Differentiate between alluvial (placer) diamonds and primary diamonds hosted in kimberlite pipes, and state the implication for mining methods.

• A. Alluvial diamonds are eroded and deposited in riverbeds and are mined via placer methods, while primary diamonds are in kimberlite pipes requiring open-pit or underground mining and blasting.
• B. Alluvial diamonds are synthetic; primary diamonds are natural.
• C. Alluvial diamonds come from the sea floor; primary diamonds come from riverbeds.
• D. Alluvial diamonds require underground mining; primary diamonds can be mined via surface alluvial.

Answer: (A)

The key idea is that where a diamond is located in the geology determines how you mine it. Alluvial (placer) diamonds come from rocks that have been weathered and eroded, then transported by water and deposited in riverbeds, floodplains, or beaches. Because these diamonds are free in sediment and not embedded in hard rock, you recover them with placer methods that rely on gravity and screening to separate diamonds from gravel and sand.

Primary diamonds, on the other hand, are still hosted in their original rock, typically within kimberlite pipes that carried them to the surface. To extract diamonds from these pipes you must mine the hard rock itself, which usually means open-pit mining if the pipe is shallow or underground mining if it lies deeper, and blasting is often needed to break the rock before processing to separate the diamonds.

So, the mining method implications line up with the geology: simpler, surface-level placer mining for alluvial diamonds; more intensive hard-rock mining with blasting for kimberlite-hosted primary diamonds. The other statements mix up the source or the method and don’t fit how placers and kimberlite-bearing diamonds are actually encountered.