gold becomes a tier 1 asset class for banks, page-23

Central banks were mostly selling at the bottom of the market, I suspect some may be buying near the top of the market.

Gold isn't really suitable as a banking asset because of its volatility. The major currency pairs typically move20-30% against each other over a ten year period, maybe 50% in an extreme case, so somewhere between 1-4% p.a might be expected (though they can appear more volatile in the short term). Gold is up 600% in a decade, but previous history shows these spikes may be followed by equally sharp falls, and long term stagnation (when ironically it may be most suitable as a banking asset). Most central banks (excluding Kazakhstan) would only want to hold a very small amount of something so volatile, and regulators probably wouldn't want the banks they supervise to hold much either. They aren't meant to be in the business of speculation (though of course it does happen).