diamond deposit types
The Two Types of Diamond Deposits
Geologic processes create two
basic types of diamond
deposits, referred to as primary and secondary sources. Primary sources
are the kimberlite and lamproite pipes that raise diamonds from Earth's
mantle, where they originate. Secondary sources, created by erosion,
such deposits as surface scatterings around a pipe, concentrations in
channels, and fluxes from rivers moved by wave action along ocean
past and present. Mining of these deposits depends upon sufficient
and quality of diamonds.
The diagram here shows the trail of diamonds left by geological processes.
The primary deposits, or diamond pipes, are the vertical portion. The flared top of the pipes can yield substantial quantities of diamonds, but following the narrowing pipe downward eventually becomes unprofitable. Note how erosion of the landscape moves surface minerals -- including the diamonds -- from the pipes down hills, streams, and rivers to their ultimate destination, the ocean.
Because diamonds are dense they
the bottom of active zones of moving sand and gravel. These secondary
are eluvial Ð above a pipe, colluvial -- adjacent to a pipe,
Ð stream and river transported, and marine -- along beaches
wind up onshore or offshore with changing sea level. Secondary deposits
may be found far from active means of transport, in the fossilized
of now-vanished rivers or under fossil beaches.