Sulfur isotope and total studies of basalts and greenstones from DSDP Hole 504B, Costa Rica Rift; implications for hydrothermal alteration

Author(s): Kawahata, Hodaka; Shikazono, Naotatsu
Author Affiliation(s): Primary:
Geological Survey of Japan, Ibaraki, Japan
Other:
University of Tokyo, Japan
Volume Title: Sea-floor hydrothermal mineralization
Volume Author(s): Barrett, Timothy J., editor; Jambor, John L.
Source: The Canadian Mineralogist, Vol.26(Part 3), p.555-565; Sea-floor hydrothermal mineralization conference, Montreal, QC, Canada, Feb. 5-6, 1987, edited by Timothy J. Barrett and John L. Jambor. Publisher: Mineralogical Association of Canada, Ottawa, ON, Canada. ISSN: 0008-4476 CODEN: CAMIA6
Note: In English with French summary. 67 refs.; illus., incl. 4 tables, sketch map
Summary: Hole 504B, located on the flank of the Costa Rica Rift, Galapagos Spreading Centre, is the first DSDP site where both hydrothermally altered rocks and stockwork-type sulphide precipitation have been discovered. Relative to fresh basalts, basement rocks from 275 to 550 m sub-bottom depth (Zone I) (0-275 m sub-basement depth), are depleted in S (av. 420 ppm) owing to oxic weathering. S contents of basalts from 550 to 890 m sub-bottom depth (Zone II), where suboxic and anoxic alteration occurred, lie within the range of fresh basalts (av. 1040 ppm). Underlying greenstones average 5690 ppm S from 890 to 1050 m (Zone III), and 740 ppm S from 1050 to 1350 m sub-bottom depth (Zone IV). Sulphide minerals are common in the hydrothermally altered basalts of Hole 504B with pyrite the most common secondary sulphide. Some pyrite is rich in Ni (< or =1.1 wt.%) and Co (< or =0.8 wt.%). Sphalerite occurs in veins in Zone III and contains 5-14 mol % FeS (av. 11 mol%). Chalcopyrite occurs mainly in Zones III and IV. The high S values of Zone III suggest that the greenstones in this part of Hole 504B initially were located at a near-surface discharge zone. Total delta34S values of pyrite from the greenstones range 1.5-5.8 permil. The estimated delta34S values of H2S in hydrothermal solutions, assuming equilibrium with precipitated sulfides, vary between approx +0.5 and +4.6permil. The marine S contribution is calculated to be about 11% and the basaltic sulphide S approx 89% of the total S. Water/rock ratios of 2-7 by weight are calculated on the basis of S contents and S isotopic compositions of sulphides in greenstones. These values are consistent with the water/rock ratio (approx 1.6) estimated from previous Sr isotope studies. If sub-seafloor chemical environments of axial hydrothermal systems are similar to those of Hole 504B, alteration (leaching) of approx 1.2 km3 of oceanic crust could provide the S required to produce a large size (approx 3 million tonnes) sulphide deposit.
Year of Publication: 1988
Research Program: DSDP Deep Sea Drilling Project
IPOD International Phase of Ocean Drilling
ODP Ocean Drilling Program
Key Words: 02 Geochemistry; 27 Economic Geology, Metals; Basalts; Chemical composition; Chlorides; Costa Rica Rift; Crust; DSDP Site 504; Deep Sea Drilling Project; East Pacific; Galapagos Rift; Geochemistry; Greenstone; Halides; Halite; Hydrogen sulfide; Hydrothermal alteration; Hydrothermal vents; IPOD; Igneous rocks; Isotope ratios; Isotopes; Leg 69; Metal ores; Metallogeny; Metamorphic rocks; Metasomatism; Mid-ocean ridge basalts; Mid-ocean ridges; Mineral assemblages; Mineral deposits, genesis; Mineralization; Ocean Drilling Program; Ocean floors; Oceanic crust; Pacific Ocean; Petrology; Plate tectonics; Pyrite; Rift zones; S-34/S-32; Schists; Stable isotopes; Stockwork deposits; Sulfates; Sulfides; Sulfur; Textures; Volcanic rocks; Volcanism; Water-rock interaction; Weathering
Coordinates: N011335 N011338 W0834348 W0834357
Record ID: 2007039238
Copyright Information: GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from Mineralogical Abstracts, United Kingdom, Twickenham, United Kingdom