Porphyry Copper Deposits of the American Cordillera

Frances Wahl Pierce and John G. Bolm, Editors

Arizona Geological Society Digest 20 1995 Geological Summary and Perspective of Porphyry Copper Deposits in Southwestern North America

SPENCER R. TITLEY Un iversity of Arizona, Tu cson, Arizona

ABSTRACT enci, and Bisbee. Under the impetus of material requirements fo r prosecution of the war, the search for copper ores by 1942 had Porphyry copper deposits in the American southwest focused almost solely on discovery of new disseminated orebodies comprise a distinctive and important metal resource. Their and resulted in identification of 25 porphyry copper deposits by exploration and exploitation during the past hundred years 1980. Among the first recognized as having porphyry copper was accompanied by significant advances in geological knowl­ potential by mid-century were the disseminated ores at Silver Bell, edge and development of increasingly efficient mining and described by Richard and Courtright (1954). Much of the early his­ extraction methods. Cause and effect are indistinguishable be­ tory of these deposits has been recorded from economic and engi­ cause the necessity for increasing mining efficiency resulted in neering perspectives by Parsons (1933, 1957). enhancement of extractive methods and because geological In the early I 990s mining was proceeding at a dozen depos­ study of the ores resulted in recognition of broadly applicable its in Arizona that had survived the economic downturn of the geological and exploration concepts. The early view of linear 1980s: Twin Buttes, Sierrita-Esperanza, San Xavier-Mission, tectonic-based regional controls was supplanted by integra­ San Manuel-Kalamazoo, Ray, Morenci, Pinto Valley and Inspi­ tion of concepts of plate movements. Early views of the envi­ ration, and Bagdad. Leaching of copper was taking place at ronment of fo rmation of hydrothermal ores have been given Mineral Park, Lake Shore, and Silver Bell. Chino and Tyrone rigor or modified by the results of studies based on modern were operating in New Mexico, and Cananea and La Caridad methods of analysis and application of sophisticated chemical were producing copper in Mexico. At this writing, ten more de­ principles. Deposits have been sites of basic studies of hydro­ posits have been explored but are undeveloped or unmined. thermal systems, the results of which have been applicable The porphyry copper deposits of the region have been not across a wide spectrum of ore deposits. Most importantly, in­ only sites of recovery of significant mineral wealth but also sites fo rmation and methods developed in the study of ores and of detailed and extensive studies of process geology and develop­ their mining have served as bases from which the search for ment of mining and beneficiation technology. Geological studies deposits in many regions of earth has proceeded successfully of mining districts of the southwest reported mostly by geologists during the past half century. of the U.S. Geological Survey during the early part of the century developed a basis of regional stratigraphy and structural geology INTRODUCTION that is used to this day with only minor modifications. Basic con­ cepts of ore occurrence and classification developed from studies The American Southwest, comprising the southwestern half of ores at Bisbee, Ray, Miami, and Morenci have been refined of Arizona and contiguous parts of New Mexico and Mexico continuously since the beginning of the century with heightened ("the region") is the site of an extraordinary endowment of por­ study during the decades of the 60s, 70s, and 80s. Mines and dis­ phyry copper deposits. Most deposits are in southeastern Ari­ tricts of the region have been sites of development and testing of zona where historic and recent copper production amounts to now widely used exploration technology that includes both geo­ about two-thirds of newly mined copper in the United States. physical (Brant, 1966) and geochemical (Bloom, 1966; Chaffee, Significant quantities of by-product molybdenum, silver, gold, 1982a, 1982b) methods. Arizona deposits have been sites of de­ and platinum are also produced. velopment of innovative technology in mineral extraction during This paper presents a brief history of the technological evo­ the past half century and have served as field laboratories for de­ lution of southwest porphyry copper deposits as bulk low-grade velopment of methods and machinery. deposits and the evolution of knowledge of their settings, habits, and genesis over the past century. This summary sets forth im­ Production and Grade portant parameters that may be contrasted and compared with other porphyry systems in other regions. The writer has selected A tabulation of grade and tonnage of porphyry copper ores significant characteristics described in an extensive literature of the region has been published by Gilmour (1982) and sum­ developed during the past half century to serve as fundamental marized by Titley and Anthony (1989) and Titley (1994). Re­ points from which to consider the environment and processes of serves in 1989 have been listed by Beard (1989). Production formation of porphyry copper deposits as viewed in the 1990s. figures summarized for 45 porphyry copper deposits in the United States by Titley and Beane (1981) are 15.8 billion tons of Background copper ore production and reserves with a weighted copper grade of 0.68 percent. Fourteen deposits that reported molybde­ Following Daniel Jackling's innovations in mass ffilnmg at num had a weighted grade of 0.0325 percent molybdenum. Bingham, Utah, during early years of the century, mines in the southwest gradually evolved from high-grade, mostly underground Literature and the Growth of Knowledge operations to bulk low-grade, mostly open-pit operations. These districts and mines included Miami, Inspiration, Ray, Chino, Mor- Literature of the first half of the century dealt largely with

6 GEOLOGICAL SUMMARY AND PERSPECTIVE OF PORPHYRY COPPER DEPOSITS IN SOUTHWESTERN NORTH AMERICA 7

field observations and descriptions of known deposits. Much of tive and associated ore districts with major lineaments and zones this was in Monographs and Professional Papers of the U.S. of rifting. Even at this early time Schmitt invoked potential con­ Geological Survey, as Transactions of the American Institute of tinental drift as a mechanism to explain continuation and offset Mining and Metallurgical Engineering, and in serial publications of his major structures and proposed effects related to the influ­ such as Economic Geology. Viewed from the perspective of the ence of the East Pacific Rise. Using large numbers of potas­ evolution of ideas, papers of the 1940s were the first important sium-argon radiometric dates, Jerome and Cook (1967) carried reports treating alteration, mineral zoning, rock descriptions, and the notion of occurrence of districts in belts to a degree of so­ regional settings of these large systems. Collections of current phistication and examined porphyry associations with character­ reports focusing on the region and treating both deposits and istics of crustal geology. The idea that regional structures control topical infonnation have been published by Titley and Hicks (1966) the location of porphyry copper districts has withstood the ad­ and Titley (1982a). Papers treating general properties of the de­ vent of more recent notions concerning the evolutionary history posits of the region as contrasted with deposits of other areas of continental margins based on plate motions. Conflictingideas have been published by Jerome and Cook (1967), Lowell (1974), of the importance of flaws in the crustal fabric of North America Hollister (1978), Titley and Beane (1981), and Titley (1992, to district localization have been expressed by Lowell (1974) 1994). Comparable treatment of porphyry deposits in western and Sillitoe (1975). Canada has been published by Sutherland Brown (1976). A surge of scientific interest has been marked by a compa­ Areal and Structural Geology rable increase in the flux of papers treating different properties of porphyry copper systems. This increase began in the early Porphyry deposits of the region lie above the North Ameri­ 1960s, and the numbers of publications reached a peak during can craton in Arizona, New Mexico, and contiguous Mexico. the late 1970s and early 1980s. The period was witness to appli­ The geology of this region has been described in relevant parts cation of increasingly widely available techniques of measure­ by various workers including Anderson (1966, 1968) and Titley ment and applications and testing of theory. Many concepts of (198 1, 1982b, 1992). The craton basement of the region com­ hydrothermal ore genesis were refined. Porphyry systems were prises Proterozoic sedimentary and volcanic rocks at varying studied as examples of epicrustal intrusion-centered ores sys­ levels of metamorphism and batholithic scale plutons represen­ tems, of the evolution of hydrothennal processes in time and tative of at least three episodes of Proterozoic igneous activity. space, of the evolution of petrogenetic systems, of metal and al­ Most of the region's porphyry copper systems lie within or above teration zoning, and of supergene enrichment and weathering a 1.68 to 1.72 Ga basement dominated by clastic metasedimen­ processes. Many fundamental and now widely accepted notions tary rocks and included plutons; three deposits in northwestern of hydrothermal ore formation evolved from these studies. Arizona lie within a possibly older (ca. 1.8 Ga) basement of metavolcanic rocks and older plutons. Figures I A and I B show GENERAL GEOLOGICAL HABITS AND GENESIS the distribution of deposits and generalized basement ages of the region. Porphyry copper ores are phenomena of island arcs such as The Proterozoic basement is overlain by 2 to 4 kilometers the western Pacific, of cratons in continental margin settings of Phanerozoic cover consisting of Paleozoic platform strata and such as the western United States and contiguous Mexico, and a variable thickness of Mesozoic clastic and volcanic rocks. In of accreted, constructed continental margin settings such as many districts mineralized basement is exposed in intrusive western Canada. The character and complexity of deposits in contact with porphyry intrusions and in fault contact with Phan­ these different settings vary in petrological and metallogenic de­ erozoic strata, suggesting the existence of a still unresolved epi­ tail, but notwithstanding such contrasts the deposits of all these sode of Mesozoic tectonism that may have occurred in the regions share important features. The apparent association of Jurassic. Pre-Laramide Mesozoic rocks are represented by intru­ ores with subaerial andesitic volcanic activity and the affinity of sions, by basin strata in the central part of the region, and by ores with felsic intrusive porphyry centers link porphyry copper mixed volcanic and clastic strata in southern Arizona and con­ deposits with specific geologic settings which have undergone tiguous Sonora, Mexico. the effects of plate convergence, most commonly along conti­ Courtright (1958) and Richard and Courtright (1960) were nental margins and island arcs. the first workers to report observations on volcanic rock succes­ sions that established the Laramide interval as manifesting a dis­ Tectonic Settings and Geologic History tinct geological style in contrast with that of the older Mesozoic. The Laramide interval is a 25 m.y. span of time marked by both The history of modem knowledge and ideas concerningthe volcanic and intrusive igneous activity. The interval followed a regional association of ores with crust commences with Butler period of 90 m.y. of igneous quiescence and was succeeded by a (1933), who noted the distribution of porphyry districts in a belt further 25 m.y. period of similar quiescence in the region. around the Colorado Plateaus. Under the influence of work by Laramide lithologies of the region are dominated by igneous Billingsley and Locke (1935, 1941) and Mayo (1958), studies of rocks ranging from extrusive flows and pyroclastic successions the fabric of continents during the next two decades led to ideas to intrusive batholiths, stocks, and dike-sill swarms. Magmas of lineament control of ore districts. These workers showed dis­ were emplaced in the shallow crust, and their first manifestation tricts to be localized at intersections of major regional structures appears to have been development of andesitic stratovolcanoes. or associated with major tectonic belts. Harrison Schmitt (1966) Remnants of subaerial flows are widely exposed through the re­ studied the location of porphyry districts from a global perspec- gion (fig. 2). The volcanic rocks are commonly altered or miner- 8 S. R. TITLEY

,:.:"",:.,------

TD M ) 2. '\ � \ \ \ \ \ \ , \

o 100 200 ===='==�\ ======�'40C===0 ==�600' =, =, KILOMETERS SAMPLE SITE EXPLANATION

TOM AGES PLUTON AGES 1.7- 1.8Ga 4Ga intr. in 1.68 Ga I. 6 1.8-2.0Ga • basement o ) 2.0Ga 1.71 - 1.75Ga intr. o • Adapted and modified from Adapted from Bennett and OePaolo(l987) Anderson and Silver (1981) data from Lan J991 with g ( ) Figure lA. Generalized basement ages in Arizona and California as sug­ terrane boundaries are generally real, their specific definition on the gested from neodymium isotope and corresponding data of Bennett ground is general and unspecific in most instances because of paucity of To" and DePaolo (1987) and Lang (1991), and in Mexico by Anderson and appropriate outcrop. In Arizona, boundaries are modified from Bennett Silver (1981) based on radiometric ages of Proterozoic plutons and the and DePaolo (1987) and Chamberlain and Bowring (1990)_ inferred presence of the Mohave-Sonora Megashear (m-s). Although the GEOLOGICAL SUMMARY AND PERSPECTIVE OF PORPHYRY COPPER DEPOSITS IN SOUTHWESTERN NORTH AMERICA 9

where Anderson and others (1955) mapped the intrusion center at the intersection of two orthogonal Laramide fault sets.

Time and Plate Tectonics , , A link between porphyry ore genesis and tectonic events re­ lated to plate convergence was first suggested for the region by Sillitoe (1972, 1975). Two principal episodes of porphyry cop­ " "- \ per deposit formation are recognized in the region, one of Juras­ "­ I sic age as represented by the replacement and breccia complex \ \ at Bisbee and the other of Late Cretaceous to Early Tertiary (Laramide) age as represented by more than 40 mineralized cen­ \ "- \ ters in the region. Both the Jurassic and Laramide events repre­ \ \ sent short-lived episodes of near-normal convergence of the \ North American and Pacific Plates (Coney, 1978). The extensive \ \ dating of ore deposits in this region summarized in Reynolds \ and others (1985) leaves little doubt of the temporal correlation \ \ of ores with high rates of normal plate convergence during the '- Laramide. Moreover, Laramide stress directions inferred from plate convergence geometries are mimicked in fracture and dike o IQO 2Q9 490 600 patterns seen in Laramide intrusion centers (Heidrick and Titley, KILOMETERS 1982). However, precise understanding of all elements of plate Figure lB. Basement contrast map of Figure IA with positions of signifi­ convergence phenomena that led to formation of the deposits of cant porphyry copper deposits of the region shown as open circles. The de­ southwesternNorth America remains elusive. posits occur in the "copper quadrilateral" of Noble (1970) that is outlined The restoration of Baja California to a pre-rift fit along the by the Sonora Mohave megashear to the southwest and an uncertain Mexican mainland reveals that belts of deposits grossly parallel northeast trending line across northwestern Arizona. This is the crustal block with a basement of assigned age of 1.7 to 1.8 Ga in figure IA. the old continental margin (fig 4), but the inference of a craton setting for deposits of coastal Mexico is subjective (Titley, 1992). Deposits of Arizona and contiguous Mexico represent ores of 58 to 65 Ma age, while those in a subparallel belt west of alized, and radiometric dating reveals close temporal correspon­ the volcanic cover of the Sierra Madre Occidental in Mexico are dence with cross-cutting Laramide intrusions. An excellent ex­ generally of about 55 Ma age (Damon and others, 1983). ample has been mapped by Dunn (1982) at Hillsboro, New Deposits of Mesozoic and younger age in the western hemi­ Mexico (fig. 3). The widespread association of porphyry sys­ sphere are along the western continental margin, while North tems with these igneous suites coupled with observations of pet­ American porphyry copper deposits of Paleozoic age are in rologic associations in island arcs and Andean-like margins has parts of the old convergent margin now deeply eroded or hidden in led to a general notion that the porphyry systems have evolved the deformed parts of the Appalachian orogen along the in the subvolcanic intrusive roots of andesitic stratovolcanoes. eastern continental margin. The dense array of districts and depos­ However, the evidence of evolution in such settings has not been its of the southwestern United States together with Cananea and La successfully interfaced with interpretations of the existence of Caridad in Sonora have been considered a separate porphyry cop­ Laramide calderas in the region (Lipman and Sawyer, 1985). per population. Concentration of study on this population by many Since Laramide time, oxidation, leaching, and episodes of workers including Noble (1970, 1976) has resulted in a provincial erosion interrupted by younger episodes of volcanic activity and view of the cluster of deposits in the so-called "copper quadrilat­ Basin and Range uplift have modified the original character of eral" and precluded a broader regional perspective and geologic ores. Intermittent uplift and erosion has presently exposed por­ synthesis. Data do exist: Sillitoe (1976) published results of a phyry deposits of the region at levels believed to be a few kilo­ study of porphyry copper systems of Mexico, Coney and Campa meters beneath their original tops. (1987) have developed a regional view of Mexican geology based Many modern ideas of the structural setting of the porphyry upon terrane analysis, and Anderson and Silver (198 1) have pre­ deposits had their roots in the application of lineament tectonics sented results of a study of basement ages and distribution in summarized by Schmitt (1966). More recent work concerning northern Mexico. Based on these works a regional overview of the structural style of the Laramide has been summarized by porphyry copper distribution that extends beyond the border re­ Krantz (1989). Mapping and interpretation in southeasternAri­ gion of the United States and Mexico is shown in figure 4. In this zona by Davis (1979) has demonstrated a Laramide structural figurethe Gulf of Californiahas been closed to approximate the in­ style dominated by basement-cored uplift. This interpretation ferred Laramide configuration of the continental margin. Base­ demonstrates the importance of an old northwest-oriented struc­ ment ages and relationships as determined or suggested from the tural fabric parallel to the former continental margin which­ work of Anderson and Silver (1981) in Mexico and by Bennett and became rejuvenated during Laramide time (Titley, 1976). DePaolo (1987) in the contiguous United States are integrated with Despite this and other work, however, the structural controls of the terranes of northern Mexico to suggest a configuration of base­ stock emplacement have remained elusive except at Bagdad, ment and tectonics at the time of Laramide ore formation. 10 S. R. TITLEY

PHOENIX I �GIObe ARIZONA i NEW MEXICO if- Morenci I ¢- I ¢- ¢- I q.,.. I Silver -t & , , " City (l­ ¢-a �I (p'"¢'- I ¢-

CSON � \...� ' ! • )' 1+r '� ..

t �� Q � 0= ' -', : I M L S III ,------il- � I �� _ _�+-l_ �?----�, • '_ �_1 ____ 80 ____ 160 • __'(______�_ �_ _ ___ J o j _ KILOMETERS SONORA I CHIHUAHUA Explanation ananea <1 \ Areas of principal outcrops of � \ 'Laramide' volcanic, volcaniclastic and associated sedimentary rocks \ in southeast Arizona. ¢- Laramide Porphyry Copper Deposit

Figure 2. Map of southeastern Arizona, southwestern New Mexico, and rocks and Laramide porphyry ores were regionally coextensive was recog­ northern Sonora showing distribution of Laramide porphyry copper depos­ nized in the 1960s. its and outcrops of Laramide volcanic and volcaniclastic rocks. That these

Igneous Petrology 1980; Norton, 1979, 1982). Thus the petrology of igneous rocks and their cooling history is important to the understanding of Porphyry copper deposits and genetically comparable intru­ porphyry copper systems. The focus of mineralization on cen­ sion-centered deposits of molybdenum and tin are convention­ ters of porphyry intrusion indicates a close genetic tie with cool­ ally viewed as results of late stage events in the emplacement ing processes of magmas in the shallow crust, the effects offlow and cooling of felsic magmas that produce porphyritic rocks at of hydrothermal solutions are temporally and spatially associ­ shallow (less than 5 kilometers) depths during a volcanic cycle. ated with certain plutons. Moreover, certain metal assemblages That granite-associated ores may evolve in caldera rather than appear to be linked with specific igneous suites, which are also isolated volcanic systems and that some porphyry-related ores commonly regionally constrained. may have evolved as results of diatreme genesis are commonly Petrogenic studies treated the petrology of rock descent and recognized exceptions to this generalization: diatreme associa­ diffe rentiation and the questions of magma source, evolution, tion may be represented at Ok Te di in the New Guinea High­ and ascent. Results of both of these approaches have been pro­ lands (about I Ma in age), which lacks associated volcanic ductive during the past several decades in advancing knowledge strata. Notwithstanding such exceptions, the presence of closely of how porphyry-centered metal systems evolve. No unanimous contemporaneous andesitic volcanic strata with many systems view among workers has yet developed, but there exists sub­ in both cratons and island arcs lends credence to the conven­ stantial field, experimental, and theoretical bases on which study tional model. Rapid rise of magmas and their rapid cooling in a continues to progress. Stringham (1966) summarized much pet­ shallow environment is believed to result in porphyritic textures rographic data and outlined igneous associations in some copper and profound thermal disequilibrium, which in tum results in districts. The first overview of petrologic compositional trends the cracking of very large (cubic kilometers) volumes of wall of Arizona deposits was offered by Creasey (1977) in a series of rock conducive to the convective cooling processes that result in variation diagrams treating rocks from Ray. Cornwall (1982) hydrothermal fluid flow (Burnham, 1981; Burnhamand Ohmoto, further detailed chemical petrology at Ray, favoring a model GEOLOGICAL SUMMARY AND PERSPECTIVE OF PORPHYRY COPPER DEPOSITS IN SOUTHWESTERN NORTH AMERICA II

Hillsboro a

EXPLANAT ION Tertiary volcanic and sedimentary strata Paleozoic sedimentary strata I*v @ ';� Laramide Copper Flat q.monz. Precambrian rocks

Warm Springs q.monz. Dikes and veins

andesite Faults

o 2

m lies o 2 3

kilometers

Figure Geologic map modified and adapted from Dunn (1982) of the Paleozoic strata to the north, south, and west. This style of occurrence, 3. Copper Flat porphyry system at Hillsboro, New Mexico. The copper de­ protected since the Laramide by faulting of the complex, is hypothesized posit centered on the Copper Flat Quartz Monzonite, interpreted here as from data elsewhere (fig. 2) as manifesting the dominant geological style of is a subvoIcanic intrusion emplaced within a succession of subaerial andesite porphyry copper environments of Laramide deposits in the region. flows and breccias. In its present configuration it is fa ulted down against 12 S. R. TITLEY

I I I I

J " I '\ J ", I "\ rJl ------" " ' lflij-- CA ' lI AZ I "',\ " . . r::.:.:::121 )( . . : } NM 0 tj '''', .Ii. .. IH T/;I (k· r/1#!:) VZsY

,---

Laramide PC D o \ Mid- Mesozoic PCD '\"'�,:� � � 2) ",, '-'� .o 0 • Te rt. Ve in � - Rep!. 6 Te rt. I.s. Rep/. ' \ );� �': ___ _ Mexican terranes modified ',,_, , � '-..12J ':� , , from Coney and Campa \ \�!>,v� ��\ �� 187 " ,� ���� o 200 400 600 ""\ kilometers "\\\.'\�

, / ( "'-"_,, -\ W' ' Figure Map of southwestern United States and adjoining northwestern Mohave Sonora megashear of Anderson and Silver (1981). In the United 4. '\: Mexico incorporating details of figure lA and 1B, terrane designations of States, CA is California, AZ is Arizona, and NM is New Mexico; vis is ap­ Mexico, and porphyry copper and other selected ore deposit types of the proximate boundary between volcanic- and sediment-dominant Protero­ region from Tittey (1992). The Gulf of California has been closed juxtapos­ zoic basements of Arizona and contiguous Sonora. Patterned area of ing Baja California and the present northwestern coast of Mexico. The northwestern Arizona and the Caborca terranes hypothesized as common terranes of Mexico from Coney and Campa (1987) are as follow: CHIH, and older than the patterned terrane of Arizona and adjoining New Chihuahua; COA, Coahuila; CTZ, Cortez; CA in northern Sonora is Mexico; open pattern of California is partially Mohave terrane. Caborca; SMO, Sierra Madre Occidental; G, Guerrero and mJs is the GEOLOGICAL SUMMARY AND PERSPECTIVE OF PORPHYRY COPPER DEPOSITS IN SOUTHWESTERN NORTH AMERICA 13

8 BISMARCK MTNS., YANDERA, PNG (6-16Ma) 6

4 ,r- ...... " , r\ ENTRAL CHILEAN INTRUSIONS (-60Ma) 2 �\)f �� SIERRA MADRE OC. \ -.J ' ACITE/RHYOLITE o \\O (MID-TERT. ) �+\ } '\ ARIZONA LARAMIDE � --- / ENd -2 ANDESITE/DACITE (_'_) + •

- 4 - ARIZONA LARAMIDE SIE , NTRUSIVE -6 " R SUITES - , � • - ' . - . e , �. 6 , -8 RAY e e_

"0 6 � CB 6-- • -10 - 0" o �BGD -12 - ,,� �o

0- .704 .706 .708 �.710

I Sro Figure 5. Plot of Initial strontium ratios (lSI"") vs. epsilon neodymium for evolved crustal progenitors. The andesite envelope encloses those initial Laramide intrusions of Arizona compared with values for other igneous compositions seen in 5 porphyry centers of Arizona. Lines of evolution are rocks of Chile, Mexico and western Pacific Island arcs. The data for por· shown with distinctive coding for each, abbreviated TMST, Tombstone; phyry systems reveal changing sources and compositions of rocks of the SIER, Sierrita; Ray; BGD, Bagdad; DJ Diamond Joe; CB, Copper RAY, Laramide igneous complexes and linear paths of evolution that commence Basin, and CHR, Christmas. PNG is Papua New Guinea.as: Data from An­ with andesite with a significant mantle component and evolve to more thony and Titley (1988) and Lang (1991). 14 S. R. TITLEY that implies magmas and solutions from a probable source in the The Style of Alteration and Mineralization mantle. Igneous evolution of systems in the region commenced with outpouring of andesite-dacite volcanic materials followed The style of hydrothermal modification in deposits has by emplacement of intrusions which evolved to progressively been described in general terms by Titley (1982c). The most more felsic phases. Sharp contacts and striking compositional common habit of porphyry copper mineralization is as hydro­ contrasts in the intrusive suites of the region are the rule and thermally altered, copper-mineralized stockworks. The stock­ have been interpreted as representing emplacement of succes­ works comprise tens of cubic kilometers of fractured rock many sive magmatic phases rather than in situ differentiation of single tens of square kilometers in area either centered on porphyry magmatic progenitors. intrusion cores or (more commonly) distributed asymmetrically Compositions of igneous rock series associated with depos­ across intrusion wall-rock contacts. Vertical exposures and mea­ its have been repOIted from Sierrita (Anthony and Titley, 1988a, surements of paleopressures suggest mineralization and alter­ 1988b), Christmas (Koski and Cook, 1982), Aj o (Wadsworth, ation originally extended over many kilometers vertically; most 1968), and numerous additional Laramide districts (Lang, 1991). Laramide deposits of Arizona are exposed at a weathered level I In terms of long accepted rock names, evolutionary trends of to 3 kilometers below the original surface. The deposits ubiqui­ intrusions of the Laramide districts run from quartz diorite tously reveal zoning of metals and alteration in patterns and through granodiorite to a preponderance of porphyries of quartz cross-cutting habits that indicate a complex sequence of origin. monzonite. This range corresponds roughly with the I.U.G.S. Significant mineralization and the more commonly recognized (Streckheisen, 1973) nomenclature of monzodiorite through alteration types are restricted to relatively small volumes in the granodiorite to granite. hearts of stockworks. Where altered fractures of the stockworks Burnham (1967, 1979) has traced magmatic evolution of have been mapped as at Sierrita (fig. 6) (Haynes and Titley, porphyry-deposit related systems through the stage of formation 1980; Titley and others, 1986), Silver Bell (Kanbergs, 1980; of hydrothermal fluids by in situ differentiation. The role of Norris, 1981), and Red Mountain (Kistner, 1984), mineralized water is addressed in detail because of its importance to mag­ centers defined by copper grades are revealed to be located in a matic processes and ground preparation through stages of solidi­ few cubic kilometers of volume of closely spaced (centimeter) fication of igneous carapaces and their subsequent rupture as the joints within a larger volume of less abundant fractures compos­ pressure of confined volatiles increases during magma cooling. ing the stockwork. This results in the jointing of rocks, typically creating a stock­ The mineralogical, chemical, and physical conditions of work. Wyllie (198 1) reported studies of the origin of calc-alka­ alteration have been subjects of significant interest during the line melts in a subduction-related environment. Farmer and last half-century. The habits and environment of alteration have DePaolo (1983, 1984) have attributed the source of many Great been important both in the search for ore and in the advance­ Basin magmas including those related to porphyry metal sys­ ment of important elements of hydrothermal theory. Significant tems to the crust. Anthony and Titley (l988a, 1988b) and Lang data on alteration including specific information treating por­ (1991) have reported results of studies of the evolution of major phyry metal systems have been published by many authors. and trace element chemistry and neodymium and strontium iso­ Papers of the 1940s were among the fi rst to describe the physi­ topes in Laramide igneous suites of the region that reveal appar­ cal habits of alteration of deposits in Arizona. Much of this was ent deep crustal sources of porphyry magma progenitors to the the work of Peterson and others (1946) at Castle Dome and mineralization. A plot of neodymium-strontium data is shown in Anderson (1950) at Bagdad. Nearly 30 years of intense study of figure 5, where Laramide suites are compared with island arc the chemistry of the alteration process in the region, much of it and Chilean intrusions and with the mid-Tertiary volcanic epi­ receiving impetus from the classic work of Sales and Meyer at sode of the Sierra Madre Occidental of Mexico. One significant Butte (1948), developed a fundamental base of knowledge of property of the Laramide intrusive centers in the Arizona region hydrothermal processes. By the early I 960s a generalized view is that their isotopic properties reveal continuous evolution and of the essential nature of alteration had been developed and change from magmas of perhaps 50 percent mantle component many of the habits of alteration of porphyry systems had been to magmas dominated by crustal components. The youngest in­ elucidated by Jerome (1966). Fundamental mineral associations trusions are most evolved, and Anthony and Titley (1988a, and specifications of alteration stages had been outlined by 1988b) have interpreted a lower crustal amphibolite magma Creasey (1966), and Beane and Titley (198 1) outlined the alter­ source on the basis of rare earth element patterns.An additional ation mineral chemistry in porphyry systems. property of the intrusive suites is their evolution along specific The minerals of alteration suites differ fundamentally with trend lines as revealed by the isotopic habits in figure 5; changes differences in their host rocks. Host rocks are varied, and their in rock isotopic compositions are transitional, indicating gradu­ proximity to intrusions is controlled solely by geological coinci­ ally evolving magmas rather than abrupt contributions of diffe r­ dence. Porphyry copper deposits commonly manifest varied ent magmas from changing sources. Chemical and isotopic styles and compositions of alteration influenced in the main by analyses of these rocks reveal that no single rock may be consid­ the contrasts between and among mafic, carbonate, and potas­ ered as representative of a porphyry copper intrusion and that in­ sium silicate dominated hosts: Conversion of volumes of rock to terpretations of magma genesis and evolution must be premised garnetite is a phenomenon seen in carbonate rather than potas­ upon the composite signature of the suite as a whole, petrogenic sium-aluminum silicate host rocks, while conversion of volumes interpretations of porphyries must be made in the context of the of rock to orthoclase is a phenomenon seen in potassium-alumi­ properties of magma suites rather than the properties of single num silicate rather than carbonate host rocks. These seemingly samples of igneous rocks. simple contrasts form an important basis for consideration of the GEOLOGICAL SUMMARY AND PERSPECTIVE OF PORPHYRY COPPER DEPOSITS IN SOUTHWESTERN NORTH AMERICA 15

" 20 I!llOW(fEAS ! ! r�

I Figure 6. Map of isopleths of abundance of all fractures at Sierrita, Ari­ shown are in cm-'. The isopleths encircle the porphyry mass and pits of the zona. Data generalized from Titley and others (1986). Va lues of fracture Sierrita and Esperanza ore bodies shown in stippled patterns and increase abundance were determined from measurements of total fracture length in value toward the mineralized center. Spot samples of abundance in the divided by the outcrop area in which the lengths were measured. Va lues ore body had values of 0.5 to 1.0 cm-'. Scale bar is 2.5 miles origin of fluids and alteration components as well as metal and 5. Copper minerals and minerals of other economically sulfur. Details of these contrasting alteration types have been important metals occupy their own specific positions in the reported by Einaudi (1982a, 1982b) for carbonate rocks and by paragenetic succession and altered rock volume as parts of the Beane (1982) for fe lsic igneous rocks. Important features of al­ hydrothermal zoning. teration in these contrasting wall rocks are enumerated below. 6. Episodic and sequential development of alteration miner­ als attends episodes of fracturing. Each fracture generation is Alteration of Potassium-Aluminum Silicate Rocks altered in the same way at the same time. The net effect of this process is overprinting of rock volumes by discretely and 1. Alteration associated with porphyry copper deposits in uniquely altered fracture sets, each of which is different from the non-carbonate hosts occurs in the fractured rocks of stock works others. centered on porphyry plutons. 7. Host rock compositional variations in calcium, sodium, 2. The metallogenic effects of hydrothermal processes are potassium, magnesium, and iron result in the development of the deposition of sulfide minerals in large rock volumes. Sulfide contrasting alteration mineralogies in single alteration stages. composition commonly ranges from 3 to 8 volume percent py­ 8. Quartz diorite and granodiorite, chlorite, quartz, sericite, rite and chalcopyrite with ore minerals changing in specific and pyrite are equilibrium minerals of the "phyllic" stage and alteration episodes from chalcopyrite-dominant to pyrite-dominant. epidote and orthoclase are equilibrium minerals of the "potas­ 3. Alteration and most economic mineralization are con­ sic" stage. In granites, orthoclase and sericite are equilibrium trolled by the fractures of the stockwork, which are the per­ mjnerals in an early stage that lacks definitive characteristics of meable channels of the system. Some specifickinds of alteration any formally recognized stage. at specific times may be pervasive and result in wholesale con­ 9. The effects of overprinting render the definition of "alter­ version of one rock composition to another by metasomatic pro­ ation zones" difficult and commonly equivocal even when the cesses. Alteration of veinlet walls is also pervasive but is effects of contrasting wall rock are considered. Inclusion of car­ restricted to domains of mesh-like distribution along narrow bonate host rocks further heightens the difficulties in correlation (centimeter) alteration selvages. of alteration stages. 4. Alteration and mineralization are episodic and chemi­ cally sequential, and much of the alteration seen is thermally ret­ rograde. Chemical changes as manifested by mineralogy Alteration of Carbonate Rocks generally reveal an (Titley, 1994) early, locally pervasive, anhy­ drous alteration followed by fracture-localized alteration that 1. Alteration of carbonate host rocks produces exoskams becomes dominated by a progressive shift to cooler solutions and broad aureoles of metasomatized and recrystallized carbon­ and stabilization of hydrous siljcate minerals. ate rocks of hydrothermal origin. Stockwork control is signifi- 16 s. R. TITLEY cant in some systems where early alteration was pervasive and has resulted in a general view of capping formation that may be formed brittle rocks that fractured during succeeding events. applied to analysis of outcrops (Anderson, 1982). 2. Calc-silicate and hydrous magnesium-silicate minerals dominate the alteration mineralogy in carbonate host rocks. THE PROCESS OF PORPHYRY COPPER FORMATION Potassium-silicate minerals are uncommon or absent in carbon­ ate rocks but may be present in clay or clastic-bearing strata A porphyry copper deposit represents the result of dynamic, within the sedimentary succession. episodic geologic events related to magma cooling; Gustafson 3. Calc-silicate alteration is closely controlled by original (1978) has summarized important aspects of the process. Por­ stratigraphic composition. Unlike potassium-silicate host rocks phyry copper formation commences with emplacement of rap­ in which there may be little compositional change within large idly rising magma at shallow depth in the crust. The magma rock volumes, carbonate rocks are commonly part of sedimen­ column may be many kilometers high, but rapid cooling in its tary successions which may change sharply from bed to bed and upper portions develops a hardened carapace with porphyry tex­ result in distinctive differences in alteration: Diopside in origi­ ture that confines volatiles. Vo latile pressure increases beneath nal dolostones and grossularite in calcareous mudstones may the carapace released when it exceeds the strength of the chilled form at the same time and represent the same level or intensity carapace and the lithologic load (Burnham, 1979), resulting in of alteration. extensive fracturing of the porphyry and its overlying cap and 4. These stratigraphically controlled contrasts in alteration walls. Episodic fracturing results in diminishing areas of frac­ mineralogy are not easily correlated in space with the zoned al­ tured rock, with the abundance of fractures increasing as the teration stages assigned to alteration in potassium-silicate host system collapses progressively closer to the porphyry center or rocks. thermal heart of the system. 5. The temporal distribution of alteration mineralogy and At an early stage of fracturing and volatile release water styles in carbonate hosts of the porphyry systems resembles the carrying other volatiles, metal, and sulfur flows upward from the evolutionary style of alteration in potassium-silicate rocks. Gen­ still cooling magma. As cooling deepens in the magma, repeti­ erally early calc-silicate alteration is anhydrous and pervasive tive failure takes place. Gradually water from wall rocks is en­ and is followed by hydrous alteration minerals in veins and trained into the fracture system, and the pluton cools rapidly by veinlets. convection. This convection process involves great volumes of 6. In a chemical and mineralogical sense, skarn-altered water and results in development of alteration and precipitation parts of porphyry copper systems contain a lower overall sulfide of metals. Young alteration assemblages of veins overprint older content and a correspondingly higher chalcopyrite-to-pyrite ra­ vein alteration types. The process has been modeled by Norton tio than is common in potassium-silicate wall rocks. (1979, 1982), and the chemical processes have been modeled by Helgeson (1970). Field evidence from mapping of alteration Mafic Rocks sequences and temperature determinations on fluid inclusions indicate that predictable changes in alteration mineralogy take I. Amphibolites, basalt, diabase, and hornblende diorite are place under falling temperatures as the system cools The chemi­ wall rocks of a few porphyry copper systems. All alter in much cal conditions in the convection cells range from reducing at the same way: Biotite which replaces hornblende, is the domi­ depth to oxidizing and acid near the surface where meteoric nant pervasive alteration product. water is involved. The process of repetitious fracturing appears 2. Mineralization is associated mostly with quartz veins of to be enhanced by "case-hardening" of the stockwork as each biotitized masses, and vein selvages may contain minor amounts stage of fractures is altered. of orthoclase locally. MAPPING AND MODELS Supergene Alteration The 1970s and 1980s were times of great interest in ore de­ l . With only few exceptions development and mining of the posit models. Models as shown and defined by a variety of major porphyry copper deposits of the region commenced in workers in a variety of ways purport to show some common fea­ supergene-enriched copper sulfide. The weathering processes tures through which a class or some properties of a class of that formed the enriched ores also altered rocks of the original deposits can be described. As such they range from single dia­ mineral assemblage. This process and its results have been rec­ grams that show the general features of deposits to groups of ognized for more than a century and were first reported in detail diagrams that attempt to show stages in evolution of dynamic for porphyry copper deposits at Morenci by Lindgren (1905). hydrothermal systems. Much of the interest in models of the 2. The chemical process stems from the weathering of porphyry systems stemmed from publication of the Lowell and pyrite, which produces acid necessary to the formation of silica, Guilbert (1970) diagrams depicting features of lateral and verti­ clays, sulfates, and oxides in a horizontally layered body of oxi­ cal zoning of these systems, apparently adapted from the zoning dized rock and leached capping included within and overlying a shown by Lowell (1968) at Kalamazoo. zone of economic copper enrichment. A number of variants in the model for porphyry copper 3. Alteration products are those of the acid-oxidizing environ­ deposits were proposed by Sutherland Brown (1976), who drew ment and mimic to a significant degree the hypogene advanced from the examples in western Canada. Hollister (1978) sug­ argillic alteration of the shallow, near surface hydrothermal gested models based upon composition of associated porphy­ environment. Intermittent study of these processes and products ries. A useful descriptive model was developed by McMillan GEOLOGICAL SUMMARY A D PERSPECTIVE OF PORPHYRY COPPER DEPOSITS IN SOUTHWESTERN NORTH AMERICA 17

... r",,. r • ALTERATION

"\.0 ... .. , TYPES ... r .. �< > ,,� : .. marble and skarn "", ...... ,...... i±B3: skarn ore )O.5%Cu

--- quortz-sericite-- -- py veins

K- spar, qtz veins in intrusions qtz.- chlorite veins in andesite Laramide

volcanics .. . , , .

' . c disseminated biotite Paleozoic.' , D' in andesite limestone / bi

o 250 500

metres

Figure 7. Geologic map of the orebody and host lithologies at Christmas, alteration minerals on an early biotite-stable alteration in the andesite. The Arizona, after Koski and Cook (1982) and Einaudi (1982a). The intrusion shaded outer boundary in andesite is the outer limit of biotite as both re­ is in contact with Paleozoic carbonates in its western half and with placement of hornblende of the andesite and as scattered biotite veinlets. Laramide andesite on its eastern half; the disseminated copper orebody The map shows in an elegant way the habits of alteration of many ore sys­ occurs with skarn in the limestone block in the west. Alteration affects tems in the southwest. both of the contrasting lithologies and represents overprinting of K-silicate and Panteleyev (1980). A dynamic model showing the evolution ure shows a geological profile that is characteristic of regions of the EI Salvador deposit in a series of three-dimensional per­ where Paleozoic platform carbonate successions overly craton spectives was published by Gustafson and Hunt (1975), Models and have been importantly involved in alteration and mineraliz­ based upon metallogenesis (copper, copper-molybdenum, cop­ ing processes in plutonic environments. per-gold) were suggested in text and diagrams by Singer and Cox (1986). PERSPECTIVE To be accurate and useful, models must relate to the reali­ ties of geological environments and deposits. Great variation in The high rate of discovery of copper ores in the region dur­ porphyry copper deposit styles exists in the American south­ ing the last half century is a manifestation of three major devel­ west, where wall rocks and levels of exposure vary widely. opments: (I) an increasingly enhanced understanding of the Whereas the Lowell-Guilbert model portrays zoning in a homo­ nature of the deposits, (2) development and refinement of explo­ geneous (granitic) wall rock, the more common case in this re­ ration technology from outcrop interpretation to geophysical gion is that of a pluton in wall rocks of varying composition, methods, and (3) increasingly efficient mining and processing Christmas, Arizona is a system evolved in a varied wall rock methods, environment The map of this system, adapted and modified Research into the formation of porphyry copper deposits from Koski and Cook (1982) and Einaudi (1982a, 1982b), is has been significant, and published work reveals a deep insight shown in figure 7, into processes of ore formation. Modeling of fluid flow to incor­ This deposit manifests many of the diverse features of por­ porate the changing chemistry along hydrothermal paths repre­ phyry districts of the region: The presence of carbonate strata sents a significant advance in understanding hydrothermal and volcanic rocks, the overprinting of contrasting alteration process geology and geochemistry and demonstrates that types in the two host rock assemblages, and the biotite aureole at changes in alteration chemistry attend the process (Helgeson, Christmas are features common to many porphyry copper dis­ 1970; Norton, 1979, 1982). Important questions involving the tricts in the American southwest Another model portraying link between ore-forming processes and environments remain, many fundamental and relevant features of porphyry copper de­ however- The answers to these questions will significantly ad­ posits is that developed by Jerome (1966), a part of which has vance our understanding of these systems and our knowledge of been modified and adapted for discussion here (fig, 8), The fig- the nature of metallogenic regions, 18 S. R. TITLEY

ALTERATION PATTERN

PROP. (mus, ep , chi, cal,elc)

ARG. (monl, kaol, elc)

K - SIL . (mus , bi, kspar\etc)

EXPLANATION

SUPERGE NE ZONE HYPOGENE METALLIZATION

wtO/o sulfide I o copping Zone of leaching I'- 2% Leached l� jj�1 0. 3- 1.0% I�I Sup rgene enrichment 0. 5-5 HYPOGENEe ZONE

m Cu Calc-silicates Disseminated Cu ore � in m Leod -Zinc ore I��t;� Moonetite ore

ROCK TYPES

[ /M bl Marble line E'J Breccio pipe/dike � Intrusion complell � � Carbonate rocks Volcanics, SS,ork,sh. EZl Adopled ond Modified from Jerome (1966) S. E . Figure 8. Cross section through a weathered porphyry copper deposit in grammed above the section and habits of hypogene sulfide minerals have the American southwest, adapted and modified from Jerome (1966). The been added to complete the diagram. This diagram is the progenitor of section incorporates the weathered and enriched portions of a porphyry many subsequent portrayals of porphyry copper deposit "models" and reo system centered on an intrusion which penetrates a variety of different tains its value at the end of the century. wall rocks. General features of overprinted hypogene alteration are dia-

Questions concerning the crustal controls for the localiza­ Southwestern North America: Tucson, University of Arizona Press, tion of these ore deposits and the reasons for their extraordinary p. 3-16. abundance in the region remain. Further, the question of the Anderson, CA., 1968, Arizona and Adjacent New Mexico, in Ridge, 1.0., ed., source of both primary and accessory metals in these systems Ore Deposits in the United States, 193311967: New York, American has yet to be solved. Plate-tectonic theory and reconstructions Institute of Mining, Metallurgical, and Petroleum Engineers, Inc., are consistent with interpretations of localized crustal stress, but p. 1 163-1190. linear distributions of deposits in belts paralleling the old conti­ Anderson, CA., Scholz, E.A., and Strobell, 1.0., 1955, Geology and ore depos­ nental margin resurrect older notions of linear crustal controls. its of the Bagdad area, Ya vapai County Arizona: U.S. Geological Survey Professional Paper 278, 103 p. Contrasts in alteration mineralogy as functions of crustal litholo­ Anderson, 1.A., 1982, Characteristics of leached capping and techniques of gies and data suggesting a crustal provenance for both magmas appraisal, Titley, S.R., ed., Advances in geology of the porphyry in and precious metals in these ores (Anthony and Titley, 1988b) copper deposits, Southwestern North America: Tucson, University leave open important questions of the extent of crustal influ­ of Arizona Press, p. 275-296. ences. If it is held that metals are contained in and transported Anderson, T.A., and Silver, L.T., 1981, An overview of Precambrian rocks in with magmas, logic requires that the crust be the site of the Sonora: Universidad National Autonomous Mexico, Instituto penultimate metal province. Geologia, Revista, v. 5, no. 2, p. 131-139. Anthony, E. and Titley, S.R., 1988a, Pre-mineralization igneous processes at Y, ACKNOWLEDGMENT the Sierrita porphyry copper deposit, Arizona, U.S.A: Proceedings, 7th Quadrennial IAGOD Symposium, Lulea, Sweden: Stuttgart, E. Schweizerbart'sche Verlagsbuchhandlung, p. 535-546. I had the privilege of knowing Harold Courtright and Anthony, E. and Titley, S.R., 1988b, Progressive mixing of isotopic reser­ Y, Kenyon Richard, both of them gentlemen and professionals of voirs during magma genesis at the Sierrita porphyry copper deposit, the highest quality. Their contributions added significantly to the Arizona; Inverse solutions: Geochemica et Cosmochimica Acta, v. knowledge reported here. 52, p. 2235-2249. Beane, R.E. 1982, Hydrothermal alteration in silicate rocks southwesternNorth REFERENCES America, Titley, S.R., ed., Advances in geology of the porphyry ill copper deposits, Southwestern North America: Tucson, University Anderson, CA., 1950, Alteration and metallization in the Bagdad porphyry of Arizona Press, p. 117-138. copper deposit, Arizona: Economic Geology, v. 45, p. 609-628. Beane, R.E., and Titley, S.R., 1981, Porphyry copper deposits, Part II, Hydro­ Anderson, CA., 1966, Areal geology of the southwest, ill Titley, S.R., thermal alteration and metallization: Economic Geology, 75th Anni­ and Hicks, CL., eds., Geology of the porphyry copper deposits, versary Vo lume, p. 235-269. GEOLOGICAL SUMMARY AND PERSPECTIVE OF PORPHYRY COPPER DEPOSITS IN SOUTHWESTERN NORTH AMERICA 19

Beard R.R., 1989, The primary copper industry of Arizona: Arizona Depart­ Courtright, J.H., 1958, Progress report on investigation of some Cretaceous­ ment of Mines and Mineral Resources Special Report 16, 74 p. Tertiary formations in southeastern Arizona: Tucson, Arizona Geo­ Bennett, VC. and DePaolo, 0.1., 1987, Proterozoic crustal history of the west­ logical Society Digest I, p. 7-9. ern United States as determined by neodymium isotopic mapping: Damon, P. E., Shafiqullah, Muhammad, and Clark, K.E, 1983, Geochronology Geological Society of America Bulletin, v. 99, p. 674-685. of the porphyry copper deposits and related mineralization of Billingsley, Paul, and Locke, Augustus, 1935, Tectonic position of ore districts Mexico: Canadian Journal ofEarth Sciences, v. 20, p. 1052- 1071. in the Rocky Mountain region: Transactions of the American Insti­ Davis, G.H., 1979, Laramide folding and faulting in southeastern Arizona: tute of Mining and Metallurgical Engineers, v. 115, p. 59-68. American Journalof Science, v. 279, p. 543-569. Billingsley, Paul, and Locke, Augustus, 1941, Structure of ore districts in the Dunn, P.G., 1982, Geology of the Copper Flat porphyry copper deposit, continental framework: Transactions of the American Institute of Hillsboro, Sierra County, New Mexico, Titley, S.R., ed., Ad­ in Mining and Metallurgical Engineers, v. 144, p. 9-64. vances in geology of the porphyry copper deposits, Southwestern Bloom, Harold, 1966, Geochemical exploration as applied to copper-molybde­ North America: Tucson, University of Arizona Press, p. 313-325. num deposits, Titley, S.R., and Hicks, c.L., eds., Geology of the Einaudi, M.T., 1982a, Description of skarns associated with porphyry copper in porphyry copper deposits, Southwestern North America: Tucson, plutons, southwestern North America, Titley, S.R., ed., Advances in University of Arizona Press, p. 111- 120. in geology of the porphyry copper deposits, Southwestern North Brant, A.A., 1966, Geophysics in the exploration for Arizona porphyry coppers, America: Tucson, University of Arizona Press, p. 139- 1 84. Titley, S.R., and Hicks, c.L., eds., Geology of the porphyry cop­ Einaudi, M.T., 1982b, General features and origin of skarns associated with in per deposits, Southwestern North America: Tucson, University of porphyry copper plutons southwestern North America, Titley, in Arizona Press, p. 87-110. S.R., ed., Advances in geology of the porphyry copper deposits, Burnham, C. Wayne, 1967, Hydrothermal fluids at the magmatic stage, Southwestern North America: Tucson, University of Arizona Press, in Barnes, H.L., ed., Geochemistry of hydrothermal ore deposits: New p. 185-210. York, Holt, Rinehart and Winston, p. 34-76. Farmer, G.L., and DePaolo, 0.1., 1983, Origin of Mesozoic and Te rtiary granite Burnham, C. Wayne, 1979, Magmas and hydrothermal fluids, Barnes, H.L., in the western United States and implications for pre-Mesozoic in ed., Geochemistry of hydrothermal ore deposits, 2nd Edition: New crustal structure - I. Nd and Sr isotopic studies in the geocline of York, John Wiley and Sons, p. 71-136. the northern Great Basin: Journal of Geophysical Research, v. 88, Burnham, C. Wayne, 1981, Physicochemical constraints on porphyry mineral­ p. 3379-340 I. ization, Dickinson, W.R. and Payne, W. D., eds., Relations of tec­ Farmer, G.L., and DePaolo, 0.1., 1984, Origin of Mesozoic and Te rtiary granite in tonics to ore deposits in the Southern Cordillera: Tucson, Arizona in the western United States and implications for pre-Mesozoic Geological Society Digest 14, p. 71-78. crustal structure - 2. Nd and Sr isotopic studies of unmineralized Burnham, C. Wayne, and Ohmoto, Hiroshi, 1980, Late-stage processes of felsic and Cu- and Mo-mineralized granite in the Precambrian craton: magmatism, Ishihara, Shunso, and Takenouchi, Sukune, eds., Journalof Geophysical Research, v. 89, p. 10141-10160. ill Granitic magmatism and related mineralization: Society of Mining Gilmour, Paul, 1982, Grades and tonnages of porphyry copper deposits, ill Geologists of Japan, Mining Geology Special Issue No. 8, p. I-II. Titley, S.R., ed., Advances in geology of the porphyry copper Butler, B.S., 1933, Ore deposits as related to stratigraphic, structural and igne­ deposits Southwestern North America: Tucson, University of Ari­ ous geology in the westernUnited States; Part I, Summary, Finch, zona Press, p. 7-36. in J.W., ed., Ore deposits of the Western States: New York, American Gustafson, L.B., 1978, Some major factors of porphyry copper genesis: Eco­ Institute of Mining and Metallurgical Engineers, p. 198-240. nomic Geology, v. 73 p. 600-607. Chaffee, M.A., 1982a, A geochemical study of the Kalamazoo porphyry copper Gustafson, L.B., and Hunt, J.P. 1975, The porphyry copper deposit at EI Salva­ deposit: Pinal County, Arizona, Titley, S.R., ed., Advances in dor, Chile: Economic Geology, v. 70, p. 857-912. ill geology of the porphyry copper deposits, Southwestern North Haynes, EM., and Titley, S.R., 1980, The evolution of fracture-related perme­ America: Tucson, University of Arizona Press, p. 211-226. ability within the Ruby Star Granodiorite, Sierrita porphyry copper Chaffee, M.A., 1982b, Geochemical prospecting techniques for porphyry cop­ deposit, Pima County, Arizona: Economic Geology, v. 75, p. 673- per deposits: Southwestern United States and Northern Mexico, 683. ill Titley, S.R., ed., Advances in geology of the porphyry copper de­ Heidrick, T.L., and Titley, S.R., 1982, Fracture and dike patterns in Laramide posits, Southwestern North America: Tucson, University of Arizona plutons and their structural and tectonic implication; American Press, p. 297-3 12. southwest, ill Titley, S.R., ed., Advances in geology of the porphyry Chamberlain, K.R., and Bowring, S.A., 1990, Proterozoic geochronologic and copper deposits, Southwestern North America: Tucson, University isotopic boundary in NW Arizona: Journal of Geology, v. 98, of Arizona Press, p. 73-91. p. 399-416. Helgeson, H.C., 1970, A chemical and thermodynamic model of ore deposition Coney, 1978, The plate tectonic setting of southeastern Arizona, in hydrothermal systems: Mineralogical Society of America Special P.1., ill Callender J.E, Wilt, J.c., and Clemons, R.E., eds., Land of Cochise, Paper 3, p. 155-186. SoutheasternArizona: Arizona Geological Society and New Mexico Hollister, VE 1978, Geology of the porphyry copper deposits of the Western Geological Society, 29th Field Conference Guidebook, p. 285-290. Hemisphere: New York, American Institute of Mining and Metallur­ Coney, P.1 ., and Campa, M.E, 1987, Lithotectonic terrane map of Mexico west gical Engineers, 219 p. of the 9 I st Meridian: U.S. Geological Survey Miscellaneous Field Jerome, S.E., 1966, Some features pertinent in exploration of porphyry copper Studies Map MF- 1 874-D, :2,500,000 (with text). deposits, Titley, S.R., and Hicks, c.L., Geology of the porphyry I ill Cornwall, H.R., 1982, Petrology and chemistry of igneous rocks, Ray porphyry copper deposits, Southwestern North America: Tucson, University copper district, Pinal County, Arizona, ill Titley, S.R. ed., Advances of Arizona Press, p 75-85. in geology of the porphyry copper deposits, Southwestern North Jerome, S.E., and Cook, D.R., 1967, Relation of some metal mining districts in America: Tucson, University of Arizona Press, p. 259-274. the western United States to regional tectonic environments and Creasey, S.c., 1966, Hydrothermal Alteration, Titley, S.R., and Hicks, c.L., igneous activity: Nevada Bureau of Mines Bulletin 69, 35 p. in eds., Geology of the porphyry copper deposits, Southwestern North Kanbergs, Karlis, 1980, Fracturing along the margins of a porphyry copper sys­ America: Tucson, University of Arizona Press, p. 51-74. tem, Silver Bell district, Pima County, Arizona: University of Ari­ Creasey, S.c., 1977, Intrusives associated with porphyry copper deposits: Geo­ zona, M.S. Thesis (unpublished), 90 p. logical Society of Malaysia Bulletin, v. 9, p. 51-66. Kistner, 0.1., 1984, Fracture study of a volcanic Iithocap, Red Mountain por- 20 S. R. TITLEY

phyry copper prospect: University of Arizona M.S. thesis (unpub­ Sillitoe, R.H., 1972, Relation of metal provinces in westem America to subduc­ lished), 75 p. tion of oceanic lithosphere: Geological Society of America Bulletin, Koski, R.A., and Cook, D.S., 1982, Geology of the Christmas porphyry copper v. 83, p. 813-8 18. deposit, Gila County, Arizona, Titley, S.R., ed., Advances in geol­ Sillitoe, R.H., 1975, Subduction and porphyry copper deposits in southwestern in ogy of the porphyry copper deposits, Southwestern NorthAmerica: North America - a reply to recent objections: Economic Geology, Tucson, University of Arizona Press, p. 353-374. v. 70, p. 1474- 1477. Krantz, R.W., 1989, Laramide structures of Arizona, Jenney, J.P., and Sillitoe, R.H., 1976, A reconnaissance of the Mexican porphyry copper belt: In­ in Reynolds, S.1., eds. Geologic evolution of Arizona: Tucson, Arizona stitute of Mining and Metallurgy Transactions, Section B, Applied Geological Society Digest 17, p. 463-483. Earth Science, v. 85, p. 169- 190. Lang, J .R., 1991, Isotopic and geochemical characteristics of Laramide igneous Singer, D.A. and Cox, D.P., 1986, Mineral deposit models: U.S. Geological rocks in Arizona: Tucson, University of Arizona Ph.D. Dissertation, Survey Bulletin 1693., 379 p. 201 p. Streckheisen, A.L., 1973, lUGS Subcommission on the systematics of igneous Lipman, P. W., and Sawyer, D.A., 1985, Mesozoic ash-now caldera fragments rocks; Classification and nomenclature of plutonic rocks: Geotimes. in southeasternArizona and their relation to porphyry copper depos­ October 1973, p. 26-30. its: Geology, v. 13, p. 652-656. Stringham, Bronson, 1966, Igneous rock types and host rocks associated with Lindgren, Waldemar, 1905, The copper deposits of the Clifton-Morenci district, porphyry copper deposits, Titley, S.R., and Hicks, CL., eds., in Arizona: U.S. Geological Survey Professional Paper 43, 375 p. Geology of the porphyry copper deposits, Southwestem North Lowell, J.D., 1968, Geology of the Kalamazoo orebody, San Manuel, Arizona: America: Tucson, University of Arizona Press, p. 35-50. Economic Geology, v. 63, p. 645-654. Sutherland Brown, A., ed., 1976, Porphyry deposits of the Canadian Cordillera: Lowell, J.D., 1974, Regional characteristics of porphyry copper deposits of the Canadian Institute of Mining and Metallurgy Special Vo lume 15, southwest: Economic Geology, v. 69, p. 601-617. 510p. Lowell, J.D. and Guilbert, J.M. 1970, Lateral and vertical alteration zoning in Titley, S.R., 1976, Evidence for a Mesozoic linear tectonic pattern in southeast­ porphyry ore deposits: Economic Geology, v. 65, p. 373-408. ern Arizona, Wilt, J .C, and Jenney, J.P., eds., Tectonic Digest: in Mayo, E.B., 1958, Lineament tectonics and some ore districts of the southwest: Tucson, Arizona Geological Society Digest 10, p. 71-101. Mining Engineering, Nov., p. 1169- 1175. Titley, S.R., 1981, Geologic setting of porphyry copper deposits, Dickinson, in McMillan, WJ., and Panteleyev, Andrejs, 1980, Ore deposit models - I. Por­ W.R., and Payne, eds., Relations of tectonics to ore deposits in the phyry copper deposits: Geoscience Canada, v. 7, p. 52-63. SouthernCordillera: Tucson. Arizona Geological Society Digest 14, Noble, J.A., 1970, Metal provinces of the westem United States: Geological p. 75-94. Society of America Bulletin, v. 81, p. 1607- 1 624. Titley, S.R., 1982a, Advances in geology of the porphyry copper deposits, Noble, J.A., 1976, Metallogenic provinces of the cordillera of western North Southwestern North America: Tucson, University of Arizona Press, and South America: Mineralium Deposita, v. II, p. 219-233. 560 p. Norris, J.R., 1981, Fracturing, alteration, and mineralization in oxide pit, Silver Titley, S.R., 1982b, Geologic setting of porphyry copper deposits, Southeastem Bell mine, Pima County, Arizona: University of Arizona M.S. thesis Arizona: Titley, S.R., ed., Advances in geology of the porphyry in (unpublished), 72 p. copper deposits, Southwestern North America: Tucson, University Norton, D.L., 1979, Transport phenomena in hydrothermal systems; the redis­ of Arizona Press, p. 37-58. tribution of chemical components around cooling magmas: Bulletin Titley, S.R., 1982c, The style and progress of mineralization and alteration in Mineralogie, v. 102, p. 47 1 -486. porphyry copper systems, American southwest, Titley, S.R., ed., in Norton, D.L., 1982, Fluid and heat transport phenomena in pluton environ­ Advances in geology of the porphyry copper deposits, Southwestern ments, southeasternArizona, Titley, S.R., ed., Advances in geol­ North America: Tucson, University of Arizona Press, p. 93-116. in ogy of the porphyry copper deposits, Southwestern NorthAmerica: Titley, S.R., 1992, Evidence for crustal controls of metallogenesis in epigenetic Tucson, University of Arizona Press, p. 59-72. ores of the southern cordillera, United States and Mexico: Society Parsons, A.B., 1933, The Porphyry Coppers: New York, American Institute of for Mining Metallurgy and Exploration Preprint 92-210, li p. Mining and Metallurgical Engineers, 581 p. Titley, S.R., 1994, Porphyry copper deposits in the American Southwest [abs.J, Parsons, A.B., 1957, The Porphyry Coppers in 1956: New York, American In­ Thorman, CH., and Lane, D.E., eds., U.S. Geological Survey re­ in stitute of Mining and Metallurgical Engineers, 270 p. search on mineral resources - 1994, Part B - Guidebook for field Peterson, N.P.,Gilb ert, CM., and Quick, G.L., 1946, Hydrothermal alteration trips: U.S. Geological Survey Circular 1103-B, p. 15-23. in the Castle Dome copper deposit Arizona: Economic Geology, Titley, S.R., and Anthony, E. 1989, Laramide mineral deposits in Arizona, Y, in v. 41, p. 820-840. Jenney, J.P', and Reynolds, S.1., eds., Geologic evolution of Ari­ Reynolds, S.1., Florence FP., Currier, D.A., Anderson, AV, Trapp, R.A., and zona: Tucson, Arizona Geological Society Digest 17, p. 485-5 14. Keith, S.B., 1985, Compilation of K-Ar age determinations in Ari­ Titley, S.R., and Beane, R.E., 1981, Porphyry copper deposits, Part I, Geologic zona: Arizona Bureau of Geology and Mineral Tec hnology Open­ settings, petrology, and tectogenesis: Economic Geology 75th Anni­ File Report 85-8, 320 p. versary Vo lume: p. 214-235. Richard, Kenyon, and Courtright, J.H., 1954, Structure and mineralization at Titley, S.R., and Hicks, CL., eds., 1966, Geology of the porphyry copper de­ Silver Bell, Arizona: American Institute of Mining and Metallurgy posits, Southwestern North America: Tucson, University of Arizona Transactions, v. 199, p. 1095-1 099. Press, 287 p. Richard, Kenyon, and Courtright, J.H., 1960, Some Cretaceous-Tertiary rela­ Titley, S.R., Thompson, R.C, Haynes, EM., Manske, S., Robison, L.C, and tionships in southeastern Arizona: Arizona Geological Society Di­ White, J.L., 1986, Evolution of fractures and alteration in the gest 3, p. 1-7. Sierrita-Esperanza hydrothermal system, Pima County, Arizona: Sales, R.H., and Meyer, Charles, 1948, Wall rock alteration at Butte, Montana: Economic Geology, v. 81, p. 343-370. New York, Transactions of the American Institute of Mining and Wadsworth, WB., 1968, The Cornelia pluton, Aj o, Arizona: Economic Geol­ Metallurgical Engineers, v. 178, p. 9-35. ogy, v. 63, p. 101-1l5. Schmitt, H.A., 1966, The porphyry copper deposits in their regional setting, Wyllie, 1981, Magma sources in cordilleran settings, Dickinson, WR., in P.1., in Titley, S.R., and Hicks, CL., eds., Geology of the porphyry copper and Payne, W.D., eds., Relations of tectonics to ore deposition in the deposits, Southwestern North America: Tucson, University of Ari­ Southern Cordillera: Tucson, Arizona Geological Society Digest 14, zona Press, p. 17-33. p. 39-48.