What type of deposits refers to diamonds dispersed in riverbeds or ocean floors?

Alluvial deposits refer specifically to precious minerals, such as diamonds, that are found in environments where water has moved and deposited them, such as riverbeds or the floors of oceans. Over time, natural processes like erosion break away diamonds from their original source, commonly volcanic pipes, and transport them through water to accumulate in sediment beds.

This sedimentary accumulation in riverbeds and ocean floors is what characterizes alluvial deposits. Diamonds found in these locations are often easier to mine and access compared to those that are embedded deep within the earth, as seen in other types of deposits.

Other options like pipe deposits refer to diamonds located in volcanic formations, which is a primary source of diamond mining. Artificial deposits don’t apply because they imply human-made sources rather than naturally occurring ones. Surface deposits would generally point to diamonds that are exposed at or near the land's surface but do not specifically refer to the action of rivers or oceans, which is central to the definition of alluvial deposits.