Mar, 1899. THE ORES or CoLomBIA—NICHOLS. 153 
GOLD MINING DISTRICT OF MARMATO IN THE DEPARTMENT 
OF CAUCA, AND THE ECHANDIA SILVER MINES. 
Marmato is situated on the west flank of the Cauca valley and on 
the slopes of the Marmato heights, which rise 2,230 feet above the 
river. Itis a few miles south of the boundary of Antioquia in the 
department of Cauca. It is a very old mining camp and its mines 
have been worked with some interruption since 1634. 
The Marmato deposits were described in 1826 by Boussingault 
as large veins of pyrite running east and west in a ‘‘ porphyritic sye- 
nitic griinstein.”” An older account (1624) mentioned them as branch- 
ing veins and pockets which were doubtless the weathered outcrops of 
the veins. Senor Gamba in the catalogue describes the wall rock as 
a quartzose porphyry (quartz-porphyry?) and the ores as pyrite and 
blende carrying gold. 
Near Marmato upon the Loaiza Hill are the important silver 
mines of Echandia. The deposit is spoken of by Restrepo as a vein 
of auriferous silver, although from Sefior Gamba’s catalogue there 
would seem to be a number of veins. The ores are pyrite, blende, 
galena, argentite and native silver, which occur both in vein form 
and as impregnations of the rhyolites and their schistose alterations. 
The gangue is sometimes quartz, sometimes calcite, and frequently an 
ash-like substance that appears to be a decomposed rhyolite. The 
country rock, as determined by the writer from the specimens, is a 
light grey rhyolite. ; 
Sefior Gamba collected the following nineteen specimens from 
the Echandia mines : 
‘250. Porphyry, wall rock of all veins in the Echandia mines.”’ 
This specimen is not in the collection, but it is doubtless like the 
next specimen, a rhyolite. 
‘©2952. [E 1110.] Mineralized porphyry, silver ore from the 
Echandfa mines.” 
A light grey rhyolite impregnated with galena, blende and 
pyrite. Cavities are lined with quartz crystals and carry wire silver. 
‘¢253. Pyrite, ordinary ore from the Echandia mines,’’ 
‘¢254. Pyrite and blende, ore from the Echandia mines.”’ 
‘255. Pyrite and blende, ordinary ore from the Loaizita lode, 
Echandfa mines.”’ 
“¢256. [E 1111.] Mineralized schist with native silver, ore 
from the Loaizita lode, Echandia mines.”’ 
The mineralization is complete and little remains of the schistose 
altered lavas. The specimen consists of pyrite, galena and blende in 
