The copper era., 1904-02-11

would not merit the extensive devel
 opment that has been done. Some o our leading engineers condemned tn
 district altogether on this recount.
 The ieached zone varies consider ably in different places, but below
 we come to zone Of secondary en-
 richment from which nearly all the copper is produced, and still further down, we meet the primary unaitercd sulphides, pyrite and chaIcopyrite. This series Of changes is well exem- ] plefed in the lodes of the Standard T, eTYf s,lf6sons iron.staffned outcroG, wq'ii l:i a seam Of carbonates but few inches wide is visible. Perseverance and fearless exploration have been the means of opening up an exceedingly rich ore shoot which is probably the richest deposit being mined in the district today, although it is Of com paratively small dimensions. The vein is very fat, dipping into the mountain of hard quartz pOrphyry at an angle of II degrees to the )rizon- tai. Development shows 1t to be about five feet wide Frozen tightly to d well defined harging wall Is d zone of oxidized iron containing some al tered glance and carbonates, below this k barren zone of talcose matter traversed by q network of veiuules Of talcose Of copper carbonate and sili- cate, leading to a wider zone Of sec Ondary enrichment below, consisting almost entirely of chalcocite. In the lowest workings this chalcocite is seen surrounding nuclei Of pyrite and chal- cOpyritc. The oxidized copper bear ing solutions. in their underground cir culation have deposited their copper as chalcocite on the primary low grade cupriferous pyrites. The same reac- tion accounts for the rich ore body opened up in the Coronado mine Of the Arizona Copper company, for l have found pseudomorphs of chalcocite after pyritc, imbedded In the DOT phyry gangue. Indeed, nearly all the ores being mined in this sec sion are presumably Of secondary character, but exploration to the real primary unaltered sulphides has not been car ried out. There are no deep mines in the district.
 The Humboldt vein, although its doubted is not confined to definite walls. The mineralized zone extends for into the surrounding porphyry. The immense ore reserves blocked out assure d steady output for many years to come.
 The Coronado Tine, Of the Arizona Copper company, is definite fault ifs sure, having d throw Of about l,0OO feet. The ore body is proved 10 depth of 50O feet. It forms one of the most valuable assets of the Arizona Copper company.
 The second class of deposits, those due to contact metamorphism, are probably larger than the class already referred to Wherever the porphyry came into contact with the grauites or quartilites, little or no alteration took place, but where it met the limestones, immense masses of epidote and garnet were formed. The famous Longfellow mine belongs to this type of deposit, and the mines Of the shannon Copper company are due to contact meta morphi-m. Naguetite is plentiful in this type of deposit, although it is conspicuous by its absence in Assure veins. Since the origin of these de- posits seems to have been due to the metallic substances released from the intrusive porphyry mass, when forced upwards. they are probably coutem- poraueous with the qualification of the pnrphyrieS. At mospheric agen- cic, have considerably altered these deposits. leaving large masses cf oxide and carbonate ores.
 SYSTEM OF MINING.
 Owing to the blocky nature of the
 l. .l..