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In order to follow the history of the exploration and development of the Big Indian mining district it is necessary to understand a few things about the geology of the uranium ore deposits that were found after Charlie Steen discovered the Mi Vida mine. The most important thing to remember is that none of the ore deposits discovered during the next four years were exposed on the surface.
Although the ore bearing host rocks in the Moss Back member of the Chinle formation did outcrop in a few places along the face of the escarpment overlooking the Big Indian Wash, all of the uranium that was found after 1952 was discovered by exploration drilling. My father’s discovery proved that someone could walk over $100 million worth of uranium ore without knowing what lay beneath their feet unless they were willing to risk money on wildcat drilling in the search for totally hidden ore deposits.
Although the Big Indian mining district was developed from the single drill hole Charlie Steen had drilled through 14 feet of high-grade uranium ore on July 6, 1952, none of the other mines in the district were brought into production on the basis of one drill hole. After the Mi Vida mine proved the existence of uranium ore in the Chinle formation, drilling became the chief guide to finding more ore in the district.
Any drill hole that encountered good mineralization of minable thickness required additional drilling to block out the ore body. Remarkably, every hole in good ore was later developed into an ore body. Because there were no low-grade halos surrounding the ore bodies, a drill hole could miss penetrating a high-grade deposit by a few feet without finding any trace of uranium.
Perhaps the best example of this is the original discovery drill hole on the Mi Vida claim. If my father hadn’t insisted on pushing the bulldozer road as far down dip as possible before he set up his drilling rig, he probably would have missed the Mi Vida ore deposit. Once the mine was blocked out, it was found that the discovery drill hole was located near the outer edge of the ore body. If Charlie Steen had drilled another 18 feet back towards the rim, he would not have cored through the 14 feet of high-grade uranium ore that started the Big Boom at the Big Indian.
After the hole came in on the Mi Vida claim, more than 2.2 million feet of drilling was completed in over 3,000 drill holes spaced between 200 and 500 feet apart during the next twelve years of exploration activity. Drilling reached an all time high in 1956, when more than 647,000 feet were drilled. This exploration drilling delineated a mineralized belt on the southwestern flank of the Lisbon Valley anticline that was approximately eleven miles long and between one-half and one mile wide.
A five-mile long portion of the south central part of the anticline had been removed by erosion, leaving about six miles of the mineralized belt to the northwest and about five miles to the southeast. This belt of uranium mineralization follows the same trend my father reasoned existed when he was first drawn to the area. It confirmed his geologic theory that the uranium deposits in this district were structurally controlled by the anticline. As the Lisbon Valley anticline is plunging at the north end, the ore-bearing host rocks in the Moss Back member of the Chinle formation are found at greater depths to the northwest of the crest of the anticline where the Mi Vida and Big Buck claim groups were located.
All the larger ore deposits were tabular and mostly rectangular in shape with an irregular outline. The smaller ore deposits were more rounded in shape, but also tended to be elongated along the flank of the anticline. At the north end of the ore belt, the mines were developed in a cluster of nearly coalesced, large ore deposits that produced more than 30 million pounds of uranium oxide.
A dozen smaller deposits that contained over 4 million pounds of uranium oxide were scattered between the northern portion and the central portion of the mineralized belt where the large Mi Vida and Big Buck ore deposits were developed. The cluster of Moss Back hosted ore deposits in this central portion of the belt produced over 22 million pounds of uranium oxide. Another 1.5 million pounds of uranium oxide was taken from a number of widely scattered, smaller deposits in the Moss Back member of the Chinle formation at the south end of the belt.
The uranium deposits ranged in size from 500 to 1,500,000 tons of ore, and in thickness from a few feet to 45 feet with an average of about 6 feet. When my father had first examined the Lisbon Valley anticline, he figured that any uranium concentrated down dip from the low-grade rim outcrops would be found in thicker deposits on this part of the structure. And the thickest ore horizon was found in the Mi Vida and Big Buck mines, where the thickness varied from 10 to 45 feet. Ore grades averaged 0.37 percent uranium oxide, making the Big Indian mining district the highest grade of all of the large uranium districts discovered during the next ten years of exploration on the Colorado Plateau.
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