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One of many such may be cited in the Star vein at Cherry Creek, Nevada, which, nearly at right angles to their strike, cuts belts of quartzite, limestone, and slate, maintaining its peculiar character of ore and gangue throughout. This and all similar veins have certainly been filled with material brought from a distance, and not derived from the walls.
The first is used in alluvial gold and tin workings and in preparing some silver, copper, and other ores for smelting, and consists merely in separating the heavier metals and minerals from their gangues by their greater specific gravity in water. The second includes the trituration of the gangue and the extraction of its gold or silver by means of mercury.
The magnetic particles are attracted out of the straight line of the falling stream, and being heavy, gravitate inwardly and fall to one side of a partition placed below. The non-magnetic gangue descends in a straight line to the other side of the partition. Thus a complete separation is effected.
As evidence of the accuracy of the method, I subjoin the results I obtained on a sample whose gangue was free from all organic and other impurities, consisting chiefly of quartz: New Method. Combustion in Oxygen, Weighing CO . 15.51 15.54
These fragments sometimes exhibit a fracture analogous to that of ordinary coal, with sharp angles that show that they have not been rolled; and the sandstone has taken their exact details, which are found in hollow form in the gangue. In other cases these fragments exhibit the aspect of genuine shingle or rolled pebbles.
Moreover, I find it possible to moderate the colour and to produce a specimen in which the gold shall be as ruddy yellow as in the ferro-oxide gangue of Mount Morgan, or to tone it to the pale primrose hue of the product of the Croydon mines. "I note that the action of the bath in which the stone is treated has a particularly disintegrating effect on many of the specimens.
Careful dissolving of the pyrites and gangue so as to leave the gold intact failed to find it in any larger diameter. As this was a very unusual experience in investigations on many other kinds of pyrites, I was led further into the matter. "Ultimately, after a number of experiments, there was nothing left but to test for gold existing as a natural sulphide.
The second, on the contrary, is formed almost wholly of oxide of iron with but little gangue and only traces of oxide of manganese. The following are analyses of these two varieties of ore: Friable Ore.
The elementary chemical composition, which is perceptibly the same in the specimens isolated in the sandstones and in those taken from the great deposit, demonstrates that the difference in composition of the environment serving as gangue did not have a great influence upon the definitive state of the coal, a conclusion that we had already reached upon examining the structure and properties of the coal pebbles.
Fayol, we have been enabled to make such researches upon numerous specimens that were still inclosed in their sandstone gangue and that had been collected in the coal strata of Commentry. In some of their physical properties they differ from the more recent isolated fragments and from the ordinary coal of this deposit.
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