——— = 
¥ ws 
‘ , 
Mar. 1898. THE ORES or CoLomBpia—NICHOLS. } 145 
replacement proceeds in two ways, which often appear in the same 
specimen. The less common way is for the replacement to take place 
from without inward. The rock disappears on the outside of the 
fragments, and is replaced by a granular aggregate of sulphides in 
quartz which form a band around the trachyte within. The more 
common way, however, is for the alteration to take place throughout 
the body of the fragment. The number and width of quartz veinlets 
shooting across the trachyte increases as well as the amount of pyrite 
and other sulphides occurring as separate crystals, until the rock has 
been entirely replaced, and all that can be seen of the original frag- 
ments is an indistinct angular outline, which also disappears in time. 
In the specimens from the Zancudo mines the following accessory 
minerals were noticed: Cobweb-like forms of jamesonite, incrusting 
forms of aragonite, crystals of siderite and dolomite and arsenopyrite 
in needles. 
ZANCUDO ESTABLISHMENT. 
Though only four mines appear by name in the catalogue, in 
reality there are more than that number represented, since a number 
of them have long been consolidated under one management as 
the Zancudo Establishment. According to a report by Sefior Don I. 
Guitterez, the Zancudo Establishment included in 1884 the Zancudo 
mine with a smelter at Sabalétas, a smelter and mines at Titiribi 
(Sz¢zo Viejo), the Chorros and other mines. The Establishment owned, 
in 1884, 202 stamps, and a proportionate number of concentrating 
appliances, blast and reverberatory furnaces, cupels, etc. The bullion 
produced was silver, with about seven per cent. gold. 
The following specimens were collected by Sefior Gamba at the 
Zancudo mine: 
‘tag. Porphyry from Sabalétas.”’ 
-150. Porphyry from the Zancudo mine.” 
The specimens noticed: were without phenocrysts, and had better 
be termed felsite. 
‘“‘t49. Porphyzite from Sabalétas.”’ 
‘*t50. Porphyrite from the Zancudo mine.”’ 
‘‘751. Trachyte from the Zancudo mine.” 
‘*¥52. Hornblende schist, wall rock of the Zancudo mine.”’ 
*«153. Mineralized schist from the Zancudo mine.”’ 
“154. [E 1068.] Ordinary ore from the Zancudo mine, called 
molino (milling ore).”’ 
This specimen is not of vein material. It is a contact betweena 
