gold/silver ratio - future potential ratios, page-12

The 16:1 ratio is based on silver being 16 times more abundant than gold in the Earth's crust.

However, large stockpiles of silver have been used never to be seen again. Eg, when a cruise missile explodes, the silver in the electronics is vaporised. That silver still exists, but only as silver oxide floating around. Other uses of silver also result in that silver being lost forever.

Then you add the fact that silver is much more useful than gold.

So, a lower ratio makes sense.