Depends
Are the metals (Au/Ag/Sn) in "actual" metal form
Or is the Ag &/or Sn in the form of salts such as silver chloride &/or the Sn in the form of stannic tin mixed in your gold powder - (stannic tin being "kind of like" silver chloride only MUCH finer)
Edit to add; - & what 4metals asked ----------- What percentages of each metal are in the powder, how finely divided is the powder, are there any additional metals involved?
Kurt