USEFUL Ml I 



of (In- emanation! of radium, is often a product of contact 

 metamorphisra. 



Character of the Ore Bodies. Zinc ores occur in nature under 

 a great variety of conditions, which maybe classified as follows: 

 (1) As true metalliferous v -in-. (2) As cavity fillings not of 

 trur-li-Mire vein type. (3) As irregular masses in the metamor- 

 phic rocks. (4) As irregular masses, or disseminations, formed 

 by replacement or impregnation in limestones and quartzites. 

 (5) As contact metamorphic deposits. (6) In residual clays. 



The associated minerals are galenite, pyrite, marcasite, and, 

 less frequently, chalcopyrite, together with calcite, dolomite, 

 fluorite and barite as gangue minerals. In the zone of weathering 

 in zinciferous ore bodies the sulphides are altered to smithsonite, 

 hydrozincite or calamine. The oxidized ore often yields more 

 readily to metallurgical treatment than the sulphide ores, and 

 even though the percentage of zinc may be lower they may be 

 of greater value than the unoxidized ores. 



Where zinc arid lead occur together as sulphides the zinc dis- 

 integrates more rapidly than the lead and its sulphate solutions 

 are transferred downward for the enrichment of the ore bodies at 

 the lower levels. 



Geographical Distribution. The zinc ores of the United States 

 are located in three distinct belts as follows: (1) The Appalachian 

 belt; (2) the Central belt, and (3) the Cordilleran section. 



(1) Appalachian Belt. There are several scattered occurrences 

 of zinc ores in this belt. Some of these produce small quant it it s 

 of lead, as in Tennessee and southwestern Virginia. The ores 

 are associated with the Cambro-Ordovician limestones. The 

 unoxidized ores consist of sphalerite, galenite, pyrite, and belong to 

 the disseminated replacement-breccia, type. The oxidized ores, 

 which are concentrated in the residual clays in close proximity to 

 the weathered surface of the limestones, consist of smithsonite, 

 cerussite and calamine. 



In Pennsylvania, in the Saucon Valley, an ore body of zinc 

 occurs that at one time bid fair to be of considerable commercial 

 significance but the ore body has never been extensively worked. 

 In Thetford, Vermont, sphalerite and galenite occur in a fissure 

 vein with a quartz gangue in the Vershirc schists. 



The most important ore body of zinc in this belt occurs at 

 Franklin Furnace, N. J. According to A. C. Spencer, two large 

 bodies of zinciferous ore, different in character from any other 



