
Mar. 1899. THE ORES oF CoLomMBIA—NICHOLS. I4I 
GOLD MINING DISTRICTS OF WEST ANTIOQUIA. 
The districts already mentioned are upon the Central Cordillera, 
along the Cauca Valley. The districts of Frontino and Anza are 
upon the Western Cordillera. In the North-Central Districts of 
Antioquia the ores are associated with lead and zinc minerals. 
The sulphides are pyrite and arsenopyrite, associated with blende 
and galena, with but little chalcopyrite. In these western districts 
the ores assume a coppery character, and native copper has been 
reported from Frontino. The sulphides from Frontino in the Mu- 
seum collections would be considered in this country as auriferous 
copper ores. Pyrrhotite and chalcopyrite replace the pyrite and 
arsenopyrite. Auriferous tellurides are present, and in the oxidized 
specimens cubo-octahedrons of free gold are common. The ores 
occur in quartz veins. With the quartz in the specimens from 
both Frontino and Quiuna, there is more or less calcite. The gold 
from Frontino is given by Restrepo as 781 fine, while that of Quiuna 
is 919 fine. The two mines worked in the district are very old. 
The sale of the Frontino mine to an English company is men- 
tioned as taking place in 1852, and the Quiuna mine was dis- 
covered by Antonio Salzaar in the latter part of the eighteenth 
century. Frontino is situated at the head waters of the Rio Sucio, 
the largest affluent of the Atrato, which is reputed to be one of the 
richest and unhealthiest streams in the world. 
The country rock at Frontino is a coarsely crystalline diorite. 
The specimen studied came from near the vein, and was much 
altered; serpentinization of the hornblende was far advanced. None 
of the feldspar could be determined. There was very little kaolini- 
zation, and a large amount of calcite was present, The. ores are 
found in a quartz vein, which, according to Whitney (1854), varied 
from two inches to five feet in thickness. 
From the Frontino mines Sefior Gamba collected the following 
fifteen specimens: 
‘717. Diorite from the Frontino mine, Frontino.” (See No. 125.) 
‘718. Diorite from the Frontino mine, Frontino.”’ (See No. 125.) 
‘rig, [E 1066.] Quartz and chalcopyrite.”’ 
This is a specimen of vein quartz, with chalcopyrite and pyrite. 
It was apparently fresh and unaltered when taken from the ground. 
The pyrrhotite is very magnetic, and is as liable to decomposition 
as is marcasite. Since it has been in the Museum it has decom- 
posed to a great extent, covering the specimen with white crystals 
of epsomite, and with an indeterminate mixture of. oxides and sul- 
