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1 Southeastern migration of the Laramide porphyry copper mineralization in 2 northeastern Sonora based on available and new Re-Os and U-Pb geochronology: 3 implications in exploration along the Cananea lineament. 4 5 6 Rafael Del Rio-Salas (1); Lucas Ochoa-Landín (2); Martín Valencia-Moreno (1); Thierry 7 Calmus (1); Diana Meza-Figueroa (2); Sergio Salgado-Souto (3,4); Jason Kirk (3); Joaquin 8 Ruiz (3); Héctor Mendívil-Quijada (5) 9 10 (1) Estación Regional del Noroeste, Instituto de Geología, Universidad Nacional Autónoma 11 de Mexico. L.D. Colosio y Madrid S/N, Col. Los Arcos, Hermosillo, Sonora, 83240 México. 12 13 (2) Departamento de Geología, División de Ciencias Exactas y Naturales, Universidad de 14 Sonora, Rosales y Encinas, Hermosillo, Sonora, 83000 México. 15 16 (3) Geosciences Department, University of Arizona, 1040 E 4th St, Tucson Arizona, 85721 17 USA. 18 19 (4) U.A. Ciencias de la Tierra, Universidad Autónoma de Guerrero, Ex-Hacienda San Juan 20 Bautista s/n, Taxco el Viejo, Guerrero 40323, México 21 22 (5) GEO Digital Imaging de México, S.A. de C.V, Hermosillo, Sonora, México. 23 24 25 26 Corresponding Author: [email protected] 27 28 29 30 31 32 33 34 35 36 37 To be submmited to Ore Geology Reviews 38 39 40 41 42 43 44 45 46 47 ABSTRACT
48 The Cananea mining district encompasses the most important copper deposits in Mexico, which,
49 together with the porphyry copper deposits from southern Arizona and western New Mexico,
50 conform one of the largest copper provinces on Earth. The main mineralized localities within the
51 district are the Buenavista del Cobre, formerly called the Cananea mine, Mariquita, Milpillas,
52 Lucy, María, El Alacrán, and El Pilar deposits. The Buenavista del Cobre, is far the most
53 relevant site with more than 30 Mt Cu, which places it among a selected group of giant porphyry
54 copper deposits at world scale. The present paper addresses new Re-Os molybdenite and U-Pb
55 zircon ages, which help to better constrain the metallogenetic history of the district. According to
56 the Re-Os data, the earlier mineralizing pulse occurred at the El Pilar (73.9 Ma), followed by the
57 Milpillas (63.0 to 63.1 Ma), Lucy (61.6 to 61.8 Ma), María (60.4 Ma), El Alacrán (60.8 to 60.9
58 Ma), Buenavista del Cobre (59.2 to 59.3 Ma), and Mariquita (59.3 ± 0.3 Ma) deposits. Excluding
59 El Pilar, the main mineralizing pulses occurred within a relatively short time window of ~4 Ma.
60 Regarding the magmatic history, U-Pb zircon ages for the emplacement of the copper-related
61 plutons, including the El Pilar deposit, which lacks an exposed porphyritic stock, the entire
62 magmatic activity occurred from 77.7 to 57.8 Ma. The Re-Os and U-Pb geochronological data
63 indicate a NW to SE progression of the mineralizing events along the trace of the so-called
64 Cananea lineament, suggesting a regional structural control coupled with southeastward
65 migration of the magmatism. Thus, our data show a clear periodicity in the magmatic-
66 hydrothermal events responsible for the emplacement of the porphyry copper ores in the
67 Cananea district. Tertiary extension dismembered and buried part of the porphyry copper
68 systems, a fact that opens an interesting opportunity to explore dissected, tilted, and hidden parts
69 of the ore systems. Moreover, Tertiary extension promoted formation of important supergene 70 enriched chalcocite blankets, and lateral migration of copper solutions, yielding conditions to
71 develop exotic copper mineralization.
72
73
74 KEYWORDS: Porphyry copper deposits; Re-Os molybdenite age; U-Pb zircon age; Cananea
75 district
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94 1. INTRODUCTION
95 Late Cretaceous-early Paleogene Laramide porphyry copper deposits are
96 widespread in northwestern Mexico, among which the Buenavista del Cobre (before the
97 Cananea mine) and La Caridad deposits (Fig. 1) stand as the most remarkable examples,
98 comprising the largest national copper resources, being also important at world-scale,
99 accounting for more than 40 Mt of Cu (Valencia-Moreno et al., 2006, 2007).
100 The Cananea and Nacozari mining districts extend as the southern part of the
101 porphyry copper province of North American Cordillera (Titley, 1982), also referred to as
102 the “great cluster” of the porphyry copper deposits (Keith and Swan, 1996). These mining
103 districts also contain smaller porphyry copper deposits (PCD) and other metal
104 commodities and mineralization styles, including skarn, manto, and hydrothermal breccias.
105 The Cananea region has been target of several geological studies (e.g., Aponte-
106 Barrera, 2009; Carreón-Pallares, 2002; Mulchay and Velasco, 1954; Valentine, 1936;
107 Velasco, 1966), magmatic, hydrothermal, and mineralization studies (Bushnell, 1988;
108 Meinert, 1982, Varela, 1972; Wodzicki, 2001), geochemical studies focused on
109 characterizing the magmatic evolution (Wodzicki, 1995, 2001), supergene enrichment
110 processes studies (Noguez-Alcántara et al., 2007; Virtue, 1996), and fluid inclusions
111 microthermometric studies (Arellano-Morales, 2004; González-Partida et al., 2013).
112 Previous geochronological data help to constrain the age of the different magmatic
113 pulses and mineralization episodes recorded in the Cananea and Nacozari mining districts
114 (Anderson and Silver, 1977; Barra et al., 2005; Damon et al. 1983; Noguez-Alcántara et al.,
115 2007; Valencia et al., 2006). However, considering the economic importance, not only at 116 district level, but also at world-scale, the available data are not enough to have complete
117 picture of the magmatic and hydrothermal histories of the porphyry copper systems in
118 northeastern Sonora. This paper contributes with new U-Pb zircon and Re-Os molybdenite
119 geochronological data from the Cananea mining district, to better constrain the timing and
120 evolution of the different magmatic and mineralizing pulses that culminated with the
121 emplacement of world-class copper deposits, which makes this region highly attractive for
122 further exploration campaigns. In addition, our data may provide new clues to determine
123 the spatial distribution and possible links between the Cananea and Nacozari districts.
124
125 2. REGIONAL GEOLOGICAL FRAMEWORK
126 The geology of northwestern Mexico records an important part of the tectonic
127 history of the western North American Cordillera. Available geological, geochemical, and
128 isotopic data allow reconstruction of a series of continental magmatic arcs built on
129 Proterozoic crystalline basement. The older Cordilleran arc is portrayed by scattered
130 plutonic and volcanic rocks of Late Triassic to Late Jurassic age (Anderson and Silver, 1979;
131 Busby-Spera, 1988; Grajales-Nishimura et al., 1992), which were emplaced well inside the
132 continent (Fig. 1). In Early Cretaceous, a new magmatic activity took place in a region closer
133 to the paleotrench, developing a well-defined arc that extended along Baja California and
134 westernmost Sonora and Sinaloa, which is best illustrated by the Peninsular Ranges
135 batholith. The igneous activity was nearly stationary during most of the Cretaceous time,
136 from ~139 to 80 Ma (Henry et al., 2003; Silver and Chappell, 1983); however, regional
137 chrontours show a clear eastward migration of the igneous activity (Ortega-Rivera, 2003;
138 Valencia-Moreno et al., 2006). 139 After 80 Ma, the locus of magmatism migrated faster to the east, reaching eastern
140 Sonora ~59 Ma ago, although reconstructed chrontours indicate a much slower migration
141 rate to the south, across southern Sonora and Sinaloa (Valencia-Moreno et al., 2006). The
142 accelerated stage of arc migration is currently associated with the Laramide Orogeny (80-
143 40 Ma), which was triggered by a rapid increase in the rate of the Farallon-North America
144 plate convergence, in response to major global tectonic adjustments (e.g, Coney and
145 Reynolds, 1977; Damon et al., 1983). The Laramide Orogeny caused crustal shortening and
146 widespread magmatism in most of the Cordillera. In contrast to the Sierra Madre Oriental
147 fold and thrust belt of eastern Mexico, in northwestern Mexico, and particularly in Sonora,
148 the Laramide shortening is yet poorly constrained, and evidenced by block-uplifting
149 tectonics, although thin-skin deformation is documented in Jurassic to Late-Cretaceous
150 volcanic and sedimentary sequences (Calmus et al., 2011; Davis, 1979). The associated
151 magmatism left a broad belt of volcano-plutonic rocks, with the volcanic member best
152 preserved in the eastern part of it, whereas western part essentially exhibits large
153 composite batholiths. This fact may have been the result of post-Laramide exhumation
154 processes.
155 The Laramide igneous activity, coupled with a particular plate tectonic geometry
156 that allowed profuse asthenospheric mantle melting, yielded conditions, not only for the
157 generation of the relatively long-lived calc-alkaline magma chambers, required to form
158 these volcanoplutonic complexes, but also for the emplacement of subvolcanic magmatic-
159 hydrothermal systems. These systems controlled circulation of hydrothermal fluids that
160 concentrated tremendous amounts of metals, particularly Cu and Mo, giving place to
161 formation of an important number of porphyry copper type deposits. Laramide porphyry 162 copper deposits are known along the entire Cordillera, however, the region of
163 southwestern North America, particularly, southern Arizona, western New Mexico, and
164 northeastern Sonora (Fig. 2) concentrated the largest amount of copper, making this region
165 one of the largest Cu provinces on Earth (Titley, 1993).
166
167 2.1 CANANEA MINING DISTRICT
168 The Cananea mining district is located in a region underlain by the Precambrian
169 North American craton, within the Basin and Range extensional province (Fig. 1). The
170 Precambrian basement belongs to the Mazatzal Paleoproterozoic province (1.6-1.7 Ga),
171 extending through southern Arizona, New Mexico, and northern Sonora (Amato et al.,
172 2008). This basement is characterized in Sonora by the Pinal schist, which is intruded by
173 the 1.4 Ga Mesoproterozoic anorogenic Cananea granite (Anderson and Silver, 1977),
174 which is constituted by two magmatic facies: (1) a granophyric granitoid with phenocrysts
175 of quartz in a matrix of K-feldspar, quartz, and oligoclase; (2) less abundant coarse-grained
176 to pegmatitic granitoid composed of K-feldspar, oligoclase, quartz, and minor hornblende,
177 magnetite, and apatite (Valentine, 1936).
178 The Proterozoic assemblage is unonformably overlain by Paleozoic rocks of the
179 North American platform that include the Bolsa (Cambrian), Abrigo (Cambrian), Martín
180 (Devonian), and Escabrosa (Mississippian) Formations, and the Naco Group (Permian),
181 which were described in Meinert (1982), Mulchay and Velasco (1954), and Velasco (1966).
182 The Proterozoic and Paleozoic rocks are unconformably overlain by Mesozoic
183 volcanic rocks (Busby-Spera, 1988; Rodríguez-Castañeda and Anderson, 2011; Valentine,
184 1936), and intruded by granites of Jurassic age (Anderson and Silver, 1977). The oldest 185 volcanic rocks correspond to 1,800 m thick pile of rhyolite and andesite interbedded with
186 sandstone and quartzite of the Triassic-Jurassic Elenita Formation (Valentine, 1936;
187 Wodzicki, 1995). The 1,700 m thick Jurassic Henrietta Formation overlies the Elenita
188 Formation (Valentine, 1936), and is composed by medium to high-K, calc-alkaline, dacitic
189 to rhyolitic tuffs and flows (Wodzicki, 1995). A hornblende Ar-Ar age from the Henrietta
190 Formation yielded a minimum age of 94 Ma (Wodzicki, 1995). The intrusive counterpart of
191 Jurassic rocks within the Cananea district is the 175 Ma old El Torre syenite, which
192 intrudes both the Elenita and Henrietta Formations (Wodzicki, 1995).
193 Late Cretaceous-early Paleogene volcanic and plutonic rocks of the Laramide arc are
194 widespread in the district (Fig. 3). According to Meinert (1982), the base of the sequence is
195 the Mariquita diabase, which consists of a high-K basaltic-andesite flows, and intrusions
196 cross-cutting the rocks of the Henrietta Formation (Wodzicki, 1995). The Mesa Formation
197 overlies the Mariquita diabase. This formation is 1,500 m thick, and mostly consists of
198 intermediate volcanic rocks, which are interbedded with clastic and volcaniclastic deposits
199 (Valentine, 1936; Wodzicki, 2001). A flow within the Mesa Formation yielded a biotite Ar-
200 Ar age of 69 ± 0.2 Ma (Wodzicki, 1995). This age is confirmed by three biotite Ar-Ar ages
201 bracketed between 72.6 ± 1.2 and 65.8 ± 0.4 Ma (Cox et al., 2006).
202 The Precambrian to Cretaceous rocks are intruded by Laramide plutons and
203 porphyritic intrusions. The oldest Laramide intrusions are the Tinaja diorite and the
204 Cuitaca granodiorite (Valentine, 1936). Previous studies suggest that the Tinaja and Cuitaca
205 intrusions belong to the same batholith (Bushnell, 1988; Meinert, 1982; Valentine, 1936).
206 This is supported by isotopic data, which suggests a genetically related batholith (Wodzicki,
207 1995). Anderson and Silver (1977) obtained a U-Pb zircon age of 64 ± 3 Ma for a sample of 208 the Cuitaca batholith located near the Cananea town. A similar U-Pb zircon age of 63.8 ± 1.1
209 Ma has been reported for a sample of the Cuitaca granodiorite from Lucy pit (Fig. 3),
210 located ~20 km W-NW of Cananea (Del Rio-Salas et al., 2013).
211 Relatively small porphyritic plugs, mostly of quartz-feldspatic composition, derived
212 from the cooling batholith, are elsewhere reported within the Cananea district. These plugs
213 are regionally important since they are considered as the main heat source that centered
214 the alteration and most of the porphyry copper mineralization (Barton et al., 1995). The
215 available U-Pb zircon data for the porphyry stocks in the Cananea district indicate an age of
216 63.9 ± 1.3 Ma for a sample located in the Milpillas area (Fig. 3), ~20 km NW of Cananea
217 (Valencia et al., 2006), whereas samples from the Mariquita area, located ~14 km W-NW of
218 Cananea (Fig. 3) yielded younger U-Pb zircon ages of 62.7 ± 1.3 and 60.4 ± 1.1 (Del Rio-
219 Salas et al., 2013).
220 The Tinaja-Cuitaca batholith complex was intruded by late sub-vertical N60ºW
221 oriented mafic dikes, reported by Valentine (1936) as the Campana dikes. One sample of
222 these dikes located 2.8 km southwest of the Maria mine, yielded a hornblende Ar-Ar age of
223 58.4 ± 0.6 Ma (Carreón-Pallares, 2002).
224 The Cananea district, as well as most of the North American Cordillera, was
225 deformed by extension associated with the Tertiary Basin and Range extensional province
226 (e.g., Sonder and Jones, 1999). NNW-SSE oriented graben-horst structures alternate from
227 west to east within the district as follows: 1) the Cocóspera-San Antonio graben, and the
228 San Antonio-Chivato-Cuitaca horst; 2) the Milpillas-Cuitaca graben, and the Mariquita-El
229 Cobre-Elenita horst; and 3) the Río San Pedro-Río Sonora graben, and the Los Ajos horst.
230 During the Tertiary, the structural evolution of the Cananea district is controlled by the 231 post-Laramide Basin and Range extension. The Cananea district is located slightly east of
232 the Metamorphic Core Complex belt (Fig. 1), showing no evidence of deep extensional
233 structures, such as cataclastic fault zones or low-angle mylonitic detachment faults, which
234 suggests a low to moderate extension in the Cananea district.
235 Regarding mineralization, Cananea is the most important copper mining district in
236 Mexico, being among the world-class copper producers. Consequently, this mining district
237 has been target of several studies, particularly focused on characterizing the geology and
238 economic potential. The most important deposit within the district is by far the Buenavista
239 del Cobre mine, however there are several smaller porphyry copper, and other related
240 mineralization deposits, including breccia pipes, skarn, manto, pegmatite, polymetallic
241 veins, and replacement. In most cases, the mineralization of the Cananea mining district is
242 clearly related to magmatic pulses occurred during the Laramide arc activity. The district
243 includes several porphyry copper occurrences and related deposits (Fig. 2, Table 1),
244 currently under production (Buenavista del Cobre, Milpillas, Mariquita) or mined in the
245 past (María) or still develops sporadic mining activity (Lucy), or mining prospects (Alisos,
246 Toro). Other deposits, such as the El Alacrán and El Pilar, are considered as interesting
247 prospects (Broch, 2012; Dean, 1975, Arellano-Morales, 2004).
248
249 2.1.1 Buenavista del Cobre deposit 250 251 The Buenavista del Cobre mine, formerly Cananea, is the biggest porphyry copper
252 deposit known in Mexico (Fig. 3). The resources account for 7,140 Mt at 0.42% Cu, 0.008%
253 Mo (Singer et al., 2005). The mineralization is hosted mainly in the volcanic rocks of the
254 Henrrieta and Mesa Formations, intruded by porphyritic plugs, some of which were 255 mineralizing. The composition of these intrusions includes quartz monzonite,
256 monzodiorite, and granodiorite. Intense fracturing that developed stockwork zones
257 surround the porphyritic intrusions. The porphyry emplacement was accompanied by
258 intense hydrothermalism, characterized by potassic and quartz-sericite alteration (Ochoa-
259 Landín and Echávarri, 1978).
260 The secondary copper mineralization is nearly horizontal, extending by an area of
261 15 km2, reaching a maximum thickness of 500 m (Ayala-Fontes, 2009). Numerous
262 elliptical-shaped breccias bodies are found within the area, some of which reach depths of
263 hundreds meters, and were apparently developed during the stage of quartz-sericite
264 alteration (Bushnell, 1988). Also, associated with the porphyritic intrusions, there are some
265 skarn mineralization (Zn-Pb-Cu) and manto-type occurrences, which are hosted in the
266 intruded Paleozoic rocks, developing stratiform bodies of high-grade sulfide and iron oxide,
267 best represented by the Puertecitos skarn, located northwest of Cananea (Einaudi, 1982;
268 Meinert, 1982).
269
270 2.1.2 Milpillas deposit
271 The Milpillas porphyry copper deposit is located 20 km northwest of Cananea and 7
272 km north of Mariquita mine (Fig. 3). Milpillas mine is currently in production with 35 Mt at
273 2.3% of Cu (Noguez-Alcántara et al., 2007). Ore bodies are mostly hosted in volcanic rocks
274 of the Henrietta and Mesa Formations, and related to intrusion of porphyritic plugs, one of
275 them dated at 63.9 ± 1.3 (Valencia et al., 2006). The mineralization consists of various
276 supergene-enriched chalcocite and minor covellite blankets, overlain by Cu sulfates, Cu
277 carbonates, and Fe oxides (Noguez-Alcántara et al., 2007). Unusually for the Cananea 278 district, Milpillas developed underground mining, because the mineralization remains
279 beneath thick semi-consolidated gravel deposits of the Sonora Group (Grijalva-Noriega and
280 Roldán-Quintana, 1998).
281
282 2.1.3 Mariquita deposit
283 The Mariquita is a porphyry copper deposit located 15 km northwest of Cananea
284 (Fig. 3). The deposit is currently under production, and includes resources estimated of
285 about 58 Mt of Cu at 0.4-0.6% (Aponte-Barrera, 2009). The mineralization is hosted in
286 volcanic rocks from the Henrrieta, Mariquita, and Mesa Formations, intruded by 62.7 and
287 60.4 Ma quartz-feldspar porphyry stocks (Del Rio-Salas et al., 2013). The ore consists of a
288 nearly horizontal 60 m thick chalcocite enrichment blanket (Aponte-Barrera, 2009), which
289 is partially capped to the WSW by gravels of the Sonora Group.
290
291 2.1.4 Lucy deposit
292 The Lucy Cu-Mo deposit is located 21 km northwest of Cananea and 7 km northwest
293 of Mariquita mine (Fig. 3), accounting for resources of about 9 Mt at 0.8% Cu and 0.1% Mo
294 (Del Rio-Salas et al., 2013; González-Partida et al., 2009). The production of this deposit has
295 been sporadic, depending on the internal needs of the mining company and metal market
296 conditions. The geology in the Lucy area consists of Henrietta and Mesa Formations
297 volcanic rocks, intruded by the Cuitaca granodiorite, covered by gravel deposits of the
298 Sonora Group (Grijalva-Noriega and Roldán-Quintana, 1998).
299 The mineralization mostly occurs as breccias and disseminated chalcopyrite and
300 molybdenite, hosted within the Cuitaca granodiorite (Del Rio-Salas et al., 2013), although 301 the source of this mineralization is presently uncertain. Evidence of secondary chalcocite is
302 found as coating of disseminated pyrite. So far, no evidence of economical important
303 secondary enrichment has been reported for this deposit.
304
305 2.1.5 El Alacrán deposit
306 The El Alacrán porphyry copper prospect is located 18 km southeast of Cananea,
307 corresponding to the extreme S-SE Cananea district (Fig. 3). The El Alacrán has been
308 recognized as a low-grade deposit with resources of 0.7 Mt at 0.5% Cu (Dean, 1975). The
309 deposit is centered on a quartz-latite porphyry plug that intrudes intermediate volcanic
310 rocks of the Mesa Formation (Wodzicki, 1995).
311 Concerning the age of the mineralization, K-Ar dating on potassic alteration yielded
312 ages of 55.4 ± 1.2 (Dean, 1975) and 56.7 ± 1.2 Ma (Damon et al., 1983), which were then
313 considered as the approximation of the timing of the mineralization. However, more
314 precise data based on Re-Os molybdenite dating, yielded ages of 60.8 ± 0.2 and 60.9 ± 0.2
315 Ma in quartz-sericite veinlets (Barra et al., 2005).
316
317 2.1.6 El Pilar deposit
318 The El Pilar copper deposit is located on the southwest flank of the Sierra San
319 Antonio, which is the southern continuation of the Patagonia Mountains of the Santa Cruz
320 County, Arizona (Fig. 3). The mineralization and alteration are poorly documented in
321 literature, and so far it is described as a breccia body, which is spatially related to a
322 monzonite to quartz monzonite pluton, here referred to as El Pilar pluton. The breccia
323 consists of fragments of igneous rocks sustained in a more complexly fragmented matrix of 324 the same composition, containing pyrite, chalcopyrite, and molybdenite, which was
325 partially oxidized to chrysocolla (Broch, 2012). The Sierra San Antonio is limited to the
326 west by a normal fault, which is assumed to be associated with the NNW-SSE trending
327 Basin and Range fault system, which may correspond to the limit between Sierra San
328 Antonio-Cocóspera graben. Actually, the mineralization at El Pilar is centered mostly on the
329 clastic fragments occurring as gravel, sand, and finer grains, most probably derived from
330 exhumation, partial destruction, and erosion of the mineralized breccia, due to normal
331 faulting. This is suggested by the presence of fragments of sulfide-mineralized breccia in
332 the gravels. According to Broch (2012), the thickness of productive gravel ranges from 30
333 to 180 m. The El Pilar resource accounts for 0.36 Mt at 0.15% Cu.
334
335 3. ANALYTICAL PROCEDURES
336 3.1. Re-Os method
337 The Re–Os analyses were conducted following the method described in Mathur et al.
338 (2002) and Teixeira-Correia et al. (2007). Approximately 0.05–0.1 g of handpicked
339 molybdenite was loaded in a Carius tube with 10 ml of reverse aqua regia. While the
340 reagents, sample and spikes were frozen, the Carius tube was sealed and left to thaw at
341 room temperature. The tube was placed in an oven and heated to 240°C overnight.
342 Once the Carius tube was opened after the high temperature equilibration, 4 mL of
343 CCl4 solvent is added on top of the acid solution while still frozen. Once thawed, the aqua
344 regia solvent mixture is transferred to 50 mL falcon tubes, agitated and centrifuged to aid
345 the extraction and separation of Os into organic-solvent and acidic layers. The organic-
346 solvent layer containing the Os is separated from the acidic layer and the procedure is 347 repeated twice more with 3 mL of CCl4 to ensure high Os yield. The Os is then back
348 extracted from the organic-solvent into concentrated hydrobromic acid, which is dried and
349 subsequently purified for mass spectrometry by microdistillation techniques (Birk et al.,
350 1997). Osmium was further loaded on platinum filaments with Ba(OH)2 to enhance
351 ionization. After osmium separation, the remaining acid solution was dried and later
352 dissolved in 0.1 HNO3. Rhenium was extracted and purified through a two-stage column
353 using AG1-X8 (100–200 mesh) resin and loaded on platinum filaments with BaSO4.
354 Samples were analyzed by negative thermal ion mass spectrometry (N-TIMS)
355 (Creaser et al., 1991) on a VG 54 mass spectrometer. Molybdenite ages were calculated
356 using a 187Re decay constant of 1.666x10-11 per year (Smoliar et al., 1996). Ages are
357 reported with a 0.5% error, which is considered a conservative estimate and reflects all
358 sources of error (i.e. uncertainty in the Re decay constant (0.31%), 185Re and 190Os spike
359 calibrations (0.08% and 0.15%, respectively), analytical and weighing errors.
360
361 3.2. U-Pb method
362 The determination of the ages in zircons was analyzed following the procedure
363 described in Del Rio-Salas et al. (2013), and the description is outlined below. Around 1 kg
364 of the intrusive rocks were crushed and milled. Heavy mineral concentrates smaller than
365 350 µm were separated using the Wilfley Table. The zircons were concentrated using di-
366 iodomethane heavy liquid and magnetic techniques. Later, the zircons were handpicked
367 under a binocular microscope, and mounted in an epoxy resin and polished. Around 30
368 zircons from each sample were analyzed by laser ablation multicollector inductively
369 coupled plasma mass spectrometry (LA-MC-ICPMS) at the Arizona LaserChron Center. The 370 analyses involve ablation of zircon with a New Wave/Lambda Physik DUV193 Excimer
371 laser (operating at a wavelength of 193 nm) using a spot diameter of 35 microns. The
372 ablated material is carried with helium gas into the plasma source of a GV Instruments
373 Isoprobe, which is equipped with a flight tube of sufficient width for simultaneous
374 measurements of U, Th, and Pb isotopes. All measurements are made in static mode, using
375 Faraday detectors for 238U and 232Th, an ion-counting channel for 204Pb, and either faraday
376 collectors or ion counting channels for 208-206Pb. Ion yields are ~1 mv per ppm. Each
377 analysis consists of one 20-second integration on peaks with the laser off (for
378 backgrounds), 20 one-second integrations with the laser firing, and a 30-second delay to
379 purge the previous sample and prepare for the next analysis. The ablation pit is ~15
380 microns in depth.
381 For each analysis, the errors in determining 206Pb/238U and 206Pb/204Pb result in a
382 measurement error of ~1% (at 2-sigma level) in the 206Pb/238U age. The errors in
383 measurement of 206Pb/207Pb and 206Pb/204Pb also result in ~1% (2-sigma) uncertainty in
384 age for grains that are >1.0 Ga, but are substantially larger for younger grains because of
385 the low intensity of the 207Pb signal. For most analyses, the cross-over in precision of
386 206Pb/238U and 206Pb/207Pb ages occurs at ~1.0 Ga.
387 Common Pb correction is accomplished by using the measured 204Pb and assuming
388 an initial Pb composition from Stacey and Kramers (1975) (with uncertainties of 1.0 for
389 206Pb/204Pb and 0.3 for 207Pb/204Pb). Our measurement of 204Pb is unaffected by the
390 presence of 204Hg because backgrounds are measured on peaks (thereby subtracting any
391 background 204Hg and 204Pb), and because very little Hg is present in the argon gas. 392 Inter-element fractionation of Pb/U is generally ~20%, whereas fractionation of Pb
393 isotopes is generally <2%. In-run analysis of fragments of a large zircon crystal (generally
394 every fifth measurement) with known age of 564 ± 4 Ma (2-sigma error) is used to correct
395 for this fractionation. The uncertainty resulting from the calibration correction is generally
396 ~1% (2-sigma) for both 206Pb/207Pb and 206Pb/238U ages. The analytical data are reported
397 in Tables 3-9. Uncertainties shown in these tables are at the 1-sigma level, and include only
398 measurement errors.
399 The reported ages are determined from the weighted mean (Ludwig, 2003) of the
400 206Pb/238U or 206Pb/207Pb ages of the concordant and overlapping analyses. Analyses that
401 are statistically excluded from the main cluster are shown in blue on these figures. Two
402 uncertainties are reported on these plots. The smaller uncertainty (labeled “mean”) is
403 based on the scatter and precision of the set of 206Pb/238U or 206Pb/207Pb ages, weighted
404 according to their measurement errors (shown at 1-sigma). The larger uncertainty (labeled
405 “age”), which is the reported uncertainty of the age, is determined as the quadratic sum of
406 the weighted mean error plus the total systematic error for the set of analyses. The
407 systematic error, which includes contributions from the standard calibration, age of the
408 calibration standard, composition of common Pb, and U decay constants, is generally ~1-
409 2% (2-sigma).
410
411 4. RESULTS
412 4.1. Re-Os geochronological data
413 The new Re-Os molybdenite age for the mineralization from Mariquita, Lucy, and El
414 Pilar deposits are reported in Table 2. A molybdenite sample from the El Pilar deposit 415 yielded a total rhenium and 187Os concentrations of 64.8 ppm and 50.2 ppb, respectively.
416 The data yields a molybdenite age of 73.9 ± 0.3 Ma, which is the oldest age determined in
417 this study, and so far, the oldest mineralization age reported within the Cananea district.
418 The total rhenium and 187Os concentrations for two molybdenite samples from the
419 Mariquita deposit range from 83.7 to 373.5 ppm and 51.6 to 231.6 ppb, respectively. The
420 Re-Os isotope data yield a molybdenite mineralization age between 59.2 and 59.3 ± 0.3 Ma
421 for the molybdenite mineralization at Mariquita deposit.
422 The total rhenium and 187Os concentrations for a molybdenite sample from the Lucy
423 deposit are 47.2 ppm and 29.7 ppb, respectively. The Re-Os data yield an age of 61.8 ± 0.3
424 Ma for the mineralization at Lucy deposit.
425
426 4.2. U-Pb zircon data
427 The U-Pb zircon ages are shown in Tables 3-9. All reported ages have uncertainties
428 at the two-sigma level, which only includes the analytical error. The age of each sample
429 includes additional uncertainties from the calibration correction, decay constant and
430 common lead. These systematic errors (<1.4 %) are added quadratically to the analytical
431 error. The analyzed zircons from the intrusive rocks from the Cananea district have U
432 concentrations that range from 2300-180 ppm. All zircons yield U/Th ratios of ~2,
433 characteristic of igneous zircons (Rubatto, 2002).
434 Tables 3-6 show the U-Pb zircon ages for the Buenavista del Cobre porphyry
435 samples. Table 3 shows the U-Pb zircon ages for a granodiorite porphyry sample from
436 Buenavista del Cobre, which yielded a weighted average age of 60.8 ± 1.0 Ma (n = 22,
437 MSWD 3.8; Fig. 4a). Zircons from this sample produced an inherited ages from Middle 438 Jurassic (167 Ma, n = 1), Late Cretaceous (73 Ma, n = 1), and Early Paleocene (~64 Ma, n =
439 3). Zircons from a granodiorite porphyry sample yielded a weighted average age of 60.9 ±
440 1.2 Ma (n = 18, MSWD 1.4; Fig. 4b, Table 4). The U-Pb zircon data show inherited ages of
441 Early Jurassic (190 Ma, n = 2), Middle Jurassic (165 Ma, n = 3), Late Cretaceous (68 Ma, n =
442 2), Early Paleocene (64 Ma, n = 3).
443 The zircons from quartz monzonite porphyry sample yielded a weighted average
444 206Pb/238U age of 61.3 ± 1.4 Ma (n=16, MSWD =2.4; Fig. 4c, Table 5). Zircons from this
445 sample produced inherited ages from Early Jurassic (195 Ma, n = 1), Middle Jurassic (170
446 Ma, n = 1), Early Cretaceous (140 and 124 Ma), Late Cretaceous (74 Ma, n = 1), and Early
447 Paleocene (~64 Ma, n = 6). A sample from younger monzodiorite porphyry in Buenavista
448 del Cobre yielded a weighted average age of 58.9 ± 1.4 Ma (n = 24, MSWD 4.5; Fig. 4d, Table
449 6). Zircons from this porphyritic sample yielded inherited ages from Late Ordovician (458
450 Ma, n = 1), Early Devonian (396 Ma, n = 1), Early Cretaceous (100 Ma, n = 1), and Late
451 Cretaceous (90 Ma, n = 1).
452 A quartz-monzonitic porphyry sample from the El Alacrán deposit yielded an age of
453 57.8 ± 1.0 Ma (n = 14, MSWD 1.8; Fig. 5a, Table 7). Zircons from this sample yielded
454 inherited ages from Early Cretaceous (124 Ma, n = 1), Late Cretaceous (68 Ma, n = 1), Early
455 Paleocene (~64 Ma, n = 5).
456 Two U-Pb zircon ages from the granodiorite from the El Pilar deposit are shown in
457 Tables 8 and 9. U-Pb zircon data yielded ages of 74.6 ± 1.4 Ma (n = 27, MSWD 3; Fig. 5b,
458 Table 8) and 74.7 ± 1.1 Ma (n = 31, MSWD 2.9; Fig. 5c, Table 9). Only one inherited zircon
459 age from Early Cretaceous (116 Ma) was found.
460 461 5. DISCUSSION
462 5.1 U-Pb and Re-Os geochronology
463 There is a relatively large geochronological dataset of the Cananea mining district
464 (e.g. Damon and Mauger, 1966; Damon et al., 1983), however uncertainties due to
465 differences in closure temperatures of dated materials, analytical procedures and precision,
466 etc., precludes straightforward interpretations of the magmatic and hydrothermal activity.
467 Thus, filtering of the data is required in order to reproduced consistent evolutionary
468 models. The new ages reported in this study, together with other available U-Pb zircon and
469 Re-Os molybdenite dates (Barra et al., 2005; Noguez-Alcántara, 2008; Valencia et al., 2006)
470 allow to constrain more plausible interpretation regarding ages and relationships between
471 magma crystallization and mineralizing hydrothermal pulses.
472 Our results indicate that magmatic activity in the Cananea mining district occurred
473 in a time span between 75 and 58 Ma. The oldest age corresponds to a monzonite to quartz
474 monzonite pluton exposed in the area of El Pilar, in the northwestern part of the district,
475 which yielded ages of 74.6 ± 1.4 and 74.7 ± 1.1 Ma (Fig. 5b,c). These ages are in good
476 agreement with the U-Pb zircon 74.0 ± 1.1 Ma old Washington camp stock, exposed in the
477 Patagonia Mountains (Vikre et al., 2014), ~20 km north of El Pilar area. Also, the El Pilar
478 deposit yielded the oldest age for the Cu-Mo mineralization within the district, with a Re-Os
479 molybdenite date of 73.9 ± 0.3 Ma. These very similar ages indicate that the mineralizing
480 pulse was nearly synchronic with the emplacement of the El Pilar pluton, suggesting a
481 cogenetic relationship.
482 In the central part of the district, the 64 Ma old Cuitaca granodiorite (Anderson and
483 Silver, 1977) is recalled as the precursor of the Laramide mineralizing porphyritic 484 intrusions (Noguez-Alcántara, 2008; Wodzicki, 1995). This igneous body is exposed over
485 an area exceeding 400 km2 (Fig. 3), forming the bulk of the Sierras El Chivato, Cuitaca, and
486 the western flank of the Sierra Mariquita and Sierra Elenita.
487 The oldest mineralizing porphyritic intrusion recognized within the district
488 corresponds to a quartz monzonite plug that controlled the mineralization in the Milpillas
489 porphyry copper deposit (PCD). U-Pb zircon data of sample from this plug yielded an age of
490 63.9 ± 1.3 Ma (Valencia et al., 2006), which is quite similar to the age of 64 Ma reported for
491 the Cuitaca granodiorite (Anderson and Silver, 1977). The hypogene mineralization in the
492 Milpillas PCD is constrained by two Re-Os molybdenite ages of 63.0 ± 0.4 and 63.1 ± 0.4 Ma,
493 suggesting a clear temporal correlation between the hydrothermal activity and the
494 porphyritic mineralizing intrusion (Valencia et al., 2006).
495 In the case of the Lucy deposit, a sample of the Cuitaca granodiorite collected in the
496 Lucy pit, which is the host of the disseminated Cu-Mo mineralization, yielded an U-Pb
497 zircon age of 63.8 ± 1.1 Ma (Del Rio-Salas et al., 2013). The mineralizing event is
498 constrained by a Re-Os molybdenite age of 61.8 ± 0.3 Ma (Table 2), which reveals a wider
499 time span between the plutonic phase and the mineralization in Lucy (~2 Ma).
500 In the Mariquita area, the Cuitaca granodiorite is widespread, unfortunately this
501 rock has not been dated yet for this place, however, the age of 64 Ma reported by Anderson
502 and Silver (1977), comes from a sample collected 5 km southeast of Mariquita mine. So far,
503 the mineralization appears to be related to intrusions of two porphyritic stocks, which
504 yielded U-Pb zircon ages of 62.7 ± 1.3 and 60.4 ± 1.1 Ma (Del Rio-Salas et al., 2013). Here,
505 the mineralization is constrained by a Re-Os age of 59.3 ± 0.3 Ma (Table 2), from a
506 molybdenite separates collected from the younger porphyritic intrusion. 507 In the Buenavista del Cobre PCD, in the southeastern part of the district, the Cuitaca
508 granodiorite is not recognized, however it outcrops ~3 km to the west-southwest of the
509 mining area (Fig. 3). This deposit is not only the largest within the Cananea district, but also
510 the most complex in terms of the magmatic and hydrothermal histories. Here, at least four
511 lithologically distinctive porphyritic phases have been recognized and dated. U-Pb zircon
512 data in three of them yielded fairly similar ages between 60.8 ± 1.0 to 61.3 ± 1.4 Ma. The
513 fourth one yielded a younger age of 58.9 ± 1.4 Ma (Tables 3–6). The age of the
514 mineralization has been constrained by Re-Os molybdenite dates of 59.3 ± 0.3 and 59.2 ±
515 0.3 Ma (Barra et al., 2005). Field evidences do not offer definitive clues regarding the
516 contribution to the metal budget.
517 The El Alacrán represents the southernmost PCD within the Cananea district. Here,
518 the Cuitaca granodiorite is not exposed, but two quartz-monzonitic porphyries (Arellano-
519 Morales, 2004) are found intruding andesitic to quartz latite volcaniclastic rocks (Dean,
520 1975) correlatable with the Mesa Formation (Cox et al., 2006). A drill core sample from one
521 of the mineralized porphyritic intrusion yielded an U-Pb zircon age of 57.8 ± 1.0 Ma (Table
522 7). This age is younger than previously reported Re-Os molybdenite ages of 60.9 ± 0.2 and
523 60.8 ± 0.2 Ma (Barra et al., 2005). These Re-Os ages are inconsistent with the age of the
524 dated plug, suggesting that the mineralization corresponds to a different magmatic event,
525 perhaps correlatable with the other, undated, porphyritic plug.
526
527 5.2 Southeastern progression of Cu-Mo mineralization
528 The distribution of most of the Cordilleran porphyry copper deposits in
529 southwestern North America lie along a ~350 km northwest-trending regional lineament, 530 extending from Silver Bell mine, Arizona, to La Caridad mine, Sonora, which was formerly
531 referred to as the Cananea lineament (Hollister, 1978). The Mexican part of this lineament
532 includes the Cananea and Nacozari mining districts, extending for ~140 km from El Pilar
533 deposit to La Caridad mine.
534 In the Cordilleran porphyry copper belt, two main episodes of mineralization have
535 been previously documented at 74-70 and 60-55 Ma (McCandless et al., 1993). As
536 mentioned above, these episodes are also reported for the Cananea and Nacozari mining
537 districts, where ages range from 74 to 54 Ma. However, the most significant number of ages
538 lies in the range of 60-55 Ma (Barra et al., 2005).
539 Interestingly enough, a southeastward decrease of molybdenite mineralization ages
540 is discernible along the Cananea lineament, from the El Pilar deposit (~74 Ma), Milpillas
541 (~63 Ma), Lucy (~62 Ma), Buenavista del Cobre and Mariquita (~59 Ma), to La Caridad
542 deposit (~54 Ma). The only deposit that apparently does not follow this pattern is El
543 Alacrán, which yielded an age ~61 Ma. However, the slight difference in age may be partly
544 enhanced by analytical uncertainties. This southeastward decrease in the mineralization
545 ages in some way reflects a similar decrease in the emplacement ages of the mineralizing
546 intrusions (Fig. 6). The relatively minor age difference in the porphyritic intrusions and the
547 primary sulfide ores suggests a NW-SE continuum in the magmatic and hydrothermal
548 processes along the Cananea lineament.
549 The distribution of mineralization ages in the Cananea and Nacozari mining districts
550 can be coupled to the well-accepted east-northeastward migration model of the Laramide
551 magmatic arc (Coney and Reynolds, 1977; Damon et al., 1983). However, there is no doubt 552 that a southeastern migration in the Cu-Mo mineralization occurred within these districts,
553 which gives support to the Cananea lineament (Fig. 6).
554 The U-Pb zircon age of the El Pilar monzonitic pluton (~74 Ma), along with previous
555 U-Pb zircon ages, suggest a time span of ~17 Ma for the magmatic activity in the Cananea
556 district. On the other hand, the available U-Pb zircon ages suggest that the age of
557 emplacement of the porphyritic stocks occurred within a shorter period of time of about 6
558 Ma. Moreover, the Re-Os molybdenite ages allow identification of at least five discrete
559 mineralizing pulses, which took place within ~4 Ma (Fig. 6).
560
561 5.3 Tertiary tectonics
562 In the Cananea district as well as most northeastern Sonora, Mesozoic volcanoclastic
563 rocks and Laramide intrusions lack deep extensional structures, such as cataclastic fault
564 zones or low angle mylonitic detachment faults, which suggests the amount of extension
565 was low to moderate during the Basin and Range extensional tectonics. This supports the
566 conclusions reached by Nourse et al. (1994), regarding the NW-SE trending Imuris
567 lineament, which separates the Cenozoic Metamorphic Core Complex belt to the southwest,
568 from the less-deformed and unmetamorphosed region to the northeast, which
569 encompasses the Cananea mining district (Fig. 1).
570 Another argument supporting a low to moderate extension is the presence of
571 shallow porphyry copper deposits in both horsts and grabens. If a horst of the Cananea
572 mining district were limited by a low-angle detachment fault, rocks of the middle and lower
573 crust would be expected to be exposed, meaning that the shallower levels of the crust,
574 including the porphyry copper systems, should have been removed. The 1.4 Ga Cananea 575 granite in the Mariquita, El Cobre, and Elenita ranges, as well as the Pinal schist outcrops in
576 the Sierra Los Ajos, are interpreted as the result of uplift during the Laramide
577 compressional phase along high-angle reverse thrust faults, and not as a consequence of
578 tectonic denudation of the upper crust along a low-angle normal fault. The main direction
579 of extension is ~NE60°SW, which is highlighted by similarly oriented transfer faults
580 reported in Arizona (Wilkins Jr. and Heidrick, 1995), and Sonora (Calmus et al., 2011; Gans,
581 1995). Moreover, this structural pattern is also underlined by direction of metamorphic
582 lineation and S-C shear zones observed in the metamorphic core complexes mylonitic
583 zones (Vega-Granillo and Calmus, 2003; Wilkins Jr. and Heidrick, 1995). In the Cananea
584 mining district this structural pattern is probably exemplified by the lineament between
585 Imuris and Milpillas, which may represent an accommodation zone during the Basin and
586 Range extension (Fig. 7). In the Milpillas-Cuitaca graben, Carreón-Pallares (2002)
587 considered that the Milpillas and Mariquita areas formed two subdistricts, which were
588 dissected during two main Miocene to Pleistocene extensional events. The first one is
589 characterized by N30°E left-lateral faults that segmented these subdistricts, whereas the
590 second one dealt with normal faulting associated with formation of the Milpillas-Cuitaca
591 graben. According to this model, the last event caused an ~5 km offset between Lucy and
592 Milpillas mines, which is questionable if only dip-slip displacements along high-angle
593 normal faults are considered.
594
595 5.4 Implications for regional exploration
596 Traditionally, the importance of PCD lies on the presence of supergene-enriched
597 blankets, due to the leaching of primary sulfide mineralization by meteoric water (Chávez, 598 2000). In the Cananea mining district, this process was favored by the Basin and Range
599 extensional tectonics, enhanced by climatic conditions, commonly displaying multiple
600 copper enrichment cycles. Further sedimentary processes stand as critical factors to
601 preserve the secondary sulfide ores. In northwestern Mexico, examples displaying different
602 levels of erosion support this assumption. For instance, the Buenavista del Cobre mine was
603 apparently very well preserved, so most of the system is present. On the contrary, there are
604 examples where the system is more deeply eroded, such as in the case of El Crestón Mo-Cu
605 deposit in central Sonora (Valenzuela-Navarro et al., 2005). Some of the PCD within the
606 Cananea district are partially or fully covered by basin-fill clastic sediments of the Báucarit
607 Formation and the Sonora Group (Grijalva-Noriega and Roldán-Quintana, 2000), such as in
608 the Milpillas mine, where copper ores are being mined underground.
609 Cenozoic block faulting tectonics was important in the preservation vs. erosion
610 processes in PCD from northwestern Mexico and southeastern North America (Barton et
611 al., 1995). The extensional tectonics in Sonora, and particularly in the Cananea mining
612 district, may have dissected important parts of the porphyry copper systems, and even
613 more, it may have buried some systems completely, so that hidden, and potentially
614 important deposits, may remain undiscovered, becoming important targets for future
615 mineral exploration along the Cananea lineament, from El Pilar deposit at the northwest,
616 through the La Caridad deposit, at the southeastern section of the lineament.
617 In some cases, the PCD underwent geological processes where copper-bearing acid
618 solutions flow laterally along paleochannels in gravel deposits (Chávez, 2000). Copper-rich
619 solutions interact with gravel precipitating different copper mineral species controlled by
620 pH changes, currently referred to as exotic copper deposits, such as La Exótica, which is an 621 important deposit adjacent to the giant Chuquicamata PCD in northern Chile (Münchmeyer,
622 1996). Even though, no deposits of this type have been recognized in the Cananea district,
623 there are some evidences, particularly in the Milpillas and the Mariquita deposits, where
624 secondary copper minerals, including copper carbonates, silicates, and oxides, suggest that
625 formation of exotic copper may be a possibility along the Cananea lineament.
626
627 6. CONCLUSIONS
628 The Re-Os molybdenite ages from the Cananea district suggest at least five well-
629 constrained mineralizing pulses at ~74, 63, 62, 60, and 59 Ma, nevertheless, the main
630 mineralization stage occurred in a much shorter period of time of ~4 Ma. Also, the new Re-
631 Os molybdenite age for the El Pilar deposit (~74 Ma) records the oldest mineralizing pulse
632 reported so far in the Cananea district, establishing the time for the initiation of the
633 Laramide porphyry copper mineralization in northern Sonora.
634 The U-Pb zircon ages of the mineralizing porphyries suggest a continued magmatic
635 period of ~6 Ma. Including the new U-Pb zircon ages of the hosting rock from the El Pilar
636 deposit, the magmatic activity expands to ~17 Ma. Similar mineralizing and magmatic ages
637 reported in the Patagonia Mountains, in southern Arizona (Vikre et al., 2014), suggest that
638 this magmatic-hydrothermal activity occurred synchronically in northern Sonora and
639 southern Arizona.
640 Interestingly enough, the new ages indicate a NW-SE progression, from older to
641 younger ages, in both, the mineralizing magmatic intrusions and the mineralization at least
642 from El Pilar to La Caridad (Fig. 2), suggesting the existence of a regional structural control
643 of the mineralization emplacement along the Cananea lineament. This is an important 644 contribution that may bring new clues to understand the dynamics of formation and
645 regional emplacement of the PCD.
646 Further structural studies to better elucidate the Cenozoic extensional tectonics that
647 dissected and rearranged the deposits, may help not only to reconstruct the original
648 systems, but also provide hints to enhance exploration for hidden PCD and exotic copper
649 mineralization in the Basin and Range province.
650
651 7. ACKNOWLEDGMENTS
652 This research was supported by the CONACYT (project 166600), the consortium between
653 FRISCO and the Geology Department at the University of Sonora, and the Geosciences
654 Department at the University of Arizona. We thank Arizona LaserChron Center, especially
655 George Gehrels for the support. We thank Fernando Barra for preliminary Re-Os
656 molybdenite analysis. We are grateful to Grupo FRISCO and Maria Mine staff for the
657 logistics and support. We thank Ramon Ayala from Grupo México for sampling support in
658 the Cananea Mine. This work has been partly funded by the Universidad Nacional Autónoma de
659 México trough the DGAPA Program, which supported the sabbatical year of TC between July
660 2011 and July 2012 at the Thermochronology Laboratory of ISTerre, University Joseph Fourier,
661 Grenoble), during which studies were conducted on the Cenozoic exhumation of porphyry
662 copper deposits in Sonora. We are thankful for the field assistance of the geologists Roman
663 Solís, Oscar Saitz Sau, Cruz Páez, and Julio Cesar Orantes. We thank the editor(s) and the
664 referees.
665
666 667
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926
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930
931 932
933
934 Figure Click here to download Figure: Figure caption.docx
1 Figure caption
2 Fig. 1 Map showing the distribution of Laramide intrusive (black) and extrusive (grey)
3 rocks in Sonora. BC: Buenavista del Cobre mine; LC: La Caridad mine.
4
5 Fig. 2 Distribution of porphyry copper deposits along the Laramide belt of southwestern
6 North America and northwestern Mexico (modified after Valencia-Moreno et al., 2007).
7 Shaded area represents the Great Laramide porphyry copper cluster of Arizona, Sonora,
8 and New Mexico. Dashed line denotes the Cananea lineament (Hollister, 1978). Chrontours
9 according to Valencia-Moreno et al. (2006).
10
11 Fig. 3 Map showing the regional geological framework of the Cananea Mining district in
12 northeastern Sonora modified after Del Rio-Salas et al. (2013) and Servicio Geológico
13 Mexicano (Mexican Geological Survey). EP: El Pilar; LU: Lucy; TO: Toro; A: Alisos; MI:
14 Milpillas; LV: La Verde; MA: Mariquita; M: Maria; BC: Buenavista del Cobre; EA: El Alacrán.
15
16 Fig. 4 U–Pb weight average plots from the mineralizing porphyritic units from Buenavista
17 del Cobre porphyry copper deposit.
18
19 Fig. 5 U–Pb weight average plots from the mineralizing porphyritic unit from El Alacrán (a),
20 and El Pilar pluton (b-c).
21
22
23 24 Fig. 6. Diagram showing the southeast age progression of magmatic activity and
25 molybdenite mineralization. Grey bars indicate mineralizing pulses constrained by Re-Os
26 molybdenite data.
27
28 Fig. 7: Interpretative map of the main Tertiary extensional structures of the Cananea
29 mining district. The region is dissected by NNW-SSE normal faults, limiting horsts and
30 grabens, of which geographic distribution defines a NE-SW lineament between Imuris and
31 Milpillas (see text for explanation). The U-Pb and Re-Os isotopic ages shows two possible
32 progressions: 1) an ENE progression, following the classical eastward migration previously
33 documented for the whole Laramide magmatic arc (see text for more details); 2) a SE
34 progression along the Cananea lineament that may control locally the emplacement of the
35 ore bodies. The NNE-SSW dotted black lines are perpendicular to the ENE progression and
36 intercept the ore bodies dated by Re-Os method. The upper age (italic) corresponds to the
37 U-Pb zircon ages of the porphyritic intrusions, except for El Pilar Deposit. The lower age
38 (regular) corresponds to the molybdenite Re-Os ages. In the case of the Buenavista del
39 Cobre mine, the 60.8 Ma was chosen between three available ages.
40
41 Tables
42 Table 1. General geologic features of the Porphyry copper deposits from the Cananea district,
43 northwestern Mexico.
44
45 Table 2. Re-Os molybdenite data from the El Pilar, Mariquita, and Lucy copper deposits from
46 the Cananea district. 47
48 Table 3. U-Pb geochronologic analyses of granodiorite porphyry from Buenavista del Cobre
49 mine.
50
51 Table 4. U-Pb geochronologic analyses of granodiorite porphyry from Buenavista del Cobre
52 mine.
53
54 Table 5. U-Pb geochronologic analyses of quartz monzonite porphyry from Buenavista del
55 Cobre mine.
56
57 Table 6. U-Pb geochronologic analyses of monzodiorite porphyry from Buenavista del Cobre
58 mine.
59
60 Table 7. U-Pb geochronologic analyses of the mineralizing porphyry from El Alacrán PCD.
61
62 Table 8. U-Pb geochronologic analyses of the granodiorite from the El Pilar Cu deposit.
63
64 Table 9. U-Pb geochronologic analyses of the granodiorite from the El Pilar Cu deposit.
65
66 Figure 1 Click here to download Figure: Figure 1.pdf
Del Rio Salas et al., Fig. 1
32o Metamorphic core complex belt
USA MEX BC
LC
30o
Hermosillo Gulf of California
28o
Laramide rocks Plutonic Volcanic 100 km
114o 112o 110o Figure 2 Click here to download Figure: Figure 2.pdf
Del Rio-Salas et al., Fig. 2
114° Arizona 110° New Mexico
California
Tucson 32° 80
Sonora BC Gulf of LC California 70
Baja California
60 Chihuahua Hermosillo
28°
Baja California Sur
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0 N °5 )DXOW 0 Є%ROVD)RUPDWLRQ 'N D D D D D D D D 3F&DQDQHD*UDQLWH 1 0LQHSURVSHFW D D D D 110°20'W 110°10'W Figure 4 Click here to download high resolution image Figure 5 Click here to download high resolution image Figure 6 Click here to download high resolution image Figure 7 Click here to download Figure: Figure 7.pdf
Sierra San Antonio ARIZONA 111ºW Nogales 110º30’W 110ºW
SONORA Sierra Chivato Sierra Sierra San José EP
Sierra El Pinito ENE progression N
San Antonio Río San Pedro valley
MI
LU Milpillas - Milpillas Sierra Mariquita 0 10 km
MA Sierra ElenitaM
Sierra Los Ajos Cocóspera graben - Cocóspera Cuitaca - río Bacanuchi graben 31ºN Cananea Sierra Cuitaca Río Sonora graben
BC
SE progression Sierra Magdalena Sierra
Sierra El Manzanal Ímuris
EA Sierra Madera Sierra 63.8 Sierra Azul 61.8 63.8 60.8 63.0 59.2 74.6 73.9 62.7 57.8 60.4 60.8 Table 1
Table 1. Intrusive rocks Age Pre-min Porphyry (Ma) Ton Deposit name Metals Style Method Mineralogy (x106) Metal contents References
Buenavista py, cpy, mo, cc, 0.42% Cu, 0.008% Cu-Mo-Zn sw, b, sk gd, mz-di qz-feld 59.2-59.3 ± 0.3 Re-Os 7,140 1, 2, 3, 4 del Cobre co, en Mo, 0.58 gr/ton Ag, 0.012 gr/ton Au Milpillas Cu sw gd qz-feld 63.0-63.1 ± 0.4 Re-Os cpy, oxides 230 0.85% Cu 5, 6
Mariquita Cu-Mo sw, b gd, mz-di qz-feld 59.2-59.3 ± 0.3 Re-Os py, cpy, cc 100 0.48% Cu 7, 8, 9
María Cu-Mo sw, b gd qz-feld 60.4 ± 0.3 Re-Os py, cpy, mo 8.6 1.7% Cu, 0.1% Mo 1, 4
El Alacrán Cu-Mo sw, b gd qz-mz 60.8-60.9 ± 0.2 Re-Os py, cpy, cc, mo 2.4 0.35% Cu 1, 4, 7
Lucy Mo-Cu sw gd gd 61.6-61.8 ± 0.3 Re-Os mo, cpy - - 9
El Pilar Cu-Mo sw gd - 73.9 ± 0.4 Re-Os cpy, py, mo - - 9
Mineralization style: (sw) stockwork and veins; (sk) skarn; (b) breccia. Intrusive rocks: (qz-feld) quartz-feldespatic porphyry; (di) diorite; (mz) monzonite. Metallic mineralogy: (cc) chalcocite; (co) covellite; (cpy) chalcopyrite; (en) enargite; (mo) molybdenite; (py) pyrite. References: (1) Wodzicki, 2001; (2) Barton et al., 1995; (3) Singer et al., 2005; (4) Barra et al., 2005; (5) Valencia et al., 2006; (6) Noguez-Alcántara, 2008; (7) Pérez-Segura, 1985; (8) Del Rio Salas et al., 2013; (9) Present study. Table 2
Table 2.
Total Re Deposit Sample 187Re (ppm) 187Os (ppb) Age (Ma) (ppm) Mariquita Mari-1 83.7 52.6 51.6 59.3 ± 0.3 Mariquita Mari-2 373.5 234.8 231.6 59.2 ± 0.3 Lucy Lucy-1 51.55 32.41 33.28 61.6 ± 0.3 Lucy Lucy-2 47.2 47.2 29.7 61.8 ± 0.3 El Pilar Pilar-2 64.8 40.7 50.2 73.9 ± 0.4
Table 3
Table 3.
Analysis U (ppm) U/Th 206Pb/204Pb 206Pb*/238U ± (%) 206Pb*/238U* ± (Ma) ratio age 1 384 2.2 2790 0.0091 6.5 58.2 3.8 2 865 2.2 2542 0.0094 2.1 60.4 1.2 3 1408 2.1 9186 0.0090 4.7 57.8 2.7 4 1812 2.2 11160 0.0091 2.3 58.1 1.3 5 659 1.5 2032 0.0094 5.6 60.5 3.4 6 795 1.7 3964 0.0091 1.4 58.7 0.8 7 702 2.1 7108 0.0095 2.5 60.8 1.5 8 968 2.4 15772 0.0094 2.8 60.4 1.7 9 1069 1.7 6016 0.0095 2.1 60.6 1.3 10 680 2.5 14452 0.0095 1.9 60.7 1.1 11 186 1.0 940 0.0090 1.9 57.5 1.1 12 877 1.7 5760 0.0095 0.9 61.0 0.5 13 911 2.2 4822 0.0097 1.1 61.9 0.7 14 883 2.0 4968 0.0095 0.7 61.1 0.4 15 905 2.3 4564 0.0095 4.0 60.7 2.4 16 358 1.8 1850 0.0096 2.4 61.3 1.5 17 935 2.1 6034 0.0096 1.0 61.5 0.6 18 584 2.6 2326 0.0095 2.8 61.2 1.7 19 324 2.1 3400 0.0096 1.6 61.6 1.0 20 766 2.3 4542 0.0094 1.3 60.2 0.8 21 1069 2.0 7408 0.0095 1.7 61.0 1.0 22 658 1.5 3612 0.0095 4.4 60.6 2.7
Table 4
Table 4.
Analysis U (ppm) U/Th 206Pb/204Pb 206Pb*/238U ± (%) 206Pb*/238U* ± (Ma) ratio age 1 446 1.8 2680 0.0092 3.5 59.0 2.0 2 634 1.0 3684 0.0094 3.2 60.6 1.9 3 523 1.8 2482 0.0095 2.6 61.0 1.6 4 954 1.4 3958 0.0095 1.6 60.8 1.0 5 972 4.5 5264 0.0096 1.6 61.4 1.0 6 409 2.1 2496 0.0094 2.4 60.4 1.4 7 580 2.0 3636 0.0093 3.2 59.6 1.9 8 409 1.6 2218 0.0095 4.9 61.0 3.0 9 608 2.9 3656 0.0097 2.2 62.4 1.4 10 1060 0.9 4676 0.0092 3.8 59.2 2.2 11 589 2.1 2442 0.0094 2.9 60.4 1.7 12 1157 1.0 5008 0.0094 2.0 60.2 1.2 13 788 2.0 4618 0.0097 1.8 62.0 1.1 14 518 2.4 2418 0.0092 5.4 58.7 3.2 15 1739 0.9 7466 0.0095 2.0 60.8 1.2 16 551 1.6 1610 0.0090 1.8 57.6 1.0 17 545 2.0 3396 0.0095 2.0 61.2 1.2 18 424 1.9 2396 0.0094 2.7 60.2 1.6
Table 5
Table 5.
Analysis U (ppm) U/Th 206Pb/204Pb 206Pb*/238U ± (%) 206Pb*/238U* ± (Ma) ratio age 1 673 1.9 4166 0.0095 1.7 61.1 1.0 2 665 2.0 2956 0.0091 2.2 58.4 1.2 3 452 1.5 2876 0.0096 1.8 61.6 1.1 4 433 1.9 1618 0.0095 5.2 61.0 3.1 5 273 2.4 2006 0.0097 2.8 62.4 1.7 6 357 2.1 1910 0.0094 2.1 60.0 1.2 7 702 1.3 3196 0.0096 1.2 61.3 0.7 8 449 1.8 2386 0.0094 2.2 60.4 1.3 9 308 2.2 1584 0.0094 2.9 60.0 1.8 10 407 2.1 2200 0.0098 2.1 62.8 1.3 11 1313 2.0 6102 0.0091 3.2 58.6 1.9 12 840 1.5 3222 0.0095 2.9 60.7 1.7 13 381 2.1 2052 0.0095 3.7 60.9 2.2 14 369 2.2 2500 0.0098 2.4 62.8 1.5 15 482 1.9 3824 0.0096 0.6 61.4 0.4 16 741 1.7 3552 0.0093 2.1 59.9 1.3
Table 6
Table 6.
Analysis U (ppm) U/Th 206Pb/204Pb 206Pb*/238U ± (%) 206Pb*/238U* ± (Ma) ratio age 1 1774 1.7 7764 0.0094 1.6 60.4 1.0 2 118 1.0 418 0.0090 7.1 57.9 4.1 3 949 1.5 3976 0.0094 1.6 60.5 1.0 4 509 1.7 2760 0.0094 2.2 60.3 1.3 5 1918 2.1 7020 0.0089 2.3 57.4 1.3 6 1448 2.3 2590 0.0090 2.6 58.0 1.5 7 1814 2.5 7160 0.0090 2.6 57.9 1.5 8 1842 2.2 9410 0.0092 2.7 58.8 1.6 9 600 1.7 1978 0.0091 2.0 58.3 1.2 10 2018 2.0 7184 0.0090 2.3 58.1 1.3 11 2347 1.9 8246 0.0087 1.9 55.7 1.0 12 2156 1.8 7340 0.0091 1.1 58.3 0.6 13 1397 2.6 5734 0.0092 1.8 59.1 1.1 14 1379 2.2 3496 0.0094 2.0 60.5 1.2 15 1443 2.1 7160 0.0094 2.0 60.1 1.2 16 1698 2.2 8870 0.0094 1.7 60.3 1.0 17 1525 2.8 6376 0.0093 2.0 59.5 1.2 18 2106 2.0 16426 0.0092 1.8 58.9 1.0 19 1701 1.7 4758 0.0088 1.6 56.3 0.9 20 1265 3.1 11920 0.0090 1.7 58.1 1.0 21 1280 2.6 5120 0.0092 3.4 59.0 2.0 22 1458 2.8 7142 0.0094 2.9 60.2 1.7 23 1031 2.0 5168 0.0090 3.5 57.6 2.0 24 263 1.6 1170 0.0092 5.5 59.3 3.3
Table 7
Table 7.
Analysis U (ppm) U/Th 206Pb/204Pb 206Pb*/238U ± (%) 206Pb*/238U* ± (Ma) ratio age 1 889 1.9 3914 0.0091 1.3 58.5 0.7 2 340 1.7 1894 0.0090 2.6 57.4 1.5 3 899 1.8 3478 0.0091 1.8 58.3 1.1 4 442 2.0 1792 0.0090 4.7 57.7 2.7 5 263 3.1 1298 0.0090 4.8 57.8 2.8 6 611 2.2 1482 0.0090 1.7 57.9 1.0 7 1621 1.9 7274 0.0089 3.0 57.2 1.7 8 992 2.7 13054 0.0089 1.6 56.8 0.9 9 1419 2.1 2182 0.0089 2.8 56.8 1.6 10 1236 2.3 3202 0.0090 1.0 57.7 0.6 11 866 2.8 4352 0.0090 0.8 58.0 0.5 12 1478 2.3 5096 0.0087 2.4 56.1 1.3 13 653 1.9 1242 0.0089 2.0 56.8 1.1 14 1476 2.0 6416 0.0091 1.9 58.4 1.1
Table 8
Table 8.
Analysis U (ppm) U/Th 206Pb/204Pb 206Pb*/238U ± (%) 206Pb*/238U* ± (Ma) ratio age 1 274 4.1 2018 0.0116 2.7 74.2 2.0 2 140 4.1 1450 0.0115 4.1 73.6 3.0 3 382 3.7 5250 0.0116 1.8 74.5 1.4 4 281 4.0 1524 0.0113 5.2 72.2 3.8 5 535 3.0 17918 0.0113 1.5 72.6 1.0 6 416 3.5 3016 0.0114 3.2 73.0 2.3 7 191 4.3 10632 0.0113 2.9 72.6 2.1 8 296 3.9 2302 0.0114 5.0 73.1 3.6 9 306 2.5 2206 0.0117 1.3 75.1 1.0 10 327 1.9 2918 0.0113 2.3 72.7 1.7 11 426 2.7 3150 0.0118 1.8 75.5 1.3 12 304 4.2 1994 0.0120 1.8 76.6 1.3 13 468 2.9 3416 0.0115 3.0 73.9 2.2 14 495 2.1 3052 0.0115 1.2 73.9 0.9 15 179 3.9 5262 0.0118 2.7 75.4 2.0 16 220 2.6 2060 0.0118 1.9 75.7 1.4 17 309 3.0 2352 0.0118 3.3 75.8 2.5 18 205 3.5 956 0.0114 2.5 72.8 1.8 19 200 3.4 2148 0.0116 4.6 74.2 3.4 20 233 3.6 1864 0.0120 4.2 77.1 3.2 21 451 2.5 9820 0.0114 2.0 73.2 1.5 22 399 3.2 1664 0.0119 2.0 76.0 1.5 23 293 2.9 2434 0.0118 2.7 75.6 2.1 24 282 2.1 1592 0.0120 1.6 76.9 1.2 25 273 3.1 1572 0.0116 2.2 74.1 1.6 26 656 2.6 4310 0.0117 4.6 75.2 3.4 27 310 3.3 2194 0.0117 1.9 74.8 1.4
Table 9
Table 9.
Analysis U (ppm) U/Th 206Pb/204Pb 206Pb*/238U ± (%) 206Pb*/238U* ± (Ma) ratio age 1 346 2.6 2574 0.0119 3.6 76.2 2.7 2 480 3.2 4420 0.0118 2.9 75.4 2.2 3 386 2.4 3408 0.0114 2.0 72.8 1.4 4 350 2.9 2112 0.0118 4.1 75.9 3.1 5 672 2.9 4248 0.0119 1.5 76.4 1.2 6 300 1.6 2474 0.0119 2.4 76.3 1.8 7 606 3.6 4406 0.0114 2.6 73.0 1.9 8 349 2.4 7646 0.0118 1.4 75.7 1.0 9 366 3.2 2664 0.0114 3.1 72.8 2.3 10 898 2.7 6128 0.0116 2.5 74.3 1.9 11 490 2.7 3156 0.0115 1.4 73.5 1.0 12 517 3.0 2650 0.0119 4.8 76.3 3.6 13 576 2.8 5672 0.0117 5.1 75.3 3.8 14 667 1.6 4384 0.0115 1.7 74.0 1.3 15 548 1.9 4542 0.0114 3.4 73.3 2.5 16 535 2.6 5068 0.0122 0.9 78.2 0.7 17 567 3.4 3996 0.0114 3.7 73.2 2.7 18 890 3.8 1974 0.0113 2.7 72.7 2.0 19 702 3.1 4426 0.0115 1.1 73.6 0.8 20 724 2.8 5052 0.0113 3.2 72.6 2.3 21 584 2.8 4570 0.0121 3.0 77.4 2.3 22 703 2.9 4682 0.0117 2.1 75.0 1.5 23 405 2.6 3154 0.0116 2.8 74.5 2.0 24 839 2.7 6498 0.0119 1.5 76.3 1.1 25 626 1.8 6278 0.0115 3.4 73.5 2.5 26 696 2.4 6156 0.0118 3.9 75.7 3.0 27 505 2.5 3124 0.0119 2.6 76.5 2.0 28 522 3.1 6762 0.0116 2.0 74.4 1.4 29 577 4.2 2490 0.0119 1.3 76.3 1.0 30 400 2.2 2374 0.0115 3.3 73.6 2.4 31 439 3.9 3534 0.0115 2.5 74.0 1.8