The Ketchikan miner., 1909-04-24
MINES
Valueable Geological Pointers to the PrOspeCtor by A.
 Mcfarlane

thors, who have studied exhaustively the phenomena pertaining to the useful an precious minerals. as they occur in the various rock structures is that mineral is where you find it, and that copper mineral is to be found in nearly every formation. irrespective of time or epoch.
 There is, however, a vast and very material difference between finding mineral and finding ore and mine, and to the ordinary person pursuing the various walks of life, other than a mining career, this difference is not many times sufficiently made clear to them.
 To confine this article 10 brief notation of the authors personal ob- servation and study of copper mines and their attendant phenomena, short descriptions of several well known large producing mines will be of inter- est and to the point.
 The copper mines of Cerro de Pasco in the republic of Peru, are found in the blue limestone, which occurs at this point where the upper eastern plateau breaks into the eastern slope of the 1 Andes mountains. This property bids 1 fair to be, in the near future, one of our heaviest producers of copper: the development work carried on by New York capitalists is satisfactory, and additions will be made to their already large smelting unit.
 This property was famous since the time of the Incas as silver producer, the oxidized vein, or deposit filling, extended downwards to a depth of about 200 feet, silver being the pre- dominant values, with only traces of copper in the carbonate and sulphate form but on reaching nearly to the 2O0-ioot level below the general surface of the vein, zone of secondary enrich ment was reached and great copper mine was discovered which might nev- CT have been found, but only for its silver capping.
 No doubt, at one time the copper values extended upwards through the porous gossan or surface gangue. but due to internal heat and surface wa ters, teaching set in and only ceased when the agents, carrying the copper i in solution, reached zone at about i the water level, where conditions were right for deposition, and the true character of the deposit was learned.
 Four thousand miles north, along the same main vertebra of the great American continent, the great silver mines of Butte were found: worked l for their silver an gold values, with out indications of copper, the depth of 100 feet was reached. when great copper region was discovered, and from then until now the precious met als are but by-products to the copper production.
 The Butte mining district is an area of granite intruded by porpnyries and rhyoiites; the copper district of which i is remarkable for it's zone of secondary enrichment found several hundred feet below the surface.
 Another vast copper region is that of Arizona and Sonora. Here in So- nora are found crushed porphyry zones and highly brecciated igneous rocks, whose rather porous surface have only retained discolorations, or low copper values. the handwriting to the miner which invites him to dig down, or to crosscnt the structure at perhaps diff erent stratigraphical levels, in the hope of finding labors reward in some enriched iaccolte chamber fracture, plane or .oint, the pay shoot sought by all. Rich copper ores, found at the grass roots, occur mostly in small Assures, and rarely ever develop into the large producei, unless these small Assures or fractures are but radii of some larger shearage or fractured zone, and thus serve as leaders to reach their parent fracture.
 Along the lines of contact between the carbohif ferrous Iimestones aud the granite gneiss and schists in Arizona, are found a great series Of copper orc deposits: large flows of volcanic rocks cover here great areas. In fact, in the beddiny uIanes of the Iiueetoneg and