Pegmatite ores

The most important tin deposits are hydrothermal deposits (hypothermal and mesothermal). The magmatic deposits do not often contain tin mineralization. Tin may also be present in pegmatitic ore bodies. However, tin found in pegmatitic deposits can be classified into two basic types (a) quartz-cassiterite lenses in granite, when cassiterite is associated with topaz, beryl and, to a lesser degree, sulphides (b) sulphide deposits, where tin is mainly cassiterite associated with arsenopyrite, pyrite, chalcopyrite and pyrrhotite. Such deposits are common in South America (Peru, Bolivia). 

The coarse-grained tin ores are usually represented by cassiterite-quartz and pegmatitic formations. These ores can be a complex formation containing varieties of gangue minerals. The pegmatitic ore type, in addition to tin, can contain significant amounts of tantalum and niobium. 

There are two major types of pyrochlore-containing ores pegmatite ores and carbonatites. This classification is based on the mineral composition of these ore types. The main waste minerals contained in the pegmatite ores include quartz and nepheline. This ore type also includes granites, where pyrochlore is represented in a coarse crystalline form. Granites are composed of cryolite and topaz as the main gangue minerals. 

In the case of carbonatite ores, a beneficiation process involves preflotation followed by reactivation and flotation of pyrochlore. In the case of pegmatitic ores that contain silicates, biotite, albite and limonite, as the gangue minerals, direct flotation of pyrochlore can be achieved with a variety of different collectors. 

Pegmatite-containing niobium ores can be relatively complex and may contain biotite, enargite, albite, feldspar and ziron as the main gangue minerals. Some pegmatite ores (Araxa, Brazil) have a simple gangue composition, consisting mainly of quartz. 

Figure 22.3 Effect of sodium oleate on flotation of niobium from pegmatite ores.

Figure 22.4 Effect of sodium alkyl sulphate on flotation of minerals from pegmatite ores at a pH of 1.4.

Reagent scheme developed for beneficiation of niobium from feldspar-containing pegmatite ores. 

There are several operating plants treating pyrochlore-containing ores from carbonatite and pegmatite ores. Operating plants that treat carbonatite ores described in this chapter include St. Honore Niobec, Canada, and OKa, Quebec, Canada. The operating plant that treats pegmatite ore is Araxa (Brazil). 

Pavlor, D.A., Flotation of Niobium from Pegmatitic Ores, Tsvetnie Metally, No. 8, 1976. 

Bulatovic, S., Research and Development of Niobium Flotation from Pegmatite Ore, SGS Report of Investigation, 2007. 

Effect of tall oil modifications on bastnaesite flotation from pegmatitic ores... 

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. 

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. 

Medium-coarse-grained, less-disseminated ores. The size of cassiterite particles in this ore type ranges from 1.0 to 0.2 mm in size. Typical ore bodies of this type are pegmatitic and tin-containing sulphide ores. 

Carbonatite ores are mainly composed of calcite, dolomite and phosphates as the main gangue minerals. The beneficiation process for pegmatites containing pyrochlore mostly includes gravity preconcentration. Such deposits are common in Africa (Kongo, Madagascar). 

The major minerals contained in pyrochlore-containing ores are pyrochlore, columbite and sometimes ilmenorutile to a lesser extent. Table 22.1 shows pyrochlore minerals present in pegmatite and carbonatite ores. 

Pyrochlore minerals contained in pegmatite and carbonatite ores... 

Bastnaesite belongs to the carbonatite group of minerals that contain REOEs. Beside the cerium group of elements, bastnaesite also contains yttrium and europium. Typically, it contains 65-75% REOE. Bastnaesite is usually found in pegmatites, carbonatite and hydrothermal ore bodies in alkaline gangue minerals. Because it is poor chemically and stable, it is not found in mineral sand deposits. 

Loparite (Nb-mineral) contains, for example, three times more REOE than niobium. It represents titanotantalo-niobium REOE ore. Loparite is found in pegmatites and nepheline-containing ores. 

Scandium is found in ores of wolframite in Norway and thortveitite in Madagascar. It is also found in granite pegmatites and monazites. It is common in many of the ores where tin and tungsten are also found. 

Lentz, D. 1996. U, Mo, and REE mineralization in late-tectonic granitic pegmatites, southwestern Grenville Province, Canada. Ore Geology Reviews, 11, 197-227. 

---