Geologists look for secondary diamond deposits in which environments?

• A. Rivers, streams, and estuaries flowing away from cratons
• B. Deep-sea trenches
• C. Mountain peaks
• D. Desert basins

Answer: (A)

Diamonds reach secondary deposits when they are eroded from their primary host rocks (kimberlites) on cratons and are then carried by running water. Their high density causes them to settle out of the otherwise mobile sediment load, forming placer deposits in rivers, streams, and estuaries downstream from the source. These environments provide the right combination of transporting energy and quiet enough zones for heavy minerals to accumulate, creating alluvial gravels and bars that concentrate diamonds.

Deep-sea trenches, mountain peaks, and desert basins don’t typically serve as the main sites for these secondary concentrations. Trenches are deep, tectonically active settings not conducive to steady, downstream deposition; mountain peaks are where erosion supplies diamonds rather than where they settle; desert basins lack the sustained fluvial transport needed to concentrate diamonds in placers.