THE MINING DISTRICTS AND ORES OF ANTIOQUIA. 
The Department of Antioquia, situated in the heart of the Andes, 
between the Western Cordillera and the Magdalena River, is every- 
where traversed by quartz veins, which vary from 8 inches to 6% feet 
in width. These veins are of two classes: the vetas de cajon, which 
vary in inclination from vertical to forty-five degrees, and the wefas de 
sombre, which are more nearly horizontal. These veins are all aurif- 
erous and grow poorer in depth.* A third class of deposits is indi- 
cated by the specimens in this collection, and will be described with 
the Southern deposits. According to Mr. Nye F. Morton, an Ameri- 
can prospector, who spent many years in the region, these veins are 
numerous and persistent over long distances. They are everywhere 
auriferous, but generally of too low grade to work. Rich pockets are 
of frequent occurrence, but they are small and irregular in distribution. 
Workable portions are few and far between. Among the specimens 
of the Gamba collection there is an abundance of fresh, undecomposed 
sulphide ores, which indicate deep mines, as, owing to the climate, 
the surface alteration has penetrated to some depth. Besides pyrite 
and blende; arsenopyrite, galena and chalcopyrite occur in small 
quantities ; also, rarely, stibnite, chalcocite, and ruby silver. Molyb- 
denite, wulfenite, argentite and tetrahedrite have been found with 
the ores. The gangue is usually quartz, which is associated with 
dolomite and limestone in the silver districts. 
According to Restrepo, the deposits are found in granite, syenite, 
diorite, syenite- and feldspar - porphyries, mica, tale and clay 
schists, limestones and dolomites. Gamba’s catalogue gives the fol- 
lowing varieties of country rock: Granite, gneiss, syenite, diorite, 
andesite, trachyte, diorite- and syenite - porphyries, phonolite, por- 
phyrite, limestone, conglomerate, sandstone, slate, quartzite and 
schist, including hornblende and ‘‘xegro-negro”’ schists. Robert 
White+ mentions granite, syenitic granite, diorite and porphyry. 
These lists are, however, very misleading, for the names given 
are applied according to local significations, very different from the 

*Restrepo. Gold and Silver Mines of Colombia, p. 7. 
+Min. Res., iv., p. 635. 
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