Weathering profile of the Cerro de Maimón VMS deposit (Dominican Republic): Textures, mineralogy, gossan evolution and mobility of gold and silver

E. Andreu, L. Torró, J. A. Proenza, C. Domenech, A. García-Casco, C. Villanova de Benavent, C. Chavez, J. Espaillat, J. F. Lewis

Research output: Contribution to journalArticle

Abstract

Cerro de Maimón, in the central Dominican Republic, is currently the only VMS deposit under production in the Caribbean region. It is hosted in the Maimón Formation, of early Cretaceous age, which is part of the oldest and chemically most primitive island-arc in the Caribbean. From bottom to top, this deposit can be divided into (i) a primary sulfide zone, (ii) a supergene enrichment zone and (iii) an oxidized zone. This study reports new data on the textural and mineralogical characteristics of the oxidized zone (gossan/leached capping zone) with emphasis in the Au-Ag-bearing phases.The mineral paragenesis of the oxidized zone is essentially composed of goethite, hematite, quartz and barite. Botryoidal, cellular and brecciated textures can be distinguished. Botryoidal and brecciated textures dominate in the upper parts of the oxidized zone, whereas cellular textures are more common in the intermediate and lower parts. However, the weathering profile is very heterogeneous. The leached capping profile shows evidence of both transported and indigenous gossans. Gold in the oxide paragenesis is extremely pure (99% Au) suggesting that chemical refining took place. Silver occurs mainly as iodargyrite (AgI), and minor AgBr, AgCl, in botryoidal aggregates.Particles of Au-Ag alloy in the primary mineralization exposed to a weathering environment can be leached and transported by various agents (chemical and biochemical) that may exist simultaneously. In the presence of halides, gold and silver can be leached and transported in a wide range of pH-Eh conditions, especially if iodine is present. Silver is leached more rapidly and over a broader range of pH-Eh conditions, and is preferentially transported as iodine-complexes than other halides.The presence of iodargyrite in the Cerro de Maimón gossan, fully developed under tropical conditions, suggests that this mineral cannot be considered an indicator of extremely arid environments as typically claimed by many authors; iodargyrite occurrence would rather point to the presence of saline-halide rich groundwater in oxide deposits.

Original languageEnglish
Pages (from-to)165-179
Number of pages15
JournalOre Geology Reviews
Volume65
Issue numberP1
DOIs
Publication statusPublished - 18 Sep 2014

Fingerprint

gossan
weathering profile
Mineralogy
Weathering
Silver
Gold
silver
mineralogy
Deposits
gold
Textures
texture
Iodine
Oxides
Minerals
Bearings (structural)
halide
Barium Sulfate
Quartz
Sulfides

Keywords

  • Cerro de Maimón
  • Dominican Republic
  • Gold
  • Gossan/leached capping zone
  • Iodargyrite
  • Silver
  • VMS

Cite this

Andreu, E., Torró, L., Proenza, J. A., Domenech, C., García-Casco, A., Villanova de Benavent, C., ... Lewis, J. F. (2014). Weathering profile of the Cerro de Maimón VMS deposit (Dominican Republic): Textures, mineralogy, gossan evolution and mobility of gold and silver. Ore Geology Reviews, 65(P1), 165-179. https://doi.org/10.1016/j.oregeorev.2014.09.015
Andreu, E. ; Torró, L. ; Proenza, J. A. ; Domenech, C. ; García-Casco, A. ; Villanova de Benavent, C. ; Chavez, C. ; Espaillat, J. ; Lewis, J. F. / Weathering profile of the Cerro de Maimón VMS deposit (Dominican Republic) : Textures, mineralogy, gossan evolution and mobility of gold and silver. In: Ore Geology Reviews. 2014 ; Vol. 65, No. P1. pp. 165-179.
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abstract = "Cerro de Maim{\'o}n, in the central Dominican Republic, is currently the only VMS deposit under production in the Caribbean region. It is hosted in the Maim{\'o}n Formation, of early Cretaceous age, which is part of the oldest and chemically most primitive island-arc in the Caribbean. From bottom to top, this deposit can be divided into (i) a primary sulfide zone, (ii) a supergene enrichment zone and (iii) an oxidized zone. This study reports new data on the textural and mineralogical characteristics of the oxidized zone (gossan/leached capping zone) with emphasis in the Au-Ag-bearing phases.The mineral paragenesis of the oxidized zone is essentially composed of goethite, hematite, quartz and barite. Botryoidal, cellular and brecciated textures can be distinguished. Botryoidal and brecciated textures dominate in the upper parts of the oxidized zone, whereas cellular textures are more common in the intermediate and lower parts. However, the weathering profile is very heterogeneous. The leached capping profile shows evidence of both transported and indigenous gossans. Gold in the oxide paragenesis is extremely pure (99{\%} Au) suggesting that chemical refining took place. Silver occurs mainly as iodargyrite (AgI), and minor AgBr, AgCl, in botryoidal aggregates.Particles of Au-Ag alloy in the primary mineralization exposed to a weathering environment can be leached and transported by various agents (chemical and biochemical) that may exist simultaneously. In the presence of halides, gold and silver can be leached and transported in a wide range of pH-Eh conditions, especially if iodine is present. Silver is leached more rapidly and over a broader range of pH-Eh conditions, and is preferentially transported as iodine-complexes than other halides.The presence of iodargyrite in the Cerro de Maim{\'o}n gossan, fully developed under tropical conditions, suggests that this mineral cannot be considered an indicator of extremely arid environments as typically claimed by many authors; iodargyrite occurrence would rather point to the presence of saline-halide rich groundwater in oxide deposits.",
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Andreu, E, Torró, L, Proenza, JA, Domenech, C, García-Casco, A, Villanova de Benavent, C, Chavez, C, Espaillat, J & Lewis, JF 2014, 'Weathering profile of the Cerro de Maimón VMS deposit (Dominican Republic): Textures, mineralogy, gossan evolution and mobility of gold and silver', Ore Geology Reviews, vol. 65, no. P1, pp. 165-179. https://doi.org/10.1016/j.oregeorev.2014.09.015

Weathering profile of the Cerro de Maimón VMS deposit (Dominican Republic) : Textures, mineralogy, gossan evolution and mobility of gold and silver. / Andreu, E.; Torró, L.; Proenza, J. A.; Domenech, C.; García-Casco, A.; Villanova de Benavent, C.; Chavez, C.; Espaillat, J.; Lewis, J. F.

In: Ore Geology Reviews, Vol. 65, No. P1, 18.09.2014, p. 165-179.

Research output: Contribution to journalArticle

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T1 - Weathering profile of the Cerro de Maimón VMS deposit (Dominican Republic)

T2 - Textures, mineralogy, gossan evolution and mobility of gold and silver

AU - Andreu, E.

AU - Torró, L.

AU - Proenza, J. A.

AU - Domenech, C.

AU - García-Casco, A.

AU - Villanova de Benavent, C.

AU - Chavez, C.

AU - Espaillat, J.

AU - Lewis, J. F.

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N2 - Cerro de Maimón, in the central Dominican Republic, is currently the only VMS deposit under production in the Caribbean region. It is hosted in the Maimón Formation, of early Cretaceous age, which is part of the oldest and chemically most primitive island-arc in the Caribbean. From bottom to top, this deposit can be divided into (i) a primary sulfide zone, (ii) a supergene enrichment zone and (iii) an oxidized zone. This study reports new data on the textural and mineralogical characteristics of the oxidized zone (gossan/leached capping zone) with emphasis in the Au-Ag-bearing phases.The mineral paragenesis of the oxidized zone is essentially composed of goethite, hematite, quartz and barite. Botryoidal, cellular and brecciated textures can be distinguished. Botryoidal and brecciated textures dominate in the upper parts of the oxidized zone, whereas cellular textures are more common in the intermediate and lower parts. However, the weathering profile is very heterogeneous. The leached capping profile shows evidence of both transported and indigenous gossans. Gold in the oxide paragenesis is extremely pure (99% Au) suggesting that chemical refining took place. Silver occurs mainly as iodargyrite (AgI), and minor AgBr, AgCl, in botryoidal aggregates.Particles of Au-Ag alloy in the primary mineralization exposed to a weathering environment can be leached and transported by various agents (chemical and biochemical) that may exist simultaneously. In the presence of halides, gold and silver can be leached and transported in a wide range of pH-Eh conditions, especially if iodine is present. Silver is leached more rapidly and over a broader range of pH-Eh conditions, and is preferentially transported as iodine-complexes than other halides.The presence of iodargyrite in the Cerro de Maimón gossan, fully developed under tropical conditions, suggests that this mineral cannot be considered an indicator of extremely arid environments as typically claimed by many authors; iodargyrite occurrence would rather point to the presence of saline-halide rich groundwater in oxide deposits.

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