The Warren (Bisbee) Mining District Cochise County, Arizona Ralph J. Stegen Ernest Wright Donald G. Bryant Arizona Geological Society Spring Field Trip April 30, 2005 THIS PAGE INTENTIONALLY BLANK Dear Field Trip Participant, Welcome to the Arizona Geological Society Spring 2005 field trip to Bisbee, Arizona. We are grateful to our Society President, Ralph Stegen (Vice President, Mine-Site Exploration, Phelps Dodge Exploration Corp.), for organizing and co-leading this trip with Ernest Wright (Phelps Dodge Mining Co., Copper Queen Branch) and Donald Bryant (Denver, Colorado), and to the management of Phelps Dodge Corp. for granting us access to the company property in Bisbee. On this trip, we will visit one of Arizona’s most famous mineral districts with a rich history that is well documented at the Bisbee Mining and Historical Museum (a must-see!). Our trip leaders will take us to outcrops of the Jurassic porphyry copper deposit and associated base- and precious-metal-bearing manto deposits and supergene-enriched copper deposits throughout the district (see maps on pages 3 and 22). Safety is a primary concern for Phelps Dodge. Wear your personal protective equipment at all times. Look for comments regarding your safety in the guidebook at particular stops. And, please pay attention to your surroundings for your safety and the safety of your fellow participants. Enjoy the trip! Thank you, David Maher (VP Field Trips) THIS PAGE INTENTIONALLY BLANK Field Guide to the Warren (Bisbee) Mining District Cochise County, Arizona Ralph J. Stegen, Phelps Dodge Exploration Corp., 10861 N. Mavinee Drive, Suite 163, Tucson, Arizona 85737 Ernest Wright Phelps Dodge Mining Co., Copper Queen Branch, 36 West Highway 92, Bisbee, Arizona 85603 And Donald G. Bryant 714 South Fillmore Street, Denver, Colorado 80209 Guidebook for the Arizona Geological Society Spring Field Trip April 30, 2005 THIS PAGE INTENTIONALLY BLANK Introduction The ore deposits at Bisbee were discovered in outcrop in 1876 by U.S. Calvary scouts searching for water. The first mining claim in the district was staked in 1878 on a cerussite and silver occurrence. In 1880, an outcropping mass of malachite and azurite with iron and manganese oxides was found along the northern slope of Queen Hill. The near-surface ores were produced until the 1890s when copper sulfide minerals were found within the deeper levels of the orebodies. Sulfide ores became predominant and were mined from Paleozoic sedimentary rocks until the mines were closed in 1975. Chalcopyrite and bornite fragments within breccia subsequently enriched by chalcocite and a chalcocite blanket were also mined from the Sacramento and Lavender pits. Production: The district has produced copper from oxidized and sulfide manto ores and two periods of open pit mining. A summary of the production is below. The average district grade for the manto deposits is 6.0%, but in many of the oxidized orebodies grades of 12 to 23% was common. It also should be noted that the underground mining cutoff for the sulfide manto ores was around 3.5% copper. In addition to copper, the district has been a significant producer of gold (about 3 million ounces), zinc (355 million pounds), lead (324 million pounds), silver (102 million ounces) and manganese (28 million pounds). Ore Leach Grade Tons Years Type (000) Tons (000) (%Cu) 1880-1975 Manto 53,000 6.00 1919-1929 Sacramento Pit Ore 9,000 2.00 Sacramento Pit 1919-1929 Leach 12,000 0.72 1954-1974 Lavender Pit -Ore 92,674 0.81 1954-1974 Lavender Pit -Leach 109,515 0.35 Local Geology of Bisbee Previous studies : The geology of the Warren Mining District has been very well described by governmental and mining company geologists. Two excellent comprehensive descriptive papers on the Bisbee geology and orebodies have been published (Ransome, 1904; Bonillas, 1916). Later published works provided district overviews and a synthesis of the geology of the orebodies (Tenney, 1932; Trischka, 1938; Wisser, 1927). Carpenter (1941) provided a concise description of the sulfide zoning and ore controls of the 1 MISCELLANEOUS GEOLOGIC INVESTIGATIONS MAP 1-418 E X P LANATION OISCONFORMITY >­ l{ a: Alluvium Landslide deposit « Source rock indicated by color z a: Escabrosa Limestone w Medium- to light-gray thick-bedded to massive cri:noidal I­ limestone and medi'lJ.m- to dark-gray thin-bedded « limestone. 665 to 7S5feet thick :> Pediment, terrace, and fan gravels o DISCONFORMfTY Valley fill Martin Limestone Medium- to dark-gray limestone, marl, dolomite and UNCONFORMITY >­ sandy dolomite, and calcareous siltstone. 2.90 to 475 a: « feet thick j: DISCONFORMITY a: w Intrusive quartz iatite porphyry I- Includes gneissic granite in sec. 15, T. 23 S., R. 23 E.; ~ hornblende diorite in sec. 25, T. 23 S., R. 24 E.; and Abrigo Limestone altered diorite (1) in sec. 24. T. 23 S., R. 23 E. and in sec. 92, T. 23 S., R. 2S E. ~" Laminated hor:rifels with subordinate interlaminated .~ limestone, silty and argillaceous limestone, and chert in basal 250 feet; next 200 feet is mostly interlami­ h nated silty limestone and chert with limestone edge­ z ~8 wise conglomerate common; next 180± jeet is mostly ~ glauconitic sandy dolomite and dolomitic sandstone a: ~ ID Cintura Formation with minor interbedded marl; top 40 to 100 feet is :;0 Grayish-red siltstone and mudstone, pale-red /eld­ medium-gray laminated limestone that is locally « spathic sandstone, and minor greenish-gray calcar­ dolomitized. Total thickness 700± feet u eous claystone; afew thin beds ojimpurejQssilijerous limestone in basal 100 feet. Maximum preserved thickness about 1,890 feet ~.~ ~~ Bolsa Quartzite ~(i ~ '{ Resistant yellowish- fAJ reddish-brown-weathering silueous sandstone. SOO to 450feet thuk ~ UNCONFORMITY z Mural Limestone <JI Kmu. upper member, medium dark-gray limestone in :> relatively thick beds, subordinate sandstone in upper 0 W 50 feet. 220 to 275 feet thick. u .1 { Kml, lower member, interbedded light olive-gray­ « weathering calcareous sandstone and siltstone and I- ]1 Pinal Schist impure fossiliferous limestone. SSo to 435 feet thick W J; Dominantly drab muscovite, chlorite, and quartz schist a: Ha: u D-- Morita Formation Contact Grayish-red siltstone and mudstone, pinkish-gray to Dashed where approximately located pale-red feldspMhic sandstone, and minor greenish­ gray calcareous claystone; a few thin beds of impure. - -g---?-_... ... limestone in upper part and very subordinate pebble conglomerate in lower part. 2,600 feet thick Fault Dashed where approximately located; dotted where concealed; queried where doubtful. U, upthroum side; D, doumthroum side Reverse fault Glance Conglomerate Dotted where COl/cealed; R, upthrQ-wn side Locally derived boulder-to-pebble conglomerate with grayish-red matrix. 0 to more than 600feet thick Thrust fault UNCONFORMITY Dashed where approximately located. Sawteeth on upper plate Low-angle fault of uncertain displacement Juniper Flat Granite Teeth on upper plate Stock and associated dikes of porphyritic leucocratic alkali granite }r Strike and dip of beds .;1" z -+- ~ Strike of vertical beds Colina Limestone :;0 ~ Medium-gray thick-bedded limestone, slightly cherty in a: -+'- part. Maximum preserved thickness about 500 feet w BJ ! D-- Strike and dip of overturned beds .~ Strike and dip of foliation ~ II G ~.;; Earp Formation ;:,~ 0. Pale-red calcareous siltstone and mudstone with iub­ Strike of vertical foliation " ordinate medium-gray thin-bedded limestone and ~" ~ marl. S50 to 540 feet thick z <JI 0 ~ :> !Phu z o £ « a: I--- > w !Ph IPhm ...J u. I--­ >­ z !Phi <JI o li Z [* Origina l figure conta ins handwritten annotation: "174 m.y."] In 11] Horquilla Limestone Z a: Medium light-gray medium-bedded limestone with sub­ W « "~ D-- oS" ordinate pale-red calcareous siltstone and silty lime- u [** Original figure conta ins handwritten annotation: ~~ 8Urne. ~ IPhu, upper member, about «Ofeet thick. "Sacramento Hill IP h m, middle member, dominantly silty, about 180 feet thick. Cochise Por IP hl, lower member, about 600 feet thick 198-200 m. y."] 2 ~~.:I- '--J~~~ 1~'1:=;;;;;"'-l' "":..,=-=~-_~= + Campbell orebody while mining was active. Two important Ph.D. dissertations were generated in the 1960s. The first was by Bryant (1964) that discussed the nature of the intrusive hydrothermal breccias in the district. The second was by Nye (1968) who studied the relationship of structure and host rocks to the high- grade manto ores in the district. The mining companies frequently hired consultants to work with the geology department to identify and generate exploration targets. The work by Blanchard (1926) and Boutwell (1910) are notable as they formulated guides to ore that were instrumental in the development of the district through the 1930s. One of the relatively recent publications of the district was by Bryant and Metz (1966) in which the geology of the Lavender pit was presented with a clear focus on describing the Sacramento Hill intrusive rocks and breccias. Stratigraphy The stratigraphic framework of the district was described by Ransome (1904). Wisser (1926) added details from underground exposures not available to Ransome. A geologic map of the Bisbee district by Hayes and Landis (1964) is shown on page 3. Detailed rock descriptions can be found in the published references, and only general descriptions will be included here. The stratigraphy of the district includes a basement of Precambrian schist, which is overlain with 5,000 feet of Paleozoic sedimentary rocks. Cutting the Precambrian and Paleozoic rocks are Jurassic-aged stocks, dikes and breccia bodies. A thick sequence of Cretaceous conglomerate, sandstone, siltstone, and limestone crops out to the east and north of Bisbee. Pinal Schist : The oldest rock in the district is the Precambrian Pinal Schist. Neither the top nor the bottom the Pinal Schist has been found. The schist is pale green to white on a fresh surface and may be pink when weathered. These rocks are quartz-muscovite and quartz-sericite schist and phyllite.