Rocks and Gold Veins Filling

 

It is evident that if there is any relationship between rocks and gold bearing veins, the filling process is affected greatly. Basically, some gold bearing minerals or even free gold are more particularly found associated with some particular rock in preference to others, the knowledge of the facts would be of great value to the gold prospector, for when he had obtained an idea of the rocks of any particular district, he would have an idea of the minerals likely to find there, and could familiarize himself with their appearance. Gold and silver are so intimately associated in nature that all gold may be said to contain some silver; and most silver ores carry gold, from mere traces up to important values. Gold containing a large proportion of silver is pale in color, while some native gold-silver alloys are almost white. Lead and silver are also so related that lead ores as a rule carry some silver, if only a trace, and from that up to large amounts in value, though not in bulk, without any special change in their outward appearance.

The gold bearing minerals compose only a fraction of the whole vein filling, the gangue minerals being present in larger, often very much larger quantity. The rocks through which the underground waters pass must contain material suitable to form this gangue, silica for quartz, lime for calcite, and fluorine for fluorspar. The gangue minerals are closely related to the metals and gold bearing minerals. Hence the connection is really important. Probably, the most important case is quartz to gold. Next table shows the occurrence of some rocks in gold deposits. The rocks may be classified according to the amount of silica or quartz in highly and moderately siliceous.