"Where 51 Ends and the Fun Begins!"
The Hurley, WI area provides an opportunity to examine the geology of the southern portion of the ancient Superior continent as well as a century of iron mining. Part of the crust of the old Superior continent is exposed in pink and gray glacially polished and striated Archean granite (gneiss) bedrock outcrops in the area that are older than 2,500 million years old. During the Archaean time period the atmosphere was very different from today; at that time, it was a reducing atmosphere of methane, ammonia, and other gases. Also during this time, the Earth's crust cooled enough that rocks and continental plates began to form.
The nearby Cary Mine operated for about 78 years. During its active life, the mine produced and shipped millions of tons of high-grade ore. A vertical shaft was developed in the 1940’s using the latest technology that consisted of a large shot drill 5’6” in diameter. The bore hole was drilled to a depth of 2500 feet in solid granite taking over 2 years continuously running 24 hours a day, 7 days a week. Each time a section of core was removed, the entire drill and drilling machine had to be removed from the borehole. The mine closed in the 1960s when the steel industry changed from using high-grade iron ore from deep shaft mines to using the more abundant taconite ore that could be economically mined by the open-pit method.
Mr. J. B. Newsom, a prominent mining engineer, conceived the idea of the shot drill bit. The borehole at Hurley is the third time this method has been used and is the largest undertaking of the three. Debut of the Newsom drill was in 1936 at the Idaho Maryland Mine in California. The drill was 5'0" in diameter then, and took 21 months to drill 1,125 feet in serpentine rock. Venture number two was in 1938 at the Zenith Mine on the Vermilion Range, Ely, Minnesota (see Earthcache GCNXZG). Here a 1,208-foot hole was bored in greenstone within seven months, using a higher-powered, 5'6" diameter drill. The drilling is accomplished by using steel shot smaller than bird shot, which are abraded against the rock by the bit as it is rotated. Since the shot is considerably harder than the low carbon-cutting shoe, pellets of shot embed themselves in the bottom of the cutting edge as it turns, scraping and abrading the rock. As the core barrel rotates, it cuts a circular slot about 2 inches in width around the core. When a core has been cut to a depth of about 10 feet, the operator disconnects the air and power lines and the drill is lifted to the surface and swung away from the collar. The core is broken off by wedging it to one side, and is then removed by means of a core-puller.
Located at the Wisconsin Travel Information Center are sections of these large Archean granite (gneiss) cores that have dark angular fragments of older metamorphic rock that was intruded by granite. They are arranged around a huge sundial that depicts the growth and decline of iron mining in Wisconsin.
As time is measured mining has three principle periods, Discovery, Development and Decline. You will be standing on a giant sundial placed as a dynamic reminder of the mining area in Iron County and other mining communities on the Gogebic Range. The morning shadow depicts the New Dawn of Discovery. At noon the sun and mining are at their zenith. The waning sun foretells the inevitable decline of every mining operation.
TO LOG THIS CACHE:
1) During its active life, the mine produced and shipped how many tons of high-grade ore?
2) What’s the estimated percentage the darker metamorphic rock to the intruded granite in the largest core?
To log this cache e-mail me the answer HERE.
- Baird, Jerome E. (ed.) / The Wisconsin engineer Volume 47, Number 1 (October, 1942) Erspamer, Gordon New Cary mine shaft, pp. 4-5
- Dott, R.H. and J.W. Attig (2004). Roadside Geology of Wisconsin. 400 p.
- McBride, Sarah Davis. 1999. History Just Ahead. Wisconsin Historical Society –Madison.