The Amba Dongar complex, India, consists of calciocarbonatite, ankerite-dominated ferrocarbonatite and numerous nephelinitic bodies intruded into Late Cretaceous quartz sandstones and Deccan basalts. / Ankeritic (mottled) and calcite +/- barite +/- ankerite (multiphase) melt inclusions were observed in apatite hosted by calciocarbonatite. Mottled inclusions start melting at temperatures of 610°C and are completely molten at temperatures >800°C. The onset of melting, of multiphase inclusions, is at 680°C, and final melting occurs above 1100°C. Based an the coexistence of mottled (ankeritic) and multiphase (calcitic) inclusions, a model is proposed for the genesis of calciocarbonatite and ferrocarbonatite that calls upon separation of immiscible ankeritic and calcitic liquids from a parent carbonate melt. / Primary fluid inclusions, in apatite hosted by calciocarbonatite, and in quartz of the surrounding fenitized sandstones, record a complex evolution of aqueous fluids. The fluids (orthomagmatic) were trapped at temperatures between 1000 and 260°C, at pressures ranging from 12.5 kbars to 500 bars, respectively, while fenitizing fluids ranged in temperature 260 to 120°C, and were trapped at <500 bars pressure. The low temperature phase behaviour of all inclusions indicates that the fluids are NaCl-, KCl-bearing brines with salinities between 15 and 1.5 wt.%. The compositions of decrepitate residues indicate that early fluids were dominated by SO4 2- and HCO3-, and had low Na/Na+K ratios (<0.5) More evolved fluids display an increasing dependence an Cl -, over SO42- and HCO3 -, and are increasingly depleted in K relative to Na. / The replacement of quartz by potassium feldspar in fenites was accompanied by significant losses of Si and additions of K, Al, Ca, Ba, Fe, La, Ce, F, Rb, Sr, Y and HREE. The water-rock ratio during fenitization was ≈722. / The Phalaborwa complex, South Africa (2060 Ma) consists of a large intrusion of pyroxenite which was later cored by phoscorite and subsequently intruded by banded (early) and transgressive (late) carbonatites. The carbonate rocks are host to 400 Mt of early bornite and late chalcopyrite ores. / Solid-vapour and solid-liquid-vapour melt inclusions are present in phoscorite and transgressive carbonatite. The solids comprise calcite, a magnesian silicate and magnetite +/- Cu-Fe sulphide, while the fluid is a saline Mg-, Fe- and S-bearing NaCl-KCl brine (≈22 wt.% NaCl eq.). Solid-vapour inclusions in phoscorite produce immiscible carbonate and silicate liquids between 680 and 800°C. Melt inclusions in transgressive carbonatites produce only one liquid between 550°C to 670°C and homogenize above 750°C. Liquid immiscibilty was important in removing Si from the carbonate-rich melt, however, silicate and carbonate rocks are not related by liquid immiscibility. Fractionation is considered to have been the dominant process in forming the complex / Two episodes of fenitization were discerned in surrounding granites and gneisses, from chemical and mineralogical changes, and were associated with emplacement of pyroxenite and carbonatite. Both events were accompanied by significant gains in K, Ca, Ba, Mg, Fe, Sr, Th and LREE, and losses in Si and Na. / The presence of Cu-bearing sulphides in solid-vapour inclusions hosted by phoscorite indicates that Phalaborwa magmas were enriched in Cu before emplacement Solid-liquid-vapour inclusions provide the first evidence of a separate magmatic aqueous fluid phase at Phalaborwa and support interpretation of a hydrothermal origin for copper mineralization in transgressive carbonatite.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:QMM.35474 |
| Date | January 1998 |
| Creators | Palmer, David A. S. |
| Contributors | Williams-Jones, A. E. (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: 001655822, proquestno: NQ50232, Theses scanned by UMI/ProQuest. |
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