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Examples of biogenic support of mineralization in two oolitic iron ores—lorraine (France) and gara djebilet (Algeria)
Sedimentary Geology, 5I (1987) 249-255 Elsevier Science Publishers B.V., Amsterdam - Printed in The Netherlands
249
E X A M P L E S OF BIOGENIC S U P P O R T OF MINERALIZATION IN T W O O O L I T I C IRON O R E S - - L O R R A I N E (FRANCE) AND GARA
DJEBILET (ALGERIA) YVES C H A M P E T I E R 1, E L E N A H A M D A D O U 2 and M O H A M E D H A M D A D O U 1 l Laboratoire SOdimentologie-Substances Utiles et EnergOtiques, B.P. 452, 54001 Nam T COdex (France) 2 Centre de Recherche sur la Valorisation des Minerais (L.A. 235), B.P. 40, 54501 Vandoemre les Nancy (France) (Received December 12, 1985; revised and accepted July 10, 1986)
ABSTRACT Champetier, Y., Hamdadou, E. and Hamdadou, M., 1987. Examples of biogenic support of mineralization in two oolitic iron ores--Lorraine (France) and Gara Djebilet (Algeria). Sediment. Geol., 51: 249-255. After inspection, it appears that oolites in the Aalenian of Lorraine and Devonian of Gara Djebilet, are very often Nubecularidea. The mineralization of these "oolitic"-shaped elements results from a metasomatic process. This observation supports the metasomatic theory, and leads to the need for more attention being paid to the shaped elements of the microfacies.
INTRODUCTION
Oolitic sedimentation in marine environments has mainly been interpreted from two points of view: (1) The transformist or metasomatic theory was initiated by Sorby (1856), developed by Cayeux (1909) and extended by Kimberley (1979). This concept considers that the original material is represented by calcitic oolites. Later, during reworking, these oolites are transformed into iron oolites by bacterial activity. (2) The primary precipitation theory was put forward by Bichelonne and Angot (1939). For these authors, oolites are formed by primary precipitation of chlorite and siderite, transformed to hematite by oxidation. For Caill~re and Kraut (1954), the primary precipitation results from accretion of ferric gel around a sometimes metasomatic nucleus. Bubenicek (1961) was in favour of primary precipitation of an oxidized material that was diagenetically transformed to a reduced material, during or after mechanical differentiation (graded bedding). The present paper, without pretending to be a generalization for all oolitic elements, shows that in two iron ores (Lorraine and Gara Djebilet), many iron oolites are foraminifera which were initially carbonate. These observations support the metasomatic theory for the case of the two ores considered. 0037-0738/87/$03.50
© 1987 Elsevier Science Publishers B.V.
250 ORIGIN OF AND INFORMATIONON THE SAMPLESSTUDIED The present study is mainly concerned with some samples from the red and grey beds of the Joeuf mine (Orne Basin). C o ~ a r i s o n s were made with samples from the Sainte-Barbe Mine (Nancy Basin) ~ d also with raw material extracted from the Devonian oolitic ore of Gara Djebilet, Tindouf Basin (Algeria).
Lorraine Basin The characteristics of the Lorraine ore were widely described in Bubenicek (1961). This memoir remains the basic work conceming knowledge of the Lorraine iron ore. He clearly pointed out the very good roundness of the oolites, in spite of their large sphericity (from 0.5 to 1). The meaning of the shape dispersion was not very clear to him and he considered that it was related to compaction. According to Bubenicek's definition, oolites are: "des grains ovo'ides concr&ionn6s, form,s de couches concentriques (enveloppes) autour d'un noyau central quelconque". He also described some variations around the model: unilaterally concentrically developed structures, polynucleated oolites, etc. He measured the size of oolites as between 80 and 500 ~m, with a median of between 200 and 250 #m and he observed that their surfaces are always perfectly smooth. According to Bubenicek, the concentric structure would be related to a high concentration of suspended particles in the environment.
Tindouf Basin The Devonian ferruginous formation of the Tindouf Basin was discovered in the Gara Djebilet by Gevin in 1952 and described by Michel and Clariond in 1960. Recently, Guerrak and Chauvel (1985) studied some identical ore beds on the southern side of the Tindouf Basin (Mech'ri Abdelaziz). According to these authors, the iron oolites were developed by intrasedimentary processes before the final deposition, with alternating phases of oolitization and suspension. tn fact, the latest publications concerning the Lorraine Basin and the Tindouf Basin are in accordance with the primary precipitation theory (accretion). DESCRIPTION OF THE MATERIALSTUDIED
Analogy with shaped elements from phosphatic ores Analysis of the samples from Lorraine and Gara Djebilet has shown numerous elements known as "ootiths" or "pseudo-ooliths" and entirely similar to those that can be observed in phosphate ores.
251
In these ores, the shaped elements were recognized as fragments of coprolites, oncolites and nubeculars (Champetier and Joussernet, 1979; Champetier et al., 1980; Hamdadou, 1983). In the case of both iron ores and phosphate ores, the nubeculars are localized in a grain-size distribution between 125 and 800 t~m, with a characteristic mode at 250/~m. Notes on nubeculars
First cited in 1825 by Defrance, the genus Nubecularia was assigned in 1860 to the Foraminifera by Parker and Jones. The diagnosis was reviewed by Derville in 1935 and by Rat in 1966. Nubecularians are a type of encrusting Miliolidea with a test of cryptocrystalline calcite associated with iron and organic matter. The coil is biloculine and built around an organic or inorganic clast, forming a ball (plectogyroide structured) which looks like an elongated oolite. In longitudinal section, the chamber shape is pyriform (Rat, 1966) and looks like a section of a retort with an elongated neck. In transverse section, the chambers are crescent shaped. The wall is thinner around the nucleus and sometimes seems to disappear. According to Rat (1966), it is uncommon that two adjacent chambers are exactly in the same coiling plane. Nubecularian nature of many shaped elements from iron ores
For the different ores studied, microscopical observations allow us to verify that m a n y shaped elements considered as oolites show sections identical to those of Nubecularia that are known in the carbonate or phosphate facies. In particular, it is possible to recognize the typical pyriform cell (Plate I, 1-4, L). In Plate I, 4, one can observe that the streamlined parts of two pyriform chambers are relatively opposite to the lengthening direction of the section. This observation prevents any confusion with shapes resulting from the effect of compaction. It is possible to see from Plate I, 5, that the lengthening axes of the shaped elements are not in a preferential direction, but that pressure leads to some fractures. The observations of the pyriform chambers and of the structured and porous nature of their walls were made using the SEM technique (Plate II, 1-8). Arrows labelled L show the pyriform chambers and those labelled P the walls. Plate II, 5, clearly shows the streamlined part of a pyriform chamber. Plate II, 3 and 4, as well as Plate I, 4~ show that from one pole to the opposite one, there is an inversion of the orientation of the chambers in a given bilocular coiling plane. The difference in texture between the filling of the chambers and the walls is very distinct in Plate I1, 1-7. There is no particular organization in the chambers, even when the walls (Plate II, 8) have a porous lamellar structure. The type of these nubecularians is not easy to specify, but they seem to be like the illustrations by Derville (1935, pl. XXIX, fig.
252
PLATE I 1-4. Shaped elements showing typical pyriform chambers. L = pyriform chamber. On 2-4 note the asymmetry of the chambers (L) and of the opposite position of the streamlined part from one coiling plane to the other (4). 5. Favreina (F)--coprolites of crustaceans (transverse section) clearly recognizable by a regular pattern of dots (C) which are cross-sections of canals filled with sparry calcite. 6. Favreina (F) in longitudinal section, showing the canals (C) filled with sparry calcite.
1) for N. nooorossica, which was earlier n o t e d as p o l y m o r p h o u s . I n spite of a s t r o n g m e t a s o m a t i s m , it is still possible to recognize a great n u m b e r of Nubecularia with their p y r i f o r m c h a m b e r s in the shaped elements ~rom G a r a
253
PLATE II Observation by SEM technique. 1-7. Various views of pyriform chambers. Note the inversion of the orientation of chambers in the bilocular coiling plane (3, 4) and of the streamlined part of this chamber (1, 7). The difference in texture between chambers and walls is clearly visible in 6 and 7. In 5, the prolongation of the streamlined part by a tubular canal from one chamber to an other is well visible. 8. Porous lamellar structure of the wall.
254
PLATE III Observation by SEM technique. 1 and 3. N ~ r i a n s with pyriform chambers. 2. 4-6. Recrystattization of hematite and- apatite inside the nucleus. H = hematite: A = apaute.
Djebilet ( D e ~ i a a ) . The high porosity o f the walls and o f the filling of the chambers made large re,crystallizations of hematite and apatite possible inside the nucleus (Plate III, 1 - 6 : H = hematite, A = apatite). In both cases (Aalenian of Lorraine and Devonian of G a r a Djebilet), all the nubecularians recognized are affected by iron substitution. Remains of the primary calcareous wall not modified by metasomatism were never detected.
255 CONCLUSION
For the basins considered (Lorraine and Tindouf), both very representative or typical of iron-oolitic sedimentation, these observations clearly demonstrate that it is no longer possible to accept or generalize on the fact that the development of iron oolites results from successive depositions (accretion) around particles. Indeed, the basis material of Nubecularia is a cryptocrystalline calcite and it is also possible to recognize longitudinal and transversal ferruginous sections of coprolites (Favreina, Plate I, 5 and 6). The ferruginous and apatitic mineralization results from metasomatism and not from physico-chemical accretion. The nature of the support of the mineralization most often appears as biogenic. For these reasons, it is necessary to take note of the true nature of the shaped elements that seem to be like "oolites" and to review them before an interpretation of genesis is made. REFERENCES Bichelonne, J. and Angot, P., 1939. Le Bassin Ferrif+re Lorrain. Berger-Levrault, Paris, 464 pp. Bubenicek, L., 1961. Recherches sur la constitution et la r~partition du mineral de fer dans l'Aaldnien de Lorraine. Sci. Terre, VIII: 1-2. Caill+re, S. and Kraut, F., 1954. Les gisements de fer du bassin lorrain. Mrm. Mus. Nat. Hist. Nat., Paris, Sect. C, 4 (1). Cayeux, L., 1909, 1922. Les Minerais de Fer Oolithiques de France. Imprimerie Nationale, Pari~ Fasc. 1-2. Champetier, Y. and Joussemet, R., 1979. Drcouverte de nubrculaires et d'oncolithes e n t a n t qu'616ments phosphates. C.R. Acad. Sci. Paris, Srr. D, 288: 673-675. Champetier, Y., Blazy, P. and Joussemet, R., 1980. Enrichissement des phosphates carbonates. Caract~risation g~tologique et p~trographique. Comportement au traitement thermique. Proc. 2nd Int. Congress on phosphorus compounds, Boston, pp. 283-312. Defrance, M.J.L., 1825. Dictionnaire des Sciences Naturelles. Levrault, Paris, Vol. 35, 534 pp. Derville, P.H., 1935. Observations et rrflexion sur le genre Nubecularia. Bull. Soc. G~ol. Fr. 5+me S&, 5: 263-276. Guerrak, S. and Chauvel, J.J., 1985. Les minrralisations ferrif+res du Sahara algrrien: le gisement de fer oolithique de Mech'ri Abdelaziz (bassin de Tindouf). Mineral. Deposita, 20: 249-259. Hamdadou, M., 1983. Regards nouveaux sur les aspects prtro-minrralogiques des phosphates de Djebel-Onk. Ind. Min~r., Techniques. Kimberley, M.M., 1979. Origin of oolitic iron formations. J. Chem. Geol., 49: 0111-0131. Michel, R. and Clariond, L., 1960. Le gisement de fer de Tindouf (Gara Djebilet). Ann. Mines, I: 9-25. Parker, W.K. and Jones, T.R., 1860. On the nomenclature of the Foraminifera. Ann. Mag. Nat. Hist., Pt. 4, set. 3, 6: 29-40. Rat, P., 1966. Nubecularia reicheli nov. sp., Foraminif~re constructeur de fausses oolithes dans le Bajocien de Bourgogne. Eclogae Geol. Helv., 59 (1): 73-85. Sorby, H.C., 1856. On the origin of the Cleveland Hill ironstone. Geol. Polytechnic Soc. West Riding Yorkshire Proc., 3: 457-461.
249
E X A M P L E S OF BIOGENIC S U P P O R T OF MINERALIZATION IN T W O O O L I T I C IRON O R E S - - L O R R A I N E (FRANCE) AND GARA
DJEBILET (ALGERIA) YVES C H A M P E T I E R 1, E L E N A H A M D A D O U 2 and M O H A M E D H A M D A D O U 1 l Laboratoire SOdimentologie-Substances Utiles et EnergOtiques, B.P. 452, 54001 Nam T COdex (France) 2 Centre de Recherche sur la Valorisation des Minerais (L.A. 235), B.P. 40, 54501 Vandoemre les Nancy (France) (Received December 12, 1985; revised and accepted July 10, 1986)
ABSTRACT Champetier, Y., Hamdadou, E. and Hamdadou, M., 1987. Examples of biogenic support of mineralization in two oolitic iron ores--Lorraine (France) and Gara Djebilet (Algeria). Sediment. Geol., 51: 249-255. After inspection, it appears that oolites in the Aalenian of Lorraine and Devonian of Gara Djebilet, are very often Nubecularidea. The mineralization of these "oolitic"-shaped elements results from a metasomatic process. This observation supports the metasomatic theory, and leads to the need for more attention being paid to the shaped elements of the microfacies.
INTRODUCTION
Oolitic sedimentation in marine environments has mainly been interpreted from two points of view: (1) The transformist or metasomatic theory was initiated by Sorby (1856), developed by Cayeux (1909) and extended by Kimberley (1979). This concept considers that the original material is represented by calcitic oolites. Later, during reworking, these oolites are transformed into iron oolites by bacterial activity. (2) The primary precipitation theory was put forward by Bichelonne and Angot (1939). For these authors, oolites are formed by primary precipitation of chlorite and siderite, transformed to hematite by oxidation. For Caill~re and Kraut (1954), the primary precipitation results from accretion of ferric gel around a sometimes metasomatic nucleus. Bubenicek (1961) was in favour of primary precipitation of an oxidized material that was diagenetically transformed to a reduced material, during or after mechanical differentiation (graded bedding). The present paper, without pretending to be a generalization for all oolitic elements, shows that in two iron ores (Lorraine and Gara Djebilet), many iron oolites are foraminifera which were initially carbonate. These observations support the metasomatic theory for the case of the two ores considered. 0037-0738/87/$03.50
© 1987 Elsevier Science Publishers B.V.
250 ORIGIN OF AND INFORMATIONON THE SAMPLESSTUDIED The present study is mainly concerned with some samples from the red and grey beds of the Joeuf mine (Orne Basin). C o ~ a r i s o n s were made with samples from the Sainte-Barbe Mine (Nancy Basin) ~ d also with raw material extracted from the Devonian oolitic ore of Gara Djebilet, Tindouf Basin (Algeria).
Lorraine Basin The characteristics of the Lorraine ore were widely described in Bubenicek (1961). This memoir remains the basic work conceming knowledge of the Lorraine iron ore. He clearly pointed out the very good roundness of the oolites, in spite of their large sphericity (from 0.5 to 1). The meaning of the shape dispersion was not very clear to him and he considered that it was related to compaction. According to Bubenicek's definition, oolites are: "des grains ovo'ides concr&ionn6s, form,s de couches concentriques (enveloppes) autour d'un noyau central quelconque". He also described some variations around the model: unilaterally concentrically developed structures, polynucleated oolites, etc. He measured the size of oolites as between 80 and 500 ~m, with a median of between 200 and 250 #m and he observed that their surfaces are always perfectly smooth. According to Bubenicek, the concentric structure would be related to a high concentration of suspended particles in the environment.
Tindouf Basin The Devonian ferruginous formation of the Tindouf Basin was discovered in the Gara Djebilet by Gevin in 1952 and described by Michel and Clariond in 1960. Recently, Guerrak and Chauvel (1985) studied some identical ore beds on the southern side of the Tindouf Basin (Mech'ri Abdelaziz). According to these authors, the iron oolites were developed by intrasedimentary processes before the final deposition, with alternating phases of oolitization and suspension. tn fact, the latest publications concerning the Lorraine Basin and the Tindouf Basin are in accordance with the primary precipitation theory (accretion). DESCRIPTION OF THE MATERIALSTUDIED
Analogy with shaped elements from phosphatic ores Analysis of the samples from Lorraine and Gara Djebilet has shown numerous elements known as "ootiths" or "pseudo-ooliths" and entirely similar to those that can be observed in phosphate ores.
251
In these ores, the shaped elements were recognized as fragments of coprolites, oncolites and nubeculars (Champetier and Joussernet, 1979; Champetier et al., 1980; Hamdadou, 1983). In the case of both iron ores and phosphate ores, the nubeculars are localized in a grain-size distribution between 125 and 800 t~m, with a characteristic mode at 250/~m. Notes on nubeculars
First cited in 1825 by Defrance, the genus Nubecularia was assigned in 1860 to the Foraminifera by Parker and Jones. The diagnosis was reviewed by Derville in 1935 and by Rat in 1966. Nubecularians are a type of encrusting Miliolidea with a test of cryptocrystalline calcite associated with iron and organic matter. The coil is biloculine and built around an organic or inorganic clast, forming a ball (plectogyroide structured) which looks like an elongated oolite. In longitudinal section, the chamber shape is pyriform (Rat, 1966) and looks like a section of a retort with an elongated neck. In transverse section, the chambers are crescent shaped. The wall is thinner around the nucleus and sometimes seems to disappear. According to Rat (1966), it is uncommon that two adjacent chambers are exactly in the same coiling plane. Nubecularian nature of many shaped elements from iron ores
For the different ores studied, microscopical observations allow us to verify that m a n y shaped elements considered as oolites show sections identical to those of Nubecularia that are known in the carbonate or phosphate facies. In particular, it is possible to recognize the typical pyriform cell (Plate I, 1-4, L). In Plate I, 4, one can observe that the streamlined parts of two pyriform chambers are relatively opposite to the lengthening direction of the section. This observation prevents any confusion with shapes resulting from the effect of compaction. It is possible to see from Plate I, 5, that the lengthening axes of the shaped elements are not in a preferential direction, but that pressure leads to some fractures. The observations of the pyriform chambers and of the structured and porous nature of their walls were made using the SEM technique (Plate II, 1-8). Arrows labelled L show the pyriform chambers and those labelled P the walls. Plate II, 5, clearly shows the streamlined part of a pyriform chamber. Plate II, 3 and 4, as well as Plate I, 4~ show that from one pole to the opposite one, there is an inversion of the orientation of the chambers in a given bilocular coiling plane. The difference in texture between the filling of the chambers and the walls is very distinct in Plate I1, 1-7. There is no particular organization in the chambers, even when the walls (Plate II, 8) have a porous lamellar structure. The type of these nubecularians is not easy to specify, but they seem to be like the illustrations by Derville (1935, pl. XXIX, fig.
252
PLATE I 1-4. Shaped elements showing typical pyriform chambers. L = pyriform chamber. On 2-4 note the asymmetry of the chambers (L) and of the opposite position of the streamlined part from one coiling plane to the other (4). 5. Favreina (F)--coprolites of crustaceans (transverse section) clearly recognizable by a regular pattern of dots (C) which are cross-sections of canals filled with sparry calcite. 6. Favreina (F) in longitudinal section, showing the canals (C) filled with sparry calcite.
1) for N. nooorossica, which was earlier n o t e d as p o l y m o r p h o u s . I n spite of a s t r o n g m e t a s o m a t i s m , it is still possible to recognize a great n u m b e r of Nubecularia with their p y r i f o r m c h a m b e r s in the shaped elements ~rom G a r a
253
PLATE II Observation by SEM technique. 1-7. Various views of pyriform chambers. Note the inversion of the orientation of chambers in the bilocular coiling plane (3, 4) and of the streamlined part of this chamber (1, 7). The difference in texture between chambers and walls is clearly visible in 6 and 7. In 5, the prolongation of the streamlined part by a tubular canal from one chamber to an other is well visible. 8. Porous lamellar structure of the wall.
254
PLATE III Observation by SEM technique. 1 and 3. N ~ r i a n s with pyriform chambers. 2. 4-6. Recrystattization of hematite and- apatite inside the nucleus. H = hematite: A = apaute.
Djebilet ( D e ~ i a a ) . The high porosity o f the walls and o f the filling of the chambers made large re,crystallizations of hematite and apatite possible inside the nucleus (Plate III, 1 - 6 : H = hematite, A = apatite). In both cases (Aalenian of Lorraine and Devonian of G a r a Djebilet), all the nubecularians recognized are affected by iron substitution. Remains of the primary calcareous wall not modified by metasomatism were never detected.
255 CONCLUSION
For the basins considered (Lorraine and Tindouf), both very representative or typical of iron-oolitic sedimentation, these observations clearly demonstrate that it is no longer possible to accept or generalize on the fact that the development of iron oolites results from successive depositions (accretion) around particles. Indeed, the basis material of Nubecularia is a cryptocrystalline calcite and it is also possible to recognize longitudinal and transversal ferruginous sections of coprolites (Favreina, Plate I, 5 and 6). The ferruginous and apatitic mineralization results from metasomatism and not from physico-chemical accretion. The nature of the support of the mineralization most often appears as biogenic. For these reasons, it is necessary to take note of the true nature of the shaped elements that seem to be like "oolites" and to review them before an interpretation of genesis is made. REFERENCES Bichelonne, J. and Angot, P., 1939. Le Bassin Ferrif+re Lorrain. Berger-Levrault, Paris, 464 pp. Bubenicek, L., 1961. Recherches sur la constitution et la r~partition du mineral de fer dans l'Aaldnien de Lorraine. Sci. Terre, VIII: 1-2. Caill+re, S. and Kraut, F., 1954. Les gisements de fer du bassin lorrain. Mrm. Mus. Nat. Hist. Nat., Paris, Sect. C, 4 (1). Cayeux, L., 1909, 1922. Les Minerais de Fer Oolithiques de France. Imprimerie Nationale, Pari~ Fasc. 1-2. Champetier, Y. and Joussemet, R., 1979. Drcouverte de nubrculaires et d'oncolithes e n t a n t qu'616ments phosphates. C.R. Acad. Sci. Paris, Srr. D, 288: 673-675. Champetier, Y., Blazy, P. and Joussemet, R., 1980. Enrichissement des phosphates carbonates. Caract~risation g~tologique et p~trographique. Comportement au traitement thermique. Proc. 2nd Int. Congress on phosphorus compounds, Boston, pp. 283-312. Defrance, M.J.L., 1825. Dictionnaire des Sciences Naturelles. Levrault, Paris, Vol. 35, 534 pp. Derville, P.H., 1935. Observations et rrflexion sur le genre Nubecularia. Bull. Soc. G~ol. Fr. 5+me S&, 5: 263-276. Guerrak, S. and Chauvel, J.J., 1985. Les minrralisations ferrif+res du Sahara algrrien: le gisement de fer oolithique de Mech'ri Abdelaziz (bassin de Tindouf). Mineral. Deposita, 20: 249-259. Hamdadou, M., 1983. Regards nouveaux sur les aspects prtro-minrralogiques des phosphates de Djebel-Onk. Ind. Min~r., Techniques. Kimberley, M.M., 1979. Origin of oolitic iron formations. J. Chem. Geol., 49: 0111-0131. Michel, R. and Clariond, L., 1960. Le gisement de fer de Tindouf (Gara Djebilet). Ann. Mines, I: 9-25. Parker, W.K. and Jones, T.R., 1860. On the nomenclature of the Foraminifera. Ann. Mag. Nat. Hist., Pt. 4, set. 3, 6: 29-40. Rat, P., 1966. Nubecularia reicheli nov. sp., Foraminif~re constructeur de fausses oolithes dans le Bajocien de Bourgogne. Eclogae Geol. Helv., 59 (1): 73-85. Sorby, H.C., 1856. On the origin of the Cleveland Hill ironstone. Geol. Polytechnic Soc. West Riding Yorkshire Proc., 3: 457-461.