A deposit is defined as a group of occurrences large enough to be worked (also called a mine). A find is described as a single occurrence.
Primary deposits refer to gems found in their original location. The yield is generally low due to the fact that many tons of non-gem bearing material have to be excavated.
Secondary deposits refer to gems which have been transported by the actions of wind, rain and flowing water.
Fluvial deposits are created by rivers, marine deposits by the sea and aeolian Deposits by the wind.
The distribution of gems around the world is irregular. Gem deposits occupy only a tiny proportion of the earth’s crust. Some of the more favoured regions are:
The gem-rich metamorphosed limestones of Upper Mayanmar (including the “Mogok Stone Tract”) renowned for Rubies, Sapphires and Spinels.
The alluvial deposits of Sri Lanka, Vietnam, Thailand and Madagascar and the Minas Gerais and Minas Novas districts of Brazil.