Cassiterite

Cassiterite is a (generally) opaque tin oxide mineral that has thin translucent crystals. Its multiple crystal faces and luster also make it a desirable gem. Cassiterite has been the major source of tin ore from ancient times up to today. Tin was once the main method used in making containers for keeping food and drinks fresh although this role has mainly been taken over by glass, plastic and aluminium in more recent times. However, it is still used to produce polishing compounds and solder.

The History of Tin Goes back Over 5,000 Years
Tin is a metal that has been traded and used by people for over 5,000 years with one of its oldest uses being alloyed with copper to make bronze. It the first century AD copper was coated with tin and by the 16th century tin plated iron became widespread. Tin is advantaged by having a low melting point, its ability to alloy with other minerals, being easy to recycle and is non-toxic. Tin is also resistant to fatigue and corrosion and easily malleable.

Cassiterite is Associated with Granite Intrusive Rocks
Cassiterite is the most important tin ore although small amounts of tin is recovered from stannite and other sulphide minerals. The most common source of cassiterite is associated with granite intrusive rocks that have magma bodies embodied in them below the earth's surface. Not on them, as is the case with volcanic rock. The primary deposits often occur within aplites or pegmatities that are associated with granite, or within the granite rock itself.

Cassiterite Placers are Secondary Deposits
Placers, or secondary deposits, are derived from the erosion and weathering of tin deposits. Cassiterite itself is resistant to chemicals, is heavy and easily forms residual concentrations. The concentrations sometimes form over a primary (eluvial) deposit and on lower slopes below the deposit that are known as colluvial deposits. If it manages to reach a drainage system it sometimes finds its way into a river system where it can be concentrated into an alluvial placer deposit. This placer deposit becomes buried over time through sediment or lava and if this happens it is known as deep lead. This can happen in old river beds now submerged by ocean. An important source of tin in Thailand, Indonesia and Malaysia that produce half of the worlds tin production.

Renison Bell Tin Mine in Australia is the Worlds Largest Underground Tin Mine
The Renison Bell deposit in Tasmania is a primary carbonate replacement tin deposit, it holds 85 percent of the Australian tin resource. Renison Bell is one of the worlds largest underground tin mines. The next most important tin mine in Australia is located at Greenbushes in Western Australia. Tin is mined at Greenbushes along with tantalite from a weathered primary deposit.

Two Methods of Mining for Cassiterite
Most placer tin deposits are mined by bucket-line dredging. The alluvium containing tin, once excavated, is transported to the centre of the dredge where it is washed and concentrated. Disseminated and vein tin deposits are mined in a similar manner as that used in hard rock mining generally. The ore is broken by drilling and blasting. It is then taken to a concentrator plant for it to be crushed and ground and concentrated by gravity. Flotation is not as efficient when treating tin ore as it is for sulphide ores but it is still used to improve the tin recovery rate.