The most common and most likely answer to this crossword clue is the 10 letter word CARABINERO
I've seen this crossword clue in Financial Times
C
A
R
A
B
I
N
E
R
O
Buddy explains!

The straight part
We know that "Spanish copper" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case spanish copper = carabinero.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 CARABINERO mean?
CARABINERO noun- A frontier guard (or similar) in Spain or South America.