REVIEWS 327 



The principal metallic mineral of the sulphide ore is chalcocite, 

 and the average tenor of the ore thus far mined by the Ray Consolidated, 

 1.7 per cent copper. The average tenor of the ore sent to the Inspiration 

 mill in 1916 was about 1.55 per cent copper. 



The oxidized material is of two kinds. The first carries chrysocoUa, 

 azurite, and malachite, and is in part rich enough to ship to the smelter. 

 Such material is relatively little iron-stained and is formed by the 

 encroachment of oxidation in nearly pure chalcocite ore. The second 

 type of oxidized material is leached of copper; it is not stained blue or 

 green, but is mostly reddish from iron oxide. It is formed by the oxida- 

 tion of material carrying considerable pyrite. No criteria were developed 

 for recognizing capping over rich ore bodies beyond the observation that 

 very red capping is likely to overlie protore or thin, highly pyritic ore. 

 Assays of this sort of capping show from a trace to o. 2 per cent copper. 

 The average thickness of the oxidized zone at Ray is 250 feet (range 

 45 to 600 feet). 



The lower limit of oxidation and the position of the ground-water 

 level at the time mining began were far from coincident, the divergence 

 being particularly striking at Miami. Drill holes show that enriched 

 ore lies partly above and partly below that water level. This suggests 

 that enrichment was related, in important measure, to an earlier topog- 

 raphy. This conclusion is supported by evidence which shows that 

 much faulting has occurred subsequent to enrichment bringing oxidized 

 and leached material in some places in lateral contact with rich ore on 

 the same level. Rounded fragments of crushed chalcocite ore and 

 fragments of oxidized material are found in the gouges of a number of 

 these faults. The Pleistocene ( ?) Gila conglomerate appears to have 

 been deposited subsequent to most of the enrichment, for the ores lie 

 deepest in fault blocks capped by this conglomerate. 



The deposition of the protores is attributed to thermal solutions 

 coming from deep-lying portions of the granite-porphyry magmas, 

 probably in early Tertiary times. 



E. S. B. AND C. H. B. 



Gypsum Deposits of the United States. By R. W. Stone. U.S. 

 Geological Survey, Bull. No. 697, 1920. 



This bulletin was prepared to take the place of Bulletin No. 223 

 published in 1904, on the same subject. Since that time (to 1918) the 

 production of gypsum has increased more than 300 per cent. In 1918 

 the production was valued at $11,000,000. 



