THE COMPOSITION OF SOME COLORADO 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 analysis, 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 remaining in the beaker was again treated with aqua regia to be sure of complete 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 solved in dilute ammonia and added to the major portion previously obtained, the whole being then evaporated to dryness, ignited, and weighed as WO,. The iron filtrate was added to the filtrate from the aqua regia decompositions, and allowed to stand for twenty-four hours. Sometimes a slight precipitate of WO,, which had passed through the filter, settled out. This was added to the tungstic acid solution obtained after treatment with ammonia. These steps are necessary in order to be sure of getting all the tungstic acid. The iron and aluminum were separated by the sodium acetate method, the ignited precipitate fused with KHSO4, dissolved and reduced, titrated with standard KMnO,, and the alumina obtained by difference. The manganese was precipitated by ammonium sulphide, dissolved in acid, precipitated by ammonia and bromine water and estimated as MnO4. The calcium and magnesium were precipitated as oxalate and phosphate respectively. The ores were examined for moisture by Penfield's method, but in no case was an appreciable amount found. As will be seen from the following tables, the Nederland ore is mainly tungstate of iron, the mineral ferberite. Most textbooks on mineralogy give a very brief description of this mineral, classifying it as a rarity. On account of its occurrence in such large quantity in Boulder County, it would hardly come under this class. None of the Nederland specimens showed even a trace of sulphur. Mr. Hugh F. Watts of Boulder, who has made over two thousand assays of these ores, tells me that it is not often that they show sulphur; in fact he has ceased making sulphur analyses on the ores, unless for special reasons. These specimens show only a fraction of a per cent. of manganese. The multitude of commercial analyses of these ores shows that rarely does the amount of manganese present run over one per cent. The ore from Ward, Colorado, is a wolframite, carrying pyrite. The specimen showed the pyrite crystals very clearly. On this account the mineral has not been mined profitably. The two ores from Silverton, Colorado, are hubnerite and a mixture of hubnerite and wolframite respectively. The hubnerite specimen was composed of light-brown bladed crystals, a single splinter being almost transparent. The small amount of iron was shown to be in the gangue between the crystals. The hubnerite-wolframite specimen showed a structure composed of black, bladed, acicular crystals, and, as shown by the analysis, was a mixture of almost pure hubnerite and woframite. The Black Hills specimen was a wolframite, was black and of a coarsely granular structure. It contained some calcium carbonate. Below is given a series of tables showing the analyses of the various specimens. No. 1. Ferberite. Clyde Mine, Nederland, Colorado. No. 3. Ferberite. Conger Mine, Nederland, Colorado. |