Geology of the Marysville Mining District, Montana: A Study of Igneous Intrusion and Contact Metamorphism

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U.S. Government Printing Office, 1907 - 178 стор.
 

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Сторінка 105 - In general it may be said that all the veins of the district carry rich ores in bonanzas and ore shoots within the first 200 feet from the surface, but that in depth the ores rapidly decrease in value until the vein is no longer workable. It may also be said that the ore shoots were well defined, and the intervening vein matter barren and unworkable. The pitch of the ore shoots conforms to the usual habit, dipping to the right when looking down the dip of the vein. The ores consist of sulphides and...
Сторінка 89 - defined as a structure in some rocks, by virtue of which they are already separated into parallel laminae in a state of nature.
Сторінка 104 - Weed," who says: In addition to the pneumatolitic deposite on igneous contacts and those in altered strata near the contacts there are many productive mines working true veins cutting the igneous rock and the contact rocks above them. Such vein fissures are caused both by the contraction due to the crystallization and cooling of the igneous rock and by the shrinkage of the metamorphic zone above the igneous rock. Examples of this type have already been mentioned. As shown by Pirsson...
Сторінка 105 - MINE. In Bulletin No. 213 of the US Geological Survey, WH Weed gives a good description of the Drumlummon vein, from which the following quotation is made : "It is a fault plane with white opaque quartz inclosing angular fragments of black, green and drab slates, which are sometimes distinct and unaltered and at others have been much decomposed. Where the orebodies are found the replacement has been complete and the former presence of the fragments is only recognizable by the outlines of the banded...

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