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San Martin, Sabinas |
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Zacatecas, Mexico |
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Ag Au Pb
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Super Porphyry Cu and Au
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The San Martin deposit is located at Sombrerete in Zacatecas state, Mexico, and is exploited by two major mines. The San Martin Mine extracts Cu-Zn-Ag ore from veins and replacement bodies hosted by skarn alteration. The second, the Sabinas Mine, which commenced deeper operations 25 years later, and works a higher level in the mineralised system, exploits Zn-Pb-Ag ±Au from vains hosted by skarn and recrystallised limestone.
The San Martin MIne was owned and operated in the 1970s to 1990s by GIMMSA [Grupo Industrial Minera Mexico SA de], which in 2000 became part of Grupo Mexico, that in turn, in 2003, merged with and into Minera México. An industrial dispute saw the mine closed for 11 years from 2007, to be reopened in 2018. The Sabinas Mine, which takes in the northwestern sector of the same skarn orebody, commenced operation as an undeground mine in 1995 under the control of Industrias Peñoles who had acquired the old Sabinas mine in 1994.
Published reserve and historic production figures at San Martin include:
Proven+probable reserves, 1993 - 21.3 Mt @ 96 g/t Ag, with associated Pb, Zn, Cu (AME, 1995),
Production 1548 to 1821 - 0.25 Mt @ 450 g/t Ag, 0.5 g/t Au (Ruvalcaba & Thompson, 1988),
Production 1822 to 1900 - 0.05 Mt (Ruvalcaba & Thompson, 1988),
Production 1959 to 1987 - 10.5 Mt (Rubin & Kyle, 1988).
In 1992 the San Martin mill treated 1.57 Mt of ore to output 21.7 t Ag, 3923 t Pb, 12 000 t Cu, and 67 300 t Zn (AME, 1995). This would equate with recovered grades of 14 g/t Ag, 4.3% Zn, 0.25% Pb, 0.75% Cu.
The remaining Mineral Resources at San Martin, as at 31 December, 2022 (Mining Data Solutions website, viewed March, 2024 were:
Indicated Resources - 11.542 Mt @ 2.48% Zn, 0.61% Cu, 92 g/t Ag, 0.49% Pb;
Inferred Resources - 9.176 Mt @ 2.05% Zn, 0.49% Cu, 112 g/t Ag, 0.62% Pb.
The remaining Ore Reserves at Sabinas, as at 31 December 2022 (Industrias Peñoles Annual Report 2022) were:
22.115 Mt @ 2.00% Zn, 0.29% Cu, 102.93 g/t Ag, 1.18% Pb.
Production at Sabinas in 2022 totaled 1.155 Mt of ore for 2771 t Cu, 83.6 t silver, 15 219 t Zn and 6611 t of Pb., which equates to a head grade of 0.24% Cu, 73 g/t Ag, 1.32% Zn, 0.57% Pb (Industrias Peñoles website, viewed March 2024.
Regional Setting
For a brief overview of the distribution and character of the deposits in the carbonate replacement and related vein Pb-Zn-Ag belt in Mexico and the western United States, and links to the deposits of that belt, see the Regional Setting section of the Fresnillo record.
Geology & Mineralisation
The San Martin district is located on the western margin of the Mexican Thrust Belt, near the boundary with the Sierra Madre Occidental. Mineralisation occurs within a sequence of middle Cretaceous (Albian to Cenomanian) dark grey limestones of the Cuesta de Cura Limestone with common thin shale and chert bands. It is present as a skarn zone on the margin of a major 4.5 km diameter, ~46 Ma Cerro de Gloria quartz-monzonite porphyry stock, with associated quartz-rhyolite porphyry represented by apophyses and as an outer shell. In addition to the skarn, mineralisation is also present as sulphide chimneys and as veins. Mineralisation is hosted by favourable carbonate beds between shaly horizons, and has been dated at 46.2 Ma (Megaw, et al., 1988; Rubin & Kyle, 1988).
There is a zonation outwards from the intrusive contact of the stock, commencing with a Cu-Ag contact skarn, to Cu-Zn skarn veins, to Pb-Ag veins, then Au-Sb rich veins, and finally marble. Au is farthest from the contact, occurring within recrystallised limestone. The content of Fe, Cu, Zn and Pb increase with depth within the ore zone. The skarn is characterised by an assemblage comprising chalcopyrite, tetrahedrite-tennantite, molybdenite, sulphosalts, sphalerite, galena, pyrite, pyrrhotite and arsenopyrite, in a gangue of andraditic-grandite garnet, hedenbergite, tremolite, actinolite, wollastonite, vesuvianite, epidote and chlorite. The chimneys contain sphalerite, galena, chalcopyrite, tetrahedrite-tennantite, pyrite, silver and stibnite, with fluorite, calcite and quartz. Vein mineralisation is composed of galena, proustite-pyrargyrite, silver, sphalerite, pyrite and stibnite with fluorite, calcite and quartz (Megaw, et al., 1988; Rubin & Kyle, 1988).
The larger orebodies at San Martin are centred around several major veins. One of these, the San Marcial vein, which is the most economically important, has an average width of 2 m and can be traced for approximately 850 m in a direction of 30°. The dip of the vein is dependent upon the attitude of the intrusive contact. The bulk of the economic mineralisation associated with this vein is located within the skarn replacement body, which is centred on the vein, and varies in width from 2 to 100 m (Rubin & Kyle, 1988).
Due to its later commencement of deeper mining, minerals characteristic of the upper levels of the system e.g., apophyllite, stilbite and stibnite) were produced from Sabinas ~20 years after they came out of San Martin.
It has been deduced that early high temperature hydrothermal alteration produced hedenbergite and chalcopyrite bearing skarn. Garnet rich skarns followed, although as the temperature continued to drop, garnet and later clinopyroxene, became unstable relative to the retrograde calc-silicate assemblage that includes tremolite-actinolite, wollastonite, epidote and chlorite. Dissolution of CaCO3 raised the pH, while interaction with meteoric water may have resulted in the release of metals from the hydrothermal solutions. Metals were deposited within inter-crystal pores in the grandite-garnet skarn (Rubin & Kyle, 1988).
Prior to 1998 the Sabinas Mine exploited narrow high-grade veins that cut the skarn and extended beyond it. The largest of these veins continued northwest for 2 km and was exploited through the La Noria Shaft and related workings for over 300 years, producing some of the richest silver ores ever from a mine in Mexico. The Noria Mine was exhausted in the early 1970's.
For detail consult the reference(s) listed below.
The most recent source geological information used to prepare this decription was dated: 2022.
Record last updated: 19/3/2024
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.
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Selected References:
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Gonzalez-Partida, E. and Camprubi, A., 2006 - Evolution of mineralizing fluids in the Zn-Pb-Cu(-Ag±Au) skarn and epithermal deposits of the world-class San Martin district, Zacatecas, Mexico: in J. of Geochemical Exploration v.89, pp, 138-142.
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Megaw, P.K.M., Ruiz, J. and Titley, S.R., 1988 - High-temperature, carbonate-hosted Ag-Pb-Zn(Cu) deposits of Northern Mexico: in Econ. Geol. v.83, pp. 1856-1885.
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Rubin J N, Kyle J R 1988 - Mineralogy and geochemistry of the San Martin Skarn deposit, Zacatecas, Mexico: in Econ. Geol. v83 pp 1782-1801
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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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