Copper-Rich Sulfide Deposit Near 23°N, Mid-Atlantic Ridge: Chemical Composition, Mineral Chemistry, and Sulfur Isotopes

Abstract

In Snake Pit massive sulfide fragments and friable, unconsolidated material recovered during ODP Leg 106, isocubanite and pyrite are generally the predominant phases, followed by marcasite, chalcopyrite, sphalerite, and pyrrhotite. Detailed analyses of paragenetic relations of minerals indicate that isocubanite first precipitated together with pyrrhotite. With decreasing temperature, chalcopyrite and sphalerite precipitated, and at the latest stage colloform sphalerite-pyrite (or colloform marcasite) formed. Isocubanite usually has exsolution lamellae of chalcopyrite and less commonly of pyrrhotite.The average bulk chemical composition of the friable, unconsolidated material indicates that it is rich in copper, reflecting the dominance of isocubanite in the specimens, and is characterized by high Co, low Pb, and Ag contents. Sulfur isotope ratios are very uniform, ranging in S 34 S from +1.2 to +2.8%c. The obtained values are apparently low, compared to those for the eastern Pacific sulfide samples, reflecting a smaller contribution of seawater sulfate in the Snake Pit sulfide deposit.

Subsurface processes at the lucky strike hydrothermal field, Mid-Atlantic ridge: evidence from sulfur, selenium, and iron isotopes

“…Before this study, isotopic data for sulfur from MAR hydrothermal fields were reported from two drilled mounds at TAG (Chiba et al, 1998;Gemmell and Sharpe, 1998;Knott et al, 1998) and Snake Pit (Kase et al, 1990) and one active hydrothermal field at Broken Spur (Duckworth et al, 1995). Previous explanations of the low ␦ 34 S of pyrite and/or marcasite were based on: (1) late-stage pyrite precipitation in the cores of chimneys at temperatures below 200°C with a low rate of sulfate reduction, or (2) lower fluid/rock interaction in the reaction zone, as well as more focused discharge in MAR hydrothermal systems which may produce low ␦ 34 S in sulfide deposits, close to magmatic values.…”

“…Low ␦ 34 S values (around 0‰) have been reported from Snake Pit (Kase et al, 1990) and Broken Spur (Duckworth et al, 1995) on the Mid Atlantic Ridge and have been related to a smaller contribution of seawater sulfate to the deposit. At Lucky Strike, low ␦ 34 S values are observed only for low-temperature sulfides (Ͻ250°C) precipitated from a hydrothermal fluid which has probably interacted with seawater, precluding quantitative sulfate reduction in the chimney environment.…”

“…The present (2) Snake Pit (Kase et al, 1990), (3) Broken Spur (Duckworth et al, 1995), (4) TAG (Chiba et al, 1998;Gemmell and Sharpe, 1998;Knott et al, 1998), (5) Galapagos Rift (Skirrow and Coleman, 1982;, (6) EPR 21°N (Arnold and Sheppard, 1981;Styrt et al, 1981;Kerridge et al, 1983;Alt, 1988;Woodruff and Shanks, 1988), (7) EPR 11-13°N (Bluth and Ohmoto, 1988), (8) Juan de Fuca (Shanks and Seyfried, 1987).…”

Sulfide mineralization in an ultramafic-rock hosted seafloor hydrothermal system: From serpentinization to the formation of Cu–Zn–(Co)-rich massive sulfides

“…In particular, sediment-free basalthosted seafloor hydrothermal systems like TAG, MESO and Snake Pit share characteristics comparable to those of on-land mafic VMS deposits having CuZn-(Co) sulfide mineralization with high Cu/Zn ratios (e.g. Kase et al, 1990;Herzig and Hannington, 1995;Tivey et al, 1995;Herzig et al, 1998;Münch et al, 1999;Lawrie and Miller, 2000). The recent discovery of modern seafloor hydrothermal systems hosted in ultramafic rocks, i.e.…”

Sulfur isotope characteristics of the Permian VHMS deposits in Tasik Chini district, Central Belt of Peninsular Malaysia

“…Source of data: Permian VHMS deposits; Afterthought and Bully Hill, California-Gustin (1990), and Eastoe and Gustin (1996); Yanahara, Japan- Yamamoto et al (1968), and Kajiwara and Date (1971); Red Ledge, Idaho-Fifarek et al (1984), andFifarek (1985); Mount Chalmers, QueenslandHuston (1999), andHunns (2001); Permian seawater -Claypool et al (1980), and Kampschulte and Strauss (2004). Modern VHMS deposits; back-arc/arc-hosted deposits; Okinawa Trough, Japan- Halbach et al (1989); Manus Basin- Lein et al (1993); Mariana Trough- Kusakabe et al (1990);Brothers Volcano, Kermadec Tonga-de Ronde et al (2005); MORB-hosted deposits (unsedimented ridges); Southern Juan de Fuca Ridge (SJFR)- Shanks and Seyfried (1987); Galapagos Rift- Skirrow and Coleman (1982), and Knott et al (1995); Axial Seamount- Hannington and Scott (1988);Broken Spur-Duckworth et al (1995); Snakepit- Kase et al (1990);TAG-Herzig et al (1998), Chiba et al (1998), and Gemmell and Sharpe (1998; East Pacific Rise (EPR)-McConachy (1988), Bluth and Ohmoto (1988), Stuart et al (1994), Hekinian et al (1980), Arnold and Sheppard (1981), Styrt et al (1981), Kerridge et al (1983), Zierenberg et al (1984), Woodruff and Shanks (1988), and Marchig et al (1990); MORB-hosted deposits (sedimented ridges); Escanaba Trough- Koski et al (1988), Zierenberg et al (1993), and Böhlke and Shanks (1994); Guayamas Basin- Peter and Shanks (1992), and Shanks et...…”