Practical Mining in Eastern Oregon

Written in 1898

      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.
     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.
     There are but few directions to be given that will aid the prospector in his search for ore. The mere inspection of the outer surface of rock will give but a feint idea as to what it contains, and this is preeminently true in our so called rebellious ores. When a ledge is exposed the examination of the walls is often as highly important as testing the ledge matter itself. From the earliest times it has been maintained that the soil overlaping mineral veins is peculiarly adapted to the growth of certain sorts of vegetation. While this is not an infallible guide as to the location of a mineral vein, It is interesting to note that many plants are eagerly looked for by many prospectors. For instance, near Giesen, Germany, an iron vein is traceable for over two miles by a growth of birch trees, while the surrounding country is thickly wooded with oak and beech. Gum trees, and trees with dead tops, are found most numerous in soil containing "float" galena in clay. The beech tree prefers a limestone soil, and extensive limestone beds have been found by working out this hint. In Montana prospectors look for silver where they find a speies of Erigonium growing. This plant is closely related to our common dock, which it also closely resembles, and to our sorrel and smart-weed. And lastly, all plants growing over zinc deposits nave yellow flowers. Here is a great field for some energetic student in which to create an -logy that deals with the influence of the soil constituents on the selection and growth of plants.
     It is universally conceded that ledges formed as fillings of true fissures make our largest and most permanent mines. Therefore the prospector should be able to easily and surely distinguish a fissure vein. Other veins have been able to produce very rice working ore, but the true fissure vein is a reasonably sure indication of permanency and values. It has comparatively smooth, generally striated surface, and frequently covered with a clayey or talcose selvage. This selvage or "gouge," is supposed to be evidence of pressure and movement. Of course the clay selvage is not always present unless the finely comminuted material produced by the grinding of the faces has been subjected subsequently to the action of the water, which carries off much of the soluble matter, principally the alkaline constituents, leaving the argillaceous or talcose residue. These striated walls and selvages are frequent concomitants of ore-bearing fissures, but by no means absolutely essential. Both may be wanting, and such occurrences are frequent. The ledges or rather ore bodies are of a very eccentric nature, sometimes, as one familiar with Cripple Creek said, "The tenderfoot is looking for gold where he finds it, while the old miner Is looking for it where it ought to be," and the former were quite as successful as the latter.
     Now as to the ledge matter itself. It is quite beyond question, at the present day, that by far the largest amount of gold ore deposits are those wherein the metal exists in very finely divided particles disseminated more or less uniformly through the vein matter, and it is perhaps safe to say that a very large proportion of this exists in connection with the various sulphides and arsenides of iron, copper, lead, zinc, antimony, and bismuth. The miner, as a rule, classifies all these various minerals under the common term "sulphurets," which term, by the way, means very little.
     Whether the gold under these associations is chemically combined with the "sulphurets," or only held mechanically is very difficult to tell. It is the opinion of metallurgists generally that the gold is perfectly free and mechanically associated with the various minerals. It is very evident that where the gold so' occurs it is in such all extremely finely divided condition that the term "flour gold" is not inappropriately applied to it. The localities where the gold is found 'free," or unassociated with the above mentioned minerals are comparatively few, when much of the free milling ore contains more or less "sulphurets" carrying a goodly proportion of the precious metal. There are also larger districts where the gold found is entirely in connection with the sulphides and arsenides of iron, copper, etc.
     The most common gangue matter of the gold-bearing ledges is quartz, with smaller amounts of calcite, siderite, borite and occasionally some of the feldspars, pyroxine, siderite, blend and related compounds. The origin of the metalic contents of veins must be traced either to the igneous rocks of the district or to the ocean. The precise method by which the entire vein matter was placed in the fissure is one of dispute. The weight of opinion, however, is that it was by means of hot alkaline solutions-hydroplutonically. Space wid not permit of a complete discussion of the subject further.
     All operations employed for the extraction of the valuable part of the ores is termed "ore-dressing." The ideal way would be as we crack a nut and extract the kernel unbroken, while nothing is left in the shell. Any process of ore dressing that approaches this is nearing perfection. This is done moth mechanically and chemically to-day, and the precise process to employ in any given case is a problem often difficult of successful solution.
     In ancient Egypt many years before the time of Christ, gold ore was crushed between heavy stones, and the more or less finely comminuted material washed with a stream of water. The gangue and much of the values were swept away, and any gold remaining secured. Very early records also mention the addition of mercury to facilitate the collection of the gold. To-day we use toe selfsame method, inn with about the same results, as pre-historic man used. The only improvement for years past has been toward development in rock crushing tilling to save values is only a secondary matter. The average mill man bends his every effort toward crushing rock and any remonstrance directed against their accepted but antedated methods is looked upon as coming from one but a short way removed from an accredited lunatic. He is conservatism run wild when it comes to the treatment of his ore, but a most profligate liberal when it comes to saving his gold. When assays showed $40 to $60, while the mill returns showed from $15 to $20, some bright genius discovered the terms "refractory and "float gold," to explain why so much eluded their grasp, and the amount of consolation afforded the average miner during years past, by the use of these terms, has been Infinite. Many camps have been entirely abandoned because, for instance, a stamp mill would not save sufficient values to pay running expenses, and still assays showed exceptional values; but the ore was "refractory," and refused to lie worked. The day has come when a single operation. or any one "patent" process will suffice. The stamp and manner Is not to be considered a universal specific fur gold extraction. The only proof of the pudding is the eating.
     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.

Eastern Oregon Gold Fields
Mining in Oregon

Baker City | Baker County

 

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