This paper concerns analyses of over 2500 Parthian, Sasanian, and Umayyad coins. The data are part of a coin analysis data base consisting of over 4000 determinations of silver content by a low intensity irradiation technique, along with over 7000 determinations of a larger list of elements by a streak method of analysis which employs higher intensity irradiations. The ratio of gold to silver in coins tend to show a strong clustering by region and place of manufacture. This is interpreted as evidence that gold:silver ratios are peculiar to veins of silver which were exploited at particular time periods. Spread in the gold:silver ratios may reflect mixture of silver from several sources or re-minting of coins. The number of sources indicated by clusters of gold:silver ratios and trends in relative purity of silver coins (percent silver) are noted for each of the periods considered.