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Cuale Mining District - Naricero, Mina de Oro/Grandeza, Socorredora, Coloradita, Las Talpas, La Prieta-Rubi, Chivos de Abajo, San Nicolas, Jesus Maria, Refugio, Chivos de Arriba |
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Jalisco, Mexico |
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Ag Au Zn Pb Cu
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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.
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The Cuale Mining District is located in the Cordillera Madre del Sur, ~30 km southeast of Puerto Vallarta, and ~4 km southwest of the small town of Cuale, in Jalisco State, southwest central Mexico. It comprises a cluster of small, polymetallic Pb, Zn, Cu, volcanic hosted massive sulphide (VHMS) deposits, and vein and stockwork-hosted deposits with low-sulphidation epithermal characteristics, distributed over an area of ~10 km2. Mineralisation is hosted by an Upper Jurassic volcano-sedimentary sequence. The main deposits include Naricero, Mina de Oro/Grandeza, Socorredora, Coloradita, Las Talpas, La Prieta-Rubí, Chivos de Abajo, San Nicolas (not to be confused with the large deposit of the same name, 360 km to the NE), Jesus Maria, Refugio and Chivos de Arriba (#Location: centred on 20° 22' 37"N, 105° 6' 24"W).
Mining in the Cuale District dates back to 1805, when the Spanish exploited the Prieta orebody to extract silver-rich ore zones averaging 500 g/t Ag (Hall and Gomez-Torres, 2000). To date, some 2.5 Mt of ore averaging 0.83 g/t Au, 103 g/t Ag, 1.03% Pb, 3.22% Zn, 0.23% Cu have been mined from >18 small, high-grade orebodies. All but the Chivas de Abajo deposit were discovered and high graded prior to 1919 (Berrocal and Querol, 1991; Hall and Gomez-Torres, 2000). The principal attraction for mining in the 19th century was the high grade silver with mined intervals of up to 9630 g/t Ag, whilst Pb, Zn, Cu, Ag and Au were the main commodities produced in the 1980s by Zimapán S.A de C. V., which bulk mined orebodies previously selectively mined for high-grade silver ore. Mining in the district ceased in 1989, once the easily accessible reserves were mined out (Bissig et al., 2008).
Regional Setting
The volcanic sequence that hosts the deposits of the Cuale District is part of the Zihuatanejo Sub-terrane of the extensive Guerrero Composite Terrane. The latter is interpreted to underlie much of the southwestern half of Mexico over a NW-SE interval of ~1500 km and width of ~200 to 250 km. The Guerrero Terrane has been sub-divided into five sub-terranes on the basis of differences in basement geology, stratigraphy, style and intensity of deformation (Campa and Coney, 1983; Centeno-García et al., 1993, 2003; Centeno-García, 2005). Of these five sub-terranes, the two larger are the ~850 x 200 km Tahue Sub-terrane, to the NW, and the ~650 x 200 to 250 km Zihuatanejo Sub-terrane to the SE which together constitute the bulk of the terrane. The Zihuatanejo Sub-terrane is bounded to the east by the Guanajuato Sub-terrane, and to the SE, by the narrow Arcelai and then the outer Teloloapan sub-terranes.
The large Tahue Sub-terrane, to the NW is mainly composed of basement Ordovician marine rhyolitic to andesitic lavas, and clastic and calcareous rocks. The Zihuatanejo Sub-terrane consists of Upper Jurassic to Cretaceous shallow marine limestones and marine to subaerial basaltic to rhyolitic volcanic rocks, overlying a heavily deformed but poorly metamorphosed Late Palaeozoic to Triassic basement of pelitic schists and minor basalts, which is locally intruded by ~160 Ma Jurassic calc-alkaline, I-type granitoids. The narrow Arcelia Sub-terrane to the immediate SE, is an intensely deformed sliver of Upper Cretaceous basalt and ultramafic rocks, intercalated with black shale and chert (Ramírez et al., 1991). It is, in turn, bounded to the SE by the Teoloapan Sub-terrane composed of Lower Cretaceous shallow submarine, basaltic to andesitic lavas with subordinate limestone intercalations. This sequence has been thrust eastward over Lower to Upper Cretaceous platform carbonates deposited on the adjacent Mixteco Terrane. The Guanajuato Subterrane, abuts the eastern margin of the Zihuatanejo Sub-terrane, and consists of primitive arc basalts and deep marine sedimentary rocks, with similarities to the Arcelia Sub-terrane along strike to the south.
However, the Mesozoic metavolcano-sedimentary assemblages that define the Guerrero Composite Terrane, are only exposed over <5% of its surface area, occurring as scattered erosional windows through the extensive Tertiary and Quaternary volcanic and sedimentary strata of the Sierra Madre Occidental Province. The Guerrero Terrane is the composite product of complex subduction-related processes, major translation, and periods of rifting during the Mesozoic along the southwestern margin of Mexico (Campa and Coney, 1983; Centeno-García et al., 2008). The complex arc and arc-back arc system of the Guerrero terrane was accreted to the North American continent late in the Early Cretaceous (Dickinson and Lawton, 2001) and hosts the majority of the VHMS occurrences in Mexico (Miranda-Gasca, 2000; Mortensen et al.). These VHMS deposits occur within two distinct belts in the Guerrero composite terrane: i). a coastal belt which includes the Cuale, Bramador, La Minita-Sapo Negro and Arroyo Seco districts, deposits and prospects; and ii). another, inland, close to the eastern boundary of the Guerrero Composite Terrane, encompassing San Nicolás-El Salvador, the deposits in the Guanajuato Ranges, Tizapa-Santa Rosa, Tlanilpa-Azuláquez, Rey de Plata, the 31 Mt Campo Morado-Suriana, etc.
Geology
The oldest rocks in the Cuale District are a >800 m thick sequence of intercalated pelitic, chloritic and sericitic schists and meta-arkoses that crop out in the west of the district (Berrocal and Querol, 1991). These rocks are gently folded and metamorphosed to sub-greenschist facies assemblages. They are overlain, across an angular unconformity, by Early to Middle Jurassic (U-Pb dates) volcanic rocks, and are locally intruded by hypabyssal rhyolite (Macomber, 1962). Although not dated, the intercalated basement schists may well be as old as late Palaeozoic to Triassic. The volcanic rocks of the Cuale mining district, the Cuale Volcanic Sequence, range from basalt to dacite. Although they have been interpreted to be Lower Cretaceous to Early Tertiary in age (JICA-MMA, 1986), the bulk of this sequence is more recently interpreted to be almost entirely composed of Late Jurassic rhyolite and rhyolitic volcaniclastic sedimentary rocks, with an overall thickness exceeding 800 m. The youngest rocks are massive and unaltered granodiorite that has intruded the Cuale Volcanic Sequence, assigned to the Cretaceous Puerto Vallarta Batholith, which, in the vicinity of the Cuale district, exhibits weak peraluminous characteristics (Schaaf et al., 1995).
The stratigraphy of the Cuale Volcanic Sequence has been subdivided, relative to the massive sulphide mineralisation and alteration, into a footwall sequence, a mineralised unit, and a late intrusive phase, as follows:
• The footwall sequence is >400 m thick, and is dominated by quartz and feldspar phyric rhyolite flows and crypto-domes, commonly enveloped by volumetric monomictic, commonly matrix-supported, volcanic breccias, interpreted as a carapace or flow breccias and hyaloclasites. The rhyolite flows are rarely massive, but normally exhibit flow banding, spherulitic devitrification, amygdules, and lithophysae. They contain 5 to 8 vol.% weakly embayed quartz phenocrysts that are up to 3 mm in diameter and, where not obliterated by alteration, similar amounts of euhedral feldspars. Coarse, polymictic volcaniclastic breccias to finer grained conglomerates are interbedded with the volcanic rocks of the sequence, with clasts all derived from the Cuale rhyolitic sequence. The coarse polymictic volcaniclastic breccia units are commonly matrix supported, with angular clasts of up to 30 cm in diameter, and are generally neither graded nor welded. The footwall sequence is interpreted to have been extruded subaqueously and, at least partly, in an explosive regime as hyaloclasites. The overall stratigraphy of the footwall is dominated by proximal volcanic rocks, e.g., quartz-feldspar phyric rhyolite flows, monomictic volcanic breccias, and unstratified, coarse polymicitic volcaniclastic breccias. Stratified volcaniclastic sedimentary rocks are relatively subordinate, whilst fine-grained silt and mudstone are absent.
• The mineralised unit includes quartz and feldspar phyric to aphyric rhyolite, occurring as massive bodies with no internal structure, as well as units with flow banding, spherulites developed in banded arrays, and rare horizons or lenses of hyaloclastite. These textures and structures are interpreted as representing flow and/or dome complexes (e.g., McPhie et al., 1993). These flow and/or dome complexes dominate on the peripheries of the district, particularly to the SW and NE, whereas the mineralised unit in the centre is dominated by volcaniclastic sedimentary rocks ranging from conglomerate to sandstones, interbedded with rhyolitic tuffs and lenses of black argillite. The absence of finer grained sedimentary rocks on the peripheries, combined with the relatively abundant rhyolite flows, has been interpreted to suggest these areas may represent palaeo-topographic highs bounding a central sedimentary basin(s). Syn-depositional tectonic activity at the western boundary of the central basin is inferred from soft-sediment deformation, e.g., ESE-vergent slump folding and locally reworked shale to siltstone deposits, as well as localised coarse boulder conglomerates. In contrast to the footwall sequence, the rhyolites of the mineralised unit only contain minor (<<5%) and small (<1 mm) quartz phenocrysts, but may be locally intercalated with quartz and feldspar phyric rhyolites similar to those in the footwall. The ore bearing unit is characterised by relatively abundant fine grained sedimentary rocks, interbedded with rhyolitic tuffs and volcaniclastic conglomerates, although rhyolite flows and hyaloclastic breccias are volumetrically subordinate compared to the footwall. However, in contrast to the footwall sequence, the tuffaceous rocks of the mineralised unit include welded horizons, and locally, tuffaceous strata containing accretionary lapilli.
Bedding planes of the fine-grained sedimentary units of the mineralised unit, where not affected by synsedimentary slumping, have dips that vary from flat lying to 35° with variable strikes.
• The late intrusive phase, which intrudes both the footwall sequence and the mineralised unit, and comprise dykes, sills and small hypabyssal bodies of quartz- and feldspar-phyric rhyolite, with a variable, but predominantly, NW strike. Unlike the intrusives of the two older units, these rhyolites are more massive and lack spherulitic devitrification textures, lithophysae and amygdules, although flow banding is common in some dykes. They are also marginally less altered, containing a moderately developed assemblage of quartz-sericite ±pyrite ±chlorite, which dominates, with local chloritised mafic phenocrysts, likely biotite pseudomorphs. Columnar jointing in some dykes suggests intrusion into cold wall rock. This late rhyolitic magmatism possibly constitutes several discrete intrusive pulses.
Structure
The major control on erosional landforms in the Cuale District is the type and degree of alteration, rather than fault traces. Never the less, the structural grain can be seen in the orientation of dykes, and in a few exposed major fault structures. The late andesite and many rhyolite dykes cutting all of the previous units within the volcanic pile have an east-west to SE-NW strike direction. This dominant dyke orientation, together with very sparse north-south striking cleavage, is consistent with emplacement of the rhyolite in tension fractures associated with sinistral transtensional rifting along north-south to NNW-SSE striking faults (Bissig et al., 2008).
Late normal faults with offsets of typically <30 m are observed throughout the district. These are important as they locally separate the Cuale Volcanic Sequence from older Triassic basement units.
A NE-dipping district-scale structure, the Paso Caracol Fault, has been inferred from limited outcrop exposure as well as from image interpretation along strike to the NW and SE. It is interpreted to extend from the centre of the district, from near the Socorredora deposit, to the northwestern corner of the district. Whilst no definite kinematic indicators have been sighted, Bissig et al. (2008) interpret the offset to have a reverse sense, based on smaller scale, similarly oriented NW-SE striking reverse faults seen throughout the district.
The late, ENE-WSW to NE-SW La Prieta Fault, with a minimum normal offset of 200 m, has been inferred from drill core and exposure in open pits. This structure extends from the centre of the district to its NE corner, and follows immediately to the NW of a linear string of 5 of the main deposits of the district, namely Socorredora, La Prieta, Coloradita, Chivos de Arriba, and Chivos de Abajo. Where exposed in the Coloradita open pit, it is a ~30 m thick zone filled with gouge and brecciated rocks. It dips at ~45° NNW, steepening at depth (Macomber, 1962). A normal offset is implied by parallel, smaller scale fractures in the vicinity of the fault trace, which have a demonstrably normal offset. Massive sulphide mineralisation within the string of deposit it follows is terminated to the NNW at the La Prieta fault.
Alteration
Moderate to intense hydrothermal alteration is ubiquitous throughout the district and affects all rocks within the Cuale Volcanic Sequence. Alteration associated with the deposits within the footwall sequence is considered proximal to mineralisation where characterised by intense quartz-sericite-pyrite alteration, grading laterally into more chlorite-rich assemblages, although that association at the Socorredora and Naricero deposits is only moderate to intense. The black argillite, which hosts part of the ore, is locally ony slightly carbonaceous, and may be cut by calcite veinlets, but it is unclear whether or not this carbonate is related to hydrothermal alteration. The late intrusive rhyolites are less intensely altered, being moderately silicified with only modest amounts of sericite, whilst disseminated pyrite is absent or much less abundant than in the lower parts of the stratigraphy. Ferromagnesian minerals (most likely biotite) are preserved as chloritised relicts in the rhyolites of the late intrusive phase.
Mineralisation
Eleven separate deposits/lenses of polymetallic sulphide mineralisation, ranging from 20 000 to 783 000 tonnes, along with a number of smaller occurrences, were in production in the 1980s (Hall and Gomez-Torres, 2000), and have since been mined out. The following is dawn from Bissig et al. (2008) quoting Berrocal and Querol (1991) and Hall and Gomez-Torres (2000).
The style of mineralisation and relative abundance of metals vary significantly between deposits.
The Naricero, Socorredora, La Prieta-Rubí, San Nicolas, and Refugio deposits, which yielded ~50% of the ore mined in the district, are hosted by, or spatially associated with black argillites. The massive sulphide mineralisation within these deposits, compared to those in the rest of the district, is characterised by high average silver grades, up to several hundred g/t. The silver is contained within fine-grained galena and sphalerite that is locally brecciated (e.g., Naricero) or finely banded (e.g., Socorredora). As the Pb-Ag rich orebodies are locally finely banded, interpreted to be sedimentary textures, Bissig et al. (2008) interpret them to be in a distal setting, possibly reworked and transported into anoxic basins adjacent to proximal sulphide mounds. These massive sulphide bodies progress laterally and vertically from massive pyrite, into sphalerite- and galena-rich massive sulphides.
The Coloradita, Chivos de Arriba and Chivos de Abajo deposits, contain up to 3 g/t Au and 0.4 to 1.5% Cu but are relatively low in Ag and Pb compared to those listed above. The precious and base metals are partly hosted by pyrite- and chalcopyrite-rich stockwork zones within hydrothermally altered envelopes. These stockwork zones are overlain by massive sulphide bodies, mostly composed of pyrite with chalcopyrite that grade laterally and vertically into sphalerite and galena rich zones. The host at Coloradita is aphyric rhyolite.
Minas de Oro/Grandeza, which is ~2 to 3 km SE of the other deposits of the district, consists of stockwork mineralisation with gold grades of 1.9 g/t, but only 0.2 wt.% Cu, which distinguishes it from other gold-rich orebodies of the district where Cu is more abundant. The described ore mineralogy at this deposit (Macias and Solis, 1985) is essentially sphalerite and pyrite with lesser galena and freibergite [(Ag,Cu,Fe)12(Sb,As)4S13], whilst the gangue is predominantly composed of quartz and calcite. Limited fluid inclusion data on liquid-rich inclusions in quartz and sphalerite from this deposit (Macias and Solis, 1985), support the interpretation that Minas de Oro/Grandeza has similarities to low-sulphidation epithermal mineralisation, i.e., homogenization temperatures of between 220 and 265°C, salinities of ~5 wt.% NaCl Equiv., together with the estimated average density of 0.86 g/cm3) and having formed at 400 to 700 m below surface. An ~4 m thick quartz vein with epithermal textural characteristics, such as open-space filling and local colloform texture, was mined historically (no grade and tonnage data available) and crops out ~300 m NW of, and along strike from, the stockwork mineralisation at Minas de Oro/Grandeza. Both the vein and the stockwork mineralisation are hosted within the late intrusive phase rhyolite. Additional support for a late mineralisation event with epithermal characteristics comes from quartz-carbonate ±adularia vein material found in the float on the northern margin of the district, as well as from stream-sediment geochemistry further to the north, where anomalous As and Hg concentrations have been reported (International Croesus Ventures Corp. unpub. reports).
Resources
The total tonnes and grade estimates of the main mines of the district, after Bissig et al. (2008) are as follows:
Naricero - 782 544 tonnes @ 0.34 g/t Au, 157 g/t Ag, 1.05% Pb, 2.85% Zn, 0.06% Cu;
Mina de Oro/Grandeza - 756 661 tonnes @ 1.89 g/t Au, 22 g/t Ag, 1.41% Pb, 2.35% Zn, 0.2% Cu;
Socorredora - 200 492 tonnes @ 0.13 g/t Au, 187 g/t Ag, 1.89% Pb, 6.93% Zn, 0.16% Cu;
Coloradita - 170 055 tonnes @ 0.66 g/t Au, 85 g/t Ag, 1.99% Pb, 6.51% Zn, 0.37% Cu;
Las Talpas - 141 425 tonnes @ 0.34 g/t Au, 24 g/t Ag, ;0.65% Pb, 1.91% Zn, 0.24% Cu;
La Prieta-Rubí - 113 335 tonnes @ 0.73 g/t Au, 226 g/t Ag, 3.8% Pb, 9.24% Zn, 0.32% Cu;
Chivos de Abajo - 85 771 tonnes @ 1.08 g/t Au, 179 g/t Ag, 1.48% Pb, 4.71% Zn, 1.54% Cu;
San Nicolas - 79 965 tonnes @ 0.19 g/t Au, 121 g/t Ag, 1.57% Pb, 3.18% Zn, 0.13% Cu;
Jesus Maria - 46 751 tonnes @ 0.06 g/t Au, 109 g/t Ag, 1.85% Pb, 3.31% Zn, 0.09% Cu;
Refugio - 34 569 tonnes @ 0.14 g/t Au, 156 g/t Ag, 0.89% Pb, 1.95% Zn, 0.1% Cu;
Chivos de Arriba - 23 588 tonnes @ 2.79 g/t Au, 70 g/t Ag, 0.85% Pb, 2.18% Zn, 0.74% Cu;
Eight other small deposits - 39 199 tonnes
TOTAL - 2.474 355 Mt @ 0.83 g/t Au, 103 g/t Ag, 1.03% Pb, 3.22% Zn, 0.23% Cu.
Most of the information in this summary, except where noted otherwise, has been drawn from Bissig et al. (2008) as cited below.
The most recent source geological information used to prepare this decription was dated: 2008.
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.
Cuale District centre
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Bissig, T., Mortensen, J.K., Tosdal, R.M. and Hall, B.V., 2008 - The Rhyolite-Hosted Volcanogenic Massive Sulfide District of Cuale, Guerrero Terrane, West-Central Mexico: Silver-Rich, Base Metal Mineralization Emplaced in a Shallow Marine Continental Margin Setting: in Econ. Geol. v.103, pp. 141-159.
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