The geology and ore deposits of the Cuprite mining district

Item Type text; Thesis-Reproduction (electronic)

Authors Lee, Charles Albert, 1908-

Publisher The University of Arizona.

Rights Copyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.

Download date 01/10/2021 16:18:24

Link to Item http://hdl.handle.net/10150/551627 THU GKOICGY IdW OKK DliPOtilTS

OF

bhi coprits i m n m district

by

Charles A« Lee aM G erald C, Borland

Subnit tod in partial fulfi linen t of tho recplremnts for the degree of

L'-ostor of scienoo

in tho Graduate College

University of Arizona

1935

Approved: TABLti OF CvSlBHIb lifi’HouUo'riuii ...... Acknowledgemente ...... Scope of the Present ,/ork Previous Geologic ,Vork .. GSOLuGiU HiiLuAflOIIS ...... % Location and Means of Approach ...... 2 Settlements and Means of Communication ••* 5 C lim ate and V e g e ta tio n ...... • 3 Physiography ...... 5 R e l i e f ...... 5 D rainage ...... * • 6 HI of JAY OF imiiRG Hi TMii GLSERAL RLGIul ... 7 SIIUTIj GuAFHY...... 9 Principal Rock Groups ...... 9 Sedimentary Rocks ...... 11 P ale o z o ic ...... 11 Pennsylvanian ...... 11 Post Pennsylvanian ...... 12 Igneous Rooks ...... 19 P lu to n ic ...'-19 E x tru siv e ...... 21 Dike Rocks ...... 22 STRUCTURAL GEulvGY ...... 25 General Features ...... 25 Early Folding ...... 26 Over thrust Faults ...... 2 7 Early Sormal Faults ...... 28 Doming by I n t r u s i o n ...... 3u Post-Granodlorlte Pre-Dike Fracturing .... 3u Post Dike Transverse Faulting ...... 51 Basin Range Faulting ...... 51 Age o f F o ld in g ...... 32 Age of F a u ltin g ...... 32 GEOouGIC RISTjaY ...... 32 MittERAjj RESOURCES ...... 35 uRE DEPOSITS ...... 35 History of production ...... * * 55 Geographic and. Geologic Distribution ..... 36 General Character of the Deposits ...... 37 Pyromet a somatic Deposits ...... 58 General Features ...... 38 M ineralogy ...... cQ Replacement Deposits ...... *. 35 G eologic F e a tu re s ...... 5v C ontents ./

Description of Bustervilic nine ...... 3y Vein D escription ...... 39 Wall Rook A l t e r a t i o n ...... 41 Mineralogy ...... 42 G eneral Summary ...... 42 Detailed Description of Minerals .. 42 Mineral Parage no sis ...... 45 Genetic Classification ...... 46 Age and Genes! s ...... 46 EXiX...HATlv>a OP SYMBOLS ...... 48

LIST OP ILLUSTRATIONS

PLaTL I P ig . 1 , P hotograph lo o k in g so u th e a st from Buehman H i l l . 2. Photograph looking south from Buehman H ill. 3# Photograph looking so it invest from Duehmam H i l l . PL.Vi’B I I , Fig. 4. Photograph of the northeastern part of the area, looking southwest• . 5* Photograph looking south from Buehman H ill. 6. Photograph of the B usterrille Mine. PLATE I I I A. Photomicrograph showing treeclated pyrite surrounded fcy sphalerite and chaloopjrite veining sphalerite. B. Photomicrograph showing the minerA1 relation­ ships between pyrrhotitc, sphalerite, ohal- copyrite, galena, and calcitc• PLATE IV ' A. Photomicrograph showing tetrahedrite vein­ ing sphalerite. B. xhotomicrograph showing bournonite replacing tetrahedrite. PLATE V A. Photomicrograph showing ouloite replacing ehalcopyrlte in bournonite. B. Photomicrograph showing galena replacing chal oopyrite and bournonite and being replaced by culeite. PLATE VI Geologic Map. (In Pocket) C ontente

PjjATii VI1 Structure Sections, (In Socket) PLATS V III ! . Bueterville iline, (In Pocket)

Page 10, Strutiographic Column 13, Photograph of breeda overlying Maco linestone, 15. Photograph showing contact between rhyolite porphyry and quartzite# 17. Photograph of limy shale in Upper Cretaceous s e r i e s , 18. Photograph of boulder conglomerate, 2S, Photograph of andesite breccia. 24. Photograph of andesite porphyry, rhyolite porphyry dike, and boulder conglomerate. I'Miiob'MivM A ^ o wlfidfiaent s.

The authors \^Lsh to express their appreciation to Dr. B. S. Butler, Dr. It. N* Short, and Dr. A. A. Stoyenoo, all of the Unireralty of Arizona. Their helpful suggestions and aid in the field were extremely valuable. The writers are also indebted to Mr. Frank Estrada for permission to work on his lend; also to Hr. Foster of the Bustorville Mine, who permitted the vriters to go to the mine and to collect samples.

Scope of the Present Work

This report discusses the stratigraphy, petrography, structure , ore deposits, end general geologic history, Inter­ pretations and conclusions are made where the facts seem to justify them. Field work was begun the middle of October, 1994, and continued on weekends and vacations through tie winter and spring of the following year. Aq no satisfactory topograph­ ic map was available much of the time available for field work was used in the preparation of a base map, and hence the geolo­ gical study was not as complete as desired. The writers fool that there is yet much that needs to be more fully investigated.

P re' M G eologic iTork

Previous information on the region is confined to -8 -

9. S, Geologicnl Survey Bulletin 582, “Mineral Deposits of the Santa Hi to md Patagonia Mountains," by Prank C. Schrader and Janes M*. H ill, published in 1915. Tho work was of n re- eonnaiseance nature and the map was on such a snail scale that no details of geology were shown. However, the report contains much valuable and pertinent information, which has 1m part bom incorporated in this manuscript. 2tore recent work has been done in the general region by candidates for advanced degrees end by classes in field geology at the University of A rizona.

GEOGRAPHIC RELATIONS

Location and Means of Approach

The Cuprite district is in southeastern Arizona in the southeastern part o f Pima County, approximately 28 miles southeast of Tucson, Arizona. It is in the northern pert of the Santa Rita Mountains at a general elevation of 4,000 foot. The portion of the district mapped by the authors extends for two miles in a north-south direction, about two and a half miles in an cast-west direction anl, comprises about four and a half square miles. It may be reached by turning south from U. S. High­ way 80 one mile east of Vail Junction and traveling 8 miles on a fair desert road. The main line of the Southern Pacific Railroad goes through Vail one mile north of Iho highway and -5 over thio line several passenger and freight trains pans in each direction daily#

S e ttle m e n ts and Means o f Corsaun lo o t ion

The only settlement is Bustervllle, in the eastern part of the area, consisting of four houses in vdiich live the non who operate the Bus tervllle Hino. The only other habitation within the area is the hone of Mr# Frank Estrada located in the western port, about two and one-half miles from the Bustcr- ville Mine, There is no telephono, electric, or moil service in Bus tervllle. The residents obtain their mail at Vail Station, eight miles to the north# Siator also must be hauled-but at the time of writing H ft woll is being drilled just off the northern edge of the nap. from which it is hoped that sufficient water w ill be developed to supply the needs of Bustervllle.

Bie climate is arid with hot days end cool nights# Summers are extremely hot,but due to the mild winters it is possible to continue field work throughout the year. Rain in the summer is likely to fall in cloudbursts which cause floods of short duration but extreme violence. These summer rains may be expected frem July to September. The winter rains come from from December to March and enow fa lls occasionally. On the higher peaks In the Santa Hita Mountains to the south of this area mow may remain till the latter part of March or the middle of April* Mo official weather records ware consulted, but by reference to Mr. Schrader’s report one finds the following:

\ According to the records of the weather Bureau kept at Tuoscn, which may bo regarded as approxi­ mately representing the valley portion of the area, the average maximum temperature for the 13 years ending with 1911 was 108 degrees and the minimum 17 degrees. The average rainfall for tho valley at Tucson is shout eleven inches annually. Vegetation is o f the desert typo consisting chiefly of ocotillo, sawtooth yucca, Spanish Bayonet, century plants, prickly pear, a few saguaro cacti, rainbow cacti, cholla of several varieties, md creosote bushes. Trees present consist of mesqulte, Palo Verde, desert buckthorn, juniper, and several types of spinoy trees that are unknown to the authors. Mistle­ toe is found as a parlsitic growth on certain types of trees. Higher in the mountains outside of this area one may find live oak, spruce, and walnut. Forage grosses are not abundantly developed in the area although a considerable number of cattle range over tho la n d . However, on the higher leads to the south the forage grasses grow more abundantly. B e lie f

Dio area is ono of rather broken topography consist­ ing of steep h ills and mountains with washes having steep sides. The mountains charsotor 1stloally rise abruptly frca the debris of tlie desert plains. These mountains consist of a number of nearly parallel ridges, separated by deep canyons, and arc in a youthful to nature stage of erosion. One of the h ills within tho d istrict has been named Bushman HiU, and may readily be distinguished by its capping of metamorphosed lino- stono breccia. There is a gradual decrease in elevation from the southern end of the district to the northern end. Tho highest point on tho mapped area is a mountain on the southern edge of the area having an elevation of about 4,850 foot. The low­ est spot is 3,600 feet and is on tho northern edge of the map. The average elevation is about 4,200 feot. To tho south of the portion mapped arc the rugged Santa Rita Mountains vhich extend in a north-south direction for about 45 m iles. This range reaches its maximum height of 9,432 feet at Mt. Wright son, formerly known as Old Baldy Peak, which is the highest point in southern Arizona. About two and a half miles south frem the boundary of the area mapped by the writers is Mt. Fagan, with an elevation of 6,175 feot. It was frem the triangulation point on top of this mountain that an in itial elevation for the topographic map was obtained. An idea of the general topography nay be obtained fir on tho following illustrations, Plate I and II.

The drainage of the district is north end northwest fraa the abruptly rising nountains, into Pantano wash. Biese strem s are interm ittent, flowing only after violent stems. Host of them evaporate or sink beneath the surface before they reach the intermon tane basins. The subsequent streams follow, chiefly* the less resistant strata and often enter the rain washes at right angles. The jointing, as well as tho bedding, in certain places, has considerable effect upon the streams, causing many of Him to exhibit a zig-zag course, following tho jointing for a way, and then abruptly changing and follow­ ing along the bedding, almost at right angles. Tho mountains are in a youthful to mature stage of dessieation, exhibiting even crested or gently sloping ridges, ' but th® descents into the valleys below are usually quits steep. The formations are not characterized as cliff foim- ing and usually weather to smooth slopes, but as is common in arid regions, the linestones tend to form the high areas and the granitic bodies the low areas. In the Cuprite area there are no higher terraces above the present erosion sur­ face but to the south of the area na pped, near the town of PLATS 1 .

Fig* X« Looking southeast from Bushman H ill. The main wash in the area is shown by the dark band. Empire Mts* in back­ ground.

F ig . 2. Looking south from Bushmen H ill. Mt^agan in background.

F ig . 3 . Looking southwest from Bushman H ill. PLA2E I I .

F ig . 4 . Hopthenstern pert of area looking southwest. Buehnan H ill in right background.

F ig . 5 . Looking south from Bushman H ill. Notice dike at base of h i l l .

Fig# 6 . Bus ter vi lie Mine, showing type of topography in lower portions of area. Patagonia there are several old gravel terraces in the Quaternary sediments*

HISTORY OP MI11BG IN TiU OMdiiAL REGION

IhOst o f the material gathered for this section was obtained from Mr. Schrader’s report^ and hence it applies to the thole region, o f which the detailed report is but a small p a r t .

Papogo Indiana carried on mining in the Santa Rita Mountains before the Spanish conquest of Mexico in the six­ teenth century and here are found the oldest mines on the Pacific slope north of Mexico. The Spanish Jesuit missionaries, who were the first white men to v isit the Arizona region, cane about 1687 end with­ in a period of about twenty years established the missions of San Xavier del Bac, Tumaoacori, Santiago, ani San Cayetano. Apache Indians periodically massacred-or drove out the settlers and destroyed the missions and settlements, yet they were con­ tinually rebuilt. Those Jesuit fathers carried on mining in the Santa Rita Mountains with the aid of friendly Indians. Their success is shown by die fact that at the Son Xavier Mission

4 Schrader, F. G. and H ill, J. K.' - Ore Deposits of the Stinta Rita and Patagonia Mountains. U. 5. Geological Survey Bulletin 582, 1915. 8 olios south of Tucson, 540,000 in solid silver was used to n6om the altar. The largo silver deposits of Sonora on the south also stimulated interest in this region. One m ss of native silver was found about 20 miles southwest of Nogales that weighed 2,700 lbs.* The ora in the Santa Rita district was very rich, one mine (Santa Rita del Gobre, operating about 1835) producing, ore that was 75/3 copper. The silver ore was also very rich* the Helntzelman mine operating in 1857 produced silver sulfide ore that averaged 51,400 per ton. This ore was so rich that the raw ore was sent to Mexico City on mule back, a distance of over 1,000 miles of hazardous country. A mine in the Patagonia re­ gion, knom as the Howry mine, in 1863 was producing 54,50© worth of silver a month. This was cast into bars and sent to Europe, yielding a profit of 5100 a ten of raw ore. When th e C iv il War broke out, the troops stationed in the district to protect the settlors from Indians were with­ drawn, and the Apache Indians massacred or drove out the miners and settlers. This stopped practically all mining till about 1875. On completion of the Southern Pacific Railroad in 1879 mining was again stimulated. The Total Wreck Hino in the Empire Mountains yielded silver chloride with associated lead earbonato and was one of the most important producers of silver Is the district. Ore from this nine averaged about #0 a ton

^ Schrader end Hill - Op. Git. p. 21 end in five months produced 450,000, Hines producing silver, gold, lead, and copper were being operated in various parts of the region about the beginning of the twentieth century. Copper ore was being shipped from the Helvetia dis­ trict to the Old Dominion smelter at Globe in 1009. The total output from the Helvetia district that year was about 5157,000. In recent years, horavor, there has not been much ac­ tivity in the above mentioned districts. This is due in part to the low price of copper and also to the fact that most of the high grade deposits havo been worked out. In the Helvetia dis­ tric t, however, there has been some production of molybdenum. It has boon estimated that about 100 tons of nolybdeni to con­ centrate have been produced In the Helvetia district since 1915. The total value of ore produced in the above districts, up to 1915, has been estimated at 52,500,000.

STBAfIGKABiY

Principal Rock Groups

The rocks within the area range in age fren Ponnsyl- vcnlrm to Cretaceous inclusive, and consist of both sedimentary and Igneous rocks. Sedimentary rocks of Pennsylvanian and Cretaceous ago are separated by a disoonfonalty. Igneous rocks consist of lavas, stocks, and dikes, all later than the known Cretaceous -1 0 - STRATIGRAPHIC SEdOEirCB o f th e CUPRITE HILL DISTRICT ,ARIZ. Andesite porphry flows and breccias. ' Thickness unknown. Boulder conglomerate.Rounded boulders of glassy quartzite,Cret.foBslllferouB Is., Naco Is..cemented by red,yellow-brown,or greenish cement.Bed of apparently thin red quartzite at base. 200-600 f e e t .

Limestone.Thin bedded la.w ith Interbedded gray argillaceous shale .90 f e e t . Quartzite.Coarse gray quartzite.230 feet. A rgillite.Black argillite.22 feet. Limestone.Gray fosslllferous Is.9 feet. Quartzite.Fine grained quartzite.From bottom to top this quartzite grades from buff to gray to almost white In color.615ft.

Lime stone.Impure dark llmfy rock.Weathers dove g r a y .135 f e e t .

Quartzite.Gray to light brown or buff argillaceous quartzite of extremely fine grain.Thick bedded but may contain thin laminae.Weathers dark reddish brown.830 feet

A rgillite.Fine grained gray brown to green- ish brown arg.Grain Invisible to naked eye. Color variable.260 feet. Limestone and Interbedded fine grained ••v. v^/»^ white quartzite.Ls. thin bedded and upon exposureweathers differentially to form aHlayer-cakeHe*tructure In which the harder ‘Y layers are silica and the softer are Is. 400 f e e t . Interbedded black shale and gray quartzite. 200 feet.These and iheunderlying formation were mapped as one unit. Red q u a r t z i t e .M assive b e d d e d .170 f e e t . Breccia.Coarse unstratlfled angular breccia of Naco Is.and glassy quartzite.Limestone fragments at the bottom and quartzite eg, q> ,0 9, fragments at the top. Saco Is.Light gray fosslllferous Is.150 feet 11 rocks and they my be of essentially the sane age as the Lara- mid o R ev o lu tio n . I t vaa possible to establish three stratigraphic horizons, namely, the Haco limestone (Pennsylvanian), tho breccia overlying the Haco, of post-Pennsylvanian ago, and an upper Cretaceous limestone. These three units are described below.

Sedimentary Rooks P aleo zo ic

Penhsiyivanlan - Haco limestone. The Haco limestone is found in only a few scattered patches in the area mapped, although just off the northern boundary thoro is a well exposed body of it. These small patches occur as inliers or "windows” in tho over­ lying breccia. One patch is in a saddle between two hills about a quarter of a mile north of the Cuprite Mine shaft. It was formerly quarried as marble. Other patches are on the north side of Bushman H ill. Another small patch is on the crest o f a h ill about a quarter of a mile northeast of Buehman H ill. Due to its light color as contrasted with tbs dark overlying breccia its outcrop is easily recognized, oven from a distance. It is a light gray limestone, weathering almost white. In places it is coarsely crystalline. Chert is present as nodules and layers in some beds, and locally tho limestone has been extensively silicifled. Since its base is nowhere ex- 12- pooed, its thickness is unknown. The exposed thickness is about 150 f e e t . Its age was determined as Penn sylvan! on by the presence of tho corals Syrin&ogoro, Axonhyllusi radio, Lophophylltua pro- fundm, and Cmpophjtllim tqrquiua (?).

Poot Pennsylvanian Interval Breccia. 22ie breccia forms the upper slopes and top of Bushmen H ill, cap® a small h ill directly to the northeast of Bushman H ill, and still another h ill about half a mile east of Bushman H ill. It is also beautifully exposed in the wadi be- low the Cuprite Mine diaft. The rock is a dark gray, cocrse, nnguler»unstratified breccia consisting of fragments of the underlying limestone and of glassy epartsite unlike the overlying silicified sandstone. The fragments reach a dinmotor of three feet and are characteris­ tically angular. At the base of the breccia tho fragments are mostly limestone and are cemented by a lime cement. Higher in the breccia glassy quartzite fragments, unlike anything seen elsewhere in the area, predominate, and the cement is a silicified sandstone; this grades upward into the silicified sandstone for­ mation. The whole formation has been extensively metamorphosed with the local development of wollastonite and garnet. On wGathering the rock beecmes darker in color end in several places is nearly black. However, due to i ts variable composition the weathered surface is pitted end knobby. Weather- 13-

Ing also tends to bring out the differenee In color between the cement and the breccia fragments* This formation la no doubt of variable thickness but where exposed is about 370 feet thick* After withdrawal of the Pennsylvanian sea it would be possible for the upper part of the Haco limestone to be brecclat- ed and other angular material added* Such conditions can be seen today idxere a formation Is overlain by rubble of its own and dissim ilar fragments* Cretaceous sediments were deposited on this rubble* Such an origin Is favored by the writers*

Limestone breccia exposed on the east end of Buehaan Hill* -1 4 -

Red uuartzito. This fornntion, which is directly above tho breccia, io wideepread• 2» the cmitral part of tlie i region it occupies a considerable area to the east and to the west of the Cuprite mine, where it emposes a largo part of Buehoan H ill. It is found on tho north, northeast, and also to the south of Buehman H ill for three-quarters of a mile. There is about ISO feet of the formation. i It is slightly reddish on tho fresh surface and is massive bedded although containing thin beds locally. The texture is fine-grained to glassy, apparently depending on tho amount of silicifia& tion that the formation has undergone since deposition. It breaks with a sharp angular fracture. | The rock is a rather pure quartz sandstone that has been strongly cemented. Despite its red color there appears to be but little iron or other impurity, such as feldspar, present. Weathering and disintegration of tho formation tends to color tho soil a rather distinctive red although there is i not much change in color between the weathered and umreathered ro c k . I It everywhere conformably overlies the breccia.

i -15

Contaot between dike (li^ t colored rock along crest of hill) and red quartzite (to right of dike In the foreground j•

Black Shales and Gray uartzltes. This formation forms a belt that extends from the central part of the area about half way to the eastern edge of the map, a distance of about one-half mile. It la about 800 feet thick• The shales are dark gray to black and are inter- bedded with lighter gray quartzites. The black color of the shale is thought to be due to organic material since the shale bee am s lighter gray upon weathering. Both shale and quartzite are thin bedded but the quartzite is not as thin bedded as the diale. The quartzite is very fine grained. It conformably overlies the red quartzite. tladlfferontiated Upper Grutaoeoua Series. 'Oils series occupies almost the entire eastern md southern parts of the area. Its thickness is approximately 2,600 foet. The series contains almost all kinds of sedimentary rooks including limestones, shales, quartzites, argillites, and arkose. In general the limestones are in the lower port al­ though one fossiliferous limestone containing Upper Cretaceous fossils is in the higher part of the series. The thin bedded limestone® in the lower part are characterized by large amounts of silica occurring as thin layers• The rock weathers differ­ entially, the 11 m3 stone layers dissolve more easily than the siliceous layers. This produces a characteristic "layer-cakeH structure which is easily recognized. Higher in the series the prevailing rocks are quartz­ ites and argillites with abundant interbeddod arkose. The most fossiliferous horizon in this series is a sllioified fossiliferous light gray limestone that weathers dove gray. Its thickness is 9 feet. The fossils are not well enough preserved to make their identification positive, but Dr. Stoyanow has placed their age as Upper Cretaceous. These are not open sea fossils. A more detailed subdivision of the scries is fbund in the accompanying stratigraphic column. This series lies conformably on the underlying sediments. 17

Showing some of the limey Aale type of sediments found In the undifferentiated Upper Cretaceous series.

Boulder Conglomerate. This formation outcrops as a north-west striking belt in the southern part of the area# Its thickness varies from 200 to 600 feet* The formation varies from a brilliant red to a yellow- brown or green* It is a very coarse conglomerate of rounded boulders* In places the fragments may reach a diameter of four feet, while in other places they may be as smell as one inch or less in diameter* The rounded fragments consist of Pennsylvanlen limestone. Upper Cretaceous fossiliferous limestone, and glassy quartzite dissimilar to anything seen elsewhere In the area* These are cemented together by a fine yellow-brown to greenish argillaceous material In most parts but In two localities the cement is red In color* The relation of the conglomerate to the underlying bade has not been determined* It Is overlain by the andesites

Boulder Conglomerate near southern edge of area. 19 -

Igneous Rooks

P lu to n ic

Granodiorlto. Granodiorite is exposed from tho cen­ tral part of tiie area to the north comer and occupies about two sq u are m ile s o f the a re a mapped • It occurs as a largo body intrusive in the sediments* Tho granodiorite is easily rccogiized in the fie hi by its gray color, granitic texture, and by weathering to round­ ed boulders which eventually disintegrate to a characteristic crumbly, porous gray soil* In general this rock ibras the low parts of the area duo to rapid disintegration resulting from differential expansion of the constituent minerals under rapid heating and cooling* The rook is prevailingly light colored and has a granitic appearance. Feldspars of two varieties predominate. One is light buff, docs not exhibit twinning on cleavage sur­ faces and is probably orthoolase or microcline. Tho other is white and exhibits well defined Albito twinning. The feld­ spars range from 1 to 4 millimeters in maximum dimension. Some grains show subhedral outlines. Tho orthoolase is perthitic. Feldspars have well defined euhedral boundaries and show rec­ tangular cross-sections. Some have a length of S millimeters. Ollgoelaee, Abg^myg as determined by the oil immersion method constitutes two-thirds of the feldspar present. Biotlte is the predominant dark constituent. The cleavage plates which ore black and highly refracting range - 80- fraa 1 to 2 milllmetors in diamotor. Biotite and hornblende usually occur togeth er associated uith magnetite. In some specimens they form dihedral crystals, while in other specimens they ere interstial to feldspar end later than the plagioclnse. Elongated patches of chlorite ho re end there in the specimen may be alteration re manta of hornblende, quartz occurs as small rounded grains. Accessory minerals are spheno, apatite, zircon, hematite , and magnetite. The plagioolase nay be slightly to extensively soricitized. The plagloclase alters before ortho- ©lase. Secondary caloito is abundant as an alteration product of the feldspars. Alasldtte. A small elliptical exposure of nlasklto appears about half a mile to the north of Buehman H ill. It is a nearly white rock with little difference in color between the weathered and unweathered rock and is easily recognized by its total lack of dark constituents. quartz and white orthoolase as the predominant minerals arc present in about equal proportions. Grains of both minerals are rather uniform i» size, averaging slightly less than 1 millimeter in diameter with occasional grains up to 2 milllme tors. A few small flakes of muscovite are found. In thin section neither the quartz nor the orthoolase show euhedral boundaries. Plagioolase is almost totally ab­ sent and no accessory minerals were found, quartz appears to have been replaced by feldspar since a graphic intergrowth of the two minerals is exhibited in which all the quartz grains -4&-‘ aro oxtinguiohoa in tho snra position* Orthcclano hns been knolinised to soao extent* The ala eld. to cute both tho granodiorite rna the loeor part of tlio Crotaceouo eediioritary series*

E xtrueivo Hoc leu

' /Jidoolto /^ndooito occupies the western corner of the napped area nnu extends for an unhnora distance off tlio area. It occurs so a series of mrfaco flows end breccias, in port sedimentary; which lie above tho boulder cm ^onsrnto. It is a dark gray rock containing phenoorysts of lighter color. Phcnocrysts aro of plagioolaso and hornblende with n naxiviun dlnneter o f 6 n illin c to r s . Plaglooiasc pheno- Me gas c o p ic a lly ©ryots are distinctly Wnned. (Albito twinning). She con­ stituent ninorals of the dark gray gramonass aro undetomimtble In thin motion tho greundnasn is predominantly fcldspathic. Tiny grains of hornblende aro interstitial to tho feldspar needles* Groundnaas exhibits spherulitio structure. The phenoorys ts mr# hornblende end labrador it o of composition Ah^gA%Q, as determined by tho maximum extinction nnglo in tho zone parpondioulnr to (010). Feldspar crystals have sharp euhcdrnl boundaries and rectangular cross-scoticn. Feldspars arc remarkably fresh but nuch of the horn­ blende is altered to serpentine and epidote. Some calotte is present. —££•

Due to the abundance of phenooryeta and the oopiple te lack of flow banding in any of the thin sections examined it was decided to call this an andesite.

Andesite, exhibiting a breeclated structure Which is locally present in th e formation.

Dike Rooks

Rhyolite Porphyry. Rhyolite porphyry dikes are widespread through the area, but there is a marked concen­ tration of them adjacent to the outcrop of the granodiorlte. Owing to th e ir le n g th and t h e i r p re v a ilin g l i g h t color the dikes are a prominent feature of the landscape, where they out the granodiorlte they form ridges that may be seen for several miles. In the sedlnaentary series the dikes usually occupy saddles between h ills. Two distinct types are recognized and are here d e s c rib e d . Typo A. Typo A is brownish gray in color containing calcite phenccrysts that are pseudmorphs after feldspar, a few needles of hornblende and a few very snail flakes of fresh biotite are present. Quartz was not observed in the hand specim en. F eld sp ar phenoorysta have a maximum d ia m e te r o f 5 miHlnetcrc. The hornblende is present in thin needles of the same length (5 millimeters} and 1 millimeter thick. The groundmass is ephnnitic. The phenoeryeta form 15 per cent, and the groundmass 85 per cent of the reek. In thin section the groundmass is prevailingly fold spathic but the individual minerals cannot be determined. There may be some quartz in the groundmass. The untwinned feldspar phenocrys ts are probably sanidina. There is calcite both in the groundmass and in the phenocryste. Serioite has developed in the feldspar pheno- orysts. Hornblende has gone completely to chlorite, and biotite has been replaced by serioite. Typo B. In the hand specimen the rock is light gray to white with phenocrys ts of rounded quarts grains from 1 to 4 millimeters in diameter, hornblende up to 2 m illi­ meters in length, ard highly altered feldspars, some with reetangulea* outlines v&th a maximum length of 5 m illim eters. Biese are set in a glassy groundmass. 24-

In thin section the quartz phenecrysts are rounded and have been partly resorbed by the magma• Die groundmass is fine grained but the individual minerals are easily visible* It Is mostly feldspathie with small rounded feldspar grains and probably some quartz. Die feldspars are completely serleltlzed. Biotlte grains are altered to chlorite, and epldote is present as an alteration product of biotlte*

Rhyolite porphyry dike* A« Andesite BxBoulder conglomerate. STKUCTUIUL GEOLOGY General Features

The Culprit© mining d istrict possesses many of the structural features that are characteristic of the Rocky foun­ tain region* fortod regional folding and great low-angle over- thrust faults have been described in the Santa Rita and Patagonia fountains to the south, the Empire fountains to the east, and the Tuosm. fountains to the west of the district, ihe block faulting of the Basin Range type is superimposed on these earlier structures, its effect being seen in the many nearly parallel northwest-southeast trending raises* The faulting and folding in the Cuprite district are related in origin to those regional structures observed over wide areas. However, from the study of the Cuprite district, which is such a small part of the entire mountain range, the writers do not feel warranted in making generalizations. The following discussion and interpretation will bo confined, as much as possible, to such structural features ns have been recognized in the area under Investigation. The sequence of structural disturbances as recorded in the Cuprite district is: 1* Regional folding. B. Pre-iBtru»lo*i normal faulting. S. Doming of the strata by the intrusion of the Cuprite stock. 4. Post intrusion-pre-dike fracturing and Jointing. 5. Post dike faulting. Early Foldings

Folding has affected all the pre-Tertiary strata, although the character of the formations has somowhat governed the complexity* The more competent beds have been less fault­ ed end deformed than the weaker incompetent beds; Folding is therefore more intense in the Cretaceous beds than in the Paleozoic limestone. Also, certain limey and ahnly horizons in the Cretaceous have been much more crumpled and folded than the more competent quartzites, arkosos, grits, and andesite porphyries; This early folding has boon somewhat obscured in the Cuprite district by tha pro-intrusion faulting that has off­ s e t the beds horizontally and vertically, by the intense jo in tin g of the beds, and by tho intrusion of the Tertiary granodlorito sto c k . Buehman Kill is a large anticlinal fold that has been faulted in a northwesterly direction about 1600 feet from its original position by the Ho scut fault. The axis o f the fold on both sides of the fault strikes about S45°u. Tho Haco limestone, the overlying breccia, quartzite* Cre­ taceous limestones, and tho Cretaceous undifferentiated series of shales and quartzites are involved in the folding. The top of the fold has been denuded by erosion so that ”windows’1 o f the Hnco limestone are exposed. Oils folding has been more fully described in the Santa Ritn and Patagonia fountains.*

Over thrust faulting is not evident in the Cuprite district. It has boon described further south in the Santa Rita fountains 8 as well as in other ranges3 *1 paralleling the Santa Rita and Patagonia Mountains. The following quotation was taken from Wilson’s description of thrust faulting in the Empire Mountains4’ which lie but a short distance to tho cast of the Cuprite district.

The strike is northwest and dips to the southeast indicating direction of force from the southwest or northeast.... The thrusting is characterised by two fault zones that are warped and locally intensively folded. Tho result is Upper Paleozoic strata overriding Upper Cretaceous bods. At least sane over- thrusting followed the granitic intrusion and has cut it. Recent hi 01 angle faulting followed thrusting. In age it is not earlier than the very close of the Cretaceous o r early Tertiary, or may extend well into the Tertiary.

1. Schrader, F.C., Mineral Deposits of the Santa Rita and Patagonia Mountains. U. S. Geological Survey Bull. 562. Thomas# W.L., Geology and Ore Deposits of tho Rosemont D istrict. Master’s thesis. Univ. of Arizona. 1931. B. Schrader. Op. oit. 3. Brown, H. Unpublished manuscript on the Tucson Mount®ins. 4 . W ilson, R.A. Thrust faulting in the Empire Mountains, A rizona. Journal of Geology, Vol. 42, p. 427. 1934. Following coon after over thrust faulting or in part overlapping It, are normal faults striking in a northwest direction that are closely connected with the folding. These faults have dislocated or offset the earlier and older struc­ ture a, such as tho Bushman H ill fold, but are themselves affected by still later faults, probably related to the Basin Bange faulting. The more important of these earlier faults will bo described. Hoscut Fault. The Noscut fault is located in the northeastern part of the district. It strikes H38°$? and is apparently a steep normal fault with downthrow to the south­ west. All the folds are cut off by it. Erosion along tho fault has produced saddles or low divides, but much of its trace lies in the floor of tho valleys. The horizontal movement along the fault is approxi­ mately 1600 feet. This is measured by the displacement of tho Buehraan H ill fold in a northwest direction frcct the corresponding part of the fold on tho northeast side of the fault. It lias brought different rocks together and caused the development of drag folds. Gn the northeast side of the fault the drag is to the northwest and down. This suggests relative movement of the southwest block to the northwest. Tho vertical component can hardly be estimated because of the lack of suitable horizon markers in tho Cre­ taceous beds. This fault separates the formations in the northeast­ ern part of the district frm that in the middle of tho district Long Hilo Fault. The Long Kile fault is located in the southwestern part of the district. It strikes 1732°U md Is nearly vertical. This fault is vary sim ilar to the XTosout fault and parallels it, but is o f greater magnitude. There is an abrupt change in the strike end dip of the strata on opposite sides of the fault. Drag folds are well developed, indicating that movement on the southwest side of the fault has been to the northwest. Tho vortical or horizontal component is not known, but it must have been large to account for the great change in attitude of strata. The southwest side moved northwest, with reference to the northeast side, and the down-throw side is to the southwest, bringing Upper Cretaceous rocks in contact with what is believed to be a much lower horizon in the same series of beds. The reason for believing this is that in the normal stratigraphic section for the district the thin bedded limestones, that are out off by the Long Mile fault, are about la the middle of the section and are overlain by a tremendous thickness of diales, argillites, quartzites, and a rk o se .

This fault separates the southwestern pert of the district from the middle block. The effect of those normal faults is to offset a series of blocks in a northwest direction in going from north to south with the downthrow on the southw est s id e s o f thQ faults, as nay bo seen by referring to the geologic rap. (F l.V iU

The intrusion of the Cuprite stock has resulted in the gentle doming of the strata over and around it. The geologic nap (Pi«Vl) shovrs a. general dip away frcra tho center of tho intrusion.

Post Granodiorite Intrusion-Pre-Dike Fracturing md Joint­

ing in the In true 1 vo and Surrounding Hocks.

Tills division is made to separate pro-stock and post-stock faults. Tho great number of dikes that cut the stock and surrounding rock indicate that stresses were acting on the region, following tho intrusion of the stock, but before the dikes wore formed. This may in pert be attributed to fractur­ ing of tho shell of the partly solidified mass, but one would hardly expect the fractures to be oriented in definite trends and to persist for miles across intrusive and sediments with­ out interruption, unless seme regional stress had acted pro­ ducing shear and tensional strain. In general there is a northwest, northeast, and north- south set of dikes, all apparently of the same age. The northwest trending dikes are the largest, most persistent, and most abundant. There are also many strongly slieken- sided fracturea with apparently little displacement not filled with dikes or with mineralized matter, that conform to these trends. The northwest fissures and dikes closely parallel the pre-Intrusion faulting, They nay represent a continua­ tion or a recurrence of the stresses producing the early fault­ ing. Joints in the rooks of the district arc closely related in attitude to the larger faults and fractures in having approximately the same directions of break.

This group is described separately because trans­ verse faulting in a northeast direction foliowad dike in­ trusion and offset tha dikes in the southwest port of the district foming a series of faulted blocks. It has also dis- pl&oed the early pre-intrusion Long Hilo fault. The hori­ zontal displacement is not over a few hundred feet on each individual fault, but the group has displaced the fault plena and dikes about 1000 f e e t . This faulting that offset the Long Kile fault and dikes was probably due to renewed movement along fractures that wore developed before the dikes wore intruded. However, they might be related to the later Basin Range deformation.

Basin Range Faulting.

Tho Cuprite district is located on one of the large block ranges attributed to normal faulting, probably in Into Tertiary tine. There is no faulting of this type noted In the district.

Strata involved in the early folding range in age from Paleozoic through the Cretaceous. Folding has been described in the Santa Rita Mountains by Schrader1 and in the vicinity of Kt. Fagan by Thomas.12 In the Cuprite.district the early folding is pre-intrusion and is believed to belong to the mountain building period at the end of the Cretaceous end oarly Tertiary, time, generally knom as the La rani de Re­ v o lu tio n . The arching or gentle dening of the strata around the Cuprite stock aooaapcniod the intrusion which followed soon after the regional folding.

The early faults offset the folds. The e a r ly faulting is pre-intrusion, b ecau se i t has not o f f s e t th e grnnodiorite» « The pre-dike fractures cut tho intrusive and other rocks

1. Schrader, F. C. Op.olt. 2. Thomas, V/. L. Op. elS. -1* 35 — and provide fractures in which the dikes f,.r:aed# The north­ west set of pre-dike fractures are parallel , 1th the early normal faults and were probably periodically a continuation of the same forces« This deformation is part of the laramide Rev­ o lu tio n . Post dike faults that offset the dikes and older structures are probably renewed movement on earlier faults and would then be a part of the L&ramide disturbance. There, is a possibility however that it represents the late Tertiary Basin Range faulting.

GEOLuGlU HISTvRY During Pennsylvanian time, the earliest rooks repres­ ented in the district were deposited as thick limestone beds, Immediately above the Haeo limestone and without discordance in attitude is a well cemented breccia composed of angular and subangular fragments of Paleozoic limestone which grades up­ ward into a narrow zone containing gragments of limestone and quartzite. The age of the, breccia is not known, but it was deposited in the interval between Pennsylvanian time and Upper Cretaceous time* If other beds were deposited during this interval, the rocks have not been exposed or have teen removed by erosion. This does not seem to be a particular feature, of the Cuprite district, but has been observed in several places ! in southern Arizona. The breccia is in turn overlain by quartzites, argill­ ites, shales, thin bedded impure foliiiiferous lime- stem , orkooic sandstones and quartzites, grits, and conglom­ erates of Upper Cretaceous age and capped by andesitic breccias tuffs, md intercalated andesitic flows. The sequence of bods indicates deposition in fluctuating shallow bodies of water. The outpouring of the volcanic rate rial is the forerunner of the Laramide Revolution vMeh took place in late Cretaceous and early Tertiary time. The Laramide Revolution has resulted in the fold­ ing and faulting of all the strata in the Cuprite district. This was closely followed by the intrusion of the Cuprite gronodiorito stock, the doming of the strata, and the de­ velopment of the contact metasomatio deposits in the Ifaco limestone. Renewed or continued stresses resulted in the fracturing of the stock and surrounding rocks. Into those fractures and older faults dikes were intruded. Mineraliza­ tion of the rasothomnl lead-zinc type followed as a late stage of igneous activity. In soro places the dikes seem to have exdr ted an influence on those deposits by obstructing and localizing the mineralizing solutions along certain frac­ t u r e s . Bate faulting has displaced many of these dikes, probably along older structural linos, but it nay be relat­ ed to the late Tertiary Basin Range faulting. Post-mineral brecciation is found in the Bustervillo mlno. Oxidation and enrichment followed, especially in the contact copper deposits, and is still in progress. MKERAL imSOURCBS

Tho mineral deposits of the Cuprite mining district are predominantly ores of lead and zinc, v.lth aono copper and snail amounts of gold, silver., and molybdenite • The production has boon small and there is little Indication that there vrill bo renewed prospecting for copper in the d istrict. However, the occurrence of molybdenite with the copper my bo an incentive for further exploration of these deposits. The lead-zinc deposits, of which the BustervilJe and Hosout mines are the most important, have been worked more recently than the copper nines. The Hosout nine was operated about twenty years ago, and the Euoterville Mine is being developed at the present time.

OHS DEPOSITS

In tiie Cuprite district tho copper nines are the Cuprite Mine, the How York Mine, the Pauline Mine, the Copper Aleak, and .adjacent prospects .1 Most of these properties were located before 1900 and were worked for a few years, large­ ly for their enriched copper ores. Tiie Hosout Mine was worked about 20 years ago. In­ formation concerning it, gathered from the cattlemen of the

1. Schrader, F. C. Op. oit. area, indicates that it produced lead raid silver. Specimens found on the dump seem to confirm this. She Bustervillo Mine is the only property .operat­ ing at present. This property vms knorai and located in the early part o f the twentieth century, but was not worked un­ til the past few years. A vertical shaft has been sunk 200 feet end several hundred feet of drifts and crosscut have been made. An effort is being made to obtain water for a proposed m ill. Thoro is on the surface at present, about 50 tons of lead-zinc ore, with reported low values in gold and silver. Tile re is no record available of the total production for the district.

Geographic and Gaolordc D istribution.

The Cuprite Mine is located at the base of the east elope and the Hew York Mine is located cm the west slope of Buehman H ill. The Pauline Kino, Copper Aleck, and adjacent properties are all located north of Buehman H ill. The de­ posits all occur at the contact of Pennsylvanian limestone or the overlying limestone conglomerate with tho Cuprite granodicrite. About ono thousand foot southeast of the Cuprite shaft, across the wash, on tho west slope of a long north- west-southeast ridge is tho Noscut LU.no. Tho Bus torvilie Mine is located a mile southeast of tho Cuprite shaft near the eastern boundary of the area. Both of these deposit# -3 7 - are in the Cretaceous llnestone beds.

General Character of the Deposits.

The deposits are all essentially replacements in limestone. Ore-shoots in the Cretaceous limestones have forma by replacement along and adjacent to fractures and bedding planes in the rocks. Those occurring at the contact of the gronodiorlte intrusive and limestone are replacement® of the pyrometasomatio type. The most important ratals of the district ore copper, lead, and. zinc. Other ratals present in minor amounts arc silver, gold, and molybdenum. Classifying the deposits as to metal content there are those of lead-zinc, and those of iron-eopp er-molybdenum. The lead-zinc deposits, which are replacements in the Cretaceous limestone, are high me so thermal, that is, form­ ed at moderately high temperature and pressure by magma tie emanations• The copper deposits in the Kaco lira stone and over lying lira atone conglomerate are classed as pyrone tasm atic deposits or replacements formed at high terpernturo at or near tho contact of llmostono bods uith igneous intrusions. -IBS'*

Pyromefrasonatlo Copper Deposits.

Goologio Features*

The deposi ts m Bushman K ill and the outlying h ills to the north are ocnflnod to the Maoo limestone of Pennsylvanian as© and an overlying limestone conglomerate, Mineralization occurs at or near the contact of those beds and the gronodior- ito intrusion. The limestone is metamorphosed and the typical contact matamorphic minerals uollastonito, andradite garnet, epidoto, msgnetite, and spoculori to are abundant. The lime- etone anl overlying breccia have had much silica added, and near its contact with the intrusive has become green, dark brown, and often black in color. Amoy from the contact the lima stone has in places been converted to noil crystal 11 zed white marble. Such a marble h ill is located about 400 yards north of the Cuprite shaft. Much hornblende and to u rm a lin e have form ed n ear the contact of the intrusive with quartzites. In short, the results are a recombination of the original constituents of the rocks with material introduced as emanations from the magma.

M ineralogy

The mineralogy is simple, the primary sulfides con­ sisting of pyrite, cheleopyrlte , and molybdenite. The gsnguo minerals are magnetite, specular!to, wollastonito, andradite garnet, epidota, quartz, and calcite. -3 9 -

Secondnry minerals aro azurlto, malachite, chryso- oolla, and the enriched copper sulfides chancedto and c o v e l l l t e .

Replacement Deposits Geologic Features

The Buoterrillo and Kosout mines aro in tho Cre­ taceous limestones and aro replacements directed by faults. Im many places tho limestones aro so intensely jointed that all bedding character is lost. Tlieso deposits differ from the contact deposits in the absence of high tenperaturo minerals such as magnetite, speeularite, uollastenito, and garnet, and in the presence of those minerals characteristic of tho meaothermal le a d -zln e deposits such as serloito, Ohiorlto, pyrite, small amounts of pyrrhotite, sphalerite, galena, aid a little chalcopyrlto Mid t e t r a h o d t i t e .

Detailed Description of the Busterville Mine. Vein Description

This deposit represents a replacement of limestone directed along fissures or faults of small magnitude. The contact between the vein and the wall rock is not sharp, but very irregular in shape and size and pinches and swells along the strike of the fissure. The ore body probably also -4 0 - pinohes end sw e lls doim the dip ae well as along the strike. The vein strikes IT 18° 2 and dips 5CP to the east. On the 140-foot level tho ore zcno is approximately 15 foot wide • The sane vein on the H)0-foot level is about 0 foot wide This is as deep as development has gone. A rhyolite porphyry dike is associated with, tho de­ posit. It strikes IT 75° XI and dips about 45° to tho north. The m in ore zone is below the dike. There is abundant evidence of recurrent movement on the fissure during mineral deposition and after it had ceased. Movemmt occurred after the deposition of tho quartz and pyrite before the deposition of the chalcopyrite , and again before the oalcite mineralization. Post mineral movement was suffi­ cient in places to reduce the vein filling to a breccia. The ore minerals are scattered irregularly through­ out the vein, although they tend to favor parts that were bro­ ken during the early stages of mineralization. They aro also found along the bedding planes of the lirastone. M ineralization in the BusterviULe Mine has not been along the major faults in the district, but along fractures or fissures of relatively a lig h t displacement. There is little doubt but that they aro related to the major stru c­ tu ra l features of the region. The vein has a northeast trend which closely parallels some of the dikes and post-dike f a u l t s . -4 1 -

Wall Rook /J.toratlon

Tlio rhyolite porphyry diko has been hydro thermally altered so that very little of the original minerals is l e f t exeept quarts which remains clear, and is present as the phenoeryste of the reek. The plngioolase is completely seri- oitized but the outlines of tho crystals can bo distinguished• The alteration seems to have gone beyond the stage of tho leaching of sodium and calcium, and part of the potash has been removed so that kaolin is present as a residual mi nerd of aluminum and silica. From the appearance of tho altered rock apparently much silica has been added to tho original con­ tent, Fractures in the rock are filled with pyrite. Alter­ ation minerals are the secondary titaniforous mineral leucoxene and a little chlorite* Tho limestone has been altered very little except in the mineralized zone where chlorite is very abundant, and much silica and crystalline calcite have been added. Pyrite has penetrated farther into the limestone walls than the other s u lf id e s . M ineralogy

General Summary

The ore minerals are galena, sphalerite, tetrahedrlte (silver bearing?), bournonite, dad chalcopyrite• The minor minerals are quarts, pyrite, pyrrhotlte, calcito, and chlorite. Most of the genguo is unreplaced llncstm e. There are no super- gene copper sulfides. Galena is the most abundant mineral, but considerable sphalerite is present and the two make up the bulk of the valuable constituents. The ore assays a few ounces of silver per ton, and a fraction of an ounce in gold.

■Detailed scription of Minerals The descriptions of the minerals are given in order of deposition from vein solutions and mot in order of their abun­ dance o r other distinctive features. The listing is therefore paragon#tie. Quartz (SiOg). quartz is apparently tho oldest mineral and is hot abundant in the ore. It occurs usually as well defined crystals that havo been partially replaced end surrounded by tho later sulfides and calcito. Pyrite. (FoSg) Pyrite seems to be tho oldest sul­ fide but its relation to pyrrhotito is not known. It occurs in tho much altered limestone nnd dike rock as well as in the mineralized zone, and is characterized in most places by its distinct cubical c r y s ta l outline. In the intensely mineralized zone it is often mono massive and much breccia ted indicating movement after deposi tion. The younger minerals have been de­ posited around pyrito and in part have replaced it. PI, III A shows pyrite that has been partly replaced by sphalerite and later minerals, PyrrhotAte. (Fo3^+). Pyrrhotite occurs in small amounts in the deposit and is difficult to find in quantities large enough to identify, . No definite ago relationship was established, PI, III B shows microscopic romants of pyrrhotito in sphalerite which suggests its being older than sphalerite. Prom this and from its occurrence in similar deposits whore an ago relationship has been established, it was concluded to bo one of the earliest minerals and older than sphalerite. Sphalerite. (2nS>, Sphalerite was deposited after the iron sulfides and replaces pyrito and apparently pyrrho­ tito as in PI. IIIA and. IIIB. It is definitely older than the following minerals, Tetrahedrlte, (5 CugS.2 (Cu,Fe,2n,)5.2 SbgSg). Tetrahedrite is younger than sphalerite and older than chaloo- pyrito. Tho relation Is seen in PI. IVA which shows tetra­ hedrlte voining sphalerite and replacing it. Tetrahedrlte also surrounds angular pieces of pyrite end quartz crystals, Bournonito, (CugS.BPbS.SbgSg). Bournonlte is a younger mineral than tetrahedrlte. As shorn in PI. IV B it traverses tetrahedrlte as a small voinlot and fingers out into it definitely replacing it. Chaleopyrite* (CuFoS2). Chalcopyrite, PI. IV A, replaces sphalerite end totrekedrite as shorn by the many small ▼elnlets dong fractures in the two minerals. It Is also soon as small drop-like masses In the sphalerite which on close ex­ amination are aligned m l would indicate deposition along cleavage planss. The chalcopyrite also follows the contact of the two minerals and in places cuts directly across the contact of the minerals giving definite evidence of its later deposition Chalcopyrite is also later than bournonite. As shown in PI. V A chalcopyrite occurs in part as remnants in a calcito ve inlet traversing boumonite. It is interpreted that the fracture was originally filled with chalcopyrite; that some­ time after galena mineralization there was recurrent movement along old fractures and calcito followed some of these old ohannelwaye and replaced a great deal of the broken chalcopyrite that filled them. Four age relations are established; bour- nonite, chalcopyrite, galena, and calcito. A remnant of totra- bedrite and a small stringer of chalcopyrite are seen in tho b o u m o n ite . (PbS) Galena. / Galena was the last sulfide deposited. Its relation is shorn in PI. B B where it is shown surround­ ing remnants of chalcopyrite, bournonite, and sphalerite. Because of the lack of much chalcopyrite in the ore it is difficult to find positive evidence as to Its age relation, but it probably followed chalcopyrite, preceded calcito, and was the last sulfide deposited. -4 5 -

CaXcite> (CaCOg). Calclte, tbo Is st mineral deposit ed, roplsooa all the other mineralo. It is quito abundant as a network of volnlets throu^i the mineralized zone. PI. V B shows onloito traversing galena and surrounding other sulfides.

Mineral Paragenesis

The sequence of mineral deposition, frcza oldest to youngest follow : quartz, pyrito (pyrrhotito), sphalerite, totrahodrito. bournonite. chalcopyrito. mien a. md calc it o. The most v a lu a b le minerals are underlined, md those whoso positions are not accurately fixed me in parentheses. From a study of the polished sections, clear evidence was obtained that the mineral® did not crystallize simultaneously, but were deposited successively. The intimate intermingling of the minerals suggests that the pro fbnaed by solution that under­ went gradual change in composition, aril not by a succession of different solutions. Shattering or fracturing during deposition of the minerals occurred after the deposition of the quartz and pyrito end again after the late sulfides. Post-mineral movement has shattered and brecelated the mineralized zoic. The mineral sequence in the Buster villa Mine is rather characteristic of the me so thermal load-zinc deposits of the western United States. -4 6 -

Genetic Classification

Iho mineralization in tho Bustorvillo 211 no falls Into the group regarded by Lindgron1 as nasothermal or Intormadiato temperature deposits formed by ascending thermal solutions gene tie ally conn eo tod with intrusive rooks. Tho absence of such minerals as magnetite, garnet, tourmalino, and pyroxenes shows that n high temperature did not prevail*

Me and Genesis.

It is generally recognized that ore deposits aro de­ rived from solutions that had thoir origin in intrusive ig­ neous roekm* There is little doubt that the mineralization in the Cuprite district is related to Iho graaodiorlte in­ trusion* All the deposits examined, with the exception of the Busterville and lioscut load-zinc deposits, aro pyrooota- somatio or so-callod contact deposits and occur at or near tho contact of the granodiorito intrusion and the Haco lime­ stone and the overlying limestone conglomerate. Tho Bustorvillo and Noscut deposits aro of replace­ ment origin and formed some tine later than the contact de­ posits, at least late enough for the outer crust of tho in­ trusion to solidify, to be fractured end for many of tho fractures to bo intruded by dikes* Proof for a late post- dike mineralization in tho Bustorvillo 2/JLne is the alteration

1 . L in d g rea, ><., M in eral D e p o sits. McGr&w-Hi’PL. 1986. —#9—

o f q rhyolito porphyry dike and its impregnation with minor amounts of sulfides*. At this Into stage after the main in­ trusion wo cannot oscapo genetically conn#oting the oro solutions with the magma. According to tho more recent be­ liefs of magmatic differentiation a magma gradually changes in composition fran more basic to acid. This is exemplified in the Cuprite stock by the border facies that are more basic than the center which is a product of a further differentiated magma. Also the rhyolite porphyry dikes that cut the intrusive and sediments are still more acid in composition. It is in the last phase of the differentiating magma that the metals collect­ ed are expelled as emanations, and deposit their metallic con­ tent under favorable conditions. In the Bustcrvilla and Kosout Mines the limestone was the favorable environment. Fissures, and locally fractures md bedding pianos in tho limestone formed the favorable ehannolweys for tho circulation of th e o re forming solutions. As has been previously described, flssurlng is re­ lated to erogenic disturbances in which strata were folded and broken by faults. The Cretaceous sediments wore involved in this epoch of mountain building, md it is known that the granodiorite intrusive and dikes out these beds. The minerali­ zation is therefore definitely later than late Cretaceous and probably extended into early Tertiary or,in other words, a lota stage of the Laraaido Revolution. -4 8 -

BXPLAiTATIon Of STimOLS

Hio symbols listed below ore used la the ex- plemetdon of the following plates:

q u a rtz P y rlte S p h a le rite Totrahodrite bnn B oum onite op Chalcopyrite G alena S i ' C o lc lte po • P y rr h o tite - t 9 -

!

f E PIATB I I I A and B

Am Photoaierograph showing pyrlte breooiated, surrounded, end replaced by sphalerite. Chalcopyrito as vainleto md drop-ilk® nasaes are ropla elng sphalerite. Cal- clte has traversed the some fracture and partly replaced ohaloopyrlte. X88.

B. Photoalorograph showing ohaloopyrlte re­ placing sphalerite. Pyrrho tit e appears to occur as an occasional remnant in sphalerite. Galena replaces the other sulfides. Late oolcito traverses and replaces the sulfides. X150.

PLATS IV A and B.

2A. Photonicrograph showing tetrahodrlto velning sphalerite. Chnlcopyrlte as snail vcinlets traverses both nlnorals and In places crosses the contact of tho two minerals* Bonn ants of quarts and pyrito ore in the tetrahodrlto. X15Q.

2B. Photomicrograph showing brcocistod pyrito. Bournonite is traversing tetrahodrlto and fingers out into it replacing it. Galena as a snail veinleS cuts bournonite. X170*

PLA.T23 V A acd B

A. Photcsaicrograph ohofiing a remnant or tetra- h e d r its In boumonito. Chaloopyrite as veln- le to outs tlio b our nonit e. Calolte ham f o l i o vad the same f r a c tu r e o r ve i n l e t of chalcopyrito and has replaced most ' of it leaving only remnants of I t . 1150.

B. Photonlorograph shOTdlng galena replacing boumonito and chaloopyrite, the minerals being le ft as remnants and surrounded by it. Calolte traverses the galena and is definitely younger. X82. - > z Plan eto loig Nerth looking Section UTRIL MINE BUSTERVILLE vein strike strike vein e . e f . le a c S d« p ewtfe n . i »*£

ete leif I**t leekiHf Sect«en SS* sss/s* SS/SsSS' S S s /fS S /S s s * s / s s /s S * S /S S y ? s s ' / / ss/s ' y Plate.VIII Univ. of Arizona Library sect ion along A A

explanation

I ** 1 AZ/wtriee kHweefc I ^ I t#e atittziu

( » A njes.te L<"motene <»« y»Jftzif« Pie*.o« GEOLOGIC STRUCTURE SECTIONS,CUPRITE DISTRICT, ARIZONA RE 1 1 fc" I NatO f,meat*we

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Noscut Fjult y c *» e' .4000'

\ S4CC' Sec tion alor^ B-B* mimyws- Univ. of Arizona Library

n z s — EXPLANATION

V SCtXMCNTAMJ eOCwS

I Alluvium , NiHwask

Cen^lemeratc c#ese«n«iif pakoaitci Cret. 1*$. Red quartzite Bed at Base

h s g e -w unJiflereniisteJ BrHqujrt- Ziic, darlt Skate,ArqiHite, I,me* to Tie , anJ arkese. n s

a u undiHercutiatea alter- V TlttiYiq tBin-beideJ liinestema an j liqlit coloreJ quartzites 5-

i u n d iffere n tiated red quart­ z ite , s aales. amd dark and liqht quartzites

A Breccia ceasistiaqef fraq- meatset paleezeie limestone and vitreous quartzite

Naco Limestone massive limestone witk silica lenses aid Red Wes Locally marWe

kxeoos ROCKS

Rhyolite porphyry Brown, qray .and white dike rock with quartz fAenecrysts

X. z

V- — Ala a kit e sm all massof liqktcolored rock W ments ^ r*7,^*0Tite

Gramodiorite cuprite stock, ft is composed mainlyefqranod*ent€, Outnksnpnal facies are d.yfctly Afferent in comp- •eition r*rwrr-Tnn ...

Andesite porphyry Andesitic flows and brec­ cias in part oedimentarudep­ osited.

Fawr

In # er ou 4 ••i

Concealed fault

Reconnaissance boundary

Shrike end *f

Ankck'o#

Mine or prospect

# •Soft

Trianqwlat ion points

O Bui Id i wys

Roods

Trei Is

.8$

\

\ \ j ------^ / X X. ; X h,1 \ ' x. Y

Z . V /

Topegr»pny b> CA.LSC jr»d GuC Borland GEOLOGIC MAP OF THE CUPRITE DISTRICT Geology by CA Lee end aCBerierd S u rv ey ed in 1935 ARIZONA Surveyed in 193S Scale f % 440*

Contour interval 50feet

1835 v ' - c= 3 <*

> I 3Q) c. a* 3 5

/ 9 a r