Pegmatite

World Reserves and Resources. A summary of demonstrated and inferred worldwide reserves of lithium is given in Table 2. The reserve base and the lithium equivalent represent resources in the ground. An overall lithium recoverabiUty of 65% for pegmatites and 33% for brines must be apphed to these values to estabUsh the amount of lithium that could eventually reach the marketplace (15). 

Muscovite mica formed as a primary mineral in pegmatites and granodiorite differs in physical properties compared to muscovite mica formed by secondary alteration (mica schist) (Table 2). The main differences are in flexibiUty and abiUty to be delaminated. Primary muscovite is not as brittle and delaminates much easier than muscovite formed as a secondary mineral. Mineralogical properties of the principal natural micas are shown in Table 3. The make-up of muscovite, phlogopite, and biotite are as follows ... 

Sheet Mica. Pockets of mica crystals ranging in size from a few square centimeters to several square meters are found in pegmatite sills and dikes or granodiorite (alaskite) ore bodies. In order to be used industrially, manufacturers must be able to cut a 6 cm pattern in the mica. "Books" of mica, ranging from 12.9 to 645 cm or more, are cut from the crystals. The books can be punched into various shapes and spHt into thicknesses varying from 0.0031 to 0.010 cm (12). The highest quaUty micas maybe used in aerospace computers, and those of lower quaUty find use as insulators in electrical apphances. 

Sheet mica occurs in pockets within pegmatite. When exploring for sheet mica, test pits are sunk to determine the presence of pockets and quaUty of the mica. The size, shape, and attitude of the pegmatite is deterrnined by stripping and trenching. These procedures are cosdy and problematic, but the quahty can be deterrnined to a sufficient degree (5). 

The soft weathered granodiorite and pegmatites can vary in color from white to pink, depending on iron content and type of feldspar present. The mica content of these deposits ranges from 6—15% and varies in particle size from tiny (<44 specks to thumbnail size. Large books of mica that weigh several hundred kilograms have been found in these deposits. 

Flake Mica. Flake mica is mined from weathered and hard rock pegmatites, granodiorite, and schist and gneiss by conventional open-pit methods. In soft, residual material, dozers, shovels, scrapers, and front-end loaders are used to mine the ore. Often kaolin, quartz, and feldspar are recovered along with the mica (see also Clays Silicon compounds). 

Occurrence. Niobium and tantalum usually occur together. Niobium never occurs as the metal, ie, ia the free state. Sometimes it occurs as a hydroxide, siUcate, or borate most often it is combiaed with oxygen and another metal, forming a niobate or tantalate ia which the niobium and tantalum isomorphously replace one another with Htde change ia physical properties except density. Ore concentrations of niobium usually occur as carbonatites and are associated with tantalum ia pegmatites and alluvial deposits. Principal niobium-beariag minerals can be divided iato two groups, the titano- and tantalo-niobates. 

Intrusive Deposits. Deposits included in the intmsive deposit type are those associated with intmsive or anatectic rocks of different chemical composition, eg, alaskite, granite, monzonite, peralkaline syenite, carbonatite, and pegmatite. Examples include the uranium occurrences in the porphyry copper deposits such as Bingham Canyon and Twin Butte in the United States, the Rossing Deposit in Namibia, and Ilimaussaq deposit in Greenland, Palabora in South Africa, and the deposits in the Bancroft area, Canada (15). 

One useful classification of graphite depends on the mode of formation that leads to three physically distinct common varieties dake, lump, and amorphous. The term dake is self-explanatory dake forms occur disseminated in rock. Lump graphite occurs in fissure-filled veins in pegmatite dikes, also associated with chip and the rarer needle forms. Amorphous graphite occurs in beds that were once coal, but fine-grained, easily ground vein graphite is also classified as amorphous. 

P. Cemy, Short Course in Granitic Pegmatites in Science and Industry, Mineralogical Association, Winnipeg, Canada, 1982, p. 150. 

Beryllium, like its neighbours Li and B, is relatively unabundant in the earth s crust it occurs to the extent of about 2 ppm and is thus similar to Sn (2.1 ppm), Eu (2.1 ppm) and As (1.8 ppm). However, its occurrence as surface deposits of beryl in pegmatite rocks (which are the last portions of granite domes to crystallize) makes it readily accessible. Crystals as large as 1 m on edge and weighing up to 60 tonnes have been reported. World reserves in commercial deposits are about 4 million tonnes of contained Be and mined production in 1985-86 was USA... 

Pech-stein, m. pitchstone. -steinkohle,/, pitch coal, -tanne, /. pitch pine, -torf, m. pitch peat, blaek peat, -uran, n. pitchblende. Pegel, n. level water gage, pegmatitisch, a. (Patrog.) pegmatitic. 

B. Residual liquid injection Same as above, followed by injection Most pegmatite and carbonatite veins... 

Pegmatite type Typical mineral association Economic potential Examples... 

The five types of molybdenum deposits include (i) molybdenum and copper porphyry deposits (ii) Quartz vein and pipes (iii) Pegmatites and apatites dikes (iv) Contact-meta-morphic rocks and tactite bodies of silica bearing limestone and (v) Sedimentary rocks containing bedded deposits. 

Intrusive-type (carbonatite, pegmatite, quartz-monazite, etc.)... 

P. Cewmy, Rare Element Granitic Pegmatites, Pt. I. Anatomy and Internal Evolution of Pegmatite Deposits, Geoscience Canada, vol. 18, No. 2, 49,1991. 

Lentz, D.R. 1998. Late-tectonic U-Th-Mo-REE skarn and carbonatitic vein-dyke systems in the southwestern Grenville Province a Pegmatite-Related Pneumatolytic Model linked to Marble Melting (limestone syntexis). In Lentz D.R. (ed) Mineralized intrusion-related skarn systems, 519-657, Mineralogical Association of Canada Short Course 26. 

Group 1 Cassiterite contained in pegmatitic veins contain significant quantities of (TSIb,... 

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