Sentence Structure Question

Hi Everyone,

I'm stuck on the sentence below. I don't know for certain whether the phrase "on the border of the two countries" acts as an adjective, originally of the form " which is on the border of the two countries" or an adverb, which describes where the prospect happens?

To clarify my question, I will write the three cases out here. The first one is the original sentence, followed by the adjective case. The last one is the adverb case.

1) The team was sent out to prospect for gold on the border of the two countries.

2) The team was sent out to prospect for gold which is on the border of the two countries.

3) The team was sent out to prospect on the border of the two countries for gold.

N.B The third sentence was restructured on purpose to highlight its nature.

I would like to ask just one last favour. Would you please also help me correct my grammatically mistakes if there's any ?

Thank you very much in advance

Kenny