海洋地质与环境重点实验室知识库

西太平洋麦哲伦海山区是重要的铁锰结壳勘探合同区，具有极大的资源潜力。本文对麦哲伦海山区Kocebu海山的11个铁锰结壳表层样品（<1 mm）进行形态学、矿物学和地球化学研究，利用X射线衍射（XRD）、电感耦合等离子体发射光谱和质谱（ICP-AES/MS）等测试技术分析了结壳矿物组成、主微量元素和稀土元素含量，探讨其元素组成特征、生长速率特征、成因和物质来源，运用数学统计方法分析中西太平洋结壳生长的环境控制因素，进一步揭示了影响Kocebu海山结壳生长速率与稀土元素富集的环境因素和作用机制，初步评价了该海山铁锰结壳的资源潜力。

结果表明：Kocebu海山铁锰结壳呈砾状产出，厚度在3~12 cm，基岩以蚀变玄武岩为主。表层样品发育较致密纹层状构造，矿物组分以水羟锰矿为主，铁相矿物为无定形针铁矿，含少量石英。主要金属元素Mn、Fe、Co、Ni、Cu和Zn平均含量分别为21.7 %、16.0 %、0.62 %、0.54 %、0.05 %和0.06 %，Mn/Fe比值平均为1.4。∑REY平均含量为1 366 µg/g，低于前人在麦哲伦海山区以及马尔库斯－威克海山区的分析结果，轻重稀土平均比值为3.73，总体呈轻稀土富集特征，北美页岩标准化图解显示Ce正异常（平均值为1.45）和Y负异常（平均值为0.51）。结壳的生长速率平均值为0.96 mm/Myr，高于中西太平洋同水深样品。样品的矿物组成、主微量和稀土元素特征、生长速率特征、成因图解和元素分配系数均表明该海山结壳属于水成成因。

中西太平洋海区远离陆地，碎屑输入较少，最低含氧带（OMZ）发育，底层流活动较为强烈，海表面营养盐与叶绿素a含量偏低，属低营养盐、低生产力区域。对收集的中西太平洋5个海山区117件表层铁锰结壳样品23种元素数据进行统计分析，发现该海区结壳组成变化较大；Q型因子分析的4个因子方差累计贡献率为98.32 %，分别代表锰相、铁相、碎屑相与生源组分，因子载荷分别与海水中溶解氧含量、碳酸盐离子含量、风尘输入存在明显相关性，表明上述条件是控制该区结壳生长的关键环境因素。

碎屑矿物含量、最低含氧带强度和构造位置对铁锰结壳生长速率具有显著影响，Kocebu海山表层结壳生长速率高于中西太平洋相同水深样品，主要归因于该海山区海水中较弱的最低含氧带强度，而未受碎屑矿物与热液输入的影响。碎屑矿物稀释、海水中REY含量和溶解氧含量是影响表层结壳中REY富集的关键因素，Kocebu海山表层结壳中ΣREY含量偏低与采样水深较浅导致的海水稀土元素含量和溶解氧含量较低密切相关，未受碎屑矿物的稀释作用影响。

与太平洋主要结壳区（PCZ）相比，Kocebu海山铁锰结壳Ni元素品位较高，Mn、Fe、Co、Cu、Zn元素和关键金属元素品位相当，Ce元素品位较低，粗略估计每吨矿石的价值约1 117美元，具有一定资源潜力和经济价值，已达到相应开采标准。目前采集到的结壳样品数量较少，水深范围不够广泛，尚不足以进行结壳资源量定量估算或远景区划定，这还需要后续调查研究来进一步完善。

浅水结壳或最低含氧带强度较高海区的结壳具有较低的生长速率，关键金属元素潜力较大；深水结壳或海水中REY含量较高海区的结壳具有更高的REY资源价值。在开展铁锰结壳地球化学特征研究和资源勘探评价时应充分考虑采样点水深的分布范围，而采用局部水深范围样品的分析结果可能会对评价认识带来较大偏差。

The Magellan Seamounts in the Western Pacific is an important contract area for the exploration of ferromanganese crusts, contains abundant potential resources. In this paper, the morphology, mineralogy, geochemistry of 11 top surface ferromanganese crust samples (<1 mm) collected from the Kocebu Guyot were studied by using X-ray diffraction (XRD), inductively coupled plasma-mass spectrometry and atomic emission spectroscopy (ICP-MS, ICP-AES). We analyzed the chemical composition, growth rate characteristics, genesis type of the samples. The oceanographic factors that control the growth of the crusts from Western and Central Pacific were discussed by mathematical statistical methods. Comparative study revealed the environmental influences and mechanism that affect the growth rate and enrichment of rare earth elements of Kocebu crusts. The resource potential of crusts was also evaluated preliminarily.

The results show that the crusts were primarily formed by plate-like shape with thickness between 3~12 cm and the substrate rocks are mainly alteration basalts. Laminar structure was observed in the top surface crust layer. XRD patterns show that the mineral component is mainly vernadite, amorphous goethite, and a small amount of quartz. The average contents of the main metal elements Mn, Fe, Co, Ni, Cu, and Zn are 21.7 %, 16.0 %, 0.62 %, 0.54 %, 0.05 %, 0.06 %, respectively, and the average Mn/Fe ratio is 1.4. The average REY(rare earth elements and yttrium) abundance(∑REY) of the crusts is 1 366 µg/g, which is lower than the previous analysis results in Magellan Seamounts and Marcus-Wake Seamounts. The crusts show enriched LREE (average LREE/HREE ratio 3.73), strongly positive Ce anomalies (mean value 1.45) and negative Y anomalies (mean value 0.51). The average growth rate is 0.96 mm/Myr, which is higher than that of the Western and Central Pacific samples at the same water depth. The mineral component, chemical composition, growth rate characteristics, genetic classification diagram, seawater-crust partition coefficient indicate that all crusts are hydrogenetic origin.

The Western and Central Pacific is typical low-nutrient, low-chlorophyll-A region of the ocean, far away from the land and characterized by minor detrital input, well-developed oxygen minimum zone (OMZ), relatively strong bottom current activity, low content of nutrient and chlorophyll a in surface water. The Fe-Mn crust samples growing in this area are situated within a variety of oceanographic environments. Statistical analysis methods were employed to determine statistically variance in major and trace element concentrations for 117 Fe-Mn crust samples from 5 different seamount chains along this area from literature. The chemical composition for 23 elements in the Fe-Mn crusts show a large variation, four factors produced by Q-mode factor analysis account for 98.32 % of the variance and is interpreted to represent elements associated with Mn oxide phase, Fe oxyhydroxide phase, debris phase and biogenic phase, respectively. The factor loadings are correlated or anticorrelated with dissolved oxygen concentration, carbonate ion concentration and detrital input in seawater, suggesting these primary parameters as the dominant controlling factor for Fe-Mn crust components in this area.

Detrital input, OMZ strength and tectonic position have significant effects on the growth rate of Fe-Mn crusts. The growth rate of surface layer Kocebu crusts is higher than that of other samples at the same water depth from Western and Central Pacific, which is mainly due to the higher OMZ strength, without being affected by detrital minerals and hydrothermal input. Detrital mineral dilution, REY abundance and dissolved oxygen content in seawater are the key factors that affect the REY abundance in surface layer crusts. The low ΣREY in surface layer Kocebu crusts is related to the sampling water depth and affected by lower REY and oxygen content in overlaying water-column, but not observably diluted by detrital minerals.

Comparison of grades between Kocebu crusts and PCZ (Pacific Prime Crust Zone) crusts are presented for elements of economic interest. Kocebu crusts have a higher grade for Ni, and a lower grade for Ce than PCZ crusts. Otherwise, concentrations for Mn, Fe, Co, Cu, Zn, and critical metals are roughly comparable between them. The value of the contained metal in one ton of Kocebu crusts is about $1 117 USD, confirm its resource potential and economic value. Kocebu crusts have reached the mining standard. However, the deficient sample amounts and limited water depth by far are still insufficient for quantitative estimation of crust resources or define regions of interest for Fe-Mn crust exploration. Further investigation and research are needed for exploration and mining.

Crusts grown in shallow waters or sea areas with higher OMZ intensity have a lower growth rate and a greater potential for critical metals. The crusts at deeper permissive depth and grown in seawater with higher REY concentrations may have higher REY abundance. These inferences need to be verified by further investigation and analysis. Geochemistry research, resource exploration and evaluation of Fe-Mn crusts should take the influence of water depth into further consideration, the analysis of samples from limited water depth may cause large deviations in the research results.

第1章 引言... 1

1.1 研究背景与意义... 1

1.2 研究现状... 2

1.3 存在问题... 10

1.4 研究内容与研究方法... 10

第2章 研究区地质背景... 11

2.1 麦哲伦海山区... 11

2.2 Kocebu海山... 11

第3章 材料与方法... 13

3.1 样品采集... 13

3.2 数据收集... 14

3.3 分析方法... 15

第4章 铁锰结壳形态学与矿物学特征... 17

4.1 样品描述与构造特征... 17

4.2 矿物学特征... 19

第5章 铁锰结壳地球化学特征... 20

5.1 主微量元素地球化学特征... 20

5.2 稀土元素地球化学特征... 21

5.2.1 含量特征... 21

5.2.2 标准化图解... 24

5.3 生长速率... 25

5.4 成因与物质来源... 26

5.4.1 成因机制... 26

5.4.2 物质来源... 29

第6章 铁锰结壳成矿的环境控制因素... 32

6.1 中西太平洋铁锰结壳成矿特征及其成矿控制因素... 32

6.1.1 海洋环境特征... 32

6.1.2 铁锰结壳组成变化... 39

6.1.3 结壳组成的环境控制因素... 43

6.2 Kocebu海山铁锰结壳成矿控制因素... 50

6.2.1 生长速率特征的控制因素... 50

6.2.2 稀土元素特征的控制因素... 56

第7章 铁锰结壳资源潜力... 62

7.1 Kocebu海山铁锰结壳资源潜力分析... 62

7.2 海洋环境调查对结壳资源勘查的意义... 64

第8章 结论... 65

参考文献... 67

致 谢... 85

作者简历及攻读学位期间发表的学术论文与研究成果.... 86