Significance of organic material and pyrite in mineralized black shales

Conference · Wed Jan 01 04:00:00 EST 1992 · Geological Society of America, Abstracts with Programs; (United States)

OSTI ID:5895443

Heyck, H L.O.

Black shales host a wide variety of ore deposits, including Cu, Pb, Zn, Co, Ag, and Au, and anomalous concentrations of Ni, U, Va, Mo. Age of shale deposition, timing of mineralization relative to deposition, tectonic setting and degree of metamorphism vary among deposit types. One common characteristic of these host shales is significant total organic carbon (TOC) content. Although most these metals correlate positively with organic carbon in mineralized shales, study of black shales has created a more complex picture. For example, not all organic shales are metalliferous--a source of metals is required. Different metals have affinities for different types of organic material. Metals in black shales occur in both sulfides and organic phases. Organic material acts as host for metals, reductant for mineralizing fluids, or recorder of mineralizing event conditions. Related characteristics of black shales that affect metal concentrations are: presence of sulfate-reducing bacteria and degree of pyritization (DOP). The bacteria are responsible for formation of H[sub 2]S, which reacts with available iron to form pyrite, or, in presence of metal rich fluids, may form other metal sulfides. This accounts for syngenetic enrichment of metals in black shales, but does not generally form minable concentration. DOP, the ratio of iron-in-pyrite to pyrite-plus-acid-soluble iron in sediments, reflects reduction-oxidation conditions of deposition, and indicates metal-bearing potential. Metal deposition in black shales commonly requires interaction of organic carbon and/or pyrite with metal-bearing fluids of either syn- or post-depositional age.

• OSTI ID: 5895443
• Report Number(s): CONF-921058--
• Conference Information: Journal Name: Geological Society of America, Abstracts with Programs; (United States) Journal Volume: 24:7
• Country of Publication: United States
• Language: English

Related Subjects

04 OIL SHALES AND TAR SANDS
040200* -- Oil Shales & Tar Sands-- Reserves
Geology
& Exploration
BACTERIA
BLACK SHALES
CHEMISTRY
GEOCHEMISTRY
GEOLOGIC DEPOSITS
MATTER
MICROORGANISMS
MINERAL RESOURCES
MINERALIZATION
MINERALOGY
MINERALS
OIL SHALE DEPOSITS
ORES
ORGANIC MATTER
PYRITE
REDOX POTENTIAL
RESOURCES
ROCK-FLUID INTERACTIONS
ROCKS
SEDIMENTARY ROCKS
SHALES
SULFATE-REDUCING BACTERIA
SULFIDE MINERALS