SAN FRANCISCO (MarketWatch) — In another two decades, rare commodities may become seriously scarce.

According to Goldman Sachs, the world has about 20 years’ worth each of known minable reserves of gold US:GCJ5, diamonds and zinc. Platinum US:PLJ5, copper US:HGK5 and nickel reserves only have about 40 years or less left.

“The combination of very low concentrations of metals in the Earth’s crust, and very few high-quality deposits, means some things are truly scarce,” Eugene King, European metals and mining analyst at Goldman Sachs, wrote in a recent research note.

“Gold has been used as a measure of wealth for more than 4,000 years, as the ancient Egyptians soon worked out that gold was not only shiny and heavy, but rare,” he said.

All told, their “relatively scarcity and the market’s belief that new discoveries will be limited, is what drives the price of these super-rare commodities,” King said.

Making gold rarer still, production of gold may also hit a peak this year.

A Goldcorp US:GG slide show last year revealed a gold-mining-industry forecast that 2015 would be the year that production would peak in the mining industry, according to a piece in ZeroHedge, dated Friday.

“Peak gold is not a new concept at all,” said Peter Grant, an analyst at precious-metals dealer USAGOLD. “Mining output has been fairly flat for years, but new discoveries of gold have been falling rapidly.”

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Still, “if we do reach peak gold in the near future, one would logically expect this to be broadly supportive to the price of gold for years to come,” said Grant.