东太平洋CC区深海稀土资源潜力:沉积物地球化学标志

doi:10.3969/j.issn.1001-909X.2023.04.005

摘要/Abstract

摘要：

深海沉积物蕴藏着丰富的稀土资源,富稀土沉积物的空间分布特征、稀土赋存形态与富集机制是近年来研究的热点。东太平洋克拉里昂—克里帕顿断裂带(简称CC区)是全球海底最重要的多金属结核成矿带,但对该区域沉积物中伴生富集的稀土资源分布特征和资源潜力认识尚不清楚。该文对CC区西部125个站位沉积物全岩地球化学成分(728组主量元素和625组微量元素)进行了分析,结果表明研究区沉积物中显著富集MnO和P₂O₅,总稀土含量(∑REY)与P₂O₅、CaO含量和Ce负异常存在较好的空间正相关性,生物成因钙磷灰石是稀土元素的主要赋存矿物。研究区沉积物∑REY平均值为470±202 μg/g,部分区域∑REY含量高于富稀土沉积物标准(∑REY>700 μg/g),表明研究区具有一定的稀土资源潜力。研究区富稀土沉积物主要分布在以丘陵地形为主的北部,南部海盆区的沉积物稀土含量相对较低。研究区地貌特征差异影响了区域沉积速率和钙磷灰石水动力分选,导致研究区稀土资源分布的南北分带性。

关键词: 深海沉积物, 稀土元素, 钙磷灰石, 资源潜力, 东太平洋CC区

Abstract:

Deep-sea sediments have attracted much more attention in recent years because of their potential resources for rare earth elements plus Yttrium (REY). However, the host minerals and enrichment mechanism of REY in deep-sea sediments, and the spatial distribution characteristics and metallogenic regularity of the REY-rich sediments are still unclear. The Clarion-Clipperton Fracture Zone (CCZ) in the East Pacific is the most important polymetallic nodule metallogenic belt, and its potential of REY resources has not been well evaluated. In this study, the whole-rock geochemistry (728 groups of major elements and 625 groups of trace elements) of sediments from 125 stations in the west CCZ over an area of 27 800 km² was analyzed. The results show that the sediments in the study area are significantly rich in MnO, P₂O₅ and REY than those from Australian shales and global subducting sediments. Spatially, ∑REY has a positive correlation with P₂O₅, CaO, and Ce negative anomalies, indicating that calcium apatite is the main host minerals of REY. The average value of ∑REY in the sediments over the study area is 470±202 μg/g, some samples meet the criteria of REY-rich sediments (∑REY>700 μg/g), indicating that the study area has a certain potential of REY resources. Spatial interpolation analysis shows that REY-rich sediments are mainly distributed in the northern area characterized by hilly terrain, while they are poorer in the southern basin with flat terrain. The difference of geomorphology in the study area affects the regional deposition rate and the hydrodynamic sorting of calcium apatite, leading to the north-south zoning of REY resources distribution in the study area.

Key words: deep-sea sediments, rare earth elements and Y (REY), calcium apatite, resource potential, Clarion-Clipperton Fracture Zone (CCZ)

中图分类号:

P736.2

邬欣然, 董彦辉, 李正刚, 王浩, 章伟艳, 李怀明, 李小虎, 初凤友. 东太平洋CC区深海稀土资源潜力:沉积物地球化学标志[J]. 海洋学研究, 2023, 41(4): 46-56.

WU Xinran, DONG Yanhui, LI Zhenggang, WANG Hao, ZHANG Weiyan, LI Huaiming, LI Xiaohu, CHU Fengyou. Deep-sea rare earth resource potential in the Eastern Pacific Clarion-Clipperton Fracture Zone: Constraint from sediment geochemistry[J]. Journal of Marine Sciences, 2023, 41(4): 46-56.

图/表 9

图1 研究区区域位置(a)及地形图(b) (图a指示了东太平洋克拉里昂—克里帕顿断裂带(CC区)的区域位置,其中黑色线条为断裂带,白色线条为洋壳年龄等时线[14],红色方框代表研究区在CC区的地理位置。图b中白色虚线为研究区南北部界线。)

Fig.1 Tectonic location (a) and topography (b) of the study area (Fig.a indicates the regional location of the Clarion—Clipperton Fracture Zone (CCZ) in the East Pacific Ocean, where the black line is the fracture zone, the white lines are the oceanic crust age isochron[14], and the red box represents the geographical location of the study area. The white dash line in fig.b indicates the boundary that separates study area into north and south parts. )

表1 Statistical results of major element compositions of sediments in the study area 单位:%

Tab.1

类别	SiO₂	Al₂O₃	CaO	TiO₂	FeO_t	MnO	MgO	Na₂O	K₂O	P₂O₅
最大值	80.01	16.53	6.47	0.88	9.28	6.16	6.29	13.23	3.91	2.62
最小值	52.21	5.30	1.06	0.20	2.54	0.10	2.08	3.56	1.07	0.26
平均值	60.36	14.78	1.92	0.75	7.62	0.91	3.92	6.16	2.99	0.60
标准差	2.55	1.22	0.78	0.09	0.59	0.54	0.39	0.94	0.30	0.51
变异系数	0.04	0.08	0.41	0.12	0.08	0.59	0.10	0.15	0.10	0.86
GLOSS	58.57	11.91	5.95	0.62	5.21	0.32	2.48	2.43	2.04	0.19
PAAS	65.89	15.17	4.19	0.50	4.49	0.07	2.20	3.89	2.80	0.20

图2 研究区沉积物主量元素配分模式图

Fig.2 Major element distribution pattern of sediments in the study area

图3 研究区沉积物稀土元素配分模式图 (数据来源:西南太平洋底层海水数据来自文献[20],生物成因钙磷灰石和钙十字沸石数据来自文献[16],CC区结核数据来自文献[21],中国黄土数据来自文献[22]。)

Fig.3 REY distribution pattern of sediments in the study area (Data sources: bottom seawater of Southwest Pacific Ocean data are from reference [20], biogenic calcium apatite and calcium zeolite data are from referende [16], CCZ nodules data are from reference [21], Chinese loess data are from reference [22].)

图4 研究区沉积物主量元素空间分布图 (底图为灰阶地形图。)

Fig.4 Spatial distribution of major elements of sediments in the study area (The base map is a gray-scale topographic map.)

图5 研究区沉积物∑REY含量及相关地球化学指标空间分布特征 (底图为灰阶地形图。)

Fig.5 Spatial distribution of ∑REY and other related geochemical index of sediments in the study area (The base map is a gray-scale topographic map.)

图6 ∑REY与P2O5(a)、MnO(b)的协变关系图

Fig.6 Covariant relationship of ∑REY with P2O5 (a) and MnO (b)

图7 CC区西部∑REY含量分布柱状图及太平洋不同区域沉积物∑REY含量累计频率分布图

Fig.7 Histogram of ∑REY content distribution in the western CCZ and cumulative frequency of ∑REY content in sediments from different regions of the Pacific Ocean

图8 研究区沉积物与太平洋富稀土沉积物∑REY配分模式对比图

Fig.8 Comparison of ∑REY distribution patterns between the studied sediments and the Pacific REY-rich sediments

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