ECONOMIC GEOLOGY. 233 



MINING OPERATIONS. 



Nickel ore is said to have been discovered at Sierra Prieta by Senor 

 Manuel Delmonte, who obtained a concession and held it through several 

 revolutions. The disturbed state of the country prior to American occupa- 

 tion prevented development. Senor Delmonte sold the concession to the 

 syndicate of which Dr. Rogelio Diaz Pardo of Havana is the principal 

 owner, and a small amount of shafting and trenching has been done for the 

 syndicate under the supervision of a mining engineer named Pagliuchi. 

 The work done includes a shelf excavation wide enough for a cart road ex- 

 tending around the east and north sides of the hill at about the 195 meter 

 contour. A shaft having a depth of about 25 meters and about 15 meters 

 of cross cuts have been dug near the highest part of the hill. The under- 

 ground work has been discontinued and a tunnel is being started on the 

 southeast side, opposite the shaft and about 50 meters below its mouth. 

 Samples of "picked ore" sent to Havana from time to time are said to have 

 yielded very favorable assays. The mine foreman who selected these 

 samples assisted in the sampling in the shaft and also selected samples of 

 "picked ore," the assays of which are given on pages 234-235. 



The exploratory work done prior to 1918 consisted of digging trenches 

 and pits at irregular intervals over the most promising part of the deposit. 

 On the assumption that the entire hill consisted of ore, a civil engineer named 

 Henderson was engaged to make a survey and estimate the quantity of 

 minable ore. His report showed that 95,000,000 tons lay above the level 

 of the plain. The same engineer was then engaged to survey a railroad 

 route from the mine to the harbor of Santo Domingo. 



MODE OF OCCURRENCE OF NICKEL. 



The nickel in the outcrop occurs as the mineral garnierite (genthite), 

 a hydrated silicate of nickel and magnesium of pale apple-green color 

 which is associated with a fine network of quartz veins. The mineral is 

 probably a product of weathering, the nickel being in the form of another 

 silicate a few meters below the surface. The mineralization appears at 

 widely separated points over the upper part of the hill, and the weathered 

 outcrops appear as spongy, honeycombed rock of rusty brown to greenish 

 color, showing the garnierite stain when freshly broken. Below the surface 

 the garnierite green becomes less and less noticeable, and at a depth of 

 about 15 meters the vein material is almost entirely white and consists of a 

 soft, amorphous mineral, possibly magnesite, with dark stains and a few 

 quartz veins. The analyses of samples from a depth of over 15 meters 

 below the surface indicate that the nickel is disseminated through the vein 

 material and country rock, forming an "ore" of lower grade than that 

 nearer the surface, where enrichment has more or less localized the mineral. 



