Bluebird aplite in Boulder batholith. Partial differentiation of granite in upper part of batholith resulted in basic phase (Butte granite), and acidic phase (Bluebird aplite).
Notable exposures in Butte district, [Silver Bow Co.], MT. [Bluebird Mine located at Lat. 46 deg 00 min. 42 sec. N., Long. 112 deg. 35 min. 38 sec. W., Butte North 7.5-min quadrangle, Silver Bow Co., MT.]
Source: Modified from GNU records (USGS DDS-6; Denver GNULEX).
†Bluebird aplite. A name that was applied by W.H. Weed to the aplite in Butte district, Montana, in Jour. Geol., v. 7, 1899, p. 744-747, and USGS Bull. 213, 1903, p. 170, but which he mapped as "aplite," without geographic name, in USGS Butte Special folio, no. 38, 1897. The geographic name is not considered necessary and is not now [ca. 1938] used by the USGS.
Source: US geologic names lexicon (USGS Bull. 896, p. 217).
For more information, please contact Nancy Stamm, Geologic Names Committee Secretary.
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