Sulfide composition and microthermometry of fluid inclusions in the leg 111 sheeted dike section of Ocean Drilling Program hole 504B, Costa Rica rift

Journal Article · Sun Jun 10 00:00:00 EDT 1990 · Journal of Geophysical Research; (United States)

DOI:https://doi.org/10.1029/JB095iB06p08405· OSTI ID:5009746

Schoeps, D ^[1]; Herzig, P M ^[2]

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1. Technische Hochschule Aachen (West Germany)
2. Univ. of Toronto, Ontario (Canada)

Hole 504B of the Ocean Drilling Program is dedicated to the study of crustal structure and hydrothermal processes in 5.9-m.y.-old oceanic basement. Continuing the work of previous legs, hole 504B was extended 212.3 m to a total depth of 1,562.3 m below seafloor (bsf) during leg 111 in 1986. Quartz-sulfide veins occur at a depth of 1,369-1,388 m bsf in basalts of the sheeted dike complex. The ore minerals are predominantly pyrite, less chalcopyrite, rare Co-rich Cu-Fe-S phases, and a thiospinel (linnaeite/carrollite). Microprobe analyses yield a high Co content in zoned vein pyrites (>8 wt%) as well as in the Cu-Fe-S phases (>5 wt%). Up to 35.8 wt% CO was detected in the thiospinel. A Co/Ni ratio of > 100 distinguishes the vein pyrite from pyrite in the basaltic wall rock and from pyrite formed as an alteration product of olivine (Co/Ni < 5). The Co/Ni ratios correlate positively with Cu and negatively with As. Co-rich, nonstoichiometric Cu-Fe-S sulfides in chalcopyrite are interpreted as metastable phases which have been quenched at a high temperature and prohibited from exsolution of the stable products chalcopyrite and pyrite. Fluid inclusions in quartz from the quartz-sulfide veins are two-phase and vary from liquid- to vapor-dominated. Their salinities range from 4.2 to 7.2 wt% equivalent NaCl and average 5.5 wt%. Pressure (360 bars) corrected average filling temperatures vary from 271 to 408 C with a maximum of 486 C. This is consistent with calculated quartz formation temperatures for a single quartz separate (+4.2{per thousand} {delta}{sup 18}O) using oxygen isotope thermometry. The {delta}{sup 18}O value of the hydrothermal fluid was determined to be +1.7{per thousand}. The temperature data indicate fluid alteration of the sheeted dikes at about 350 to 500 C.

• OSTI ID: 5009746
• Journal Information: Journal of Geophysical Research; (United States), Vol. 95:B6, Issue B6; ISSN 0148-0227
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
OCEANIC CRUST
GEOCHEMISTRY
ARSENIC
BASALT
BOREHOLES
CHEMICAL COMPOSITION
COBALT
COPPER SULFIDES
COSTA RICA
DEPTH
DIKES
DRILL CORES
ELECTRON MICROPROBE ANALYSIS
GEOLOGIC STRUCTURES
HYDROTHERMAL SYSTEMS
INCLUSIONS
IRON SULFIDES
ISOTOPE RATIO
LIQUIDS
MINERALOGY
NICKEL
OXYGEN 18
PHASE STUDIES
PYRITE
QUARTZ
RESERVOIR PRESSURE
RESERVOIR TEMPERATURE
SALINITY
SPINELS
SULFIDES
VAPORS
WELL DRILLING
CAVITIES
CENTRAL AMERICA
CHALCOGENIDES
CHEMICAL ANALYSIS
CHEMISTRY
COPPER COMPOUNDS
DEVELOPING COUNTRIES
DIMENSIONS
DRILLING
EARTH CRUST
ELEMENTS
ENERGY SYSTEMS
EVEN-EVEN NUCLEI
FLUIDS
GASES
GEOTHERMAL SYSTEMS
IGNEOUS ROCKS
IRON COMPOUNDS
ISOTOPES
LATIN AMERICA
LIGHT NUCLEI
METALS
MICROANALYSIS
MINERALS
NONDESTRUCTIVE ANALYSIS
NUCLEI
OXIDE MINERALS
OXYGEN ISOTOPES
ROCKS
SEMIMETALS
STABLE ISOTOPES
SULFIDE MINERALS
SULFUR COMPOUNDS
TRANSITION ELEMENT COMPOUNDS
TRANSITION ELEMENTS
VOLCANIC ROCKS
580000* - Geosciences