The square shape of the crystals makes me think of pyrite. There's no visible gold in that picture.
Not saying there isn't more, but I doubt there's much value in it. My favorite experiment I would use to find out if there is more, is to crush it down to a powder and use a gold pan.
I'm in agreement that you're seeing pyrite -- fools gold. Hammer something like a nail punch into one of those yellow chunks. What's there will crumble if it's pyrite.
Nokta FoRs Gold, a Gold Cube, 2 Keene Sluices and Lord only knows how many pans....not to mention a load of other gear my wife still doesn't know about!