Gold-mining stocks just delivered one of their strongest weekly rallies in decades as investors piled into the sector following bullion gains.

The VanEck Gold Miners ETF (NYSE:GDX) has rallied 21% for the week through midday Friday, putting it on track for its biggest weekly gain since December 2008.

Miners received a powerful two-sided boost to earnings.

On the revenue side, gold jumped more than 7% to a two-month high near $4,350 an ounce after July’s payrolls report showed the U.S. economy unexpectedly lost 23,000 jobs, versus expectations for an 80,000-job gain. The weaker labor data slashed expectations for a September Federal Reserve rate hike, sending investors rushing into bullion.

At the same time, miners’ cost base improved sharply. Crude oil prices tumbled nearly 8% for the week, reducing one of the industry’s largest operating expenses.

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