QUEST FOR GEMS AND MINERALS IN MEXICO 



By W. F. FOSHAG 



Curator, Division of Mineralogy and Petrology 



U. S. National Museum 



In continuation of previous work in the mining districts and min- 

 eral localities of Mexico, I visited some new localities and revisited 

 some old ones where desirable material had been reported. It was 

 planned to visit, by car, a number of smaller mining districts, remote 

 from the railroad lines and main highways, which gave promise of 

 yielding unusual material. Owing to the condition of the roads and 

 the state of the mining industry of Mexico, however, my program 

 could be carried out only in part, and more time was spent at accessi- 

 ble localities. 



Among the places visited was Diente, a small district lying in a 

 rugged range of limestone mountains that extend from Monterrey 

 to the valley of Saltillo. It is chiefly interesting because of the geo- 

 logic structure of the rocks that contain the lead-zinc ores. A simi- 

 lar occurrence of lead-zinc ores is found at Higueras, near Saltillo. 

 Mining operations at this place have been reduced to the production 

 of iron oxide ores for fluxing. 



From Saltillo, I went to Ojuela, near Mapimi, in the state of 

 Durango, a famous old mining district now in its last stage of ex- 

 ploitation. I had visited this mine in 1926, when it was in fullest 

 operation, but the active mining was confined to the lower sulfide ore 

 zones (now under several hundred feet of water). The reopening 

 of the upper oxide ore zone by Mexican miners working on a small 

 scale provided a last opportunity to obtain specimens from this zone, 

 one in which the finer minerals are usually found. The extent of 

 the mine workings at Ojuela are tremendous, for the ores were 

 abundant and yielded rich returns. It is reported that there are 

 about 200 miles of tunnels in this single mine. The mine workings 

 are situated at the base of a high limestone bufa (cliff), 3,000 feet 

 high and unscalable along most of its front. The name Ojuela ("little 

 eye") is derived from one of the limestone spires of the cliff that is 

 pierced by a small hole, suggesting the eye of a needle. To go from 

 level to level in the mine, one must now use notched beams called 

 "chicken ladders," and the search would have been difficult without 

 the aid of the Mexican miners who knew the location of many pockets 

 of the unusual ores. 



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