Even if there are indicators for gold, which are found by on site visual inspection and testing, additional sampling would have to be done to determine if there is gold, and if it is in paying quantities. Most of these questions are better asked on any of the several mining forums available online.
Testing samples is paramount. Even if no gold is present, there may be profitable deposits of many other items, such as gemstones, metals, and minerals. Learn to take and test samples in the field.
Time for more coffee.