All the ore of the Magnolia district occurs in very rich but small fissures or veins of the gold-telluride type, although a small amount of tungsten ore (ferberite, an iron tungstate, is the chief tungsten-bearing mineral) and vanadium ore was also recovered, both mostly from the Kekionga mine. "The district is noted for the variety of telluride minerals found and for the unusual association of gold telluride with tungsten, molybdenum, and vanadium minerals. Native gold, native tellurium, telluride, ferro-telluride, melonite, sylvanite, hessite, petzite, coloradoite, altaite, calaverite, lionite, magnolite, nagyagite, henryite, ferberite, molybdenite, and roscoelite, and some galena, sphalerite, pyrite, marcasite, calcite and fluorite have been found in the district. The chief ore mineral is sylvanite" [(Au, Ag)Te2] (Lovering and Goddard, 1950, p. 226). With the exception of a little gold and tungsten mineralization 2.5 miles south of Magnolia town site, all ore deposits lie in a zone about a mile and a half long and a half mile wide; the long axis of the district extends northeastward through the Magnolia town site.
The veins are steep and most trend due west to west-northwest; a few, short, northeasterly cross veins are also mineralized. The veins are highly silicified, composed mostly of a greasy-textured gray, fine-grained quartz called "horn quartz." Most veins are a few hundred feet long, although the longest, the Kekionga vein, is 6,000 feet long. Ore was mined to a maximum depth of 400 feet and extends over a vertical range in elevation greater than 1,250 feet; individual deposits, however, were "pockety" and discontinuous, rarely extended for more than a hundred feet and were no more than a foot or so wide. The largest ore shoot in the district, in the Keystone mine, was as wide as 20 feet, extended 500 feet horizontally and about 150 feet "down-slope."
Mineralization is thought to be related to the intrusion of granitic rocks during the Laramide orogeny, and may be associated with the Caribou stock, which intruded several kilometers away to the northwest. Nonetheless, hot-metal and water-rich fluids (hydrothermal fluids) emanated from these intrusive rocks, precipitating silica, sulfur, tellurium, iron, and precious metals (among other elements) in veins. Why deposition favored the east-trending veins over other possible orientations is largely unknown.
Ore grades were reported as high as a fabulous 2,500 oz./ton gold, although most ore milled in Magnolia or shipped to Boulder for milling and smelting before the turn of the century averaged about 4 oz./ton gold and 2 oz./ton silver (compare these values to the grades mined today, which are usually less than 0.1 oz./ton gold; the difference, of course, is in the total number of tons!). "Tungsten ore shipped from the Kekionga vein averaged about two percent WO3. Ore was also shipped from the Kekionga mine for its vanadium content; some ore contained as much as 6.28 percent vanadium oxide and a moderate tonnage averaging 2 percent was blocked out." (Vanderwilt, 1947, p. 317).
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