Katie Mine, Boulder County Tungsten Mining District, Boulder County, Colorado, USAi

Regional Level Types
Katie Mine	Group of Mines
Boulder County Tungsten Mining District	Mining District
Boulder County	County
Colorado	State
USA	Country

The Dorothy and Katie mines are the chief mines in Millionaire Gulch, a tributary of Bummer Gulch, at the east edge of the district (pl. 1). Several productive veins have been worked in the gulch, as shown in plate 24. The Dorothy mine comprises an inclined shaft whose collar is at an altitude of 6,930 ft and three levels at vertical depths of 100, 184, and 281 ft. The Katie shaft is 1,120 ft north-northeast of the Dorothy shaft, at an altitude of 6,809 ft. The shaft dips northwest, and four levels at vertical depths of 79, 136, 195, and 248 ft are turned from it. The second level of the Dorothy and the first level of the Katie are connected by an irregular winze. The second level of the Katie connects through a short winze with the first level of the Princess Eulalia shaft. Several veins east of the Dorothy shaft have been worked extensively at the surface and underground in the Crete and Crackerjack tunnels. Most of the workings in Millionaire Gulch are on claims owned by George Teal, but the Gold Coin claim, which includes the northern part of the Dorothy mine, and the Princess Eulalia claims are owned by Homer Pennock.

The veins in Millionaire Gulch were first worked on an extensive scale from 1915 through 1918, and more than half the total output dates from this period. The Dorothy was worked by a leasing company in 1926-27 and was worked by Teal from 1940 to 1945. The Katie has been operated only on a minor scale since 1918. It was operated in 1942 by Syd West. The Princess Eulalia mine was last worked on an extensive scale in 1938. Most of the underground workings on the Crete vein were driven in 1943, when the mine was operated by Messrs. Ralston, Tenhaeff, and Lowery. According to Teal, the output from the Dorothy mine was about 13,000 units of WO3 through 1944, and the Katie production was about 7,000 units. The output from the several smaller mines and extensive surface workings in Millionaire Gulch is unknown, but the total is probably fairly large.

There are two well-defined sets of veins in Millionaire Gulch (pi. 24). The Dorothy, Crete, Crackerjack, and Princess veins trend about N. 30° E., and except for the Princess, all dip southeast. The Katie, Peter, Nile, Tungsten, and High Tungsten veins trend about N. 60° E.; veins of this group dip both southeast and northwest. The veins trending N. 30° E. are the older and are faulted by the veins trending N. 60° E., but later movement on some of the older veins has displaced slightly the veins trending N. 60° E. The veins are in coarse-grained, moderately gneissic Boulder Creek granite that is cut by several dikes of aplite and pegmatite. The dikes all trend northeast, and most of them dip northwest. Much of the granite in the gulch is stained red by iron oxide. This granite is weakly sheeted, and much of it is slightly granulated. Many of the tungsten veins contain reddish gouge at places, and some of them are characteristically red wherever they have been exposed. The main zone of reddish rock and red veins extends down the center of the gulch, along the line of the Crete and Princess Eulalia tunnels. This is a minor breccia-reef fracture zone that trends north-northeast. Its location suggests that it is a cross fracture between the Hoosier and Livingston breccia reefs, but it may end against other cross-fracture zones that trend about due east between the two main reefs.

The Dorothy vein strikes about N. 30° E. and dips 60°-85° SE. in most places, but locally it is vertical or dips steeply northwest. The hanging or east wall of the premineral fault that is followed by the vein moved 2 to 5 ft south almost horizontally. The vein is a well-defined single fissure on the first and second levels of the Dorothy mine, but below the second level it splits up and is locally very weak (pl. 25). The main drift in the southern part of the third level follows a northwestward-dipping vein that joins the Dorothy vein about 30 ft above the level near the crosscut from the shaft. The Dorothy vein steepens sharply and becomes weak and barren below this junction. The junction plunges gently northeast and is exposed in the drift about 275 ft northeast of the shaft station. Near this point several veins branch into the walls of the drift, and a hole drilled down and northeast was in a red, iron-stained fracture zone through most of its length. Near the northeast end of the second and third levels the Dorothy vein splits and the drifts follow the stronger, ore-bearing, right-hand branch, which trends about N. 45° E. This branch is evidently a younger fracture that connects the Katie and Dorothy veins, and the branch that continues northward is the older Dorothy vein (pl. 24).

The Katie vein strikes about N. 45° E. and dips 55°-65° NW. near the Katie shaft, but farther southwest, near the junction with the Dorothy, it turns N. 60° E. The vein occupies a fault fissure whose hanging wall moved up and southwest at about 30° for about 5 ft. The Katie and Dorothy veins intersect about 400 ft north of the Dorothy shaft at the surface. The Dorothy vein has not been traced on the covered hill slope north of the intersection, and the Katie vein is not exposed southwest of the intersection, but the Katie vein is known to continue to the southwest in the Dorothy mine. The intersection of the Katie vein and the younger branch of the Dorothy vein is exposed in a stope near the north end of the second level. There the Katie cuts the Dorothy and displaces it about 1 ft, with the northwest side down, and it is probable that the Katie displaces the older branch of the Dorothy a few feet more.

The Katie vein splits near the Katie shaft, and the branch that strikes in a more easterly direction has been followed in the Princess mine. Some ore was obtained from it near the surface and in the southwestern part of the Princess mine. In 1942 West mined some ore from a winze near the southwest breast of the Princess, but a heavy flow of water forced him to stop work there. The hanging-wall branch of the Katie vein is a wide sheeted zone that contains a few veinlets of ferberite on the first level of the Katie, but it apparently has not been explored beyond the junction.

Two main ore shoots have been worked in the Dorothy mine, and one large irregular shoot was worked in the Katie (pi. 24). The southern and larger ore shoot in the Dorothy extended from the surface down to about 30 ft above the third level. Although the shoot was irregular in shape, it had a general rake to the northeast at about 60°. The stope had a length of about 200 ft on the second level. On the first level the richest part of the shoot had a similar stope length, but lower-grade ore was later mined for about 175 ft northward from the edge of the older stopes. These later workings were inaccessible in 1942. The ore shoot was localized in a segment of the vein whose strike was a little more easterly than the average. The vein exposed near the edges of the old stopes consists of 6 to 18 in. of sheared silicified granite seamed by veinlets of gray and black horn quartz and find-grained ferberite, but relatively rich ore is said to have been found in widths of as much as 4 ft at places in the ore shoot. The Dorothy ore is typically fine-grained "steel ferberite," some of which contains considerable intergrown fine-grained quartz. Sulfide minerals and hematite are locally present in minor quantity, and a few lenses of galena are said to have been found in the large ore shoot. A photomicrograph of fine-grained Dorothy ore is shown in figure 45.

The northern ore shoot had a stope length of about 75 ft and extended from the intersection of the Dorothy and Katie veins, about 35 ft above the second level, down to and below the third level. The shoot raked steeply northeast, and its localization appears to have been influenced both by an aplite dike and by the eastward turn in the vein. Teal says that the vein in the stope above the second level was about 3 ft wide and averaged about 2% percent WO3 . This stope is on the Dorothy vein up to the junction and then follows the Katie vein upward for a few feet. Near the junction the Dorothy consists of gray horn and ferberite veinlets in 2 ft of silicified sheeted granite. The Katie consists of 6 in. of gray and brown horn quartz and ferberite. Ferberite seams occur in both the gray and brown horn, but some of the brown horn appears to be later than the ferberite. The Dorothy vein has not been explored above the junction, and the Katie has not been explored below it except that one flat diamond drill hole was drilled toward the Katie vein from the second level. This hole cut shattered iron-stained granite in which no definite vein was discerned.

As exposed on the third level early in 1944, the ore in the northern shoot ranged from 6 to 36 in. in width and comprised seams of "peanut ore" up to 3 in. wide and veinlets of ferberite in sheeted and locally brecciated sericitized granite and aplite. This ore assayed more than 3 percent WO3 . The ferberite was finely crystalline but was not so dense as the ore from most parts of the mine. Teal says that the ore continued to the bottom of a 30-ft winze, but the phosphorus content increased rapidly and the concentrates assayed as high as 0.60 percent phosphorus. The fine-grained ore itself may contain some phosphorus mineral, but it is probably significant that the aplite in which the ore occurs is abnormally rich in apatite. A thin section of green, sericitized aplite adjacent to a ferberite seam in the drift on the third level contains an estimated 5 percent apatite by volume. At least a part of this apatite was introduced during the period of wall-rock alteration. The altered rock also contains a few minute grains of scheelite.

In 1943 a little low-grade ore was obtained from an eastward-striking vein near the shaft on the third level. The vein is ore bearing where it crosses a small aplite dike, but several feeders split from the vein and follow the dike, and the vein weakens on the east side of the dike, where it turns to a N. 70° E. course. Several small hematite-stained fractures are present in the walls of the vein, and the stope was in reddish, iron-stained granite. This vein is correlated with the ore that crosses the Crete vein and displaces it slightly in the Crete tunnel 310 ft from the portal; it is probably a branch of the Nile vein. The Nile vein was worked south of the Dorothy shaft at the surface and on the first level. At the south end of the first level it faults the Dorothy vein a few feet.

The Katie ore shoot lay southwest of the shaft, along the part of the vein that trends in a more northerly direction. The ore thus occurred where the vein turned to the left, as might be expected of a vein whose right-hand wall moved ahead. The best ore came from the first level and is said to have been 3 to 4 ft wide and to have assayed 5 to 9 percent WO3 after the coarse waste was sorted out. Much of the ferberite was a filling in moderately open breccia, and judging by ore fragments on the dump, it was somewhat coarser grained than most of the Dorothy ore. At places feeders in the hanging wall of the Katie vein were abundant enough to mine, and the resulting stopes were several feet wide. Most of the Katie workings have been inaccessible for many years; the two upper levels end in open stopes, and the lower levels are under water.