Fluid inclusion and stable isotope data for the Pea Ridge Fe-REE orebody, Missouri

Conference · Mon Mar 01 00:00:00 EST 1993 · Geological Society of America, Abstracts with Programs; (United States)

OSTI ID:7281342

Sidder, G B; Day, W C; Rye, R O ^[1]

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1. Geological Survey, Denver, CO (United States)

New fluid-inclusion and stable-isotope data define the character of the mineralizing fluids that formed the iron and rare-earth-element ore deposit at the Pea Ridge Mine, southeast Missouri. These fluids were very hot and highly saline brines that may have been magmatically derived. Early, pre-magnetite ore skarn alteration of the host rhyolitic tuff took place at temperatures greater than 420 C and possibly as high as 680 C based upon calculated temperatures of quartz-magnetite pairs. Halite homogenization of three- or more phase (liquid + vapor + salts) fluid inclusions in quartz indicates that the skarn-forming fluid had a temperature of about 460 C to > 530 C and a salinity of about 45 to 57 equivalent weight percent NaCl. Analyses of [delta][sup 18]O in quartz from the skarn zone average about 14.5[per thousand], compared to a value of about 13.0[per thousand] for quartz in the host rhyolite. Average [delta][sup 34]S values for pyrite of about 2.3[per thousand] in the skarn zone may reflect a magmatic source. Magnetite ore was deposited at temperatures between about 340 C and 530 C from a fluid with a salinity between about 54 and 60 equivalent weight percent NaCl. The large apparent range of temperatures indicated by both fluid-inclusion and stable-isotope data within each zone may be due to contamination by quartz from multiple stages of quartz deposition. Also, the assumed isotopic equilibrium between some mineral pairs may be incorrect. Moreover, fluid inclusions are relatively rare in all ore and alteration zones except the silicified zone, and only a few inclusions are clearly primary in origin. Nonetheless, the predominance of high temperatures and high salinities in all of the mineralized and altered zones supports the interpretation that Pea ridge is a magmatic hydrothermal deposit. This magmatic hydrothermal model is also supported by paragenetic relations defined by geologic mapping and geochemical modeling of major-, minor-, and trace-element data.

• OSTI ID: 7281342
• Report Number(s): CONF-9303210-; CODEN: GAAPBC
• Journal Information: Geological Society of America, Abstracts with Programs; (United States), Vol. 25:3; Conference: 27. annual Geological Society of America (GSA) North-Central Section meeting, Rolla, MO (United States), 29-30 Mar 1993; ISSN 0016-7592
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
15 GEOTHERMAL ENERGY
GEOLOGIC DEPOSITS
HYDROTHERMAL ALTERATION
MINERALIZATION
MAGNETITE
HYDROTHERMAL SYNTHESIS
MISSOURI
RARE EARTH COMPOUNDS
RHYOLITES
ISOTOPE RATIO
GEOCHEMISTRY
GEOTHERMOMETRY
INCLUSIONS
ROCK-FLUID INTERACTIONS
CHEMISTRY
DEVELOPED COUNTRIES
IGNEOUS ROCKS
IRON ORES
MINERALS
NORTH AMERICA
ORES
OXIDE MINERALS
ROCKS
SYNTHESIS
USA
VOLCANIC ROCKS
580000* - Geosciences
152002 - Geothermal Data & Theory- Properties of Minerals & Rocks
152004 - Geothermal Data & Theory- Isotope & Trace Element Studies