Enrichment Mechanism of REY and Geochemical Characteristics of REY-Rich Pelagic Clay from the Central Pacific
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摘要: 深海沉积物中的稀土资源是一种新发现的、潜在的海底稀土资源.对太平洋中部重力活塞取样获得的90个深海粘土样品的矿物组分、常量和稀土化学分析结果进行了系统分析，并与中北太平洋以及西北太平洋南鸟岛附近海域深海沉积物稀土元素地球化学特征进行了对比.研究结果表明：太平洋中部深海粘土以富含沸石、富P及富REY为特征，其碎屑矿物中含有较多的鱼牙骨，其P2O5与CaO之间、P2O5、CaO与∑REY之间呈良好的正相关关系；其稀土分布模式表现为明显的Ce负异常、一定程度的重稀土元素富集和Y正异常.太平洋中部深海粘土REY富集的主要原因是深海粘土中含有过量的磷酸盐组分，推测过量的磷酸盐组分是由于深海粘土中鱼牙骨碎屑的加入引起的.在北太平洋海域，未受到热液活动影响的条件下，富REY的深海沉积物的稀土元素富集机制具有统一性和普遍性，可以归纳为深海沉积物中高REY磷酸盐的混入作用.Abstract: REE resources from deep-sea sediments is a kind of newly discovered and latent REE resources deposited on the ocean floor. Mineral component, major element and rare earth element analysis of 90 pelagic clay samples by piston core from the central Pacific have been conducted and compared with the geochemical chemistry of pelagic sediments from the central North Pacifc and Minami-Torishima area in the western North Pacific in this study. The results show that the pelagic clay from the central Pacific is rich in phillipsite, P, and REY, and significant fish teeth debris are contained in detrital component of pelagic clay; CaO and P2O5, CaO, P2O5 and ∑REY are positively correlated, and characterized by clear Ce negative anomaly and certain HREE enrichment and Y positive anomaly in REE distribution. The REY enrichment of pelagic clay from the central Pacific is mainly caused by excess phosphate component which may have resulted from the fish teeth debris mixed in the pelagic clay. The REY enrichment mechanism of REY-rich pelagic sediments in the North Pacific with no hydrothermal effect shows uniformity and universality, which can be attributed to the admixture of high-REY phosphate in the pelagic clay.
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Key words:
- central Pacific /
- pelagic clay /
- sediment /
- REY-rich deep-sea mud /
- phosphate /
- geochemistry
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图 2 太平洋中部深海粘土中的沸石晶体
单偏光×250，样品号REUL001-23，视域中沸石含量65%，可见少量微结核
Fig. 2. The phillipsite crystal in the pelagic clay from the central Pacific
图 3 太平洋中部深海粘土中的鱼牙骨碎屑
样品号REUL001-23，视域中主要碎屑矿物有沸石、鱼牙骨与微结核
Fig. 3. The fish teeth debris in the pelagic clay from the central Pacific
图 4 太平洋中部深海粘土的稀土元素分布模式
图中不同区域的稀土含量取值范围与表 1相对应
Fig. 4. Distribution pattern of REE of the pelagic clay from the central Pacific
图 5 太平洋中部深海粘土主要元素与REY之间的关系
数据来源参见表 1
Fig. 5. The content of main element versus REY of the pelagic clay from the central Pacific
表 1 太平洋中部深海粘土的常量元素(%)、稀土元素(10-6)及特征参数结果统计
Table 1. Statistics of the content of major element (%), REE(10-6) and REE parameters of the pelagic clay from the central Pacific
区域 太平洋中部① 中北太平洋② 中北太平洋③ 最小值 最大值 平均值 最小值 最大值 平均值 最小值 最大值 平均值 SiO2 45.88 55.69 50.14 23.66 71.20 50.30 2.72 81.33 51.28 TiO2 0.31 0.77 0.56 0.12 1.82 0.52 0.01 3.12 0.41 Al2O3 11.06 16.24 14.54 2.98 21.00 12.50 0.22 21.55 7.88 Fe2O3 3.92 9.13 6.49 2.36 33.10 10.00 0.12 33.76 5.41 MnO 0.54 1.97 1.33 0.04 7.57 1.85 0.04 11.76 0.75 MgO 2.24 4.7 3.22 1.44 6.69 3.52 0.27 10.70 2.46 CaO 1.39 6.99 3.12 0.77 4.15 2.08 0.39 68.43 14.48 Na2O 3.99 7.75 5.46 - - - - - - K2O 2.34 4.31 3.36 0.89 5.37 3.02 0.01 5.54 1.57 P2O5 0.45 4.38 1.70 0.13 2.25 0.83 0.04 3.31 0.47 La 64.10 344.00 156.62 33.28 175.22 94.79 5.31 209.68 44.37 Ce 56.60 136.00 100.68 23.32 190.60 95.26 1.69 126.20 41.83 Pr 17.40 60.50 37.30 10.00 51.09 28.84 1.28 52.74 12.58 Nd 77.00 272.00 168.80 33.86 212.97 115.44 5.31 193.22 51.66 Sm 17.10 60.20 37.68 8.18 50.01 27.61 1.21 45.30 11.84 Eu 4.19 12.90 8.16 1.82 12.43 6.73 0.26 11.42 2.92 Gd 18.10 65.30 40.42 6.76 56.46 28.97 1.43 46.82 12.96 Tb 2.96 11.00 6.74 1.07 8.43 4.38 0.23 7.37 1.94 Dy 16.90 65.70 39.49 6.36 52.56 26.61 1.51 45.71 11.99 Ho 3.67 15.20 9.02 1.26 10.76 5.30 0.32 9.19 2.43 Er 9.71 40.10 24.08 3.62 30.41 14.85 0.94 25.52 6.91 Tm 1.33 5.80 3.41 0.52 4.14 2.05 0.14 3.54 0.96 Yb 8.48 34.90 20.72 3.46 25.83 12.87 0.88 21.89 6.12 Lu 1.27 5.25 3.15 0.54 3.93 1.93 0.13 3.13 0.92 Y 92.90 626.00 334.81 31.84 329.84 144.37 8.20 249.31 68.28 ∑REY 430.91 1 748.77 991.07 201.52 1 132.54 610.01 31.80 944.61 277.74 δCe 0.19 0.67 0.35 0.17 1.34 0.46 0.10 1.73 0.45 δEu 0.91 1.13 0.97 0.95 1.18 1.09 0.86 1.53 1.08 LaN/YbN 0.30 1.08 0.73 0.53 1.17 0.76 0.43 1.36 0.76 YN/HoN 0.97 1.67 1.37 0.84 1.21 1.03 0.44 1.51 1.07 注：①本次研究的太平洋中部深海粘土90个样品，由广州海洋地质调查局实验测试所分析；②中北太平洋深海粘土284个样品；③中北太平洋其他类型和未知类型沉积物706个样品(据 Kato et al., 2011 )；稀土参数相对北美页岩计算据Gromet et al.(1984) .
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表 2 典型的太平洋深海粘土及磷灰石的常量元素(%)、稀土元素含量(10-6)及稀土参数
Table 2. Content of major element (%), REE(10-6) and REE parameters of Pacific pelagic clay and apatite
类型 太平洋深海粘土① 太平洋深海粘土② 高REY磷灰石③ 低REY磷灰石③ SiO2 53.50 54.90 2.05 1.32 TiO2 0.77 0.78 0.05 0.02 Al2O3 15.90 16.60 0.53 0.35 Fe2O3 9.30 7.70 0.42 0.32 MnO 0.87 0.56 0.09 0.06 MgO 3.50 3.40 0.54 0.25 CaO 1.40 0.70 44.70 44.70 Na2O 3.80 1.30 1.02 1.26 K2O 3.00 2.70 0.11 0.06 P2O5 0.34 0.25 27.32 31.21 La 42.00 - 3 100.00 270.00 Ce 101.00 - 1 200.00 110.00 Pr 10.00 - 900.00 71.00 Nd 43.00 - 4 000.00 320.00 Sm 8.35 - 920.00 75.00 Eu 1.85 - 230.00 19.00 Gd 8.30 - 1 100.00 92.00 Tb 1.42 - 170 16 Dy 7.40 - 1 000.00 100.00 Ho 1.50 - 210.00 23.00 Er 4.10 - 590.00 72.00 Tm 0.57 - 80.00 11.00 Yb 3.82 - 500.00 77.00 Lu 0.55 - 77.00 13.00 Y 40.00 - 6 800.00 760.00 ∑REY 273.86 - 20 877.00 2 029.00 δCe 1.15 - 0.17 0.19 δEu 1.02 - 1.04 1.04 LaN/YbN 1.10 - 0.62 0.35 YN/HoN 1.03 - 1.25 1.27 注：①据Li and Schoonmaker, 2003；②据 Bischoff et al., 1979 ；③据Kon et al., 2014 ；稀土参数相对北美页岩计算据Gromet et al., 1984 .
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