What best defines a Primary Deposit in diamond geology?

• A. A deposit where gems are found away from their primary source.
• B. A deposit where gems are found in the rock that carried them to the surface.
• C. A deposit at the surface with no host rock.
• D. A deposit where gems are found in the surrounding soil only.

Answer: (B)

Primary deposits are diamonds still within the rock that brought them to the surface, typically in kimberlite or related ultramafic rocks. In this context, the diamonds remain embedded in the carrier rock that carried them from depth up to near the surface, rather than being released and deposited elsewhere by erosion or weathering. This is different from placers, where diamonds have been liberated from their original rock and later concentrated in surface sediments or soils by water and other processes. So the best definition is that a primary deposit is when gems are found in the rock that carried them to the surface, reflecting their origin in the host carrier rock rather than being transported to a new location.