Papers - Mining Geology - Ore Deposition in Open Fissures Formed by Solution Pressure (With Discussion)

The problem of vein formation has been of particular interest to the writer for years. As his work for a long time was confined largely to districts showing large deposits of copper ore, it was natural that the efficiency of replacement, as one if not the chief control of the emplacement of the ore, seemed a particularly attractive hypothesis. Of late years, in almost daily underground work in the Guanajuato district, he has collected evidence which makes it certain that in a number of cases the ore solutions were under sufficient pressure to force the rock walls apart and to hold them apart, thus offering an open space for the deposition of vein and ore-bearing material. This paper will concern itself with conditions frequently met with in hypogene ore deposits of the vein type, and will deal in particular with ore occurrence in precious-metal veins of the type classified by Lindgrenl as epithermal deposits, or metalliferous deposits formed near the surface by ascending thermal waters2 and in genetic connection with igneous rocks. To account for the emplacement of this type of ore deposit various writers have suggested the following agencies: 1. Shattering of the wall rocks. 2. Pressure of growing crystals. 3. Magmation, as treated at length by Spurr3. 4. Replacement. 5. Openings produced by folding. 6. Shearing due to gravity. 7. Shrinkage produced by the passage of pre-ore solutions. 8. Contraction joints produced by lateral secretion. To this list there may be added another agency, a discussion of which forms the basis of this paper: 9. Pressure of the ore-bearing solutions.