The copper era., 1904-01-14

GEoLDuICAt fEATCEF5.
 Near Clifton original high elevation
 and extensive subsequent erosion have
 combined in forming an exposure oi
 prr-Tertiary rocks consisting Of gran
 i'e. porphyry, quartzite and limestone.
 The Clifton area Of older rocks may be considered small isolated mass pcrhap9 twelve miles long from east to west and eight miles broad from north to south, appearing like an island in thc -urroIudjng vast lava flows. The oldest rocks and that which occu pies the largest area is granite, evidently of prc-Cambrian age. It forms the great mass of Coronado mountain. and inc larger part Of the precipitOus com plcx of mountains between Chase creek and San Francisco river. On the somewhat irregular surface of this granite rests q sedimentary series Of Paleozoic age, the lower part consist Ing of POO feet of quartzite conglom- crate, in places reaching a thickness of fifty feet This quartzite, in which mo fossils have been found, is probably of Cambrian age. The quartzite is covered by sOO feet Of limestone, the lower part of which belongs to the Silurian system, the middle part to the Devonian, and the upper 100 feet to the To ger carbocifcrous series. Be-
 ginning from the base, the limestone gradually becomes purcr and top stratum, well exposed at Morcnci, is almost entirely pure carbonate of lmc. Within the Dcvonian portion about 100 feet Of clay shale is inter- calatcd in the limestone. 4 large mas, of porphyry, running out al various points entering into compli- cated dihc systems, has been ,ntrudcd into these rocks, granites, well as quartzites and limestones, and this porphyry seems most intimately con occtcd with the origin of the ore. It's character varies somewhat The pre- vailing rock near Morcnci is inter mediate between q granitc-porphyry and a diorite-porPhyry, but at some points diorite porphyries Of typical l character also occur. The porphyry | at Netcalf is more acidic and contains | large quartz cry stals. It may more | closely approach granite-pOrphvr vrv. but i-. ecologically, probably the same 1 body a. the Morenci porphyry. At | the Coronado mine and other places in that vicinity small dikcs of diabase occur Southwest Of Morenci a sedi- meutary series has been found which l appears to cover the Pateozoic rocks. ] At one place fossils, indicating a Gre l !aceou- age were obtained. These ! rocks. however, are only ot secondary l importance a. far ae the ore deposits are concerned,
 The geological structure Of the pre- Tertiary rocks is rendered very com plicatcd by extensive faulting. In few places does this faulting affect the coy cring ba-alt and rhyolite, from which | it. k to hc concluded that the main !. epoch of disturbance autcdates the volcanic cruptionS of the Tertiary period The Paleozoic era in this re- giou was evidently one of quiescence and deposition, and il is believed that undisturbed deposition continued through the larger part of the Gre taccous pcrod. The intrusion Of DOT phyry took place during ihe late Gre tuccous or the earliest Tertiary, for we Gud bodies Of that rock intruded into Crctaceous sediments, aS well as .,lI T, t,l,.. l. intrusion was accompanied by very great disturbance, causing a frsctur- ing and shattering O. the scdimeutary series into which it was iutruded. The important ore deposits were formed during and short time after this intrusion of porphyry. Altera- tion. gradua changing and often euriching these ore deposits, has, however continued from their deposi- tjon to the present time. The deposi- ton ot the ores was followed by very extensive fracturing and faultiug, af- lccting all of the rocks in the district except tho younger lavas. From the form ot the remaining patches Of quartzitc it would seem as if the sur face ot the granite and the whole overlying series had been buckled, perhaps elevated in dome-like shape and then fractured extensively.
 The geological map will show the complicated nature of this faulting. The main faults extend in an east west or northeast-southwest direction. Faults having throw of over 1000 feet are common and in the Paleozoic series the complication is particularly apparent Among more important faults may be mentioned that at the Cornado mine, where the souh side is dropped 1000 feet and that cutting across Chase creek east Of Moreuci. where again the Paleozoic series has been dropped l 300 feet or more. An extensive erosion, resulting in very irregular surface forms, followed these disturbances. Then, probably in the latter part ot the Tertiary period, the whole region was Hooded by rhyolites and basalts. Following this, proba- bly in the early part Of the Pleisto- cene, the level ot the Gila river be- came greatly raised by accumulations