ECONOMIC GEOLOGY. 235 



richest ore. No trace of the garnierite green color appears in any of this material. 

 With this soft, white vein material are chalcedonic quartz and thin films of a darker 

 mineral. The principal veins are 2 to 4 inches thick and lie nearly vertical as seen in the 

 mine and trend N. 20° W. to N. 60° W. Many fine lateral veinlets extend from the 

 principal veins into the adjacent serpentine. 



A section from north to south along the wall of the deepest workings at right angles 

 to the principal veins is as follows: 



Serpentine, 60 cm.; white vein, 8 cm. thick; serpentine, 120 cm., with intricate 

 network of fine white veinlets and one vertical white vein 2.5 cm. thick; mass of large and 

 small white veins intimately mixed with serpentine 60 cm. ; dark serpentine with black, 

 film of mineral material on joint surface; few veinlets. 



Sample 15. Taken from dump selected to represent white material from deepest 

 workings; regarded by mine foreman as very rich. Assay result: Nickel, 0.14 per cent. 



Sample 16. Similar to sample 15, but contains some dark rock, probably also min- 

 eralized. Assay result: Nickel, 0.14 per cent. 



Sample 17. Selected to represent dark material, apparently mostly serpentine from 

 deepest workings. Assay result: Nickel, 0.17 per cent. 



Sample 18. Pale green and white vein rock selected from dump to represent part of 

 shaft that lies 15 to 20 meters below the surface. Assay result: Nickel, 1.27 per cent. 



Sample 19. Dark material from dump; same position in shaft as sample 18. Assay 

 result: Nickel, 0.37 per cent. 



Sample 20. Complete section across 2.5 meter face of deepest workings, including 

 serpentine and vein material. Assay result: Nickel, 0.15 per cent. 



Sample 21. Selected sample, including only light-gray part of face in deepest workings, 

 intricately cut by veinlets. Assay result: Nickel, trace. 



Sample 22. Selected sample of dark rock, mostly serpentine, excluding vein material. 

 Assay result: Nickel, 0.19 per cent. 



CONCLUSIONS. 



The richest of the open pit samples taken by Ferguson come from the 

 highest part of the hill. They are Nos. 10 to 14, which contain from 1.29 

 to 3.01 per cent of nickel. The shaft was sunk near the summit of the hill 

 at a point that was apparently the most promising. Of eight samples 

 selected to represent the material at a depth of 15 to 25 meters in this 

 shaft one contained 1.27 per cent, and all others less than 0.4 per cent, 

 some of these samples represent rock that was classed as very rich by 

 the mine foreman, the same man who selected the samples of "picked ore" 

 that gave "very good returns" as assayed in Havana. 



Evidently enrichment through weathering has played an important part 

 at Sierra Prieta. The higher results of assay of the samples from the out- 

 crop appear to be a result of concentration through leaching and redeposi- 

 tion of the disseminated nickel. 



In New Caledonia, where there are nickel deposits of a type somewhat 

 similar to the one at Sierra Prieta, the ore mined generally contains 4.5 to 

 7 per cent of nickel and can therefore be smelted directly by fusion with 

 limestone and gypsum. This treatment is not, however, applicable to a 

 low grade ore, such as that at Sierra Prieta. The only practicable process 

 would involve leaching with sulphuric acid. An ore deposit of this type 



