Tungsten's density is 19.25 g/cm^3, and gold's is 19.3 g/cm^3. Given the variations in density inherent in casting, it would seem that tungsten would indeed be an ideal 'substitute' for gold, that would probably pass Archimedes' test. It would not, however, stand up to x- or gamma ray scans, or other more sophisticated methods that need not destroy the bars.