THE COMPOSITION OF SOME COLORADO 

 TUNGSTEN ORES 



By John B. Ekeley 



For several years the mining of tungsten ores in Colorado has been 

 carried on with profit, the richest deposits of this metal being found 

 in Boulder County, principally in the Nederland region. It seemed, 

 therefore, to be of interest to investigate the exact composition of these 

 ores. Analyses were carefully made of samples from three different 

 claims at Nederland. For the sake of comparison similar analyses 

 were made of an ore from Ward, Colorado, of two from Silverton, 

 Colorado, and of one from the Black Hills, South Dakota. These 

 latter ores were not chosen for any particular reason, but were used 

 simply because specimens happened to be at hand. 



The method of analysis used was as follows. The ore was ground 

 as finely as possible and decomposed with aqua regia. Complete 

 decomposition takes place with difficulty in the case of high-grade ores, 

 because the tungstic acid which first separates out forms a coating 

 over the undecomposed particles, thus protecting them from further 

 action by the acid. To avoid this a small quantity was taken for analy- 

 sis, about 0.3 gram. The decomposition was carried out in a 600 c.c. 

 beaker, the ore being spread out evenly on the bottom of the beaker 

 after the addition of the acid. The beaker was heated upon a hot 

 plate at a gentle heat without stirring the ore. In this manner, the ores, 

 except in a few cases, were completely decomposed in about two hours. 

 After dilution with water, the tungstic acid was washed with dilute 

 acid, filtered off, and dissolved in dilute ammonia. The silica remain- 

 ing in the beaker was again treated with aqua regia to be sure of com- 

 plete decomposition of any ore particles remaining. The residue was 

 washed, filtered, and treated with dilute ammonia as before. The silica 

 was burned, weighed, and treated with hydrofluoric acid. The weighed 

 residue was treated with concentrated hydrochloric acid, diluted with 

 water, and any tungstic acid remaining was filtered off, washed, dis- 



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