ECONOMIC GEOLOGY. 239 



The volcanic rocks are a series of altered tuffs, breccias, and lavas, cut 

 by a few small porphyritic dikes. The tuffs and breccias appear to pre- 

 dominate, but the rocks are so much metamorphosed that their identifica- 

 tion is difficult. They appear to be finely fragmental, and most of them 

 are green to purple. The coloring is in streaks and blotches and usually 

 is extremely variable. Some of the rocks are uniform in color, green or 

 black, and aphanitic or nearly so. The volcanic rocks are everywhere 

 much jointed and fractured and in places are sheeted. 



The contact between the limestone that forms the upper part of the 

 ridge on the southwest side of Rio Nigua and the volcanic rocks is probably 

 a normal fault. The fault plane apparently strikes about N. 55° W. and 

 dips to the northeast. The limestone is gray to cream-white, granular 

 near the contact, and fine-grained and thin-bedded farther up hill. The 

 beds strike approximately east and dip southward 20°-30°. 



In the bed of Rio Nigua there are many boulders of a coarse pink granitic 

 rock, but this rock was not found in place. The first outcrop is reported 

 to be about 5 kilometers upstream from Naranja Dulce. 



BUCARO HILL ORE DEPOSITS. 



The volcanic rock in and near the workings on Bucaro Hill is full of small 

 slips. Some of the slips in the tunnels that were examined strike northwest- 

 ward and have copper stains along them, but no ore. The dumps of several 

 of the caved tunnels, however, show ore, some of it of good grade. The 

 ore is of two types — (1) malachite, with some quartz, hematite, and usually 

 some sulphide, in chloritized volcanic rock; (2) chalcopyrite, pyrite,bornite, 

 and specular hematite in quartz, with limonite as an alteration product of 

 the sulphides. The quartz seen on the dump appears to have been in 

 narrow stringers or veinlets in chloritized tuff. There are fragments of 

 calcite veins 30 centimeters wide, but these are barren. No chalcocite 

 was noted in the ore on any of the dumps in the district, but a specimen of 

 high-grade massive chalcocite, reported to have come from one of the 

 workings on Bucaro Hill, was shown to the writer by a former employee of 

 the Blanton syndicate. At the end of a drift in the Francis Chini tunnel 

 there is an infaulted block of black, hard slate full of small cubes of pyrite. 

 This is the only sedimentary rock found in the volcanic series. 



Mr. F. Lynwood Garrison 1 considers the deposits of Bucaro Hill 

 segregations in tuff rather than veins, but states that in the lower part of 

 the hill, where erosion has exposed fresher rock, the deposits have the 

 appearance of discontinuous veins. 



The mineralization appears to occur along slips or shear zones and the 

 deposits are therefore veins rather than segregations. The slips seem to be 

 small, and the mineralization is nowhere great. It is extremely doubtful 



1 Garrison, F. L., Mining and Scientific Press., vol. 95, p. 308, 1907. 



