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Tizapa |
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Mexico, Mexico |
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Zn Ag Au Cu Pb
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Super Porphyry Cu and Au
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IOCG Deposits - 70 papers
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All papers now Open Access.
Available as Full Text for direct download or on request. |
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The Tizapa Zn-Ag-Au-Cu-Pb volcanic hosted massive sulphide (VHMS) deposit is located in the state of Mexico, ~70 and 120 km WSW of the cities of Toluca and Mexico City respectively, and ~5 km SSE of the town of Zacazonapan (#Location: 19° 2' 14"N, 100° 14' 7"W).
It comprises stacked Kuroko-style ore lenses within the Guerrero Terrane, a Late Palaeozoic to Cretaceous assemblage of calc-alkaline volcanic arc and clastic sedimentary rocks, and overlying platform carbonates. The main units exposed include the:
• Triassic to Jurassic Tejupilco Schist, which comprises gneisses and phyllite with minor interbeds of sericitic phyllite (Monod et al., 1993).
• Late Jurassic to Early Cretaceous Teloloapan volcanic assemblage - intermediate to felsic metavolcanic rocks which define the Teloloapan Subterrane, a tectono-stratigraphic division of the Guerrero Terrane (Campa and Coney, 1983). It comprises a calc-alkaline volcanic arc sequence altered and metamorphosed to sericitic and chloritic phyllites and schists, and is the host to the Tizapa deposit;
• Middle to Upper Cretaceous Amatapec Formation, composed of metamorphosed calcareous carbonaceous mudstone/phyllite, siltstone and limestone.
The Teloloapan Sub-terrane arc is bordered on the west by Cretaceous basalt and marine sedimentary rocks of the Arcelia Subterrane. All of the Mesozoic rocks of the region have been subjected to Late Cretaceous to Early Tertiary polyphase shortening and greenschist facies metamorphism during the Laramide orogeny, resulting in both east- and west-vergent thrust faults and recumbent folds, and two generations of moderate to shallow-dipping foliation (Salinas-Prieto et al., 1993; Monod et al., 1993). The similar Capela VHMS deposit some ~80 km to the south also lies within the Teloloapan Sub-terrane.
The deformed Mesozoic sequence is unconformably overlain by Lower Tertiary felsic to intermediate volcanic and clastic rocks, and by Neogene to Quaternary volcanic rocks of the Trans-Mexican volcanic belt (Sedlock et al., 1993). Tertiary, north and NW-trending normal faults cut rocks as young as Oligocene, locally forming grabens filled with Neogene volcanic rocks (Jansma and Lang, 1997).
An east-west-striking, subvertical to steeply north dipping brittle fault, the Falla Riolita, cuts the deposit area just south of the Tizapa mine. The fault is occupied over much of its length by a flow-banded to brecciated rhyolite dyke. The stratigraphic displacement across the structure is >600 m, with north side down.
Deposit Geology
The sequence in the deposit area is as follows, from the base (after Lewis and Rhys, 2000):
• K-feldspar megacrystic quartz metadiorite - exposed southeast of the Tizapa mine, in the core of a regional west-trending anticline. It is described as an augen gneiss and comprises medium-grained biotite-muscovite-quartz-plagioclase schist with 0.2 to 4 cm long K feldspar porphyroclasts. The homogenous nature and texture of this unit is interpreted to suggest it is a deformed K feldspar megacrystic diorite intrusion. An ~50 m thick, compositionally similar, but texturally distinct, border phase separates it from the overlying phyllites of the Tejupilco Schist. As such this border phase may represent a chilled margin.
• Lower phyllite Unit of the Tejupilco Schist, comprising up to 800 m of non-calcareous, silver-grey to black phyllite/meta-mudstone. The unit includes subordinate metasiltstone, and local 0.3 to 10 m thick interbeds throughout of pale grey to tan sericitic phyllite and schist, representing possible tuffaceous or volcaniclastic beds, occur throughout the lower phyllite. In the lower parts of the sequence, the phyllites are commonly carbonaceous, with local limestone and chert beds.
• Metavolcanic Sequence of the Teloloapan volcanic assemblage, which is estimated to be >200 m in thickness. In the Tizapa mine area it is composed of of chlorite, chlorite-sericite and sericite schists, the mineralogy and geochemistry of which suggest a bimodal sequence, comprising a thick, structurally lower andesitic unit and a thinner, less continuous structurally higher felsic volcanic unit. The felsic part of the sequence is found to the south of the Falla Riolita, but is absent 2 km to the NE of the deposit.
The chlorite and chlorite-sericite schist after andesitic metavolcanic rocks is composed of green to tan plagioclase-porphyritic chlorite and chlorite-sericite schist. These are the dominant exposures proximal to and NE of the Tizapa mine. They contain 2 to 10 % plagioclase phenocrysts set in a fine-grained, green to pale grey or tan, muscovite ±chlorite + plagioclase + quartz ±calcite matrix. Biotite, tremolite and actinolite are found locally at surface and in deep drill holes beneath the deposit. Two subunits are distinguished, based on the dominant phyllosilicate: i). schists composed primarily of chlorite with minor sericite, which are overlain by ii). mixed sericite-chlorite schist. Grey phyllite interbeds are locally found near the top of the sequence in the mine area, whilst several limestone beds occur within 50 m of its top to the NE of the deposit area. Preserved primary textures various suggest flow or intrusive protoliths, whilst some contain interlayered mudstone and preserve fragmental textures (lapilli), indicative of interstratified tuffaceous or volcaniclastic intervals.
The overlying sericite schist after felsic metavolcanic rocks, are composed of pale grey to white, plagioclase ±quartz porphyritic
sericite-quartz phyllite and schist. It is characterised by the absence of chlorite in the matrix, few plagioclase phenocrysts, the absence of quartz phenocrysts and by it's pale grey, yellow or white fine-grained quartz-rich matrix that commonly has 0.5 to 3 mm thick grey and white laminae as well as beds of grey sericite phyllite and carbonaceous phyllite that occur at the Esmeralda prospect, 0.7 km to the north. Texturally it is interpreted to represent a felsic meta-tuff. It's thickness varies from 1 to 40 m at Tizapa and up to 140 m at the Esmeralda prospect.
• Upper Meta-sedimentary Rocks of the Amatapec Formation, which everywhere conformably and stratigraphically overlie the Metavolcanic Sequence, and comprise calcareous carbonaceous phyllite and meta-limestone.
The carbonaceous phyllite is calcareous grey to black, and is up to 100 m thick. It commonly forms the lower sections of the upper meta-sedimentary sequence. Thinly-bedded grey limestone is commonly interstratified, increasing in abundance up-section. No meta-volcanic rocks are found in the carbonaceous phyllite at Tizapa, although at the Esmeralda prospect, beds of sericite phyllite resembling the underlying felsic unit are intercalated within the lower 50 m of the carbonaceous phyllites. Two kilometres NE of the mine, the carbonaceous mudstone at the base of the upper sequence is only ~40 m thick and is strongly gossanous. To the SW, at Cerro de la Pila, the carbonaceous phyllite is absent and limestone directly overlies the volcanic sequence.
The Limestone of the Upper Meta-sedimentary Rock sequence is gradationally developed from a calcareous carbonaceous mudstone near the base of the unit to a thinly to thickly bedded pale grey, recrystallised and foliated limestone that is >300 m thick. It contains pale to dark grey bands that are commonly interlayered with thin beds and laminae of carbonaceous phyllite, sericite phyllite, and locally, greywacke.
• Minor intrusions. Various dykes and small intrusions of felsic to mafic composition, varying from Cretaceous to Quaternary age, cut the sequence.
Mineralisation and Alteration
The mineralisation is primarily located at the contact between the Metavolcanic Sequence and overlying carbonaceous phyllite of the Upper Meta-sedimentary Rocks. It comprises several stratabound beds of massive sulphides, that range from a few cm, up to >20 m in thickness, as well as sulphides in breacciated structures and as disseminations. Widespread disseminated, banded, and stringer pyrite and chalcopyrite also occur in footwall metavolcanic rocks. Several periods of deformation affected the minerlisation, including extensive compressional faulting (Giles and Garcia 2000; Alfonso et al., 2011).
According to Lewis and Rhys (2000), the deposit at that time covered an area of ~700 x 500 m and comprised five main sulphide lenses. However, mining and exploration since then has continued and the remaining reserves at the end of 2022 were near double the production + reserves calculated in 2000 (see below).
Contacts of the sulphide bodies are sharp, whilst the individual lenses can be traced through the mine, suggesting that, together, they define a single
sulphide lens that is folded and partially dislocated into a tight, west-verging recumbent fold.
Pyrite is the dominant sulphide in the Tizapa ore deposit, occurring as massive accumulations, and as disseminations in the schists and phyllites. It forms both anhedral grains and euhedral crystals, generally up to 2 mm in size. It often contains inclusions of other sulphides, such as galena and chalcopyrite, as well as sulphosalts. Pyrite crystals control the schistosity of the rock and are sometimes broken and affected by deformation. They are therefore considered as porphyroclasts formed prior to metamorphism.
Arsenopyrite is locally frequent, and it occurs as anhedral grains or euhedral crystals.
Sphalerite was formed in two different generations. The earlier is the most abundant and has chalcopyrite disease and up
to 7.5 wt.% Fe, whereas the late generation is found as small grains filling minor fractures, and it is Fe-poor.
Chalcopyrite is replaced by bornite and covellite.
Galena, like sphalerite, exhibits at least two generations of emplacement, the second during the late stages of the formation of the
deposit and is rich in silver, with up to 1.04 wt.% Ag.
Pyrrhotite is present in minor amounts.
Sulphosalts are abundant at Tizapa. The most abundant cation is Sb3+. They are poor in Te4+, and the As content us usually low, but locally reached 4.59 wt.% in some tetrahedrites. Pb-rich sulphosalts are predominantly boulangerite and bournonite, whilst meneghinite and zoubeckite are locally present. Ag and Cu sulphosalts are abundant, particularly tetrahedrite, although high Ag varieties with up to 31 wt.% are present, but rare and belong to the freibergite family. Pyrargyrite and stannite also often occur.
Footwall alteration has a consistent textural and mineralogical zonation with increasing distance below the massive sulphide bodies, made up of (after Lewis and Rhys, 2000):
• Sericite-pyrite alteration characterises the first 3 to 10 m below the massive sulphide, overprinting the felsic rocks, usually sub-divided into an,
- upper 0.3 to 4 m thick zone containing abundant 0.5 to 25 cm thick bands of coarse-grained pyrite ±quartz ±chalcopyrite spaced at 2 to 30 cm intervals, separated by a matrix of sericite-disseminated pyrite-quartz. These bands commonly merge obliquely and bifurcate, suggesting they are vein related, rather than 'sedimentary layers'.
- pyrite bands abruptly decrease in abundance with depth below this upper interval and grade into assemblages of intense sericite-disseminated pyrite-quartz in lower portions of this alteration zone.
- Peripheral to the deposit, elliptical, green chlorite-sericite blebs, interpreted to represent retrograde metamorphism of cordierite, occur locally in sericite-pyrite in the altered footwall rocks.
• Chlorite-pyrite alteration persists for up to 45 m beneath the sericite-pyrite interval, primarily in the andesitic metavolcanic rocks. This interval is defined by assemblages of intense chlorite + disseminated pyrite ±Fe-carbonates, with chlorite commonly forming >75 % of the country rock. Coarse bands of pyrite, similar in texture and abundance to those in the 'sericite-pyrite zone', are commonly found in the upper 10 m of the chlorite zone. Relict porphyritic textures are sometimes visible, but plagioclase phenocrysts have been altered to sericite.
• Primary plagioclase is preserved beneath the chlorite zone, and alteration is not pervasive. Pyrite + quartz ±sphalerite stringers are common, and calcite is abundant.
Hanging wall alteration - Carbonaceous phyllite in the hanging wall sequence contain no significant pyrite or any other visible indication of alteration, other than local slivers of pyrite-sphalerite within 5 m above ore. These slivers can usually be traced laterally back into the ore and may be tectonically imbricated.
Reserves, Resources and Production
Mined and remaining proven + probable ore as at 31 December 2000 totalled
- 4.5 Mt @ 0.7 % Cu 1.9 g/t Au, 325 g/t Ag, 1.8 % Pb, 7.9 % Zn (Giles and Garcia, 2000).
Production for the 2022 financial year totalled (Industrias Peñoles Web site, viewed March, 2024)
- 0.921 Mt of milled ore for 1372 t of copper, 178 t of silver, 1.17 t of gold, 8514 t of lead, 37 770 t of zinc, equating to a head grade of
- 0.15% Cu, 193 g/t Ag, 0.78 g/t Au, 0.92% Pb, 4.10% Zn.
Remaining Reserves as at December 2022 were (Industrias Peñoles Annual Report, 2022)
- 8.061 Mt @ 0.23% Cu, 196.52 g/t Ag, 1.26 g/t Au, 1.16% Pb, 4.68% Zn.
In 2024, the operation was owned by a joint venture of 51% Peñoles; 39% Dowa Mining and 10% Sumitomo Corporation, with Industria Peñoles as the operator. Mining commenced 1994 and has continued until 2024. It is an underground mine with a >0.98 Mt per annum capacity beneficiation plant, producing separate lead, zinc and copper concentrates.
The most recent source geological information used to prepare this decription was dated: 2011.
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.
Tizapa
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Alfonso, P., Torro, L., Mesa, C., Parcerisa, D., Mata-Perello, J.M., Gonzalez-Partida, E., Canet, C., Garcia-Valles, M., 2011 - Mineralogical characterisation of the Tizapa ore deposit, Mexico: in Lets Talk Ore Deposits, 11 th SGA Biennial Meeting, 26-29th September 2011 Antofagasta, Chile, Proceedings pp. 781-783.
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Lewis, P.D. and Rhys, D.A., 2000 - Geological setting of the Tizapa volcanogenic massive sulphide deposit, Mexico State, Mexico,: in Sherlock, R., (Ed.), VMS Deposits of Latin America, Geological Association of Canada, Special Publication No. 2, Chapter 1, pp. 87-112.
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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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