con-1: "the calcJ.te compensation depth levels. This centratJ.ons and grades were extracted from the.range of depth is the first and main controlling above references, from a printout. published byfactor of abundance. Inside this range, the M~nget ~~. (1~!6), and another p~J.ntout of pub-bathymetry represents a secondary factor in flu- IJ.shed and unpub~J.shed data made avaJ.lable to CCOP/encing both abundance and grade. Some correla- SOPAC by Jane Frazer of SID in 1978. Previouslytions appear locally between nodule grade and unpublished CCOP/SOPAC data is presented in Tableabundance. Nodule grade seems to be generally 1. The region studied (Figs. 1 and 2) cov~rs aboutrelated to the bottom morphology. Ni, Cu and Mn 3,600 ,000km 2 , a~d. nodu~es .hav~ been ob,taJ.ned from

grades are positively correlated and are highest about 130 10calJ.tles wJ.thJ.n J.t. AvaJ.lable datain topographic lows. On the contrary, Co and Cu indicate that nodules are commonly present whereare negatively correlated and Co presents higher the water depth exceed~ ~OOm, and proba~ly occurgrade on topographic highs." over about 2,500,000km J.n the area studJ.ed. The

Cook Islands nodules form part of a South PacificAn examination of smear slides of surface sedi- nodule province, which a recent compilation by

ments was a major part of their study, and the Rawson and Ryan (1918) suggests ~overs an area ofresults for the South Penrhyn 8asin (their "Aitu- alrnost 20,000,000km. The provJ.nce extends fromtaki area") reveal an interesting sediment distri- the Manihiki Platf3au in the north, to the Agassizbution pattern. In water depths of 4700-4800m Fracture Zone in the east, ar,d the Chatham Rise inpelagic clays are dominant, but these still contain the west. .some calcareous particles (foraminifera 1-3%, nan-nofossils 1-10%). At greater depths the pelagicclays are free of calcareous particles, showingthat the calcite compensation depth (CCD) liesbetween 480Om and 5000m. The pelagic clays areenriched in hydroxides (10-25%) and zeolites (5-15%) around 5000m. Major contributions to this review have come

from data collected by the USSR Institute of Ocean-Pautot and Melguen also found two main facies in ology (VITYAZ), SID (AGASSIZ, ARGO, BAIRD, MEL-

the deep parts of the South Penrhyn Basin: "a VILLE, WASHINGTON), Lamont (VEMA, CONRAD), Woodspelagic clay rich in zeolites and bearing volcanic Hole (CHAIN), HIG (MAHI), NZOI (TANGAROA), ORSTOMglass and siliceous debris, and a pelagic clay (CORIOLIS), and CCOP/SOPAC (RAVAKAI, MACHIAS).relatively rich in siliceous debris and bearingzeolites and volcanic glass." The first faciesoccurs between 11° and 13°S and. contains particu- The information comes in the form of the gradeslarly abundant and large zeolJ.tes; the secorld of various metals including Mn Fe Ni Cu and Cofacies occurs between 13° and 200S. and in some case~ in concentration~ (kilograms of

wet nodules per square metre) or population(percentage of bottom covered by nodules in bottomphotographs). Samples which were taken by dredge

As regards nodules, Pautot and Melguen (1979) or normal corer yield information about nodulestated that in the South Penrhyn Basin: size, shape and grade only, but samples taken by

free-fall or tethered grabs also give nodule con-I. Nodules are most abundant between ~800m and centrations. Deep sea cameras reveal the nodule

5200m. Concentrations reach 25kg/m in pla- population; if they are attached to the samplersces. the population can be directly related to concen-

tration. The term abundance is used here to cover2. Ni grades increase with increasing water both concentration and population.

depths. The highest grades are around 5400m,the maximum being 1.1%.

3. Cu grades also increase with increasing waterdepth. The highest grades are again around Nodule abundance and grades have been related to5400m, the maximum being 0.7%. geography in Figs. 1 and 2.. Rather heterogeneous

information was used to plot abundance (Fig. 1).4. Co grades are not correlated with ~ater The best data are concentrations measured from grab

depth. The highest grades (ca 0.6%) occur at samples (kg/m2). These come from BHcker ~ ~.4800m and 5200m. (1976); Landmesser ~~. (1976); Monzier and

Missegue (1977); Recy ~~. (1977); Gauss andThe Dresent review Moreton (1980); and Russian data tabulated by J.

Frazer. Inferior data are abundances visuallyAfter the most recent CCOP/SOPAC cruise was estimated from grab (or small-diameter core)

completed, it was decided that enough data on samples. These were classified as of "low, mediumnodule concentrations and grades now existed within or high" abundance. Such data come from Eadethe Cook Islands region for a detailed review to be (1977 1978); Meylan ~~. (1978) and Lewiscarried out. This would clarify the question of (1980~. In a few instances photographic evidencepossible economic development, and define the most supplemented concentrations (e.g. B~cker ~ ~.prospective areas in the region. 1976; Landmesser ~~. 1976).

49

f~~;f?'@

.

,

++ +

0 0 0

0(Somoo)

0 + 0 +

BASIN ' 0

~ 00

0 I0 ~/. pe: 0

0 ,.. [Jft-f .°Polmerston ~ SO. ', ,.,. ~tutOki I

~ " + eJ~Monuoe I

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Man~aia ~.

8A' BASIN 8,

~ '@Fabert Bank

0,Measured concentrations Estimated abundances(f~om qrabs) (larqel y frorn qrab!}) + Nodules absent

, Nodules present, abundance unknown.0-10kg/m2 0 Low abundance .Stations of HAKUREI MARU cruise810-20kg/m2 0 Medium abundance GH81J-l (see Addendum)tt > 20kg/m2 () High abundance ~ Approximate 200 n.m. limit

/- Basin limit

Fig. 1. Relationship of nodule abundance to geography. "Stations" marked A, B, C, D actuallyrepresent small areas within which a number of stations were occupied. Bathymetry inmetres (after Mammerickx 2i~. 1973).

50

St.Q,(;jjj)(Kiribati)

BASIN......~

++ +.

SAMOA

, +

BASIN ..~ .,

,, 0

,

+

.~Raratonga 1

fZJ. Mangoia ~.PACIF,;. .A. BASIN ..

""<) .~ ...1000,"""',...",- -.@ Fobert Bonk165. .

.0 -1.0~~ + Nodules absent ~ Approximate 200 n.m. limit.1.0 -1.5% , Nodules present, --BolO °t.1.5 -2.1~~ grade unknown r asJ.n J.mJ.

Fig. 2. Relationship of nodu]e grade (% Ni+Cu+Co) to geography. "Stations" markedA, B, C, D represent small areas within which a number of stations wereoccupied. Bathymetry in metres.

51

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Consolidated information on metal grades in the a) Minimum concentrations of about 10kg "wet"various basins has been tabulated (Table 2), and nodules/m2 (i.e. about 15kg dry nodules).plotted (Fig. 3). In order to see what variationin grade occurs in a small area, the percentage of b) Combined contents of Ni+Cu+Co of more than 29~the valuable metals Ni+Cu+Co has been plotted (or Ni+Cu of about 1.769~ assuming an averageagains~ the number of samples, from an area of of 0.249~ associated Co).1000km sampled in detail by R.V. VITYAZ (Fig. 4).The prop?rtions of.Ni, Cu a~d Co have been plo~~ed c) Areal extent of fields of at least 20-on a trJ.angul.ar dJ.agr~m (FJ.g.. 5) to see how e~ 30,000km2. This assumes an area of favoura-vary from basJ.n to. ba.sJ.~. T~J.s plot shows that 73,. ble relief, favourable engineering propertiesof ana;ys7s ~al! wJ.;,hJ.n -10~ of the average val~e of underlying sediments, and lack of harda~d 92~ wJ.thJ.n -20,. o! the avera.ge. T~u~ there J.S rock obstacles, to give an operation life ofIJ.~tle chance of r7gJ.onal samplJ.ng gJ.vJ.ng gr~des at least 20 years. (Recoveries of 1-3

whJ.ch are greatly dJ.fferent from averages obtaJ.ned mJ.. IIJ.. n t S f d d 1b d t .1 d 1 .0 onne 0 ry no u es per year seem

y e aJ. e samp J.ng. to be necessary).

The nodule concentrations and the grades of Other authors have made rather different assess-valuable metals have been plotted against water ments of the concentrations and grades necessarydepth in Figs. 6, 7, 8 and 9, and against the Mn/Fe for a mining operation to be considered possible.ratio in Figures 10, 11, 12 and 13. The nodule For example Menard and Frazer (1978), drawing evi-grade has been related to the concentrations in dence from various sources, have suggested that theFigs. 14, 15 and 16. cut-off concentration may be as low as 5kg/m2.

However this paper assumes that Seibold's figuresSeibold (1978) suggests that prerequisites for are a reasonable gujde to the economic significance

first-generation mining sites are as follows: of nodule occurrences in the Cook Islands region.

TABLE 2: Summary of nodule metal grades in various areas

Area ~~n %Fe Mn : Fe ~~Ni ~~Cu. ~~Co ~~Ni+Cu+Co

Manihiki Plateau Mean 16.9 0.30 0.17 0.51 0.98(Horn, Horn &Delach, 1973)

Samoan Passage Min 15.1 13.8 0.74 0.18 0.10 0.25 0.61(12 samples) Max 20.5 20.7 1.33 0.48 0.40 0.66 1.15

Mean 17.9 18.3 0.98 0.30 0.18 0.40 0.88

Samoa Basin Min 13.0 8.1 0.75 0.21 0.11 0.11 0.45(9 samples) Max 18.6 21.2 1.85 0.45 0.28 0.55 1.08

Mean 16.3 14.6 1.13 0.34 0.20 0.28 0.67

Southwest Pacific Min 12.2 14.7 0.57 0.15 0.11 0.20 0.61Basin Max 21.2 25.8 1.20 0.70 0.33 0.52 1.47(18 samples) Mean 16.2 18.6 0.87 0.43 0.24 0.40 1.07

South Penrhyn Basin Min 7.9 5.6 0.50 0.11 0.07 0.22 0.54(48 samples) Max 23.0 22.5 2.12 1.08 0.69 0.56 2.02

Mean 15.2 15.4 0.99 0.41 0.22 0.36 0.99

North Penrhyn Basin Min 7.5 5.3 0.58 0.20 0.09 0.09 0.48(10 samples) Max 24.1 16.6 4.46 0.99 0.95 0.43 2.10

Mean 16.3 10.1 1.61 0.57 0.38 0.23 1.18

Equatorial NorthPacific* '

Red clay Mean 17.4 11.4 1.53 0.76 0.50 0.28 1.54Siliceous ooze Mean 22.4 8.1 2.76 1.16 1.02 0.25 2.43

* Data from Horn, Horn and Delach (1972) and Horn, Delach and Horn (1973).

53

uQ) ;0::01 .-0 c:: (.) c:: c::III -0 >- >-III 1110 a.. .c:: .c::0 c:: '- '-

CD -C::c:: c::a.. -(/I Q) .-Q) c::

(/I 0 a.. 1/1 a.. .inc:: Q)CD 0 00 0 ~ .c::CD.c::ID0 0 £ --

~ ~ ~ ~ £ RESULTS

2 Manihiki Plateau

A number of stations on the Manihiki Plateauhave yielded nodules. or photographs of nodules(Heezen ~~. 1965; Horn, Horn, Delach, 1973).These are mainly on the eastern margin of the pla-

E Q) E teau, in water depths ranging from 2,OOOm to1 :J g'~ 4,700m. Camera evidence indicates that the nodule

.~ ~'x population varies from low to high..-> 0~<1~

Nodules were recovered f~om nine stations, andtheir analyses show a mean grade of O.98~~ (Co>

Ni>Cu). There is little chance of population,grade and size of mining area on the plateau being

I. great enough for it to have any economic

significance.

.Samoan Passaqe

No information is available about nodule concen-o. trations or populations in the Samoan Passage (Fig.

1), but 12 samples have been ana lysed from stationsranging in water depth from 4500m to 5500m (Fig.2).

The results (Table 2) show a mean Mn/fe ratio of0.98, and a mean grade of O.88~~ (Co>Ni>Cu). Thereis no systematic relationship between grade andwater depth (Fig. 9), but there is a direct

Fig. 3. Histograms summarizing nodule relationship b~tween .grade and M~/Fe ratio (Fig.grades (~~ Ni+Cu+Co) in various 11). The rat~o of N~ to.Cu rema~ns r~ughly con-basins. Averages are similar st~nt whereas the proport~on of Co var~es greatlyin Southwest Pacific and Pen~ (F~g. 5).rhyn Basins, but maxima areconsiderably higher in Penrhyn The maximum grade of 1.15~~ Ni+Cu+Co suggestsBasins that this area has little economic potential, al-

.though it really has not been adequately sampled.

30

Samoa Basin25

10 The 28 stations in this basin are well spread,

~ 20Q) and nodules were recovered from only 18 of themCi g' (Figs. 1 and 2). According to Meylan et ala (1978)E ~ about 90~~ of the nodules are small k3cm maximumg 15 ~ diameter). Spherical nodules and polynucleate

~ 5 ~ nodules predominate, and these have microbotryoidal0 10 a.. surface textures. Nodules are essentially absent

~ From the northern areas near the Manihiki Plateau.

5 The nodule concentration is known at only two

stations, one in the northeast (5.7kg/m2), and the0 0 other in the southeast (15.6kg/m~. However nodule

05 10 15 population is known at 15 stations (Fig. 1) andGrode (% NI + Cu + Co) varies from low to high.

Nine samples have been ana lysed (Table 2), fromFig. 4. Histograms showing variations water depths ranging ,from 500Om to 5600m. They

in nodule grade (% Ni+CU+Co) in show a mean Mn/Fe rat~o of 1.13, and a mean grade42 samples taken by R.V. VITYAZ 0: 0.67% (Ni>Co>Cu). There is no systematic rela-in Area A in the Southwest t~onsh~p apparent between grade and water depthPaciFic (location in Figs. 1 (F~g. 9), or between metal grades and Mn/Fe ratioand 2). this area covers about (F~gs. 11, 12 and 13). Not enough analyses are1000km'2. The plot indicates available for any comparison between population andthat widely-spaced sampling is grade to be made.

most unlikely to yield an error+of more than -20~~ from actualaverage grade in regionsampled.

54

0;0 Ni

~cific Basin.

Pacific Basin.

Area E Passage +North Penrhyn

% Cu % Co

Fig. 5. Triangular diagram showing variations in proportions of Ni, Cu and Co in selected smallareas. Values are percentages, where Ni+Cu+Co = 100~.. Areas A-D located in Figs. 1and 2; Area E at ca. 3.51°5, 158.5°W. A = 40 VITYAZ samples, B = 9 VITYAZ samples,C = 16 VITYAZ samples, D = 11 Scripps samples, E = 6 CNEXO samples. Illustratesgeneral dominance of Ni and Cu in Penrhyn Basin, and lUide 'Jariation in Cu~..

The basin has not been adequately sampled to be dominate south of Rarotonga. Most nodules are ofabsolutely sure of its economic potential, but the small to medium size «6cm maximum dimension) butmaximum grade to date of 1.15% Ni+CU+Co is not large nodules predominate at a feIU stations. Theencouraging. surface texture is generally granular.

The nodule concentration is knolUn from only sixareas (Fig. 1) and ranges up to 35.2kg/m2 at VITYAZ

SouthlUest Pacific Basin station 6298-48. Nodules have been found in lUaterdepths of 3000-5600m, but concentrations exceeding

The eighteen stations sholUn in Figs. 1 and 2 are 10kg/m2 are generally restricted to 4500-5100mconcentrated in the east. TlUo of the "Stations" (Fig. 7). HolUever abundant nodules (19.2kg/rrf) lUeresholUn (A and B) are actually small areas (1000km2 also found in a lUater depth of 3180m at VITYAZand 400km2 respectively) IUhere VITYAZ occupied a station 6298-9. Eighteen samples have been ana-number of stations. Nodules lUere recovered from lysed (Table 2), and their mean Mn/Fe ratio is 0.87all except three stations, IUhich lUere on the flanks and mean grade 1.07~. (Ni>Co>Cu). They come fromof volcanic r,fses. According to Meylan ~ ~. lUater depths ranging from 4700m to 5250m, and the(1975), and Backer ~~. (1976) the nodules are highest grades lie betlUeen 4800m and 5100m (Fig.predominantly spheroidal, but ellipsoidal nodules 9). The nodule grade is directly proportional to

55

the Mn/Fe ratio (Fig. 11). There is no obvious Analyses of 16 VITYAl sarnples from Area C (Figs.relationship between concentration and grade (Fig. 1 and 2) show that, as is the case in the Samoa14). However, a concentration of 32.6kg/m2 is Passage and Southwest Pacific Basin, the Ni/Cufound with a grade of 1.26~~, southeast of Mangaia ratio remains fairly constant, while the proportion(Figs. 1 and 2). of Co varies considerably (Fig. 5). However, in

the South Penrhyn Basin, the proportion of Co isAnalyses of 40 samples from Area A, and 9 from relatively s~lall.

Area B, which lie about 300km apart (Figs. 1 and2), show similar relationships between the propor-~ions of Ni, Cu and Co, in both.cases (F.ig. 5). .As The South Penrhyn Basin, in which there are~n. the Samoan Passage, the N~/~u rat~o rema~ns nodules wjth a grade of just over 2~~, and nodulefa~r~i constant, but the proport~on of Co var~es concentrations of over 30kg/m2, is clearly the mostgrea y. prospective part of the Cook Islands region.

...However, the combination of really high grades with.Desp~te the h~gh nodule con.centrat~o~s present high concentrations (say 2.5~~ Ni+Cu+Co with 15kg of~n plac.es, t~e low g.rades (max~~um 1.47,.) suggest nodules per square metre) has not yet been found,that th~s bas~n has l~ttle econom~c potent1al. and may well not occur. The highest grades occur

in the area east of the Manihiki Plateau between.11° and 14°S and east of 1600W, in a region where

South Penrhyn Bas~n concentrations and populations are also fairly high

..(compare Figs. 1 and 2). This is wh~re any futureNodules have been recovered from 47 stat~ons ~n exploration should be concentratedthe South Penrhyn Basin shown in Figs. 1 and 2. .

"Station" C is actually an area of 1000km2 whereVITYAl occupied a number of stations. This basinis the mo~t adequately sampled within the Cook N t h P h B .Islands region. Nort:n r-enrnyn tjas~n

According to Landmesser ~ &. (1976) most no- Nodules have been recovered from 13 stations indules in the basin are of small to medium size «6 the area covered by Figs. 1 and 2, and additionalcm maximum dimension). Spheroidal, ellipsoidal and data, gathered by CNEXO, is available furtherdiscoidal nodules, as well as polynucleate nodules, north. According to Gauss and Moreton (1980) mostare all locally dominant. The surface texture of the nodules are of small to medium size «4cmranges from smooth to microbotryoidal. maximum dimension). Nodule shapes are highly

variable but tabular, ellipsoidal, and polynucleateThe nodule concentration is knowrl from 24 areas nodules predominate.

(Fig. 1), and reaches a maximum of 62kg/m2 at VIT-YAl station 6332. Photographic evidence confirmsthat the nodule population is high, with 90~~ cover-age of the sea bed not uncommon (Landmesser ~ &. The nodule concentration is known from 10 of1976). Nodules have been found in water depths of these stations (Fig. 1), and is generally less than3500-570am, but concentrations exceeding 10kg/m2are 2kg/m 2. Only southeast of Penrhyn is it higherrestricted to 4800-5300m (Fig. 6). (10.7kg/m2 at Station 4 of Gauss and Moreton,

1980). Nodules have been found in water depths ofForty-eight samples have been ana lysed (Table 4200-5700m, but concentrations exceeding 2kg/m2have

2), from water depths of 4300m to 5650m. They show been measured only in depths of 5200-5600m (Fig.a mean Mn/Fe ratio of 0.99, and a mean grade of 6).0.99~~ (Ni<Co<Cu). The highest grades are foundbetween 500Om and 5400m (Fig. 8). There is a directrelationship between grade and Mn/Fe ratio. The Ten samples have been analysed (Table 2) fromhighest grade of 2.02~~ corresponds to the highest water depths of 3500-5600m. They show a mean Mn/FeMn/Fe ratio of 2.12 (Fig. 10). Figures 12 and 13 ratio of 1.61, and a mean grade of 1.18% (Ni>Cu>demonstrate that this relationship is due entirely Co). The highest grades are found in water depthsto the Ni+Cu grades, and not to the Co grades. of 5100-5600m (Fig. 8). There is a direct rela-

tionship between grade and Mn/Fe ratio (Fig. 10),the highest grade of 2.10~~ corresponding to thehighest ratio of 4.46.

A plot of concentration against (Fig. 14) indi-cates that the highest grades are associated onlywith low concentration~: Onl.y in o~e case is a A plot of concentration against grade (Fig. 14)grad7 of more tharl 1.3,. a~soc~ated w~th. a concen- shows an. unfortunate association of the highesttrat~on of more than 6kg/m (VITYAl stat~on 5988-2: grades WJ.th low concentrations. In only one case1.34~~ with 12.4kg/m2). The most common grades of does the concentration exceed 3kg/m 2 and in this0.8 .to 1.0~~ occur associat}d wi~h all concen- case the grade is 1.15~~ (at the station southeasttrat~ons from 2.5 to 32k~/m ..F~gs. 15 and 16 of Penrhyn). Analyses of six (CNEXO) samples fromdemonstrate that the relat~onsh~p of grade to con- northwest of Starbuck Island (and north of thecentration is entirely caused by Ni+Cu variations. limit of Figs. 1 and 2) show that the Ni/Cu ratioThis is particularly clearly shown by 12 VITYAl remains roughly constant at 1, and that the pro-samples from Area C. portion of Co is always low (Fig. 5).

56

0000

., ., *., XX X X XX ~ Xx .

\X ~ l ~~" Xx 62 ,-5000 ~ X X- .E X x 1-" ,/'" x x x ~ xi"= X J F1g.6. Plot of nodule concentration against

i .* water depth in the Penrhyn Basin. High-~ x South Penrhyn, Qenerol .* est concentrations lie between 4800m andc ~ South Penrhyn, Areo C 5300m in South Penrh

y n Basin and between~ 4000 0 North Penrhyn * ", "

Nodules present, concentrotion unknown * 5200m and 5600m 1n North Penrhyn Bas1n.* South Penrhyn.North Penrhyn t

60 10 20 50 40

Nodule concentration lkO/ftl2)

0000

*

*-5000 . . *E ... t.c ...! .Fig. 7. Plot of nodule concentration against~ .S th W t P .f * water depth in the Southwest Pacific-ou eSOClIC * B "" ..~ 4000 ~ Nodules present, concentrotion unknown * aS1n. H1ghest concentrat1onS lle be-

* tween 4500m and 5100m.

.«

.7 «5000 .,*

0 10 20 50 40Nodule concentration (kg/ftl2)

0000

x .,.," .,

"xx,," x X .,X ,,"0 x x .,

I X ")0( ""xx X-5000., xxE x

-~"= "i' .,

: " Fig. 8. Plot of nodule grade (% Ni+Cu+Co) against~ water depth in the Penrhyn Basin. High-~4 est grades lie below 5000m.

., N«th PQnrhynx South Ponrhyn

8.,5000o~ 10 ,~ 21>

Grode (% Ni. Cu .Co)

0000

e.e.. .;.+ + +...-5000 ....s .+ ...'" .

£ +.. ++ +'; + +~ +~ Fig. 9. Plat of nodule grade (9~ Ni+Cu+Co) against~ water depth in Southwest Pacific Basin.~4000 Samoa Basin and Samoan Passage. In the

.South West Pacific Southwest Pacific Basin the highest.Samoa Bosin grades lie between 4800m and 5100m.+ Samoan possaQ8

95

o~ 10 1.& 20Grode (% NI .Cu. Co)

57

Thus, on present evidence, despite the relative- Pautot and ~elguen (1976, 1~79) have shown thatly high metal grades of nodules from the North Pen- the concentratlon of nodules ln the cental Southrhyn Basin, the basin canrlot be considered to be of Pacific, .including the South Penrhyn Basin, iseccnomic interest because the concentrations are too strongly lnfluenced by water depth. Nodules appearlaw. to be concentrated in a 300-400m thick depth in-

terval. Their data showed that the interval variedfrom area to area as follows:

a) 4000-4350m in the Tiki Basin south of theMarquesas Fracture Zone

DISCUSSIONb) 4500-4800m north of the Marquesas Fracture

ZoneThe supply of metals to nodules may come from

the sediments in which they rest, oceanic or pore c) 4800-5000m in the Tapu Basin east of the Linewaters, or the remains of planktonic organisms. The Islandsoriginal sources of the metals are the continentsor oceanic volcanic activity. d) 4800-5200m in the South Penrhyn Basin

Acc?rding to a recent ~eview of the: l.iterature The present study has shown the same importanceby Se~.bold (197~), mechanlsms for e:nrlchlng se:a of water depth in determining nodule concentrationwater ln metals lnclude the .alteratlon of volca~lc in the Cook Islands region (Figs. 6 and 7). Nodulesrocks ~y hydrothermal So~utlons, normal subm~rlne appear to be concentrated in a 400-600m depth in-weatherlng of cool volcanlc rocks, or upward dlffu- terval which varies as follows:sion of metals in the pore waters of sediments. '

There is good evidence that nodules grow both above a) 4500-5100m in the Southwest Pacific Basinthe sediment surface, where the metals come fromsea water, and just below the sediment surface, b) 4800-5300m in the South Penrhyn Basinwhere they come from pore water. (additional data have made little difference

to Pautot and Melguen's 1979 results)

Deep sea nodules grow very slowly, and are found ). .only in areas where sedimentation rates are low. c 5200-5600m ln the North Penrhyn Basln

Thus they do not occur near land, or in areas ofturbidite deposition, where micro-nodules would bedeeply buried long before they grew to an appre-ciable size. Deep currents carrying Antarctic 11any authors have noted a general increase in NiBottom Water cause erosion, and also solution of and Cu grades in nodules with increasing watercalcareous sediment, and thus keep sedimentation depth, with a very great increase below 4000m (e.g.rates low. Cronan, 1980). The grades of Co in the deep sea,

on the other hand, appear to decrease slightly withEven so, deep sea nodules normally grow much increasing water depth. The result is that

more slowly than the sediments on which they lie combined grades of the three metals in deep seagrow upward. In the deep Pacific Ocean typical nodules are highest below 4000m. Pautot and Mel-nodule growth rates are l-lOmm per million years, guen (1979) showed that, in the deep water areas ofwhereas typical sedimentation rates, at l-lOmm per the central South Pacific which they studied, Nithousand years, are a thousand times higher (e.g. and Cu grades both increased with water depth,Ku, 1977; various authors in Bischoff and Piper, whereas Co grades were unrelated to depth. In the

1979). This is the well-known "nodule paradox", Tiki and Tapu Basins high Ni and Cu gradeslIIhich leads to the question "How do nodules stay at generally occurred at similar depths to high nodulethe surface?" Piper and Fowler (1980) suggest that concentrations. However, in the South Penrhynthe most plausible answer is that bioturbation by Basin, the zone of high Ni and Cu grades generallyin fauna continuously carries the surface sediment occurred in water depths of 5200-5400m and hence diddownward, beneath the nodules. not coincide with the zone of high nodule con-

centrations (depths 4800-5200m).During the last 10 million years, the period

necessary for medium-sized nodules to form, sedi- The present study has shown the close relation-mentation rates in the Cook Islands region must ship of Ni+CU+Co grades to water depth in noduleshave been low. The area was isolated from large from the Southwest Pacific and Penrhyn Basinsland masses, most volcanism had ceased, and the (Figs. 8 and 9). The zone of high grades in thedeep basinal areas lay near the carbonate compen- Southwest Pacific Basin lies in water depths ofsation depth. Furthermore, Antarctic Bottom Water 4800-5100m, and corresponds with the lower part ofmakes its way northward through the Samoa Basin and the zone of high nodule concentrations (depthsSamoan Passage (Hollister ~ ~. 1974) and 4500-5100m). The zone of high grades in the Southnortheastward through the Aitutaki Passage between Penrhyn Basin lies in depths of 5000-5400m, so itAitutaki and Palmers ton (Pautot and Melguen 1976). partially overlaps the zone of high nodule con-The bottom water would have caused active erosion centrations (depths 4800-5300m); the overlap wasand solution of calcium carbonate along its path, not apparent from the more limited data used bythus keeping sedimentation rates low. The low Pautot and Melguen (1979). It should be stressedsedimentation rates in many areas meant that condi- that the depth zone of high nodule grades does nottions for nodule formation were favourable, and fall fully within the depth zone of high noduleabundant nodules are the result. concentrations.

58

/x«~45 0 20 ...'<'

J e<'/ .x <? x, ~'<', CI O.v .~ ~

4.0 / c81/ ' 15 01

0,E' X

<:- 1 01

~, 0 ~I x .35 [;/ ~ I ~ X / X X

n9i lox. /"", "- ~.J.~

F/ Q) 10 .)11 ~,! lJ.. * X X

30 '0""" I Xx XI C ..

/ ~ Xx ~.i X l'

, k1 I

0 1

"-5 2.5 / 05 I...'Q) / ~~lJ.. ! «0/...I '" /x 12,~,.// .C 20 / 0-:>.

~ ,x~, ~ X1 0

J( I \ 0 0.5 10 1.5 2.0I' / )( Grade (% Ni ..Cu)

01.5 / 0

0 ' XX .*x X

/ l / xd x)('V x"" 20"

xl" Ji510 ')(7~ ..»<r ~ Xx '«

x .x x x

0 x x

05' 15

X X

10 .~ x'~ .0 .x

0 "- ex XX0 05 1.0 1.5 2.0 .2 Grade (% Ni i- Cu i- Co) ~ 10 )O<x X

X ~x& c.XX

~"'~ ~.~ Xno /"',/ X

1.5 00/ 05

o~'~L ~e~'L~\~

0 .,;~ o~""/ '00:

~ .+ " + f t ~~\~\c, 13to t ~

Q) 10 + i' + ..0

~ '# ' +t ...0 Grade 0(5% Co) 1.0

c +. t~ t + t

tl t...0.5 LEGEND

0 North Penrhyn Basinx..,.South Penrhyn Basin

11 t Southwest P~cific Basin'. Samoa Basin+... Samoan Passage

00 05 10 1.5 2.0

Grode (% Ni i- Cu + Co)

Fig. 10. Plot of % Ni+Cu+Co agairlst Mn/Fe ratio in the Penrhyn Basin. showing direct relationship.

Fig. 11. Plot of % t~i+Cu+Co against Mn/Fe ratio in Southwest Pacific Basin, Samoa Basin and Samoan Passage.Direct relationship apparent in Southwest Pacific Basin and Samoan Passage.

Fig. 12. Plot of % t~i and Cu against Mn/Fe ratio in South Penrhyn and Samoa Basins. Direct relationshipapparent in South Penrhyn Basin only.

Fig. 13. Plot of % Co against Mn/Fe ratio in South Penrhyn and Samoa Basins, showing no relationship.

59

t40 x 62 Kg/m2

.;; x .

In the North Penrhyn Basin the data are sparse. ~30 x.They suggest that the zone of high grades lies in;: x .depths of 5100-5600m, corresponding well with the ~ .zone of higher nodule concentrations (which are cstill rather low in fact ) Des p ite this the 0 0 North Penrhyn

.'.. ..':;: x )( x South PenrhynhJ.ghest n.odule .grades coJ.ncJ.de wJ.th very low e x Jx .Southwest PacificconcentratJ.ons (FJ.g. 14). C ~ ~..x

U X5lUc X x0 xx. )0(. j

In any deep sea region, higher grades of Ni+Cu+ U

Co are normally correlated with higher Mn/Fe ra- x Xx xtios. This is apparently because a high Mn content ~ .x 0favours the development of the manganese oxiQe ~ 10 xtodorokite (lO~ manganite), rather than o~lnO2 (7 X, Z XXmanganite), and todorokite concentrates Ni and Cu x(Cronan, 1977). In the Cook Islands region there x x .14

is a marked direct correlation of Ni+Cu+Co grade 0 .x .x xwith Mn/Fe ratio (Figs. 10 and 11). Ir, the South 0 ..)( x .x 0)(0Penrhyn. Basin., where the m.ost dat~. are availab~e, 00 0.5 10there J.S a dJ.rect correlatJ.on of .J.+Cu grade WJ.th .Grade (~ Ni Cu C )15 2.0Mn/Fe ratio (Fig. 12), but no correlation between .0 + + 0Co grade and ~1n/Fe ratio (Fig. 13). Thus it .can be 30 x

inferred that the direct correlation of Ni+Cu+Co ~ .grade with Mn/Fe ratio, apparent in all basins Hexcept the Samoa Basin, is caused by the behaviour ~of Ni+Cu. D ..

~ XXX" x CCOP/SOPACc 20 x. .ORSTOMD d 1 tl .' .9 ~. .'Vityaz' (Area C)eep sea manganese no u es vary grea y J.n sJ.ze, -

X0 ..shape and surface texture. Where, nodules have ~ xformed at the sea bed they frequently have a smooth; ...upper surface which formed in sea water, and a g .rough (often botryoidal) lower surface which formed 810 ..in the surface sediment by precipitation from pore ..water. The smooth part of such nodules is rich in ~ .Fe and Co, and the rough part in Mn, Ni and Cu:g ..

15(Raab,1972). z. .

Moritani ~ &. (1977, 1979 a, b), working on 00nodules from just north of the Cook Islands region, as 0 .10. 15 20separated them into two classes, dominantly smooth .x Grode (Yo NI + Cu)(formed largely above the sea bed) or dominantly 30 .rough (formed largely below the sea bed). The ~dominant manganese oxide is oMn~ in the "smooth" Nnodules, and todorokite in the "rough" ones. The ~rough nodules are relatively enriched in Ni and Cu {l .because of the affinity of these metals for x xtodorokite. Thus the presence of dominantly rough 20 'Xnodules in a region could be regarded as a positive .§ .x.feature for metal prospecting. 0 .;~

~ .x CCOP/SOPAC~, .ORSTOMMenard and Frazer (1978) and Moritani ~ &. ~ ..'Vityaz' (Area C)

(1979b) have pointed out that there is often an U 10 .inverse relationship between nodule concentration ~ ..and the combined grade of Ni+Cu in sea floor no- 3 ..dules. In the South Penrhyn Basin, where the most ~ ..

6data are available (Fig. 15), the highest Ni+Cu.. 1

grades coincide with the lowest concentrations; .-

where VITYAZ had sampled in some detail (Area C) 0 5there is a clear inverse correlation. Thus it 0 10 0 15 20

appears that there is only a limited supply of Ni Grade (Yo Co)and Cu and, when the nodules are very abundant, the. 0" ~ ..Ni+Cu grade falls off. There is clearly no FJ.g. 14. Plot of ,0 N.J.+Cu+~o agaJ.nst nodule concentra~J.~nrelationship between Co grade and concentration, (kg!m ) J.n Penrhyn .and. Southwest PacJ.fJ.Cwhether one considers regional or detailed sampling Ba~J.n~. I~ Penrhyn BasJ.n hJ.~hest nodule grades(Fig. 16). The coincidence of the highest Ni+Cu+Co coJ.ncJ.de wJ.th low concentratJ.ons.grades with very low nodule concentrations in the Fig. 15. Plot of ~~ Ni+Cu against nodule concentration inNorth a~d South Pen:hyn Basins (Fig. .14), can ~ence the South Penrhyn Basin, showing inversebe confJ.dently ascrJ.bed to the behavJ.our of NJ. and correlation.Cu only.

Fig. 16. Plot of ~~ Co against nodule concentration inthe South Penrhyn Basin, showing lack ofcorrelation.

60

The combination of high grades and high concen- At this stage it is not proven that biological

trations of nodules is rather rare, the best-known productivity is the most critical factor in pro-

example being the area between the Clarion and ducing high nodule grades. Rawson and Ryan's

Clipperton Fracture Zones in the eastern equatorial (1978) map compilation suggests that the division

Pacific. This area is located around looN, and into rich and poor grades is between the eastern

covers some 800km in width and more than 5000km in and western Pacific. High grades are concentrated

length (llOOW to 1600W). Its southern part on and east of the East Pacific Rise, and grades do

coincides with a tongue of radiolarian ooze which not vary greatly with sediment type. It may be

extends from 90ow to 160oW, whose sedimentation that not only Mn and Fe, but also Ni and Cu, are

rate is estimated to be 3mm/thousand years; its derived largely from the abundant fracture zones in

northern part coincides with red deep sea clay, the East Pacific. If this is the case, the

whose sedimentation rate is estimated to be Imm/ presence of active fracture zones would be an

thousand years (Cronan 1977). The metal grades are important guide to future nodule prospecting in the

much higher on the radiolarian ooze than on the red Cook Islands region.

clay (Table 2). The better samples from the

Penrhyn Basin have similar Mn/Fe ratios, and Ni, Cu

and Co grades, to the mean values from the eastern

equatorial Pacific red clays. Pautot and Melguen (1976, 1979) studied the

relationship of sediment type, and nodule concen-

tration and grade, to the properties of the waterPlanktonic organisms are commonly believed to column. Data from their work, that of Berger et

provid~ much of the Cu and Ni in deep se~ nodules. ~. (1976), and the present study are presented Tn

AccordJ.ng to Halbach ~ &. (1979) CU J.S concen- Table 3. The deep water in the region consists of

trated in the skeletons of certain organisms during two masses: Pacific Deep Water overlying Antarctic

life, and may be scavenged from sea water as the Bottom Water (also known as Pacific Bottom Water).

dead organisms sink, whereas Ni is largely The two masses are separated by the Benthic Front

concentrated in living tissue. Dissolution in the which generally lies at about 3500m. The Antarctic

deep ocean releases the metals into bottom water Bottom Water is about 10 colder and much more

~nd pore water, and they then can be concentrated oxygenated than the overlying water, and

J.n manganese nodules. consequently is much more "aggressive" in dis-

solving calcium carbonate. Above the Benthic Front

Under this hypothesis, one of the reasons for the lack of dissolution means that carbonate oozes

the. ~igh. nodule .grad~s in. the easter~ .equatorial predominate. Below the Benthic Front there is a

PacJ.fJ.c J.S the hJ.gh bJ.ologJ.cal productJ.vJ.ty at the decrease in carbonate content with increasing

sea surface. The zone of nodule enrichment is depth and pelagic clays predominate.actually displaced 500-1000km north of the high '

productivity zone, but this can be explained by The calcite lysocline is a well-defined facies

Plate Tec.tonics con7ept~. Th~se suggest that the boundary between well-preserved and poorly pre-

sea bed J.n t~e .regJ.on J.S movJ.ng.northwestward .at served foraminiferal assemblages. In southern

about 100km/mJ.IIJ.on years. AssumJ.ng that the hJ.gh tropical areas of the Central Pacific it lies at

productivity zone has not moved much (relative to about 4000m and shallows toward the equator (Ber-

the Equator) in the past 10 million years, the time ger et al. i976; Table 3).

during which the nodules probably formed, they would have been. beneath the high productivity zone The calcite compensation depth (CCD), regarded

for much of theJ.r growth. by Pautot and Melguen (1979) as being the level at

."... which all calcite has been dissolved, (a definition.AssumJ.ng that su:face bJ.ologJ.cal productJ.vJ.ty J.S which places the CCD deeper than did Berger ~ ~.)

J.ndeed of great J.mportance, Glasby (In press) generally lies at about 4800-5000m in this regJ.on.

suggests .t~at the gen~rally low grade of the South- Pautot and Melguen determined the CCD for the South

w7s~ PacJ.fJ.c nodules ~s relat~d to t~e low produc- Penrhyn, Tapu and Tiki Basins by studies of surface

~J.vJ.ty of the subt:opJ.cal antJ.cyclonJ.c gyre cover- sediments (Table 3). The CCD levels shown in Table

J.ng most of the regJ.on. 3, for the Southwest Pacific and North Penrhyn

..' Basins, have been estimated using Pautot andTh~ nodules J.n the Cook Islands regJ.on IJ.e ~n Melguen's (1979) value for the South Penrhyn Basin

pelagJ.~ clays (Pautot and Melgue~ ~979) whose sed~- and extrapolating to the north and south using the

mentatJ.on rates are probably sJ.mJ.lar to those J.n depth changes determined by Berger et al. (1976).

the eastern equatorial Pacific (lmm/1000 years). Primary production in the region is about 50-100

grammes of organic carbon/m 2 /year, compared to theeastern equatorial Pacific maximum of 100-200 Pautot and Melguen's (1979) study showed that

grammes (Dietrich and Ulrich, 1968), and is higher manganese nodules a:e gener~lly concentrate.d be-

than in most other areas of the Southwest Pacific. tween the hydrographJ.c lysoclJ.ne and the CCD J.n the

The phosphate concentration at a depth of 100m ~entral S?uth Pac~fi~. T~ey are most abundant in a

ranges from less than 0.25uatom P/litre south and nodule-rJ.ch facJ.es whJ.ch corresponds to the

west of Rarotonga to more than 0.75 in the North "R-facies" (residual facies) of Berger ~ &.

Penrhyn Basin (Reid 1962). This suggests that, if ~1976.). Th.is res~dual facies. i~ greatly enrichedprimary organic production is a critical factor J.n dJ.ssolutJ.on-resJ.stant foramJ.nJ.fera. Pautot and

nodule grades should be higher in the north fo: Melguen concluded that bottom water circulation and

similar concentrations of nodules; there is little carbonate dissolution appear to be the major

confirmatory evidence in the data accumulated so controlling factors in the distribution offar. manganese nodules in the region.

61

Table 3: Water depths in metres of significantzones in the central South Pacific

Feature S.W. Pacific S. Penrhyn N. Penrhyn Tapu TikiBasin Basin Basin Basin Basin

A A A A ACalcite lysocline 3900-4100 3700-4000 3500-3900 3500-3900 3700-4000

Calcite compensation B C B C Cdepth 4700-4900 4BOO-5000 5000-5200 4900 4500

Zone of high nodule D D D C Cconcentrations 4500-5100 4BOO-5300 5200-5600 4800-5000 4000-4350

Zone of high nodule D D D C Cgrades 4800-5100 5000-5400 5100-5600 4600-5000 4000-4400

A. Values from Berger ~~. (1976) for various latitudes in the Central Pacific.

B. Values modified from Berger ~~. (1976) by defining CCD as lower limit of calcite preserva-tion in sediment.

C. Values after Pautot and Melguen (1979)

D. Values from this study

In the Cook Islands region the zone of high CONCLUSIONSnodule concentration appears to correspond roughlyto the CCD (Table 3). However, in the SouthPenrhyn Basin, the only area where the CCD is ac-curately defined, half of the zone lies beneath theCCD. Thus it appears that the level of thepresent-day CCD. does not tightly de~ine the zone of 1. Manganese n~d~les occur o_ver an area. of abouthigh concentratJ.ons. The zone of hJ.gh metal grades 2,500,000km J.n the Cook lslands regJ.on.lies immediately beneath the present-day CCD (Table3) 2. Despite the patchiness of nodule grades (e.g.

.Fig. 4), and especially concentrations,Pautot and Melguen (1976) developed a model of enough work has b.een ~one to. show that. the

nodule genesis in the Tuamotu region which other Cock Islands regJ.on J.S unlJ.kely to YJ.eldevidence (Pautot and Melguen 1979;' the present nodule fields of present-day economic signi-study) suggests may well apply in the Cook Islands ficanc~. An ~ttempt is mad~ to ra~k t~eregion. By including their concepts, major points econoffiJ.7 po.tentJ.al of the varJ.ous basJ.ns J.nin the search for ore-grade nodules would include: t~.e regJ.on J.n Table 4.

..3. The most prospective area in the region isa) Distance from continents (to prevent dJ.lutJ.on the South Penrhyn Basin, where high nodule

of metal ions by terrigenous debris). concentrations are associated wit~1 moderate

grades of Ni+Cu+Co.b) Thin sedimentary cover (to ensure lack of

reworking and of turbidity currents). 4. The highest metal grades are found in the

North Penrhyn Basin, but these have beenc) Proximity to active fracture zones or volcan- associated, to date, with low nodule concen-

oes (sources of metal ions). trations. Hcwever, sampling density is very

10111.d) Presence of bottGm currents (oxygenated bot-

tom water allows precipitation of Ni and Cu). 5. Any future work should concentrate on the

Penrhyn Basin. The locations of possiblee) The bottom sediment to lie below 4000m (so fracture zones should be defined befurehand,

that Ni and Cu can be released from the slow- and sampling should concentrate north andly-dissolving organisms on which they are east of them, where Antarctic Bottom WatE:rfixed). would carry any metal ions leaking from frac-

..tures. Sampling should concentrate on areasf) The domJ.nance of nod.ules w.J.th rough. surface where the water depth lies between 5000m and

texture (these are rJ.cher J.n.todor~kJ.tE:. than 5600m; the present study has shown that highsmooth nodules, and hence rJ.cher J.n NJ. and concentrations may coincide with high gradesCu). in this depth range.

62

Table 4: Economic potential of the various basinsin the Cook Islands region

Maximum Maximum Most abundant Maximum EconomicBasin concentration grade valuable grade for potential

(kg/mZ) (Ni+Cu+Co%) metal concentration as presently(Ni, Cu or Co) greater than estimated

10kg/mZ

Samoan Passage N.N. 1.15 Co N.N cannot be(North Tokelau rated. pro-Basin) bably'low

potential

Samoa 15.6 1.15 Ni 0.68 very low

potential

.Southwest Pacific 32.6 1.47 Ni 1.13 low poten-

tial

South Penrhyn 62 2.02 Ni 1.34 moderate

potential

North Penrhyn 10.7 2.10 Ni 1.15 probably low

potential

ACKNOWLEDGMENTS REFERENCES

I would like to thank G. McMurtry of the Univer-sity of Hawaii, T. Moritani of the Geological Sur-vey of Japan, and W. Gayman and G. Gauss of CCOP/ "SOPAC for commenting on drafts of this paper. P. BACKER, H.; GLASBY, G.P.; MEYLAN, ~1.A. 1976:Woodward and C. Singh drew the figures. Manganese nodules from the Southwestern Pacific

Basin. NZOI oceanoqrachic rId Rep. 6.

BERGER, W.H.; ADELSECK, C.G.; MAYER. L.A. 1976:Distribution of carbonate in surface sedimentsof the Pacific Ocean. J. qeophys. Res. 8~(15):

ADDENDUM 2617-2627.

In 1980 The R.V. HAKUREI MARU carried out re- BISCHOrr~ J.L.; PIPER, D.Z. (Eds) 1979: Marinesearch cruise GH80-1 in the central Pacific whose geology and oceanography of ti,e Pacificmain aim was to study the occurrence of ma~ganese Manganese Nodule Province. Plenum, New York.nodules. The results of this work have not yetbeen published. CRONAN, D.S. 1977: Deep sea nodules: distribution

.and geochemistry. ~ Glasby, G.P. (ed.),The Coo.k .Islands Government recently made avaJ.l- "Marine Manganese Deposits". Elsevier

able. prel.J.mJ.nary results from this cruise for 19 Oceanoqraphy Series 15: 11-44.statJ.ons J.n the northern Cook Islands region (loca-tions in rig. 1). The nodule concentrations are inline with those published in this paper. Of 11 CRONAN, D.S. 1980: Underwater minerals. Academicstations on or near the Manihiki Plateau, 5 Press, London.revealed no nodules, and the other 6 had only verysmall quantities of nodules. Of 8 stations in theSouth Penrhyn Basin, 2 revealed traces only ofnodule~, and thezother 6 had nodule concentrations DIETRICH, G.; ULRICH, J. 1968: Atlas zur Oceano-averagJ.ng 12kg/m .graphie. Bibliographisches Institut, Mannheim.

63

EADE, J.V. 1977: Cook Islands offshore survey, 20 KU, T.L. 1977: Rates of accretion. ~ Glasby,

August-6 September 1977, CK-77(1). CCOP/SOPAC G.P. (ed.), Marine Manganese Deposits. Elsevie~

Pro.lect Report Jl (unpublished). Oceanoqraphy Series 15: 249-268.

LANDMESSER, C.W.; KROENKE, L.W.; GLASBY, G.P.;EADE, J.V. 1978: Cook Islands offshore survey, 26 SAWTELL, G.H.; KINGAN,S.; UTANGA, E.;

Nov~mbeI--9 December 1978,. CK-78(2). CCOP/SqPAC UTANGA, A.; COWAN, G. 1976: Manganese nodules

Pro.lect Report 18 (unpub11shed). from the South Penrhyn Basin, Southwest Pacific.

South Pacif. mar. Qeol. Notes 1(3): 17-39.

ECAfE, 1974: Report Gf the preparatory meeting for

establishment of CCOP!SOPAC and Proceedings of LEWIS, K.B. 1980: Northern Cook Islands Offshore

fir~t an~ .Se.cond Sessions. ECAfE Science Infur- Survey, 16-28 April 1980, CK-80(2). CCOP/SOPAC

mat10n D1v1s1on. Cruise Report 42 (unpublished).

MAMMERICKX, J.; CHASE, T.E.; SMITH, S.M.; TAY-

LOR, I.L. 1973: Bathymetry of the SouthGAUSS, G.A.; MORETON, D.L.E. 1980: Coo.k Islands Pacific. Scripps Institution of OceanoaraD~

offshore survey, 21 March-7 Apr11 1980, ChartsCK-80(1). CCOP/SOPAC Cruise Report 21 .

(unpublished).

MENARD, H.W.; fRAZER, J.Z. 1978: Manganese no-dules on the sea floor: inverse correlation be-

GLASBY, G.P. 1?78: Notes o~ the surface texture, tween grade and abundance. Science 199:

ir.ternal structure and m1neralogy of manganese 969-971.

nodules fl'om the South Penrhyn Basin. South

Pacif. mar. qeol. Notes 1(7): 71-80. -"

MEYLAN, M.A.; BACKER, H.; GLASBY, G.P. 1975:

.Manganese nodule investigation in theGLA~B:Y' G.P. (In press): .Manganese rlodule stu~1es Southwestern Pacific Basin, 1974. NZOI

1n the Southwest Pac1f1c, 1975-1980: a reV1ew. oceanoqraphic rId Rep. 4 SGuth Pacif. mar. Qeol. Notes 2(3). ..

d MEYLAN, M.A.; GLASBY, G.P.; McDOUGALL, J.C.;GLAS~Y, ~.P.; LP,WRENCE, .P;.1974: Mangan:se epo- SINGLETON, R.J. 1978: Manganese nodules and as-

S1tS 1n the South Pac111c Ocean. NZOi ~h2£1~~ sociated sediments from the Samoan Basin and

Miscellaneous Seri~s: 33-38. Passage. NZOI oceanoQraphic rId. Rep. 11.

MONGET, J.M.; ~IURRAY, J.W.; MASCLE, J. 1976: A

HALBACH, P.; REHM, E.; MARCHIG, V. 1979: Distri- world-wide compilation of published, multicompo-

bution of Si, Mn, Fe, Ni, Cu, Co, In, Pb, Mg and nent analyses of ferromanganese concretions.

Ca in grain-size fractions of sediment samples ~SF-I~O~- ManQanese Nodule Proiect Technical

fI-om a manganese nodule field in the central Report 12.

Pacific Ocean~ Mar. Geol. 29: 237-252.

.MONlIER, M.; MISSEGUE, F. 1977: PolymetallicHEEZEN, B.C.; GLASS, B.; MENARD, H.W. 1965: The nodules sampling in the Cook Islands

Manihiki Plateau. DeeE Sea Res. 13: 445-458. Archipelago. QRSTOM-CNEXO Report NR/CCOP!SOPAC

(6)!CR.20 (unpublished).

HOLLISTER, C.D.; JOHNSON, D.A.; LONSDALE, P.F.

1974: Current controlled abyssal sedimentation,

Samoan Passage, Equatorial West Pacific. ~

Geol.82: 275-300. MORlTANI, T.; MARUYAMA,S.; NOHARA, M.; MATSU-

MOTO, K.; OGITSU, T.; MORIWAKI, H. 1977: Des-

HORN, D.R.; DELACH, M.N.; HORN, B.M. 1973: Metal cription, classification and distribution .of

content of ferromanganese deposits of the fflanganese nodules. Geol. Surv. Japan Cru1seT h . 1 R t I t t . 1 D d Reo. 9: 136-158.ocearls. I eCnn1Ca.L ~eport: .Lnt:ernat:10na.L uecaQe ---~. -

Ocean Exploration 3.

MORITANI, T.; MARUYAMA,S.; NOHARA,M.; KINOSHI-

HORN, D.R.; HORN, 8.M.; DELACH, M.N. 1972: Fer- TA, ~.;. KOIZUMI, T..; .I~O, T. 1979a:

romanganese deposits of the North Pacific. Descr1pt10n, types and d1str1but1on. of manganese

Technical Report International Decade Ocean nodules. Geol. Surv. Japan Cru1se ReD. l~:

Explorati~ 1. 163-205.

HORN, D.R.; HORN, B.M.; DELACH, M.N. 1973: Ocean MORITANI, T.; MOCHIZUKI, T.; TERASHIMA, 5.: MARU-

manganese nodules metal values and mining sites. YAMA, S. 1979b: Metal contents of manganese no-

!ec!:!nic21 Report International Decade Qcean dules from the GH77-1 area. Geol. Surv. Japan

Exploration 4. Cruise Rep. 12: 206-217.

64

PAUTOT, G.; MELGUEN, M. 1976: Deep bottom cur- REID, J.L. 1962: On circulation, phosphate-phos-rents, sedimentary hiatuses and polymetallic no- phorus content, and zooplankton volumes in thedules. CCOP(SOPAC Jech.BuJJ.2: 54-61. upper part of the Pacific Ocean. Limnoloqy

Oceanography 7: 287-306.

PAUTOT, G.; MELGUEN, M. 1979: Influence of deepwater circulation and sea floor morphology onthe abundance and grade of cent~al ~outh Pacific SCHLANGER, S.O.; JACKSON, E.D. et ale 1974: Legmanganese nodules. Pp621-649 J.n BJ.schoff, J.L. 33 D S D ' ll ' P .- t- t t . a.

( ) " -:- , eep ea rJ. J.ng roJec -es J.ngand PJ.per, D.I. eds, MarJ.ne Geology and h t t th G t . M h 1974. 16 200 h f th P .

f ' M N d I 0 -spo eory eo J.mes arc. -.

ceanograp y 0 e acJ. J.C anaganese 0 u e

Province". Plenum Press, N.Y. 842 pp.

PIPER, D.I.; FOWLER, B. 1980: New constraint onthe maintenance of Mn nodules at the sediment SEIBOLD, E. 1978: Deep sea manganese nodules -thesurface. Nature 286: 880-883. challenge since "CHALLENGER". Episodes 1978

ill: 3-8.

RAAB, W. 1972: Physical and chemical features ofPacific deep sea manganese nodules and theirimplications to the genesis of nodules. SKORNYAKOVA, N.S. and ~NDRU~CHENKO, ~.~. 1974:Technical ReDort International Decade Ocean Iron-manganese concretJ.ons J.n the PacJ.fJ.c Ocean.Exploration 1: 31-49. Int. Geol. Rev. 16: 863-919.

RAWSON, M.D.; RYAN, W.B.F. 1978: Ocean floorsediment and polymetallic nodules. United WINTERER, E.L.; LONSDALE, P.F.; MATTHEWS, J.L.;States of the Geoqrapher Map. ROSENDAHL, B.R. 1974: Structure and acoustic

stratigraphy of the Manihiki Plateau. Qeep SeaRECY, J.; MISSEGUE, F.; MONIIER, M. 1977: Chemi- Re~. 21: 793-814.

cal analysis results about metal contents ofpolymetallic nodule samples in the Cook IslandsArchipelago. ORSTOM-CNEXO Re ort NR CCOP WOOD, B.L.; HAY, R.F. 1970: Geology of the CookSOPAC(7)CR.28 (unpublished. Islands. N.I. qeol. Surv. Bull. n.s. 82.

Publications in this series of Notes are intended toinclude results of local studies, brief reportsdealing with field observations, and short summaries

and data relevant to the aims of CCOP/SOPAC.

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