The most common and most likely answer to this crossword clue is the 10 letter word MILLIONTHS
I've seen this crossword clue in Independent
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Buddy explains!

The straight part
We know that "minute parts" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case minute parts = millionths.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 MILLIONTHS mean?
MILLIONTHS noun- The person or thing in the millionth position.
- One of a million equal parts of a whole. Term ppm (parts per million) is also used.