The most common and most likely answer to this crossword clue is the 9 letter word SEDIMENTS
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More clues leading to the result SEDIMENTS
Buddy explains!

The straight part
We know that "Deposits" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case deposits = sediments.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does SEDIMENTS mean?
SEDIMENTS noun- A collection of small particles, particularly dirt, that precipitates from a river or other body of water.
- To deposit material as a sediment.
- To be deposited as a sediment.