Mineral DepositsMcGraw-Hill Book Company, Incorporated, 1913 - 883 páginas |
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Términos y frases comunes
abundant albite altered rock andesite arsenopyrite barite beds biotite Bull calcite calcium California carbon dioxide cassiterite cent chalcocite chalcopyrite chloride chlorite cinnabar clay concentration contact-metamorphic contain copper deposits country rock crystalline crystals depth dikes district dolomite Econ epidote fault feet feldspar ferric fissures fluorite formation formed galena gangue minerals garnet Geology gold granite gravels H₂O igneous rocks Inst intrusive iron Jour kaolin Lake limestone limonite Lindgren lode magma magnetite manganese masses metals metamorphism metasomatic mines Nevada nickel occur oölitic ore-bodies origin oxidation pegmatite phosphate places porphyry prakt precipitated present probably production pyrite pyrrhotite quantities quartz veins quartzite rarely region replacement rhyolite rich salt sandstone schists secondary sedimentary sediments sericite serpentine shale siderite silicates silver slates sodium soluble solutions springs sulphate sulphides surface Surv Survey temperature Tertiary tetrahedrite thick tion tourmaline Trans U. S. Geol volcanic Zeitschr zeolites zinc blende zone
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Página 875 - gradually and irregularly, so that the lower portion of the veins contains relatively less silver and lead. The best ore in most veins has been found in the uppermost 500 feet, although good ore extends locally down to 700 or 800 feet, and in the Colorado Central and to a minor extent in other veins down to
Página 678 - A lode formation may be defined as a more or less vertical zone of rock, usually continuous with the surrounding rock and of similar origin, but distinct from it in carrying metallic ores disseminated through it in payable quantities and, as a rule, characterized by strong foliation.
Página 678 - can have free circulation. In consequence of this, mineral deposits are formed within the rock, usually but not necessarily extending over the whole of the foliated zone, but seldom beyond it, and having no definite boundaries horizontally or vertically other than those determined by the decrease of the assay value of the rock in any one direction.
Página 132 - The fault strike is the direction of the intersection of the fault surface, or the shear zone, with a horizontal plane. The fault dip is the inclination of the fault surface, or shear zone, measured from a horizontal plane.
Página 417 - their deposition taking place in the still hot rocks. That zeolitization is far from being simply an effect of the leaching by surface waters is shown by the absence of the zeolites from large areas of basic flows, many of them full of vacuoles or blowholes.
Página 131 - A fault is a fracture in the rock of the earth's crust, accompanied by a displacement of one side with respect to the other in a direction parallel with the fracture. The fracture is usually not an open crack, and an open crack would not be a fault unless one of the sides had moved parallel with the crack relatively to the other.
Página 24 - law of movable equilibrium states: When the temperature of a system in equilibrium is raised that reaction takes place which is accompanied by absorption of heat; and, conversely, when the temperature is lowered that reaction occurs which is accompanied by an evolution of
Página 793 - irregular bunches and masses along the contacts or in the interior of the intrusive masses; frequently also it forms illdefined streaks or "schlieren." In part the ore may have a secondary origin, being developed together with magnetite during the process of serpentinization from primary chromite, picotite,
Página 133 - Slip, which indicates the relative displacement of formerly adjacent points on opposite sides of the fault, measured in the fault surface. The qualifying words relate to the strike and dip of the fault surface.