Remember that locations which catch gold also catch lead, iron, and other heavies. Also, crevices have various organic material in them as well as gold. I expect a dog could be trained to point on scents of those materials and this may lead to gold. Certain plants are known to thrive in gold bearing areas. Again, this may not necessarily be due to presence of the gold itself but to heavy nutrients which are concentrated in the same locations as the gold. There are also plants as well as bacteria which can retain gold as part of the uptake of nutrients. I have done fairly extensive mossing for gold and have found that certain species of moss will collect gold better in a given area than other species of moss. I suppose a dog could be trained to differentiate between these different types of moss using the sense of smell. Also, different plants have different root structures and some roots are better gold holders than others. Again, a dog could be trained to point on certain plants. There is still much unknown about the so called "sixth sense" of both man and animal. Keep an open mind.
