164 FIELD CoLuMBIAN MuseumM—GEo ocy, VOL. I. 
among the richest silver mines in Colombia. The mine was aban- 
doned early in the 17th century. It was rediscovered about 1871 and 
operated by an English company. According to the superintendent 
of the mine, in 1886 the ores, with an average yield of 311.4 ounces 
silver tothe ton, were ‘‘ argentiferous sulphides of lead, a zinc com- 
bined with iron and arsenical pyrites; the sulphide of silver is fre- 
quently found and at times red silver and native silver.” According 
to the same authority the gangue is quartz with calcite and siderite. 
The veins vary in width from a few inches to several feet and occur 
in micaceous and talcose schist. One of the specimens in the collec- 
tion is a typical mica schist, and Senor Gamba catalogues a limestone 
and a gneiss from the vicinity. It is to be inferred from this that the 
mine is located below the eruptives and in the basal crystalline rocks. 
In 1886 the mines had reached a depth of 600 feet. Pyrargyrite, 
referred to above as ‘‘red silver,” is abundant in the specimens of the 
Museum collection. According to John C. Randolph all the ores are 
found at the intersection of a seam with the main vein.* 
From the Frias silver mine Sefior Gamba collected the following 
thirty-two specimens: 
‘¢349. [E 1656.] Blende and galena, schezderz.”’ 
This specimen consists of bands of coarse blende, coarse galena, 
fine granular pyrite and a finely granular mixture of galena and pyrar- 
gyrite. 
“350. [E 1653.J Galena impregnated with ruby silver.” 
This is a mixture of massive galena and pyrargyrite in about 
equal quantities. Crystals of pyrargyrite are found upon the granu- 
lar mixture. 
(CAST. piatieov le hich Paleta ss 
This galena is mixed with some blende and much pyrargyrite. 
‘¢352. [E 1129.] Galena and blende in calcite.” 
This is a mixture of galena, blende, and pyrite on calcite with 
crystals of blende and galena. 
‘¢ 353. Pyrite, galena and blende, scheiderz.” 
‘(gman (( HM ar27.| Mineranzedtechistn: 
This is a mixture of galena, blende and pyrite in quartz veins 
which traverse a graphitic mica schist. 
Og 5a ee eel 20s) eet ese 
This is a coarsely granular mixture of about equal parts of 
galena, blende and: pyrite, 
“356. Concentrates, different sizes.” 
‘¢357. Concentrates, different sizes.” 

*TrA. 1M. E., Vol. X VILL, (1889) ps 205. 
