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Article

The Geochemical Features and Genesis of Ferromanganese Deposits from Caiwei Guyot, Northwestern Pacific Ocean

by
Linzhang Wang
1,2 and
Zhigang Zeng
1,2,3,*
1
Seafloor Hydrothermal Activity Laboratory, CAS Key Laboratory of Marine Geology and Environment, Institute of Oceanology, Chinese Academy of Sciences, Qingdao 266071, China
2
University of Chinese Academy of Sciences, Beijing 100049, China
3
Laboratory for Marine Mineral Resources, Qingdao National Laboratory for Marine Science and Technology, Qingdao 266071, China
*
Author to whom correspondence should be addressed.
J. Mar. Sci. Eng. 2022, 10(9), 1275; https://doi.org/10.3390/jmse10091275
Submission received: 22 July 2022 / Revised: 20 August 2022 / Accepted: 5 September 2022 / Published: 9 September 2022
(This article belongs to the Special Issue Research on Submarine Hydrothermal Activity and Its Material Circulation, Magmatic Setting, and Seawater, Sedimentary, Biologic Effects)
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Abstract

:
The ferromanganese deposit is a type of marine mineral resource rich in Mn, Fe, Co, Ni, and Cu. Its growth process is generally multi-stage, and the guyot environment and seawater geochemical characteristics have a great impact on the growth process. Here, we use a scanning electron microscope, X-ray diffraction (XRD), inductively coupled plasma optical emission spectrometer (ICP-OES), X-ray fluorescence (XRF), and inductively coupled plasma mass spectrometry (ICP-MS) to test and analyze the texture morphology, microstructure, mineralogical features, geochemical features of ferromanganese crusts deposits at different distribution locations on Caiwei Guyot. The ferromanganese deposits of Caiwei Guyot are ferromanganese nodules on the slope and board ferromanganese crusts on the mountaintop edge, which are both of hydrgenetic origin. Hydrgenetic origin reflects that the metal source is oxic seawater. Global palaeo-ocean events control the geochemistry compositions and growth process of ferromanganese crusts and the nodule. Ferromanganese crusts that formed from the late Cretaceous on the mountaintop edge have a rough surface with black botryoidal shapes, showing an environment with strong hydrodynamic conditions, while the ferromanganese nodule that formed from the Miocene on the slope has an oolitic surface as a result of water depth. What is more, nanoscale or micron-scale diagenesis may occur during the growth process, affecting microstructure, mineralogical and geochemical features.

1. Introduction

Ferromanganese deposits are common deep-sea mineral resources, which mainly exist in the form of ferromanganese crust and ferromanganese nodules. Ferromanganese crusts primarily grow on rock surfaces located without sediment on the seamount’s ridges, and plateaus at water depths of 400–7000 m [1,2], while ferromanganese nodules mainly grow on the surface of sediment-covered abyssal plains and the slope of seamounts at water depths of approximately 3500 to 6500 m [1]. They are rich in metals such as Co, Ni, Cu, Pb, and Zn, rare earth elements (REEs), and platinum group elements (PGEs), which have high economic value and resource potential [1]. Ferromanganese deposits in the ocean are primarily divided into three types: hydrogenetic, diagenetic and hydrothermal [3]. The metal ions of hydrogenetic ferromanganese deposits are sourced from seawater and form ferromanganese oxides by colloidal precipitation under oxidation conditions. The growth rates of hydrogenetic ferromanganese deposits are extremely slow (1–10 mm/Ma) [3,4]. The metal ions of diagenetic ferromanganese deposits are derived from pore water in sediments or sediment water under suboxidation conditions [5]. The metal ions of hydrothermal ferromanganese deposits are sourced from the mixture of medium–low temperature hydrothermal fluid with seawater [6,7]. In addition, the formation of ferromanganese deposits is often hydrogenetic–diagenetic and hydrogenetic–hydrothermal mixed types [8,9,10]. Ferromanganese deposits are regarded as a hydrogenetic type [11,12,13] formed in paleo-ocean and paleo-environments, recording the evolution of ocean and climate for the past 60–100 Ma, and are important in large amounts of paleo-ocean and paleo-environment information [2,14]. In recent years, several studies have shown that microorganisms are also involved in the formation of marine ferromanganese oxides [15,16,17]. After metals are adsorbed to ferromanganese oxides, the precipitation of Co can be influenced by bacterial activity. Microorganisms as catalysts not only promote the formation of ferromanganese deposits, but also the enrichment of metals [17].
Ferromanganese deposits are distributed in the Pacific, Atlantic, Arctic, and Indian oceans, though most are in the Pacific Ocean [1]. Scholars have also performed a significant amount of research on these deposits [9,18,19,20,21]. The formation and mineral and geochemistry compositions of hydrogenetic ferromanganese deposits are the most common in the Pacific [1]. The seamounts of the Western and Central Pacific are the main distribution areas of ferromanganese deposits. Caiwei Guyot, the location of samples collected in this study, is located in the Magellan Seamounts to the east of the Mariana Trench.
In this paper, a comprehensive study on the ferromanganese deposits (ferromanganese crusts on the mountaintop edge and the nodule on the slope) of Caiwei Guyot has been carried out based on detailed mineralogical and geochemical analysis including major elements, trace elements and rare earth elements. The growth rates and ages of ferromanganese deposits are estimated by Co-Chronometer. Finally, we propose the formation model of ferromanganese deposits by combining them with the paleoceanographic events in the Northwest Pacific since the late Cretaceous.

2. Geological Setting and Oceanography

The Caiwei seamounts are located along the northeast edge of the eastern Mariana basin in the western Pacific. They are distributed in a NW chain in the Magellan seamounts, which consists of the Vlinder, Loah, ITA Mai Tai, other seamounts, with a northeastern trend. The Caiwei seamounts include two relatively independent guyots: the larger main guyot is Caiwei Guyot, and the smaller subsidiary guyot is Caiqi Guyot. The distance between the two guyots is 10.2 km. Substrate rocks are mainly composed of tholeiitic basaltic pillow lavas from the early Cretaceous, subalkaline basalt from the early Cretaceous to Paleogene, alkaline basalt and pyroclastic rocks from the Neogene; sedimentary caprocks are mainly composed of bioherm limestone and mudstone from the early Cretaceous to Paleocene, foraminiferal limestone from the Eocene to the early Miocene and calcium and argillaceous sediments such as foraminiferal sand and soft mud from the Tertiary to the Holocene [22,23,24,25,26,27]. The age of the guyot is 80–120 Ma. The thickness of the overlying sedimentary layer is approximately 25–100 m. The average slope of the Caiwei Guyot is 20°–30° [28]. There are collapsed flanks and landslide topography on the Caiwei Guyot [28,29]. The existing survey results show that ferromanganese deposits are primarily distributed on the mountaintop edge and slope [29]. The samples used in this study were collected from the mountaintop edge and the slope of Caiwei Guyot (Figure 1c).
Caiwei Guyot is located in the Magellan seamounts of the eastern Mariana Basin (Figure 1a). The deep-water system in the western Pacific Ocean was primarily controlled by CDW (circumpolar deep water) and AABW (Antarctic bottom water) in the Southern Ocean [30]. CDW can be divided into upper circumpolar deep water (UCDW) with maximum temperature and lower circumpolar deep water (LCDW) with maximum salinity [31]. LCDW is mixed by AABW and NPDW (north Pacific deep water) and can upwell the depth of 2000 m–3000 m [32]. Due to the complex submarine topography of the low latitude western Pacific, after LCDW enters the Pacific, it is divided into eastern branch current and western branch current [33,34,35,36,37,38]. The eastern branch partly enters the Central Pacific Basin with a volume transport of 3.7 Sv (1 Sv = 106 m3 s−1) [39]. Additionally, the other part enters Northwest Pacific Basin through the Wake Island Passage [36,37]. The western branch current passes through the Magellan Seamounts and the Mid-Pacific Seamounts with a volume transport of 2.1 Sv [36]. UCDW and LCDW become the older NPDW by the mixing of deep water [36], and NPDW enters the western Pacific and the Philippine sea again [30] (Figure 1b). LCDW can erode and sweep sediments on Caiwei Guyot, resulting in substrate exposure that provides an ideal place for the growth of ferromanganese crusts and sediment discontinuity [28,40,41]. LCDW has high oxidation, creating an oxidation environment for the guyot, promoting the reaction of metal ions, and forming the precipitation of oxides and hydroxides [42]. The topography of Caiwei Guyot can promote the strengthening of internal waves to a certain extent, which can promote the mixing of deep water [43,44,45]. Internal waves (clockwise anticyclonic circulation called Taylor Column phenomenon) in Caiwei Guyot [40] (Figure 1c) can also communicate oxygen minimum zone (OMZ) with oxygen-enriched and iron-enriched deep water [27]. The metal ions such as Mn2+ and Co2+ in OMZ can be oxidized better [27].

3. Samples and Methods

The three ferromanganese deposit samples are collected by TV grab and Remote Operated Vehicle (ROV) on the Caiwei Guyot in Magellan seamounts during the HOBAB5 cruise expedition in 2018 (Figure 1a,b). The station information is shown in Table 1 and Figure 1. C9R-6 and C9R-7 are collected by ROV, and C9 is collected by TV grab.
The ferromanganese deposit samples were washed with clean water and dried, and photos were taken on a large scale. Then, the samples were divided into two parts with a cutter, cleaned with ultrapure water, and put into the oven for 60 min. After being dried, one is used to make probe pieces for microscopic observation, and the other is divided into many layers due to the internal structure along the growth direction as shown in Figure 2. Each layer is independent and continuous. Grind them to 200 mesh with agate mortar, and then place them into the oven for 60 min. After being dried, the samples were transferred to the dryer.

3.1. Mineralogy

The microscopic analysis of the samples was conducted in the Key Laboratory of Marine Geology and Environment, Institute of Oceanography, Chinese Academy of Sciences. The samples were carbon-coated and observed by a VEGE3 TESCAN scanning electron microscope combined with an Oxford EDS Oxford X-ray spectrometer (UK). The scanning electron microscope instrument used 20 kV high voltage, the emission current was 1.4–1.9 nA, and the working distance was 15 mm. The X-ray spectrometer used 20 kV excitation voltage. The mineral composition was determined by Rigaku D/MAX 2500 PC 18 kw X-ray diffraction (XRD) in the Key Laboratory of Marine Mineral Resources of Ministry of Land and Resources, Guangzhou Marine Geological Survey. The analytical conditions for XRD were: Cu K α radiation at 40 kV and 300 mA, graphite monochromator. The speed of continuous scanning was 2.5° (2θ)/min, the step was 0.01° (2θ) and scans ranged from 5 to 75° (2θ). Ambient temperature was 25 ± 2 °C.

3.2. Geochemistry

The composition of major element of ferromanganese nodule was carried out by 5300 DV plasma emission spectrometer (ICP-OES) in the Analytical Laboratory, Beijing Research Institute of Uranium Geology and AB104L based on “Methods for chemical analysis of silicate rocks—Part 32: Determination of 20 components including aluminium oxide etc.-Mixed acid digestion-inductively coupled plasma atomic emission spectrometer”, while the composition of major element of ferromanganese crusts was carried out by Axios-mAX wavelength dispersive X-ray fluorescence spectrometer (XRF) in the Analytical Laboratory, Beijing Research Institute of Uranium Geology based on GB/T 14506.28-2010 “Methods for chemical analysis of silicate rocks—Part 28: Determination of 16 major and minor elements content” due to different powder quality. The precision of the analysis was better than that of ±5%. The compositions of trace and rare earth elements were analyzed by ELAN 9000 inductively coupled plasma mass spectrometry (ICP-MS) in the Key Laboratory of Marine Geology and Environment, Institute of Oceanography, Chinese Academy of Sciences. Firstly, the sample was dried in the oven at 105 °C for 2 h, then approximately 40 mg powdered samples were put into Teflon digestion beakers, then 0.5 mL of HF, 0.5 mL of HNO3, and 1.5 mL of HCl were added into Teflon digestion beakers. Then, the powder was sealed and heated in an electric oven and heated at 150 °C for 12 h. After cooling, the cover of the beakers was opened, and the beaker was heated on a hot plate to dryness. After the acid in the beakers was evaporated to dryness, 1 mL of HNO3 was added, and then the acid was evaporated to dryness without sealing. After steaming dry, 1 mL of HNO3 and 1 mL of H2O were added to the beakers. Then, the beakers were again sealed and heated in an electric oven at 150 °C to dissolve the residue. Finally, H2O was added to 40 g before the compositions of trace and rare earth elements were measured by ICP-MS. The digestion process of standard samples, blank samples, and parallel samples are the same as above. Re element was used as the internal standard, and the external standard samples included (GBW07315; GBW07316; BCR-2; BHVO-2; Nod-A-1, Nod-P-1, GBW07295, GBW07296). The precision of the analysis was better than that of ±5%. The test accuracy was better than 5%.
The pattern diagram of rare earth elements is made according to concentrations normalized to the Post Archean Australian Shale (PAAS) values. CeSN/CeSN* = 2CeSN/(LaSN + PrSN), EuSN/EuSN* = 2EuSN/(SmSN + GdSN), where SN means concentrations normalized to the PAAS values [46].
The following formula is used to calculate the growth rate of the ferromanganese crusts: GR= 0.68/(Con)1.67 [47], where Con = Co × 50/(Fe + Mn) with Co, Fe, and Mn expressed as weight percent (wt.%). Pearson correlation coefficient is used to measure the linear relationship between two variables. Statistical significance will be at either 99% or 95% (CL). Q-mode factor analysis is used to analyze the relationship between each element and the influencing factors in order to determine which elements are in different factors. Here, we regard each factor as different mineral phases in ferromanganese crusts, and the elements in the factor exist in mineral phases.

4. Results

4.1. Texture and Microstructure

4.1.1. Textural Morphology

C9R-6 is a board ferromanganese crust that is about 10 cm long (Figure 2a,b). There are black botryoidal shapes whose diameter is 1–2 cm on the surface (Figure 2b). Obvious changes of layers can be seen inside, but the layers are not nearly parallel (Figure 2a). C9R-6 is divided into six layers due to the internal structure (Figure 2a): the layer composed of outermost black ferromanganese oxides is divided into C9R-6-1 and C9R-6-2; the layer composed of black ferromanganese oxides consolidated with yellow detrital minerals is divided into C9R-6-3, C9R-6-4, and C9R-6-5, which have high porosity (Figure 2a). The ferromanganese oxides at the bottom are C9R-6-6.
C9R-7 is also a board ferromanganese crust with a length of about 10 cm (Figure 2c,d). The crust has a rough surface on which black botryoidal shapes develop (Figure 2d). The diameter of each botryoidal ball is about 1–2 cm (Figure 2d). Obvious changes of nearly parallel layers can be seen inside (Figure 2c), which are mostly composed of dense ferromanganese oxide layers with low porosity and loose ferromanganese oxide layers with high porosity filled with siliceous debris. The layers grow orderly and have obvious rhythmic characteristics. C9R-7 is divided into six layers due to the internal structure (Figure 2c).
C9 is a ferromanganese nodule whose diameter is about 4 cm (Figure 2e,f), and the surface is an oolitic structure (Figure 2f). White siliceous debris can be seen in the cracks on the surface (Figure 2f). There is a substrate as the nucleus inside, and ferromanganese oxides precipitate as the outer layer (Figure 2e). In the early growth stage, the bottom structure is dark, dense, and relatively hard, while in the late growth stage, the top structure is relatively loose with high porosity (Figure 2e). Siliceous debris can be seen in the gaps (Figure 2e). It is divided into one layer every 2 mm along the growth direction with an average of five layers. The top layer is stage II (C9-1 and C9-2), and the bottom layer is stage I (C9-3, C9-4, and C9-5).

4.1.2. Microstructure

The microstructure of ferromanganese deposits is shown in Figure 3 and Figure 4. Columnar structure, laminar structure, and mottled structure are mainly developed in ferromanganese deposits on Caiwei Guyot (Figure 3 and Figure 4).
Along the growth direction of C9R-6, disorderly arranged columns can be seen along the growth direction. Branches appear in the growth process of the columns, forming a shape similar to the dendrite (Figure 3a,b). Banded Si-Fe-rich cement exists in the gaps (Figure 3b). Different from C9R-6, there are many types of structures in C9R-7. Along the growth direction, a mottled structure composed of siliceous debris and ferromanganese oxides can be seen (Figure 3c,e). Then, disorderly arranged columns developed into a columnar structure with low porosity and gradually formed a dendritic shape like C9R-6 (Figure 3d). In the later stage of the growth process, the columnar structure is rarely seen and gradually transits to a laminar structure (Figure 3d,e). Organic remnants such as foraminifera surrounded by Mn-Fe-rich oxides precipitated with seawater and were transformed by hydrogenesis and diagenesis (Figure 3f).
Along the growth direction of C9, at the junction of the nucleus and ferromanganese oxides, it is a mainly columnar structure composed of upright columns in stage I (Figure 4a,b). The columns connect end to end, whose diameter ranges from 100 µm to 300 µm (Figure 4a,b). There are gaps between the columns in the later stage of the growth process. There are mainly three groups in gaps between columns in stage II: siliceous debris; fan-shaped or circular layered Mn-rich oxides (Figure 4d–f); banded Si-Fe-rich cement (Figure 4d–f). The entry of clastic materials interrupted the precipitation of ferromanganese oxides and further promoted the formation of columnar structures. Columns connected from head to tail gradually become forked dendritic columns, and finally, the mottled structure gradually formed in stage II (Figure 4a,b).

4.2. Mineralogy

The XRD diffraction patterns of each layer of ferromanganese deposits are shown in Figure 5. The diffraction peak of XRD diffraction patterns is not sharp, and the peak intensity are widened and dispersed because of low crystallinity of minerals. X-ray diffraction data for samples of ferromanganese crusts and ferromanganese nodule show that Mn-rich oxide minerals are dominant minerals. Quartz, albite, anorthite, and phillipsite exist as accessory minerals. Fe-rich oxides with poor crystallinity are amorphous, and no obvious diffraction peak is found. Mn-rich oxide minerals are mainly Fe-rich vernadite (1.42 Å and 2.45 Å) and and 10 Å manganese minerals (todorokite). Fe-rich vernadite exists in all the layers of ferromanganese crusts and nodule. Todorokite exists in the stage II in the ferromanganese nodule. In addition, todorokite exists in all layers of C9R-6, which just exists in the younger layers (C9R-7-1 and C9R-7-2) of C9R-7. Phillipsite exists in the layers of stage I in the ferromanganese nodule, older layer of C9R-6 and younger layers in C9R-7.

4.3. Geochemistry

4.3.1. Geochemistry Compositions of the Ferromanganese Crusts

The chemical compositions of major and trace elements of each layer are shown in Table 2. The contents of Mn are 14.7–25.2% with an average value of 21.0%. The contents of Fe are 11.8–19.4% with an average value of 17.3%. The contents of Mn and Fe gradually decrease from the bottom to the top in C9R-7, while the contents of Mn and Fe in C9R-6 almost have no change during the growth process (Figure 6). The Mn/Fe ratios range from 1.06 to 1.45. The contents of Al are 0.66–2.22% with an average of 1.24%, and the contents of Si are 3.40–5.83% with an average of 4.84%. The contents of Al and Si in C9R-7 increase from the bottom to the top. The Si/Al ratios range from 2.21 to 5.28.
Among the trace elements, the contents of elements with economic value are extremely high, in which the contents of Co are 3841–8327 ppm with an average of 6163 ppm. The contents of Ni are 3000–5759 ppm with an average of 4593 ppm. The contents of Cu are 357–1664 ppm with an average of 915 ppm, and the contents in C9R-7 are lower than that in C9R-6 (nearly two-fold). The contents of Zn are 437–672 ppm with an average of 558 ppm. The contents of Co, Ni, Cu and Zn gradually decrease from the bottom to the top in C9R-7 in general (Figure 6).
The contents of REY are 1410–2117 ppm with an average of 1747 ppm. The contents of Ce are the highest in REY with an average of 803 ppm, ranging from 553–998 ppm, and accounting for nearly 50% in REY. The contents of LREE are 1079–1652 ppm with an average of 1380 ppm. The contents of HREE are 138–238 ppm with an average of 180 ppm. LREE/HREE ratios range from 6.42 to 8.81. The contents of Y range from 147 ppm to 227 ppm with an average of 186ppm. It can be seen that each layer of samples shows a positive Ce anomaly and negative Y anomaly in the PAAS standardization diagram of REY (Figure 7).

4.3.2. Geochemistry Compositions of the Ferromanganese Nodule

The chemical compositions of major and trace elements of each layer are shown in Table 3. Among the major elements, the contents of Mn are 18.5–26.0% with an average value of 22.8%, which gradually decreases from stage I to stage II (Figure 6). The contents of Fe are 9.10–15.8% with an average value of 12.8%, which gradually decreases from stage I to stage II. The Mn/Fe ratios range from 1.65 to 2.14, which gradually increase from stage I to stage II (Figure 6). The contents of Al are 0.88–1.58% with an average value of 1.31%, and the contents of Ca are 2.04–2.89% with an average value of 2.45%.
Among the trace elements, the contents of elements with economic value are significantly high. The contents of Co are 4972–6806 ppm with an average value of 5668 ppm. The contents of Co gradually increase to the maximum value in stage I, and gradually decrease in stage II (Figure 6). The contents of Cu are 2428–2833 ppm with an average value of 2538 ppm, which is much higher than ferromanganese crusts, and the contents basically do not change (Figure 6). The contents of Zn are 461–698 ppm with an average value of 550 ppm, and the contents gradually increase from stage I to stage II. The contents of Ni are 4871–5807 ppm with an average value of 5332 ppm, and gradually increase to the maximum value in stage I and gradually decrease in stage II (Figure 6).
The contents of REY (REE + Y) are 1587–1929 ppm with an average value of 1781 ppm. The contents of Ce content are the highest with an average of 1025 ppm, ranging from 875 ppm to 1114 ppm and accounting for more than 50%. The contents of LREE are 1338–1677 ppm with an average of 1531 ppm. The contents of HREE are 240–263 ppm with an average of 251 ppm. The contents of Y are 98.4–119 ppm with an average of 111 ppm. LREE/HREE ratios range from 5.39 to 6.69, which shows LREE enrichment. It can be seen that each layer of the sample shows positive Ce anomaly and negative Y anomaly in the PAAS standardization diagram of REY (Figure 7).

4.4. Growth Rates and Age Model

According to the Co empirical formula above, the growth rates of C9R-6 are 0.85–1.30 mm/Ma (Table 2), and the average growth rate is 1.11 mm/Ma. The ages of each layer of C9R-6 are estimated to be 11.75 Ma, 15.42 Ma, 24.14 Ma, 31.25 Ma, 67.77 Ma, and 72.42 Ma, which are from the late Cretaceous to the middle Miocene. The growth rates of C9R-7 range from 0.64 mm/Ma to 1.25 mm/Ma (Table 3), and the average growth rate is 0.93 mm/Ma. The age of each layer of C9R-7 is estimated to be 2.40 Ma, 34.29 Ma, 30.91 Ma, 39.48 Ma, 70.90 Ma, and 78.12 Ma, which is from the late Cretaceous to the early Pleistocene. The growth rates of C9 are 0.69–1.48 mm/Ma (Table 3), and the average growth rate is 1.02 mm/Ma, which is much lower than the growth rates of ferromanganese nodules in the Peru Basin [48]. The ages of each layer of C9 are estimated to be 5.67 Ma, 11.54 Ma, 12.55 Ma, 12.37 Ma, and 13.48 Ma, which grew from the Miocene.

4.5. Element Correlations and Factor Analysis

Element correlations of ferromanganese crusts on the mountaintop edge of Caiwei Guyot are shown in Table S1 in Supplementary Materials. Mn shows a significantly positive correlation with Ca, Co, Cd, W, Bi, Ce, and Lu (99% CL) and shows a positive correlation with Fe, Ni, Pb, U, La, Er, Tm, and Yb (95% CL); Mn is negatively correlated with Al, P, Sc, and Tl (99%CL) and shows a negative correlation with Si and Rb (95% CL). Fe shows a positive correlation with Ni, Ga, Cd, and Bi (99% CL) and shows a positive correlation with Mn, Nb, Hf, Ta, and Ce (95% CL); Fe shows a negative correlation with P, Sc and Tl (99% CL). Mn/Fe shows a positive correlation with Mo (99% CL) and shows a positive correlation with W and U (95% CL), Mn/Fe is negatively correlated with Ga and Nb (95%CL); Cu is positively correlated with Zn and Ni (99% CL); the growth rates are positively correlated with Li, Cu, Zn, Rb, Nb and Ta (95% CL) and negatively correlated with Co (99% CL). Q-mode factor analysis of ferromanganese crusts produces four factors that account for 89.6% of the variance, with Factors 1–4 accounting for 35.5%, 23.0%, 18.5%, and 12.6% of the variance, respectively (Table S2 in Supplementary Materials). Factor 1 is interpreted to represent aluminosilicate minerals: Al, Mg, K, Li, V, Cu, Sr, Zr, Mo, W, Th, U, and REY (except Ce). Factor 2 is interpreted to represent residual biogenic: Fe, Ca, Ti, Ni, Cu, Zn, Ga, Zr, Nb, Cd, Ba, Hf, Ta, Bi, Th and Ce. Factor 3 is interpreted to represent Mn-rich oxides: Mn, Si, Ca, Li, Sc, Co, Rb, U, La and Ce. Factor 4 is interpreted to represent Fe-rich oxyhydroxide: Fe, P, Be, Sc and V.
Element correlations of the ferromanganese nodule on the slope of Caiwei Guyot are shown in Table S3 in Supplementary Materials. Mn is significantly positively correlated with Fe and Na (99% CL) and negatively correlated with Sc and Zn (99% CL), Mn is positively correlated with Ca, Ni, Bi, La, and Ce (95% CL) and negatively correlated with V, Sr, Zr, Nb, Mo, and Cd (95% CL). Fe is significantly positively correlated with Ca, Na, Hf, Bi, and Ce (99% CL) and significantly negatively correlated with Sc, V, Zn, Mo, and Cd (99% CL). Fe is positively correlated with Ni and La (95% CL) and negatively correlated with Sr and Nb (95% CL). Co has no significant correlation with Fe and Mn, while Co is negatively correlated with Al and Li (95% CL) and significantly negatively correlated with Na and Be (99% CL), indicating that the entry of debris affects the adsorption of Co. Mn/Fe is extremely positively correlated with Sr, V, Mo, and Cd (99% CL) and positively correlated with the Zn and growth rates (95% CL). Mn/Fe shows a negative correlation with Fe, Hf, Bi, and Ce (99%CL) and a negative correlation with Mn, Ca, Na, Ni, Ta, and La (95% CL). The growth rates are extremely positively correlated with V and Sr (99% CL) and are positively correlated with Mn/Fe, Ti, Zn, Mo, Cd, Tl, and W (95% CL). The growth rates show an extremely negative correlation with Ba, Hf, and Bi (99% CL) and a negative correlation with K and Ce (95% CL). Q-mode factor analysis of the ferromanganese nodule produces three factors that account for 95.7% of the variance, with Factors 1–3 accounting for 44.9%, 39.8%, and 11.0% of the variance, respectively (Table S4 in Supplementary Materials). Factor 1 is interpreted to represent ferromanganese oxides: Mn, Fe, Ca, P, K, Ti, Na, Sc, V, Ni, Zn, Ga, Sr, Zr, Nb, Mo, Cd, Ba, Hf, Ta, W, Tl, Pb, Bi, U, La, Ce, and Eu. Factor 2 is interpreted to represent aluminosilicate minerals: Al, Mg, Li, Be, Co, Cu, Rb, Zr, Cs, W, Th, and REY (except Ce and Y). Factor 3 is interpreted to represent fluorocarbon phosphate: P, Li, Be, Co, Ga, and Y.

5. Discussion

Guyot is a complex environment and is controlled by geology, biological activities, geochemical properties of seawater, and physical oceanography, which further affects the characteristics of ferromanganese deposits. Ferromanganese deposits on Caiwei Guyot can be divided into ferromanganese crusts and ferromanganese nodules. In the next section, we focus on the texture morphology, microstructure, mineralogical features, and geochemical features of ferromanganese crusts and nodules. Meanwhile, mineralogical and geochemical analyses are essential for discussing growth processes and environments.

5.1. Texture and Surface

Ferromanganese crusts and nodules have different textures and surfaces due to different oceanographic and geological conditions [49,50]. The surface of the ferromanganese nodule is an oolitic structure with cracks (Figure 2f), while the surfaces of board ferromanganese crusts have a surface with black botryoidal shapes (Figure 2b,d), showing smoother surface texture at a greater depth [50]. These black botryoidal shapes are composed of ferromanganese oxides. Accumulation of ferromanganese oxides reflects the hydrodynamic conditions of the growth process. A more dynamic environment will form a botryoidal structure [2]. The speed of the bottom current (>7 cm/s) on the mountaintop edge and the hydrodynamic conditions were strong because of the Taylor Column phenomenon on Caiwei Guyot [40], while the speed of the current was low and the hydrodynamic conditions are weak on the slope of Caiwei Guyot [40]. In addition, the bottom current with a high-speed bottom on the mountaintop edge sweeps the sediment and exposes the hard substrate [40,41], which is also conducive to the rapid accumulation of ferromanganese oxide. The same phenomenon occurs in ferromanganese crusts on Takuyo-Daigo Seamount, NW Pacific, and Tropic Seamount, Atlantic [41,50], whose botryoidal shapes are bigger at shallower water depths. What is more, the speed of the bottom current and hydrodynamic intensity are in a state of equilibrium where calcareous or siliceous sediments can be cleaned, but botryoidal shapes cannot be eroded [41]. Board ferromanganese crusts generally grow in situ on the mountain top, and finally aggregate for mineralization on the hard substrate. What is more, due to the erosion of the bottom current, the increase in slope gradient, and other reasons, collapse often occurs on Caiwei Guyot, which is common in the Western Pacific Seamounts [29,51]. Ferromanganese nodule grows in an environment with relatively weaker hydrodynamic force and may be buried by sediments brought by the collapse of Caiwei Guyot.

5.2. Genesis Type of Ferromanganese Crusts and the Nodule

Mn-(Cu + Co + Ni)-Fe ternary diagram is used to divide ferromanganese deposits in the ocean into three types: hydrogenetic, diagenetic and hydrothermal [52]. (Fe + Mn)/4-100 × (Zr + Y + Ce) – 10 × (Cu + Ni + Co) ternary diagram [53] and CeSN/CeSN *-Nd and CeSN/CeSN *-YSN/HoSN [3] are also used to classify the type. Each layer in board ferromanganese crusts and layers of stage I in the ferromanganese nodule fall into the hydrogenentic area (Figure 8 and Figure 9), showing the hydrogenentic origin and the enrichment of Cu, Co and Ni. While layers of stage II in the ferromanganese nodule are closer to diagenetic origin (Figure 8a). The authors also used the Mn/Fe ratio to distinguish the genesis type of ferromanganese crusts. It is generally believed that ferromanganese crust whose Mn/Fe is less than 2.5 is hydrogenetic origin [54]. On the contrary, it is diagenetic origin. Mn/Fe of each layer in board ferromanganese crusts of Caiwei Guyot is less than 2.5, which is hydrogenetic origin. Although the Mn/Fe ratios in stage I of the ferromanganese nodule is less than 2.5, greater than 2, which is much higher than those in board ferromanganese crusts, indicating that the nodule has a diagenetic trend in the growth process. Meanwhile, the enrichment of LREE reflects the hydrogenetic origin [55]. Positive Ce anomaly and negative Y anomaly are other evidence of hydrogenetic origin. REE generally has +3 valence, while Ce has Ce3+ and Ce4+. Ce3+ in the marine environment is oxidized to Ce4+ to form CeO2, which precipitates from seawater, resulting in a strong loss of Ce in seawater [56]. Therefore, the PAAS standardization diagrams of REY of ferromanganese crusts and the nodules show strong positive Ce anomalies after PAAS standardization, which are often considered to be the influence of seawater oxidation [57]. The ion radius and valence of the Y element are similar to other rare earth elements, but Y has no 4f electrons, so it is difficult to form a more stable complex. Therefore, its chemical behavior is different from Ho. When ferromanganese crusts and nodules formed, Y and Ho would differentiate, resulting in Y negative anomaly [58,59]. Fe-vernadite is found in each layer in the XRD patterns (Figure 5), which is a nanocrystalline turbostratic phyllomanganate phase of hydrogenetic origin. The crystal structure of vernadite is a layered structure, (Mn4+O6)8− octahedron is connected to each other through the edge. The octahedron layer is mainly Mn4+, and the metal cations can replace the Mn4+ by isomorphism [60,61,62]. 10 Å manganese minerals (todorokite) are found in stage II of C9, C9R-6 and the younger layers of C9R-7 (C9R-7-1 and C9R-7-2) (Figure 5). 10 Å manganese minerals (todorokite) have tunnel structure. K+, Mg2+, Ba2+, and water molecules usually occupy the sites in the todorokite tunnel. Meanwhile, Co, Ni, and Cu may mainly replace Mn at the corner of the tunnel [63,64,65]. 10 Å manganese minerals (todorokite) are formed by the influence of pore water on the seawater-sediment interface under suboxic conditions and the formation of todorokite from vernadite is known from ferromanganese crusts and nodules when oxic conditions have been changed into suboxic conditions, which is considered to be a typical feature of diagenetic ferromanganese crust and nodule [2,66,67,68,69]. We believe that nanoscale and micron-scale diagenesis may occur in the internal layers, but bulk geochemical features are not obvious on the whole.

5.3. Genesis of Ferromanganese Deposits

Paleoceanographic events affecting ferromanganese crusts and nodule in the northwest Pacific since the late Cretaceous are consistent. According to the mineralogical and geochemical characteristics above, ferromanganese crusts on the mountaintop edge of Caiwei Guyot are hydrogenetic origin, whose metal source is oxic seawater [70]. Based on the previous empirical formula calculation of Co, the oldest layers can reach the late Cretaceous, when AABW had not been formed. The formation of ferromanganese crusts may be mainly controlled by the middle ocean current and seamount authigenic current [42]. There are relatively more ore-forming elements in seawater, providing sufficient material source for the mineralization of the ferromanganese crusts. At this stage (78.12 Ma), ferromanganese oxides precipitated in form of plaque structure with occasional siliceous debris and biological sediments in the gaps, which formed a mottled structure (Figure 3c), indicating that the ferromanganese crusts precipitated in the strong hydrodynamic environment on the mountaintop edge of Caiwei Guyot [2]. The contents of Mn and Fe are high, as well as Co, which has the characteristics of obvious hydrogenetic origin. The content of Si and Al is less, suggesting that they are less affected by terrestrial materials. With the drift of the Pacific plate, Caiwei Guyot drifted to the northwest mainly in zonal motion and crossed the current equator about 60–70 Ma ago [71]. The guyot where the ferromanganese crusts are located migrated to the equatorial high productivity zone of the open ocean. As time goes by, due to the crossing of the equator, continental weathering is gradually strengthened. The global temperature was high during this period. Without AABW (78.12–31.25 Ma), the dissolved oxygen content of deep water was very low, and the content of Mn and Co gradually decreased, while the contents of Si and Al gradually increased. Co/(Cu + Ni) and Co/(Fe + Mn) ratios reach the minimum value at 31.25 Ma (Figure 6), indicating that oxidation conditions fell into a decline. Obvious changes in layers can be seen inside. At this time, the texture of ferromanganese crusts was loose with high porosity, the precipitation of ferromanganese oxides was prevented due to the entry of silicon debris, and the growth of columnar structures was inhibited. Phillipsite existed in this stage (Figure 5a,b), which is formed by the alteration of volcanic glass leading to the increase in pH value at the sediment-water interface [72,73,74]. Phillipsite usually appears in the form of authigenic minerals and exists in the gaps of the columnar structure, which are likely to be physically combined with the columnar growth process in the growth process.
From the late Oligocene to the early Miocene, the Drake Passage and Tasmanian Passage completely opened and the deep-water channel was formed [75], which contributed to the formation of the modern circulation system. AABW with high content of dissolved oxygen has an impact on the growth process of ferromanganese crusts on the Pacific Seamounts [76,77,78]. After entering the Northwest Pacific Ocean, LCDW (mixed by AABW and NPDW) with dissolved oxygen is the main source of dissolved oxygen in the Magellan seamount area. When a significant global cooling event occurs, the degree of environmental oxidation in the Pacific Seamounts will also increase. At this stage (31.25–21.14 Ma), due to the role of LCDW, the deep water in the ocean began to have a dissolved oxygen supply, and OMZ began to develop in the Pacific Ocean. The growth process of ferromanganese crusts is related to OMZ on seamounts [12]. The water depth of OMZ in the Caiwei Guyot is less than 1000 m [79]. OMZ can promote the dissolution of Mn in OMZ and ferromanganese crusts with high Mn content form below the OMZ [20,80]. Dissolved oxygen oxidizes Mn2+, forming hydrated complex ions. Co, Ni, and Ce show a positive correlation with Mn, indicating that Ni, Cu, and Ce are distributed in the manganate octahedral layer of Fe-vernadatie [81]. Fe-vernadatie adsorbs oxidized Ce, as well as Co2+, Ni2+, and other metal cations. Higher contents of Co are the result of the oxidation of these elements on the surface of Fe-vernadite, indicating an extremely effective process of enrichment of trace elements [82]. Co/(Cu + Ni) and Co/(Fe + Mn) ratios increase with the formation of the modern circulation system, indicating the enhancement of oxidation conditions (Figure 6). The columnar structure formed in this stage (Figure 3). The formation of the southeast ice sheet of the Antarctic, colder climate and the sank of Iceland–Faroe Ridge at about 15 Ma promote the high-density deep water of the Arctic Ocean to flow into the Atlantic Ocean and other oceans [76,83], AABW is further enhanced, making the oxidation degree of Caiwei Guyot higher. At this stage (15.42 Ma–0), Co/(Cu + Ni) and Co/(Fe + Mn) ratios reach the maximum value in C9R-6-1 (Figure 6). Meanwhile, the enhancement of LCDW and the strong hydrodynamic force on the mountaintop edge promote the formation of a dense laminar structure with low porosity.
Different from the ferromanganese crusts on the mountaintop edge, the ages of the nodule on the slope are younger, whose growth process is affected by AADW that becomes LCDW when entering the Northwest Pacific Ocean. The enhancement of the LCDW oxidation degree has a great effect on the texture, microstructure, mineralogical, and geochemical features of the nodule. According to the mineralogical and geochemical characteristics, the ferromanganese nodule on the slope of Caiwei Guyot can be divided into two stages. The layers with hydrogenetic origin in stage I (13.48–11.54 Ma) are formed in the middle Miocene. Lower temperatures of deep water, the expansion of the Antarctic ice sheet, and the enhancement of deep-water circulation from the late Miocene [75,84] make the high-density seawater of the Arctic Ocean flow into the Atlantic Ocean and other oceans with the circulation system. As a result, LCDW was further strengthened. LCDW with dissolved oxygen flew through Caiwei Guyot, strengthening the oxidation of seawater. Fe2+ and Mn2+ in seawater accumulated to form Fe-rich and Mn-rich oxide colloids [80,85], which precipitated in form of a columnar structure connected end to end around the nucleus. This process is the same as that of ferromanganese crusts. The contents of Mn and Fe are relatively high, and the content of Co also gradually increases. Compared with Atlantic ferromanganese nodules, ferromanganese nodules on Caiwei Guyot enrich Mn, Co, and Ni, while losing Fe [86]. Co/(Cu + Ni) and Co/(Fe + Mn) ratios increase with the enhancement of oxidation of seawater (Figure 6). Fe-vernadite is the main Mn-rich oxide in stage I, and quartz, albite, anorthite, and phillipsite exist as accessory minerals.
The layers in stage II (11.54 Ma–0) are formed in the middle and late Miocene. The contents of Mn, Fe, and Co are reduced to varying degrees relative to stage I. High Mn/Fe ratios (>2) and 10 Å manganese minerals (todorokite) indicate nanoscale or micron-scale diagenesis occurred in the internal layers of stage II. Todorokite has a tunnel structure. Meanwhile, Co, Ni, and Cu may mainly replace Mn at the corner of the tunnel. Cu is enriched in diagenetic layers of the nodule. Meanwhile, the growth rates in stage II are higher than those in stage I. Previous studies have shown that the diagenetic process is mainly due to the following reasons: i, adsorbed metals are released due to particle dissolution and will be enriched in pore water and further have a reaction with manganese oxides [87,88]; ii. phillipsite formed by the alteration of volcanic glass leads to the increase in pH value, resulting in the additional oxidation of Mn2+ [72,74]; iii. the decomposition of organic matter and the dissolution of biological components related to biological activities promote the release of metal ions, and metal elements can be adsorbed into manganese oxides [87,89]. Metals of particle dissolution may have an impact on diagenesis at the micron level, but the specific impact is unknown. What is more, it is believed that 10 Å manganese minerals (todorokite) are considered to be the evidence of diagenesis [2,66,67,68,69], but there is no or very little phillipsite in some layers where 10 Å manganese minerals (todorokite) exist. We exclude that phillipsite may be the cause of internal diagenesis of the nodule. Biological activities on the slope in Caiwei Guyot are more active than those on the mountaintop [90]. Siliceous debris and organic matter precipitated in gaps with seawater in stage II. As a result, the texture is loose with high porosity. Siliceous debris, fan-shaped or circular layered Mn-rich oxides, and banded Si-Fe-rich cement are filled in the gaps (Figure 4). Though Co/(Cu + Ni) and Co/(Fe + Mn) ratios are higher than those of stage I (Figure 6), the internal columnar structure provides space for nano-scale or micron-scale diagenesis. The degradation of organic matter may produce a local (micron-scale) reducing microenvironment [55]. The change of redox potential promotes the reactivation of Fe from surrounding biological carbonates [55], forming banded Si-Fe-rich oxides, which are cemented and precipitated in gaps. Banded Si-Fe-rich oxides mostly appear in the middle and late stages of growth and are connected with columns or layered manganese-rich oxides dispersed in gaps (Figure 4). The mottled structure gradually formed in stage II (Figure 4b).

6. Conclusions

In this study, we analyze the texture morphology, microstructure, mineralogical features, and geochemical features of ferromanganese crusts on the mountaintop edge of Caiwei Guyot and the ferromanganese nodule on the slope of Caiwei Guyot. Global palaeo-ocean events control on the geochemistry compositions and growth process of ferromanganese crusts and the nodule.
Ferromanganese crusts on the mountaintop edge of Caiwei Guyot are board ferromanganese crusts that are of hydrogenetic origin with many black botryoidal shapes on the surface, suggesting board ferromanganese crusts grow in strong hydrodynamic conditions. Obvious changes in layers can be seen inside. Fe-vernadite is the main Mn-rich mineral. The oldest layers can reach the late Cretaceous age when AABW had not been formed. The formation of crusts in this process was related to the middle ocean current and seamount authigenic current. Ferromanganese oxides precipitated in form of plaque structure with occasional siliceous debris and biological sediments in the gaps, which formed a mottled structure. With the drift of the guyot, continental weathering is gradually strengthened, and the dissolved oxygen content of deep water was very low. Co/(Cu + Ni) and Co/(Fe + Mn) ratios reach the minimum value at 31.25 Ma. After the formation of the modern circulation system, LCDW (mixed by AABW and NPDW) with dissolved oxygen is the main source of dissolved oxygen in the guyot, which further strengthens oxidation. Global palaeo-ocean events control the geochemistry compositions and growth process of ferromanganese crusts. For example, the formation of the south ice sheet of the Arctic, colder climate, and the sank of Iceland–Faroe Ridge at about 15 Ma make Co/(Cu + Ni) and Co/(Fe + Mn) ratios continue to increase. 10 Å manganese minerals (todorokite) indicate that nanoscale or micron-scale diagenesis in the internal layers may occur.
The surface of the ferromanganese nodule is an oolitic structure, showing a smoother surface texture at a greater depth. The ferromanganese nodule on the slope grows in an environment with relatively weaker hydrodynamic conditions. The growth process is divided into two stages. Stage I is formed in the middle Miocene and is affected by LCDW. The columnar structure formed under the action of LCDW. Fe-vernadite, 10 Å manganese minerals (todorokite), quartz, albite, and anorthite can be seen. Stage I (13.48–11.54 Ma) of the ferromanganese nodule shows hydrogenetic origins due to geochemical features, indicating that the metal source is oxic seawater. As a result, the contents of Cu and Fe are high, and the growth rates are low. Stage II (11.54 Ma–0) is formed in the middle and late Miocene. Nanoscale or micron-scale diagenesis in the internal layers may occur. The texture is loose with high porosity, and siliceous debris and organic matter are carried in gaps between columns by seawater, creating a reducing microenvironment that promotes the formation of banded Si-Fe-rich oxides. The contents of Mn, Fe, and Co gradually decrease. High Mn/Fe ratios (>2) and 10 Å manganese minerals (todorokite) prove it. Meanwhile, the growth rates in stage II are higher than those in stage I. The mottled structure gradually formed in stage II. The content of Cu of the ferromanganese nodule is much higher than those of ferromanganese crusts.

Supplementary Materials

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/jmse10091275/s1, Table S1–S4. Table S1: Pearson correlation for major and trace elements of ferromanganese crusts; Table S2: Statistical factor analysis for major and trace elements of ferromanganese crusts; Table S3: Pearson correlation for major and trace elements of the ferromanganese nodule; Table S4: Statistical factor analysis for major and trace elements of the ferromanganese nodule.

Author Contributions

Conceptualization, L.W.; methodology, L.W.; software, L.W.; validation, L.W.; formal analysis, L.W.; investigation, L.W.; resources, Z.Z.; data curation, L.W.; writing—original draft preparation, L.W.; writing—review and editing, L.W. and Z.Z.; visualization, L.W.; supervision, Z.Z.; project administration, Z.Z.; funding acquisition, Z.Z. All authors have read and agreed to the published version of the manuscript.

Funding

This work was supported by the NSFC Major Research Plan on West-Pacific Earth System Multi-spheric Interactions [grant number 91958213], the Strategic Priority Research Program of the Chinese Academy of Sciences [grant number XDB42020402], the National Programme on Global Change and Air–Sea Interaction [grant number GASI-GEOGE-02], the International Partnership Program of the Chinese Academy of Sciences [grant number 133137KYSB20170003], the Special Fund for the Taishan Scholar Program of Shandong Province [grant number ts201511061], and the National Key Basic Research Program of China [grant number 2013CB429700].

Informed Consent Statement

Not applicable.

Data Availability Statement

All the data are given in the Supporting Information.

Acknowledgments

We would like to thank the crews of the R/V Kexue during the HOBAB 5 cruise for their help with sample collection. We are grateful for the valuable comments and suggestions from the anonymous reviewers and editors.

Conflicts of Interest

The authors declare no conflict of interest.

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Jmse 10 01275 g001 550
Figure 1. (a) The location of the study area. (b) The location of the study area and the modern Pacific Ocean circulation system, the yellow star represents Caiwei Guyot. The red and blue lines represent the lower circumpolar deep water (LCDW), the upper circumpolar deep water (UCDW), the Pacific deep water (PDW), the north Pacific deep water (NPDW), and the Antarctic bottom water (AABW) (modified by [30]). (c) Topographic map of Caiwei Guyot (data are quoted from https://www.gebco.net on 15 July 2022), the yellow star represents HOBAB5-C9, HOBAB5-C9R-6, HOBAB5-C9R-7 the red line represents clockwise anticyclone circulation (Taylor Column).
Figure 1. (a) The location of the study area. (b) The location of the study area and the modern Pacific Ocean circulation system, the yellow star represents Caiwei Guyot. The red and blue lines represent the lower circumpolar deep water (LCDW), the upper circumpolar deep water (UCDW), the Pacific deep water (PDW), the north Pacific deep water (NPDW), and the Antarctic bottom water (AABW) (modified by [30]). (c) Topographic map of Caiwei Guyot (data are quoted from https://www.gebco.net on 15 July 2022), the yellow star represents HOBAB5-C9, HOBAB5-C9R-6, HOBAB5-C9R-7 the red line represents clockwise anticyclone circulation (Taylor Column).
Jmse 10 01275 g001
Jmse 10 01275 g002a 550Jmse 10 01275 g002b 550Jmse 10 01275 g002c 550Jmse 10 01275 g002d 550
Figure 2. (a) Internal texture of C9R-6, which is composed of obvious changes of layers that are are mostly composed of dense ferromanganese oxide layers with low porosity and loose ferromanganese oxide layers with high porosity filled with siliceous debris, but the layers are not nearly parallel; (b) botryoidal shapes whose diameter is 1–2 cm on the surface; (c) internal texture of C9R-7, which is composed of obvious changes of nearly parallel layers that are mostly composed of dense ferromanganese oxide layers with low porosity and loose ferromanganese oxide layers with high porosity filled with siliceous debris; (d) botryoidal shapes whose diameter is 1–2 cm on the surface; (e) internal texture of C9, which is composed of a substrate as the nucleus inside, and outer layers composed of ferromanganese oxides; (f) smooth oolitic surface structure where siliceous debris can be seen in the cracks.
Figure 2. (a) Internal texture of C9R-6, which is composed of obvious changes of layers that are are mostly composed of dense ferromanganese oxide layers with low porosity and loose ferromanganese oxide layers with high porosity filled with siliceous debris, but the layers are not nearly parallel; (b) botryoidal shapes whose diameter is 1–2 cm on the surface; (c) internal texture of C9R-7, which is composed of obvious changes of nearly parallel layers that are mostly composed of dense ferromanganese oxide layers with low porosity and loose ferromanganese oxide layers with high porosity filled with siliceous debris; (d) botryoidal shapes whose diameter is 1–2 cm on the surface; (e) internal texture of C9, which is composed of a substrate as the nucleus inside, and outer layers composed of ferromanganese oxides; (f) smooth oolitic surface structure where siliceous debris can be seen in the cracks.
Jmse 10 01275 g002aJmse 10 01275 g002bJmse 10 01275 g002cJmse 10 01275 g002d
Jmse 10 01275 g003a 550Jmse 10 01275 g003b 550
Figure 3. (a) Disorderly arranged columns form a shape similar to dendrite; (b) banded Si-Fe-rich cements; (c) mottled structure composed of siliceous debris and ferromanganese oxides; (d) disorderly arranged columns developed into columnar structure; (e) laminar structure composed of ferromanganese oxides in Figure 3d; (f) foraminifera entered in gaps between columns in Figure 3d, and Mn-Fe rich oxides precipitated around it over time.
Figure 3. (a) Disorderly arranged columns form a shape similar to dendrite; (b) banded Si-Fe-rich cements; (c) mottled structure composed of siliceous debris and ferromanganese oxides; (d) disorderly arranged columns developed into columnar structure; (e) laminar structure composed of ferromanganese oxides in Figure 3d; (f) foraminifera entered in gaps between columns in Figure 3d, and Mn-Fe rich oxides precipitated around it over time.
Jmse 10 01275 g003aJmse 10 01275 g003b
Jmse 10 01275 g004 550
Figure 4. (a) Columnar structure composed of upright columns along the growth direction at the junction of the nucleus and ferromanganese oxides; (b) columnar structure gradually transit to mottled structure in stage II; (c) mottled structure composed of siliceous debris and Mn-rich oxides in stage II; (d) groups in gaps between columns in Figure 4a,i. Mn-rich oxides, ii. Ca-carbonate, iii. Si-Fe-rich cement; (e) Mn-rich oxides connected by banded Si-Fe-rich cement in Figure 4b; (f) groups in gaps between columns in Figure 4c,i. Mn-rich oxides, ii. organic matter where Mn- rich oxides scatter; iii. Si-Fe-rich cement.
Figure 4. (a) Columnar structure composed of upright columns along the growth direction at the junction of the nucleus and ferromanganese oxides; (b) columnar structure gradually transit to mottled structure in stage II; (c) mottled structure composed of siliceous debris and Mn-rich oxides in stage II; (d) groups in gaps between columns in Figure 4a,i. Mn-rich oxides, ii. Ca-carbonate, iii. Si-Fe-rich cement; (e) Mn-rich oxides connected by banded Si-Fe-rich cement in Figure 4b; (f) groups in gaps between columns in Figure 4c,i. Mn-rich oxides, ii. organic matter where Mn- rich oxides scatter; iii. Si-Fe-rich cement.
Jmse 10 01275 g004
Jmse 10 01275 g005a 550Jmse 10 01275 g005b 550
Figure 5. (a–c) The XRD patterns for ferromanganese deposits on the slope of Caiwei Guyot; Ver = Fe-vernadite, Ab = Al, Tod = todorokite, Qz = Quartz, Ab= Albite, Anorthite = An, Phi = Phillipsite.
Figure 5. (a–c) The XRD patterns for ferromanganese deposits on the slope of Caiwei Guyot; Ver = Fe-vernadite, Ab = Al, Tod = todorokite, Qz = Quartz, Ab= Albite, Anorthite = An, Phi = Phillipsite.
Jmse 10 01275 g005aJmse 10 01275 g005b
Jmse 10 01275 g006a 550Jmse 10 01275 g006b 550Jmse 10 01275 g006c 550
Figure 6. Geochemical profile of elements through ferromanganese deposits on Cawei Guyot. Major paleoceanographic and tectonic events are identified on the right. Blue color represents paleoceanographic and tectonic events “Caiwei Guyot crossed the current equator at about 70Ma”; green color represents paleoceanographic and tectonic events “Drake Passage and Tasmanian Passage opened”; red color represents paleoceanographic and tectonic events “Iceland-Faroe Ridge sanked, LCDW and AABW strengthened, and Panama Seaway closed”.
Figure 6. Geochemical profile of elements through ferromanganese deposits on Cawei Guyot. Major paleoceanographic and tectonic events are identified on the right. Blue color represents paleoceanographic and tectonic events “Caiwei Guyot crossed the current equator at about 70Ma”; green color represents paleoceanographic and tectonic events “Drake Passage and Tasmanian Passage opened”; red color represents paleoceanographic and tectonic events “Iceland-Faroe Ridge sanked, LCDW and AABW strengthened, and Panama Seaway closed”.
Jmse 10 01275 g006aJmse 10 01275 g006bJmse 10 01275 g006c
Jmse 10 01275 g007 550
Figure 7. PAAS shale-normalized rare earth element plots for ferromanganese deposits of Caiwei Guyot.
Figure 7. PAAS shale-normalized rare earth element plots for ferromanganese deposits of Caiwei Guyot.
Jmse 10 01275 g007
Jmse 10 01275 g008 550
Figure 8. (a) Ternary diagram for the genetic classification of ferromanganese deposits. (b) Ternary discrimination diagram for the genetic classification of ferromanganese deposits.
Figure 8. (a) Ternary diagram for the genetic classification of ferromanganese deposits. (b) Ternary discrimination diagram for the genetic classification of ferromanganese deposits.
Jmse 10 01275 g008
Jmse 10 01275 g009 550
Figure 9. Discrimination graphs of ferromanganese deposits from Caiwei Guyot. (a) CeSN/CeSN* ratios vs. Nd contents. (b) CeSN/CeSN* ratios vs. YSN/HoSN ratios.
Figure 9. Discrimination graphs of ferromanganese deposits from Caiwei Guyot. (a) CeSN/CeSN* ratios vs. Nd contents. (b) CeSN/CeSN* ratios vs. YSN/HoSN ratios.
Jmse 10 01275 g009
Table
Table 1. Location of samples from Caiwei Guyot.
Table 1. Location of samples from Caiwei Guyot.
Cruise IDWater DepthLatitude (N)Latitude (E)
HOBAB5-C93116 m15°51′10.883″155°35′15.620″
HOBAB5-C9R-61650.1 m15°51′08.672″155°29′17.412″
HOBAB5-C9R-71608.4 m15°51.16997′155°29.20822′
Table
Table 2. Geochemistry compositions of the ferromanganese crusts.
Table 2. Geochemistry compositions of the ferromanganese crusts.
SampleMn(wt%))FeAlSiMn/FeSi/AlCo/(Cu + Ni)Co/(Fe + Mn)CaPMgKNaTiGrowth RateLi (ppm)BeScV
C9R-6-121.618.21.205.771.184.811.381752.200.421.270.612.410.960.853.884.592.02441
C9R-6-220.519.41.505.751.063.830.981362.130.431.320.702.4 51.051.306.674.893.22455
C9R-6-320.819.01.505.081.093.390.751392.320.511.380.652.001.091.2411.354.814.05460
C9R-6-423.417.41.103.691.353.350.851372.660.491.280.611.841.321.284.985.633.80527
C9R-6-520.419.31.345.181.063.871.071712.020.431.360.541.761.090.897.774.583.67481
C9R-6-621.018.21.445.441.153.780.891502.150.401.370.531.761.101.109.693.632.32474
C9R-7-115.911.81.205.831.354.860.971391.920.781.180.401.920.911.257.675.469.94555
C9R-7-214.712.52.224.901.172.211.682081.860.721.320.631.791.050.643.084.707.43595
C9R-7-322.018.50.9804.841.194.961.361472.320.461.230.542.410.971.132.384.922.69577
C9R-7-422.018.41.054.531.204.311.151472.300.421.230.5221.991.111.143.485.475.43607
C9R-7-524.817.50.7003.681.415.281.401912.470.441.280.472.200.950.731.545.181.51595
C9R-7-625.217.40.6603.401.455.121.401962.500.431.240.492.170.950.700.874.110.97543
Sample leCoNiCuZnGaRbSrZrNbMoCdCsBaHfTaWTlPb
C9R-6-1696243007414376.467.47102650755.13185.160.75110210.20.7485.747.31740
C9R-6-25417443010715288.519.89101762674.52845.451.15133514.51.0083.444.81578
C9R-6-35556575916646469.539.58103766478.82846.701.08149316.31.0682.842.41727
C9R-6-45589509414856728.758.09125575879.23536.780.85189416.81.3411148.71556
C9R-6-56769534610025829.189.17112762975.82816.161.01135114.20.9578.936.01800
C9R-6-65872546911526009.719.89109061865.22906.601.08136613.60.9182.536.01661
C9R-7-1384132507045356.8615.8125462862.33363.271.61142411.30.5767.784.41412
C9R-7-2563930003574525.337.29131552746.33933.960.5810957.30.4869.966.51670
C9R-7-3596138165665569.158.20148068361.83766.680.76151912.50.7910223.71715
C9R-7-45932437579265010.19.85159680776.63846.960.96181315.90.9310929.41745
C9R-7-5809150757095588.525.51151864266.64597.190.42146311.110.8012730.21957
C9R-7-6832752017314847.914.32137156759.14296.720.3114169.900.7212733.41999
SampleBiThULaCePrNdSmEuGdTbDyYHoErTmYbLu
C9R-6-127.919.211.925571741.418038.19.9744.87.2740.41479.6126.04.2825.74.21
C9R-6-234.713.510.823575239.017234.98.8444.16.9239.91669.6927.04.4027.04.60
C9R-6-338.711.411.124884638.516935.28.6844.86.7438.61829.3926.34.3726.54.51
C9R-6-448.28.5111.724699842.418538.310.648.37.1541.720210.228.04.5727.94.70
C9R-6-530.217.912.026884043.719440.211.047.97.6943.617810.428.54.7428.14.63
C9R-6-637.816.511.223886142.218438.29.8746.07.2840.81649.7526.84.5927.24.63
C9R-7-115.211.910.724255344.119139.89.7746.27.2841.81929.7525.34.0225.53.92
C9R-7-216.321.212.023964346.620043.010.348.37.6143.31879.8525.24.0225.03.80
C9R-7-338.124.712.428077763.827457.813.665.510.457.521012.935.75.8634.95.70
C9R-7-445.520.913.230292366.428561.314.868.710.858.522713.637.46.1636.95.83
C9R-7-541.019.214.730385458.125253.613.860.79.9054.720012.734.35.6233.45.57
C9R-7-640.017.015.330987751.122748.112.455.28.7950.118011.932.45.3731.25.06
Table
Table 3. Geochemistry compositions of the ferromanganese nodule.
Table 3. Geochemistry compositions of the ferromanganese nodule.
SampleMn (wt%)FeMn/FeAlCaPCo/(Cu + Ni)Co/(Fe + Mn)KTiMgNaLi (ppm)BeScVCoNi
C9-120.49.522.141.332.130.460.79195.560.481.421.261.713.214.525.5249358514871
C9-218.59.102.031.362.040.510.73197.730.501.341.201.623.564.886.3849154575047
C9-326.015.81.650.8802.600.320.83163.050.581.321.291.992.003.863.4238868065807
C9-424.014.61.651.582.580.350.63136.060.871.151.241.883.935.053.9036652555545
C9-524.814.81.681.412.890.450.64125.380.731.171.271.913.664.963.7737049735390
SampleCuZnGaRbSrZrNbMoCdCsBaHfTaWTlPb
C9-12532.6396.974.93119548144.85197.280.2313926.240.7372.41031359
C9-224616987.605.79116850347.95486.980.2614707.540.8674.31151400
C9-324274726.603.7089844739.93435.210.19149110.41.083.795.21333
C9-428334878.066.2980247742.33185.250.25157512.10.9577.278.41204
C9-524394618.485.1780146438.93154.960.20158911.40.9477.773.31243
SampleULaCePrNdSmEuGdTbDyYHoErTmYbLu
C9-110.220387542.017337.08.8843.16.2233.11147.6219.23.0418.72.92
C9-210.020391543.317738.19.0844.16.3933.81137.6419.53.0818.92.97
C9-310.5265111047.819944.110.846.47.4740.198.48.6122.53.6221.63.35
C9-47.45229111342.017636.69.4642.76.2633.01097.1818.92.9818.02.83
C9-57.76249111344.718839.610.446.46.9136.01197.9520.63.2619.73.09
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MDPI and ACS Style

Wang, L.; Zeng, Z. The Geochemical Features and Genesis of Ferromanganese Deposits from Caiwei Guyot, Northwestern Pacific Ocean. J. Mar. Sci. Eng. 2022, 10, 1275. https://doi.org/10.3390/jmse10091275

AMA Style

Wang L, Zeng Z. The Geochemical Features and Genesis of Ferromanganese Deposits from Caiwei Guyot, Northwestern Pacific Ocean. Journal of Marine Science and Engineering. 2022; 10(9):1275. https://doi.org/10.3390/jmse10091275

Chicago/Turabian Style

Wang, Linzhang, and Zhigang Zeng. 2022. "The Geochemical Features and Genesis of Ferromanganese Deposits from Caiwei Guyot, Northwestern Pacific Ocean" Journal of Marine Science and Engineering 10, no. 9: 1275. https://doi.org/10.3390/jmse10091275

APA Style

Wang, L., & Zeng, Z. (2022). The Geochemical Features and Genesis of Ferromanganese Deposits from Caiwei Guyot, Northwestern Pacific Ocean. Journal of Marine Science and Engineering, 10(9), 1275. https://doi.org/10.3390/jmse10091275

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