264 ARTHUR LAKES 



of metallic copper is precipitated and collected. The center 

 of this Clifton basin is a vast mass of porphyry, surrounded 

 by carboniferous limestones and sandstone, the latter abutting 

 against an eruptive body of granite. Copper in this southern 

 region seems intimately connected with volcanic rocks, both 

 ancient and recent. 



The ores of the Clifton mines occur in hmestone, por- 

 phyry, and granite. In the limestone they occur as oxides 

 and carbonates, such as hematite, cuprite, green malachite, 

 or blue azurite mingled with black manganese. 



In the porphyry and granite the ores are oxides near 

 the surface, changing with depth into dark gray copper glance, 

 and deeper still into the original ore, viz., yellow copper 

 pyrites. 



The Longfellow is the principal mine. The first dis- 

 coveries were in pockets cropping out on the crest of Long- 

 fellow's hill in decomposed limestone altered largely into 

 clay. On approaching the underlying sandstone native 

 copper appears and the veins pinch and become barren. 



On the rise of the vein above the Longfellow adit, large 

 chambers of ore have been found in a manganese ore, yielding 

 38 per cent copper; 1,000 tons yielded 17.17 per cent copper. 

 The vein is in a vertical fissure in limestone at contact with 

 a dike of felsite. The ore replaces the lime, as at Leadville, 

 Colorado, and occurs in irregular bodies. The ore is found 

 in conjunction with large bodies of clay from decomposed 

 rock resulting from the action of fumaroles, or hot springs, 

 steam and hot solutions, during the deposition of the copper 

 ores. 



Another class of ores are in a stockwork of quartz veins 

 in the porphyry and deteriorate with depth. These ores, 

 though attractive on the surface have, Uke man}^ other metallic 

 mines, grown poorer with depth. The decomposed oxidized 

 surface ores are the richest and the undecomposed ores under- 

 lying the surface are poorer in copper and more difficult to 

 mine. This is conmionly the experience with a large ma- 

 jority of copper mines, such as the copper pyrite mines of the 

 Alleghanies and some of the Lake Superior mines, where rich 



