Classification and characteristics of lithium ore

Lithium deposits can be roughly divided into six categories, namely: lithium-cesium-tantalum pegmatite deposits, lithium-rich granite, lithium salt deposits in closed basins, lithium in other brines, lithium clay deposits, and lithium zeolite deposits.

1. Lithium-cesium-tantalum pegmatite deposits

Lithium-cesium-tantalum pegmatites are found in the hinterland of metamorphic igneous rocks in orogenic belts and are the result of plate convergence. Most lithium-cesium-tantalum pegmatites form during collisions between continents or microcontinents and are associated with aluminum-rich granites produced by melting metasedimentary rocks.

Dozens of pegmatites in the Appalachian Mountains were formed during a long-term collision between Africa and North America between 370 million and 275 million years ago. Lithium-cesium-tantalum pegmatites can be dated using isotopic dating. In pegmatites, the minerals columbite-tantalite and zircon are dated by exploiting the decay of uranium-238 to lead-206. Lithium-cesium-tantalum pegmatites from six continents have now been dated.

2. Lithium-rich granite

Some muscovite-bearing granites include areas rich in lithium, tantalum, tin, and fluorine. At the Yichun Mine in Jiangxi Province, China, the top of the biotite-muscovite granite grades into muscovite granite, which then becomes lepidolite granite, where lithium and tantalum have been mined. Lithium-rich granites are closely related to LCT pegmatites, and the two have not been distinguished from each other in recent global lithium resource assessments.

3. Lithium salt deposits in closed basins

Closed basin brine deposits account for an estimated 58% of the world's proven lithium resources. Lithium brine deposits are accumulations of saline groundwater rich in dissolved lithium. Lithium deposits in production have average lithium concentrations ranging from 160 to 1,400 ppm, with estimated lithium resources ranging from 0.3 to 6.3 million tonnes. Producing lithium deposits are located in Asia, North and South America, in northern and arid latitudes on either side of the equator. These deposits share many common features:

(a) arid climate;

(b) enclosed basins containing salt lakes or salt flats;

(c) Tectonic-driven subsidence;

(d) associated igneous or geothermal activity;

(e) Lithium-bearing source rocks;

(f) one or more aquifers sufficient to accommodate saline reservoirs;

(g) Sufficient time to concentrate the brine.

4. Lithium in other brines

Deep oilfield brines may contain up to hundreds of parts per million of lithium. Lithium levels in brines can be as high as 692 milligrams per liter (mg/L) in some locations. The brine occupies the pore space of the approximately 200-meter-thick limestone at depths between 1,800 and 4,800 meters. The brine, known as trapped seawater, was then hydrothermally enriched with lithium and other trace elements. Oilfield brines have two disadvantages as a potential lithium resource.

First, they typically occur at deeper depths (greater than 1 km) than closed basin brines. Second, unless they happen to be located in arid climates, it would not be feasible to recover lithium using the convenient and cheap method of solar evaporation. Geothermal brines are another potential source of lithium. These fluids have traditionally gained value from the heat they contain, which can be converted into mechanical energy -- but some geothermal fluids contain unusually dissolved metals, including lithium. Simbol, Inc. is reportedly now recovering lithium from geothermal brines in the Salton Sea region along the California-Mexico border.

5. Lithium clay deposits

A small fraction of the world's clay deposits are lithium-rich. Lithium-bearing clay deposits account for about 7% of the world's lithium resources. Lithium clays are found in hydrothermally altered sediments of lakes in craters. Lithium recovery by leaching clays with sulfuric acid has proven feasible. In Turkey, the world-class Bigadiç borate deposits formed in hydrothermally altered sediments filling rift-associated lake basins with associated hectorites.

6. Lithium zeolite deposits

The only documented lithium zeolite deposits come from the Neogene basin system in the Balkans of Eastern Europe. The Miocene lake beds in the Jadar Basin include oil shales, carbonates, evaporites and tuffs. These formations are autogenous with extensive layers of jdarite, a recently recognized boron-lithium silicate mineral of the zeolite family. The emerald rock formations are reported to be several meters thick. This single emerald deposit accounts for an estimated 3% of the world's lithium resources.