Is it genuine gold leaf or "pretend" ie made of metal that isn't real gold but is gold goloured? If it's real gold it won't tarnish and would be quite happy with an acrylic lacquer over the top. If it's pretend gold, you should probably use whatever lacquer is recommended by the manufacturer's of the pretend gold leaf. I have used acrylic lacquer over pretend silver leaf (actually aluminium) with success, but have had problems in the past with acrylic lacquer over pretend leaf based on copper (it discoloured the leaf - which was an interesting verdegris effect, but not what I was looking for at the time.)