Shares in Norilsk Nickel – a proxy for the nickel price – are up a third since August. But hang on: so is the Jakarta Composite. This looks like alchemy, or at least a concoction that should make investors in nickel and its miners cautious.

Many will have been tempted to go long in light of Indonesia’s ban on exports of raw mineral ore. Agreed on January 12, the ban threatens about a fifth of the world’s supply of nickel. That pushes up prices of the metal (which fell by a fifth last year, on global oversupply) and therefore the battered shares of miners. In theory. And by hitting export revenues, the ban also threatens to widen the trade deficit – bashing the rupiah and Indonesian stocks.

But while spot nickel rose more than 2 per cent the same day, shares in Bank Rakyat, a local lender, leapt 9 per cent yesterday. The ban’s terms may prove malleable. For a metal such as copper (initially covered by the ban), they already are: two big foreign miners, Freeport-McMoRan and Newmont, could get leeway to continue selling copper concentrates. Nickel investors must hope the politics keep working in their favour.