AKT. 23 DURANGO MINERALOGY AND GEOLOGY FOSHAG 27 



cussed. Our knowledge of such solutions is still too incomplete to 

 draw any reasonable deductions from the data yielded by this 

 occurrence. 



MINING METHODS AND PRODUCTION 



The occurrence of the iron ore as cliffs of hard ore or as banks of 

 soft ore make mining both easy and cheap. (PI. 2, left.) The hard 

 ores of Penascos de la Industria are blasted down upon the quarry 

 floor where the bowlders of ore are broken up either by sledge 

 hammers or by further blasting, the broken ore transported by 

 wheelbarrows and loaded directly onto the cars. The soft ore of 

 Cueva de la Marmaja needs no blasting, but is readily picked down 

 upon the quarry floor, loaded into barrows, dumped into a bin from 

 which it is drawn into cars, and trammed to the loading bins. The 

 grade of the ore is high, averaging from 65 to 67 per cent; it is 

 practically free of manganese, titanium, and sulphur, but carries some 

 ])hosphorus. The cost of mining and loading is 64 centavos a ton. 

 The total production of ore from this deposit in 1926 was 81,000 tons, 

 but this amount can easily be increased several fold should it become 

 desirable. According to the estimates of the Compafiia Fundidora 

 de Fierro y Acero de Monterrey, the ore reserved of Cerro Mercado 

 was approximately 100,000,000 tons. 



Much of the early production of the Cerro Mercado came from 

 the detrital or holeo ore that flanks the hill on the east, south, and 

 western sides. (PL 2, right.) This ore was high grade and com- 

 paratively free of phosphorus, but the richest areas have been exten- 

 sively worked out and the reserves of this type of ore are small. A 

 large amount of this ore was mined and used as flux at the smelters 

 of northern Mexico. 



o 



