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Pueblo Viejo |
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Dominican Republic |
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Au Ag
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Super Porphyry Cu and Au
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The Pueblo Viejo gold deposit is located in the Dominican Republic, on the eastern half of the island of Hispaniola, ~55 km NNW of Santo Domingo (#Location: 18° 56' 56"N, 70° 10' 52"W).
The island of Hispaniola lies within the Greater Antilles Magmatic Arc, developed along the northern margin of the Caribbean Plate. This arc rocks is exposed as a WNW trending longitudinal belt following the spine of the island. They are bounded to the north by an 8 km thick Albian (109 to 100 Ma) ophiolite complex, separating the arc from a structurally underlying sequence of Mesozoic meta-sedimentary and meta-igneous rocks to the north that represent a Lower Cretaceous primitive island arc. These suites are largely masked by post-Eocene marine strata. Immediately to the south of the ophiolite belt, the magmatic arc is discordantly underlain by Mesozoic amphibolites and meta-sedimentary rocks, part of the same the submarine, earliest Cretaceous to pre-Aptian island-arc plutonism and volcanism described to the north (Mann et al., 1991). The main arc comprises post-Albian (mid-Cretaceous) to pre-Campanian island arc plutonism and volcanism, also mainly in a submarine environment. This magmatism was interrupted by Campanian (Late Cretaceous) deformation before post-Campanian to pre-middle Eocene renewal of island arc plutonism and volcanism, again mainly in a submarine environment (Mann et al., 1991). The arc intrusives and volcanic rocks are similar to those in Cuba. Much of the remainder of the island to the south is overlain by post-Eocene marine strata, with fault dislocated exposures of Cretaceous volcanic arc rocks along the peninsula to the SW.
Pueblo Viejo is hosted by the Los Ranchos Formation, part of the Lower Cretaceous primitive arc that predated the main Greater Antilles Magmatic Arc. The primitive arc is composed of a series of stratigraphic units, commencing with the
• Duarte Formation, which may, with the ophiolite complex, represent oceanic crust sea floor basement of the Caribbean Plate. These are overlain by the
• Maimon Formation largely consists of a bimodal fore-arc assemblage of metavolcanic rocks with lesser metasediments. The metavolcanic rocks include metabasalt (pyroxene-plagioclase and related mafic plagioclase porphyry), metadacite/metarhyolite (quartz porphyries), undivided metavolcanic rocks, largely plagioclase porphyry and metasediments, including limestone/marble, iron formation, and carbonaceous slate (Kesler et al., 1990).
• Amina Formation which comprises a sequence of volcanic protoliths, that have been variably deformed and metamorphosed, including tholeiites, boninites, calc-alkaline basalts and low-K rhyolites, and are possibly equivalents of the Maimon and Los Ranchos formations (Escuder-Viruete et al., 2007).
• Los Ranchos Formation represents the axial portion of the primitive island arc, and is a >3 km thick sequence of volcanic and volcaniclastic rocks with variable geochemical characteristics. It is regionally intruded throughout by 106 to 115 Ma tonalite batholiths, minor diorite to gabbro plutons and mafic dykes. The lower basaltic unit is dominated by spilitised polymict volcanic breccias and flows of boninite, boninitic and tholeiitic basalt to basaltic andesite, with local pillow lavas and interbedded well-stratified, fine-grained volcaniclastic rocks. The intermediate rhyodacitic unit comprises altered dacite to rhyolite flows, brecciated extrusive domes and cryptodomes, with minor intermediate to felsic silicified tuffs, crystal-rich tuffs, lapilli tuffs and bands of upward-fining volcaniclastic sandstones to siltstones. The upper basaltic unit is ~1000 m thick and comprises dark green to black altered tholeiitic basalt to andesite, forming massive flows, autoclastic breccias and syn-volcanic gabbroic intrusions. There are local vesicular/amygdaloidal textures and autoclastic breccias are generally composed by monogenetic clasts (Escuder Viruete et al., 2006).
These units represent the first stage of arc magmatism related to Early Cretaceous southwest-directed subduction. The volcanic arc underwent a change in polarity in the Mid-Cretaceous (Aptian to Early Albanian). Subsequent Late Cretaceous arc magmatism formed the overlying Tireo, Peralvillo South and North, and Siete Cabezas Formations, and continued intermittently until the end of the Campanian (about 72 Ma; Escuder-Viruete et al., 2007; 2008). This magmatism shifted location with time but was focused mainly to the west of the Los Ranchos Formation in the central and western parts of the Central Cordillera, producing a broad zone of granodiorite and quartz diorite intrusions, most of which range in age from 87 to 80 Ma (Kesler et al., 1991). The final arc magmatic phase formed the mid-Eocene Loma Caballero tuffs and probable Eocene diorites (Bowin, 1966).
Mineralization at Pueblo Viejo occupies the upper part of Lower Cretaceous Los Ranchos Formation. The ore deposit comprises an oxide resource developed from weathering of an underlying funnel shaped, acid sulphate type sulphidic, gold-quartz-pyrophyllite deposit that formed in a small basin of conglomerates, agglomerates, sandstones and carbonaceous sediments interpreted to have represented a maar diatreme complex.
There have been two views on the occurrence of mineralisation at Pueblo Viejo, specifically:
• That the mineralisation is essentially coeval with the Early Cretaceous Los Ranchos Formation that hosts ore (e.g., Bowin, 1966; Kesler et al., 1981; Sillitoe and Bonham, 1984; Muntean et al., 1990; Mueller et al., 2008). In this version, Pueblo Viejo was developed in the upper part of the Lower Cretaceous Los Ranchos Formation, a series of spilitic and keratophyric volcanics and volcaniclastics on the eastern side of the Central Cordillera. A maar diatreme complex in the upper part of the formation was formed in the latter stages of volcanism in this sequence and includes fragmented spilite, re-deposited pyroclastics, quartz eye lapilli tuff and carbonaceous lacustrine sediments. Primary magmatic minerals have been entirely altered to albite, quartz, calcite, chlorite, illite, smectite, epidote, actinolite and prehnite. The district contains several acid sulphate gold orebodies of which Moore and Monte Negro are the largest. -or-
• That mineralisation is the product of a Late Cretaceous magmatic-hydrothermal event that overprinted the Los Ranchos Formation (Redwood et al., 2006; Sillitoe et al., 2006). These authors suggest the Pueblo Viejo deposit (Moore and Monte Negro) is located within the southeastern segment of a 10 km long, advanced argillic lithocap that is dominated by pervasive quartz-pyrophyllite-pyrite alteration underlying the prominent Loma la Cuaba ridge, and was developed within the Los Ranchos Formation. To the west of Moore and Monte Negro, the lithocap lacks significant known gold-silver mineralisation, although the trace element suite that is typical of Pueblo Viejo remains strongly anomalous (GoldQuest Mining Corp., unpub; Kesler et al., 2003). However, further to the west the advanced argillic alteration of the lithocap extends into the alunite-bearing zone at Loma la Cuaba where massive, stratabound layers of silica are enclosed within foliated rock consisting largely of quartz and pyrophyllite with local areas containing alunite. Both the stratabound bodies of silica and the enclosing foliated rock dip to the SW, following regional structural trends. These alunite-hosting rocks have been subjected weathering that removed pyrite, but are otherwise similar in mineralogy to those in the Moore and Monte Negro deposits.
The bulk of the high grade Au-Ag mineralisation at Pueblo Viejo occurs in a shallowly dipping sequence of laminated carbonaceous siltstone and sandstone at the top of the Los Ranchos Formation, where pervasive silicification is typically intense and accompanied by pyrophyllite (Muntean et al., 1990). However, according to Sillitoe et al. 2006) underlying coarse-grained fragmental units, including conglomerate and basaltic andesite flows are also partly ore bearing. Quartz-alunite alteration is subordinate to the overprinting quartz-pyrophyllite assemblage, and is located at depth (Kesler et al., 1981; Muntean et al., 1990), well below the zone of weathering, and is clearly hypogene in origin (Kesler et al., 1981; Muntean et al., 1990), whilst vuggy quartz is only present in trace amounts. Fault localised feeders are recognised, although there is a marked stratigraphic control of the two main broadly mushroom-shaped orebodies, Moore and Monte Negro (Sillitoe et al., 2006). Alunite coexists with pyrite and quartz and is locally replaced by diaspore, pyrophyllite, kaolinite, and sparse sericite (Muntean et al., 1990). The main alteration minerals in the upper parts of the deposits are kaolinite and quartz, which are partly or completely replaced in many places by pyrophyllite and grade farther upward into intensely silicified rocks at the top of the deposits (Arribas et al., 2011).
The hypogene ore is present as relatively late stage massive pyrite veins, which both cut and follow bedding, as well as being associated with an extensive earlier generation of disseminated pyrite (Kesler et al., 1981; Muntean et al., 1990). The pyrite veins also carry low iron sphalerite and lesser galena, several sulphosalt minerals of the enargite and boulangerite groups, quartz, barite and pyrophyllite (Kesler et al., 1981; Muntean et al., 1990; Ruiz, 2002). Pyrite contents range from 10 to 20 vol.%. The shallow sections of the orebodies, now fully exploited, underwent strong supergene sulphide oxidation, to produce ~170 t of Au, mainly native gold, and ~775 t Ag (Kesler et al., 2003) contained in halide minerals (Russell et al., 1981).
The hypogene sulphide ore is chiefly composed of telluride species, dominantly calaverite, with subordinate electrum (Kesler et al., 1981; Muntean et al., 1990; Ruiz, 2002). The average zinc content of the sulphidic gold-silver ore is ~0.8 wt.%, more than four times the Cu grade (Kesler et al., 1981).
The ore zone at Monte Negro is around 1500 x 500 m at surface, while Moore covers an irregular 'Y' shaped area with maximum dimensions of some 900 x 900 m.
Mining, mainly from Moore and Monte Negro, commenced in 1975 on oxide reserves of:
27 Mt @ 4.23 g/t Au and 21.6 g/t Ag.
The underlying hypogene mineralisation grades were 3 g/t Au, 23 g/t Ag, 0.8% Zn, 0.2% Cu.
The largest deposit in the group, Monte Negro had:
oxide ore: 14 Mt @ 3.35 g/t Au, 7.6 g/t Ag (0.8 g/t Au cutoff)
sulphide ore: 37 Mt @ 3.95 g/t Au, 22.4 g/t Ag (2.5 g/t Au cutoff)
The total resource in the complex is quoted at 600 tonnes of Au.
Published ore reserves and mineral resources at 31 December 2015 were (Barrick Gold Corp. Annual Report, 2015):
Proved + probable reserves - 93.877 Mt @ 2.97 g/t Au, 17.94 g/t Ag, 0.095% Cu [278.8 t of Au]
Measured + indicated resources - 97.881 Mt @ 2.46 g/t Au 14.19 g/t Ag, 0.083% Cu, [240.8 t of Au]
Inferred resources - 2.33 Mt @ 1.96 g/t Au 13.93 g/t Ag, 0.041% Cu, [4.6 t of Au]
NOTE; Resources are inclusive of reserves.
In 2015, 37.893 Mt of ore and waste were mined, with 6.917 Mt @ 4.944 g/t being processed (Barrick Gold presentation, 2016)
Published ore reserves and mineral resources at 31 December 2022 (Barrick Gold Corp. Annual Report, 2022) were:
Proved + probable reserves - 170 Mt @ 2.19 g/t Au, 13.60 g/t Ag [372.3 t of Au]
Measured resources - 46 Mt @ 2.08 g/t Au 11.69 g/t Ag, [95.7 t of Au]
Indicated resources - 190 Mt @ 1.99 g/t Au 12.32 g/t Ag, [378 t of Au]
Inferred resources - 4.6 Mt @ 1.8 g/t Au 10.5 g/t Ag, [8.2 t of Au]
TOTAL resources - 240.6 Mt @ 2.0 g/t Au 12.16 g/t Ag, [482 t of Au]
NOTE; Resources are inclusive of reserves.
For more detail see the reference(s) listed below.
The most recent source geological information used to prepare this decription was dated: 2011.
Record last updated: 1/2/2017
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.
Pueblo Viejo
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Selected References:
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Arribas A, Arribas I, Draper G, Hall C, Kesler S E, McEwan C and Muntean J L, 2011 - 40Ar/39Ar dating Of alunite from the Pueblo Viejo gold-silver district, Dominican Republic: in Econ. Geol. v.106 pp. 1059-1070
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Kesler S E, Campbell I H, Smith C N, Hall C H and Allen C M 2005 - Age of the Pueblo Viejo Gold-Silver Deposit and Its Significance to Models for High-Sulfidation Epithermal Mineralization: in Econ. Geol. v100 pp 253-272
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Kesler S E, Russell N, McCurdy K 2003 - Trace-metal content of the Pueblo Viejo precious-metal deposits and their relation to other high-sulfidation epithermal systems: in Mineralium Deposita v38 pp 668-682
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Kesler S E, Russell N, Seaward M, Rivera J, McCurdy K, Cumming G L, Sutter J F 1981 - Geology and geochemistry of sulfide mineralization underlying the Pueblo Viejo gold-silver oxide deposit, Dominican Republic: in Econ. Geol. v76 pp 1096-1117
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Kirk J D, Ruiz J, Kesler S E, Simon A and Muntean J L, 2014 - Re-Os Age of the Pueblo Viejo Epithermal Deposit, Dominican Republic : in Econ. Geol. v.109 pp. 503-512
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Mueller, A.G., Hall, G.C., Nemchin, A.A. and OBrien, D., 2008 - Chronology of the Pueblo Viejo epithermal gold-silver deposit, Dominican Republic: formation in an Early Cretaceous intra-oceanic island arc and burial under ophiolite: in Mineralium Deposita v.43, pp. 873-889.
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Muntean J L, Kesler S E, Russell N, Polanco J 1990 - Evolution of the Monte Negro acid Sulfate Au-Ag deposit, Pueblo Viejo, Dominican Republic: important factors in grade development: in Econ. Geol. v85 pp 1738-1758
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Nelson C E 2000 - Volcanic domes and gold mineralization in the Pueblo Viejo district, Dominican Republic: in Mineralium Deposita v35 pp 511-525
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Sillitoe R H, Hall D J, Redwood S D and Waddell A H, 2006 - Pueblo Viejo High-Sulfidation Epithermal Gold-Silver Deposit, Dominican Republic: A New Model Of Formation Beneath Barren Limestone Cover: in Econ. Geol. v101 pp 1427-1435
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Sillitoe R H, Hannington M D, Thompson J F H 1996 - High Sulfidation deposits in the volcanogenic massice Sulfide environment: in Econ. Geol. v 91 pp 204-212
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Torro, L., Camprubi, A., Proenza, J.A., Leon, P., Stein, H.J., Lewis, J.F., Nelson, C.E., Chavez, C. and Melgarejo, J.C., 2017 - Re-Os and U-Pb Geochronology of the Dona Amanda and Cerro Kiosko Deposits, Bayaguana District, Dominican Republic: Looking Down for the Porphyry Cu-Mo Roots of the Pueblo Viejo-Type Mineralization in the Island-Arc Tholeiitic Series of the Caribbean: in - [60 km east of Pueblo Veijo] - Econ. Geol. v.112, pp. 829-853.
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Vennemann T W, Muntean J L, Kesler S E, ONeil J R 1993 - Stable isotope evidence for magmatic fluids in the Pueblo Viejo epithermal acid sulfate Au-Ag deposit, Dominican Republic: in Econ. Geol. v88 pp 55-71
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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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