I know that my 3 great uncles who opened up gold claims from 1900 through 1940s did make some gold and I found no tax records except this nugget - on a 1921 census, one listed income for year as $800 CAD. I would imagine that most men would not admit to what they made unless the gold was cleaned in town where the true value of what they pulled out was recorded at the Gold Bureau.
You could check with early censuses and see which ones listed Income as a column heading.
When I visited the Yukon Archives for 3 weeks and daily poured over all the obviously named books and reports and records, I found nothing. If a miner in the 1920s said he made 800, don't you think he is likely to have pulled out 1600 instead? Men resented that they had to pay anything in taxes. You could check the Klonodike Library which is part of the Dawson Museum (online). They will also do research for you - cheaper if you are a member. They are located in Dawson.
I would love to hear more of your research.
jderenas@gmail.com I went to the Yukon knowing that I had 4 men and 2 wives, and returned 2 months later with 22 total relatives and 1 living descendant in Carcross. Now I have found a 2nd living descendant outside of Whtiehorse.