None
In the Mogollones District, New Mexico,^ the country rocks are a series of flows, fragmental beds and tuffs, composed of soda- rhyolite, andesite and basalt. The rocks in the mineralized areas exhibit propylitic alteration; silicification, resulting in a green- ish-gray hornstone, is prominent along the veins. Sericitic alter- ation is absent. The veins are partly filled fissures and partly the result of replacement of the walls along fractured zones. The topography is rugged, and the veins being harder than the altered wall rocks, form bold outcrops. The veins carry native silver, argentite, chalcocite, pyrite, chalcopyrite, and bornite associated with specularite in a gangue of quartz, calcite and fluorite. In certain of the veins in which copper is present in small quantity the ore minerals are finely disseminated through the gangue. In another type of vein copper forms a large proiDortion of the total value of the ore and sulphides are abundant. Oxidation has reached a slight depth only in these veins and secondary enrich- ment does not appear to have effected any important rearrange- ment of the values. The water level in this district is deep, and the slight depth of secondary alteration and oxidation must be explained by the geologic youth of the region, erosion having proceeded more rapidly than oxidation. The degree to wdiich the rocks have been shattered and the presence of abundant druse- lined cavities in the veins, together with the type of rock altera- tion, indicate a slight depth at the time of ore deposition, and that no great depth of rock has been removed by erosion since the veins were formed. The oxidized ores found at the surface contained chiefly malachite, cerargyrite, and gold, associated with limonite. * L. C. Graton, P. P. 68, U. S. G. S., p. 195. INDEX Adirondack Mts., deposits of, 87 Aereal geologj', 40 Agmlera, J. G., 80 Alaska- Treadwell mine, 7, 47, 77 Alteration, alunitic, 150 contact, 146 decomposition, 153 depth of, 167 dynamo-regional, 145 to greisen, 150 hydro me tamorphic, 153 hydrothermal, 146 influence of channels on, 160 kaolinitic, 155 leaching, 154 metasomatic, 82, 84 migration, 158 oxidation, 156 primary, 145, 204 propyUtic, 148 secondarj', 153 sericitic, 149 silicification, 150 by surface agencies, 153 of wall rocks, 145 •weathering, 153 Alunitic alteration, 150 Anticlines, 31 ore-deposits at tops of, 134 Antiguas, examination of, 4 Apatit« veins, 83 Apex, 7 Appalachians, deposits of, 71 Aspen, Colo., 126, 141 Associations, of metals, 160 of minerals, 76 Bain, H. F., 193 Bald Mountain, S. D., 59, 106 Ballerat, Australia, 141 Basin, 31 Bassick mine, Colo., 54 Bayley, W. S., 30 Beck, R., 32, 33, 53, 55, 63, 79, 80, 109, 110, 112, 128, 129, 185 Bed vein, 45 Bedded ore-deposits, 110 Bendigo, Australia, 124, 135 Bertha mines, Va., 206 Bibliography, search of, 6 Bingham, Utah, 58, 108, 126, 184, 210 Bisbee, Ariz., 79, 150, 181, 209 Black Hills, S. D., 32, 103, 106, 129, 132, 213 Blanket vein, 45 Boehmer, Max, 160 Booms, mining, 3 BoutweU, J. M., 58, 80, 105, 108, 126, 184, 210 Branching veins, 54, 61, 81 Breccia lodes, 52 Broken Hill, N. S. W., 189 Bullfrog, Nev., 198 Bunker Hill mine, Ida., 104 Burro Mts., N. M., 108 Butte, Mont., 118, 140 Carbon, precipitation by, 138 Casts in resistant minerals, 200 Cassiterite veins, 83 Catalina Mts., deposits of, 7 Cerro de Potosi, S. A., 59 215 216 INDEX ChaJcanthite, 9, 15 Chalcocite, enrichments, 180 disseminated, 182 Chalcopjoitic enrichments, 184 Chimneys, 53 Church, J. A., 133, 134 Clark, F. W., 195 Classification of ore-deposits, 86 Cleavage, 26 CUfton, Ariz., 78, 108, 179, 181 Clinton ore measures. 111 Coeur d'AIenes, Ida., 46, 80, 104, 117, 124, 210 Compensating faults, 35 Comstock lode, Nev., 212 Compound veins, 46, 47 Concentrations, surface, 171 Concretions, oolitic. 111 Conglomerate beds, 109 Conjugate faults, 35 joints, 56 veins, 56, 57 Contact deposits, 87, 88, 157 metamorphism, 146, 152 ores, 79, 124 veins, 47 Contouring, 40 Copper, enrichment of, 180 oxidized ores of, 169 primary ores of, 78, 79 secondary ores of, 176 Copper King mine, Ariz., 181 Cordilleras, deposits of, 71, 72 Cornwall, England, 137, 138 Cost of mining, 22 Cripple Creek, Colo., 48, 49, 59, 60, 77, 119, 129, 213 Crosscutting, 9, 42, 49, 57 Crosscut tunnels, 9 Crustification, 39, 74, 94, 96, 97, 136 Crystallization, interrupted, 77, 200 Curie, J. H., 5, 24, 141 Darton, N. H., 29 Decomposition of rocks, 153 Deep-seated veins, 83 Deformation, 37 De la Beche, 138 De la Mar mine, Utah, 171 Development, 40 Devil's Tower, Wyo., 29 Diller, J. S., 78 Displacement, 33, 34, 37 Disseminated enrichments, 182 mineralizations, 107 Dolcoath mine, England, 137 Dolomitization, 152 Dome, 31 Drag, 36 Dressing a mine, 10 Ducktown, Tenn., 78, 91, 181 Dunnington, F. P., 195 Efflorescent salts, 15, 159, 203 Emmons, S. F., 35, 80, 171, 189, 215 Emmons, W. H., 75, 79, 91, 92, 122, 164, 165, 181, 191 Encampment, Wyo., 30, 56 Enrichment, chalcocitic, 180 chalcopyritic, 184 of copper, 180 depths of, 163, 165 disseminated, 182 of gold, 189 of gold and silver with copper, 185 irregularity of, 162 of lead, 191 of lesser metals, 195 of metals, 158 relation of, to topography, 161 relation of, to water level, 161 of silver, 186 of zinc, 194 zones of, 158, 163 INDEX 217 Epigenetic deposits, 26 Examinations, of antigiias, 4 formal, 1 preliminary, 1 preparing a property for, 9 of prospects, 3 for rescue of capital, 2 Exploration, 71, 139 amount of, compared with results attained, 9 and development, 40 for faulted ore-body, 36 of prospects, 6 Extrusive rocks, 69 Fahlbands, 90 Falim, Sweden, 79 Faribault, E. R., 135 Fault*, 33 blocks, 40 compensating, 35 depth of formation, 35, 36 development from folds, 31 expression in topography, 39, 199 lodes, 51 normal, 34 reverse, 34 step, 35 torsion, 34 Filled fissures, 39, 74, 93, 95, 96, 97, 136 Filling of open spaces, 93 Finlay, J. R., 22 Fissility, 27 Fissures, gouge filled, 39 Fissuring, time of, 68 Flexures, 32, 33 Folds, 31 Formal examinations, 1 Foster, Le Xeve, 137 Fractures, 32 Freiberg, Germany, 63 Gale, H. S., 30 GaUup, X. M., 31 Garrey, G. Hundt, R., 31 Hydrometamorphism, 153 Hydrothermal metaraorphism, 146 alunitic, 150 distinction from weathering, 1 48 to greisen, 150 propylitic, 148 sericitic, 149 silicification, 150 Idaho Springs, Colo., 66 Inclusions, fluid, 74 Indicator seam at Ballerat, 142 Intercalated veins, 67 Intergrowth, structural, 74 Intrusive rocks, relation of minerali- zation to, 69, 70 Irving, J. D., 32, 35, 79, 105, 129, 132, 188, 213 Jerome, Ariz., 208 Joints, 27 compression, 27 conjugate, 56 mineralization of, 51, 56 tension, 28, 31 Jones sampler, 13 Kaolin, precipitation by, 168 KaoUnization, 154, 155 Kemp, J. F., 34, 44, 87, 90, 110, 111 Keweenaw Point, Mich., 110 Kingston, N. M., 133 Krumb, H., 184 LaccoUths, 70 Lake City, Colo., 79, 188 Lake Valley, N. M., 133 Laney, F. B., 91, 181 Large vs. small properties, 11 Leaching, 154, 159 Leaching (process), 9 Lead, enrichment of, 191 oxidized ores of, 169 primary ores of, 80 Leadv-ille, Colo., 35, 80, 160, 195 Ledges, 44 Lincoln, F. O., 187 Lindgren, W., 44, 49, 71, 75, 77, 78, 79, 82, 86, 88, 89, 90, 92, 108,116,119,123,127,129, 145, 146, 157, 158, 160, 176, 179, 184, 195, 211, 213 Linked veins, 55 Local data, better than general data, 37, 114, 138 Lodes, 44 breccia, 52 fault, 51 sheeted, 48 stringer, 50 Losses, metallurgical, 21 Low grade ores, 11 McCaffery, R. S., 79 Magmatic segregations, 86 Malcolmson, J. W., 102 Manganese, distribution of, by oxi- dation, 172 Mansfeld, Germany, 112 Marmorization, 152 Meandering of outcrops, 197 Metals, associations of, 123, 160 migration of, 158 vertical sequence of, 123 Metallogenetic epochs and provinces, 71 Metallurgical losses, 8, 21 Metamorphism, contact, 146, 152 dynamo-regional, 91, 146 hydrothermal, 146, 148, 150 I INDEX 219 Metasomatic alteration, see altera- tion, metasomatic. replacement, 99 Metcalf, Ariz., 108, 177, 209, 211 Miami, Ariz., 184 Michigan, copper deposits of, 110 Microscopic sUdes, 73, 206 Migration of metals, 158 of gangue minerals, 195 upward, 160 Mill runs, 17 Mine dressed for examination, 10 Minerals, accessory, 76 both primary and secondarj-, 75 primary, 74, 75 secondary, 76 Mining, cost of, 22 Mining examinations, 1 formal, 1 for rescue of capital, 2 preliminary, 1 of prospects, 3 Mogollones, N. M., 214 Monocline, 31 Monte Cristo, Wash., 51, 191 Montpelier, Ida., 30 Monzonite, association of ores with, 72 Morenci, Ariz., 89, 108, 174, 177, 184, 209 Nacozari, Mex., 8, 207 Negaunee, Mich., 30 Neihart, Mont., 65, 67, 140, 189 Nieggen, Germany, 31 Nogal, N. M., 109 Normal faults, 34 Nova Scotia, gold deposits of, 135 Offset, 33 Old Jordan mine, Utah, 210 Oolitic concretions. 111 Open spaces, 95 Ordonez, E., 80 Ore deposition, loci of, 69, 70 Ore-deposits, associated with cer- tain rocks, 71 behavior of in depth, 81 deep-seated, 81 distribution in districts, 71 epigenetic, 26 formed at shallow depths, 81 lenticular, 92 pegmatitic, 90 regionally metamorphosed, 91 replacement, 99 syngenetic, 26 Ores, contact, 79, 88 low grade, 11 oxidized, 169, 170 primary, 69 criteria of, 73, 115 decrease in value of, in depth, 123 depth to which persistent, 72, 81, 124, 139 refractory, 8 residual, 73 secondary, 173 criteria of, 174 minerals of, 176 Ore reserves, calculation of, 19, 24 Ore-shoots, distinction between pri- mary and secondary, 115 primarj', 24, 114 at tops of anticUnes, 136 deep-seated, 24, 124, 143 due to impounding, 130 due to intersections, 127 due to open spaces, 127 factors determining, 114 influence of wall rocks on, 136 irregularity of, 114, 118 lenticular, 120, 144 overlapping, 120 220 INDEX Ore-shoots, primary, shapes of, 118 structure, influence of, on, 125 terms used to describe, 116 residual, 171 secondary, 24, 173, 176 effect of porosity on, 179 effect of primary mineral- ization on, 179 effect of structure on, 178 effect of wall rocks on, 178 effect of water level on, 178 lenticular, 92 shapes of, 190 Ouray, Colo., 90, 130, 132 Outcrops, 196 casts in, 200 composition of, 201 conditions of indicating enrich- ments, 202 of contact deposits, 205 down hill creep of, 198 of kaolinized rocks, 204 meandering of, 197 porosity of, 200 relation of length to depth, 196 size of compared with size of vein, 197 of superficial deposits, 200, 205 Overlapping veins, 57 Oxidation, 156 minerals resistant to, 157 irregularity of, 162 1 elation to topography and water level, 161 Pachuca, Mex., 80, 195 Paige, Sidney, 96, 175 Park City, Utah, 80, 210 Pecos, N. M., 90 Pegmatitic deposits, 90, 124 Phillipsburg, Mont., 164 Pilares mine, Sonora, 8, 207 Pinos Altos, N. Sections, geological, 37, 40 Segregation of values, indications of, 76 Segregations, magmatic, 86 Selective precipitation, 88, 139 Sericitization, 82, 149 Shafts, sampling, 13 Shasta County, Cal., 78, 105 Shear zones, 52 Sheeted zones, 49 Sheeting, 28, 34 Sierra Mojada, Mex., 102 Sierra Nevada, deposits of, 71 SilicificationlSO Silver, distribution of, by oxidation, 172 enrichment of, 185, 186 primary ores of, 79, 80 Silver Lake, Colo., 54 Silver Peak, Xev., 86, 87 Silverton, Colo., 50, 94, 120, 185, 212 Size of ore-deposits, 11 Smith, C. H., 112 Snowstorm mine, Ida., Solution, enlargement of cavities by, 94 Solution breccias, 207, 208 Specific gravity, determination 20 Spencer, A. C, 30, 47, 56, 77 Spurr, J. E., 33, 80, 87, 126, 130, 141, 187, 188, 191, 192, 212 Step faults, 35 Stocks, 53 Stockworks, 53 Stoping width, 20 Stratification, 26 Striations, 36 Stringer lodes, 50 222 INDEX Structural geology, 26 Structure, gneissic, 27 schistose, 27 Surficial deposits, 205 Syncline, 31 Syngenetic deposits, 26 Systems of related veins, 57 Tecoripa, Mex., 143 Telluride, Colo., 118 Terms of sale, 5, 6 Throw, 33 Title, 7 Tomboy mine, Colo., 56 Tombstone, Ariz., 134 Tonopah, Nev., 36, 41, 80, 84, 130, 212 Topography, expression of faults in, 39, 199 of mineralization in, 198 Trail, 36 Tularosa, N. M., 113 Veins, distinction between inter- calated and fissure, 67 fissure, 43 follow faults of small displace- ment, 62 formed near the surface, 82 gash, 44 in schist, 68 intercalated, 67 linked, 55 movement along, 63 overlapping, 57 persistence of, in depth, 61 pinching and swelling of, 127 pockety, 73 relation between depth and num- ber of, 62 replacement, 98, 136 structure, influence of country rock on, 63 systems of, 57 Virginia City, Nev., 212 Union\ille, Nev., 65 United Verde mine, Ariz., 208 Values, minerals indicating a segre- gation of, 76 Van Hise, C. R., 26, 27, 30, 62, 95 Veins along dikes, 48 bed, 45 blanket, 45 branching, 54, 61, 81 compound, 46, 47 conjugate, 56, 57 contact, 47 deep-seated, 83 Watson, T. L., 206 Weathering, 153 minerals resistant to, 88 Weed, W. H., 67, 78, 79, 93, 107, 136, 140, 156, 189, 190, 191 Witwatersrand, South Africa, 109 Yung, M. B., 79 Zinc, enrichment of, 194 oxidized ores of, 170 primary ores of, 81 Zones developed by surface agen- cies, 163 9 TH Gunther, Charles Godfrey 260 The examination of prospects G85 1st ed. 