Answer: heavy eroded particles settle out of moving water
Placer deposits forms when rocks weathered due to the effect of water. The heavy minerals from the rocks get settled down in water. Minerals that form placer deposits have high specific gravity, they are resistant to chemical weathering process and are durable.
Placer deposits form when (D) organic matter is compressed over millions of years.
Further Explanation:
During the sedimentaryprocess when the heavy and valuable minerals accumulate, placer deposits/ placer is formed. These are found in the mountain streams. Placer deposits are usually associated with precious metal mining like gold. Sedimentation is the process of settling down of the particles in a medium according to their size.
In the presence of gravity sedimentation occurs. The larger particles have more gravitational force that pulls them down followed by the lighter ones. When the heavy and stable minerals are introduced to weathering, the particles get eroded and flow down through a stream. Because of the heaviness, the metals then settle down at some place and this phenomenon results in the formation of placer deposits.
Placer deposits are usually used in economic geology because metals of high specific gravity which settle down and are concentrated over time are used for valuable purposes.The few varieties of the so-called placer deposits would include: stream or alluvial placer deposits; beach placer deposits; eluvial placers; and eolian placer deposits. Stream or alluvial deposits are so far the most significant placer deposits because these have yielded the most placer gold, cassiterite, platinum, and gemstones. Placer deposits can demonstrate to be truly significant because of a similar reason of high measures of important metals found there.
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AnswerDetails:
Grade:Middle School
Subject:Biology
Chapter:Types of Soils
Keywords:
Sedimentary process, heavy metals, sedimentation, minerals, minerals accumulation, gravity, gravitational pull, placer deposits, economic geology, high specific gravity.
