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Velardena Mining District - Minera Roble, Santa Maria, Antares, La Industria, La Esperanza, San Mateo, Minera William
Durango, Mexico
Main commodities: Zn Ag Au Pb Cu


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The Velardeña (or Minera Roble) cluster of Zn-(Pb-Cu-Ag-Au) skarn-epithermal/carbonate replacement deposits are located in the Santa María and San Lorenzo ranges of NE Durango State, ~60 km southwest of the city of Torreón and 10 km north of Cuencamé in central-SW Mexico. The more significant deposits of the cluster include Santa María, Antares, La Industria, La Esperanza and San Mateo, distributed over a NE-SW trend of ~8 km (#Location: 25° 3' 30"N, 103° 43' 59"W).

  Mining in the Velardeña district began in the sixteenth century with the arrival of the Spaniards. Exploitation of the limited oxide ores continued sporadically on a small scale until 1888, when the Velardeñia Mining and Smelting Company was formed and a smelter built. The American Smelting and Refining Company (ASARCO) purchased the latter in 1902 and continued operations until the 1920s. Renewed exploration began in 1968, involving ASARCO Mexicana (which became Industrial Minera de Mexico, then Grupo Mexico and is now Minera México), Servicios Industriales Peñoles, S.A. de C.V., Minera Ramid, S.A., and Astumex, S.A. In the early 1980s, Industriales Peñoles acquired Minera Ramid's and Astumex's interests.
  In 1980, Industrial Minera de Mexico had begun ore production in the Sierra de Santa Maria, exploiting carbonate-replacement ore from the Santa Maria Mine and stockwork mineralisation found in the Los Azules mine. However, in September 2000, due to a decrease in the grade and quality of the ore, Minera México management decided to temporarily close their operation, and in 2005, Peñoles acquired their properties. Other smaller titles relinquished by Minera México are being explored and have been briefly mined, including the Mina William in the San Lorenzo Ranges.
  Following an extensive drilling program, Industrias Peñoles commenced construction of a mine and beneficiation plant in 2010 which was completed at the end of 2012, with commercial operations commencing in May 2013. Production has continued to the present (2024), and been expanded in a two-stage optimisation project performed in 2018 and 2019.

Regional Setting

  The Velardeña District lies near the westernmost extremity of the east-west trending Sector Transversal de Parras (or Trans Mexican Volcanic Belt) that cuts across and offsets the Mexican Orogen and marks the southern termination of the Guerrero Terrane. It is ~50 km north of the east-west boundary with the Mesa Central, and ~100 km east of the easternmost margin of the Sierra Madre Occidental (Ortega-Gutiérrez et al., 1992). It also lies within the younger Basin and Range Province, that is characterised by extensional tectonics that were active between ~13 and 5.5 Ma (Henry and Aranda-Gomez 2000).
  The Mexican Orogen, or Mexican Fold and Thrust Belt, extends over a NW-SE trend of ~2000 km, and comprises >3 km of deformed late Mesozoic carbonate and clastic successions that overlie Lower to Middle Triassic rocks that, in turn, overlie high-grade Proterozoic metamorphic rocks of the Oaxaquia subcontinental block (Eguiluz y de Antuñano et al., 2000; Fitz-Díaz et al., 2018; Ortega-Gutiérrez et al., 2018). To the north, much of the Mexican Orogen corresponds to the Guerrero Terrane which hosts many similar intrusion related base and precious metal deposits (see the Fresnillo record).
  The Mesa Central to the south, lies between the Mexican Orogen to the east and the younger capping Sierra Madre Occidental to the west. It is a plateau located in north-central Mexico, occupied by marine sedimentary strata deposited during two regional regressive-transgressive cycles in the i). Upper Triassic to Lower Jurassic and ii). Upper Jurassic to Upper Cretaceous sequences (Nieto-Samaniego et al., 2005, 2007).
  The Sierra Madre Occidental is a major silicic large igneous province (Bryan 2007) that runs from the USA-Mexico border in the north, and trends to the SE through western Mexico for ~1500 km. It comprises three main magmatic events: i). the compressive 100 to 50 Ma Laramide felsic volcanism; ii). a 45.0 to 12.5 Ma syn-extensional silicic pulse; and iii). bimodal volcanism associated with the opening of the Gulf of California that began in 12.5 Ma and has continued to the present (Ferrari et al., 2005, 2007, 2018). The second event included large felsic pulses that deposited thick packages of ignimbrites, rhyolitic domes and intrusive bodies, with which polymetallic skarns along the Sector Transversal de Parras are associated (Camprubí 2013).

Geology

  The sequence in the Santa María Range includes the following, from the base (after Cano, et al., 2024):
Aurora Formation, which is the oldest unit exposed in the range. It includes reefal limestones with abundant Albian (late-Lower Cretaceous) fauna;
Cuesta del Cura Formation, composed of ~300 m of monotonous Albian to Cenomanian limestone strata, interbedded with black flint, siltstone and carbonaceous mudstone (Imlay 1937; Ángeles-Villeda c, 2005).
Indidura Formation, mudstone and Cenomanian to Turonian muddy limestone that is ~90 m thick (Imlay 1937).
  All three of these units, as well as the overlying Santonian to Coniacian (mid Upper Cretaceous) terrigenous-volcanic Caracol Formation, which is not exposed in the Santa María range, mark a progressive shallowing of the basin. This resulted from a regional regressive or uplift event which ended marine conditions that had prevailed since the Upper Jurassic (Nieto-Samaniego et al., 2005, 2007).
  This sequence is overlain by the Ahuichila Formation molassic succession with an average thickness of ~450 m (Eguiluz y de Antuñano et al., 2022) and is capped by volcanic rocks of the Sierra Madre Occidental Province (e.g., Ferrari et al. 2005, 2007, 2018). This latter magmatic activity commenced in the Oligocene and continued through the Miocene, producing welded rhyolitic tuffs followed by andesitic and basaltic lavas. The rhyolitic tuffs form a ~160 m thick succession that fills the Cuencamé graben and is covered by up to 300 m of Quaternary alluvial sediments (Jiménez-Franco, et al., 2020).
  The Velardeña Intrusive Complex crosscuts all of these rocks, except the younger Sierra Madre Occidental volcanics (Ramírez-Peña 2014). This complex is composed of felsic rocks, of which a rhyolite dyke has been dated at 33.4 ±1.7 Ma and a quartz-latite at 33.1 ±1.4 Ma (K/Ar; magmatic biotite; Felder 1979). It has been divided into quartz-latite porphyries, rhyolitic dykes, and quartz-sanidine porphyries (Gilmer et al., 1988), which exhibit metaluminous and calc-alkaline characteristics (Jiménez-Franco 2012) and belong to the magnetite series of Ishihara (1977), based on an accessory magnetite phase. The ore deposit-related igneous rocks of this complex have been petrographically classified as monzogranites with porphyritic to granular textures (Jiménez-Franco, 2012). The Velardeña Intrusive Complex has been shown to be related to the formation of several skarn and epithermal deposits in the district, including the Santa María and Antares skarn deposits (Spurr and Garrey 1908; Hernández 1991; Industrias Peñoles 2010; Jiménez-Franco et al. 2005, 2020). These zones of skarn alteration are found along the contact between the intrusive rocks and the Cuesta del Cura Formation limestones, and generally strike NW-SE.

The exoskarn zones of the Velardeña District are irregular in shape and size, and may be up to 50 m or more in thickness (Jiménez-Franco, et al., 2020). The ore zones within these would appear to vary from <10 to >30 m in width (Cano et al., 2024). The sulphides within the skarn alteration and ore zones occur as i). massive, centimetre- to metre-sized, coarse-grained aggregates, ii). disseminations; and iii). in veins and veinlets within the exoskarn that are interpreted to be epithermal. Most of the veins in the Velardeña Mining District are not exposed at surface, and are hosted in the carbonate sequence, generally striking NW-SE and dipping steeply to the NE. Their maximum thickness is generally up to 20 m, and may extend for several kilometres. Some are brecciated proximal to intrusive rocks. They are characterised by an assemblage of calcite and fluorite with subordinate adularia and quartz with ore minerals that include Fe-poor, pale sphalerite, arsenopyrite and pyrite, with minor galena and chalcopyrite. The mineralised structures are cut by NW-SE striking, extensional Oligocene Basin and Range normal faults (Jiménez-Franco, et al., 2020).

  The Santa María mineralisation has been shown to be associated with the Santa María aplitic dyke which strikes at 120°, whilst the Antares ore bodies are linked to a rhyolite stock and other aplitic dykes. Prograde phase skarn was developed at temperatures of from ≥470 to 335°C in conditions of low ƒ(CO2), followed by a retrograde stage from 335 to 220°C and a general increase in ƒ(O2). The prograde skarn exhibits replacement textures and is dominated by calcic clinopyroxene and garnet, whilst the retrograde stage mostly comprises actinolite, epidote and chlorite (Jiménez-Franco et al. 2020). Ore assemblages include sphalerite/marmatite, galena, pyrite, pyrrhotite, chalcopyrite and arsenopyrite, with minor boulangerite, marcasite, tetrahedrite-group, Bi-sulphosalts and scheelite (Cruz-Pérez and López-Escalona 1981; Hernández 1991; Industrias Peñoles 2010). These deposits are interpreted to be the result of intermediate-temperature, magmatic-derived hydrothermal fluids, emplaced at hypabyssal depths of ~3 to 4 km (Gilmer et al., 1988; Jiménez-Franco et al., 2020).

Santa María

  As detailed above, the Santa María deposit is found along the contact between the Santa María dyke and limestones or marbles of the Cuesta del Cura Formation. This dyke comprises pervasively altered aplites with scarce relicts of tabular plagioclase phenocrysts. Unaltered limestone is mud-supported with <10% grains plus bioclasts (i.e., mudstone; Dunham 1962), while marbles vary from fine- to coarse-grained, depending on the degree of recrystallisation. Skarn development is divided into the following four stages:
Prograde Stage, which has been largely obliterated by the overprinting retrograde alteration. Exoskarns have a locally banded medium- to coarse-grained granoblastic texture, and are composed of garnet and wollastonite replacing limestones. Idiomorphic garnet crystals can be zoned, whilst wollastonite forms feathery aggregates. No endoskarn zone has been observed at Santa María, although in igneous rocks, the prograde stage is limited to local biotite alteration.
Retrograde Stage, which in the exoskarn zone has largely obliterated the prograde assemblage and crystallised in four assemblages:
  i). scarce poikiloblastic, fine-grained garnet encapsulating tremolite and sphalerite crystals, all of which are embedded in calcite and quartz;
  ii). sericite, epidote, chlorite, calcite, quartz, tremolite, with lesser green biotite, epidote and muscovite;
  iii). actinolite, sphalerite, quartz, calcite and pyrite;
  iv). chlorite, fluorite, quartz, calcite, epidote, tremolite, muscovite and lesser tourmaline and actinolite, accompanied by, or intergrown with, massive bodies, bands, veins and patches of sulphides and sulphosalts.
  In contrast, the igneous rocks contain two endoskarn retrograde assemblages
  i). actinolite, quartz, pyrite and lesser scapolite, occurring as irregular patches in biotite-altered aplites, overprinted by
  ii). adularia, fluorite, quartz, very fine-grained muscovite (sericite), and calcite. This second assemblage is associated with the massive ore. The dominant alteration mineral in the aplites is fine-grained adularia, which occurs as distinctively beige massive replacements, whilst pseudo-rhombohedral adularia crystals are frequently intergrown with the sulphides.
  The development of the retrograde stage and these assemblages at the Santa María deposits is divided into four phases, from 1 to 4, from oldest to youngest:
  Phase 1. involves minor Ca-garnet as the trailing end of the prograde stage. The main minerals are calcite, quartz and tremolite;
  Phase 2.  deposition of calcite, quartz and tremolite continues, with significant muscovite, sericite and chlorite, and lesser biotite and epidote, accompanied by minor pyrite and sporadic sphalerite and arsenopyrite;
  Phase 3. major quartz, calcite and chlorite continue to be formed, with minor sericite, sporadic scapolite and major actinolite, as well as minor pyrite and sphalerite;
  Phase 4.  the main ore stage, comprising Zn-Pb-Cu ±Ag massive sulphide ore, overprinting both the exoskarn and altered aplites. Sulphides and sulphosalts normally form massive replacement zones that obliterate any remaining sedimentary or igneous textures, thus precluding the identification of protoliths. The ore occurs in the styles described above, taking the form of i). carbonate replacement ore bodies in marble and limestone; ii). mantos in prograde exoskarns; and iii). small, <1 cm diameter patches in aplites.
  Pyrite and sphalerite, commonly exhibit chalcopyrite disease and form cm-scale clusters closely associated with galena, arsenopyrite, pyrrhotite and chalcopyrite. Sphalerite varies from deep red to light orange. Arsenopyrite is euhedral and can be replaced by pyrrhotite, whilst pyrrhotite is normally encapsulated in pyrite and sphalerite. Arsenopyrite also forms clusters and irregular masses with lesser pyrite, and can be, but seldom is, concentrically zoned. Galena forms isolated crystals and inter-crystalline masses. Locally, Pb-Bi ±Sb sulphosalts replace pyrrhotite or are intergrown with galena and/or sphalerite. Scant magnetite is restricted to inclusions in sphalerite.
Post‑ore Stage, occurs as blocky, <5 cm wide, massive calcite veins and veinlets, crosscutting the massive sulphide assemblages. The calcite is accompanied by minor quartz and barite and locally contains small, <3 cm clusters of arsenopyrite, pyrite, and lesser galena, chalcopyrite, and sphalerite. Late tetrahedrite-group minerals fill vugs between sulphides and/or replace them. The post-ore stage locally contains breccias cemented by coarse-grained blocky calcite, in which angular clasts of aplite, marble or massive sulphide ore may be slightly rotated.
Late Stage, alteration assemblages comprise chlorite, calcite, sericite and epidote, which also led to the crystallisation of widespread 'bird’s-eye-textured' pyrite and marcasite replacing pyrrhotite, as well as tetrahedrite-group minerals replacing chalcopyrite, galena, pyrrhotite and/or sphalerite. Epidote from this stage is fine-grained and poorly crystallised, in contrast with well-developed larger crystals from the preceding Phase 4.

Antares

  Both the North and South Antares deposits are developend along the contact between a porphyritic rhyolite stock, or aplite dykes, and the Cuesta del Cura Formation. The porphyritic rhyolites are composed of quartz, plagioclase and sanidine phenocrysts, set in a fine-grained quartzo-feldspathic groundmass.
Prograde Stage - in contrast to Santa María, well-developed exoskarn and endoskarn zones are preserved at Antares. The exoskarn is up to 20 m wide and is dominated by beige and green garnet, clinopyroxene and wollastonite, whilst the endoskarn is ~ 10 to 15 m wide and is dominated by garnet and clinopyroxene. Coarse, ~5 mm, garnet is frequently zoned and may form monomineralic bands. Clinopyroxene forms aggregates that usually overprint garnet, whilst wollastonite occurs as radial aggregates of tabular crystals that overprint garnet and clinopyroxene.
Retrograde Stage - the retrograde exoskarn includes a replacement assemblage of actinolite, tremolite, quartz, calcite, epidote, chlorite, prehnite and lesser scapolite. The prograde endoskarn is progressively replaced by two retrograde assemblages, namely i). an early biotite ±K feldspar or tremolite-actinolite, fluorite, scapolite, quartz and calcite suite, overprinted by ii). muscovite, sericite, epidote, quartz and prehnite. The retrograde assemblages were developed contemporaneously with the economically most important mineralisation, which comprises a first stage pyrrhotite, arsenopyrite, sphalerite, chalcopyrite, and molybdenite, overprinted by arsenopyrite, pyrite, galena, and minor pyrrhotite, molybdenite, Pb-Sb ±Bi sulphosalts, and marcasite. The bulk of the ore occurs as disseminations, veinlets, and massive bodies. Pyrrhotite is abundant and forms massive aggregates and veins with calcite and quartz. Traces of tabular molybdenite were recognized in the endoskarn. Euhedral arsenopyrite crystals are embedded in pyrrhotite and sphalerite masses. Massive sphalerite and chalcopyrite tend to concentrate in the proximal exoskarn zone, and in some instances, pyrrhotite and sphalerite replace the outer rims of garnet crystals or occupy vugs between garnet crystals. Galena infills and may host exsolution lamellae of Pb-Sb ±Bi sulphosalts.
Late Stage, which comprises chlorite, epidote, calcite and sericite assemblages with associated fine-grained pyrite + bird's-eye textured marcasite, replacing pyrrhotite. Late calcite and fluorite veins crosscut the endoskarn and are haloed by epidote and Fe-oxyhydroxides.

Reserves and Production

Pre-mining Reserves at Velardeña as of 2010 were (Industrias Peñoles Internal Report, 2010, quoted by Cano et al., 2024)
  - 14.6 Mt @ 5% Zn, 0.4% Pb, 0.2% Cu, 20 g/t Ag, 0.3 g/t Au.

Production from Velardeña during financial year 2022 (Industrias Peñoles Annual Report, 2022) totalled:
  2.805 Mt of ore milled for 86 525 t of zinc, 4665 t of lead, 2400 t of copper, 26 t of silver, 0.12 t of gold, with a head grade of,
  3.45% Zn, 0.24% Pb, 0.14% Cu, 14.74 g/t Ag, 0.14 g/t Au.

Remaining Reserves at Velardeña as at December 2022 were (Industrias Peñoles Annual Report, 2022)
  - 41.078 Mt @ 3.34% Zn, 0.19% Pb, 0.20% Cu, 14.56 g/t Ag, 0.08 g/t Au.

Remaining Reserves at Mina William as at December 2022 were (Golden Minerals Company NI 43-101 Technical Report, 2015)
  Measured + Indicated Resource - 1.79 Mt @ 1.5% Zn, 1.4% Pb, 272 g/t Ag, 3.8 g/t Au.
  Inferred Resource - 2.14 Mt @ 1.5% Zn, 1.5% Pb, 271 g/t Ag, 4.1 g/t Au.

The most recent source geological information used to prepare this decription was dated: 2024.    
This description is a summary from published sources, the chief of which are listed below.
© Copyright Porter GeoConsultancy Pty Ltd.   Unauthorised copying, reproduction, storage or dissemination prohibited.


Velardena - Santa Maria

  References & Additional Information
   Selected References:
Cano, N., Camprubi, A., Gonzalez-Partida, E., Gonzalez-Ambrocio, A.K., Alfonso, P., Miggins, D.P., Fuentes-Guzman, E., Cienfuegos-Alvarado, E. and Iriondo, A.,  2024 - Metallogenic model of the Eocene Santa Maria and Antares Zn-Pb(-Ag) skarn deposits, Velardena Mining District, Durango, Mexico: in    Mineralium Deposita   v.59, pp. 671-698.
Gilmer, A.L., Clark, K.F., Conde, J., Hernandez, I., Figueroa, J.I., Porter, E.B.,  1988 - Sierra de Santa Maria, Velardena Mining District, Durango, Mexico,: in    Econ. Geol.   v.83 pp. 1802-1829.
Jimenez-Franco, A., Canet, C., Alfonso, P., Gonzalez-Partida, E., Rajabi, A. and Escalante, E.,  2020 - The Velardena Zn-(Pb-Cu) skarn-epithermal deposits, central-northern Mexico: New physical-chemical constraints on ore-forming processes: in    Boletin de la Sociedad Geologica Mexicana,   v.72 (3), 26p. dx.doi.org/10.18268/BSGM2020v72n3a270719.


Porter GeoConsultancy Pty Ltd (PorterGeo) provides access to this database at no charge.   It is largely based on scientific papers and reports in the public domain, and was current when the sources consulted were published.   While PorterGeo endeavour to ensure the information was accurate at the time of compilation and subsequent updating, PorterGeo, its employees and servants:   i). do not warrant, or make any representation regarding the use, or results of the use of the information contained herein as to its correctness, accuracy, currency, or otherwise; and   ii). expressly disclaim all liability or responsibility to any person using the information or conclusions contained herein.

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