Bisbee daily review., 1911-08-11
Copper Creek District

ait tune TOT tue zoe-toh PtaNt-
 Geology of Camp
 Tn giving the geology of this
 extremely interesting camp will
 quote from the report of walter
 Harvey Weed. who remained in the
 camp for two weeks. conducting a thorough examination in conjunction
 with the wall known Retrographist Prof. Chas. P. Berkey of Columbia
 who colaborated in the report: The 1 geological structure of the district consists of a pro-Cambrian igneous
 crystalline rock, forming the basal complex of the range This rock
 has been classified as diorite.
 grading into grane-diorite in certain areas On this formation all the
 later of the district have been de poslted. The diorite is closely sheet 1 ed and iointed and usually fine
 grained and granite in appearance l It is composed of about equal parts of piagiociase ard +erthoclase, as 7 sociated with hoTnhlefre a
 i tite. Succeeding the igneous rocks | is a considerable area of eambrian
 ouartzite, somewhat altered and py- i ritized along the borders adjacent
 to the area containing the ore brec- l cia The Quartzite is hard, fine i grained, and contains s5.4 per cent
 silica. Above the qaartzite occurs | a narrow zone of paleoboie n1ne-
 stones and shales. the latter being so altered in places as to more
 closely resemble in places the quart. ! zite than the original shale. There 1 is no observed uniformity between
 the cambrian quartzites and the paleozoic limestones, and hence we | conclude that the formation og the
 sediments went on uninterruptedly well into paleozoic times. or until 1 it's close. Above the limestones | and sHales occurs great deposit of
 basalt, which doubtless belongs to the tertiary time. There are no
 rocks representing the long peried 1 Eetween the, clos of th paiczoic and
 the intrusiyes of the tertiary periods ! During this space. however, the ed and the deformation Of the region commenced. Erosion cut l deep valleys into the sedimentaries,
 and in places removed the entire body of such deposits. Tertiary 1 times witnessed two and perhaps
 more great basalt flows, which spread over the surface, filling the
 ancient valleys and covering the mountain crests. While erosion has
 removed vast quantities of these flows, there still remains a large
 area The rock is a typical dark
 brown mass, with phenocrysts Of
 olivene, augite and occasional blebs | of glass and yescicles filled with | quartz crystals. The basalt exhib- l it's a decided tendency to form ta-
 ble mountains and cliffs, which are | locally known as rimrocks of ire | range. The crest Of the range is l capped by a dacite effnsive sheet or flow This dacite varies in col or from a dark greenish gray to ! almost black, and consists of pla- | gioclase, quartz and hornblende em- | bedded in a glassy round mass. The | rock exhibits a characteristic spher- oidal weathering and the formation | of boulders. Following the sresf period of intrusiyes, the region
 gained in elevation, thereby increas- ing the erosive action of the streams which SculptuTed the complex rock
 masses. giving them their present
 topographic form. The condition of
 quarternary time was not unlike
 that of the present day, heavy down pours succeeding long periods of
 dry weather. The torrentiaI streams
 of those great rains cut deep cah- yons in the range and carried
 away vast quantities of the mass. l depositing the coarse and some
 times angular fragments along the
 lower slope of the mountains in the
 roughly-bedded deposits of the Gila
 eonglomerate Still further eleya
 ton of the range and the forma
 ton of a great lake in the present San Pedro valley caused the cut , ting of the many hex canEaus ln ! the oongiomerste and
 the San Pedro lacustrine deposits Ore in Masses
 i The ore deposits of the Copper
 Creek region, which have now reach
 ed stage of development assuring
 the permanence and importance oi
 the district as q copper producer
 are found in large masses or kid
 neys of crushed and mineraiizet . dlorite These masses are breccias
 in which the cementing material be tween the angular fragments i. l, composed Of pyrite, chalcopyTite and bornite There is no regular sys tenn Of occurrence to the ore brec eia, the 50 or more outcrops whicl : are to be seen on the Copper Creel c0mpany's property being irregular ly scattered over the area. Tho
 shape of the ore bodies, both T
 outcrop and underground, IS usual D ly eiliptical, but some occur Of ex
 tremely irregular form. Within th' ? breccias themselves the circulating mediums have wrought marked changed. The fragments have beel siricitized and silicifed, and tn, r interspaces as well as the frcquen sheer seams in the fragments : themselves, filled with pyrite, chalco ]. pyrite, bornite. chrystai quartz ans ! tourmaline. In places, Limited amounts of woifamite, sheelite, mo ' lyodeni.e and chalcopyrite occur as : soeiated with quartz crystals ana ealcite. lining vugs in highly silici ? fed masses of the breccia. Chal eoeite is common in all parts o - the ore body. Wherever 1t il found it is Of secondary origin II R-off~-<. <.-..,,~~ har k1o~. 1~