Show aqueous solutions and ore D deposits BY CHARLES A PORTER in III modern theories on the origin of ore deposits there is nothing better established than that lode deposits of lead copper silver and gold were in the beginning laid down dowa by hot aqueous solutions now it will be well at this point to make a few remarks on the word theory as used among geologists briefly it is a hypothesis supported by subsequent observation this conception is in sharp contrast with the common use of the term as we so often hear it used to dignify the wild vagaries of every dreamer who may feel inspired to unlock the mysteries of the hills this digression is made to guard the reader against treating geological theories too lightly for a theory when it emerges from the hypothetical state will be the result of a tremendous amount of observation the days of parlor speculation have passed and if new ideas are to be accepted the reasons upon which the thee rest must be shown the principle of solutions outlined have is based upon the worldwide world wide work of many engineers and in the fullest sense the solution principle deserves the name of a theory when we approach the vicinity of great mineral deposits we usually note a violent change in the color of the rocks this is due to the wholesale action of mineralize ing solutions these solutions are very active in a chemical sense and upon reaching new regions will attack at least some of the constituents of the fresh rocks removing some elements and replacing 0 them with others it is these changes which make the difference in color referred to above we often hear that geologists have said that ore of certain kinds cannot occur in this or that kind of rock but let me tell the reader that geology has to answer for every story true or false that has become current in the minin mining el world the truth of the matter is that deposits as will be shown by this discussion of the solution theory are a possibility in any kind of rock which is laid open to the attack of mineral bear ing solutions we often hear that the silver deposits at silver reef utah are opposed to all geological theories this is decidedly decd edly false as there happens to be a striking agreement and modern geology needs no better excuse for its existence than silver reef the loose structure of the sandstone allowed the free flow of solutions which reached the sand stratum through fault fissures which occur 1 in 11 close association with the ore deposits lying in these sandstones were organic remains or fossils which set up chemical reactions with the mineral bearing solutions resulting in a precipitation of the valuable mineral it has been observed that the best minar aliza tion occurs in close proximity to the fissures the reader can readily see that had some other rock which permitted even a slight spreading of the solutions and the necessary chemical reactions reaction s been in the place of the sandstone an ore deposit would have occurred although p perhaps showing different characteristics we must therefore come to the conclusion that solutions and their action are the key to the subject and any rock that is subject to attack from mineral bearing solutions may become the seat of an ore deposit A common error often exists with men of limited experience in mining that ore deposits as a rule increase with depth without going exhaustively into reasons it may he said that as a general rule the contrary is true the present discussion will show some of the reasons for this A solution may flow upward along a fissure passing through a quartzite a limestone and a stand stone thus aithus leaving an ore deposit in a second bed of limestone existing above the rest on the other hand the vein may be a paying one regardless of the changes of the wall rock the lesson to be observed here Is to pay attention to the wall rocks for it should now be obvious that the character of a deposit is apt to change as it passes from one formation to another in the solution theory we find an explanation of the extreme irregularity to which ore deposits are subjected in order to have the necessary flow cracks and fissures are essential such fractures would necessarily exhibit every degree of irregularity and these irregularities are often reflected in the resulting ore deposit thus giving us some scientific basis for the time honored maxim follow the ore to persons for whom this article is intended namely men unfamiliar with the modern theories of ore deposits the question naturally arises as to the origin of these solutions while there has been much discussion on this point the opinion that they are emanations from such molten masses as would form lava should they overflow the surface has of late gained such support that this conclusion may be accepted as settled these magmas hagmas when they consolidate under ground and consequently under great pressure form such rocks as granite syenite and the various other intrusive rocks which the prospector usually calls pory pairy and which would be a good term were it not for the fact that it is used as a cloak for much ignorance |