An advice for the prospecting geologist from 1731 - observe the water

“The miner needs in his art to have the most experience, so that he knows the place, the mountain or the hill, the valley or the field, that can be mined with success, and to avoid to dig were nothing can be gained.”
from Agricola, "Zwölf Bücher vom Berg- und Hüttenwesen", I. Buch (1549)

Georg Grandtegger was a mine inspector in the Prettauer mine (Tyrol) who published in 1731 a field guide to find ore. Some of his suggestions may be useful even today, so he writes:
 

"The water of a spring must be tasted for the dissolved substances in it"
 

It is true that minerals like salt, sulfur and some metallic ores are water-soluble and can alter the taste and smell of water. Water saturated with metals can also precipitate new minerals (mostly oxides and hydroxides) in a river, like reddish-brown sediments when saturated with iron or greenish crusts when saturated with copper.
 

So Grandtegger continues:

"The brand [a term referring to color-alteration of the rock] comes from an ore along the creek. Follow it as long as you see it, then you will find the ore.”
"If you find in fountains [read springs], feed by the mountain, many reddish, bluish or black stones, or even colored green, even if the rocks itself have no ore, so flows the water out from veins of ore."
 

Fig.1. A spring, the mud around is colored by iron-oxides and -hydroxides, a clue that in the underground there is ore-rich schist to be found.

Grandtegger correctly suggest that a prospecting geologist should observe carefully if rocks are colored by precipitations of metals in a river. If so the geologist can follow the river until the spring. The source of the dissolved metals will likely to be found here in the underground. 

Fig.2. The reddish colors of the pebbles in this creek suggest the presence of iron and copper. Sometimes even the name of certain localities can help the prospecting geologist, like here, as this small creek is found in the “red valley”.

A last important observation, as dissolved copper is poisonous for animals and plants, rivers flowing in copper-rich rocks will likely show a diminished presence of insects and fish – so it may be a good idea to ask local fishermen about spots were they don´t get to catch anything, it may be the right spot for the geologist.