Question about combined NMR frequencies

[BigDRN]

From reading the previous posts concerning frequency calculation I understand how to calculate a frequency using the NMR combined with the total field. (Thanks carl for the formula!) My question has to do with combined elements. For instance I can calculate the frequency for pure gold, but the gold coins that I search for are 90% gold and 10 % copper. The same goes for silver coins. Is there a formula or process for determining the frequency for combinations of elements? What if the gold is buried in a container - how do you compensate for the container?

Also, some say that there are NMR frequencies for non - elements like diamonds or paper currency. Do you have a source for these frequencies (or know how to get them?)

Thank you in advance for any input that you can give.

Dave