|
|
 |
|||||||||||||||||
|
|||||||||||||||||
 |
|||||||||||||||||
| JOURNAL HOME | HELP | CONTACT PUBLISHER | SUBSCRIBE | ARCHIVE | SEARCH | TABLE OF CONTENTS |
Laboratoire des Mécanismes de Tranfert en Géologie, UMR 5563, Equipe de Minéralogie, 39 Allées Jules Guesde, 31000 Toulouse, France
Department of Earth and Planetary Sciences, McGill University, 3450 University Street, Montreal, Quebec, Canada H3A 2A7
Laboratoire des Mécanismes de Tranfert en Géologie, UMR 5563, Equipe de Minéralogie, 39 Allées Jules Guesde, 31000 Toulouse, France
Corresponding author: e-mail,
salvi{at}cict.fr
The Tamazeght alkaline complex (High Atlas Mountains of Morocco) is a middle Eocene volcanic to plutonic mass, ranging from silica-saturated to silica-undersaturated rocks and carbonatites. Some of the most evolved units are nepheline syenites and pegmatites, which show evidence of hydrothermal alteration. These rocks also contain the highest concentrations of Zr in the complex, although these concentrations are not sufficient to form exploitable reserves. High field strength element (HFSE) minerals (predominantly the zirconosilicates) commonly occur as secondary phases that are richer in Ca and F (cancrinite (Na6Ca(CO3)) (AlSiO4)6•2H2O), calcic catapleiite ((Ca,Na)ZrSi3O9•2H2O), rinkite ((Ca,Ce)4Na(Na,Ca)2Ti(Si2O7)2F2(0,F)2). Furthermore, they partly or completely replace primary HFSE phases (e.g., zircon, eudialyte (Na4(Ca,Ce)2(Fe2+,Mn,Y)ZrSi8O22(OH,Cl)2)). Altered nepheline crystals adjacent to these replaced minerals host fluid inclusions that, based on textural evidence, are interpreted to have formed during alteration. The inclusions have high salinity (25 wt % NaCl equiv), are Ca rich, and were trapped at ~300°C. They contain several solids in addition to a liquid phase and a vapor bubble. One of the most common daughter minerals is a Ca-La-Ce phase (parisite?). Other daughter or trapped minerals include zircon, a Ti (±Nb) silicate or oxide (rutile?), an Mn hydroxide(?), and less commonly, sphalerite and galena. The occurrence of zircon, parisite, and rutile are evidence for mobilization of Zr and other HFSE during hydrothermal alteration.
Based on data available for the solubility of ZrO2 in H2O-HF solutions and estimates for the concentration of Zr in the fluids at the Tamazeght complex (possibly as high as ~0.05 m), we suggest that HFSE transport occurred by mixed metal OH-F complexing. This transport requires a fluid with an elevated F concentration and a temperature of ±300°C. In addition, it can only take place in the near absence of Ca. We propose that a residual F-rich brine evolving from crystallization of pegmatites at <500°C leached and transported HFSE. Upon interaction with surrounding limestone, the fluid cooled rapidly and gained Ca. This caused deposition of fluorite (fluorite is very sparingly soluble), which buffered aF to low levels in the fluid causing precipitation of the HFSE in the form of secondary minerals. Because the hydrothermal event was short-lived and relatively restricted in space, HFSE were not concentrated to ore grades.
This article has been cited by other articles:
|
|
 |
|
  J. Schilling, M. A.W. Marks, T. Wenzel, and G. Markl RECONSTRUCTION OF MAGMATIC TO SUBSOLIDUS PROCESSES IN AN AGPAITIC SYSTEM USING EUDIALYTE TEXTURES AND COMPOSITION: A CASE STUDY FROM TAMAZEGHT, MOROCCO Can Mineral, April 1, 2009; 47(2): 351 - 365. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 M. A. W. Marks, J. Schilling, I. M. Coulson, T. Wenzel, and G. Markl The Alkaline-Peralkaline Tamazeght Complex, High Atlas Mountains, Morocco: Mineral Chemistry and Petrological Constraints for Derivation from a Compositionally Heterogeneous Mantle Source J. Petrology, June 1, 2008; 49(6): 1097 - 1131. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
G. Graser and G. Markl Ca-rich Ilvaite-Epidote-Hydrogarnet Endoskarns: a Record of Late-Magmatic Fluid Influx into the Persodic Ilimaussaq Complex, South Greenland J. Petrology, February 1, 2008; 49(2): 239 - 265. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
E. V. Badanina, R. B. Trumbull, P. Dulski, M. Wiedenbeck, I. V. Veksler, and L. F. Syritso THE BEHAVIOR OF RARE-EARTH AND LITHOPHILE TRACE ELEMENTS IN RARE-METAL GRANITES: A STUDY OF FLUORITE, MELT INCLUSIONS AND HOST ROCKS FROM THE KHANGILAY COMPLEX, TRANSBAIKALIA, RUSSIA Can Mineral, June 1, 2006; 44(3): 667 - 692. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
A. M. McDonald and G. Y. Chao BOBTRAILLITE, (Na,Ca)13Sr11(Zr,Y,Nb)14Si42B6O132(OH)12{middle dot}12H2O, A NEW MINERAL SPECIES FROM MONT SAINT-HILAIRE, QUEBEC: DESCRIPTION, STRUCTURE DETERMINATION AND RELATIONSHIP TO BENITOITE AND WADEITE Can Mineral, April 1, 2005; 43(2): 747 - 758. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
P. C. Piilonen, A. E. Lalonde, A. M. McDonald, R. A. Gault, and A. O. Larsen INSIGHTS INTO ASTROPHYLLITE-GROUP MINERALS. I. NOMENCLATURE, COMPOSITION AND DEVELOPMENT OF A STANDARDIZED GENERAL FORMULA Can Mineral, February 1, 2003; 41(1): 1 - 26. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 A. K. Schmitt, A. K. Schmitt, R. B. Trumbull, P. Dulski, and R. Emmermann Zr-Nb-REE Mineralization in Peralkaline Granites from the Amis Complex, Brandberg (Namibia): Evidence for Magmatic Pre-enrichment from Melt Inclusions Economic Geology, March 1, 2002; 97(2): 399 - 413. [Abstract] [Full Text] [PDF]
|
|
| JOURNAL HOME | HELP | CONTACT PUBLISHER | SUBSCRIBE | ARCHIVE | SEARCH | TABLE OF CONTENTS |
