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Most people have heard about the California gold prospecting rush in what is better known as the California gold rush. What most people are not aware fo is that the California gold prospecting rush was only one of many different gold rushes that have occurred over the last couple of hundred years. Also what many people are unaware of is that these gold prospecting rushes have actually been the impetus for many periods of economic grow throughout the nation and also have done much in promoting the expansion of our great nation. Interestingly enough like the California gold prospecting rush many of the other gold rushes were followed by silver rushes and often ended in the mining of base metals in the same areas where gold was once mined. As in the California gold prospecting rush the heyday of a placer gold rush would last only a few years. The free gold supply in streambeds would become depleted somewhat quickly, and the initial phase would be followed by prospecting for veins of lode gold that were the original source of the placer gold. The gold rush may also quickly change from placer mining to lode or hard rock mining, as the placer miners follow the gold upstream to its source, and discover vein gold deposits. Hard rock mining, like placer mining, may evolve from low capital investment and simple technology to progressively higher capital and technology. The surface outcrop of a gold-bearing vein may be oxidized, so that the gold occurs as native gold, and the ore needs only to be crushed and washed, which is known as free milling ore. As in the case of the California gold prospectors the first miners may at first build a simple arrastre to crush their ore; later, they may build stamp mills to crush ore more quickly. As the miners dig down, they may find that the deeper part of vein contains gold locked in sulfide or telluride minerals, which will require smelting. If the ore is still sufficiently rich, it may be worth shipping to a distant smelter (direct shipping ore). Lower-grade ore may require on-site treatment to either recover the gold or to produce a concentrate sufficiently rich for transport to the smelter. As the district turns to lower-grade ore, the mining may change from underground mining to large open-pit mining. |
