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Organic geochemical investigations of organic matter-mineralization relationships in the White Pine district
ABSTRACTS FROM IGCP 1991 ANNUAL MEETING
233
Turekian, K.K. and Wedepohl, K.H., 1961. Distribution of the elements in some maj or units of the earth's crust. Geol. Soc. Am. Bull., 72: 175-191. Vine, J.D. and Tourtelot, E.B., 1970. Geochemistry of black shale deposits - - A summary report. Econ. Geol., 65: 253-272. IMMOBILIZATIONAND PRECIPITATION OF METALS BY MICROORGANISMS F.G. Ferris (Department of Geology, University of Toronto, Toronto, Ontario MSS 3B1, Canada)
Microorganisms are the most abundant form of life on Earth. They live wherever there is liquid water, even up to temperatures of 110 ° C. Indeed, microbial life exists in the harshest of environments, from the Antarctic to the depths of the oceans and porous subsurface materials. Microorganisms also perform many biogeochemicaltransformations that are carried out poorly or not at all by higher organisms, for example the oxidation of sulfide minerals to sulfuric acid or the reduction of sulfate to hydrogen sulfide. In addition, microbial cells are capable of adsorbing significant quantities of dissolved metallic ions. This uptake and retention of metals is generally facilitated by electrostatic interactions with anionic carboxyl and phosphoryl groups that reside within structural polymers of the cells. The macromolecular components in cell walls and external sheaths of microorganisms are particularly reactive, so metals tend to concentrate near the cell surface. Once immobilized, the metals can be efficiently partioned into sediments and precipitated epitaxially on the surfaces of microbial cells by hydrolysis, a change in oxidation state, or through reactions with other ionic species in solution. In this way, microorganisms serve as distinct nucleation sites for the growth and crystallization of authigenic minerals. Depending on the environment and species of microorganism involved, carbonate, phosphate, oxide, sulfide, and/ or silicate minerals may be formed. There are many examples of microbially supported mineralization in modern sedimentary environments, and there is abundant evidence that analogous processes contributed to the genesis of some mineral deposits in the past. ORGANIC GEOCHEMICAL INVESTIGATIONS OF ORGANIC MATTERMINERALIZATIONRELATIONSHIPS IN THE WHITE PINE DISTRICT P.A. Meyers, E.S. Ho and J.L. Mauk (Department of Geological Sciences, The University of Michigan, Ann Arbor, MI 48109-1063, USA)
Metallic ore deposits are often found associated with rock layers having elevated concentrations of organic matter, leading to the implication that the organic matter was involved in emplacement of the mineralized strata. Organic matter may participate in formation of ore deposits by causing precipitation of the minerals from migrating solutions via reduction of the soluble
234
ABSTRACTSFROMIGCP 1991ANNUALMEETING
forms of the metals. Oxidation and consequent alterations of the character of the organic matter would result. The 1.1 billion-year-old Nonesuch Formation of northern Michigan hosts deposits of elemental copper and silver and copper-iron sulfides in a lacustrine black shale setting. The deposits are best developed at White Pine, Michigan, where they provide an opportunity to investigate the geochemical processes which have contributed to formation of metal sulfide ores. We have collected a suite of several hundred rock sampies from within the White Pine mine and from boreholes from outside the mineralized section of the Nonesuch Formation. Total organic carbon (TOC) concentrations typically are low, averaging less than 0.1%0by weight, but range up to 1.5%. Comparison of TOC and copper concentrations in these samples has corrected an earlier impression that TOC has been destructively oxidized in copper-rich zones. Instead, higher levels of TOC and of copper correlate. Many samples contain evidence of petroleum migration in the past; petroleum is still present in some parts of the mineralized zone. Most mineralized rocks, however, contain little extractable hydrocarbon material, whereas rocks from outside the mineralized zone have full petroleum-like distributions of aliphatic hydrocarbons. Organic carbon stable isotope contents of rocks from within and outside the mineralized sections are typically depleted in 13C, having ~13C values in the - 31 to - 34%0 range. Attempts to assess incorporation of oxygen or sulfur as functional groups into organic matter in mineralized rocks by FTIR spectroscopy have not been very informative; kerogen appears to be thermally mature and to contain no functional groups in these rocks. ORGANIC GEOCHEMISTRY OF DEVONIAN AND PENNSYLVANIAN METALLIFEROUS BLACK SHALES OF INDIANA N.R. Shaffer and E.M. Ripley (Department of Geological Sciences, Indiana University, Bloomington, IN 47405, USA)
Previous studies have documented the presence of thin but highly metalenriched shales in southern Indiana. Metals that are enriched include Zn, Mo, Ni, V, and U. Isotopic and microscopic studies have demonstrated early formation of metal sulfides and stratigraphic and paleogeographic patterns in metal enrichment and organic matter. New gas chromatography and pyrolysis-gas chromatography data have been used to refine details of organic materials associated with metal-rich zones. Indiana black shales are immature and variations in organic materials are more related to original organic input and to conditions of sedimentation than to degree of maturity. CPI values range from 0.6 to 1.3 and probably reflect proportions of terrestrial input with slightly higher values in metal-rich beds. Pristane:n-C17 ratios are lower (0.9) in metalliferous beds than in the rest of the shale ( 1.5 ) as are phytane:n-Cls values of 0.6 and 0.9 respectively. These
233
Turekian, K.K. and Wedepohl, K.H., 1961. Distribution of the elements in some maj or units of the earth's crust. Geol. Soc. Am. Bull., 72: 175-191. Vine, J.D. and Tourtelot, E.B., 1970. Geochemistry of black shale deposits - - A summary report. Econ. Geol., 65: 253-272. IMMOBILIZATIONAND PRECIPITATION OF METALS BY MICROORGANISMS F.G. Ferris (Department of Geology, University of Toronto, Toronto, Ontario MSS 3B1, Canada)
Microorganisms are the most abundant form of life on Earth. They live wherever there is liquid water, even up to temperatures of 110 ° C. Indeed, microbial life exists in the harshest of environments, from the Antarctic to the depths of the oceans and porous subsurface materials. Microorganisms also perform many biogeochemicaltransformations that are carried out poorly or not at all by higher organisms, for example the oxidation of sulfide minerals to sulfuric acid or the reduction of sulfate to hydrogen sulfide. In addition, microbial cells are capable of adsorbing significant quantities of dissolved metallic ions. This uptake and retention of metals is generally facilitated by electrostatic interactions with anionic carboxyl and phosphoryl groups that reside within structural polymers of the cells. The macromolecular components in cell walls and external sheaths of microorganisms are particularly reactive, so metals tend to concentrate near the cell surface. Once immobilized, the metals can be efficiently partioned into sediments and precipitated epitaxially on the surfaces of microbial cells by hydrolysis, a change in oxidation state, or through reactions with other ionic species in solution. In this way, microorganisms serve as distinct nucleation sites for the growth and crystallization of authigenic minerals. Depending on the environment and species of microorganism involved, carbonate, phosphate, oxide, sulfide, and/ or silicate minerals may be formed. There are many examples of microbially supported mineralization in modern sedimentary environments, and there is abundant evidence that analogous processes contributed to the genesis of some mineral deposits in the past. ORGANIC GEOCHEMICAL INVESTIGATIONS OF ORGANIC MATTERMINERALIZATIONRELATIONSHIPS IN THE WHITE PINE DISTRICT P.A. Meyers, E.S. Ho and J.L. Mauk (Department of Geological Sciences, The University of Michigan, Ann Arbor, MI 48109-1063, USA)
Metallic ore deposits are often found associated with rock layers having elevated concentrations of organic matter, leading to the implication that the organic matter was involved in emplacement of the mineralized strata. Organic matter may participate in formation of ore deposits by causing precipitation of the minerals from migrating solutions via reduction of the soluble
234
ABSTRACTSFROMIGCP 1991ANNUALMEETING
forms of the metals. Oxidation and consequent alterations of the character of the organic matter would result. The 1.1 billion-year-old Nonesuch Formation of northern Michigan hosts deposits of elemental copper and silver and copper-iron sulfides in a lacustrine black shale setting. The deposits are best developed at White Pine, Michigan, where they provide an opportunity to investigate the geochemical processes which have contributed to formation of metal sulfide ores. We have collected a suite of several hundred rock sampies from within the White Pine mine and from boreholes from outside the mineralized section of the Nonesuch Formation. Total organic carbon (TOC) concentrations typically are low, averaging less than 0.1%0by weight, but range up to 1.5%. Comparison of TOC and copper concentrations in these samples has corrected an earlier impression that TOC has been destructively oxidized in copper-rich zones. Instead, higher levels of TOC and of copper correlate. Many samples contain evidence of petroleum migration in the past; petroleum is still present in some parts of the mineralized zone. Most mineralized rocks, however, contain little extractable hydrocarbon material, whereas rocks from outside the mineralized zone have full petroleum-like distributions of aliphatic hydrocarbons. Organic carbon stable isotope contents of rocks from within and outside the mineralized sections are typically depleted in 13C, having ~13C values in the - 31 to - 34%0 range. Attempts to assess incorporation of oxygen or sulfur as functional groups into organic matter in mineralized rocks by FTIR spectroscopy have not been very informative; kerogen appears to be thermally mature and to contain no functional groups in these rocks. ORGANIC GEOCHEMISTRY OF DEVONIAN AND PENNSYLVANIAN METALLIFEROUS BLACK SHALES OF INDIANA N.R. Shaffer and E.M. Ripley (Department of Geological Sciences, Indiana University, Bloomington, IN 47405, USA)
Previous studies have documented the presence of thin but highly metalenriched shales in southern Indiana. Metals that are enriched include Zn, Mo, Ni, V, and U. Isotopic and microscopic studies have demonstrated early formation of metal sulfides and stratigraphic and paleogeographic patterns in metal enrichment and organic matter. New gas chromatography and pyrolysis-gas chromatography data have been used to refine details of organic materials associated with metal-rich zones. Indiana black shales are immature and variations in organic materials are more related to original organic input and to conditions of sedimentation than to degree of maturity. CPI values range from 0.6 to 1.3 and probably reflect proportions of terrestrial input with slightly higher values in metal-rich beds. Pristane:n-C17 ratios are lower (0.9) in metalliferous beds than in the rest of the shale ( 1.5 ) as are phytane:n-Cls values of 0.6 and 0.9 respectively. These