Which statement best characterizes secondary deposits compared with primary deposits?

Which statement best characterizes secondary deposits compared with primary deposits?

• A. Diamonds are more concentrated in secondary deposits and secondary deposits have a higher percentage of gem-quality diamonds.
• B. Diamonds are more concentrated in primary deposits and secondary deposits have a higher percentage of gem-quality diamonds.
• C. Diamonds are more concentrated in secondary deposits and primary deposits have a higher percentage of gem-quality diamonds.
• D. Diamonds are equally concentrated and gem-quality percentages are equal.

Answer: (A)

Diamonds reach secondary deposits by being eroded from their original host rocks and carried by water until they settle in placer (alluvial) deposits. The moving water acts as a strong concentrating force, so heavy diamonds accumulate in limited areas such as riverbeds and gravels, creating a much higher local concentration than in the primary source rocks. During transport, hydraulic sorting and abrasion tend to remove damaged or smaller stones, leaving a larger fraction of intact, robust gems. This combination—greatly concentrated deposits and a higher proportion of gem-quality stones—makes secondary deposits stand out compared with primary deposits, where diamonds are dispersed within host rock and yield a broader mix of quality.

Diamonds reach secondary deposits by being eroded from their original host rocks and carried by water until they settle in placer (alluvial) deposits. The moving water acts as a strong concentrating force, so heavy diamonds accumulate in limited areas such as riverbeds and gravels, creating a much higher local concentration than in the primary source rocks. During transport, hydraulic sorting and abrasion tend to remove damaged or smaller stones, leaving a larger fraction of intact, robust gems. This combination—greatly concentrated deposits and a higher proportion of gem-quality stones—makes secondary deposits stand out compared with primary deposits, where diamonds are dispersed within host rock and yield a broader mix of quality.