File:Transactions (1871) (14768034365).jpg

Identifier: transactionsmining35amer (find matches)
Title: Transactions
Year: 1871 (1870s)
Authors: American Institute of Mining, Metallurgical, and Petroleum Engineers
Subjects: Mineral industries
Publisher: New York (etc.)
Contributing Library: Gerstein - University of Toronto
Digitizing Sponsor: University of Toronto

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any masses of the CoastRange diorite were forced through to the surface, it is doubt-ful whether any of these particular dikes ever extended as faras the surface which then existed. Taken together they repre-sent intrusive material which was arrested en route, whilelarger masses of related rocks in the region are regarded asthe once deep-seated portions of intrusions which probablyhad actual surface-exit. In the underground workings theblind endings of certain of the dikes show that some of themdo not extend even to the present surface. How much fartherthe larger ones may have penetrated the slates nowT removedby erosion cannot be estimated. Basalt Dikes.—In several places in the mine-workings basaltdikes, which cut all the other rocks, have been encountered.They are narrow, usually from a few inches up to 3 ft. inwidth, and have sharply-defined wTalls. Locally, the dikesoccur in pairs, and in several places are seen to divide, par- 496 GEOLOGY OK THE TREADWELL ORE-DEPOSITS, ALASKA.
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910L0O1 i mi: IRIADW1LL 0RB-D1PO8IT8, ALASKA. 197 ticularly when they occur in zones of sheeted rock. The fis-Buree in which they occur are transverse to tin- Btrike f therocks and trend from N. l(> W, to about north and southtrue meridian, with a rather Bteep dip toward the west Aj arule they are uol mineralized to any important extent, thougha small amount of pyrite Bometimee appears, and occasionallythey contain a considerable amount of this mineral. In sev-eral places veinleta of calcite occur along the Belvage, but theseare readily determinable as of later origin than the greaterpart of the quartz and calcite which form a reticulation through-out tin- mass of the ore-material. IV. Tin: Ores.d Description.—The occurrence of the albite-diorite dikeswhich constitute the Treadwell ore-bodies has already beengiven. The ore consists mainly of rock impregnated with sul-phides, principally pyrite, and in part shattered and filled byreticulated veins of calcite and quartz, wh

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