XRF analysis.12 Mar 2021 12:23
I was a technical manager/ chemical analyst in the electroplating industry for 40 years.
I found XRF to be fast, typical measurement times were 30secs.
A semi technical person has to set the method up and then anyone can get a result.
Gold shows up well. All heavy elements do because they have many electrons. Nickel, iron, copper also give signals but weaker than gold, platinum, tungsten. Gold gives a distinctive double peak.
The Xrays target a small area, mine looked at under a sq mm. In order to collect as many emitted Xrays as possible the detector had to be close, this limited the size of the measurement chamber and therefore the size of the sample. The Xrays penetrated several microns (millionths of a metre), I could not measure a thick sample directly. I could measure a wide area by moving the sample under the incident Xray beam but the sample had to be flat.
Usually there are no suitable standards. I mean a piece of ore containing a known amount of gold and comparable amounts of all the other elements. Without standards the analyst relies on the computer program to calculate the gold content based on assumptions the manufacturer made. If you want to dig up and process millions of tons of ore you have to get the drill samples into a laboratory. The results will be slow and expensive but reliable. If you want to know where to drill next, an XRF may be good enough.