JOURNAL OF RARE EARTHS http://www.paper.edu.cn

Vol. 23, No. 3, Jun. 2005, p. 323

Rare Earth Elements Compositions and Genesis of Xinhua Ξ Large2Scale Phosphorite Deposit in Western Guizhou , China Wang Min (王 敏) 1 ,2 , Sun Xiaoming (孙晓明) 1 , 3 3 , Ma Mingyang (马名扬) 2 ( 1. State Key Laboratory of Organic Geochemistry , Guangzhou Institute of Geochemistry , Chinese Academy of Scienc2 es, Guangzhou 510640, China; 2. Department of Earth Sciences , Sun Yat2Sen University , Guangzhou 510275; China ; 3. National Key Laboratory for Mineral Deposit Research , Nanjing University , Nanjing 210093 , China)

Abstract : Zhijin County in Western Guizhou is one of the most important production areas of phosphorites in China . In or2 der to investigate genesis of the phosphorites , their REE compositions were analyzed by using inductively coupled plasma emission mass spectrometry (ICP2MS) method. For comparison , phosphorites from the Lower Cambrian black rock series in Southern China , such as Zunyi in Guizhou and Zhangjiajie in Hunan Province , were also analyzed. The analytical data show that : (1) Xinhua phosphorites possess a quite high and greatly varied total rare earth elements (ΣREE) , which vary2 ing between 164. 23 × 10 - 6 and 1395. 01 × 10 - 6 with average of 642.54 × 10 - 6 , remarkable differentiation between light (LREE) and heavy rare earth elements ( HREE) , and the ΣLREEΠΣHREE ratios varying between 5. 04 and 6. 52. The ΣREE and ΣLREEΠΣHREE ratios of the Zunyi and Zhangjiajie phosphorites are 156. 69 × 10 - 6～637. 41 × 10 - 6 with av2 erage of 431175 × 10 - 6 and 3. 17～6.95 with average of 4.37 respectively; (2) All the phosphorites from Xinhua , Zunyi

and Zhangjiajie show remarkable negative Ce anomalies. Besides , the Xinhua phosphorites possess lowerδCe , which vary2

ing between 0.26 and 0.53 with average of 0.35 , while δCe of the Zunyi and Zhangjiajie phosphorites are 0. 30～0. 66 with average of 0. 47 , suggesting that all of the phosphorites are typical marine sediments deposited mainly in ancient peri2 continental seas , and the depositional position of the Xinhua phosphorite might be deeper ; (3) Most phosphorites from Xinhua , Zunyi and Zhangjiajie possess unremarkable positive Eu anomaly , and only a few of samples show obvious ones.

The δEu varies between 0. 98 and 2. 4 , suggesting that hot ( > 200 ℃) and strong reductive hydrothermal fluids might have been involved in genesis of the phosphorites ; (4) The Xinhua phosphorite is relatively depleted in HREE , and LaNΠNdN

and δY of most samples are > 1 and > 1. 5 respectively. Besides , there exists no correlation betweenδY and δCe , suggest2 ing that the phosphorite was subjected to quite strong weathering and leaching processes , and catagenesis do not greatly modify its REE compositions.

Key words : phosphorite ; Lower Cambrian black rock series; Zhijin County of Western Guizhou; rare earths CLC number : P618.7, P611 Document code :A Article ID : 1002 - 0721(2005) 03 - 0323 - 08

Marine sediment phosphorite is the main source the Sinian2Cambrian marine phosphorites and their re2 of phosphor in the world[1 ,2 ] . There exists a logical serves ranked third in China[9 ] . Main distribution ar2 space2time relation between the phosphorites in the eas of those phosphorites include Kaiyang , Wengfu , Sinian to Cambrian marine phosphorites deposits and Zhijin etc. , among which the former two areas were genesis of the Ni2Mo2PGE ore layers in the Lower systematically studied since discovering of abundant Cambrian black rock series in Southern China[1 ,3～8 ] . Acritarch fossils there[10 ,11 ] , but for the latter, al2 The research on the genesis of the phosphorites not though a primary mineralogical and petrochemical re2 only may provide evidences for insoluble mystery of search has been carried out [12 ] , there still lacks a sys2 PGE origin in the Lower Cambrian black rock series , tematic study on its geochemical characteristics and but also can provide some important geochemical infor2 genesis. In this paper , the REE compositions of phos2 mation for enigma of Sinian2Cambrian“biological ex2 phorites in Zhijin area were analyzed by using ICP2MS plosion”. Phosphorite deposits in Guizhou belong to method and compared with those from other areas in

Ξ Received date : 2004- 09- 14; revised date : 2004- 12- 01 Foundation item : Project supported by the Natural Science Foundation of China (40173025 , 49928201) , National Key Basic Research Develop2 ment Program (2002CB412610) , Trans2Century Training Program Foundation for Talents by the Ministry of Education ; Project of State Key Laboratory of Organic Geochemistry , Guangzhou Institute of Geochemistry , CASC (OGL2200301) Biography : Wang Min (1978 - ) , Female , Doctor ; Major in noble metal deposits 3 Corresponding author (E - mail : eessxm @zsu.edu.cn) 中国科技论文在线 http://www.paper.edu.cn

423 J OURNAL OF RARE EARTHS , Vol . 23 , No. 3 , J un . 2005

South China , then the genesis of the phosphorites was siltstone and sandstone , while the underlying stratum discussed primarily based on the analytical results. is the Upper Sinian light grey to grey2white siliceous [14 ] 1 Regional Geological Setting and dolomites . The ore types of the mine consist mainly of intrabioclastic phosphorites , gelatinous phosphorites Geology of Phosphorite Deposit and nodular siliceous phosohorites. Precious research Xinhua phosphorite deposit is located in the showed that major mineralogical components of the northwestern side of F1 fault , which occurred in north2 phosphorites include carbonate2fluorapatite , dolomite , western wing of Xinhua Anticline. The outcropped calcite , barite , quartz , chalcedony , illite , pyrite and strata include Upper Sinian , Lower Cambrian , Middle organic matter[12 ] . Carboniferous , Permian , Lower Triassic and Quater2 [13 ] nary strata . Located near axial portion of the Xin2 2 Samples and Analytical Method hua Anticline , the ore district is NW2SW striking , 2. 1 Samples with a length of about 20 km and a width of 0.4 to 4 km , and an area of about 32 km2 . The trending angles Most samples for this work were collected from of the most strata range from 10° to 15°. The faults in the sections 1 and 2 in Gezhongwu ore zone of Xinhua the phosphorites deposit are relatively simple and most phosphorites deposit . For the purpose of comparasion , of them are positive ones. From SW to NE , the depos2 phosphorite samples in the Lower Cambrian black rock it is divided into four ore zones , including Gaoshan , series of Zunyi in Guizhou Province and Zhangjiajie in Gezhongwu , Guohua , Jiakua2Dage ( Fig. 1 ) . Most Hunan Province were also collected. rock samples in this work were collected from On the sections of Gezhongwu ore zone , the deep Gezhongwu ore zone. There exist two phosphorus2 colored granular dolomitic bioclastic phosphorites are bearing sections in the ore district . The lower one con2 interlayered with light colored phosphorous dolomites sists of interlayers of dolomitic bioclastic phosphorite in nearly parallel , and their thickness varies greatly and phosphorous dolomites , containing abundant fos2 (Fig. 2) . The phosphorite layers become thinner and sils of microbe and small shelly fauna , and belonging thinner from NE to SW , and even thin out locally. to bottomland bioclastic sediments. The upper one is Detailed observation under the microscope dem2 composed of black phosphorous mudstones and silt2 onstrates that the mineral components of the phospho2 stones , with a bottom consisting of siliceous phospho2 rites consist mainly of 25 % to 75 % micritic apatites , rite nodules and lensoids , belonging to suspended and trace to 60 % carbonate minerals , trace to 20 % quar2 lag sediments deposited under the wide sea tide. The tzs , trace to 10 % sericites , trace to 40 % opaque or2 phosphorite deposit is located in the lower part of the ganic matters and sulfides , a few ferromanganese ox2 Lower Cambrian strata and on the ancient karst weath2 ered surface of the Upper Sinian siliceous dolomite , and is generally called as“upper phosphorite layer”in Guizhou. Its overlying stratum is the Lower Cambrian

Fig. 1 Geological map of phosphorite deposit in Xinhua of Guizhou Province. (modified after Ref. [12 , Fig. 2 Profile of Xinhua phosphorites deposit in Zhijin 13 ]) County (modified after Ref. [13]) 中国科技论文在线 http://www.paper.edu.cn

Wa ng M et al . Compositions a nd Genesis of Xinhua L arge2scale Phosphorite Deposit 523

ides and clay minerals , as well as trace chlorites , zeo2 lites , barites and plagioclases. Most micritic apatites 3 Results and Discussion occurred by replacing the bio2debris , or inlaying and 3. 1 REE compositions surrounding the fine2grained quartzs and filling the caves, with a thin2layered oolitic micritic cemented REE compositions and the PAAS2normalized structure , or in the form of gel in the phosphorites of REE distribution patterns of phosphorites of Xinhua South China. The micritic apatites were dyed by ferro2 phosphorite deposit and the Lower Cambrian black manganese oxides and appear filemot2colored and rock series in Zunyi and Zhangjiajie are presented in translucence under the single polar and complete ex2 Tables 1 and 2, Figs.3 and 4, which show that: 1. tinction under the crossed polarizer. The main carbon2 The total REE concentrations (ΣREE ) of Xinhua ate minerals are dolomites , whose proportion is phosphorites are relatively high and greatly varied , - 6 - 6 20 %～30 % in granular bioclastic phosphorites and ranging from 164. 23 × 10 to 1395. 01 × 10 and av2 - 6 higher than 50 % in phosphorous dolomites. Quartzes eraging 642154 × 10 , which is in accord with the occur in the phosphorites as micrites and fill in caves general characteristics of the Lower Cambrian phos2 [16 ] or replace the bio2debris with micritic apatites and car2 phorites or “old phosphorites” . In general , the bonate minerals , and most quartz crystals possess cor2 ΣREE are in inverse proportion to contents of carbon2 rosion edges. Sericite is usually of fine2grained and ate minerals in the phosphorites. On the contrary , the striped crystals. Ferromanganese oxides appear rufous ΣREE of Zunyi and Zhangjiajie phosphorites are rela2 - 6 to filemot under single polar and mostly distribute in tively less2varied and varying between 156. 69 × 10 - 6 the cracks or on the surface of other minerals. and 637. 41 × 10 . 2. All phosphorites are enriched in LREE while depleted in HREE, and the ΣLREEΠ 2. 2 Analytical methods ΣHREE ratios are 3117 ～ 6195. Compared with the ICP2MS analysis in this work was carried out in Zunyi and Zhangjiajie phosphorites , the fractionation ICP2MS laboratory of Department of Earth Sciences in Hongkong University. The samples are prepared as follows : 100 g powdered sample was placed in a PTFE bomb. To each sample was added 1 ml of HF (38 %)

and 0. 5 ml of HNO3 (68 %) . The bombs were then placed on a hot plate , and the solution evaporated to dryness to remove most of the silica. One milliliter of

HF and 0. 5 ml of HNO3 were then added. The sealed bombs were then placed in an electric oven and heated to 190 ℃for 12 h (overnight ) . After cooling , the bombs were then opened , 1 ml of 1μg·ml - 1 Rh solu2 tion was added as an internal standard and placed on a Fig. 3 PAAS2normalized REE distribution patterns of phospho2 hot plate (at about 150 ℃) , and the solutions evapo2 rites from Xinhua deposit . PAAS denotes Post2Archean

rated to dryness. One milliliter of HNO3 was added , Australian shale evaporated to dryness and followed by a second addit2

ion of HNO3 and evaporation to dryness. The final res2

idue was re2dissolved by adding 8 ml of 40 % HNO3 , resealing the bombs and returning them to the electric oven heated at 110 ℃for a period of 3 h. After cool2 ing , the final solution was made up to a 100 ml by ad2 dition of distilled de2ionized water. The reagent blanks were treated exactly as were the samples. The VG Plasma2Quad Excell ICP2MS has been utilized for this study. The reference used is USGS2 SDO21. Analytical precision for REE concentrations is better than < 5 %. All data were normalized by the Fig. 4 PAAS2normalized REE distribution patterns of phospho2 Post2Australian Archean Shale ( PAAS ) in this rites in Lower Cambrian black rock series from Zunyi [15 ] paper . and Zhangjiajie 中国科技论文在线 http://www.paper.edu.cn

623 JOURNAL OF RARE EARTHS, Vol. 23, No. 3, Jun. 2005

Table 1 REE compositions ( × 10 - 6)and related parameters of phosphorites in Xinhua deposit and Lower Cambrian black rock series in Southern China

Sample No. Location Lithology La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Mu 200228 Section 1 in Xinhua deposit Black massive phosphorite 386. 61 75. 34 58. 23 238. 68 43. 36 10. 98 44. 98 7. 11 44. 08 9. 70 24. 16 2. 72 15. 15 1. 78 200230 Laminated phosphorite 93. 87 57. 09 16. 28 66. 32 12. 17 2. 93 12. 66 2. 02 12. 92 2. 91 7. 33 0. 88 5. 06 0. 63 200231 Laminated phosphorite 162. 88 167. 39 49. 39 200. 54 36. 40 8. 66 38. 37 5. 96 36. 35 8. 06 19. 58 2. 21 12. 21 1. 39 200232 Deep grey massive phosphorite 77. 04 45. 25 12. 88 53. 23 9. 57 2. 23 10. 09 1. 63 10. 41 2. 40 6. 21 0. 75 4. 60 0. 58 200234 Section 2 in Xinhua deposit Deep grey massive phosphorite 306. 84 187. 55 56. 17 238. 24 43. 72 13. 72 45. 91 7. 10 42. 78 9. 34 22. 47 2. 48 13. 53 1. 60 200235 Light massive phosphorite 73. 73 49. 19 13. 76 58. 42 10. 84 3. 91 11. 09 1. 77 10. 85 2. 39 6. 05 0. 72 4. 23 0. 53 200236 Laminated phosphorite 446. 86 296. 10 74. 15 320. 64 57. 66 14. 06 59. 70 9. 14 54. 41 12. 04 28. 62 3. 06 16. 67 1. 91 200237 Black massive phosphorite 44. 92 35. 57 9. 09 38. 86 7. 70 2. 39 7. 56 1. 19 7. 27 1. 63 4. 11 0. 48 3. 06 0. 40 200202 Xintugou , Zunyi Black nodule phosphorite 39. 23 49. 30 7. 39 29. 11 5. 99 3. 19 6. 32 0. 93 6. 00 1. 36 3. 65 0. 49 3. 30 0. 43 200205 Black nodule phosphorite 111. 36 144. 16 30. 12 131. 24 28. 91 7. 87 29. 63 5. 39 38. 96 9. 79 27. 31 3. 77 24. 24 3. 22 200211 Zhongnancun , Zunyi Black massive phosphorite 76. 47 90. 16 19. 86 81. 56 17. 34 3. 68 17. 63 3. 05 20. 43 4. 72 12. 17 1. 58 10. 13 1. 30 200213 Grey massive phosphorite 142. 90 139. 76 33. 26 142. 79 28. 72 6. 65 29. 51 4. 91 31. 77 7. 26 18. 40 2. 24 13. 30 1. 67 200223 Dayuan , Zunyi Black massive phosphorite 71. 78 91. 33 12. 78 50. 05 9. 61 3. 84 9. 79 1. 58 9. 80 2. 22 5. 71 0. 69 4. 14 0. 53 200241 Daping , Zhangjiajie Black massive phosphorite 143. 49 109. 06 36. 19 153. 43 33. 73 8. 50 34. 49 6. 29 44. 39 10. 50 27. 52 3. 59 23. 24 2. 99 200243 Black massive phosphorite 124. 02 74. 44 26. 74 109. 85 22. 54 5. 90 24. 57 4. 40 31. 49 7. 63 20. 05 2. 69 17. 27 2. 25 200248 Ganziping , Zhangjiajie Black massive phosphorite 129. 12 74. 51 22. 41 91. 78 18. 27 4. 62 20. 48 3. 54 24. 48 5. 90 15. 84 2. 04 12. 64 1. 66 200251 Houping , Zhangjijie Black nodule phosphorite 88. 94 67. 14 20. 04 84. 12 17. 03 4. 02 18. 72 3. 20 21. 85 5. 10 13. 32 1. 75 10. 92 1. 42

Table 2 REE compositions ( × 10 - 6)and related parameters of phosphorites in Xinhua deposit and Lower Cambrian black rock series in Southern China Sample ΣLREEΠ ΣREE ΣLREE ΣHREE δEu δCe δY δPr La NΠNd N DyNΠSmN Sc Ba Sr Zr Y No. ΣHREE 200228 1062.86 913.2 149.68 6.10 1.15 0.26 2.19 1.36 1.36 1.29 3.025 905.175 887.826 19.097 583.034 200230 293.07 248.66 44.41 5.60 1.09 0.33 1.90 1.31 1.19 1.35 2.558 527.266 274.935 14.715 149.634 200231 749.39 625.26 124.13 5.04 1.07 0.43 2.12 1.33 0.68 1.27 3.914 419.509 729.32 19.27 467.987 200232 236.86 200.2 36.67 5.46 1.05 0.33 1.92 1.30 1.22 1.38 2.041 127.022 224.258 10.67 123.531 200234 991.45 846.24 145.21 5.83 1.42 0.33 2.07 1.29 1.08 1.25 2.523 2690.08 891.882 19.742 532.134 200235 247.48 209.85 37.63 5.58 1.65 0.35 1.87 1.27 1.06 1.27 2.383 386.23 240.503 8.914 122.598 200236 1395.01 1209.47 185.55 6.52 1.11 0.37 1.94 1.21 1.17 1.20 5.003 306.268 590.268 35.91 639.995 200237 164.23 138.53 25.7 5.39 1.45 0.40 1.73 1.23 0.97 1.20 1.891 159.175 140.152 7.14 76.684 200202 156.69 134.21 22.48 5.97 2.40 0.66 1.75 1.09 1.13 1.27 8.574 2312.74 266.083 113.028 64.3 200205 595.94 453.66 142.31 3.19 1.25 0.57 2.16 1.15 0.71 1.72 5.584 637.32 415.258 15.469 542.48 200211 360.07 289.07 71.01 4.07 0.98 0.53 1.55 1.21 0.79 1.50 6.984 1741.64 218.842 99.681 195.773 200213 603.12 494.08 109.06 4.53 1.06 0.47 1.84 1.20 0.84 1.41 2.921 1840.3 329.843 18.19 360.07 200223 273.84 239.39 34.46 6.95 1.84 0.69 2.01 1.06 1.21 1.30 4.36 585.08 533.757 24.578 120.79 200241 637.41 484.4 153.01 3.17 1.16 0.35 1.62 1.32 0.79 1.67 3.268 2252.675 1310.957 27.928 449.37 200243 473.82 363.49 110.35 3.29 1.16 0.30 1.83 1.38 0.95 1.78 2.034 612.39 711.306 9.396 365.42 200248 427.29 340.71 86.58 3.94 1.10 0.31 2.08 1.33 1.18 1.71 1.646 552.35 458.094 11.635 321.39 200251 357.56 281.29 76.28 3.69 1.04 0.37 1.42 1.30 0.89 1.63 3.847 3612.59 413.515 35.327 193.34

between LREE and HREE of Xinhua phosphorites are anomalies were also calculated by using another formula :

more remarkable. ΣLREEΠΣHREE ratios of the former δCe = 3Ce NΠ(2La N + Pr N ) . The results calculated by the range from 3.17 to 6. 95 , averaging 4. 37 , and that of the two different formulae are nearly identical. Table 2 and latter are 5104～6. 52 , averaging 5. 69. 3. Though the Fig.6(b) show that : 1. All samples possess strong negative

phosphorites in this study are depleted in HREE , whose Ce anomalies , and the δCe ranges from 0. 26 to 0. 69. The Σ - 6 - 6 HREE ranging from 22.48 × 10 to 185.55 × 10 and av2 δCe values of Xinhua phosphorites are relatively less than - 6 eraging 91.44 × 10 , which is still higher than the average those of Zunyi and Zhangjiajie phosphorites. The former - 6 value of that of PAAS (17. 5 × 10 ) . Zircon is a well2 ranges between 0. 26 and 0. 43 , averaging 0. 35 , and the known HREE enriched mineral. The low concentrations of average of the later is 0.47. 2. There exists no correlation Σ Zr shown in the Table 1 demonstrate that the high HREE betweenδCe andΣREEin Xinhua phosphorites , while an are probably not caused by zircon in the phosphorites. inconspicuous negative correlation between the two val2 3.2 Ce anomaly ues in the Zunyi and Zhangjiajie phosphorites has been recognized. δ The Ce anomalies ( Ce = 2Ce NΠ(La N + Pr N )) of the Most phosphorites are enriched in LREE. In samples are presented in Table 2. For comparison , the Ce some cases , the concentrations of La are extremely 中国科技论文在线 http://www.paper.edu.cn

Wa ng M et al . Compositions a nd Genesis of Xinhua L arge2scale Phosphorite Deposit 723

high that leads to a considerable uncertainty inδCe cal2 The former shows more remarkable negative Ce anoma2 culation[17 ] . To solve this problem , Bau et al[18 ] prop2 lies , which is in positive proportion to depth of the osed a definition of Pr anomaly , which is calculated seawater , while most of the latter appear positive or no

using an equation δPr = 2Pr NΠ( Ce N + Nd N ) . Since Ce anomalies. The main reason is that the former di2 there is no chemical reasons for creation of Pr or Nd rectly connected with the ocean , and the deposited anomalies in any geological process because both of phosphorites inherited the REE characteristics of sea2 them are positive three2valence elements , the negative water, while the latter is isolated with the ocean ,

Ce anomalies should lead to δPr >1. On the contrary , source of the phosphorites may mainly come from the surrounding continents. Comparatively speaking , all if samples show δPr = 1 , this suggests that extreme La enrichment would be the sole cause of any negative Ce of the phosphorites from South China were deposited in anomalies[18 ]. Fig. 5 shows that all phosphorite sam2 the ancient peri2continental sea , and Xinhua phospho2 ples are projected in the C2 field , indicating that the rite might be deposited in a deeper sea than others. Ce anomalies are true negative ones. 3. 3 Eu anomaly The middle rare earth elements (MREE) enrich2 ment in phosphorites may also cause the uncertainty in Eu anomalies were calculated using an equation [17 ] [19 ] δEu = 2Eu NΠ(Sm N + Gd N ) and are given in Table 2. δCe calculation . Holser (1997) proposed using a Most of the samples show unremarkable positive Eu ratio of 2Gd NΠ(La N + Lu N ) to estimate the effects of anomalies , excepting a few which show quite remark2 MREE enrichment , but the quite high La concentra2 able ones. The δEu varies between 0. 98 and 2. 40, tion and depletion in HREE including Lu in apatite ( ) will influence the accuracy of the ratios. Hence , and Fig. 6 C shows that no correlation exists between [17 ] δEu andΣREE. Shields et al introduced another ratio DyNΠSm N , be2 Negative Eu anomalies are very common in the cause the effects of MREE enrichment will lead to phosphorites from Hunan and Guizhou[21 ] . Compara2 DyNΠSm N <1. Table 1 and Fig.6 (g) show that the tively , the totally different REE compositions of the DyNΠSm N ratios of all phosphorite samples are > 1 , phosphorites in this study indicate that their REE were there exists no correlation between δCe and DyNΠSmN , not modified by diagenesis , since catagenesis will lead implying the δCe calculation was not affected remark [17 ] 2 to Ce enrichment and Eu depletion in phosphorites . ably by the MREE enrichment effects. The unobvious correlation between δEu and δCe shown The researches of Ilyin demonstrated that the in Fig. 6 (a) also confirms this conclusion. phosphorites might be deposited in sedimentary basins [17 ] [16 ,20 ] Shields et al . indicated that the high concentra2 of both peri2continental sea or epi2continental sea . tions of Ba would interfere with determination of Eu in ICP2MS analysis , and lead to positive Eu anomalies. Fortunately , the fact that nearly no correlation ( r2 =

010016) exists between δEu and Ba concentrations in our samples shown in Fig. 6 (d) implies that the high

Ba contents did not influence calculation of δEu . Mazumber et al . [22 ] found remarkable positive Eu anomalies in the Lower Cambrian phosphorites from Krol Belt in India and believed high content of barite in the phosphorites samples was the cause. The weak

correlation between δEu and Ba concentrations in our samples eliminates this possibility basically. Excepting Ce , Eu is believed to be the only va2 δ δ 3 + Fig. 5 Pr2 Ce diagram of phosphorites from Xinhua deposit lence changeable rare earth element , and Eu can be and Lower Cambrian black rock series from Zunyi and reduced to Eu2 + under certain conditions , such as δ δ Zhangjiajie. The definitions of Ce and Pr are shown strong reductive and slightly alkaline conditions. In in Table 1 normal seawater , Eu can only exist as Eu3 + . Hence , ● - phosphorites from Xinhua deposit ; ○ - phosphorites in the normal marine sediments usually show unobvious black rock series from Zunyi and Zhangjiajie ; Field A : no anomaly ; Field B1 : positive La anomaly causes apparent nega2 Eu anomalies , or unremarkable negative Eu anoma2 tive Ce anomaly; Field B2: negative La anomaly causes appar2 lies . There are two possibilities of remarkable Eu ent positive Ce anomaly ; Field C1 : real positive Ce anomaly ; anomalies to be found in normal marine sediments : 1. Field C2 : real positive Ce anomaly (modified after Ref. [18]) Involvement of volcanic debris which containing calci2 中国科技论文在线 http://www.paper.edu.cn

823 J OURNAL OF RARE EARTHS , Vol . 23 , No. 3 , J un . 2005

Fig. 6 Correlation plots of various parameters of REE and trace elements in of phosphorites from Xinhua , Zunyi and Zhangjiajie ●: Xinhua phosphorites ; ○: phosphorites in black rock series of Zunyi and Zhangjiajie

(a) δCe2δEu diagram ; (b) δCe2ΣREE diagram ; (c) δEu2ΣREE diagram ; (d) δEu2Ba diagram ; (e) δCe2δY diagram ; (f) La NΠNd N2δY

diagram ; (g) δCe2DyNΠSmN diagram

um enriched feldspars during the sedimentation , be2 might be the main cause for HREE depletion in the cause most calcium enriched feldspars show positive Eu phosphorites , because REE incline to be removed anomaly. 2. Addition of relative hot ( > 200 ℃) and from the phosphorites during weathering and leaching , strong reductive hydrothermal fluid during deposition of and HREE are easier removable in geological process2 the sediments , within which Eu2 + can stably exists[23 ] . es than LREE[17 ,26 ] . No any volcanic rocks were recognized within and To verify this idea , Shields et al . [17 ] introduced

around the Xinhua deposit , so that the first possibility definitions of La anomaly (La NΠNd N ) and Y anomaly

may be eliminated , and the only cause for the remark2 (δY) , and the later was calculated using an equation 3 + able positive Eu anomalies in some Xinhua phosphorite δY = 2YNΠ(DyN + Ho N ) , because radius of Y fits samples is probably involvement of relatively hot ( > within those of Dy3 + to Ho3 + . 200 ℃) and reductive hydrothermal fluid during sedi2 REE compositions of the original phosphorites mentation. The hydrothermal fluid is thought to be would be modified during catagenesis and weathering composed mainly of formation water or basinal hot bri2 [23 ] and leaching. The catagenesis caused enrichment of ne . In fact , systematically He2Ar isotopic studies of Ce and MREE , depletion in Eu , and gradually reduc2 fluid inclusions in pyrites clearly show that the ore2 tion of La anomaly (La NΠNd N < 1. 0) and Y anomaly forming fluids of PGE2polymetallic deposits in the Low2 (δY < 1. 5) . On the contrary,La , Gd and Yprefer to er Cambrian black rock series in Southern China were stay in phosphorites compared with other rare earth el2 mainly made up of basinal brine and seawater[24 ] . ements due to tetrad effect and gradually increase the

3. 4 HREE depletion La anomaly (La NΠNd N > 1. 0) and Y anomaly (δY > 2. 0) during weathering and leaching[17 ] . Table 2 , Most Lower Cambrian phosphorites possess geo2 [16 ,17 ] Figs. 6 (e , f) show that : 1. La NΠNd N and δY of the chemical characteristics of HREE depletion , so do the Xinhua phosphorites. Figs. 3 and 4 show that most phosphorites in this study are >1.0 and >1.5 both the phosphorites from Xinhua and other areas in respectively , implying that the main cause for HREE Southern China are of HREE depleted , and the former depletion may be weathering and leaching. 2. The rel2 δ is more remarkable. atively high ratios of La NΠNd N and Y in Xinhua phos2 Regarding the causes for HREE depletion in the phorites suggest that it might have been subjected to Lower Cambrian phosphorites , MaArthur et al . [25 ] and stronger weathering and leaching than other phospho2 [16 , 20 ] Ilyin believed this was the reflection of HREE rites. 3. There exists no correlation between δY and depletion in the Lower Cambrian seawater. But δCe in the phosphorites samples , also implying that Shields et al [17 ] argued that weathering and leaching catagenesis did not modify their REE compositions 中国科技论文在线 http://www.paper.edu.cn

Wa ng M et al . Compositions a nd Genesis of Xinhua L arge2scale Phosphorite Deposit 923

35 , while δCe of Zunyi and Zhangjiajie phosphorites are 0. 30～0. 66 , averaging 0147 , suggesting that all of the phosphorites are typical marine sediments , which were mainly deposited in ancient peri2continen2 tal seas , and depositional position of the Xinhua phos2 phorite might be deeper. 3. Most phosphorites from Xinhua , Zunyi and Zhangjiajie possess unremarkable positive Eu anoma2 lies , only a few of samples show marked ones. The

δEu values vary between 0. 98～2. 4 , suggesting that hot ( > 200 ℃) and strong reductive hydrothermal flu2 ids might have been involved in genesis of the phos2 phorites. 4. The Xinhua phosphorite is relatively depleted

in HREE, and La NΠNd N and δY of most samples are > 1 and > 1. 5. Besides , there exists no correlation Fig. 7 (LaΠYb) N2ΣREE diagram of phosphorites from Xinhua between δY and δCe , suggesting that the Xinhua phos2 deposit and the Lower Cambrian black rock series from Zunyi and Zhangjiajie (modified after Ref. [7])(the phorite was subjected to quite strong weathering and legends are same as that in Fig.6) leaching processes , and catagenesis did not greatly modify its REE compositions. greatly. 4. Existence of a certain positive correlation Acknowledgements: We wish to sincerely thank Dr. Hu

between La NΠNd N and δY demonstrates that the geo2 Ruizhong and Dr. Luo Taiyi of the Guiyang Institute of Geo2 chemical behaves of La and Yare quite similar during chemistry , Chinese Academy of Science , and Mr. Jiang Hua of weathering of phosphorites. the Mineral Resources Bureau of Zhijin County in Guizhou Province , for their kind support during our field work ; Wang 3. 5 Source of phosphor Min thanks Dr. Zhou Meifu , Mr. Qi Liang and Ms. Fu Xiao in the Department of Earth Sciences in University of Hongkong for In Fig. 7 , most of the phosphorites samples are their help in ICP2MS analysis. projected in the granite area , only a few in alkaline

basalt area. Besides , SiO22TiO2 relationships show References :

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10 - 6 , averaging 642. 54 × 10 - 6 , and remarkable dif2 [5 ] Zhang Aiyun , Wu Damao , Guo Lina , et al . Marine Black Shale Formation Geochemistry and Mineralogenetic ferentiation between light and heavy rare earth ele2 Significance [M ]. Beijing : Science Press (in Chin. ) , ments , the ΣLREEΠΣHREE ratios varying between 5. 1987. 1. 04 and 6.52. The ΣREE and ΣLREEΠΣHREE ratios [6 ] Li Shengrong. The study on geochemistry of gold and of the Zunyi and Zhangjiajie phosphorites are 156. 69 silver and platinum in black rock series of Lower Cam2 × - 6 ～ × - 6 × - 6 brian in Hunan and Guizhou [ D ]. Dissertation of post 10 637. 41 10 (averaging 431175 10 ) PhD. The Institute of Geochemistry of Chinese Academic and 3. 17～6. 95 (averaging 4. 37) respectively. of Science (in Chin. ) , 1994. 1.

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3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3

Variation of REE in Process of Smelting of Copper Ores in the Ancient Times Wei Guofeng1 3 , Qin Ying1 , Luo Feng2 , Qu Yi 3 , Wang Changsui 1 ( 1. Department of History of Science and Archaeometry , University of Science and Technology of China , Hefei 230026 , China ; 2. Ningxia Institute of Cultural Relics and Archaeology , Yinchuan 7500003 , China ; 3. Huangshi Museum , Huangshi 435000 , China) Abstract : Variation of REE in the process of smelting that REE are concentrated in slag mainly during the of copper ores and their potential application in ar2 smelting process , and total content of REE in the cop2 chaeo2metallurgy were investigated. All samples of per ingots is very low. With low total content of REE copper ores , slag and copper ingots are from the an2 in the copper ingots , it is almost impossible to find out cient sites of mining and smelting , which include provenance of the ancient bronze wares through REE. Tonglüshan site in Hubei province , Zhaobishan site in Nevertheless , this research finds that REE distribution Ningxia municipality , Zhongtiaoshan site in Shanxi pattern of the slag is possible to be used to ascertain province and Dajing site in Inner Mongolia municipali2 smelting technology of the copper ores adopted by the ty autonomous region. REE analysis was conducted by ancient smelters and export route of the ancient copper Inductively Coupled Plasma Atomic Emission Spec2 ores. trometer (ICP2AES) . The result of this study reveals Key words : bronze wares ; copper ores ; slag ; provenance ; rare earths (SeeJ. Chin. RE. Soc. (in Chin. ) , 2005 , 23 (3) : 357 for full text)

© 1995-2005 Tsinghua Tongfang Optical Disc Co., Ltd. All rights reserved. 中国科技论文在线 http://www.paper.edu.cn

323 Rare Earth Elements Compositions and Genesis of Xinhua Large2Scale Phospho2 rite Deposit in Western Guizhou , China

(LaΠYb) N2ΣREE diagram of phos2 3 Wang Min , Sun Xiaoming , Ma Mingy2 phorites from Xinhua deposit and ang the Lower Cambrian black rock se2 ries from Zunyi and Zhangjiajie (modified after Ref. [7 ])( the ) J . Rare Earths , 2005, 23: 323～330 legends are same as that in Fig.6

331 Upconversion Emission in Er3 + Doped Nov2 el Bismuthate Glass

Sun Hongtao 3 , Dai Shixun , Xu Shiqing , Upconversion fluorescence spectrum of Zhang Liyan , Chen B aoyu , Hu Lili 3 + Er 2doped S10P60B30 glass under 975 nm excitation

J . Rare Earths , 2005, 23: 331～335

336 Synthesis and Characterization of Quaterna2

ry Complex of Sm2CH3C (CH2OH) 2COOH2 Phen

Xi Peng , Wang Lianjun , Huang Chemical structure of complex Xiangan 3

J . Rare Earths , 2005, 23: 336～339 340 Preparation and Methanol Decomposition Activity of Ruthenium Supported Ce2

Doped Mesoporous TiO2 Oxide

Zhang Xuehong , Luo Laitao 3 , Duan Arrhenius plot of rate of metha2 Zhanhui nol decomposition over rutheni2 um supported catalysts

J . Rare Earths , 2005, 23: 340～344

345 Phase Constitution in Mixed Gd2O3 and

B4C by Sintering at High Temperature

Wu Wenyuan 3 , Xu Jingyu , Bian Xue , XRD patterns of products sin2 Hu Guangyong Sun Shuchen Tu Gan , , 2 tered at 1470 ℃for (1) 2 h , feng (2) 4 h and (3) 6 h

J . Rare Earths , 2005, 23: 345～348