I remember have heard this long ago on Reddit but was never interested in doing the research needed, then I found it was indeed even more rarer 
Here is what I got:
"The World Gold Council estimates that all the gold ever mined totaled 187,200 metric tons in 2017" so this means there is a total equivalent in ounces of 187200000/0.02835 = 6,603,174,603 ever mined at this point in earth.
So with a total of 21,000,000 that would be ever created this means a total of 6,603,174,603/21000000 = 314 bitcoin ratio against gold, so you can say per one bitcoin there is 314 gold ounces
Links: https://en.wikipedia.org/wiki/Gold_reserve
Availability of gold maybe too abundant still because man only went to the top layer of the earth but no one really know what is at the centre of earth's crust so in future gold may found too much if people can go deeper.But why did you compare bitcoin with gold?Here is what I got:
"The World Gold Council estimates that all the gold ever mined totaled 187,200 metric tons in 2017" so this means there is a total equivalent in ounces of 187200000/0.02835 = 6,603,174,603 ever mined at this point in earth.
So with a total of 21,000,000 that would be ever created this means a total of 6,603,174,603/21000000 = 314 bitcoin ratio against gold, so you can say per one bitcoin there is 314 gold ounces
Links: https://en.wikipedia.org/wiki/Gold_reserve