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Pegmatites also are the major source of sheet mica and important sources of gemstones, particularly tourmalines and the gem forms of beryl (aquamarine and emerald).dolomite; they sometimes also contain the rare-earth ore minerals bastnaesite, parisite, and monazite, the niobium ore mineral pyrochlore, and (in the case of the carbonatite deposit at Palabora in South Africa) copper sulfide ore minerals. Most carbonatites occur close to intrusions of ultramafic igneous rocks (rocks with silica contents below approximately 50 percent by weight) known as kimberlites and lamproites.
These associations suggest a common derivation, but details of the way that carbonatite magmas might concentrate geochemically scarce metals remain conjectural.
Magma is molten rock, together with any suspended mineral grains and dissolved gases, that forms when temperatures rise and melting occurs in the mantle or crust.
When magma rises to Earth’s surface through fissures and volcanic vents, it is called igneous rocks formed from lava tend to consist of tiny mineral grains.
The (U-Th)/He picking and grain measurement facilities were funded through JSG start-up funds to Stockli and are also used for U-Pb (LA-ICP-MS and TIMS) and other geochronologic sample preparation.
Automated He Extraction Line for (U-Th)/He Dating The UT (U-Th)/He laboratory houses three state-of-the-art, all metal, ultra-high vacuum noble gas extraction and purification lines for measuring 4He.
Certain rare chemical elements, such as lithium, beryllium, and niobium, that do not readily enter into atomic substitution in the main granite minerals (feldspar, quartz, and mica) become concentrated in the water-rich residual magma.
If the crystallization process occurs at a depth of about five kilometres or greater, the water-rich residual magma may migrate and form small bodies of igneous rock, satellitic to the main granitic mass, that are enriched in rare elements.
Addition of this state-of-the-art instrumentation will allow the UT (U-Th)/He laboratory to engage in 4He/3He thermochronometry, analyze very young low He-yield volcanic samples and other low radiogenic samples (e.g., young magnetite), and also enter the world of He laser ablation measurements. Certain magmas, such as those which form granites, contain several percent water dissolved in them.When a granitic magma cools, the first minerals to crystallize tend to be anhydrous (e.g., feldspar), so an increasingly water-rich residue remains.Therefore, the geometry (A) of the mineral grain is very important (Meesters and Dunai, 2002a, b).A correction has to be applied for the loss of radiogenic He generated within an outer rim of the mineral grain by the α-stopping distances (apatite: 25m).