Mohave County miner., 1915-03-27

NOW lC IS one Cnlng to QerlVe lme-- iron silicate from an ordinary lime stone, and another thing to derive a lime-alumina silicate. Limestones con- tain very little iron, but the contact zones contain a great deal. They habitually display, besides the sili- cates, large bodies of magnetic and sometimes of specular hematite. We thus still found great difficulty in be- lieving that such rich iron-bearing zones produced by the recrystallization of limestone. We both, therefore, urged that emissions from the igneous rock in the form of steam or its dis sociated gases, and of silica, probably in the form of orthosilicic acid, and of iron salts, probably iron chlorides, had been fed into the limestones and had produced the zones. These views were quite revolutionary with regard to the zones, as anyone can learn by reading the earlier literature. No one has ever been able satisfactorily to explain the iron-bearing minerals in any other way. The evidence of the zones is therefore a strong argument in favor of magmatic emissions.
 There is still another far-reaching argument in favor of this form of water. If, in accord with the older conception, we imagine the rain water sinking into the rocks and going only to moderate depths, as we are obliged to do, in conformity with our under ground observations; and if we imagine it again rising to the surface this con- paratively short journey during which we require it to dissolve the irregular and sparcely distributed metalliferous components of the rocks and again to precipitate them in our views in its up- ward journey, we require it to perform two contradictory reactions under the same physical conditions. We can hardly believe that under one set of conditions solution would take place, and in another without essential con- trasts, precipitation would result. But, on the contrary, if we imagine highly heated and even vaporized emissions to come from the interior of great ig- neous mass and to be charged with our ores and gangue, we see that they must very soon be subjected to mark ed change in conditions and we may reasonably infer precipitation.
 The recent studies of Edwin T. Hogde, which have been based upon the mine waters of sulphide bodies, show that when the rain water starts to percolate downward it becomes, in the gossan, an acid solution of iron, zinc, and copper. As it passes lower through the rocks, especially in the wall rocks of mine already open, so as to make circulation possible, it gradually be- comes neutral; the copper and zinc are quickly precipitated, but iron remains to somewhat greater but still only to comparatively shallow depths. Be- fore long, the iron also is precipitated and the water becomes alkaline, with no metals at all in solution, other than alkalies and alkaline earths. A strong argument is therefore made against the efficiency of descending rain waters and against their ability to produce the veins with which we are familiar.
 Somewhat of compromise view has lately been strongly advocated by Pro- lessor Lawson, of the University of California. Professor Lawson is well aware of the almost universal associa- tion of ore deposits in the Western country with igneous rocks. He believes that the igneous rocks have often entered synclinal basin as lacco- liths, and have extensively cracked the overlying strata, but have remained in the depths, with the strata on both sides dipping from heights of land downward and forward toward them. After the laccohthic mass has cooled enough to permit the circulation of meteoric ground-waters through it, he believes that the waters pass down. ward by an artesian flow through DOT ous beds at the sides, into and through the igneous rock, dissolve from it the