Chemical Variation & Element Correlation in Manganese Nodules from a Dredge Haul in the Central Pacific

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Indian Journal of Marine Sciences Vol. 9, December 1980,pp.2J5-239

Chemical Variation & Element Correlation in Manganese Nodules from a Dredge Haul in the Central Pacific

as

Department of Geology, University of Delhi, Delhi 110007 and

G H FRIEDRICH

Institut fUr Mineralogie und Lagerstiittenlehre, R.W. Technische Hochschule, Aachen, W. Germany Received 2S'February 1980; revised received 9 July 1980

Local variations in composition of Fe-Mn nodules from the nodule belt of the central Pacific Ocean indicate that these variations are similar to those seen on the regional scale. Mn varies from8.4"23.4~oanGFe S.8-14%. Heavy metal content also shows a corresponding trend. C.orrelation between major and minor elements shows that to a large extent the minor elements follow the major elements, viz. eu and Ni follow Mn, and Co, Pb and Ti follow Fe. Interelement relationship shows that Zn and Mo tend to follow Ni, and Cu-Ni show a mutual relationships. Nodules show Mn/Fe ratio 1.4 to 3 and a relatively higher concentration of heavy metals. They are predomin~ntly todorokite rich and also show high barium content. On the Bonatti diagram, they occupy the central field of hydrogenous type.

Variations in the composition of manganese nodules from the Pacific - Ocean were shown1 -3. These variations on regional scale were also found in very small areas4-7. Therefore, in the present study, the extent of local chemical variation of nodules from a small area of the central Pacific lying between Clarion and Clipperton Fracture Zones in the siliceous ooze zone was investigated. A preliminary· geochemical study of the nodules from this area was reported earlier8. Chemical composit,ion and elemental correlation of nodules obtained from one dredge haul (c 2 km length) atlocation 26 (dredge No. 109; 11⁰ l' N lat. 147038' 4" W,long, at a depth of 5360 m to 11⁰7" N lat. 147038' 6" W at a depth of 5308 m) from this area are presented in this communication.

Materials and Methods

Details of dredge,. depth of sampling and methods .went reported earlier8.Of the 26 nodule samples collected during VA-04 cruise of R V Valdivia during 1972, 19 were nodules of different forms, 4 ferromanganese crusts and 3 cylindral nodules. These were not included in the earlier report8•

Nodules were air dried and pulverised.In case of cylindrical-types and, crust material, the clayey- calcareous filling and core materials were removed.

The powder was dried at 110°Cfor 24 hr. Samples were digested in an autoclave 'BOMB' with a mixture of HF-HCI-HN03 according to the method of Langmyhr and Paus9• Determinations were carried out on a PE atomic absorption spectrophotometer.

Titrisol standards were used for each element and

ferromanganese nodule standards of Metallgeselschaft A.G., were used as control standards.

Results and Discussion

Morphology of nodules-Nodules are spheroidal to ellipsoidal (Fig. I A and B) in which the individual constituents tend to be spherical, ellipsoidal or even angular (Fig. I A). Cylindrical nodules (Fig. I

q

comprise ferromanganese tubes filled with clayey- calcareous material. Ferromanganese crust (Fig. 1 D) is irregular mass of Fe-Mn oxides of varying colours, loose to compact with clayey calcareous patches in them. Details of core material in the nodules have been discussed earlierlO• "

Chemical composition and elemental correlation- Composition of nodules and ferromanganese material (Table I) shows the chemical variation in the nodules within this small dredge haul. Mn varies frqm 8.4·

23.4%, Fe 5.8-14%, and correspondingly Ni fromO.62- 1.34%, Co 0.14-035% and Cu 0.22-0.52%. Average composition of these nodules (Table 2) compares well with the average of a mixture of 10 different nodules analysed from the station on board by EDX sy~tem.

The causes for minor difference observed in the values have been discussed by KunZendorf et a/.11,

Correlation between the major and minor elements shows that to a large extent the minor elements follow the major elemynts. Cu and Ni follow Mn (Fig. 2a and b), and Ni-Mn relationship is, however, slightly dispersed. Co and Pb are anticorrelated to Mn and foIlow- Fe (Fig. 2 c and d). Similarly Ti and V also follow Fe. Although the other elements show less

c

Fig: I-Morphology of the nodules [A, round to ellipsoidal to angular; B, polynodule in which 2 large and small nodules are seen;

C, cylindrical; and D, C.S. of ferromanganese crust]

distinct variation in the nodules, definite trends still exist. For example within minor elements, Zn and Mo tend to followNi (Fig. 2 e and f) and Cd follows zinc.

However Zn also follows Ca (Table 3). Cr does not show any trend. Cu and Ni show an excellent liner.

relationship.

For demonstrating relationships, a measure of correlation for every combination of elements, taking 2 at a time has been computed. The standard method of correlation analyses (Pearson's correlation coefficient) has been used and the resulting correlation matrix is given in Table 3. Before using the standard measure of correlation, it is desirable to transfer the scale of each variable to give a scaler plot. This has been done as tests of significance and further statistical analyses of the measure of association have not been carried out.

Study of the correlation matrix reveals the following relationships between elements: Mn-Cu and Mn-Ni 236

show a strong positive correlation (Fig.2 a and b). A moderate to strong positive correlation exists between Co and Fe and between Pb and Fe (Fig. 2c and d).

Among the minor elements Ni-Cu have strong positive correlation. An equally strong positive correlation is seen between Ni and Zn, and Ni and Mo (Fig. 2 e and f) show a poor linearity.

Cu against Mn/Fe shows a linear relationship (Fig.

2h). Friedrich et al.8 have suggested that such relationships are valid up to a value of 3 and thereafter the nodules are not likely to take other additional Ni and Cu into them with increasing Mn content. Cu vs Mn/Fe plot (Fig. 2 h) indicates a relationship of 2: 1.

However, Ni-Mn relationship (Fig. ²g) needs further investigation.

Causes of precipitation of elements- Triangular plot for(Cu+Co+ Ni) x 10: Fe: Mn(Fig. 3) shows the field of plots generally in the middle. This central field according to Bonatti et af.12 in the field of hydrogenous deposits is produced by slow pre- cipitation of the elements from the sea water under oxidising environments. Hydrogenous ferrom- anganese deposits are also characterized by a MnjFe ratio 0.5 to 5 and a relatively higher concentration of minor metals. In the present area, Mn/Fe ratio varies between 1.4 and 3 (avo2) which is well under the hydrogenous deposits of Bonatti et al.12 and is tentatively accepted. However, it is important to mention that diagenic processes playa significant role in the concentration of metals released either through the volcanic or through usual alteration processes.

Concentration of minor metals in the manganese nodules depends on the chemical factors as also the mineralogy of the nodules. X-ray diffraction pattern for the nodules indicates predominance of todorokite in them. Although Mn02 has been recognised in them, a major part of the nodules consists of amorphous substance like wad, and occasionally psilomelane where barium could be associated with it. Together with Ba, Mn and K may substitute for MnH. It is known that todorokite has relatively loose structure than Mn02' Therefore, todorokite can host the trace metals better than Mn02' The sum of(Ni+Co+Cu) in todorokite nodules is 1.71 (Table 2,columns G and H) whereas the sum of elements in Mn02 rich nodules is 1.3. Composition of nodules in column' A corresponds to that of column E, which according to Bonatti et al.12 is of hydrogeneous origin. One can conclude from this that the nodules of hydrogeneous origin are rich in todorokite and that such nodules have a higher manganese content. Since Co follows Fe, it will be seen that maximum Co occurs in nodules rich in Fe.

Roonwal and Friedrich ^{1 0} have described the occurrence of micron-size basaltic grains in the core

ROONWAL & FRIEDRICH: CHEMICAL VARIATION &ELEMENT CORRELATION IN MANGANESE NODULES

Table I-Chemical Composition of Manganese Nodules from the Central Pacific

Nodules

2' 345

678109

II

/' Mn ~)/~

8A 15.915.314.713.517.720A211223A2111.423.4 Fe%

5.8 11.412.16.56.8 . 12.811.78.5147.212.46.8lOA Co /j,

0.14 0.320.290.230.31 0.320.310.280.240.20.260.240.28 Ni/j,

0.62 0.9 0.941.261.02 0.861.181.060.840.720.9411.28

eu%

0.22 0.4 0.370.430.5 0.360.50.440.260.390.330.430.52 Zn ppm

440 700 550940800 620 7408601000700600780520 Pb ppm

290 540 370380540 600 480450410460500580560 Sr ppm

28 1241604836832 2728416036436818476 V ppm

170 340 200340340400 270370240240500500500 Cd ppm

18 18 1416 2014 16132216201422 Cr ppm

13 277773

23 9463 7 Mo ppm

170 350 300440530 440430440260280570510750 Ba %

0.3 0.56 0.420.420.56 0.480.530.480.580.700.440.60.6 Ti%

0.5 0.8 0.840.581.20.96

0.860.660.920.661.16 1.02 Mg /.,

0.45 1.04 0.890.540.571.410.8Oi850.850.961.21.140.83 Ca%

0.72 1.28 0.981.15 . 0.841.281.10.980.881.141.141.21.16 Na%

5.96 5.68 6.085.385.34 .5.6 5.125.45.765.585.585.585.28 K%

2.98 1.24

2.21.321.40.880.761.942.040.920.96 2.88 AI%

3.4 5.8 6.34.24.2 4.75.63.96.34.93.43.33.2 Si%

13.5 9.1 14.66.28.989.711.66 6.211.877.1 Fe/Mn

0.72 0.69 0.480.330.57 0.840.580.570.560.60.50.590.44 Mn/Fe

1.45 1.39 2.073.051.731.191.741.762.001.731.672.251.69

Nodules 15

161718 19 20*21*23+22*24+25+26+

Mn%

14.7 22.5023.419.821.614.710.722.518.69.6014.415.38.4 Fe~o

96.412.110.87.8 12.511.84.36.807.15.35.78.5 Co%

0.31 0.27 0.230.250.28 0.350.240.170.290.270.130.180.24 Ni%

1.34 0.98 1.261.281.181.26 0.920.780.60.720.761.020.98 Cu%

0.37 0.5 0.470.50.40.480.320.280.50.360.310.320.34 Zn ppm

620 880 9008605601040420860520600640500660 Pb ppm

200 500 380540560 620 400300580480480340340 Sr ppill

80 24819628888372104248160408016068 V ppm

170 370 200710370430 240210400340240200200 Cd ppm

16 201516181616142213161614 Cr ppm

13 7 2037 8

20 9979 10 Mo ppm

170 570600660590 570360400240390300260590 Ba %

0.3 0.460.70.510.58 0.510.420.310.480.530.420.420.37 Ti%

0.36 0.78 0.801.260.9 1.06 0.780.46'0.841.20.880.880.68 Mg%

1.20 0.911.241.291.231.19 0.910.720.510.890.561.140.91 Ca %

0.74 1.58 1.041.301.26 1.55 0.950.780.980.880.140.980.9 Na%

5.58 5.24 5.55.765.16 5.56.125.725.85.165.586.085.28 K%

1.8 0.960.762.241.920.763.340.881.22.121.782.21.84 AI%

6.6 3.8 4.93.33.64.4 6.47 5.64.63.95.26.3 Si %

14.2 9 6.87.36.65.9 Il.l 7.81011.210.314.67.6 Fe/Mn

0.53 0.320.40.560.48 0.530.480.450.630.550.630.530.47 Mn/Fe

1.88 2.51.873.091.782.08 2.072.231.571.801.581.882.12

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237

Table 2-A verage Composition of Manganese Nodules from the Central Pacific Compared with Data from Other Locations

B·A·

C·FED GH EDX Mn ~~o

18.03 12.90 13.25 19.1418.6 15.7119.53 15.321.1 Fe~o

9.73 6.067.8 8.4 17.39.069.06 13.78

II

Ni'lo

0.890.770.910.321.05 0.950.98 0.390.7·

Co%

0.210.27 0.21 0.210.44 0.210.17 0.790.29 Cu'lo

0.42 0.35 0.32 0.550.11 0.710.56 0.100.43 Pb ppm

470 346

470330490 1200 115

In ppm

757 546 565 780600 Mo ppm

452

286420 540

410380460 V ppm

350 213

295 360

420 550 Cr ppm

10

128 12

107 Ba0/0

0.51 0.31

0.46 0.49

0.15.0.19 0.221 Ti ~o

0.640.85

0.95 1.01

0.560.9430.4

·Present work

A: Av. of 19 analyses (Table I) from dredge line 169. B: Av. of 3 cylindrical nodule material (Table I). C: Av. of 4 ferromanganese crust material (Table I). D: Av. of a mixture of 10 nodules from dredge line 109. st 26. VA 05, the Central Pacific. E: Nodules from equatorial Pacific I,location S 45': W 141' 36'

f'

composition of nodules rich in mineral birhasite1. EDX: Preliminary data of nodule mixture as analysed on board R. V. Valdivia by EDX- ry~m ..

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Fig. 2- Relation between Cuand Mn(a), Ni and Mn(b), Coand Fe (c), Pband Fe (d), Zn and Ni(e), Moand Ni(O, Niand MnjFe(g)andCu and Mn/Fe (h)

238

ROONWAL & FRIEDRICH: CHEMICAL VARIATION &ELEMENT CORRELATION IN MANGANESE NODULES

Table 3-Correlation of Elements in the Manganese Nodules from the Central Pacific

Mg Ca Na K AI Si

Cr Mo Ba Ti

Cd Sr V

Pb

Mn Fe Co.· Ni Cu Zn

Mn I

Fe 0.74 I

Co 0.67 0.73 I Ni 0.87 0.44 0.6 I Cu 0.89 0.61 0.66 0.89 I Zn 0.9 0.56 0.51 0.9 0.87 I Pb 0.64 0.82 0.56 0.42 0.59 0.54 I Sr 0.38 0.41 0.14 0.22 0.43 0.29 0.43 I V 0.77 0.78 0.56 0.57 0.64 0.64 0.82 0.36

Cd 0.55 0.28 0.05 0.5 0.45 0.65 0.33 0.01 0.46 I Cr 0.21 0.03 0.08 -0.16 -0.01 -0.21 -0.06 0.02 -0.3 -0.23 I Mo 0.86 0.6 0.43 0.78 0.85 0.87 0.75 0.4 0.71 0.57 -0.23 I Ba 0.62 0.52 0.43 0.52 0.57 O.ill 0.66 0.47 0.48 0.41 -0.09 0.73 1 Ti 0.54 0.74 0.41 0.3 0.49 0.42 0.86 0.56 0.63 0.08 -0.07 068 0.60 I Mg 0.41 0.31 0.3 0.39 0.57 0.38 0.26 0.79 0.28 0.06 0.24 0.37 0.42 0.29 I Ca 0.65 0.55 0.53 0.6 0.7 0.58 0.71 0.53 0.67 0.31 0.07 0.67 0.51 0.55 0.58 Na -0.55 -0.4 -0.39 -0.58 -0.47 -0.61 -0.42 0.01 -0.45 -0.44 0.33 -0.53 -0.36 -0.18 -0.05 -0.27 I K -0.71 -0.68 -0.74 -0.66 -0.72 -0.69 -0.62 -0.27 -0.'56 -0.12 -0.09 -0.66 -0.46 -0.51 -0.41 -0.680.51 I AI -0.63 -0.55 -0.2 -0.48 -0.45 -0.63 -0.6 -0.16 -0.68 -0.66 0.35 -0.68 -0.41 -0.48 -0.04 -0.390.57 0.38 1 Si -0.72 -0.64 -0.41 -0.59 -0.71 -0.64 -0.76 -0.36 -0.7 -0.51 0.1 -0.79 -0.54 -0.55 -0.27 -0.620.620.520.57

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(Cu+Co+NtI xlO

material of nodules from this dredge. Therefore, it is possible that Co has come through the local supply of it along with Fe by the alteration of volcanic material.

The role of iron minerals in controlling the growth of MnOz about the core material has been indicated 13.14.

Ba along with Mn and K generally substitute for Mnz+

in nodules. Ba is also responsible for Sr-diadochy.

Some Sr may however be present with Ca. As the core material of these nodules comprises clayey-calcareous matrix with abundant fossils and basalt grains, some Ca in the nodules will be of biogenic and some of lithogenic origin. In the clay part it will be the enrichment of AI,K,Na, Ca and Sr during the diagenic processes and remobilization of these elements will continue as nodule growth continues.

Acknowledgement

One of the authors (GHF) thanks the German Federal Ministry of Science and Technology for support to take part in R V Valdivia cruise VA-04 . GSR thanks the German Academic Exchange Service (DAAD) for support to work at Aachen.

References

I Mero J L,Mineral resources of the sea(Elsevier, Amsterdam) 1965, 312 pp.

2 Cronan D S, in Ferromanganese deposits on the ocean floor, edited by D R Horn (IDOE/NSF, USA) 1972, 19.

3 Cronan D S, inMarine manganese deposits, edited by G P Glasby (Elsevier, Amsterdam) 1977, II.

4 Calvert S E&Price N B,Mar Chem, 5 (1977) 43.

5 Calvert S E, Price N B, Heath G R&Moore (1r) T C,Jmar Res, 36 (1978) 161.

6 Dugolilfsky B K, Chemistry and morphology of dee-sea manganese nodules and the significance of associated encrusting protozoans on nodule growth, Ph.D. thesis, University of Hawaii, 1976.

7 CraigJ D,Mar Geol, 29 (1979) 165.

8 Friedrich G H, Kunzendorf H&Pliiger W L, in The origin and the distribution of manganese nodules in the Pacific and prospects of exploration, edited by M Morgenstein (Hawaii

Inst. Geophysics, Univ. of Hawaii) 1974, 31.

9 Langmyhr F 1&Paus P E,Analytica chim Acta, 43 (1968) 397.

10 Roonwal G S& Friedrich G H,BMFT marine research report, M-7502, 1975, 151.

I I Kunzerdorf H, Friedrich G&-Pliiger W L,Erzmetall, 27 (1974) 85.

12 Bonatti E, Kramer T&Rydell H, inFerromanganese deposits on the ocean floor, edited by D R Horn (IDOEjNSF, USA) 1972, 149.

13 Burns R G & Brown B A, in Ferromanganese deposits on the ocean/loor, edited by D R Horn (IDOEjNSF, USA) 1973, 51.

14 Burns R G&Burns V M, inMarine manganese deposirs, edited by G P Glasby (Elsevier. Amsterdam) 1977.85.

Mn Diagenetic

oNQdvJel

+CylindriCOl _du_

• Crutt materiOI

Fig. 3- Triangle Plot of (Cu+Co+Ni) x 10: Fe: Mn

Fe