|
|
 |
|||||||||||||||||
|
|||||||||||||||||
 |
|||||||||||||||||
| JOURNAL HOME | HELP | CONTACT PUBLISHER | SUBSCRIBE | ARCHIVE | SEARCH | TABLE OF CONTENTS |
1 Department of Geology, Lakehead University, 955 Oliver Road, Thunder Bay, Ontario, Canada P7B 5E1
2 825 Fitzpatrick Road, Nashville, TN 37214, USA
* E-mail: Roger.Mitchell{at}lakeheadu.ca
Lapilli and spatter of natrocarbonatite extruded from the T56B cone of Oldoinyo Lengai (Tanzania) in August 2003 are unusually rich in apatite, silicate, oxide and sulphide minerals. These minerals occur primarily within inclusions of quenched natrocarbonatite in gregoryite and fractures in nyerereite-gregoryite intergrowths. Silicates include members of the sodian cuspidine–niobian cuspidine–niocalite solid-solution series and manganoan monticellite. Oxides are represented by members of the magnesioferrite–jacobsite–magnetite solid-solution series. Sulphides occurring in decreasing order of abundance include: ferroan alabandite, manganoan ferroan sphalerite, galena and pyrrhotite. Petrographic and compositional data for these minerals are interpreted to indicate that all are high-temperature (<900–650°C), early-crystallizing phases from relatively-unevolved natrocarbonatite magma, with the sulphides forming prior to the silicates, and the latter before gregoryite. Sulphur fugacity and oxygen fugacity of natrocarbonatite magma are considered to decrease and increase, respectively, during the formation of the sulphide-oxide assemblage. Crystallization of cuspidine-niocalite, monticellite and Si-bearing apatite rapidly depletes natrocarbonatite magma of its initial low silica content, preventing crystallization of late-stage groundmass silicates.
KEYWORDS: natrocarbonatite, carbonatite, cuspidine, niocalite, monticellite, sulphides, Oldoinyo Lengai, Tanzania
This article has been cited by other articles:
|
|
 |
|
  S. N. Britvin, A. N. Bogdanova, M. M. Boldyreva, and G. Y. Aksenova Rudashevskyite, the Fe-dominant analogue of sphalerite, a new mineral: Description and crystal structure American Mineralogist, May 1, 2008; 93(5-6): 902 - 909. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 R. H. Mitchell and J. B. Dawson The 24th September 2007 ash eruption of the carbonatite volcano Oldoinyo Lengai, Tanzania: mineralogy of the ash and implications for formation of a new hybrid magma type Mineralogical Magazine, October 1, 2007; 71(5): 483 - 492. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
R. P. Liferovich and R. H. Mitchell Apatite-group minerals from nepheline syenite, Pilansberg alkaline complex, South Africa Mineralogical Magazine, October 1, 2006; 70(5): 463 - 484. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
R. H. Mitchell Mineralogy of stalactites formed by subaerial weathering of natrocarbonatite hornitos at Oldoinyo Lengai, Tanzania Mineralogical Magazine, August 1, 2006; 70(4): 437 - 444. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
R. H. Mitchell An ephemeral pentasodium phosphate carbonate from natrocarbonatite lapilli, Oldoinyo Lengai, Tanzania Mineralogical Magazine, April 1, 2006; 70(2): 211 - 218. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
R. H. Mitchell Sylvite and fluorite microcrysts, and fluorite-nyerereite intergrowths from natrocarbonatite, Oldoinyo Lengai, Tanzania Mineralogical Magazine, February 1, 2006; 70(1): 103 - 114. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 R. H. Mitchell CARBONATITES AND CARBONATITES AND CARBONATITES Can Mineral, December 1, 2005; 43(6): 2049 - 2068. [Abstract] [Full Text] [PDF]
|
|
| JOURNAL HOME | HELP | CONTACT PUBLISHER | SUBSCRIBE | ARCHIVE | SEARCH | TABLE OF CONTENTS |
