This is an art deco style mirror made in the 1930-40 time period
based on the shape and incised decoration. This style was also popular/revived in 1980,
but you said the mirror has been in your family longer than that.
It is not true that gold is used to make the mirror blue. A mirror can be tinted blue from
age or created with this tint by using a different backing method (but has nothing to do with gold).
This mirror has a current value of $300 to $400.00.
Some sites that I recommend for selling are Varagesale.com, Ioffer.com, OfferUp.com, Ebay and letgo.com.
You can also go to invaluable.com or liveauctioneers.com and search their directory for an auction house near you and consign to them.
To finish, I will need you to click the five stars at the top right of your screen and hit the green submit button, thanks!