but, in general, to the east. Underground, below where the two faults wedge out, the dips are consistently east. Surrounding Sacramento Hill, to the south and southwest is a dropped block, which we may call the Contact Block. It is bounded on the north and northeast by the Dividend Fault and Sacramento Hill, and on the south and southwest by the Dixie-Howell-Senator Faults. To the southwest of this Contact Block and up to the Oliver Fault is the Oliver Block of relatively upthrown beds. Southwest of the Oliver Fault is the Cole Block and northeast of the same fault is the Briggs Block which extends east to the post-Cretaceous Mexican Canyon Fault. The dips of all these blocks more or less surrounding Sacramento Hill are nearly due east. The Oliver Fault has tended, however, to swing the up-thrown side, especially where the throw becomes greatest, around to the northeast as is shown in the detailed geological map of the district, Plate 4.

To the east of all these blocks is an eighth block, the Bakerville Block, almost entirely covered by Glance Conglomerate. This block is bounded on the west by the Mexican Canyon Fault, striking about N. 15° to 30° east and dipping to the northwest. This fault is a late one and extends beyond the Dividend Fault, causing the prominent dislocations of the Mural Limestone seen north of Lowell and Warren.

As is shown in section B-B, Plate 6, the apparent dip of the beds in the whole block is very much less than the actual. This is due to minor faulting or slipping which has had the effect of dropping the beds very consistently to the west and raising them to the east. This is one of the typical structural features of the camp and seems to be caused by the extreme resistance of the beds to folding.

There are two ages of faulting, one pre-Cretaceous and the other postCretaceous. As has previously been shown, the porphyry in the district is pre-Cretaceous. The age of the faulting has therefore been determined in large part relative to the age of intrusion. The only large fault which is definitely post-Cretaceous is the Mexican Canyon Fault. As the fault apparently blocks with the Oliver Fault as shown in Plate 8, the Oliver is probably also post-Cretaceous. This is borne out by the character of the exposures underground. There, practically no mineralization accompanies it, and in Oliver ground it apparently cuts off an orebody, which as will be seen later, would make it post-Cretaceous. Both of these faults have the same effect, that is to raise the sediments to the east, and to drop them to the west. The probability is that the Junction Fault, shown in section B-B, Plate 6, is also post-Cretaceous, as it is reported to cut off certain parts of the Junction orebodies, and it is also possible. that a large part of the north to south slipping in Lowell and Gardner ground is also post-Cretaceous. Here the throw of each individual fault. is so slight, and the ground so highly metamorphosed, that it is not susceptible of proof one way or another.

All other faults, so far as observed, have had their major movements in pre-Cretaceous time and before the introduction of the porphyry. Some faults have had movements in both ages. The Dividend shows some movement at the present time, and enough movement occurred in post-Cretaceous time to throw out the Glance Conglomerate. Some post-intrusion slipping has also undoubtedly taken place along the Czar Fault.

Intrusions

As has previously been shown, the block has been extensively intruded by granite porphyry. The largest and most important mass is that of Sacramento Hill, the other occurrences being more or less radial offshoots of dikes and sills from this central mass. It has also been shown that underground exposures below the Escabrosa horizon are much greater than surface exposures.

The path of the Sacramento Hill porphyry was the previously openedup Dividend Fault. Underground development has shown that the porphyry acted as a plug, and that none of the later movements on the fault have taken place along the original line through the mass. The offshoots of the mass have generally followed major lines of weakness such as the Czar, and Silver Bear Faults. Some, however, such as the Shattuck dike, have cut across the country irrespective of fault lines.

The Sacramento Hill, and the connecting Lowell, mass differ from all the other porphyry occurrences in the range, in that they were accompanied by mineralizing emanations, which have completely altered them. These emanations, besides altering the porphyry itself, changed and broke up the surrounding sediments. In consequence of this, as the mass worked its way up, it dragged in pieces of schist, quartzite and limestone along its edges. The final result was a central core of metamorphosed porphyry, with a periphery of contact breccia, made up of highly silicified. and altered fragments, sometimes rounded and sometimes angular, of schist, porphyry, quartzite and metamorphic limestones. This contactbreccia zone has a variable width, with a maximum of about 1,000 ft. It has fairly sharp contacts with the surrounding limestone, but tends to grade off into brecciated porphyry, and finally blocky unbroken porphyry, toward the center of the intrusive mass.

DON LUIS BLOCK

The Don Luis Block is an elliptical-shaped block up-thrown relative to the Copper Queen. It is bounded on the north and east by the WhiteTail Deer fault system, throwing Abrigo and Martin limestone against schist, Bolsa, quartzite, and some Abrigo limestone. To the south it is bounded by the Bisbee West Fault, which is covered by the Quaternary

wash toward the east and toward the west it is bounded by the Quarry Fault. The dips are variable, but for the most part are to the northeast and east.

Intrusions and Orebodies

The block is intruded both by granite porphyry and by andesite, the latter, however, not outcropping. There are two ore occurrences in the block, one at the northern boundary, and rightfully in the Copper Queen Block, and one at the southeastern end. The first of these, the WhiteTail Deer orebody, occurs as a replacement of Abrigo limestone, about 50 ft. from the base of the Martin. It is not associated with any known intrusion, but is close to the White-Tail Deer fault system. The second occurrence is that of the Wade-Hampton. Here the ore occurs as lead and copper ore 'in a fault separating Abrigo limestone from Bolsa quartzite. The ore here is apparently associated with a dike of andesite and occurs in the crushed Abrigo limestone on the fault.

VI. GEOLOGIC HISTORY

The earliest geologic age is recorded in the district by the preCambrian Pinal Schist. As has been previously stated, this was probably derived from arenaceous sediments.

Due to the extreme metamorphism, the geologic history subsequent to the deposition of these early sediments, and up to the deposition of the Cambrian sediments, is obscure. The sediments were probably subjected to extreme folding, intruded by diabase, and deeply buried. After the metamorphism was complete, the schist was intruded by a large mass of granite. From then on to Cambrian time, erosion worked on the whole complex, wearing it down to an even peneplain.

At the beginning of Cambrian time, a gentle subsidence took place, resulting in shore-line deposits of quartzites, the subsidence becoming more rapid toward the end of the period, in which time were deposited finer sands and some shales. The land surface toward the end of the Cambrian period became more distant, as evidenced by the deposition of the Abrigo shales, and shaly limestones.

At the end of Cambrian time, a gentle rise took place over an extensive area, bringing the flat sea bottom close to the surface, with land actually emerging probably toward the south. During the Ordovician and Silurian ages, this lowland surface of Cambrian beds was subjected to slow erosion simultaneously with the deposition in the district of an 8-ft. bed of quartzite. A slow subsidence then took place to the north of the district, allowing the thicker deposits of quartzite in the Yellowstone Range of 40 ft., and at Globe of 500 to 700 ft.

At the end of the Silurian, a sudden subsidence took place, resulting

in deeper-sea conditions and thus the Devonian age is represented by fairly pure dolomitic limestones.

The sea evidently continued to deepen all through Mississippian time with the deposition of the pure Escabrosa limestone. During Pennsylvanian time, subsidence did not keep pace with deposition and the sediments became increasingly more shaly, and cherty showing a nearer approach of land surface and shallower seas. At the end of the Pennsylvanian, and probably during the Permian age, a violent uplift took place, resulting in the doming of the sediments around the pre-Cambrian granite mass. The sediments were shattered by extensive faults, the major lines of weakness being northwest and southeast. The granite mass itself resisted this shattering to a great degree except around its edges. Immediately following the faulting, or partly accompanying it, granite porphyry was intruded, following generally the major lines of weakness, but also shooting sills and dikes into the less resistant sediments. Accompanying one of these porphyry intrusions, that of Sacramento Hill, were mineralizing emanations, which metamorphosed the surrounding sediments and the porphyry itself, and were the source of our present orebodies.

During Jurassic and Triassic time, the whole area was subjected to erosion, during which time most of the upper Carboniferous beds were stripped off, and at the crest of the dome, around the granite and schist of Juniper Flat, the old pre-Cambrian complex was laid bare. During this erosional period, the orebodies were subjected to oxidation, which would place the age of primary ore formation definitely at or near the age of the uplift.

At the end of this period, a remarkably sudden subsidence took place, before any of the land except the top of the dome had been leveled off, and the rough topography surrounding was filled up with the extremely coarse Glance Conglomerate. The subsidence was so sudden that the fragments making up this conglomerate were hardly worked over at all, it being made up of angular boulders, some as large as a yard in diameter, of schist, quartzite and limestone. The roughness of this old topography is well shown in the basin covered by conglomerate, in which the town of Warren is situated.

After the whole country was leveled off by the Glance Conglomerate, the subsidence became less rapid, and shore-line deposits of sandstones and sandy shales were laid down, followed by deeper-sea conditions, during which the pure Mural Limestone was deposited, showing abundant Cretaceous (Comanche) fossils. Shore-line deposits followed this again to the end of Cretaceous time.

During Tertiary time, a second uplift took place, along almost the same axis as the previous one. This also took the form of a dome around the old granite mass, and the Escabrosa Ridge porphyry intrusion. This uplift, however, was not as violent. It was accompanied by extensive

block faulting, with little disturbances of the beds within the blocks. The major faults took the form of overthrusts, the largest being the Tombstone and Gold Hill faults. Either accompanying the uplift or subsequent to it, some intrusion of monzonite porphyry took place, at the southern end of the range. Probably some of the extrusive rhyolite also belongs to this age of intrusion. Finally the whole range was subjected to a tilt to the northeast of about 15°.

From then on to the present time, erosion has been steadily at work, and has again laid bare the old pre-Cretaceous sediments along the crest of the dome, with Cretaceous beds exposed to the northeast. To the southwest, the Cretaceous has been all eroded, due to the final tilting. The only evidence left of the second doming is found at the southern end of the range, as shown by Plate 1. During this last erosion period the orebodies have been further subjected to oxidizing and enriching processes, so that we owe their condition as we find them today, to two widely separated periods, in each of which the original primary ores were worked over by surface waters.

VII. METAMORPHISM AND MINERALIZATION

GENERAL METAMORPHISM

In a region that has been subjected to as many geological changes as the Warren district, it was to be expected that the rocks would show many variations in texture and mineralogy from the unaltered types. The effects of regional metamorphism as well as dynamic are represented in the Pinal Schist as has been shown in describing the lithological characters of this formation.

The Cambrian formations have also been changed throughout their occurrence in the district by a process related to regional metamorphism in the wide scope of its action. The induration of the pure Bolsa quartzite has gone on until it is of glassy texture, but in the clayey, magnesian Abrigo limestone, besides the segregation of chert, the impurities have everywhere combined into such minerals as epidote, zoisite, chlorite, serpentine, and possibly albite. No such action is at all observed in the conformably overlying Martin limestone, which strongly suggests that the changes took place in the long period separating the middle Cambrian from the Devonian. But since field evidence excludes any great disturbance during the unrepresented period, it is probable that the general metamorphism in the Abrigo was caused by the deep burial under more than 4,000 ft. of overlying limestones after the impurities in the beds had had a chance to segregate and rearrange themselves due to the slow action of cold surface solutions during Ordovician-Silurian times. The necessary temperature conditions were probably obtained by the rise in iso