The primary and secondary mafic silicates from the Amba Dongar carbonatitic-alkaline complex, Gujarat, India and the Strange Lake peralkaline granitic complex, Quebec-Labrador, Canada are the subject of this investigation of their origin, evolution and relationship to mineralization. Primary minerals are transformed by a variety of processes related to their crystallization history. The most important of these processes are: magma evolution, magma degassing and metasomatism. These processes are commonly associated with the evolution of peralkaline granitic and carbonatitic-alkaline complexes, and with the formation of associated mineral deposits (e.g., fluorite in the Amba Dongar complex; Zr-, REE- (rare-earth elements), Be-, Nb-and Y-rich deposit in the Strange Lake complex). Although all minerals in these complexes may be subject to these changes, the mafic silicates amphibole, pyroxene and mica are of particular interest, as they remain poorly studied and may comprise up to 10 vol.% of the rock. Moreover, they can contain significant quantities of high field-strength elements (HFSE), which may be mobilized following interaction with later fluids, and deposited as secondary minerals in the ore zone. / In the Amba Dongar complex, Na-metasomatism followed by K- (or Mg-) metasomatism resulted in the formation of fenites, with mobilization of HFSE, among other trace elements. Vermiculite was formed by a subsequent stage of hydrothermal alteration, which is also responsible for formation of the fluorite deposit. In the Strange Lake complex, enrichment of the primary arfvedsonitic amphibole in HFSE and REE is related to magmatic evolution, whereas later degassing released sufficient amounts of volatiles and Na that the amphibole became more potassic and aegirine crystallized. This amphibole acted as a sink for trace elements such as Li, HFSE and REE. These elements were remobilized during Na-metasomatism through replacement of amphibole by aegirine, and deposited as secondary, generally Ca-rich, minerals (e.g., winchitic amphibole and biopyriboles) during later, lower-temperature Ca-metasomatism. Primary mafic silicates in alkaline complexes can thus undergo metasomatic reactions that result in the mobilization of elements that contribute to formation of related ore deposits. These findings concerning the solid phases involved in both localities correlate very well with indications of mixing of two distinct fluid phases.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:QMM.34440 |
| Date | January 1997 |
| Creators | Roelofsen, Jeanette N. |
| Contributors | Martin, R. F. (advisor) |
| Publisher | McGill University |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | English |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Format | application/pdf |
| Coverage | Doctor of Philosophy (Department of Earth and Planetary Sciences.) |
| Rights | All items in eScholarship@McGill are protected by copyright with all rights reserved unless otherwise indicated. |
| Relation | alephsysno: 001564911, proquestno: NQ30372, Theses scanned by UMI/ProQuest. |
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