Bulletin - United States Geological Survey, Ausgabe 219

Cover
 

Was andere dazu sagen - Rezension schreiben

Es wurden keine Rezensionen gefunden.

Andere Ausgaben - Alle anzeigen

Häufige Begriffe und Wortgruppen

Beliebte Passagen

Seite 15 - The most important veins of the Tonopah district, and all those that have been proved to be of immediate economic importance, occur in the early andesite, and do not extend into the overlying rocks. Hence, when the early andesite is not exposed at the surface, the later rocks form a capping to the veins, and this capping must be passed through before anything can be learned of the presence or the nature of the veins beneath. This circumstance shows pretty plainly that the vein deposition took place...
Seite 11 - ... or little-faulted region on the northwest. Near the dacite necks the observed faults are rather more numerous than elsewhere, and in many instances it may be established that the blocks adjacent to the dacite have been downsunken in reference to blocks farther away. From these intrusive necks the faults run in a roughly radiating fashion and seem to follow no regular system of trend. Detailed study of the contact phenomena of the dacite shows that the minute faults in the tuffs at these points...
Seite 22 - As exceptions there are found streaks of quartz, usually small, within the vein, which show crustincation and comb structure, and thus bear evidence of having been formed in cavities. These cavities, however, were of irregular shape and were not fissures, properly speaking, but spaces of dissolution, and were the effect of the mineralizing waters themselves. The largest example of a crustificd...
Seite 17 - Mineralization subsequent to the dacite intrusions. — Finally, the contacts of the large dacite necks (Butler, Golden, and other mountains) are accompanied in many places by the deposition of chalcedony, manganese, etc., in cracks and crevices. These are not usually in veins, or when so are small and irregular. Considerable values in the precious metals have been claimed in some cases, but it is the writer's experience that the content of these metals is insignificant. Resume. — To sum...
Seite 28 - Tonopah veins. Judging from these districts it is possible that in depth a rather larger proportion of the baser metals, such as copper, and possibly lead and zinc (although no traces of the last two have as yet been found in the veins), may come in, and that the values in gold and silver may decrease somewhat. This, however, if it happens, should do so at a considerable depth.
Seite 24 - In the Stone Cabin shaft the change from the oxidized to the unoxidized andesite came just below the 200foot level, but at 400 feet the ore is partly oxidized. The reason for this appears to be that the quartz veins, on account of their brittleness, have been more readily fractured by strains than has the softer country rock, and so the veins afford channels for oxidizing waters coining from the surface.
Seite 20 - Mizpah group; and there is some radiation in the strike of the veins, although not so much as in the former case. The Valley View veins are affected by post-mineral faulting, like the Mizpah vein. The Montana Tonopah group shows a strong main vein running east and west and dipping north at a moderate angle. A number of lesser veins have been cut in the workings, and although development at...

Bibliografische Informationen