What is most likely the reason Padma decides to buy the gold necklace? The new mine means the supply is high and the price is low, so she can afford the necklace.
She wants to buy it before the supply is so high that the gold is worthless and the mine closes.
She thinks the mine will run out of gold and prices will increase as demand increases.
Since gold is a nonrenewable resource, demand will be high so she has to buy now before it runs out and the price increases.