Boulder County Colorado Gold Production
The Magnolia district, about 4 miles southwest of Boulder along the east side of the Front Range, is small, and most of the productive veins crop out in an area of less than 1 square mile.
Gold telluride ore was discovered in the district in 1875, 3 years after the discovery of gold telluride in the Gold Hill camp (Wilkerson, 1939, p. 82), and most of the known veins were being worked by 1877. Small amounts of tungsten ore also have been mined. The productive life of the district was largely spent by 1905, and even the increased price of gold in 1934 failed to excite more than a spark of revival. The production of the district before 1906 was valued optimistically at $2,815,000 and was mostly in gold (Lovering and Goddard, 1950, p. 227). Total gold production through 1959 was about 130,000 ounces.
Almost all the district is underlain by gneissic Boulder Creek Granite of Precambrian age, which is cut by numerous aplite and pegmatite dikes (Wilkerson, 1939, p. 84). Most of the ore deposits are in gold telluride fissure veins that trend west or northwest, and ore seems to be localized at intersections of fissures.
The Magnolia district, whose ore minerals consist chiefly of gold tellurides, was the first in Colorado to produce considerable quantities of telluride ore. Much of the ore was very rich. The district is of interest also because of the variety of the telluride minerals and the unusual association of gold tellurides with tungsten, vanadium, and molybdenum minerals (Lovering and Goddard, 1950, p. 228). Sylvanite is the main ore mineral but it is almost everywhere accompanied by one or more of the following tellurides: calaverite, hessite, petzite, coloradoite, and altaite. Other minerals found in the district are native gold, lionite, magnolite, nagyagite, henryite, tellurite, ferro-tellurite, melon-ite, native tellurium, ferberite, molybdenite, and roscoelite, and some galena, sphalerite, pyrite, mar-casite, calcite, and fluorite (Lovering and Goddard, 1950, p. 228). Gangue minerals are present in only minor amounts and consist mainly of light- to dark-colored varieties of extremely fine grained quartz or "horn."