Semi-massive to massive sulfides with abundant late native sulfur were drilled in a shallowwater hydrothermal system in an island arc volcanic setting at the Palinuro volcanic complex in the Tyrrhenian Sea, Italy. Overall, 12.7 m of sulfide mineralisation were drilled in a sediment-filled

depression at a water depth of 630 - 650 m using the

lander-type Rockdrill I drill rig of the British Geological

Survey. Polymetallic (Zn, Pb, Sb, As, Ag) sulfides

overlie massive pyrite. The massive sulfide mineralisation contains a number of atypical minerals, including enargite-famatinite, tennantite-tetrahedrite, stibnite, bismuthinite, and Pb-,Sb-, and Ag-sulfosalts, that do not commonly occur in mid-ocean ridge massive sulfides. Analogous to subaerial epithermal deposits, the occurrence of these minerals and the presence of abundant native sulfur suggest an intermediate to high sulfidation and/or high oxididation state of the hydrothermal fluids in contrast to the near-neutral and reducing fluids from which base metal-rich massive sulfides along mid-ocean ridges typically form. Oxidised conditions during sulfide deposition are likely related to the presence of magmatic volatiles in the mineralising fluids that were derived from a degassing magma chamber below the Palinuro volcanic complex

Augustin, Nico

Gemmell, J. B.

Gibson, H.

Hannington, Mark D.

Lackschewitz, Klas

Monecke, T.

Perrin, K.

Petersen, Sven

Sharpe, R.

Simpson, K.

English

OceanRep

High to Intermediate Sulfidation, Shallow Marine, Sulfide Mineralisation in the South-eastern Tyrrhenian Sea, Italy  J. Bruce Gemmell CODES, ARC Centre of Excellence in Ore Deposits, University of Tasmania, Private Bag 79, Hobart, 7001, Australia  Sven Petersen Leibniz-Institute of Marine Sciences, IFM-GEOMAR, Wischhofstraße 1-3, Kiel, 24148, Germany  Thomas Monecke Dept of Geology and Geological Engineering, Colorado School of Mines, 1516 Illinois Street Golden, CO 80401, USA  Mark D. Hannington Department of Earth Sciences, University of Ottawa, 140 Louis Pasteur, Ottawa, K1N 6N5, Canada  Klas Lackschewitz, Nico Augustin Leibniz-Institute of Marine Sciences, IFM-GEOMAR, Wischhofstraße 1-3, Kiel, 24148, Germany  Harold Gibson Dept of Earth Sciences, Laurentian University, 935 Ramsey Lake Road, Sudbury, P3E 2C6, Canada  Katie Perrin, Robina Sharpe Neptune Minerals, 56 Alfred Street, Milsons Point, NSW 2061, Australia  Kirstie Simpson Mineral Deposit Research Unit, University of British Columbia, 6339 Stores Road, Vancouver, BC, V6T 1Z4, Canada   Abstract: Semi-massive to massive sulfides with abundant late native sulfur were drilled in a shallow-water hydrothermal system in an island arc volcanic setting at the Palinuro volcanic complex in the Tyrrhenian Sea, Italy. Overall, 12.7 m of sulfide mineralisation were drilled in a sediment-filled depression at a water depth of 630 - 650 m using the lander-type Rockdrill I drill rig of the British Geological Survey. Polymetallic (Zn, Pb, Sb, As, Ag) sulfides overlie massive pyrite. The massive sulfide mineralisation contains a number of atypical minerals, including enargite-famatinite, tennantite-tetrahedrite, stibnite, bismuthinite, and Pb-,Sb-, and Ag-sulfosalts, that do not commonly occur in mid-ocean ridge massive sulfides. Analogous to subaerial epithermal deposits, the occurrence of these minerals and the presence of abundant native sulfur suggest an intermediate to high sulfidation and/or high oxididation state of the hydrothermal fluids in contrast to the near-neutral and reducing fluids from which base metal-rich massive sulfides along mid-ocean ridges typically form. Oxidised conditions during sulfide deposition are likely related to the presence of magmatic volatiles in the mineralising fluids that were derived from a degassing magma chamber below the Palinuro volcanic complex.  Keywords: Seafloor sulfides, Tyrrhenian Sea, high-sulfidation hydrothermal systems, Palinuro   1   Introduction  Seafloor hydrothermal systems in island arcs have seen increased exploration efforts by the scientific community in the past years due to their resource potential. These hydrothermal systems are different to those commonly studied at mid-ocean ridges (Hannington et al., 2005) because of magmatic contributions of gases and possibly metals to the convecting fluids and their shallow water depths (Stoffers et al., 2006; de Ronde et al., 2007). The southeastern Tyrrhenian Sea in the Mediterranean is host to several shallow-water (<700 m) sites (Palinuro, Panarea, Figure 1) of hydrothermal activity that are associated with island arc volcanism and may be a modern analogue for deposits that form the transition from deep marine base metal volcanic-rock-hosted massive sulfide deposits to subaerial magmatic-epithermal precious metal deposits. In August 2007, we deployed the British Geological Survey (BGS) Rockdrill from the German research vessel Meteor (cruise M73/2). The drill rig was lowered to the seafloor on a power-and-lift umbilical and takes up to 5 m of core using either a rotary diamond bit coring system for hard rock or a vibro-coring tool kit for sediments. Our drilling campaign has documented the nature of unique, island arc polymetallic massive sulfide mineralisation in three dimensions.  2   Tectonic Setting  The Tyrrhenian Sea is a semi-closed basin in the western Mediterranean that is bounded by the Italian mainland to the east, Sicily to the south, and Corsica and Sardinia to the west. The SE portion of the Tyrrhenian Sea comprises a small, oceanic back-arc basin, referred to as the Marsili abyssal plain, and the Aeolian island arc (Figure 1) that formed as a consequence of roll-back of the NW-dipping Ionian subduction zone and migration of arc volcanism from 438 "Smart Science for Exploration and Mining"  P. J. Williams et al. (editors)the island of Sardinia towards the E-SE (Savelli, 2001). Volcanism in the Aeolian volcanic arc was initiated about 1 Ma ago and changed from tholeiitic through calc-alkaline to shoshonitic over time (Beccaluva et al., 1985; Savelli, 2001; Calanchi et al., 2002). Present-day Aeolian volcanism is likely related to post-collisional extensional processes in an arc collision zone rather than to subduction processes (de Astis et al., 2003).  Figure 1 Location of the Palinuro volcanic complex in Aeolian arc of the Tyrrhenian Sea, Italy. Diagram from Beccaluva et al (1985).   3   Geology of the Palinuro Seamount   Palinuro is a complex, 50 km-long volcanic feature that consists of five coalesced volcanic edifices lying along an E-W trending fault system. Palinuro can be divided into two sectors, a western part (min. water depth of 570 m) and an eastern part (min. water depth of 70 m). The two sectors appear to be offset by an NE-SW trending fault system. High-alumina basalt, low-silica andesite, and high-K andesite, (all less than 0.35 Ma old), have been recovered from the Palinuro volcanic complex (Colantoni et al., 1981).  4   Mineralisation and Metal Content   Hydrothermal sulfides at the Palinuro volcanic complex were first described from two localities 5 km apart at a water depth of 400 to 600 m on the western sector by Minniti and Bonavia (1984) and Puchelt and Laschek, (1987). At that time the areal extent of the polymetallic mineralisation at Palinuro was poorly constrained and no information on the third dimension of the mineralisation was available. The mineralisation previously recovered contained, in addition to base metal sulfides, unusual minerals such as tennantite-tetrahedrite, famatinite, enargite, stibnite, native silver, and rare Bi-, Se-, Pb-, and Ag-sulfosalts (Dekov and Savelli, 2004). During our research cruise, 11 holes were successfully drilled into a sediment-covered, basalt-hosted, sulfide/sulfate occurrence located in a small topographic depression (ca. 610 to 650 m water depth) on the summit of a volcanic edifice in the western sector of the volcanic complex. Shallow drilling was conducted at a closely spaced grid covering 70 by 50 m in an area of active fluid venting as indicated by the discovery of small tubeworm clusters at the seafloor in 2006 and by TV-guided grab-sampling of warm (60°C) sediment in 2007. In total, 12.7 m of mineralised and brecciated rocks were recovered, with up to 4.9 m of continuous mineralised core in a single drill hole. Drilling proved the occurrence of semi-massive to massive sulfide mineralisation below a centimeter- to several meter-thick cover of unconsolidated sediments and a locally occurring polymictic breccia containing pumice clasts. Footwall volcanic rocks or sediments were not recovered during drilling; all drill holes ended in sulfide mineralisation and the vertical extent of the mineralised zone remains unknown. From this drilling campaign, a vertical distribution of sulfide and sulfate mineral facies can be determined (Figure 2). The uppermost portion (<1 m depth) is an exhalite and/or low temperature altered sediments comprising banded amorphous silica, pyrite ± barite, Fe-Mn oxides and oxyhydroxides, and rare orpiment. The next facies (1-2.5 m depth) consists of barite breccias with minor amounts of clay, pyrite, marcasite, sphalerite, galena, tennantite-tetrahedrite, famatinite, chalcopyrite, covellite, stibnite, and Pb-, Sb-, and Ag-sulfosalts. From 2.5 to 4 m depth the mineralisation comprises semi-massive pyrite, barite, and traces of clay. The deepest core recovered (>4 m depth) contains massive pyrite with minor barite. Late veins of pyrite, marcasite and native sulfur crosscut all other mineralisation styles.     Figure 2. Schematic cross section of the Palinuro hydro-thermal system. The system comprises an upper exhalite unit underlain by barite-cemented breccias and a polymetallic sulfide section. The lower part consists of massive pyrite with minor barite. Late pyrite/marcasite-native sulfur veins crosscut all mineralisation stages.  Geochemical analyses of the drill core (Table 1) indicate that the mineralisation at Palinuro is base- and precious-metals-rich, with one 4.74 m intersection containing 1.44 wt% Cu, 0.39 wt% Pb, 0.72 wt% Zn, 50 ppm Ag, and 0.2 ppm Au. Metal enrichment at the top of the mineralisation is evident in some cores with Proceedings of the Tenth Biennial SGA Meeting, Townsville, 2009 439polymetallic (Zn, Pb, Ag) sulfides overlying more massive pyrite. The polymetallic sulfides are enriched in trace metals that are more commonly associated with epithermal deposits forming in volcanically active areas on land (some drill core intervals contain up to 925 ppm Ag, 3.4 ppm Au, 1.5 wt % As, 1190 ppm Bi, 2032 ppm Hg, and 2.2 wt.% Sb).  5   Discussion and Conclusion  In comparison to ancient volcanic-hosted massive sulfide deposits that typically contain low amounts of Au and Ag (average Au content ~ 1-3 ppm; Hannington et al., 1999), modern seafloor systems with anomalous Au concentrations typically occur in boiling hydrothermal systems that are located in comparably shallow water (<1500 m; Hannington et al., 1999; 2005). Elevated concentrations of Au, As, Sb, and Hg have also been reported from some modern seafloor hydrothermal systems in island arc settings and young back-arc rifts (Hannington et al., 2005). In many respects, deposition of metals in the shallow water environment can be compared to the formation of epithermal deposits on land suggesting that there is a continuum from submarine base metal massive sulfides to subaerial epithermal gold deposits (Hannington et al., 1999). The massive sulfide mineralisation at Palinuro contains a number of minerals that are not commonly encountered in base metal massive sulfide deposits, including enargite, famatinite, and tennantite-tetrahedrite. Similar to epithermal deposits forming on land, the occurrence of these minerals and the abundance of native sulfur at Palinuro suggest an intermediate to high sulfidation and/or high oxidation state of the hydrothermal fluids rather than near-neutral and reduced, typical of those forming base metal-rich massive sulfide deposits (Hannington et al., 1999). In conclusion, the oxidised conditions during sulfide deposition at Palinuro are likely related to the presence of magmatic volatiles that were derived from a degassing magma chamber.  Acknowledgements  We thank the crew of RV Meteor cruise M73/2 for their technical support. We are indebted to D. Baxter, N. Campbell, E. Gillespie, D. Smith, H. Stewart, and D. Wallis for the professional handling of the BGS  Rockdrill I. The research was supported by the German Research Foundation, Neptune Minerals, ARC Centre of Excellence in Ore Deposits (CODES) at the University of Tasmania and the Leibniz-Institute of Marine Sciences IFM-GEOMAR, Kiel, Germany.  References  Beccaluva L, Gabbianelli G, Lucchini F, Rossi PL, and Savelli C (1985) Petrology and K/Ar ages of volcanics dredged from the Eolian seamounts: Implications for geodynamic evolution of the southern Tyrrhenian basin: Earth and Planetary Science Letters 74: 187-208 Calanchi N, Peccerillo A, Tranne CA, Lucchini F, Rossi PL, Kempton P, Barbieri M, and Wu TW (2002) Petrology and geochemistry of volcanic rocks from the island of Panarea: Implications for mantle evolution beneath the Aeolian island arc (southern Tyrrhenian sea): Journal of Volcanology and Geothermal Research 115: 367-395 Colantoni P, Lucchini F, Rossi PL, Sartori R, and Savelli C (1981) The Palinuro volcano and magmatism of the southeastern Tyrrhenian Sea (Mediterranean): Marine Geology 39: M1-M12 de Astis G, Ventura G, and Vilardo G (2003) Geodynamic significance of the Aeolian volcanism (Southern Tyrrhenian Sea, Italy) in light of structural, seismological, and geochemical data: Tectonics 22: 17 Dekov VM, and Savelli C (2004) Hydrothermal activity in the SE Tyrrhenian Sea: An overview of 30 years of research: Marine Geology 204: 161-185 de Ronde CEJ, Baker ET, Massoth GJ, Lupton JE, Wright DJ, Sparks RSJ, Bannister SC, Reyners ME, Walker SL, Greene RR, Ishibashi J, Faure K, Resing JA, and Lebon GT (2007) Submarine hydrothermal activity along the mid-Kermadec Arc, New Zealand: Large-scale effects on venting: Geochemistry Geophysics Geosystems 8: citation Q07007 Hannington MD, Poulsen KH, Thompson JFH, and Sillitoe RH (1999) Volcanogenic gold in the massive sulfide environment: In, Barrie CT, and Hannington MD, eds, Volcanic-associated Massive Sulfide Deposits: Processes and Examples in Modern and Ancient Settings. Reviews in Economic Geology 8: 325-356 Hannington MD, de Ronde CEJ, and Petersen S (2005) Sea-floor tectonics and submarine hydrothermal systems: In, Hedenquist JW, Thompson JFH, Goldfarb RJ, and Richards JP, eds, Economic Geology 100th Anniversary Volume: 111-141 Minniti M, and Bonavia FF (1984) Copper-ore grade hydrothermal mineralization discovered in a seamount in the Tyrrhenian Sea (Mediterranean): Is the mineralization related to porphyry-coppers or to base metal lodes?: Marine Geology 59: 271-282 Puchelt H, and Laschek D (1987) Massive sulphide and oxide ores in the Tyrrhenian Sea from Sonne cruise 41: Terra Cognita. 7: 188 Savelli C, 2001, Two-stage progression of volcanism (8-0 Ma) in the central Mediterranean (southern Italy): Journal of Geodynamics 31: 393-410 Stoffers P, Worthington TJ, Schwarz-Schampera U, Hannington MD, Massoth GJ, Hekinian R, Schmidt M, Lundsten LJ, Evans LJ, Vaiomounga R, and Kerby T (2006) Submarine volcanoes and high-temperature hydrothermal venting on the Tonga arc, southwest Pacific: Geology 34: 453-456  Table 1.  Weighted averages for selected massive sulfide/sulfate cores from the Palinuro volcanic complex  Hole from to Intercept N Cu Zn Pb As Sb Au Ag Bi Hg  (cm) (cm) (cm)  (%) (%) (%) (%) (%) (ppm) (ppm) (ppm) (ppm)  M73/2 851RD 0 134 134 (5) 1.85 2.29 1.84 0.44 0.82 0.23 71 19 2032  M73/2 852RD 38 96 58 (1) 1.76 0.76 1.40 0.86 0.73 0.38 189 4 499  M73/2 853RD 0 34 34 (1) 5.58 1.67 4.01 1.14 2.23 1.62 925 8 1200  M73/2 857RD 2 47 45 (3) 3.75 6.83 5.35 0.46 0.96 0.73 353 1190 1284  M73/2 865RD 10 484 474 (14) 1.45 0.73 0.39 0.30 0.39 0.21 50 34 120  M73/2 931RD 0 45 45 (3) 0.67 6.50 2.68 0.41 0.22 0.32 61 11 317  M73/2 932RD 18 291 273 (6) 1.74 3.44 2.97 0.58 0.52 0.14 160 8 256  (N = number of subsamples analysed) 440 "Smart Science for Exploration and Mining"  P. J. Williams et al. (editors)

Drilling of shallow marine sulfide-sulfate mineralisation in south-eastern Tyrrhenian Sea, Italy; Seafloor sulfides, Tyrrhenian Sea, highsulfidation; hydrothermal systems, Palinuro

Drilling of shallow marine sulfide-sulfate mineralisation in south-eastern Tyrrhenian Sea, Italy; Seafloor sulfides, Tyrrhenian Sea, highsulfidation; hydrothermal systems, Palinuro

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