Thank you for the suggestions. Indeed the composition range is quite similar to what we see in the bronze age Near East. Evidently as you said I should start looking for parallels in the royal cemetery of Ur
The values you give are fairly standard for natural gold alloys save for the high Cu content, which would likely be due to a deliberate addition. As for intentional depletion gilding it can be compromised by burial conditions which must be taken into account,
as in the case of some artifacts from Ur. Mercury gilding is to be excluded for the time frame you mention. At the most gold foil was applied with an organic glue. It is fairly easy to to identify gold foil with an optical microscope.
If possible, the quickest test is to determine specific gravity. This would require immersing the artifact in pure water which may not be acceptable.