374 T. L. WATSON VIRGILINA COPPER DISTRICT 



The Dacktown copper deposits in southeastern Tennessee have been 

 shown by Weed { to represent a different type from the Virgilina deposits. 

 Both Kemp f and Weed J agree that the Ducktown ores are replacement 

 deposits of an original calcareous sedimentary. A further difference 

 consists in the Tennessee deposits being composed chiefly of chalcopyrite 

 and pyrrhotite, which minerals are essentially absent from the Virgilina 

 district. 



Weathering 



The superficial weathered product consists of a scanty covering of 

 light gray to brown soil. At comparatively shallow depths beneath the 

 surface the rock manifests no tendency toward disaggregation, nor to 

 crumble and change color when exposed at the surface, but on the con- 

 trary remains hard and fresh appearing. 



The greatly altered nature of these rocks has already been emphasized. 

 The resulting minerals from such change, epidote and chlorite, are 

 present in large amounts in these rocks, replacing in whole or in part 

 the original essential minerals from which the above two have been de- 

 rived. Epidote is usually regarded as a dynamo-metamorphic mineral, 

 while chlorite is usually given as a product of weathering. The origin 

 of chlorite, however, is sometimes closely associated with dynamic 

 agencies. It is not possible, therefore, to separate the products of the 

 processes which have produced the degree of alteration manifested in 

 the rocks of this area. Without stating more detail, vastly the majority 

 of change in the rocks of this area is due to dynamic action. 



A suite of specimens representing the fresh and decayed rock were col- 

 lected at the Anaconda mine in Virginia, a short distance north of Vir- 

 gilina, for illustrating the chemical changes incidental to weathering. 

 Here the decayed product is several feet deep, the brown color of the 

 decayed rock passing gradually into the moderately fresh and firm green 

 rock underneath. In columns VI and VII of the table of analyses are 

 given chemical analyses of the fresh rock and its corresponding decayed 

 product. The decayed rock was of a pronounced yellowish brown 

 color, readily crumbling under slight pressure of the hand. It effer- 

 vesced very feebly in dilute acid, indicating hardly more than apprecia- 

 ble traces of carbonates. When further digested for some time in very 

 dilute warm HC1, the brown coloring matter was removed and the resi- 

 due consisted of the usual green mineral products composing the fresh 

 rock. The percentage of residue composed of the green colored minerals 

 was very large. 



♦Ibid., pp. 449-504. 



flbid., Richmond Meeting, February, 1901, pp. 18-20 (author's edition). 



I Ibid., 1891, vol. xxx, pp. 480-494. 



