Archean Rare-Metal Pegmatites in Zimbabwe and Western Australia

Lithium-cesium-tantalum (LCT) pegmatites are important resources for rare metals. For Cs, only the LCT pegmatites with the zeolite group mineral pollucite at Bikita (Zimbabwe Craton) and Tanco (Superior Province Craton) are of commercial importance. Common characteristics of world-class LCT pegmatite deposits include their Meso- to Neoarchean age and geological setting within greenstone belt lithologies on Archean Cratons.

This study presents the first coherent and comparative scientific investigation of five major LCT pegmatite systems from the Yilgarn, Pilbara and Zimbabwe Craton. For the evaluation of their Cs potential and of the genetic concepts of pollucite formation, the pegmatites from Wodgina, Londonderry, Mount Deans and Cattlin Creek were compared to the Bikita pollucite mineralization.

The integration of the new data (e.g., geochronological and radiogenic isotope data) into the complex geological framework: 1) enhances our knowledge of the formation of LCT pegmatite systems, and 2) will contribute to the further exploration of additional world-class LCT pegmatite deposits, which 3) may host massive pollucite mineralisations.

Contenu

1 Introduction1.1 Motivation and Scope of the Thesis1.2 Structure of the Thesis2 Geological Settings of Archean Cratons 2.1 Yilgarn Craton2.1.1 Tectonostratigraphic Framework and Geological Development2.1.2 Tectonic Models for the Development 2.1.3 Pegmatites within the Yilgarn Craton 2.1.4 Geological setting of the Londonderry Pegmatite Field 2.1.5 Geological Setting of the Mount Deans Pegmatite Field2.1.6 Geological Setting of the Cattlin Creek Pegmatite Deposit3 Fieldwork and Sampling of Selected Pegmatites and Pegmatite Fields3.1 Londonderry Pegmatite Field 3.1.1 Londonderry Feldspar Quarry Pegmatite 3.1.2 Lepidolite Hill Pegmatite3.1.3 Tantalite Hill Pegmatite 3.2 Mount Deans Pegmatite Field3.2.1 Type I Flat Lying Pegmatites 3.3 Cattlin Creek Pegmatite4 Petrography and Mineralogy4.1 Quantitative Mineralogy by Means of Mineral Liberation Analysis4.2 Mineralogical and Petrographical Characteristics of Individual Mineral Groups 4.2.1 Feldspar 4.2.2 Quartz4.2.3 Mica4.2.4 Petalite5 Geochemistry5.1 Major Elements5.2 Selected Minor and Trace Elements5.3 Fractionation Indicators5.4 Rare Earth Elements 6 Geochronology 6.1 40Ar/39Ar-Method on Mica 6.1.1 Mount Deans Pegmatite Field6.1.2 Londonderry Pegmatite Field6.1.3 Cattlin Creek Pegmatite 6.1.4 Wodgina Pegmatite6.2 Th-U-Total Pb Monazite Dating 6.2.1 Monazite Ages6.3 U/Pb Dating of Selected Ta-, Nb- and Sn-Oxide Minerals6.3.1 Londonderry Pegmatite Field 6.3.2 Mount Deans Pegmatite Field6.3.3 Cattlin Creek Pegmatite6.3.4 Wodgina Pegmatite7 Stable and Radiogenic Isotopes 7.1 Whole Rock Sm/Nd-Isotopy7.1.1 New Whole Rock Sm/Nd Data