Volcanogenic Massive Sulfide ore deposits - in honour of James Franklin 2091

mineralizing system is uncertain. The strong spatial correlation between gold mineralization and the thick (~20 m) rock unit that contains these sulfates and the systematic concentration of sulfides in its volcanogenic matrix provides some insight. The anhydrite-gypsum nodules are mineralogically very homogeneous and lack of either sulfide or gangue mineral inclusions ruling out a dominantly replacive origin; an exhalative genesis and later sedimentary reworking are, in contrast, very plausible. Significant amounts of exhalative anhydrite-gypsum are characteristic of many submarine hydrothermal deposits on mid-ocean ridges and back arc basins in the modern seafloor and in ancient Kuroko-type VMS deposits (Ogawa et al. 2007). Further analytic work on these nodules is planned.

The lower domain is characterized by extensive disseminated and stockwork mineralization with locally high grade gold contents. A mineralogic-petrologic study of the sulfide-silica veins reveals incipient early brecciation and later open-space infill. The ore mineralogy of the studied samples is fairly simple, with extensive evidence for a pyrite-sphalerite-chalcopyrite crystallization sequence, suggesting an increase over the time of the mineralizing fluid temperatures. Gold and telluride crystallization is linked to the chalcopyrite stage.

The fact that Ag-rich electrum occurs as inclusions in chalcopyrite, pyrite and to a lesser extent gangue and sphalerite in contrast with Ag-poor electrum detected only within pyrite grains indicates the existence of two electrum formation stages. Detailed observations suggest that the Ag-poor electrum is systematically in spatial correlation with fracturing of its hosting pyrite. The authors suggest that chemical refining of an originally Ag-rich electrum by late fluids circulating through fractures (largely occurring in fragile minerals such as pyrite) could have taken place.

The δ34S values of the Romero analyzed sulfides tightly span around 0 ‰; these values are consistent with a magmatic source of the sulfur either from a direct contribution from a vapor-rich magmatic fluid or from leaching of the volcanic host rocks (Ohmoto 1986). Nevertheless, the occurrences of Au- and Bi-tellurides can be considered indicative of participation of magmatic fluids during the ore formation (Spooner 1993).

In a short technical report, Sillitoe (2013) assigned the Romero mineralization to an intermediate-sulfidation epithermal category. Lack of the diagnostic tennantite-tetrahedrite (Simons et al. 2005) and outstanding predominance of chalcopyrite over sphalerite in the studied deposits challenge this classification. We also note the absence of silver sulfosalts, characteristic of intermediate-sulfidation deposits (e.g. Gamarra-Urrunaga et al. 2013).

Occurrence of exhalative anhydrite levels, surely merits attention. Further analytical, currently under way,

is necessary in order to better understand the Romero mineralizing system. Acknowledgements This research has been financially supported by the Spanish project CGL2012-36263, the Catalan project 2014-SGR-444 and a FPU Ph.D. grants to L.T. by the Ministerio de Educación of the Spanish Government. The help and hospitality extended by the GoldQuest staff at Hondo Valle camp are also gratefully acknowledged, as well as the technical support in EMP sessions by Dr. X. Llovet. References Escuder Viruete J, Contreras F, Stein G, Urien P, Joubert M, Pérez-

Estaún A, Friedman R, Ullrich T (2007) Magmatic relationship and ages between adakites, magnesian andesites and Nb-enriched basalt-andesites from Hispaniola: Record of a major change in the Caribbean island arc magma source. Lithos 104:378-404

Escuder Viruete J, Joubert M, Urien P, Friedman R, Weis D, Ullrich T, Pérez-Estaún A (2008) Caribbean island-arc rifting and back-arc basin development in the Late Cretaceous: Geochemical, isotopic and geochronological evidence from Central Hispaniola. Lithos 104:378-404

Gamarra-Urrunaga JE, Castroviejo R, Bernhardt HJ (2013) Preliminary mineralogy and ore petrology of the intermediate-sulfidation Pallancata deposit, Ayacucho, Peru. Can Mineral 51:67-91

Lewis JF, Amarante A, Bloise G, Jimenez JG, Dominguez HD (1991) Lithology and stratigraphy of Upper Cretaceous volcanic and volcaniclastic rocks of the Tireo Group, Dominican Republic, and correlations with the Massif du Nord in Haiti. Geol S Am S 262

Lewis JF, Escuder Viruete J, Hernaiz Huerta PP, Gutierrez G, Draper G, Pérez-Estaún A (2002) Subdivisión geoquímica del Arco de Isla Circum-Caribeño, Cordillera Central Dominicana: Implicaciones para la formación, acreción y crecimiento cortical en un ambiente interoceánico. Acta Geológica Hispánica 37:81-122

Nelson CE, Proenza JA, Lewis JF, López-Kramer J (2011) The metallogenic evolution of the Greater Antilles. Geol Acta 9:229-264

Ogawa Y, Shikazono N, Ishiyama D, Sato H, Mizuta T, Nakano T (2007) Mechanism for anhydrite and gypsum formation in the Kuroko massive sulfide-sulfate deposits, north Japan. Miner Deposita 42:219-233

Ohmoto H (1986) Stable isotope geochemistry of ore deposits. Rev Mineral Geochem 16:491-559

Sillitoe RH (2013) Comments on geology and exploration of the Romero gold-copper prospect and environs, Las Tres Palmas Project, Dominican Republic. Technical Report. Santo Domingo

Simmons FS, White NC, John DA (2005). Geological characteristics of epithermal precious and base metal deposits. Econ Geol 100th Anniversary Volume:485-522

Spooner ETC (1993) Magmatic sulphide/volatile interaction as a mechanism for producing chalcophile element enriched, Archean Au-quartz, epithermal AuAg and Au skarn hydrothermal ore fluids. Ore Geol Rev 7:359-379

Au- and PGE-Rich Massive Sulphide Deposits Associated with Serpentinized Peridotites of the Havana-Matanzas Ophiolites, Cuba Guillem Sánchez, Thomas Aiglsperger, Lisard Torró, Joaquín A Proenza Departament de Cristal·lografia, Mineralogia i Dipòsits Minerals. Universitat de Barcelona, Spain Antonio García-Casco Departamento de Mineralogía y Petrología, Universidad de Granada, Spain Angélica Isabel Llanes-Castro Departamento de Mineralogía y Petrología, Instituto de Geología y Paleontología, Cuba Abstract. The Havana-Matanzas ophiolites, western Cuba, contain the only ultramafic-hosted massive sulphide deposits in the Caribbean region. Here we present data on the mineralogy and geochemistry of the Loma Majana and Salomón deposits hosted in highly serpentinized harzburgites with tectonite textures. The sulphide assemblage consists of pyrrhotite (up to 90 %), pyrite and chalcopyrite, with minor Co-Fe-Ni arsenides/sulfoarsenides (largely löllingite-safflorite, cobaltite), and trace amounts of Co-pentlandite. Ores from the two deposits returned low Ni/Co ratios. Loma Majana ores are more enriched in Au (up to 4.8 ppm), PGE (1.5 ppm) and Co-rich arsenides/sulfoarsenides and Cr-spinels than those from Salomón. Gold grains (~ 16 wt% Ag) are predominantly associated with safflorite-lollingite rimmed by cobaltite. Composition of the relicts of Cr-spinel grains evidence that the mineralization developed by replacement of peridotites that were part of an oceanic lithosphere formed in a supra-subduction fore arc environment. Textural relations provide evidence of at least three-stage depositional history: i) primary mineralization dominated by pyrrhotite in connexion with subsea-floor hydrothermal process, ii) metamorphic-hydrothermal overprint leading to several generations of pyrrhotite, pyrite and chalcopyrite, and iii) late mineralization represented by Co-Fe-Ni arsenides/sulfo-arsenides and native gold. Keywords. Gold, cobalt, platinum-group elements, massive sulphides, Havana-Matanzas Ophiolites, Cuba 1 Introduction The Cretaceous ophiolite-related rocks in Havana-Matanzas region (western Cuba) contain several mineralization types including Al- and Cr-rich chromitites, ultramafic-hosted Au-rich massive sulphides and volcanic-hosted massive sulphides (Llanes et al. 2001).

Havana-Matanzas ophiolites (HMO) crop out to the north of the Cuba island, along the so-called “northern ophiolite belt” (Iturralde-Vinent 1996, 1998) (Fig. 1). The western part of the belt, Havana region, host several ultramafic (serpentinized peridotites)-hosted Cu-Au-Co rich massive sulphide deposits (Fig. 1). The main deposits and occurrences include Salomón, Rosario, José Cándido, Elena, Caridad, Vigilantes, Majana and Majana-1 (see Abdulin et al. 1999; Llanes et al. 2001, 2013). These deposits were extensively exploited in the past (for copper since 1580), and represent the only

example of ultramafic-hosted massive sulphide deposits along the Caribbean region; nevertheless only a few detailed studies have been published (Abdulin et al. 1999; Llanes et al. 2001, 2013).

In this work we present new data on the Au and PGE geochemistry of massive sulphide deposits from HMO with special emphasis on their Au mineralogy.

Figure 1. Location of HMO within the Northern Ophiolite Belt of Cuba (green colour), and simplified geological map of the eastern Havana City showing the location of the main deposit (Salomón Mine). 2 HMO and massive sulphide deposits

The Cuban orogenic belt formed during the Cretaceous–Tertiary convergence of the Caribbean oceanic plate and

MINERAL RESOURCES IN A SUSTAINABLE WORLD • 13th SGA Biennial Meeting 2015. Proceedings, Volume 52092

the North American margin. The HMO (Fig. 1) are part of the Northern Ophiolite Belt of Cuba (Upper Jurassic− Cretaceous; Iturralde-Vinent 1998). The collision in latest Cretaceous–Tertiary times triggered the tectonic emplacement of ophiolitic units (including oceanic volcanic arc, and subduction mélange units) onto the margin of North America (García-Casco et al. 2008). Although tectonically dismembered, all the components of an ideal ophiolite sequence have been identified in the HMO. The predominant rocks are peridotites and serpentinites representative of the mantle sequence of both deep levels and mantle-crust transition zone (Iturralde-Vinent 1996; Lewis et al. 2006). The ophiolitic sequence is represented by serpentinized mantle tectonites, mafic cumulates, diabase bodies, and volcanic rocks and sediments. The most abundant ultramafic rocks are harzburgite displaying porphyro-clastic textures with strongly deformed orthopyroxene porphyroclasts, as commonly observed in ophiolitic mantle tectonites (Llanes et al. 1997; Lewis et al. 2006). Volcanic rocks, tectonically embedded in deformed serpentinites and serpentinized peridotites from the Havana-Matanzas, have been described as IAT and boninites (Fonseca et al. 1989; Kerr et al. 1999).

Ore bodies are systematically restricted to the upper part of the Moho Transition Zone (mantle-crust transition zone) made up of residual harzburgites, minor dunites, and “impregnated peridotites” with plagioclase and clinopyroxene. Sills and dykes of gabbro also occur in this transition zone (Llanes et al. 2001, 2013). Ultramafic host-rocks underwent important hydro-thermal alteration and metasomatic processes, mainly serpentinization, carbonatization, silicification, and to a lesser extent, chloritization.

Loma Majana and Salomón deposits are hosted by serpentinized ultramafic rocks, and are associated to tectonically deformed zones along NE–SW to E-W trending shear faults (Llanes et al. 2001). The massive sulphide deposits are small sized and form lenses, veins and disseminations (Fig. 2). Oxidation zone developed resulting in the formation of secondary copper minerals and goethite/hematite rocks.

Figure 2. Photograph of serpentinized peridotite-hosted massive sulphide body at Loma Majana deposit, HMO (W Cuba).

3 Au and PGE distribution

Two samples of massive sulphide ore (from Salomón and Majana), and 1 sample from oxidized ore (from Salomón) were analysed for gold and platinum group elements (PGE) at the Genalysis Laboratory Services Pty. Ltd. at Maddington, Western Australia. The samples were analysed by ICP-MS after concentration from nickel sulphide fire-assay collection.

The analysed sample of massive sulphides from Loma Majana (HAV-5) contains 1541ppb PGE and 4848 ppb Au. This sample shows a chondrite-normalized PGE pattern characterized by relatively flat segment from Os to Ru, a negative slope from Ru to Pd, and significant enrichment in Au (Fig. 3).

The analysed sample of massive sulphides from Salomón (HAV-16A) returned lower total PGE (105 ppb) and Au (209 ppb Au) contents although a similar chondrite-normalized PGE pattern than HAV-5 (massive sulphide from Loma Majana) (Fig. 3).

The analysed sample of oxidized ore (gossan) from Loma Majana (HAV-5A) contains 44 ppb PGE and 752 ppb Au. The oxidized ore shows lower total PGE and Au than the sample of massive sulphides (HAV-5). Its chondrite-normalized PGE pattern exhibits a nearly flat segment from Os to Pt, a small positive anomaly in Pd, and significant enrichment in Au (Fig. 3).

0,001

0,01

0,1

1

10

100

Os Ir Ru Rh Pt Pd Au

HAV‐5

HAV‐5 A

HAV‐16 A

Figure 3. Chondrite-normalized patterns of ultramafic-hosted massive sulphide deposits from HMO. Normalization values are from Naldrett and Duke (1982). 4 Mineralogy and ore description

Representative samples of Salomón and Loma Majana deposits were investigated on thin and polished sections and on heavy concentrates obtained using a hydro-separation technique at the Universitat de Barcelona (http://www.hslab-barcelona.com/; see Aiglsperger et al. 2015 for details).

The studied sulphide ores from Salomón and Loma Majana mainly show massive, brecciated and disseminated textures. The sulphide assemblage consists of pyrrhotite, pyrite and chalcopyrite, with minor amounts of Co-Fe arsenides and sulfoarsenides and accessory Co-pentlandite. In general, ores from Salomón and Loma Majana have similar textures and mineralogical composition, but Co-Fe-rich arsenides and sulfoarsenides minerals are more conspicuous in Loma Majana.

Textural relations provide evidence of at least three-stage depositional history: i) primary mineralization dominated by pyrrhotite, ii) metamorphic-hydrothermal overprint leading to several generations of pyrrhotite, pyrite and chalcopyrite, and iii) late mineralization represented by Co-Fe-Ni arsenides/sulfoarsenides and native gold. Pyrrhotite occurs as strongly deformed crystals, and is systematically replaced by pyrite. Chalcopyrite is intergranular to pyrrhotite and pyrite grains. The composition of chalcopyrite is relatively constant. Pentlandite occurs as inclusions within pyrrhotite. According to its Co content (from 10.9 wt. % to 21.2 wt. %), analysed pentlandite is characterized as high-Co.

Cobalt-Fe-Ni arsenides and sulfoarsenides occur along fractures and grain boundaries of pyrrhotite and pyrite. Systematically, Co-rich arsenides and sulfoarsenides ores predominate over Fe-Ni rich ones. The Co-Fe-Ni bearing arsenide minerals are replaced by Co-Fe-Ni sulfoarsenides (Fig. 4a). Arsenide minerals mainly include members of the löllingite–(clino)safflorite solid-solution series (Fe,Co)As2, while cobaltite (CoAsS) is the main sulfoarsenide mineral in all the studied samples.

Gold grains (~1 to 4 μm), with about 16 wt. % Ag, are predominantly associated with Co arsenides and sulfoarsenides (Fig. 4a). Gold is present within salflorite-lollingite rimmed by cobaltite. Moreover, gold is often observed within fractures in pyrrhotite and pyrite. The largest gold grains, from heavy concentrates obtained by hydroseparation device, consist of particles of 30 µm in diameter (maximum dimension) showing euhedral and subhedral habits (Fig. 4b, c).

All studied sulphide ores contain abundant relicts of Cr-spinel grains (up to 5 % modal), which is an evidence that the mineralization developed by replacement of ultramafics rocks. Chromian-spinel displays average values of Cr#=0.68, Al2O3=15.5 wt%, TiO2= 0.26 wt%, Fe2O3= 5.1 wt% (Fig. 5).

Sulphur isotopes have been studied in pyrrhotite from massive sulphide ores from Salomón and Loma Majana. 34S values are homogeneous, in the range of -1.7 to -0.1‰. 34S close to zero indicates that sulphur isotopic composition of pyrrhotite is within the range of magmatic values. However, sulphur isotopes values are inconclusive as to the origin of the sulphur. 5 Concluding remarks

According to the geochemistry, mineralogy and the geological relations, Loma Majana and Salomón deposits can be classified as Au- and PGE-bearing mantle peridotite-hosted massive sulphides. Deposits of this type have been described in ophiolites and in the modern mid-ocean ridges and mature back-arc basins (e.g. Shanks and Thurston 2012; Melekestseva et al. 2013 and references therein). In the modern oceans, hydrothermal systems associated with ultramafic rocks are connected to oceanic core complexes formed during attenuation of the ocean crust at magma starved ridges (Shanks and Thurston 2012). According to Cr-spinel composition in Havana-Matanzas ore deposits, associated serpentinized peridotites are a fragment of

oceanic lithosphere formed in a fore arc environment, and represent an ophiolitic mantle sequence from a supra-subduction zone (Fig. 5). A supra-subduction setting has been also proposed for Cu–(Ni–Co–Au)-bearing massive sulphide deposits associated with mafic–ultramafic rocks of the Main Urals Fault, South Urals (Melekestseva et al. 2013 and references therein).

Figure 4. SEM-BSE images of gold grains from ultramafic-hosted massive sulphide deposits located within the mantle section of Havana ophiolites.

Volcanogenic Massive Sulfide ore deposits - in honour of James Franklin 2093

the North American margin. The HMO (Fig. 1) are part of the Northern Ophiolite Belt of Cuba (Upper Jurassic− Cretaceous; Iturralde-Vinent 1998). The collision in latest Cretaceous–Tertiary times triggered the tectonic emplacement of ophiolitic units (including oceanic volcanic arc, and subduction mélange units) onto the margin of North America (García-Casco et al. 2008). Although tectonically dismembered, all the components of an ideal ophiolite sequence have been identified in the HMO. The predominant rocks are peridotites and serpentinites representative of the mantle sequence of both deep levels and mantle-crust transition zone (Iturralde-Vinent 1996; Lewis et al. 2006). The ophiolitic sequence is represented by serpentinized mantle tectonites, mafic cumulates, diabase bodies, and volcanic rocks and sediments. The most abundant ultramafic rocks are harzburgite displaying porphyro-clastic textures with strongly deformed orthopyroxene porphyroclasts, as commonly observed in ophiolitic mantle tectonites (Llanes et al. 1997; Lewis et al. 2006). Volcanic rocks, tectonically embedded in deformed serpentinites and serpentinized peridotites from the Havana-Matanzas, have been described as IAT and boninites (Fonseca et al. 1989; Kerr et al. 1999).

Ore bodies are systematically restricted to the upper part of the Moho Transition Zone (mantle-crust transition zone) made up of residual harzburgites, minor dunites, and “impregnated peridotites” with plagioclase and clinopyroxene. Sills and dykes of gabbro also occur in this transition zone (Llanes et al. 2001, 2013). Ultramafic host-rocks underwent important hydro-thermal alteration and metasomatic processes, mainly serpentinization, carbonatization, silicification, and to a lesser extent, chloritization.

Loma Majana and Salomón deposits are hosted by serpentinized ultramafic rocks, and are associated to tectonically deformed zones along NE–SW to E-W trending shear faults (Llanes et al. 2001). The massive sulphide deposits are small sized and form lenses, veins and disseminations (Fig. 2). Oxidation zone developed resulting in the formation of secondary copper minerals and goethite/hematite rocks.

Figure 2. Photograph of serpentinized peridotite-hosted massive sulphide body at Loma Majana deposit, HMO (W Cuba).

3 Au and PGE distribution

Two samples of massive sulphide ore (from Salomón and Majana), and 1 sample from oxidized ore (from Salomón) were analysed for gold and platinum group elements (PGE) at the Genalysis Laboratory Services Pty. Ltd. at Maddington, Western Australia. The samples were analysed by ICP-MS after concentration from nickel sulphide fire-assay collection.

The analysed sample of massive sulphides from Loma Majana (HAV-5) contains 1541ppb PGE and 4848 ppb Au. This sample shows a chondrite-normalized PGE pattern characterized by relatively flat segment from Os to Ru, a negative slope from Ru to Pd, and significant enrichment in Au (Fig. 3).

The analysed sample of massive sulphides from Salomón (HAV-16A) returned lower total PGE (105 ppb) and Au (209 ppb Au) contents although a similar chondrite-normalized PGE pattern than HAV-5 (massive sulphide from Loma Majana) (Fig. 3).

The analysed sample of oxidized ore (gossan) from Loma Majana (HAV-5A) contains 44 ppb PGE and 752 ppb Au. The oxidized ore shows lower total PGE and Au than the sample of massive sulphides (HAV-5). Its chondrite-normalized PGE pattern exhibits a nearly flat segment from Os to Pt, a small positive anomaly in Pd, and significant enrichment in Au (Fig. 3).

0,001

0,01

0,1

1

10

100

Os Ir Ru Rh Pt Pd Au

HAV‐5

HAV‐5 A

HAV‐16 A

Figure 3. Chondrite-normalized patterns of ultramafic-hosted massive sulphide deposits from HMO. Normalization values are from Naldrett and Duke (1982). 4 Mineralogy and ore description

Representative samples of Salomón and Loma Majana deposits were investigated on thin and polished sections and on heavy concentrates obtained using a hydro-separation technique at the Universitat de Barcelona (http://www.hslab-barcelona.com/; see Aiglsperger et al. 2015 for details).

The studied sulphide ores from Salomón and Loma Majana mainly show massive, brecciated and disseminated textures. The sulphide assemblage consists of pyrrhotite, pyrite and chalcopyrite, with minor amounts of Co-Fe arsenides and sulfoarsenides and accessory Co-pentlandite. In general, ores from Salomón and Loma Majana have similar textures and mineralogical composition, but Co-Fe-rich arsenides and sulfoarsenides minerals are more conspicuous in Loma Majana.

Textural relations provide evidence of at least three-stage depositional history: i) primary mineralization dominated by pyrrhotite, ii) metamorphic-hydrothermal overprint leading to several generations of pyrrhotite, pyrite and chalcopyrite, and iii) late mineralization represented by Co-Fe-Ni arsenides/sulfoarsenides and native gold. Pyrrhotite occurs as strongly deformed crystals, and is systematically replaced by pyrite. Chalcopyrite is intergranular to pyrrhotite and pyrite grains. The composition of chalcopyrite is relatively constant. Pentlandite occurs as inclusions within pyrrhotite. According to its Co content (from 10.9 wt. % to 21.2 wt. %), analysed pentlandite is characterized as high-Co.

Cobalt-Fe-Ni arsenides and sulfoarsenides occur along fractures and grain boundaries of pyrrhotite and pyrite. Systematically, Co-rich arsenides and sulfoarsenides ores predominate over Fe-Ni rich ones. The Co-Fe-Ni bearing arsenide minerals are replaced by Co-Fe-Ni sulfoarsenides (Fig. 4a). Arsenide minerals mainly include members of the löllingite–(clino)safflorite solid-solution series (Fe,Co)As2, while cobaltite (CoAsS) is the main sulfoarsenide mineral in all the studied samples.

Gold grains (~1 to 4 μm), with about 16 wt. % Ag, are predominantly associated with Co arsenides and sulfoarsenides (Fig. 4a). Gold is present within salflorite-lollingite rimmed by cobaltite. Moreover, gold is often observed within fractures in pyrrhotite and pyrite. The largest gold grains, from heavy concentrates obtained by hydroseparation device, consist of particles of 30 µm in diameter (maximum dimension) showing euhedral and subhedral habits (Fig. 4b, c).

All studied sulphide ores contain abundant relicts of Cr-spinel grains (up to 5 % modal), which is an evidence that the mineralization developed by replacement of ultramafics rocks. Chromian-spinel displays average values of Cr#=0.68, Al2O3=15.5 wt%, TiO2= 0.26 wt%, Fe2O3= 5.1 wt% (Fig. 5).

Sulphur isotopes have been studied in pyrrhotite from massive sulphide ores from Salomón and Loma Majana. 34S values are homogeneous, in the range of -1.7 to -0.1‰. 34S close to zero indicates that sulphur isotopic composition of pyrrhotite is within the range of magmatic values. However, sulphur isotopes values are inconclusive as to the origin of the sulphur. 5 Concluding remarks

According to the geochemistry, mineralogy and the geological relations, Loma Majana and Salomón deposits can be classified as Au- and PGE-bearing mantle peridotite-hosted massive sulphides. Deposits of this type have been described in ophiolites and in the modern mid-ocean ridges and mature back-arc basins (e.g. Shanks and Thurston 2012; Melekestseva et al. 2013 and references therein). In the modern oceans, hydrothermal systems associated with ultramafic rocks are connected to oceanic core complexes formed during attenuation of the ocean crust at magma starved ridges (Shanks and Thurston 2012). According to Cr-spinel composition in Havana-Matanzas ore deposits, associated serpentinized peridotites are a fragment of

oceanic lithosphere formed in a fore arc environment, and represent an ophiolitic mantle sequence from a supra-subduction zone (Fig. 5). A supra-subduction setting has been also proposed for Cu–(Ni–Co–Au)-bearing massive sulphide deposits associated with mafic–ultramafic rocks of the Main Urals Fault, South Urals (Melekestseva et al. 2013 and references therein).

Figure 4. SEM-BSE images of gold grains from ultramafic-hosted massive sulphide deposits located within the mantle section of Havana ophiolites.

MINERAL RESOURCES IN A SUSTAINABLE WORLD • 13th SGA Biennial Meeting 2015. Proceedings, Volume 52094

Figure 5. Primary compositions of Cr-spinel in ultramafic-hosted massive sulphide deposits from HMO in terms of Al2O3 vs Cr2O3. The MORB peridotite and suprasubduction zone (SSZ) peridotite fields are from Kamenetsky et al. (2001).

The abundance of Cr-spinel grains included in massive pyrrhotite indicates that primary sulphide mineralization was developed by replacement of serpentinized peridotite. The pyrrhotite rich mineralization of Havana-Matanzas deposits is characteristic of many ancient and modern ultramafic-hosted massive sulphide deposits. Low ƒS2 and ƒO2 during ultramafic rock/water reaction favour formation of pyrrhotite (Hannington et al. 1995; Melekestseva et al. 2013). The presence of triple junctions at 120º in pyrrhotite suggests deformation and metamorphic-hydrothermal overprint leading to several generations of pyrrhotite, pyrite and chalcopyrite.

On the other hand, textural relations provide evidence that Co-Fe-Ni arsenides/sulfoarsenides mineralization and native gold is late.

Although the studied mineralizations from Salomón and Loma Majana deposits have similar textures and mineralogical composition, Co-rich arsenides/sulfoarsenides and Cr-spinels are more abundant in Loma Majana. Gold abundance correlates with the presence of Co-Fe-Ni arsenides/sulfoarsenides.

Finally, the absence of discrete PGM in the studied ores of the Havana-Matanza deposits in spite of high total PGE contents in Majana massive ores (up to 1.5 ppm) could be related to high capacity of arsenide and sulpharsenide minerals to include PGE in their lattice (e.g. Gervilla et al. 2004; Hanley 2007). Further work, currently under way, is necessary to better understand the mineralogical expression of PGE in the studied deposits. Acknowledgements This research has been financially supported by the Spanish project CGL2012-36263.

References Aiglsperger T, Proenza JA, Zaccarini F, Lewis JF, Garuti G,

Labrador M, Longo F (2015) Platinum group minerals (PGM) in the Falcondo Ni-laterite deposit, Loma Caribe peridotite (Dominican Republic). Miner Deposita 50:105-123

García-Casco A, Iturralde-Vinent MA, Pindell J (2008) Latest Cretaceous collision/ accretion between the Caribbean Plate and Caribeana: Origin of metamorphic terranes in the Greater Antilles. Int Geol Rev 50:781-809

Gervilla F, Cabri LJ, Kojonen K, Oberthür T, Weiser TW, Johanson B, Sie SH, Campbell JL, Teesdale WJ, Gilles Laflamme JH (2004) Platinum-group element distribution in some ore deposits: results of EMPA and micro-PIXE analyses. Microchim Acta 147:167-173

Hanley JJ (2007) The role of arsenic-rich melts and mineral phases in the development of high-grade Pt-Pd mineralization within komatiite-associated magmatic Ni-Cu sulfide horizons at Dundonald Beach South, Abitibi subprovince, Ontario, Canada. Econ Geol 102:305-317

Hannington MD, Jonasson IR, Herzig PM, Petersen S (1995) Physical and chemical processes of seafloor mineralization at mid-ocean ridges. In: Humphris SE, Zierenberg RA, Mullineaux LS, Thomson RE (eds) Seafloor Hydrothermal Systems: Physical, Chemical, Biological, and Geological Interactions. Geophysical Monograph, 91. American Geophysical Union, pp 115-157

Iturralde-Vinent MA (1996) Geología de las ofiolitas de Cuba. In: Iturralde-Vinent M (ed) Ofiolitas y arcos volcánicos de Cuba: Miami, USA, IGCP Project 364, pp 83–120

Iturralde-Vinent MA (1998) Sinopsis de la constitución geológica de Cuba. Acta Geologica Hispanica 33:9-56

Kamenetsky VS, Crawford AJ, Meffre S (2001) Factors controlling chemistry of magmatic spinel: an empirical study of associated olivine, Cr-spinel and melt inclusions from primitive rocks. J Petrol 42:655-671

Kerr AC, Iturralde-Vinent M, Saunders AD, Babbs TL, Tarney J (1999) A new plate tectonic model of the Caribbean: Implications from a geochemical reconnaissance of Cuban Mesozoic volcanic rocks. Geol Soc Am Bull 111:1581-1599

Lewis JF, Draper G, Proenza JA, Espaillat J, Jimenez J (2006) Ophiolite-related ultramafic rocks (Serpentinites) in the Caribbean region: A review of their occurrence, composition, origin, emplacement and nickel laterite soils. Geol Acta 4:237-263

Llanes A (2013) Field trip guide to Havana-Matanzas ophiolite and associated mineralization. Field Workshop, Havana-Matanzas, Cuba April 6-7, 2013, 16pp

Llanes A, Santa Cruz-Pacheco M, García I, Morales A, Palacio B, Fonseca E (2001) Petrología y mineralización de la asociación ofiolítica de Habana-Matanzas (Cuba occidental). Memorias GEOMIN 2001, La Habana, 19-23 de marzo. pp92.101, ISBN 959-7117-10-x

Melekestseva IY, Zaykov VV, Nimis P, Tret'yakov GA, Tessalina SG (2013) Cu–(Ni–Co–Au)-bearing massive sulfide deposits associated with mafic–ultramafic rocks of the Main Urals Fault, South Urals: Geological structures, ore textural and mineralogical features, comparison with modern analogs. Ore Geol Rev 52:18-36

Shanks III WCP, Thurston R (eds) (2012) Volcanogenic massive sulfide occurrence model: U.S. Geological Survey Scientific Investigations Report 2010-5070-C, 345pp

Massive Sulfides on Land and on the Seafloor Steven D Scott Department of Earth Sciences, University of Toronto, Canada Marine Mining Consultants, Toronto, Canada Abstract. Volcanic-hosted massive sulfide deposits (VMS) of Cu, Zn and Pb together with silver and gold, consisting of a massive lens underlain by a stockwork, are found within submarine volcanic rocks of all types. Their age is controlled by the evolution of supercontinents with abundant deposits forming during times of stability and few or none during continental breakup. The modern equivalent of ancient VMS are the seafloor massive sulfides (SMS), some large, that are forming by high temperature “black smoker” hydrothermalism. Ocean mining of large SMS is imminent. The VMS and SMS were/are formed in the same manner but the source of their metals is debated. In the conventional model, deeply penetrating seawater heated by sub seafloor magma extracts metals and other elements from the hot volcanic rocks and is subsequently discharged onto the seafloor. However, this produces rather dilute solutions. To make a very large VMS or SMS deposit requires an excessive amount of discharging fluid and the extraction of metals from a very large volume of rock. In an alternative model, magmatic fluids that are known from melt inclusions to be very metal-rich mix with the modified seawater. The enriched fluid can produce giant deposits without the shortcomings of the conventional model. Keywords. VMS, SMS, ages, metal sources, magmatic fluids, melt inclusions, ocean mining The descriptive (Figure 1) and genetic models for volcanic-hosted (or volcanogenic) massive sulfide (VMS) deposits are decades old and well tested (e.g., Franklin et al. 2005; Hannington 2014). The deposits typically contain a compositionally zoned massive ore lens that formed on a predominantly volcanic seafloor from discharging high-temperature fluids and are underlain by disseminated to semi-massive mineralization within highly altered rocks. Host volcanic rocks can range from ultramafic to rhyolite in composition and typically are accompanied by volcaniclastic sediments. VMS deposits are attractive exploration targets mainly because of their compact nature and their multi-element composition. VMS ores are significant producers of copper, zinc, lead, silver and gold together, in some cases, with significant by-production of cadmium, bismuth, tin, mercury, selenium and tellurium.

The age distribution of VMS is not uniform through time. There are no known VMS from about 1.9 to 2.6 Ga and only a few at 1.7 – 1.3 Ga and 0.9 – 0.6 Ga (Figure 2). These are times of breakup of supercontinents when subduction, a necessary tectonic process to form VMS, was greatly diminished to absent. VMS form when supercontinents are stable and subduction is occurring under their margins or just offshore.

VMS deposits are formed in extensional terrains that later through tectonic processes may become compress-ional.

STOCKWORK ZONE

MASSIVE SULFIDE LENS

Gradational footwallcontact (volcanic breccia)

Bedded or layered structure(chemically heterogenous)

Massive rubbly or brecciated mound(strong chemical zonation pattern)

Hydrothermalalteration pipeor can be a broad zone

Cpy ± Py ± Po

Py ± Sp ± Gn

Sp ± P ± Gn y ± Ba

Sharp hangingwall contact

"Exhalite" or"Tuffite" horizonSiO ± Py ± Hem2

Cpy ± Py ± Po sulfide mineralization chloritic hydrothermal alteration

Py ± Sp ± Gn sulfide mineralization sericitic-chloritic hydrothermal alteration

AncientSeafloor

Figure 1. Descriptive model in vertical section for a volcanic-hosted massive sulfide deposit modified by Noel White and the author after Lydon (1984).

The preferred although not exclusive environment, where such can be determined, is an island arc and specifically the back-arc. Seemingly especially important are VMS deposits in arcs that were built on continental instead of oceanic crust. Examples of the former include Bathurst, New Brunswick; the Iberian Pyrite Belt of Spain and Portugal; and the Kuroko deposits of Japan. The giant VMS deposits of the Urals are an apparent exception having been formed in oceanic arcs although there is lead isotopic evidence for the involvement of at least some continental material.

Seafloor massive sulfides (SMS) are modern analogues of the ancient VMS. They offer the opportunity to observe first-hand how the seafloor hydrothermal system works and to sample fluids as well as the associated rocks that are undergoing alteration. The main ore types and textures in Figure 1 of a VMS can also be identified in SMS. Chimney fragments and fossilized vent animals have been found in undeformed VMS deposits as old as 430 Ma in the Urals (Little et al. 1999) and elsewhere in younger deposits.

An age-old discussion on VMS genesis is whether the ore fluids and their contained metals were heated and compositionally modified seawater that extracted metals from hot rocks in the vicinity of a magma beneath the seafloor (leaching model) or were entirely magmatic in origin (magmatic model). The former produces rather dilute solutions whereas the latter can produce extremely metal-rich solutions as observed in melt inclusions in phenocrysts of volcanic rocks associated with VMS and SMS (Yang and Scott 2006). Most likely both processes occurred with the latter dominating where giant (>50 million tonnes) deposits were formed.