Indicator plants are peculiar to a certain place. Though they aren’t necessarily rare, they don’t grow just anywhere. They tolerate only a narrow range of growing conditions, so their presence in a forest signals some distinctive aspect of that place.
Indicator plants can be used for a variety of reasons. They can tell us if we are the wetlands, an old field, a young woodlands, mature woodlands, human impacted sites or whether the soil is alkaline or acid and so on, as seen here and here.
Field horsetail indicates a wet, poorly draining soil and is soggy at different times of the year as is mentioned here.
Horsetail is a perennial plant that is found in or near watery areas such as marshes, streams, or rivers. Horsetail grows in temperate northern hemisphere areas of Asia, Europe, North America, and North Africa. It flourishes where it can root in water or clay soil.
There are some who claim that horsetail can be used as an indicator plant for finding gold, such as the following:
Some of the most useful plants for mineral prospecting are:
The following site has this to say about horsetail:
The horsetail is a type of plant that grows in sandy soil usually very close to a water supply. Its uses are many as it has a high silica content that allegedly can be of some medicinal value, but its primary function during the gold rush days was for... - Horsetail Gold
My question is this: How can one know the differences between what makes a site possibly gold bearing over one that in simply wet, poorly drained and/or sandy, using horsetail as a plant indicator, while gold panning along a river or stream in the Great Outdoors?