Regional stratigraphy and distribution of epigenetic stratabound ...

Miner Deposita (2009) 44:343–361 DOI 10.1007/s00126-008-0212-4

ARTICLE

Regional stratigraphy and distribution of epigenetic stratabound celestine, fluorite, barite and Pb–Zn deposits in the MVT province of northeastern Mexico Francisco González-Sánchez & Antoni Camprubí & Eduardo González-Partida & Rafael Puente-Solís & Carles Canet & Elena Centeno-García & Viorel Atudorei

Received: 24 February 2007 / Accepted: 23 September 2008 / Published online: 1 November 2008 # Springer-Verlag 2008

Abstract Northeastern Mexico hosts numerous epigenetic stratabound carbonate-hosted low-temperature hydrothermal deposits of celestine, fluorite, barite and zinc-lead, which formed by replacement of Mesozoic evaporites or carbonate rocks. Such deposits can be permissively

Editorial handling: F. Tornos F. González-Sánchez : A. Camprubí (*) : E. Centeno-García Departamento de Geoquímica, Instituto de Geología, Universidad Nacional Autónoma de México, Ciudad Universitaria, Delegación Coyoacán, 04510 México, DF, Mexico e-mail: [email protected] E. González-Partida Centro de Geociencias, Universidad Nacional Autónoma de México, Campus Juriquilla, Boulevard Juriquilla 3001, 76230 Santiago de Querétaro, Qro, Mexico R. Puente-Solís Programa de Posgrado en Ciencias de la Tierra, Universidad Nacional Autónoma de México, Ciudad Universitaria, Delegación Coyoacán, 04510 México, DF, Mexico C. Canet Departamento de Recursos Naturales, Instituto de Geofísica, Universidad Nacional Autónoma de México, Ciudad Universitaria, Delegación Coyoacán, 04510 México, DF, Mexico V. Atudorei Department of Earth and Planetary Sciences, The University of New Mexico, Northrop Hall, Albuquerque, NM 87131, USA

catalogued as Mississippi Valley-type (MVT) deposits. The deposits studied in the state of Coahuila are associated with granitic and metasedimentary basement highs (horsts) marginal or central to the Mesozoic Sabinas Basin. These horsts controlled the stratigraphy of the Mesozoic basins and subsequently influenced the Laramide structural pattern. The Sabinas Basin consists of ~6,000-m-thick Jurassic to Cretaceous siliciclastic, carbonate and evaporitic series. The MVT deposits are mostly in Barremian and in AptianAlbian to Cenomanian formations and likely formed from basinal brines that were mobilized during the Laramide orogeny, although earlier diagenetic replacement of evaporite layers (barite and celestine deposits) and lining of paleokarstic cavities in reef carbonates (Zn–Pb deposits) is observed. Fluid inclusion microthermometry and isotopic studies suggest ore formation due to mixing of basinal brines and meteoric water. Homogenization temperatures of fluid inclusions range from 45°C to 210°C; salinities range from 0 to 26 wt.% NaCl equiv., and some inclusions contain hydrocarbons or bitumen. Sulfur isotope data suggest that most of the sulfur in barite and celestine is derived from Barremian to Cenomanian evaporites. Regional geology and a compilation of metallogenic features define the new MVT province of northeastern Mexico, which comprises most of the state of Coahuila and portions of the neighboring states of Nuevo León, Durango and, perhaps extends into Zacatecas and southern Texas. This province exhibits a regional metal zonation, with celestine deposits to the south, fluorite deposits to the north and barite and Zn–Pb deposits mostly in the central part. Keywords MVT deposits . Zinc–lead . Fluorite . Barite . Celestine . Red-bed deposits . Mexico . Coahuila

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Miner Deposita (2009) 44:343–361

There are several fluorite, celestine, barite and Zn–Pb epigenetic stratabound deposits in northeastern Mexico (mostly in the state of Coahuila and in parts of the states of Nuevo León, Durango and Zacatecas; Fig. 1) that can be classified as MVT deposits but have been traditionally attributed to other deposit types or are unclassified. However, these deposits define a mineralized area, which may extend to Texas and New Mexico in the USA, where these deposits are of major economic importance. Some of the “Type III deposits” of northern Chihuahua (Megaw et al. 1996) could also belong to this province. Such regional mineralization is linked with the evolution of the prominent Mesozoic marine basin of southeastern North

Introduction In northeastern Mexico, there are small Zn–Pb Mississippi Valley-type (MVT) deposits that were mined between 1950 and 1980, such as the Sierra Mojada and Reforma deposits, in the state of Coahuila, and El Diente, in the state of Nuevo León. The present economic interest in MVT deposits in northeastern Mexico, however, is focussed on fluorite, celestine and barite. Most of the production of these minerals in Mexico, a major producer in the world, comes from MVT deposits in this region, with the sole exception being the giant Las Cuevas fluorite deposit in San Luis Potosí.

MAJOR MVT DISTRICTS IN NORTH AMERICA 1 Tennessee 2 Southeast Missouri 3 Tri-State 4 Upper Mississippi or Wisconsin 5 Pine Point 6 Polaris 7 Nanisivik 8 Daniels’ Harbour 9 Gays River 10 Gayna River 11 Robb Lake 12 Encantada Buena Vista 13 Sierra de Los Alamitos 14 Barosa (Muzquiz) 15 Reforma 16 Las Cuevas (El Realito, El Refugio)

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Fig. 1 Location of epigenetic stratabound MVT-like deposits in Mexico

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America. However, the information about this basin is fragmentary and incomplete, and none of the available work provides any overview of the basin, particularly its complete stratigraphy and evolution. In this paper, we review such evolution and identify for the first time all the Mississippi Valley-type deposits in northeastern Mexico as the first necessary step in characterizing their genesis. The occurrence of red-bed Cu deposits in the area is seen in the same framework. Furthermore, we compile and add new fluid inclusion and isotopic data for these deposits.

The mesozoic basins of northeastern Mexico The structural, stratigraphic and paleogeographic patterns of northeastern Mexico were essentially determined by the Ouachita–Marathon orogenies, during the PermianTriassic (Goldhammer 1999), and by the opening of the Gulf of Mexico, associated with the breakup of Pangea, during Late Triassic to Middle Jurassic (Salvador and Green 1980; Anderson and Schmidt 1983; Winker and Buffler 1988; Wilson 1990). The resulting Mesozoic marine basins in this area were deformed during the Laramide orogeny, between the Late Cretaceous and the Early Tertiary (Goldhammer 1999). During the breakup of Pangea, a series of horst and grabens formed. These controlled the sedimentary patterns of the region during the Mesozoic (Padilla y Sánchez 1986a, b) and later Laramide deformation (Wilson 1990). The main horsts that formed during the rifting and opening of the Gulf of Mexico are the Burro–Peyotes Peninsula, the Coahuila Block (or Island), the Tamaulipas Archipelago and the La Mula and Monclova islands, whereas the main grabens in the area are the Sabinas Basin in central Coahuila and the Parras Basin in southern Coahuila (Fig. 2). The above are named islands or peninsulas when they remained emerged and blocks when they remained submerged. The Coahuila Block is a horst that contains PermianTriassic (Wilson et al. 1984) or Late Triassic (Jones et al. 1995; Molina-Garza 2005) granites and granodiorites and comprises a Middle Pennsylvanian to Permian volcanoclastic and flysch sequence in its western part (Valle Acatita–Las Delicias area; McKee et al. 1988; Wilson 1990). It is inferred to have a Proterozoic basement due to the isotopic signatures in Permian-Triassic intrusives (López et al. 2001). The Coahuila Block is limited to the north by the San Marcos Fault, a dextral lateral fault that was active during the Late Triassic to Late Jurassic rifting, and to the south by the Parras Basin. This block was covered by Cretaceous platform carbonates slightly deformed during the Laramide orogeny (Imlay 1936; Charleston 1981; Johnson et al. 1991; Johnson 1989, unpublished report).

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The Tamaulipas Archipelago is located east of the Sabinas Basin and shows a NW–SE trend. Its basement consists of Permian-Triassic intrusions, as the remains of a Paleozoic archipelago (Goldhammer 1999). The Burro–Peyotes Peninsula is located north of the Sabinas Basin and consists of metasedimentary rocks deformed during the Late Paleozoic, and it is limited to the southeast by the La Babia Fault, a dextral lateral fault associated with the Late Triassic to Middle Jurassic continental rifting (Charleston 1981). Thus, the Sabinas Basin was a graben limited by the Coahuila Block to the south, the Burro–Peyotes Peninsula to the north and the Tamaulipas Archipelago to the east. It includes two minor horsts named La Mula and Monclova islands that contain Permian-Triassic granitic intrusives as well (Jones et al. 1984; Wilson 1990). The above structures and the associated paleogeographic features are contained in the Coahuila Fold Belt (see Goldhammer 1999 and references therein). It formed during the Laramide orogeny and consists of isolated NW–SE oriented tight and long anticlines separated by wide synclinal valleys. Other common deformation features are evaporite domes formed by salt tectonics (Padilla y Sánchez 1986a, b; Goldhammer 1999). The Parras and La Popa Basins formed during the Late Cretaceous (Campanian-Maastrichtian) and contain a ~5,000-m-thick sequence of deltaic and shallow siliciclastic marine sequence that belong to the La Difunta Group (Padilla y Sánchez 1986a, b; Goldhammer 1999). In the southern and eastern part of the Parras Basin, the closest areas to the deformation front of the Sierra Madre Oriental (Late Cretaceous to Paleogene) have long tight folds and minor thrusts facing north and the intensity of such deformation decreases northwards (Goldhammer 1999). The La Popa Basin contains domes formed by salt diapirism and eroded synclines (Johnson 1989, unpublished report).

Mesozoic stratigraphy It is inferred that thick Early Jurassic red bed deposits probably formed in the Sabinas Basin (Huizachal Group; Goldhammer 1999; Rueda-Gaxiola et al. 1999; Fastovsky et al. 2005). Such classic rift sequences probably formed in grabens and half-grabens and may have been accompanied by calc-alkaline volcanic rocks interbedded with continental conglomerates during initial and intermediate stages of rifting (Garrison and McMillan 1999). The clastic sequences were overlain by evaporite deposits during the initial marine transgression (Padilla y Sánchez 1986a, b). Up to 1,000-m-thick evaporitic deposits (Goldhammer 1999) formed in the central part of the basin (Minas Viejas Formation; Eguiluz de Antuñano 2001; Fig. 3). Towards

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the Tamaulipas Archipelago, these deposits grade laterally into anhydrite deposits interfingered with carbonates at the base and into high-energy carbonates at the upper part of the Olvido Formation; the overall thickness is about 500 m (Eguiluz de Antuñano 2001). In areas of shallow marine sedimentation near to emerged basement blocks, up to 600-m conglomerates and sandstones were deposited (La Gloria Formation; Padilla y Sánchez 1986a, b; Eguiluz de Antuñano 2001). The La Gloria Formation correlates with the platform carbonates of the Zuloaga Formation towards the central part of the basin (Oivanki 1974). The subsidence of the basin increased between the Early Kimmeridgian and the Tithonian, and the La Gloria and Olvido Formations were overlain by 60- to 800-m thick, Kimmeridgian to Early Berriasian black shales of the La Casita Formation (Eguiluz de Antuñano 2001). During the Early Hauterivian 250- to 350-m-thick shallow marine clastic sediments of the Barril Viejo Formation were deposited (Eguiluz de Antuñano 2001). These rocks overlie high-energy platform carbonates that correspond to the Berriasian Menchaca Formation, 250- to 300-m thick (Imlay 1940). In the vicinity of the Burro– Peyotes Peninsula, sandstones and red conglomerates of the Hosston Formation of Berriasian to Late Barremian age formed in alluvial plains, whereas in the vicinity of the Coahuila and La Mula islands, the San Marcos Formation represents alluvial fans (Eguiluz de Antuñano 2001; Chávez-Cabello et al. 2005, 2007). The reef facies of the Padilla Formation, Late Hauterivian to Barremian, is up to 150-m thick (Eguiluz de Antuñano 2001) and grades into lagoonal carbonates to the northeast. During the Late Hauterivian the Burro–Peyotes Peninsula was overlain by the Hosston Formation, which is coeval with the La Mula Formation at the northeastern part of the basin (Imlay 1940). The La Mula Formation grades into sandstones of the Pátula Formation towards the Coahuila Island. The carbonate reef rocks of the Cupido Formation, Late Barremian to Middle Aptian, led to the development of a sabkha environment characterized by 600–800 m of alternating carbonates and evaporites of the La Virgen Formation (Eguiluz de Antuñano 2001). This formation correlates with the Hosston Formation to the north, the San Marcos Formation to the south and the pelagic carbonates of the Lower Tamaulipas Formation to the east and the southeast (Eguiluz de Antuñano 2001). During the Early Aptian, high-energy lagoonal carbonates of the back-reef Cupidito Formation, up to 250-m thick (Wilson and Pialli 1977), formed. At this time, the Coahuila Island, rimmed by beach sandstones of the San Marcos Formation, was the last emerged land (Eguiluz de Antuñano 2001). This formation, in the contact with the overlying La Peña Formation, hosts several red-bed Cu deposits.

Miner Deposita (2009) 44:343–361 Fig. 2 Structural configuration, tectonic features, simplified geology and distribution of MVT and associated deposits of the State of Coahuila and neighboring areas. The distribution of these deposits determines the four subprovinces of the MVT province of northeastern Mexico. The A–A′ section is shown in Fig. 3. Modified from ChávezCabello et al. (2005, 2007). The regional geology is simplified from Romo-Ramírez et al. (2003) and Sánchez-Bermeo et al. (2003). CFB Coahuila Fold Belt, LBF La Babia Fault, LMI, La Mula Island, LPB La Popa Basin, MC Monterrey Curvature, MI Monclova Island, MPNM MVT province of northeastern Mexico, MSMS Mojave– Sonora Megashear, PB Parras Basin, PR Parras Rise, SB Sabinas Basin, SMF San Marcos Fault, TA Tamaulipas Archipelago, TL Texas Lineament. Barite deposits (green circles): B1 Sierra de Santa Rosa (Barosa); B2 San Juan; B3 María Elena, El Palmito, Santa Rosa, El Potrero; B4 El Cedral; B5 Mina; B6 La Luz. Zn–Pb deposits (red stars): Z1 Puerto Rico; Z2 Carmen; Z3 Diamantina; Z4 San Lorenzo; Z5 Cerritos I and II; Z6 Viky, Santa Elena, La Cruz; Z7 La Esperanza; Z8 Dos Hermanos; Z9 San Francisco; Z10 Puerto Arturo; Z11 La Bayoneta; Z12 El Porvenir; Z13 Carrizalejo; Z14 Las Águilas; Z15 Cedro I; Z16 Las Torres, Las Torres I; Z17 El Cedro; Z18 Agrupamiento Fortaleza; Z19 Agrupamiento Reforma; Z20 La Luz; Z21 Nueva Reforma; Z22 Roca Verde; Z23 Roca Flores; Z24 Roca Rica, San Eugenio, Rama Azul; Z25 Rincón Rojo; Z26 Bonanza; Z27 Agrupamiento Mina; Z28 Sacramento; Z29 Minas Viejas; Z30 Nuevo México, La Carmencita; Z31 La Cucaracha; Z32 El Diente, Victoria I and II; Z33 El Socorro. Celestine deposits (blue crosses): C1 Oasis; C2 Elvia; C3 Max II; C4 El Gari, El Cuadrangular; C5 El Tule; C6 La Victoría; C7 Santa María; C8 Las Peñitas; C9 La Noria; C10 Pirámide III; C11 La Candelaria; C12 Angélica; C13 El Lucero; C14 San Marcos; C15 Blanquita; C16 San José; C17 Sotolito; C18 Ocotillo; C19 San Fernando; C20 El Quemado; C21 Ampliación San Marcos, Prospecto 5; C22 Australia; C23 Montejano I; C24 Montejano II; C25 El Latrisco; C26 La Bola; C27 La Carroza; C28 La Tinaja; C29 San Lorenzo; C30 El Venado; C31 Campo Patricio 2; C32 Campo Patricio 1; C33 El Diablo; C34 El Volcán; C35 Campo Patricio 4; C36 Campo Patricio 3; C37 Campo Patricio 5; C38 La Chenta Norte; C39 La Chenta Sur; C40 El Caviar; C41 La Guadalupana; C42 La Ilusión; C43 Del Rincón; C44 La Yesuda; C45 San Agustín; C46 La Discordia; C47 San Lorenzo 3; C48 San Luis; C49 Santo Tomás; C50 Cerro Bola; C51 La Milagrosa; C52 La Flor; C53 Ampliación La Flor. Fluorite deposits (purple diamonds): F1 San Genaro, Evelyn, Evelyn 2; F2 Tres Hermanos; F3 Ponchito; F4 La Bonita; F5 Josefinas; F6 Navideño 4; F7 Ima, Último; F8 Totopos 1; F9 Oasis 4; F10 Aries 1; F11 Peñón Blanco; F12 El Otomí; F13 Osiris, F14 Santa Anita; F15 Santa Anita 2; F16 Un Día De Estos 1 and 3; F17 El Jardín; F18 Minas Fronterizas; F19 Lorena; F20 San Felipe; F21 Nueva York; F22 Santa María; F23 La Victoria; F24 Susana; F25 Las Indias; F26 Bonanza; F27 Alba Iris; F28 Pandita, Tohui; F29 San Cristóbal; F30 Los Fresnos; F31 Cinco Hermanos; F32 Arquímedes; F33 Europa; F34 Graciela; F35 Las Carmelas; F36 Navidad, Año Nuevo; F37 San Cachito; F38 Kentucky; F39 María; F40 San Pedro; F41 San Miguel 1; F42 Los Buras; F43 El Número Nueve; F44 Cerro Colorado; F45 La Paloma; F46 El Patrón; F47 La Purísima–El Paso; F48 Los Cuates; F49 Fátima; F50 La Güera, La Güera 1, La Gorriona 3; F51 Amigos; F52 Gaby; F53 Ataco; F54 El Alto; F55 Rosalba; F56 San Roberto 2; F57 San José; F58 San Rafael, San Rafael 1; F59 El Güero, El Güero 1; F60 Camarón 2, Camarón 14; F61 Alcón 0–3; F62 El Gari, El Cuadrangular, Alcón 0–4; F63 Las Delias; F64 Tayoltita; F65 La Macarena, Valencia; F66 La Muralla; F67 Sofito Tercero; F68 Chubasco 1, Chubasco 2; F69 La Mariposa 1, 2, 3 and 4; F70 San Antonio; F71 Sierra San Marcos, Pinos (La Becerra); F72 La Reina, Los Amigos; F73 Eva 13; F74 Margarita 4. Red-bed Cu deposits (yellow pentagons): R1, R2 Sierra de la Gavia; R3, R4 El Jabalí prospect (El Jorobado); R5–R8 Cuatrociénegas area


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During the Late Aptian, the entire Coahuila Block submerged. This transgression is marked by shales of the up to 200-m thick La Peña Formation, which can be used as a regional key horizon. This formation grades southwards and eastwards to typical deep basinal facies of the Otates Formation (Tinker 1982, in Goldhammer 1999). In the shallowest parts of the submerged Coahuila Block, up to 15-m-thick carbonate-rich sandstones of the Las Uvas Formation, which

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unconformably overlies basement rocks, formed (Lehmann et al. 1999; Eguiluz de Antuñano 2001). At the same time, carbonates of the Glen Rose Formation formed on the Burro– Peyotes Peninsula (Fig. 6 in Goldhammer 1999). The subsidence during the Albian and Cenomanian allowed the deposition of 100- to 200-m-thick mudstones to wackestones of the Upper Tamaulipas Formation in the eastern part of the basin. The former Coahuila Island was

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Fig. 3 Schematic cross-section of the Mesozoic Sabinas Basin and adjacent areas. See location in Fig. 2. Similar shades of gray denote synchronicity between formations. Based on information in Imlay (1940), Humphrey and Díaz (1954, 1956), Humphrey (1956), Ramírez

(unpublished manuscript), Wilson and Pialli (1977), Aguayo (1978), Wilson et al. (1984), Padilla y Sánchez (1986a, b), Goldhammer (1999), and Eguiluz de Antuñano (2001)

then rimmed by platform carbonates of the 500- to 700-mthick Aurora Formation (Goldhammer 1999). At the same time, the Acatita Formation was deposited, with a basal sequence of 60- to 80-m-thick bioclastic massive limestones and a ~500-m-thick unit of alternating evaporites and dolostones, corresponding to the Early to Middle Albian (Lehmann et al. 1999). The Acatita Formation is covered by the upper member of the Aurora Formation, 190- to 260-m thick (Goldhammer 1999). In the Burro– Peyotes Peninsula, the Aurora and Acatita Formations are divided into the Glen Rose–Walnut, Edwards, Kiamichi– McKnight and Georgetown Formations, with a total thickness of ~1,000 m, spanning the entire Albian. At the same time, the Del Río and Buda Formations deposited on the Burro–Peyotes Peninsula. The Del Río Formation (Early to Middle Cenomanian) consists of shales and sandstones, up to 40-m thick. The Buda Formation (Late Cenomanian) consists of 10 to 50-m-thick mudstones (Eguiluz de Antuñano 2001).

Between the Late Cenomanian and the Turonian, up to 300-m-thick interbedded black shales, limestones and sandstones of the Eagle Ford Formation were deposited (Eguiluz de Antuñano 2001). This formation grades into platform facies of the Indidura and San Felipe Formations towards the southern and southeastern parts of the basin, respectively (Eguiluz de Antuñano 2001). The sea level dropped between the Coniacian and the Middle Santonian, with an increase in the formation of carbonates and a decrease in the formation of shales, as shown by the carbonate-dominated Austin Formation (Padilla y Sanchez 1986a, b; Eguiluz de Antuñano 2001). The effect of the Laramide orogeny on post-Middle Santonian rocks in the Sabinas–Olmos, Parras and La Popa Basins is the sedimentation in continental alluvial plains and deltas. The Upson Formation, of Late Santonian to Middle Campanian age (Padilla y Sánchez 1986a, b), was deposited in a prodelta environment, which correlates with the Parras Shale (Eguiluz de Antuñano 2001). The San


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Miguel Formation, of Campanian age, was deposited in a delta front environment (Eguiluz de Antuñano 2001). The Olmos Formation, of Middle Maastrichtian (Padilla y Sánchez 1986a, b) or Late Campanian age (Eguiluz de Antuñano 2001), contains important coal deposits and correlates with part of the La Difunta Group of the La Popa Basin, Maastrichtian to Paleocene (Padilla y Sánchez 1986a, b). The Escondido Formation, Late Maastrichtian (Padilla y Sánchez 1986a, b), correlates with the upper part of the La Difunta Group of the La Popa Basin (Eguiluz de Antuñano 2001).

Identification of MVT Deposits in northeastern Mexico In northeastern Mexico, several evaporite- and carbonatehosted epigenetic stratabound deposits have not been properly ascribed to any specific deposit type. Thus, it is necessary to discriminate MVT deposits from other deposit Fig. 4 a Stratabound celestine orebody hosted by the Acatita Formation, Víbora mine, Sierra de los Alamitos. b Rhythmic layering at the bottom of a massive celestine orebody, Víbora mine, Sierra de los Alamitos. c Automorphic crystals of celestine as cavity lining, El Volcán mine, Sierra de los Alamitos. d Celestine veinlets, hosted by the Acatita Formation, San Agustín mine, Sierra de La Paila district. e Diagenetic silex nodules in carbonate rocks of the Acatita Formation, also found embedded in celestine mantos of the Víbora mine, Sierra de Los Alamitos district. f Native sulfur formed after thermochemical sulfate reduction (TSR) in the Potrero de Berrendos celestine mine, hosted by a gypsum unit of the La Virgen Formation. TSR is interpreted from the paragenetic sequence, with native sulfur after celestine

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types with similar mineralogy (e.g. skarns or carbonatehosted epithermal deposits). In this paper, we consider the following characteristics as permissive for the definition of MVT deposits in this region: 1. The deposits are associated with the Laramide orogeny or a post-orogenic event 2. The deposits are not associated with magmatic rocks 3. The host rocks did not experience metamorphism 4. The deposits are generally controlled by evaporitebearing sequences and carbonate rocks formed in shallow platforms with some degree of dolomitization 5. The deposits are generally (but not exclusively) found on basin borders, in their vicinities or in former highlands (horsts) between basins 6. The deposits are epigenetic (Fig. 4a) 7. The orebodies are stratabound (generally mantos) and/ or are due to karstic cavity filling, with banded internal structure and rhythmites with alternate dark and clear bands (Fig. 4a,b)

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8. The veins, veinlets and fractures in host rocks are lined by the same minerals as the mantos (Fig. 4d) 9. There are relicts of the pre-replacement rocks (dolomitized limestones and/or silex nodules) concordant to the mineralized mantos and to the host rocks (Fig. 4e) 10. Thermal sulfate reduction phenomena occur as part of the mineralization (Fig. 4f) 11. The mineralization is found replacing fossils (Fig. 5a) 12. The ores are cementing collapse, tectonic or hydraulic breccias (Fig. 5b) 13. Ore associations show dendritic, skeletal and botryoidal (colloform) crystal growth (Fig. 5c)

14. Hydrothermal alteration typical of MVT deposits (e.g. dolomitization) occurs around the orebodies (Fig. 5d), and 15. Ore and gangue minerals contain hydrocarbon-rich inclusions (Fig. 5e,f).

Using these criteria, we compiled and analyzed about 500 documents on stratabound barite, celestine, fluorite and Pb–Zn deposits located in the states of Coahuila, Nuevo León and Durango. These documents include the few scientific papers published, some thesis works and, mostly,

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Vapor Hydrocarbon liquid

Th = 110°C Tmi = -8°C Aqueous liquid

E Fig. 5 a Unidentified fossil replaced by black fluorite in the Georgetown Formation, La Encantada–Buenavista area. b Hydrothermal breccia cemented by yellowish fluorite with inclusions of uranium minerals, hosted by the Georgetown and Del Río Formations; Alicia mine, on the El Burro–Peyotes Peninsula. c Colloform growth of sphalerite in the Zn–Pb deposits of the Sierra de Santa Rosa (Múzquiz district), hosted by the Aurora Formation. d Dolomite and sphalerite

F solid inclusions in barite from the Berrendos mine, bottom of the La Virgen Formation. e Fluid inclusions in fluorite showing aqueous fluids and liquid hydrocarbons, from the La Sabina mine, La Encantada–Buenavista area. f Typical low-temperature biphasic (with very high L/V ratio) or monophasic aqueous fluid inclusions in fluorite from the La Sabina mine, La Encantada–Buenavista area


mining and exploration reports from the technical archives of the Servicio Geológico Mexicano (formerly Consejo de Recursos Minerales). There are over 200 deposits that were positively identified as MVT in the state of Coahuila and neighboring areas (full references of all the technical reports in Puente-Solís 2007). Their location and main ore mineralogy is synthetically presented in Fig. 2, and their main characteristics are compiled in Table 1. The deposit classification criteria and a description for all mineralized areas are given in Puente-Solís (2007). The deposits identified as MVT are generally monomineralic. They contain hypogene celestine, barite, fluorite or sphalerite-galena ± barite, gypsum, calcite and clay minerals. Locally, there are also subordinate uranium minerals (hypogene pitchblende and supergene carnotite). The associated host-rock alteration consists of poorly developed dolomitization and/or silicification. Supergene alteration is well developed, with replacement of sulfide ores by Zn or Pb carbonates, oxides or sulfates. Some of the deposits predate and others postdate the Laramide orogeny (Fig. 6). Those deposits deformed during this orogeny show faulting at a large scale as well as cracking and crystal deformation at a small scale that is not attributable to other causes.

Distribution of MVT deposits in northeastern Mexico The spatial distribution of MVT Zn–Pb deposits and associated celestine, barite, fluorite deposits and their corresponding host formations in northeastern Mexico are shown in Fig. 2. There is a regional zoning according to the distribution of deposits formed by characteristic minerals or mineral assemblages (celestine, fluorite, barite and Zn–Pb). Such zoning is linked to the occurrence of Triassic and Jurassic paleotectonic and/or paleogeographic elements. These elements are structures associated with a system of horsts and grabens that formed during the opening of the proto-Gulf of Mexico, and ruled the distribution patterns of sedimentary facies and consequently the distribution of MVT deposits as well. The stratabound celestine deposits occur mainly in the Albian platform carbonate rocks that correspond to evaporitic facies of the Acatita Formation and/or in similar formations (Fig. 7). The celestine deposits are preferentially located on the Coahuila Block, whereas barite, fluorite and Zn–Pb deposits are located on the Burro–Peyotes Peninsula, the La Mula Island, the Tamaulipas Archipelago or in the central part of the Sabinas Basin. There are other groups of celestine deposits (1) in the Parras Basin (Fig. 2), (2) in the Berrendos area, hosted by the upper part of the La Virgen Formation and (3) at the El Tule area on the Burro– Peyotes Peninsula. These deposits, like those in the Sierra

351

de La Paila (San Agustín district) and in the Sierra de Los Alamitos–Poza La Becerra (Fig. 7), contain sub-economic fluorite layers in their upper part. There is a high concentration of fluorite deposits along the border of the Burro–Peyotes Peninsula (Fig. 2) hosted by rocks of the Washita Group (Cenomanian, equivalent to the Aurora Formation) in the contact between the Georgetown and Del Río Formations. These formations consist of platformal carbonates and lutites, respectively, and the latter limit the vertical extent of the mineralized mantos (Fig. 7). There are also some fluorite deposits as cavern fillings hosted by the Georgetown Formation. The barite deposits are found in the internal part of the Sabinas Basin (Fig. 2) and are hosted by evaporites and platform carbonate rocks of the La Virgen and Cupido (Cupidito) Formations. The main barite deposits of this area (Fig. 7) are Reforma, Berrendos, and Sierra de Santa Rosa (Múzquiz district). The Berrendos barite deposits are associated in space with stratabound Zn–Pb deposits, which are located at stratigraphic levels higher than the barite deposits. At the Sierra de Santa Rosa deposits, the barite mantos are hosted by the evaporite facies of the Cupido Formation or, occasionally, by the facies transition between the La Virgen and Cupido Formations. In the same area, there are small Zn–Pb deposits in karst cavities or in fracture zones hosted by the Aurora Formation (Fig. 7). The Berrendos and Potrero de Berrendos deposits show a vertical zonation, bottom to top, from barite to Zn–Pb, to celestine, to native sulfur mineralization in the La Virgen Formation (Fig. 7). The stratabound Zn–Pb deposits are mainly found in the internal part of the Sabinas Basin, north and northeast of the La Mula Island. There is a second group of deposits in the San Marcos and La Fragua Ranges, south of the Sabinas Basin, and these are roughly distributed following the trace of the San Marcos Fault (Fig. 2). The Zn–Pb deposits are found mostly as 100- to 200-m long and 0.40- to 2-m-thick mantos and interstratified lenticular bodies. Some deposits formed as tectonic breccias, paleokarsts, cavity linings and veinlets associated with both disseminated and massive mantos. These contain more sphalerite than galena, together with subordinate amounts of Ag and Cu minerals (Ag > Cu). The main gangue minerals in these deposits are barite, calcite, iron oxides and, sporadically, gypsum. The host rocks of the stratabound Zn–Pb deposits are platform carbonates and evaporites of the Cupidito Formation in the Reforma deposit, the Aurora Formation in the Sierra de Santa Rosa deposits and the La Virgen Formation in the Berrendos and Potrero de Berrendos deposits (Fig. 7; Puente-Solís 2007). There are several red-bed Cu(–Co–Cr–Pb–Zn) deposits hosted by siliciclastic rocks on the roof of the San Marcos Formation in contact with the La Peña Formation, over the

C28

C13

C45

C34

C30

C33

C32

C7

La Tinaja

Lucero

San Agustín

Volcán

Venado

Diablo

Víbora

Berrendos

Limestones/ Aurora Limestones/ Cupido (Cupidito)

Cuatro Ciénegas Sierra de Santa Rosa (Barosa)

B3

F71

Shales and limestones/Del Rio-Georgetown

La Encantada F18 Buenavista

Limestones and gypsum/La Virgen (top)

Limestones/ Acatita

Limestones/ Acatita

Limestones/ Acatita

Limestones/ Acatita

Limestones/ Acatita

Limestones/ Acatita

Limestones/ Acatita

Key in Host rock/ Fig. 2 formation

Ore deposit

Gangue mineralogy

Barite

Fluorite

Fluorite

Calcite, gypsum, celestine, silex nodules, iron oxyhydroxides

Calcite

Calcite, silex nodules

Celestine Barite, calcite, sulfur, gypsum

Celestine Little calcite ± barite



Celestine Barite, calcite, sulfur, gypsum, fluorite, silex nodules Celestine Little calcite ± barite

Celestine Calcite, silex nodules ± barite

Celestine Gypsum, calcite ± barite

Ore

Texture

Coarse crystals, vuggy, homogeneous crystallization, fine crystals, rhythmites Stratabound, Coarse crystals, homogeneous mantos, lentils, veins crystallization, fine crystals, rhythmites Stratabound, Coarse crystals, vuggy, mantos, homogeneous lentils, veins, karst crystallization, filling fine crystals, rhythmites Stratabound, Homogeneous mantos, lentils, crystallization, veins coarse crystals, fine crystals Stratabound, Coarse crystals, vuggy, mantos, lentils, homogeneous veins crystallization, fine crystals, rhythmites Stratabound, Coarse crystals, vuggy, mantos, lentils, homogeneous veins crystallization, fine crystals, rhythmites Stratabound, Coarse crystals, mantos, lentils, vuggy, homogeneous veins crystallization, fine crystals, rhythmites Stratabound, Coarse crystals, mantos, lentils, homogeneous fine crystals, veins crystallization, fine crystals Stratabound, Coarse crystals, mantos, lentils, vuggy, homogeneous fine crystals, crystallization, veins fine crystals Lentils, veins, Fine crystals, vuggy stratabound Stratabound, Soft sucrose, mantos, lentils, hard sucrose, collapse breccias rhythmites

Stratabound, mantos, lentils, veins

Ore body shape

Dol >> Sil

Dol

Dol >> Sil

Dol >> Sil

Ltdol >> Sil

Ltdol >> Sil

Ltdol >> Sil

Ltdol >> Sil

Ltdol >> Sil

Ltdol >> Sil

Ltdol >> Sil

Samll/not available Medium/ 70%

Large/>50%

Medium/not available

Small/ 92%

Small/ 92%

Small/ 90%

Medium/ 92%

Large/ 93%

Medium/ 91%

Small/ 97%

Alteration Deposit size/avg. grade

Table 1 Summary of the main characteristics of some representative MVT and associated deposits in Northeastern Mexico

No/no

Yes/yes

Yes/yes

No/yes

No/yes

No/yes

No/yes

No/no

Yes/yes

No/yes

No/yes

Occurrence of hydrocarbons/ organic matter

Southern edge Central part

Northern edge

Central part

Southern edge

Southern edge

Southern edge

Southern edge

Southern edge

Southern edge

Southern edge

Position in the basin

Pre-orogenic

Post-orogenic

Post-orogenic

Post-orogenic

Post-orogenic

Post-orogenic

Pre-orogenic

Post-orogenic

Post-orogenic

Post-orogenic

Post-orogenic

Relative age

Pérez-Peña (1946), this work

This work

González-Partida et al. (2003), this work

González and Izaguirre (1988b)

This work

This work

Ortiz-Hernández and Castillo-Nieto (1997), this work

Villarreal-Fuentes (2007), this work

Salas (1973), this work

This work

This work

Reference

352 Miner Deposita (2009) 44:343–361

González and Izaguirre (1988b)

Fluid inclusions

Deposit size: large=>10 Mt, medium=≤10 Mt>1 Mt, small=≤1 Mt Ltdol little dolomite, Sil silicification, Oxd oxidation

Central part No/no Pb-Zn Z14 Berrendos

353

edge of the regional San Marcos Fault. The host rocks of these deposits have greenish color, instead of the red color, typical of the San Marcos Formation, thus indicating reduced environments. The mineralogy of the red-bed mineralization consists of chalcocite, digenite, chalcopyrite, azurite, malachite, pyrite, sphalerite and galena. Along with locally Pb- and Zn-rich zones, there are portions of the deposits that are relatively rich in Co and Cr. Small irregular Pb–Zn and fluorite bodies occur at the basal portion of the La Peña Formation, associated in space with the mineralization in the San Marcos Formation. These deposits were not studied in detail, but they are metallogenically accountable: Although they are not attributable to a MVT model, they are part of the geologic history that encompasses the formation of MVT deposits of the region.

Post-orogenic

González and Izaguirre (1988a) Central part No/no Z14 Berrendos

Limestones/ La Virgen (bottom) Limestones/ La Virgen (bottom)

Barite

Pb-Zn oxides, calcite, silex nodules Barite, celestine, silex nodules

Stratabound, Nodules mantos, lentils, veins Stratabound, mantos, Colloform, lentils, botryoidal, fine crystals, speleothems veins

Oxd+ Small/60% Dol >> Sil Oxd+ Small/> Dol >> 20% Sil (Zn+Pb)

Post-orogenic

Reference Relative age Position in the basin Occurrence of hydrocarbons/ organic matter Alteration Deposit size/avg. grade Texture Ore body shape Gangue mineralogy Ore Key in Host rock/ Fig. 2 formation Ore deposit

Table 1 (continued)


Kesler (1977) reported homogenization temperatures that ranged from 125°C to 165°C for the El Triángulo, El Tule and Santo Domingo fluorite deposits. Other microthermometric data in MVT deposits of Mexico were obtained recently (González-Partida et al. 2002, 2003; Levresse et al. 2003). In this paper, we report microthermometric data of fluid inclusions from two Zn–Pb deposits (Berrendos and Reforma), a barite deposit (Sierra de Santa Rosa) and nine celestine deposits (five from the Sierra Los Alamitos district and Berrendos, El Lucero, San Agustín and Mina Úrsulo). These deposits are considered to be among the most representative for the various mineralogical subtypes of deposits. The results can be considered representative though still preliminary. The complete data set is shown in Table 2. The inclusion fluids from MVT celestine deposits in NE Mexico have homogenization temperatures that range from 45°C to 160°C, with the sole exception of the fluids in the Berrendos deposit that are hotter (homogenization temperatures range from 150 to 211°C) than in the other deposits. Salinities of inclusion fluids in celestine deposits range from 0 to 21.7 wt.% NaCl equiv. Fluid inclusions from fluorite deposits have homogenization temperatures that range from 50°C to 170°C and salinities that range from 3 to 18 wt.% NaCl equiv., generally up to 14 wt.% NaCl equiv. Fluid inclusions from barite deposits have homogenization temperatures that range from 49°C to 155°C and salinities that range from 8 to 26 wt.% NaCl+CaCl2. Fluid inclusions from Pb–Zn deposits have homogenization temperatures that range from 76°C to 150°C and salinities that range from 6.8 to 22 wt.% NaCl equiv. Fluorite deposits exhibit lower salinities than celestine, barite, and Pb–Zn deposits, and the MVT-associated deposit that shows the lowest salinities in the region is the Aguachiles

354


Fig. 6 Sketches illustrating the relative timing of formation of MVT deposits in the Sabinas Basin of northeastern Mexico and neighboring areas, based on Fig. 3, and the plausible sources for mineralizing fluids. a Formation of pre-orogenic (deformed, faulted and cracked) MVT deposits, associated with an initial mobilization of basinal brines due to lithostatic pressure. b Formation of post-orogenic and deformation of pre-orogenic MVT deposits during the compressive stages of the Laramide orogeny

fluorite deposit (3 to 4 wt.% NaCl equiv.). The salinities recorded are higher than those reported in the fluorite deposits found at the border of the San Luis–Valles Platform in Central Mexico. In that region, the world-class Las Cuevas deposit exhibits fluid inclusions with salinities that range from 0.1 to 1 wt.% NaCl equiv. and homogenization temperatures that range from 60°C to 110°C (Levresse et al. 2003). Other deposits in the region (El

Refugio, El Realito and La Constancia) also show very dilute fluids, in the same range of salinities as Las Cuevas, and homogenization temperatures that range from 45 to 130°C. These data ranges are similar to those obtained in oil fields in the basin of SE Mexico (González-Partida et al. 2003). Besides aqueous fluids, fluid inclusions in fluorite and celestine from such MVT deposits contain methane, liquid hydrocarbons and bitumen.


355

Fig. 7 Stratigraphic columns of selected locations with MVTlike deposits in northeastern Mexico, showing the stratigraphic sections where ore bodies are hosted and the types of ore bodies: Sierra de La Paila (San Agustín district; celestine deposits), Reforma and Sierra de Santa Rosa (barite and Zn-Pb deposits), El Tule (celestine and fluorite deposit), Sierra de Los Alamitos (celestine deposit), La Encantada–Buenavista district (fluorite deposits), and Berrendos (barite, Zn–Pb, celestine and native sulfur deposits)

Isotopic data Kesler (1977) and Kesler and Jones (1981) reported δ34S and 87Sr/86Sr data for several deposits of the Sierra de La Paila, Sierra de Los Alamitos, Cuatro Ciénegas and Múzquiz areas. In this study, δ34S values were determined for representative samples from the Sierra de Santa Rosa (barite), La Tinaja, El Venado and El Volcán deposits (celestine). Sulfur isotope values (Table 3) were analyzed in 13 hand-picked pure separates of barite (four) and celestine (nine). The sulfates were combusted with CuO at 1,000°C to release SO2. The SO2 was analyzed in a VG SIRA 10 mass spectrometer. Precision of the analyses is better than ±0.2‰. Sulfur isotope composition is expressed in delta permil notation with respect to the Canyon Diablo Troilite standard. The analyses were carried out in the Laboratorio General de Análisis de Isótopos Estables of the Universidad de Salamanca (Spain).

The analyzed barite samples of the Sierra de Santa Rosa deposits exhibit a δ34S range of +14.9–+19.5‰. The analyzed celestine samples of the La Tinaja, El Venado and El Volcán deposits have δ34S data that range from +17.2‰ to +17.8‰, +18.0‰ to +18.1‰, and +17.2‰ to +17.8‰, respectively. The overall range of +14.9‰ to +19.5‰ is similar to that obtained by Kesler and Jones (1981) in both celestine and barite deposits. The lowest δ34S values were obtained by Kesler (1977) for the El Tule celestine deposits, which range from +6.4‰ to +13.2‰.

Discussion The MVT metallogenic province of northeastern Mexico The more than 200 analyzed epigenetic stratabound evaporite- and carbonate-hosted deposits share enough

356


Table 2 Fluid inclusion data of representative MVT deposits and mining districts of Northeastern Mexico Mine or district

Mineral/key in Fig. 2

Celestine deposits Tinaja Volcán

Celestine/C28 Celestine/C34

Víbora Venado Lucero Diablo San Agustín

Fluorite deposits Santa Anita El Triángulo El Tule Santo Domingo El Triángulo and La Purísima Aurora Encantada-Buenavista Aguachiles Alicia Cuatro Ciénegas

Mina Úrsulo Barite deposits Barosa (Múzquiz) Upper mantle Lower mantle

Barite–Pb–Zn–celestine deposits Berrendos Barite body Barite + sphalerite body Celestine body Quartz + sphalerite body Zn–Pb deposits San Marcos (Reforma) a

Salinity range (wt.% NaCl equiv.)

References

Celestine/C32 Celestine/C30 Celestine/C13 Celestine/C33 Calcite/C33 Celestine/C45 Calcite/C45 Fluorite/C45

70–160 65–140 62–120 83–106 80–140 48–121 80–140 40–50 98–160 62–110 127–150

2–19 0–17.9 3–15.9 10.1–13 0–19.5 2–13 0–16.9 1.7–7.2 7.9–18.6 7.9–16.1 17.8–18.4

González-Partida et al. (2003) González-Partida et al. (2003) Villareal-Fuentes et al. (2005) González-Partida et al. (2003) Ramos-Rosique et al. (2005) Puente-Solís (2007) This work

Fluorite/F14 Fluorite/F47 Fluorite/F5 Fluorite/F45 Fluorite/F47 Fluorite/F18 Fluorite/F18 Fluorite/F19 Fluorite/F15 Fluorite/F71 Fluorite/F71 Calcite/F71 Fluorite/C53

125–165 125–160 130–165 127–160 55–150 70–148 50–170 130–165 70–130 82–120 80–160 91–125 125–146

Not reported Not reported Not reported Not reported 8–14 8–14 6–14 3–4 Hydrocarbon inclusions Hydrocarbon inclusions 3.1–18.6 12.9–26a 17.8–21.7

Kesler (1974) Kesler (1977) Kesler (1977) Kesler (1977) González-Partida González-Partida González-Partida González-Partida This work This work

80–125 60–122 52–155 49–150

18.6–22.4 21.3–24a 20.2–26a 7.9–27a

This work

191–210 152–180 150–211 165–225

12.9–26a 15.6–19.5 13.2–19.5 22.4–27a

This work

6.8–22

González-Partida et al. (2003)

Barite/B3 Calcite/B3 Barite/B3 Calcite/B3

Barite/Z14 Barite/Z14 Celestine/C7 Barite/Z14 Sphalerite/Z19

Th Range (°C)

76–150

This work

et al. (2002) et al. (2003) et al. (2003) et al. (2003)

This work

CaCl2 + NaCl brines

“intra-deposit” features that allow their grouping into a single deposit type, identified as MVT and MVT-associated deposits. Furthermore, the majority of these deposits are located at similar tectono-stratigraphic position within the Mesozoic basin of northeastern Mexico. They are

(2) Located on (or near) the margins of horsts cored by basement, or (3) Located around large fault systems active at different times, which are actually reactivated old structures that formed during the opening of the Gulf of Mexico.

(1) Hosted by platform carbonate rocks and/or evaporites that generally formed during the initial stages of marine transgressions on basement horsts (i.e. the Coahuila Block)

These deposits formed in similar environments were probably associated to the same geologic processes (including the Laramide orogeny) and occur in specific areas and geologic units. Thus, it is reasonable to group them into


357

Table 3 S and Sr isotopic data available to date from MVT deposits of Northeastern Mexico Mine or district

Mineral/Key in Fig. 2

El Tule Torreón area Cuatro Ciénegas area San Agustín area (Sierra de La Paila) Alamitos area La Tinaja mine El Venado mine El Volcán mine Múzquiz area Upper mantle Lower mantle Las Lilas (Pb-Zn) Berrendos area

Celestine/C5 Celestine/C46–50 Celestine/C12–39 Celestine/C45

Lucero

Celestine/C28 Celestine/C30 Celestine/C34 Barite/B3 Barite/B3 Barite/B3 Galena/B3 Barite/Z14 Gypsum/C7 Sphalerite/Z14 Celestine/C7 Celestine/C13

Number of analyses

3 11 2 11 15 3 8 8 3 6 5

a newly defined metallogenic province, the MVT province of northeastern Mexico. This province can be subdivided into four subprovinces, from south to north: (1) the Southern Celestine Subprovince, associated with the Coahuila Block and the Parras Basin; (2) the Central Zn–Pb Subprovince, partly associated with the San Marcos Fault, but also distributed in the central part of the Sabinas Basin; (3) the Central Barite Subprovince, located in the central part of the Sabinas Basin; and (4) the Northern Fluorite Subprovince, associated with the Burro–Peyotes Peninsula and the La Babia Fault (Fig. 2). Each subprovince hosts a majority of deposits with characteristic ore minerals. Their geographic extent does not significantly overlap and can be directly associated with significant geologic or paleogeographic elements (paleoislands, paleopeninsulas, faults, horsts and grabens). A fifth subprovince can be proposed, the Southern Cu Subprovince, which contains red-bed Cu(–Co–Pb–Zn– fluorite) deposits hosted by the San Marcos Formation on the northern shoulder of the San Marcos Fault. These are not MVT deposits but can be attributed to the same metallogenic framework. Their distribution can be traced as north as northern Chihuahua or western Texas and as south as southern Nuevo León or northern San Luis Potosí. It is proposed that the deposit zonation in this province is an expression of mineral solubility (barite < celestine < fluorite) according to the obtained temperatures of homogenization. A fluid with any natural Sr/Ba ratio will always first precipitate a solid that is going to be Ba-rich and will finally precipitate celestine (Hanor 1968; Prieto et al. 1993, 1997). The barite deposits are hosted by older stratigraphic

δ34S (‰)

87

References

+6.4 to +13.2 +13.2 to +17.9 +13.6 +16.4 to +38.3 +16.3 to +17 +17.2 to +17.8 +18.0 to +20 +17.2 to +17.7 +14 to +17 +14.9 to +21.2 +11.4 to +20.2 +6.3 to +8.9 +25 to +31.9 +17.1 to +25.2 +25.7 to +29.3 +24.4 to +33.0 +18.5 to +20.0

0.70762 to 0.70794 0.70731 to 0.70773 0.70776±0.0004 0.70752 to 0.70942 0.70753 to 0.70772

Kesler (1977) Kesler and Jones Kesler and Jones Kesler and Jones Kesler and Jones This work This work This work Kesler and Jones This work This work This work

Sr/86Sr

0.70843 to 0.70891

(1981) (1981) (1981) (1981)

(1981)

This work This work

units than the celestine and fluorite deposits (Fig. 2), preferentially near the margins of the basin. Such a distribution can be explained by the migration of metalbearing fluids from the central part to the margins of the basin. Thus, the first precipitated mineral would be barite and/or Pb–Zn sulfides in the deepest mineralized stratigraphic units (i.e. La Virgen or Cupido Formations; Figs. 2 and 7), then celestine and, finally, fluorite, both in shallower stratigraphic units than the barite deposits. Such units are the Aurora and Acatita Formations for the deposits of the celestine subprovince and the Georgetown and Del Río Formations for the deposits of the fluorite subprovince (Figs. 2 and 7). In contrast, the Zn–Pb deposits are less clearly associated with any stratigraphic unit, as they are hosted by the evaporites of the La Virgen Formation and lining karstic cavities in both the Cupido and Aurora Formations (Figs. 2 and 7). However, how can the existence of two separated celestine and fluorite subprovinces be explained instead of celestine and fluorite deposits on both sides of the Sabinas Basin? The regional basement rocks are mostly PermianTriassic or older. However, the rocks in the horsts of the southern part of the MVT province are mainly granitic and volcanic, whereas the rocks in the horsts of the northern part of the province are metasedimentary. Both types of basement rocks were the source areas for the clastic rocks of the Mesozoic basins of the region. Due to their characteristics, such clastic rocks (especially conglomerates, sandstones, arkoses and sandy carbonate rocks; e.g. the San Marcos and Hosston Formations) were the most likely aquifers for basinal brines. The distribution areas of

358


the granitic and metasedimentary basement highs and of their adjacent clastic rocks derived from them roughly coincide with the celestine and fluorite subprovinces, respectively. As already noted, most deposits are located close to the margins of horsts that consist of Permian-Triassic rocks. Regional fault systems and the faults that shaped the Mesozoic basins have been reactivated several times under different stress regimes (see Horner and Steyrer 2005; Fig. 6). That would favor the circulation of hydrothermal fluids, a link already proposed for the Central Mesa of Mexico (Nieto-Samaniego et al. 2005, 2007). One of the faults that were reactivated several times in this region is the San Marcos Fault (Chávez-Cabello et al. 2005, 2007), with many Zn–Pb and celestine deposits located nearby (Fig. 2).

2004) and on celestine and organic matter from the El Venado deposit (Ramos-Rosique et al. 2005). The generation of basinal brines by seawater evaporation is one of the main mechanisms regarded by Hanor (1980, 1994), along with continental water evaporation, evaporite dissolution, and inverse osmosis. Most of the identified ore bodies are mantos due to the epigenetic stratabound replacement of favorable lithologies as gypsum- and anhydrite-rich beds or dolostones. For instance, some barite deposits (e.g., Sierra de Santa Rosa in the Múzquiz district or the Berrendos deposit) exhibit “chicken wire” textures, which are diagnostic of the replacement of anhydrite nodules that formed after gypsum dehydration. Thus, the generation of brines by this mechanism appears to be possible.

Fluid sources

Three regional stages of mineralization are permissive: (1) mobilization of brines by lithostatic pressure, (2) mobilization of brines by the Laramide orogeny and (3) incursion of descending meteoric water. Hot and deep basinal brines can be squeezed upwards due to lithostatic pressure through active faults in the basin and siliciclastic units (e.g. the San Marcos and Hosston Formations). The latter would have been leached and the resulting Sr-rich fluids eventually migrated through evaporitic rocks, reacted with them and formed pre-orogenic stratabound deposits (Fig. 6a). The migration of basinal brines would have been enhanced by the Laramide orogeny, and stratabound deposits would form either in non-deformed rocks, in previously deformed rocks, or simultaneously to deformation. Fracturing and faulting would favor the downward incursion of meteoric water, the formation of karsts and the dilution of basinal brines, leading to the formation of ore deposits filling karstic cavities (Fig. 6b). Stages 2 and 3 would be in accordance with fluid mixing as an efficient mechanism of precipitation (e.g. the Buenavista and El Venado deposits; González-Partida et al. 2003; Tritlla et al. 2004; Ramos-Rosique et al. 2005). In addition, free thermal convection through faults (Yang et al. 2004) may contribute to mineral formation.

The fluid inclusion data compiled in this paper (Table 2) are similar in both salinity and homogenization temperature to those summarized for MVT deposits (e.g. Roedder et al. 1968; Kesler 1974, 1977; Richardson and Pinckley 1984; Roedder 1984; Kaiser et al. 1987; Spirakis and Heyl 1988; Machel et al. 1995). One exception is the high homogenization temperatures (up to 225°C) in the Zn–Pb, barite and celestine deposits of the Berrendos area. Although temperatures this high are not common in MVT and related deposits, McLimans (1977) recorded similar temperatures in some of the richest Zn deposits of the Mississippi Valley area. The relatively high salinities and CaCl2 contents in the MVT-associated deposits of northeastern Mexico are similar to those in both oil-related brines (e.g. GonzálezPartida et al. 2003) and “classic” MVT deposits (e.g. Roedder et al. 1968; Roedder 1984; Wilkinson 2001). This suggests that the fluids associated with these deposits were essentially basinal brines. However, the low salinities recorded in inclusion fluids from most of the studied deposits indicate that those brines were diluted through interaction with fresh water. The chemical characteristics of the mineralizing fluids and their evolution are similar regardless of their (1) mineralogy, (2) position in the basin or with respect to the structural boundaries of the basin, and (3) position in the stratigraphic sequence. This suggests that the fluid sources and the geochemical processes during the fluid migration were similar. The occurrence of methane, liquid hydrocarbons and bitumen in fluid inclusions of these deposits further suggests that the evolution of the mineralizing fluids was associated with the migration and maturation of hydrocarbons. The role of basinal brines (similar to evolved and evaporated seawater) and meteoric water in the formation of ores is supported by Na–Br–Cl–I data on fluorite from the Buenavista district (Tritlla et al.

Stages of mineralization

Conclusions There are over 200 MVT Zn–Pb and associated celestine, fluorite and barite deposits in the state of Coahuila and neighboring areas of northeastern Mexico. These deposits are hosted in specific stratigraphic units in Mesozoic basins, whose geometry was determined by horsts and grabens that segmented the Permian-Triassic basement. Some horsts were represented by emerged land during part of the Mesozoic and partially controlled the sedimentation of the adjacent basins. These horsts are the


Coahuila Block, the Burro–Peyotes Peninsula, La Mula Island and the Tamaulipas Archipelago. The celestine deposits are hosted by evaporites and carbonate rocks of La Virgen, Aurora and Acatita Formations, and the fluorite deposits occur at the contact between the Georgetown and Del Río Formations. The barite deposits are hosted by evaporites and platform carbonate rocks of the Cupido (Cupidito) and La Virgen Formations, and the Zn–Pb deposits are hosted by carbonates and evaporites of the Cupido, Aurora and La Virgen Formations. Thus, the celestine and fluorite deposits formed in some of the youngest stratigraphic sections of the Mesozoic basin. The barite and Zn–Pb deposits, which are hosted at similar stratigraphic intervals, also formed in older sections. Most of the deposits are found on horsts (or close to their edges) like the Coahuila Block (celestine and Zn– Pb deposits), the Burro–Peyotes platform (mostly fluorite deposits) and the La Mula Island and the Tamaulipas Archipelago (barite deposits and most Zn–Pb deposits). These deposits define a metallogenic province, here named the MVT province of northeastern Mexico. This province is defined on the basis of the similarity of geological setting and lithologies to which the mineral deposits are associated and their location in specific stratigraphic sections. The uneven regional zonation of these deposits in the Mesozoic basin allows to define five subprovinces: (1) Southern Celestine Subprovince, (2) Southern Cu Subprovince, (3) Central Zn– Pb Subprovince, (4) Central Barite Subprovince and (5) Northern Fluorite Subprovince. It is postulated that Sr and Ba that formed celestine and barite deposits were leached from basement-derived clastic rocks. The abundance of celestine deposits in the Southern Celestine Subprovince is due to the abundance of Sr in clastic rocks, which were derived from both Pennsylvanian volcanic rocks and Permian-Triassic granites of the Coahuila Block. On the other side of the Mesozoic basin, MVT fluorite deposits formed (Northern Fluorite Subprovince) from fluids that reacted with clastic sediments that derived from the erosion of Permian-Triassic metasedimentary rocks. The available fluid inclusion and isotopic studies suggest that the formation of the deposits of the MVT province of northeastern Mexico is related to basinal brines that were diluted by meteoric water. The δ34S values of barite and celestine deposits of northeastern Mexico suggest that the most likely sources for sulfur were Albian–Barremian anhydrite deposits. Acknowledgments This work has benefited from funding through the research projects IN107203 and IN102107 granted by DGAPAPAPIIT (UNAM) and project 58825 by CONACYT. We are very grateful to the staff at the office of the Servicio Geológico Mexicano (SGM) in Saltillo (Coahuila) for logistic assistance and help during our fieldwork, especially through Carlos Martínez Ramos y Carlos Rivera Martínez, and to the staff of the Centro Documental de

359 Recursos Minerales of the SGM in Mexico City, for their splendid help dealing with nearly 500 mining reports that were reviewed during our research. Special thanks are due to Samuel Baca, Agustín Rodríguez Santos and Salvador Esquivel Victoria of Fluorita de México S.A. de C.V. and to César Pérez Rodríguez and Servando Rodríguez Favela from the Aguachile mining district. During our early fieldwork, we had the kind guidance of Antonio González Ramos a.k.a. El Gavilán and were also assisted by Hugo Martínez, Arturo Cantú y Cantú, Fausto Cantú Arocha, Miguel Ángel Heredia, Amador Núñez Miranda, Gilles Levresse and Jordi Tritlla. This paper improved substantially after the critical reviews and comments by Wayne Goodfellow, an anonymous referee, Bernd Lehmann and Fernando Tornos.

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