COLUMN-How vulnerable is copper to supply disruption? Andy Home

(Repeats with no changes. The opinions expressed here are those of the author, a columnist for Reuters)

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By Andy Home

LONDON, Feb 9 (Reuters) - The copper market is facing the imminent prospect of the simultaneous closure of the world's two largest copper mines.

Strike action is due to start today at the largest, the Escondida mine in Chile.

There seems little prospect of a last-minute settlement between unions and the mine's majority owner and operator BHP Billiton. The union didn't even bother attending talks on the fifth day of statutory government mediation and the company has started shutting down operations.

In Indonesia, meanwhile, Freeport McMoRan is threatening to partly suspend operations at its Grasberg mine due to the lack of an export permit, the latest turn in the long-running stand-off between the company and the Indonesian government.

At risk is combined production of around 1.7 million tonnes, equivalent to around eight percent of global output last year.

The potential for lost production from one or both may be partly priced into the market, which is currently trading around $5,870 per tonne in London. Fund money has been steadily accumulating since copper's big upside move from below $5,000 last November.

But with copper's notoriously unpredictable supply already back in full focus this year, how well prepared is the market for significant production losses?

Because despite the much-vaunted "wall of supply" coming on stream over the last couple of years, there has been no significant rebuild of refined metal stocks on the world's exchanges.

Indeed, those registered with the London Metal Exchange (LME) are once again shrinking at a fast pace.

DOUBLE IMPACT

Escondida produced around one million tonnes of copper last year in a combination of concentrates and refined metal.

It was a relatively low production year for the world's biggest mine due to low grades. Output in both 2014 and 2015 was around 1.15 million tonnes.

Analysts are calculating a loss of around 20,000-25,000 tonnes of metal for each week of strike action.

There were strikes at Escondida in both 2006 and 2011, lasting 25 and 15 days respectively.

It's worth noting that Chilean labour laws mitigate against long walkouts since after 30 days individual union members are allowed to return to work if they chose to, shifting negotiating leverage back to management.

That may limit both the length of a walkout and the resulting production hit.

There is no such comfort for Grasberg, which is facing multiple threats.

The most pressing is the lack of an export licence for the material not sent to the local Gresik smelter for processing. With limited storage capacity Freeport has warned it will be forced to reduce drastically production to the tune of around 32,000 tonnes per month.