https://www.explorationinsights.com/pebble.asp?relid=2408

Here is an excerpt (my bold added):

There are in the order of 2,000 junior companies listed on the Canadian exchange and maybe 1,000 more listed in Australia, London, and elsewhere. In round numbers they are exploring 10,000 mineral properties of which only 1 in 1,000, on an annual basis, will produce an economic discovery. Worse, only 1 in 10,000 will result in the delineation of a gold deposit of greater than 4 million ounces (Stephen Enders, Society of Economic Geologists Newsletter, July 2011).