Higher purchases by India, the world's second-biggest consumer, could lend support to global prices that are trading near their highest level in a week.
By tracing the air backwards in time, the scientists found that high-mercury air travelled over the Indonesian archipelago before arriving in Australia.
Freeport agreed in August to divest a 51% stake in Grasberg to local interests in return for full operational control until 2041 plus fiscal and legal guarantees, but a final deal has still to be reached.