264 ECONOMIC GEOLOGY 



resentative is found in Colorado. This belt possesses argentif- 

 erous zinc sulphide with sufficient lead and iron to render the 

 ore undesirable for the manufacture of zinc. In 1899 Wales and 

 Belgium entered the market and bought largely of the Colorado 

 ores. Favorable freight rates were obtained by way of Galveston, 

 Texas, to Swansea and Antwerp, viz., $10 per ton. The value 

 placed at the mine was $3 per ton. Although the commodity 

 purchased by Wales and Belgium was a zinc concentrate, it was 

 removed as a by-product which enhanced the value of the remain- 

 der of the products, thereby leading to a more profitable develop- 

 ment of the zinc resources of the state. There is now in operation 

 a zinc smelter at Pueblo, Colorado, and a zinc oxide plant at 

 Canyon City, Colorado. 



In Cumberland and Derbyshire, England, sphalerite with some 

 smithsonite occurs in the Carboniferous limestones. ' Here, as at 

 Joplin, Missouri, the sulphide of zinc is far more abundant in the 

 lower portions of the ore body than the sulphide of lead. In 

 both localities smithsonite is fairly abundant and occurs as a true 

 metasomatic deposit due to the reaction of zinciferous solutions 

 upon the associated limestones. On the island of Sardinia, meta- 

 somatic zinc ores occur at the junction of limestones with non- 

 calcareous beds, which contact may represent either a fault line 

 or a plane of normal sedimentation. Many of the Sardinia 

 deposits below the zone of weathering carry the characteristic 

 zinc sulphides as their permanent ore. The Grecian ore to the 

 southwest of Athens consists largely of the sulphides of lead and 

 zinc, associated with siderite. Thomas and MacAlister consider 

 the zinciferous solution of hydrothermal origin. As they came up 

 from below they passed through small fissures in the associated 

 shales without depositing their metallic content. The presence of 

 the calcareous material caused a deposition of the ores at the junc- 

 tion of the limestones with interbedded shales. 



In Upper Silesia the ores of zinc occur in Triassic limestone and 

 dolomite interbedded with mottled sandstones. In the Picos de 

 Europa district in the Province of Asturias, Spain, the zinciferous 

 ores are associated with limestones of Carboniferous age, and of 

 Cretaceous age in the Santander district. 



Geological Horizon. The ores of zinc do not seem to be con- 

 fined to any particular geological horizon. Those of the Appala- 

 chian belt as already noted are Cambro-Ordovician. On the 

 island of Sardinia they belong to the same age. At Joplin, 



