Ch. 2: Platinum in 1913

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	454	MINERAL RESOURCES, 1913—PART I.

	of the serpentine which accompanies the dunlte in the original deposit Is to be found In that very alluvium far down the river. The development of platinlferous alluvium all over the Urals is the same—post Tertiary. * * * The distribution of the platinum in the alluvium is very irregular, and depends on the form of the river channel and the nature of the rock through which the river flows, on the existence of lateral platinlferous tributaries, etc. Wherever the solid rock forms a bar across the river, platinum gathers from the upper sources as in a natural riffle. Near the original center the platinum is large, slightly rounded, and often of a dark color. Small nuggets are not infrequently found. Further down, the platinum begins to become smaller, more and more rounded, and slightly white. At a great distance from the original center— as, for example, on the River Tura—the platinum is changed Into sandy grains of uniform size, formed by contact with stones. Generally the content of platinum in the alluvium, which is fairly regular, decreases from the upper reaches to the mouth of the river, with the exception of cases where there are platinlferous tributaries. Besides this, in every given section the very richest part is seldom found in an existing river channel, as the axis of the old bed along which the richest content is distributed is often deflected to the right or to the left, and is often found at a considerable distance from the existing channel. Sometimes in the alluvium of the tribuatries of the large platinlferous rivers we find platinum in large quantities, while these tributaries from the source to the mouth flow through barren ground, for example, in limestone or crystalline schist. In this occurrence we shall find nothing abnormal if we remember that at the beginning the alluvial covering of some rivers was very extensive. The lateral tributaries, which were fresher in development, once more broke open this covering, and scoured it in places, so that the platinum contained in it underwent a second concentration. This particularly applies to some tributaries of the Lower Iss—for example, the Shuravlika. * * * Sometimes certain rivers formed a kind of alluvial cover, which corresponded to the succeeding change of their channel. In this category we lind the River Martian, as in its upper reaches there is the old channel to the east of the present one at the foot of the White Mountain, and on the upper level the alluvium is hidden under a deep bed of material carried down, and of eluvium. It is the same in the River Iss. On looking at the chart of the platinum placers on this river, we are at once struck with the unusual width of the alluvial plateau of the river, and see that there exist at least two distinct directions in which the deposits of alluvium took form. The presence of this platinlferous alluvium in places where all the rock is not productive explains the existence of platinum In some of the large rivers, which ought not to be platiniferous, as, for example, the Aktai. * * *



	As the production of platinum in Russia will probably decline in the next few years, the attention of the platinum trade is directed more and more toward Colombia as a favorable source of the future supply. This country has already far outstripped all other regions except Russia, and yet most of the metal obtained is only the irregular production of the natives, using crude methods for its extraction. The main region in Colombia for platinum is the Choco, including the tributary rivers. This is the only region in the world, aside from Russia, where platinum is obtained in much greater pro-

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