"But even that wasn't complicated enough for Mother Nature. In those same eruptive rocks, both of the early and later periods, gold is mainly found in veins. These veins are of dozens of different sorts, depending on the rock in which they occur and on Nature's ways of putting them there.
"To make it simple to you, I'll only mention two. The most general method was by fumaroles. These are subterranean blow-holes of vapor containing sulphur, tellurium, and chlorine compounds, as well as super-heated steam. These vapors, projected from deep down in the earth with incredible pressure and energy, acted on the new-made rocks, formed compounds with the metals, or, when united with hydrogen in the steam, separated the metals from solutions of their salts, and forced the metals into cracks in the new-made and cooling eruptive rocks. According to the kind of rock and the nature of the chemical agent, a geologist will know for what type of vein to search. The other most general agent of vein-making was hot water—generally heavily saturated with sulphur and other chemicals—which dissolved the gold. This hot water, with gold in solution, seeped into the cracks and crevices made by the rock as it cooled, thus forming other types of veins."
"Hold on a minute, there!" protested Jim. "Water won't dissolve gold."
"It will and does," was the retort, "especially when certain chemicals are in the water. As a matter of fact, even to-day, the geysers at Steamboat Springs, California, and at several places in New Zealand, deposit gold and silicon in their basins. But let me go on.
"After the gold was placed in veins in these primary rocks, there came a period of erosion, and the mountains were worn away. The gold being harder than rock, it remained and made alluvial deposits of a very early age. Some, of these old 'placers' are several miles below the surface, now, others have come again to the surface by all the superposed rock having been washed away, anew. Some of the gold was dissolved, as before, and got into the crevices of the newly deposited rocks made by erosion, known as sedimentary rocks. So, you see, Jim, even millions of years ago, there was gold in the crystallized eruptive rock, gold in veins of igneous rock, gold in alluvial deposits, and, again, gold in veins in the sedimentary rocks.
"Then came another period of elevation, with a second raising up of mountain ranges, and with a renewal of violent volcanic action. The crust was getting more and more unequal, the way in which the metals were distributed became more and more scattered. Mountains of the Secondary Age were often made of Primary sedimentary rocks, or of Primary igneous rocks, so much changed that geologists call them metamorphic rocks. And, Jim, every time that the rock was changed, the gold changed either its place or its compound character, or both. Then came another period of erosion, lasting millions of years, the gold was washed away to form new placers, or made its way into veins in the Secondary sedimentary rocks.
"Then came the great upheaval of the Third or Tertiary Age, in which new mountains rose, new volcanic vents were opened, and, once more, much of the gold was acted upon by chemicals, mainly sulphur and tellurium. In many places silver showed a strong affinity with gold, forming deposits where the ores were commingled. Once more the hundreds of centuries of erosion came, to be followed by the upheaving of the newer mountains of the Fourth or Quaternary Age. So, you see, Jim, as I told you before, gold can be found in almost every rock and of every geological period."
"I don't see that it helps much, then!" declared the old prospector. "You can go lookin' where you durn please."
"There's nothing to stop you," agreed Owens cheerfully, "but that's a hit-and-miss method. And I can show you just how even this little bit of geology comes in to help the miner.
"Get this clearly in your head, Jim! Three-quarters of the present gold production of the world comes from gold that is mixed with pyrites—which is a sulphide of iron, or from tellurides—in which a tellurium-hydrogen compound has been the chemical agent. A prospector, therefore, who uncovers a new field where the gold is in the pyritous or the telluride form has ten times more chance of attracting capital than one who finds lumps of native gold lying around loose.