The Enrichment of Ore Deposits, Volume 625

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U.S. Government Printing Office, 1917 - Ore-deposits - 530 pages
 

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Page 32 - Remarks on the changes which take place in the structure and composition of mineral veins near the surface, with particular reference to the East Tennessee Copper Mines.
Page 233 - The important ore constituent is chalcopyrite, associated with varying proportions of pyrite and sphalerite. Bornite has been reported but was not noted in 1912. Neither galena nor pyrrhotite was observed at the time of visit. The sulphides occur partly in small irregular fractures and along planes of schistosity, but to a large extent they have metasomatically replaced the schist, particularly the fine-grained sericitic variety. The ore contains vejy little vein quartz or other gangue mineral.
Page 298 - Geology and gold deposits of the Cripple Creek district, Colorado: US Geol. Survey, Prof. Paper 54.
Page 45 - Thus confined, the granite sustained loads of nearly 100 tons per square inch, a load more than seven times as great as that which will crush it at the surface of the earth in the usual laboratory tests. Adams concludes that, under the conditions of pressure and temperature that are believed to prevail within the earth's crust, cavities and fissures may exist in granite to a depth of at least 11 miles and may exist at still greater depths if they are filled with water, gas, or vapor, owing to the...
Page 28 - PURINGTON, CW Preliminary report on the mining industries of the Telluride quadrangle. Colorado.
Page 301 - ... been enriched by this process from ore which has been enriched lower down by the solution and precipitation of gold, and which, as a result of erosion, is now nearer the surface. It cannot be denied that fine gold migrates downward in suspension; but in all probability this process does not operate to an important extent in the deeper part of the oxidized zone. If the enrichment in gold is due simply to the removal of other constituents, it is important to consider the volume- and mass-relations...
Page 287 - The oxidized ore contains limonite and manganese dioxide, with plentiful horn-silver and some bromides and iodides of silver. The so-called oxidized ore from the outcrop down is, according to Spurr, a mixture of original sulphides (and selenides), together with secondary sulphides, chlorides, and oxides. At a depth of 500 ft.
Page 285 - The upper part of this manganiferous zone was not of high grade in general, especially in its uppermost portions. The longitudinal projections 2 show that many of the stopes carried from below stop some distance below the surface. Von Richthofen (quoted by Becker) says that "the proportion of gold to silver decreased during the early period of working the lode but is now (1865) on the increase again.
Page 332 - ... removed from these deposits since they were formed, there is little reason to suppose that much gold has migrated into the existing bonanzas from above. The gold is very finely divided and could easily have been scattered if it had been eroded with the ledges.
Page 324 - Although the schists contain stringers of gold of uncertain genesis, the principal deposits are steeply-dipping lodes of quartz and calcite, stained with iron and manganese oxides. Some placers are developed. Rich ore was found very near the surface, but it was richer a few feet below the outcrop than at the surface. Some fracturing has taken place since the deposits were formed.

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