The Analytical Fingerprint of conflict minerals (TTT) Focus on coltan (tantalum) ores.

Transcription

1 The Analytical Fingerprint of conflict minerals (TTT) Focus on coltan (tantalum) ores. Dr. Frank Melcher for the AFP working group of the BGR: T. Graupner, M. Sitnikova, T. Oberthür, F. Henjes-Kunst, H.-E. Gäbler, S. Goldmann and C. Savu-Krohn, G. Rantitsch (MU Leoben), A. Gerdes (U Frankfurt), H. Braetz (U Erlangen), S. Dewaele (RMCA) Tervuren, Dec.02, 2010

2 AFP a method to fingerprint the origin of conflict minerals Tantalum / coltan The basics of the fingerprint: mineralogy and chemical composition of coltan Tantalum in Africa Methods to fingerprint tantalum ores How does it work? Tin (and tungsten) Summary and Outlook

3 Tantalum ore/ coltan

4 Buranga Ruhanga Nyarigamba Gatumba district, Rwanda Coltan & tin mining in Africa

5 Coltan: trade name, used in Central Africa for tantalum niobium ores and concentrates, mainly columbite tantalite (Fe,Mn)(Nb,Ta) 2 O Tantalum mine production in Africa Coltan boom Mozambique? Tantalum [t] Congo, DR Rwanda Zimbabwe?? Burundi Nigeria Ethiopia Namibia Uganda Source: USGS, BGR data base???

6 Tantalum ores: in concentric, zoned rare-metal pegmatites Regional zoning patterns of rare-metal pegmatites Nb>Ta Ta>Nb CGM = columbite-tantalitegroup minerals GSWA, Mineral Resources Bulletin 22 (2004) (Fe,Mn)(Nb,Ta) 2 O 6

7 Behaviour of tantalum-niobium minerals in pegmatites Columbite-Fe Fractionation Kibeke Pangi, DRC CGM chemistry: variation within deposit variation within single crystals fractionation trends

8 Coltan - Mineralogy Columbite-Tantalite (CGM) (Fe,Mn)(Ta,Nb) 2 O 6 orh Magnocolumbite Mg(Nb,Ta) 2 O 6 orh Tapiolite series (Fe,Mn)(Ta,Nb) 2 O 6 tetr Ixiolite group (Ta,Nb,Sn,Fe,Ti) 4 O 8 orh Wodginite group (Mn,Sn,Fe,Ti)Ta 2 O 6 mcl Stibiotantalite Sb(Ta,Nb)O 4 orh Bismutotantalite Bi(Ta,Nb)O 4 orh Pyrochlore group A 1-2 B 2 O 6 (O,OH,F) cub A = Ca, K, Ba, Y, Ce, Pb, U, Sr, Cs, Na, Sb, Bi, Th B = Ta, Nb, Ti, Sn, Fe, W (microlite) Euxenite (Y,REE,U,Pb,Ca)(Nb,Ta,Ti) 2 (O,OH) 6 Strüverite, Ilmenorutile (Ta,Nb,Fe,Ti)O 2 and many more

9 Important Tantalum Provinces in Africa ) Kibaran 2) Ituri 3) Alto Ligonha 4) Adola Belt 5) Nigeria ) Damara 7) Namaqualand 8) West Africa 7 9) Egypt 10) Zimbabwe

10 DRC > 1900 Ma Kibaran ca Ma Uganda Rwanda Burundi Ituri Lueshe Central African coltan provinces Coltan in Kibaran (ca Ma) and Archean to Paleoproterozoic pegmatites (>2000 Ma) Kibaran DRC Kivu Maniema Katanga Ituri Rwanda Burundi Uganda Niobium in younger carbonatites

11 Ituri 100*Ta/(Ta+Nb) *Mn/(Mn+Fe) Ituri Ituri province DRC-CAR craton, northern DR Congo Investigated: Enehe, Mambasa, Lubero artisanal production Model ages: Ma Mineralogy: columbite-(fe), tantalite-(fe), tapiolite, (Pb-U-)microlite Cassiterite, wolframite were mined in the area Geochemistry of CGM high Ti, W, Zr, Hf, U, Th, Pb, As, Mg, Sc, Y, REE low Sn REE: variable slopes, moderate negative Eu anomalies (Eu* Md = 3.5) Sample/CI ,1 0,01 La Ce Pr Nd Sm Eu Gd Tb Dy Y Ho Er Tm Yb Lu

12 Kibaran rare-element pegmatites DRC, Rwanda, Burundi, Uganda >100 samples, >75 locations Production ca. 500 t Ta 2 O 5 Formation ages: ca Ma Mineralogy: columbite-(fe-mn), tantalite-(fe-mn), tapiolite, wodginite, microlite, uranmicrolite, cassiterite, wolframite rare euxenite, bismutotantalite, foordite, thoreaulite, rankamaite, simpsonite etc. Geochemistry of CGM Variable Mg, Li, REE high Sn, Ti, W, Zr Low Sc, Bi REE patterns Commonly flat, unfractionated Usually no Eu anomaly (Eu* Md = 1.7; range ) Occasionally positive Ce anomalies (Ce* Md = 0.9; range )

13 10000 LA ICPMS: Trace elements in CGM Katanga Kibaran, Katanga Tantalite Valley, Namibia Sample/CI Sample/CI ,1 1 0, La Ce Pr Nd Sm Eu Gd Tb Dy Y Ho Er Tm Yb Lu Nigeria 0, Nuweibi, Somalia La Ce Pr Nd Sm Eu Gd Tb Dy Y Ho Er Tm Yb Lu Egypt, Somalia Sample/CI Sample/CI ,1 0,1 0,01 La Ce Pr Nd Sm Eu Gd Tb Dy Y Ho Er Tm Yb 0,01 La Ce Pr Nd Sm Eu Gd Tb Dy Y Ho Er Tm Yb Lu

14 Parameters Methods of the fingerprint for tantalum ores Concentrate Equipment BGR Mineralogy of concentrate (quantitative) Polished section Polishing Laboratory Composition of CGM -Major elements -Trace elements SEM / MLA FEI Quanta FEG ESEM U-Pb age EPMA not routinely, occasionally only LA-ICP-MS Finnigan Element 2 SF-ICP-MS 193 nm Excimer laser

15 Rehwald polishing machine

16 Scanning electron microscope / Mineral Liberation Analysis Mineralogy mode Grain sizes Grain shapes Intergrowths Bijyojo, Ruanda Pangi, Kongo

17 Laser ablation ICP mass spectrometry Laser El. beam

18 AFP in practice Step 1: calculate a U-Pb age from LA-ICP-MS data Attribute the sample to a coltan age province Grenvillian Sveconorwegian e.g.: U-Pb age CGM = Ma Kibaran Namaqualand

19 Estimated U-Pb age from LA-ICP-MS data

20 AFP in practice Step 2: mineralogical composition discriminate a group of deposits based on the presence of specific heavy minerals prerequisite: minerals are not easily removable by classification methods Example: Kibaran coltan Age group Kibaran <2 cas >2 cas >1 tap >1 wdg >1 tap <1 wdg <1 tap >1 wdg <1 tap <1 wdg >1 Umc <1 Umc >5 tap 1-5 tap >1 Umc <1 Umc cas = Cassiterite tap = Tapiolite wdg = Wodginite/Ixiolite Umc = Uran-Microlite + Microlite SE = SEE-Ta-oxides >1 UMc <1 UMc >0.5 SE >0.5 SE

21 Similar ages ( Ma), but different mineralogical compositions

22 AFP in practice Step 3: chemical composition of CGM (or other ore minerals) Acquire a dataset for >50 grains from a concentrate One analysis per grain Major (Mn, Fe, Nb, Ta) and trace elements (>40 elements) Data are stored in a SQL Database, together with details on location and textures Statistical tests identify the origin (the match with a dataset contained in the database) Fraternity test!

23 Wilcoxon-Mann-Whitney (rank-sum) test for unrelated medians Chemical data of columbite-tantalite minerals from concentrate samples of known origin Number of Sample No Country Origin Sum of all p indistinguishable parameters p (TiO 2 ) MnO SnO 2 unknown CD Manono 12, , , , CD Manono 5, , , , CD Manono 5, ,1264 0, , CD Manono 4, , , , CD Manono 4, , , , CD Comptoir in Goma 3, , , , CD Manono 3, , , , CD Manono 1, ,057 0, , RW Gatumba (plant) 1, , , , CD Manono 3, , , , CD Manono 3, , , , CD Manono 3, ,2931 0, , RW Gatumba (plant) 2, , , , RW Gatumba (plant) 1, , , , RW Nyarigamba 1, , , , RW Nemba 7,442 Ranks 2tested for 16 elements 0 0, , RW Gatumba (plant) 3, , , , RW Rutsiro (plant) 3, concentrate 2 data sets 0 0, , CD Yubili Riv., Kivu 3, , , ,00083 p = rankits 209 RW Nemba 3, , , , CD Mapimo Mulungu, Nzovu 2,769 Test sample 2 correctly 0,69061 classified 0 0, RW Ruhanga A 4, , , ,95342

24 Lulingu Mines FDLR Pounia Nyabiondo Legend Kalimbi (Nyabibwe) Will the analytical fingerprint have a positive influence on the situation in Mubi Bisie Mpama the eastern DRC? CEEC cataster 84 locs coltan 217 locs Sn Lubutu Kanyabayonga Kipese Manguredjipa Manguredjipa Uwe Näher (BGR) and CEEC

25 Multivariate statistics and Machine learning Software Kivu Provinces Rwanda Mineral chemistry Error-validated classification West East East West Confusion matrix to distinguish measurements (grains) from localities east (Rwanda) and west (Kivu) of the rift valley, depending on λ as a result of a randomized cross-validation. λ gives the distribution of allocation accuracies

26 Ituri: >1.9 Ga Rwanda (Kibaran) 0.1 Maniema and Kivu (Kibaran) 0.01 Katanga (Kibaran) Zr+W (ppm) Trace element chemistry of CGM

27 Cassiterite samples Kivu-Region Rutongo

28 Cassiterite: LA-ICP-MS analysis Cassiterite: LA-ICP-MS trace elements N = 50 measurements per field Bisie, DRC Rutongo, Rw

29 1) Ta / Sn / W provinces in Africa are distinguished based on modal mineralogy, age and geochemistry of ore minerals (columbitetantalite, cassiterite, wolframite) 2) Ta-Sn pegmatites and Sn-W veins of Central Africa have roughly the same age ( Ma, Kibaran ) similar host rocks (metapelites, amphibolites, granitoids) similar genesis but they differ in Results (1) mineralogy and mineral chemistry 3) Fingerprinting the origin of TTT ores is feasible - from regional scale down to deposit scale - using ore concentrates

30 Results (2) The analytical fingerprint (AFP) of coltan ores: Application (1): Positive certification Fraternity test Identify the origin of a tantalum ore concentrate by comparison with a standard data base of samples from known locations (AFP sensu strictu) Application (2): Identify samples of mixed origin (more than one, with end members present in the data base) Application (3): Forensic method Estimate the origin (tantalum province, district, mine) of an unknown sample with no data present in the data base

31 Vision: Regional certification system Raw materials from ASM Extension of CTC to additional countries Documentation Standards Coltan DRC 300+t* Rwanda ca t** Bur 50 t, Uga 100t*** Cassiterite DRC t* Rwa ca. 4000t** Bur 20t, Uga 1200 t*** Wolframite DRC 1100 t* Rwanda t** Uganda 800t*** Gold DRC??, Rwa?? Uganda 930 kg*** *Export numbers 2007 from Garrett & Mitchell 2009 **Export ordinaire (OGMR, BGR) ***Production 2008 Sasirwe & Turyahikayo 2009 AFP Sampling Central laboratory Checking instrument for CTC Standard 1 Use for Whistle blowing ICGLR + EU / UN / WB Industry (ITRI)

32 Tantalum coltan

33 Thank You!

34 Projects of the BGR in the Great Lakes region (ICGLR) Analytical fingerprint (AFP) for coltan ( ) Egypt Sudan CAR Ethiopia Uganda Congo DRC Kenya Rwanda Burundi Tanzania Angola Sambia Malawi NamibiaZimbabwe Mozambique Botswana Certified Trading Chains (CTC) in Rwanda ( ) Enforcing controls in the raw material sector, DR Congo ( )

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36 Tantalum production 2008: ca t Ta 2 O 5 Kougarok + Recyclers Fir + Thor Lake Tanco + Ningxia, + Jiujiang (China) + Motzfeldt AS Silmet (Estland) Coldwell Blackstairs+ Mitsui (Japan) + Forcarey + Solikamsk (GUS) + McAllister Mineral producers Talison (Aus) Parapanema (Braz) Metallurg (Braz) Cabot (Can) Noventa (Moz) EMSDC (Eth) Pitinga Buyers/Powder makers H.C.Starck (GER, USA, Thailand) Cabot (USA, Japan) Mibra Abu Dabbab Lovozero Rosendal NAC Kazatomprom (Kazakhstan) Mineral dealers A&M Rittenhouse Traxys Kivu Metals + + Ghurayyah Kenticha + Morrua Vishnjakovskoje Capacitor Orlovka manufacturers Etykinskoye AVX, Hitachi, Kemet, Sanyo, Ma Ar Kan Thailand Malaysia 500 t/a from tin slags + Yichun Wodgina 801 Nanping Electronic industry end users (OEMs, original equipment manufacturer) Nokia, Samsung, Dell, Sony, Artisanal producers Marropino Greenbushes + (Semi-) industrial producer Area with artisanal production + Exploration projects (selection)

37 African Tantalum Provinces Ethiopia 1) 530 Ma 2) Mn-columbite/Mn-tantalite 3) no tapiolite, cassiterite 4) no bismutotantalite 5) no or neg. Eu anomaly CAR-DRC Kraton (DRC) 1) > Ma 2) Fe-columbite/ Fe-tantalite 3) Tapiolite, rare cassiterite 4) no bismutotantalite 5) negative Eu anomaly Kibaran (DRC, Rwa) 1) Ma 2) Fe-columbite/ Mn-tantalite 3) Tapiolite, cassiterite 4) no bismutotantalite 5) no Eu anomaly Mozambique 1) Ma 2) Mn-tantalite, microlite 3) no tapiolite, cassiterite 4) Bismutotantalite 5) strong negative Eu anomaly 6) anomalous Bi, Th, U > 2.5 Pan-African Kibaran Eburnean Archean South-Namibia (TV) 1) 980 Ma 2) Mn-tantalite 3) no tapiolite, cassiterite 4) no bismutotantalite 5) negative Eu anomaly