Ojuela mine, The

The Ojuela mine, well known among collectors worldwide, is probably Mexico's greatest mineral locality and surely its most beloved. Discovered by the Spanish in 1598, the deposit was actively mined for 350 years, but did not come to the notice of mineralogists until W.F. Foshag's visit in 1927. Mineral specimens in significant numbers did not appear until the discovery of a huge adamite grotto by Dan Mayers and Francis Wise in 1946. The 117 species now known from the deposit include the world's finest adamite (in a gorgeous array of colors and habits), legrandite, kottigite/parasymplesite, and paradamite, as well as superb specimens of scorodite, hemimorphite, plattnerite, aurichalcite, rosasite, fluorite, calcite, wulfenite and other species. It is also the type locality for paradamite, lotharmeyerite ,metakottigite, mapimite and ojuelaite, and the co-type locality for scrutinyite. Collecting activity at the mine complex is now relatively small-scale, but good specimens continue to be found sporadically.

Mapimi, Durango, Mexico

with a review of the Geology by Peter K.M. Megaw

5800 N. Camino Escalante

Tucson, Arizona 85718

Introduction

The Mapimi mining district consists of a scattering of small mines to the east and south of the town of Mapimi (25[degrees]50' N latitude, 104[degrees]51' E longitude, in north-central Durango State), and one central, great mine. Were it not for this extraordinary mine, the Ojuela, the district would be of little significance for the mineral collector. The other mines, exploiting small deposits of fluorite, celestine, apatite, and magnetite iron ore, have produced few noteworthy specimens. But the polymetallic deposit at the Ojuela mine has proven to be one of Mexico's greatest troves of lead, copper and silver ore-and of crystals of secondary minerals for the collector. Some 117 species are known from the Ojuela mine; it is the type locality for five of them (lotharmeyerite, mapimite, metakottigite, ojuelaite, paradamite) and the cotype locality for one (scrutinyite).

The Ojuela mine today is a labyrinth of over 450 kilometers of underground workings within the Bufa de Mapimi, a limestone thrust escarpment which begins rising about 2 km to the southeast of Mapimi, then sweeps upwards, striking southeast, to a peak called La Bufa, some 5 km from the town. Large-scale commercial ore mining at the Ojuela ceased in the mid-1940's, but the fame of the mine as a specimen-producing locality has been growing, thanks to the activities of a local mining cooperative, for the past 60 years.

Some like to call the Ojuela mine "the Tsumeb of Mexico," which invites some interesting comparisons. Both Tsumeb and Ojuela are large mines, of immense economic importance in their respective heydays, exploiting hydrothermal polymetallic ore de-posits. The Tsumeb deposit, however, is geologically a single huge pipe (of enigmatic genesis), whereas the Ojuela orebody is many times more complex in its structure. The Tsumeb mine is only 100 years old, whereas the Ojuela mine is 400 years old; but Tsumeb produced specimens for the collector market throughout its 100-year history, while Ojuela has done so only during the last 60 years, after ore mining had largely come to an end (we almost dare not think of what extraordinary specimens the miners probably en-countered and crushed as ore or discarded as waste during those 340+ years). Both localities are noted for their rare species, their abundant specimens for the micromounter, and their world-class examples of several major minerals. But the Tsumeb deposit, with its simpler geology, exhibits more complex mineralogy: roughly 250 Tsumeb species are known, whereas Ojuela offers only half that number. Around a dozen major Tsumeb species attain world's-best status, and for Ojuela the number is likewise about half that. Nevertheless, the most revered of the classic specimens from both localities are very beautiful and utterly distinctive. Experienced collectors today will have grown up regarding both localities as familiar sources, and acquiring immense respect for both-so there is ample justification for thinking of the Ojuela mine as the "Tsumeb" of the Western Hemisphere.

Bancroft (1984) lists three possible derivations of the name "Ojuela": perhaps the mine was named for a long-ago missionary, one Don Pedro de Ojuela; perhaps it was named for a hole resembling the eye of a needle (ojuela, "little eye") visible at one point on the mountain above the mine; or perhaps the name derives from hojuela, an old Spanish mining term for argentiferous galena of a leafy texture. The needle-eye hole near the peak of the Bufa de Mapimi is clearly visible from a certain vantage along the road into Mapimi, but, for what it is worth, the present miners seem sure that the leaf-ore etymology is the correct explanation for the mine's name. Indeed it is easy enough to imagine the first cries-something like "hojuela, hojuela!"-at the first sight of a leafy lead-gray metallic outcrop, when the first party of adventuring Spaniards rode their horses up the echoing, pristine canyon in 1598, the official year of discovery.