The most common and most likely answer to this crossword clue is the 5 letter word TAELS
I've seen this crossword clue in The Times
T
A
E
L
S
Buddy explains!

The straight part
We know that "Old Chinese coins" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case old chinese coins = taels.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 TAELS mean?
TAELS noun- Any of several units of measure used in China and elsewhere in eastern Asia, approximately 40 grams.
- Any of several monetary units equal to the equivalent weight in silver.
- Leung, a traditional unit of weight, in modern usage legally defined as 1/16 of a catty or kan (斤) or 0.0377993638 kilograms