Well this an opinion I respect from Deano from down under. No stranger to gold in it's natural form.
Many times in my career I have been sent samples of ore that were not assayable by standard methods, either qualitatively or quantitatively. Yet the owner was convinced there was payable gold in the ore. None of them ever would own up to how they determined that this mystery material contained gold.
Best we can tell you from what you have told us is to screen the soil through a 5 micron screen with the hope the fine monovalent gold passes through the screen with some of the fines in the soil. This sample, having passed the screen may be separable by density in a gold pan enough to give you a sample to test further.
Still open to answers from other regions of the world about gold found in unlikely places.