In the topographical survey of the United States, all that portion laying between the Rocky Mountains and the Sierra Nevada, up into the southeastern portion of Washington, is known as the Great Basin. This basin was once an extensive lake bottom, and now, for the most part, filled with alkaline plains of the quaternary age. The surface Is diversified by subordinate ranges of mountains, formed of tilted paleozole rocks and extensive overflows of igneous eruptions. These ranges are barren and shattered, and the stratafied rocks are often found in confusing and irregular positions.
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The chief characteristics of the Great Basin, alkaline deserts and subordinate north and south ranges of mountains, are carried into Eastern Oregon, Washington and Idaho.
Along the coast we find a prolongation of the Coast Range with its fertile valleys of the cretaceous and tertiary. East of the Coast Range we have the quarternary valleys, covered more or less thoroughly with immense outpourings of igneous rocks. These extend into Idaho. On the north we have the characteristic carboniferous rocks extending into Northern Montana interspersed with quarternary and tertiary lake deposits.
The mountains of Eastern Oregon present strong evidence as belonging to the Sierra Nevada Range.
The Northeastern portion of Oregon is formed by the prolongation of the igneous plateaus of Washington, while the southeastern portion belongs to the Great Basin which comes up from Nevada. It is traversed by the same block-tilted ranges peculiar to the basin region farther south. The general surface is covered by quaternary lake deposits, and outflows of igneous rocks. The basin ranges of mountains are all of the block-tiling sort, and, where exposed show paleozoic rocks of great thickness. In these ranges is where mining is almost exclusively confined while between them lay great alkaline plains.
The characteristic rocks are of the igneous type-granite, seyenite, diorite, gabbo, and diabose in the holocrystallime varieties, and phorphyries, trachytes, and basalts in the porphyritic sorts, with some pitchstone and obsidian. In Baker County we find slates and granites predominating, although, for the most part, covered by igneous overflows.
As a producer of gold and silver, Oregon is taking a prominent place, and Baker County is the seat of the chief mining districts of the state, and presents the characteristic placers and quartz ledges of the Sierra Nevada region of California, Grant and Union Counties are also important gold producing localities.
Outside the counties forming Southeastern Oregon, the gold and silver production is very limited. Some auriferous beach sands are encountered at Port Orford, where the ocean has access to cliffs of gravel, which is broken down by the waves. A sorting action occurs and the gold is accumulated and can be gathered up at low tide. The quantity, however, is small, and the deposit is of interest chiefly as to its scientific aspects. The placer mining of Eastern Oregon is of considerable importance. Our placers have produced many millions and they are extensively worked to-day.
Quartz mining is in its Infancy yet. Probably not more than 800 stamps, or their equivalent, are cropping in Baker and Grant Counties. It is safe to conclude, however, that this number will be doubled in the near future Whether our ores are workable at the highest saving by the stamp mill will be subsequently considered. Where we find the Great Basin tilted sort of mountain ranges we can reasonably expect to find sufficiently rich quartz ledges to work into mines.
But by far the must blighting element to the advancement of scientific metallurgy is the “mining expert.” He has learned a few mining phases. He possesses the ability to put them together fit connection with a few poorly made assays from more poorly taken samples and deduce fabulous dividends from a ridiculously small investment. Perhaps the source of the trouble is that any one is permitted to attach those mysterious cabalistic letters, M. E., to his name. There are many honest, conscientious men in the profession, but it is no easy task for the busy business man to distinguish the genuine from the false.
There is another class, who, though well-meaning, are no less a retarding force to the advancement of scientific mining applied in a rational, business-like way. These are the class called by a friend of mine, “kidgloved Frieburgers.” They have been just turned loose from some educational mining hot-bed. They confront the miner with a lot of crude, unapplicable theories, and of course, failure results. This only more firmly weds the miner to his own methods.
But to return to ore dressing. In this I can but broadly hint at some of the things that influence treatment, and which I trust will lean to a more careful study of the conditions presented in each case. More attention paid to this in the beginning of our equipment will reduce greatly the numbers of failures, and render many a property a dividend produced instead of a financial loss. Perhaps the first great question to settle is what elements are found in the ore, if any, that will influence treatment. The ordinary classification of ore into “tree milling” and “refractory” is hardly sufficient. The hitter term is of a too indefinite meaning. The following schedule embraces the present methods of dealing with various ores:
1st. If free gold, with no “sulphurets,” free gold milling.
2rd. If some free gold with “sulphurets,” free gold milling, with fine concentration and chlorination or smelting of the product.
3rd. Heavy iron pyrites, carrying gold, fine concentration and chlorination or smelting of product.
4th. Chloride of silver ores, free milling.
5th. If silver ores with base metal “Sulphurits,” fine concentration and smelting of product.
6th. Heavy mineralized ores of lead, copper, tin or zinc, Course concentration and smelting.
7th. Light mineralized ores of copper, lead or zinc, tine concentration and smelting.
8th. Copper pyrites or chalcapyrite, coarse or full concentration, with partial roasting and melting.
In treating ores by course or title concentration, there are certain minerals, of no value in themselves, that must be taken into very careful consideration.
1st. The partially decomposed ores are very difficult to concentrate, especially if they are easily pulverized.
2nd. It is very difficult to separate iron pyrites, copper pyrites, mispickel, or sulphate of barium, from silver ores.
3rd. The rocks chlorite and epidate are very difficultly removed from copper ores.
4th. Lead and antimony, especially in the form of sulphides, are very injurious to the amalgamation of either god or silver.
5th. Talic is injurious to chlorination.
6th. Copper pyrites, chalcapyrite, sulphate of copper and all soluble acid salts to treatment by cyanide.
The practice of free milling is familiar to all who are conversant with the present stamp milling practice. There are many things to consider in this method at treatment where various ores are subjected to it, and the losses are sometimes very heavy, but the limits of this article are too small to consider them further. When, however, our ore contains valuable “surphurets, or is familiarly known as refractory, the question of the economic treatment of them is then one of the most complex that mining and metallurgy has to consider, and the one who would solve it must put favorite methods religiously away. The conditions of mine and ore are to be the chief elements in the solution. The process must be adapted to the ore, and no attempt made to adapt the ore to any prejudiced process. The question of crushing must receive must careful attention. It is not rock crushing that is wanted by scientific milling. After the rock has been properly reduced the subsequent treatment would appear simple, but in fact, it is peculiar to itself. Concentrators that work well on one ore may not on another. Each system must, be peculiar to itself.
After the concentrates have been produce, their subsequent treatment would appear simple, but, in fact, it is often most difficult. If they are to the smelted the question is perhaps quickly adjusted, but if they are to be treated by chlorine, they must be at least partially roasted. The process of roasting pyrites in order to effect the extraction of the highest percentage of values is not -so simple as many suppose. Pyritic roasting is almost as old as gold mining, and its importance is increasing each year. True, there are many processes suggested for the extraction of the gold and silver from pyretic ores without roasting, but their success is limited to peculiarly consituted ore. There is no subject connected with gold mining which demands more careful consideration than the economic treatment of our pyritic ores. The driving off of the sulphur and arsenic by the application of heat, is, no doubt, very easily accomplished, but very fee ores are so simple as to contain but the sulphides and arsenides of iron. Subsequent treatment will determine how thoroughly the roasting process must be done, if the roasted ore is to be amalgamated. The roasting must be absolutely dead, for partially rousted ore is worse than no roasting at all.
Many ores have a tendency to agglutinate on roasting. To obviate this evil sand or charcoal are added, but the addition of charcoal to ore containing lend or antimony is very detrimental.
A detailed consideration of tile various “processes” for the treatment of our “refractory” ores would occupy more space than is allotted to me. Mining in all its departments is a most legitimate form of manufacturing, and when properly conducted furbishes the safest investments for capital. It is like any other form of manufacturing, subject to the law of diminishing returns, and each special process must be adapted to the conditions.