Gold is one of the best electric conductors out there (being only the second best after silver, if I'm not mistaken).
Good old Copper beats it, but gold is favorable for switches and connectors or extremely thin wires due to it's higher corrosion resistance.
Resistivity (Ω across faces of 1m³ cube)
Carbon (graphene) 1×10−8
Silver 1.59×10−8
Copper 1.68×10−8
Gold 2.44×10−8
Aluminium 2.82×10−8
Calcium 3.36×10−8
Tungsten 5.60×10−8
So, if you can't get out of the noise, you've been had and are playing with a fake gold bar.
I mean measurement noise.
A tungsten loaded bar can be thought of as a short stubby wire. A tungsten core surrounded by quite a thick gold sheath.
If you take any high impedance resistance measurement (like a multimeter) then the difference in resistance will be buried deep within the noise, you could amplify the voltage signal as much as you like but no good relative measurements could be made, you would only find noise.
I don't think a resistance test could be accomplished using simple push contact probes.
The cross sectional area of a 400 Oz bar is ~0.0036 M²
The length of a 400 Oz bar is ~0.2 M
So its resistance end to end is ~= ( 2.44*10-8 * 0.2 ) / 0.0036 ~= 5.6 * 10-7 Ω that's 560 nΩ
A tungsten loaded bar would be on the order of 700 nΩ
To bring the resistance reading into a range where one could detect a tungsten core you would have to push significant current through that bar, in the order of 10A or more if you had the most sensitive galvanometer on a Wheatstone bridge. Plus the apparatus would need good environment control ( whole apparatus as same temperature ).
You would need a known interface layer at each end. Otherwise you could take a measurement and see a relativley higher resistance but that might just be a relativley poor connection on one end.
Machining flat areas is needed to give a known electrical interface when dealing below µΩ, the flatness reuired would not be super flat optical though as you could apply pressure to the contact blocks and take advantage of golds high malleability.
