Geochemical Journal, Vol. 17, pp. 41 to 49, 1983 Terrestrial ferro-manganese nodules formed in limestone areas of the Ryukyu Islands Differential thermal analysis, infrared absorption and thermal transformation of mineral phases KIY0sHI KANESHIMA and HATSUO TAIRA Department of Chemistry, College of Sciences, University of the Ryukyus, Nishihara-cho Okinawa 903-01, Japan (Received January 16, 1982: Accepted October 8, 1982) Physical studies such as differential thermal analysis, thermal gravity analysis, infrared absorption and thermal transformation of mineral phase have been carried out for terrestrial ferromanganese nodules formed in limestone areas of the Ryukyu Islands. The differential thermal analysis data indicate that they are grouped into four different types regardless of indistinct patterns of X-ray diffractometry. The first group shows endothermic peaks at near 120, 320 and 560°C. The second goup is close to the first group except showing a quite enhanced endothermic peak at 320°C. The third type of nodules shows one more additional endothermic peak at near 800°C. The final fourth group shows only two endothermic peaks at near 120 and 560°C. The X-ray diffraction patterns for heated samples at various temperatures indicate that magnetite is formed at temperatures over 700°C. Braunite also seems to be formed at the same tem perature range but it disappears at 1,000°C. The mineral composition of the manganese nodules has been also discussed by the study of infrared absorption patterns with particular reference to quartz, goethite, amorphous state of ferrihydrite and artifitially formed silica gel. INTRODUCTION (16± 2) X 104 y for a nodule to attain a maximum size of 2cm in diamter (TAIRA et al., 1979). The occurrence and the distribution of ter There are quite a few reports on differential restrial ferro-manganese nodules which are thermal analysis (DTA) and infrared (IR) ab formed in reddish soils on the Ryukyu Islands sorption studies for oceanic manganese nodules, are largely concerned with Riukiu Limestone and which show either a discrete endothermic peak its weathering processes. The nodules well con in the 120-240° C temperature range or some centrate minor elements such as Ni, Cu, Pb and weak endothermic peaks at temperatures higher Co as oceanic nodules, but Pb and Cd are more than 3000C (SHIMA and OKADA, 1968; OKADA concentrated in terrestrial ferro-manganese nod and SHIMA, 1969; OKADA et al., 1972). There ules than in oceanic nodules (KANESHIMAand are, however, few studies on terrestrial ferro IREI, 1968; OOSHIROand NOHARA 1976; NOHA manganese nodules. RA and OOSHIRO,1978; TAIRA et al., 1981). This paper deals with differential thermal The study on the mineral composition of the analysis and infrared absorption for terrestrial nodules shows only a peak for quartz and the ferro-manganese nodules together with thermal most part of the nodules remains as amorphous transformation of the mineral phase. state for manganese and iron minerals (KANE SHIMAand IREI, 1968). Recent detailed study EXPERIMENTAL clarifies the existence of very weak signals from todorokite and birnessit (NOHARAand OosHIRO, Samples 1978). The growth rate of the nodules is found Fifteen samples were collected from Okina to be about 61±9mm/106y and it takes about wa, Kume, Ie and Miyako Islands. The samples 41 42 K. KANESHIMA and H. TAIRA and locations are: Oyakebaru Sashiki-son (S-1), average physical states of nodules, ten to fifteen Sobe Yomitan-son (Y-1,3), Ganeko Ginowan individual nodules collected from the same area shi (Gi-4), Sakiyama Nakijin-son (N-6B) and were compositely ground rather than taking a Bise Motobu-cho (BI-1) on Okinawa Island. The single nodule. The DTA measurements were others were collected from Ie Island (1-1,4), carried out by the use of a Rigaku Denki Ther Kume Island (K-1) and Miyako Island (M-3,5, moflex TG-DSC. The sample of 0.25-0.35g 8,9). The sampling locations are shown in Fig. was taken for the analysis with the use of stan 1. dard aluminum oxide. The DTA data were The maximum size of the nodules used was obtained with 500µV, 10°C/min in air free 1.5 cm in diameter and most of the others varied circumstance. The results are shown in Fig. 2. from 0.5 to 1.0 cm in diameter. Color is dark For some limited samples, thermal gravity brown. The major and minor chemical com changes were measured and the results are ponents of the samples used in this work have shown in Fig. 3. The DTA data on goethite already been reported in the previous paper and quartz samples from North Korea are shown (TAIRA et al., 1981). in Fig. 4 for reference. Measurements Thermal transformation of mineral phases DTA measurement For the study of the Thermal transformation of mineral phase 125°20' E 24°50' 128°00'E I P, N-6B M-8~~ rl--n29PT M-9 i e I-1, M-3,5 BI-1-' v Miyako Is. 126°50'E K-1 Okinawa Is. ® :Riukiu Limestone 26°20 N 25030'N Kyushu Kume is. °o S 0°O0'N Y-1 GI-4 P Ryukyu Is, 6 S-1 Kume I s 4 0 '. 6PO Tai wan Okinawa Is. 0 10 20km Miyako is. --f 25°30'N 0 5km 125000'E 130°00'E Fig. 1. Sampling locations for terrestrial ferro-manganese nodules. 0 Terrestrial ferro-manganese nodules 43 of the nodules at various temperatures was also measured by the use of X-ray powder method. The air dried powder samples were heated at 0 110, 600, 700, 800, 900 and 1,000'C for 6 hours. The X-ray diffraction patterns were 5 taken for the above samples by a Rigaku Denki a Geigerflex 2011 B with Ni filter, Cu Ka-ray, X10 30KV, l0mA, 2°/min scan speed and 20mm/ 15 o min chart speed. The results are shown in 20 S-1 Fig. 5. 100 300 500 700 900 Temp (°C) Infrared absorption For the study of identification of the existence of hydroxides of Fig. 3. Thermogravimetry patterns for some terrestrial manganese and iron in the nodules, the infrared ferro-manganese nodules. absorption spectra with KBr crystal were ob tained on a Hitachi EP1-52 type spectrometer. are four types of endothermic peak patterns in The results are shown in Fig. 6. DTA curves for terrestrial manganese nodules, depending upon the sampling locations. Endo thermic peaks at 123-135°C and at 552-573°C RESULTS AND DISCUSSION temperature ranges are common thoughout all DTA patterns As seen from Fig. 2, there samples, whereas the modes and appearances of the endothermic peaks at 270-325°C and 765 815°C temperature ranges are characteristic for each sample. This introduces a method to S-1 classify nodules into 4 types. 130 317 558 Y-1 The first group in Fig. 2 (Type I) includes 125 320 555 K-1 Type I 315 the nodules collected from both Okinawa Island 123 558 Gi-4 (S-l, Y-1, Gi-4 and N-6B) and Kume Island (K 315 555 x.125 N-6B 1). The DTA pattern of this type shows 3 130 325 565 endothermic peaks at temperatures 123-130, Y 565 M-3 315-325 and 555-565°C. The second type 13 ~ 0 ,3 M-5 (Type II), which is found in Miyako Island, Type II C. 560 _125 M-8 ~3 323 560 M-9 130 560 325 I-1C Goethite 123 315 552 765 BI-1A Type III 125 270 573 815 BI-1E 808 1 5 329 570 BI-1B 808 Quartz 1"25 ' 325, 570 --f- I-4 Type IV 558 550 100 200 300 400 500 600 700 800 ~ 5 15 0C 100 200 300 400 500 600 700 800 900 Temperature C) Fig. 2. Differential thermal analysis patterns for ter Fig. 4. Differential thermal analysis patterns for goe restrial ferro-manganese nodules. thite and quartz. 0 44 K. KANESHIMA and H. TAIRA also has 3 endothermic peaks as in Type I but show an endothermic peak near 360°C as seen gives endothermic peaks at 323-325°C tem in Fig. 4. d) OKADA(1959) reported the occur perature range stronger than that in Type I. The rence of an endothermic peak at 350°C in a third type which was collected from Bise, Moto goethite which was collected from Hayaseno bu Peninsula, Okinawa Island, exhibits one more mineral deposits. The occurrence of the peak extra peak at 765-815°C temperature range may most probably be due to hydrous iron besides the 3 peaks in Types I and II. This type oxides in reddish soils which have been in of nodule has CaCO3 content higher than any corporated in manganese nodules in accretion other types of nodules (TAIRA et al., 1981). processes. The final fourth type nodule exhibits only two The third endothermic peak at the 552 endothermic peaks at 123-135°C and 550 573°C temperature range may be originated 558°C temperature ranges. This type of nodules from the phase transition from a-quartz to are formed only in le Island. a-quartz, since quartz transition takes place at Besides the DTA study, thermal gravity about 570°C as seen in Fig. 4. The other types changes (TG) were also measured for some of transitions from Mn02 to Mn2O3 or from limited samples. The results are shown in Fig. 3. Figure 3 indicates that the rate of weight loss M M between room temperature and 120'C is fairly Q M M M B M rapid and it becomes slow and monotonic up 1000°C BH HQ B MB to 1,000°C.