The Ward district takes in the headwaters of Lefthand Creek and Fourmile Creek and includes the area near Sunset and Copper Rock. The town of Ward is 12 miles west of the mountain front and about 19 miles from Boulder by automobile road. It lies at an altitude of 9,200 feet, but the hills just to the west reach 10,400 feet, and the valley bottoms a few miles east range from 7,500 to 8,000 feet. The town of Sunset, at the junction of Fourmile Creek with Pennsylvania Gulch, is about 3 miles southeast of Ward and about 10 miles west of Boulder. It had a population of less than 20 in 1940, and Copper Rock, 1 1/2 miles to the east, was uninhabited.
The Ward district was one of the first discovered in Boulder County and has been one of its most productive. In 1861 gold was found by Calvin Ward, just east of Indiana Guleh on the hillside north of Lefthand Creek. In 1862 the Columbia vein was found by John Deardorf, and soon afterwards the town of Ward was founded. Before 1870 nearly all the important lodes in the district had been discovered, and oxidized ore was being treated in several mills, including the outstanding Niwot Mill, which was built in 1865 and was operated steadily for many years. Several attempts have been made to build a mill that would treat the primary low-grade pyritic gold ores economically, but so far none have been entirely satisfactory.
ORE DEPOSITS
Gold, silver, lead, copper, zinc, and tungsten, in the order named, are the valuable constituents in the ores of the Ward district, and of them, gold, silver, and lead have been responsible for most of the output. Nearly all the ore occurs in tabular shoots or in chimneys of roughly elliptical cross section that appear to be local enlargements of veins. The largest of the chimneys, in the White Raven mine, is about 30 feet wide and extends 200 feet along the vein. The most productive veins have been found in the granite or the granite gneiss along dikes of quartz monzonite, quartz latite, latite, and felsite, but some of the dikes are later than the ore. The veins in the Idaho Springs formation are much less continuous and in general are of lower grade. In many places well-defined veins in granite and gneiss feather out in the schist. Post-mineral faulting is common, but the displacement of the veins is generally small, as most of the movement has occurred along the vein fissure. In nearly every place where such faults cut across the vein the faulted segments have been found with little difficulty.
Although there are approximately 200 mines in the Ward district that have supplied some ore, probably not more than 50 have supplied ore having a gross value of more than $5,000 and probably not more than 15 have had an output valued at more than $100,000. Of this group the Baxter, Columbia, Niwot, Madelaine, Sullivan No. 5, and Utica are on the Columbia vein. Among the other productive mines are the Celestial, Celestial Extension, and Morning Star on the Celestial vein. The output of the Big Five property came from the White Raven vein system and the Columbia vein. The B. and M., the Ruby, the U. P. group, the Ward Rose, and the White Raven are the other mines credited with an output valued at more than $100,000 each.
Pyrtic gold-silver ore.-The gangue minerals of the pyritic gold-silver ores are chiefly quartz with some fluorite and sericite. Most of the quartz is early and is massive and white, but druses of colorless quartz crystals are late. Nearly all the gold mined in the district has been found in the quartz veins associated with pyrite or chaleopyrite or both. Ore containing chalcopyrite is commonly richer in gold than ore containing only pyrite. Silver occurs with the gold and chalcopyrite but is most abundant in the galena ore. Many assays of the pyritic gold-silver ore indicate that the average proportion of silver to gold is about 10: 1 by weight; the two are apparently alloyed. Although chalcopyrite is generally much less abundant than pyrite, locally the reverse is true. Molybdenite and wolframite are economically unimportant but are present in most of the pyritic gold veins and seem most abundant in the deep workings. Wolframite is earlier than chalcopyrite and most of the pyrite.
Enrichment of the pyritic gold ores in the oxidized zone above the water table has been responsible for an the rich free-milling gold ore in the region. The level of ground water in the Ward district ranges from 50 to 250 feet below the surface of the ground but in general is not more than 100 feet. The enriched zone is clearly defined in all the pyritic veins. Near the surface the vein minerals are oxidized, and limonite is abundant. The iron-stained quartz is loose and honeycombed and contains drusy cavities lined with late quartz crystals. This "rotten quartz" is well known for high values in gold. Below the water level the gold tenor of the pyritic gold ore is commonly 0.1 to 0.5 ounce to the ton, but in the oxidized zone much of the ore contains 3 or more ounces of gold to the ton. Lead-silver ore.- The lead-silver ore is largely limited to the White Raven vein system. The gangue minerals are calcite and barite. Galena is abundant and is usually in large well-formed crystals. Silver alloyed with gold occurs as a primary mineral included in the galena. Sphalerite is not abundant except locally. Gray copper (tennantite) occurs sparingly below the 700-foot level. Galena, primary silver, and gold are apparently contemporaneous with some calcite and are earlier than barite and a second generation of calcite. Later than all these minerals is abundant supergene wire silver, which has been found between level 6 and the top of the water table in the White Raven mine. In the oxidized zone the silver content is somewhat lower than immediately below the water table. Gold is not an important constituent of the silver-lead ore. Zinc is commercially unimportant and where found is a minor constituent of the ore. Copper Ore.-In most of the mines of the Ward region copper-bearing ore has been valuable chiefly for its gold content, but both chalcopyrite and chalcocite are sufficiently abundant to be of commercial interest. From the Sunset area, in the southeastern part of the distriet, chalcopyrite ore has been shipped in which the content of gold and silver were of less value than that of copper, which approximated 20 percent. Chalcopyrite is everywhere the most important copper mineral and occurs chiefly with pyrite in pyritic gold-copper ore. Gold-telluride ore.-Gold-telluride ore has been found locally in some of the mines. It is common on the eastern side of the Ward district and has also been reported from the Morning Star mine in Spring Gulch. Tungsten ore.- Wolframite intimately associated with quartz and pyrite and with a small amount of chalcopyrite is widely scattered through the veins of the Ward district. It is not found far south of Ward and is most abundant north of town and in the eastern part of the district near Gold Lake.
References
USGS PROF PAPER 223
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