7 Geochemistry (Posters)

Monday, 21 March 2016
8:00 AM - 12:00 PM
Convention Hall

FLUID INCLUSION ANALYSIS OF FLUORITE IN POST-ALLEGHANIAN VEINS, VALLEY AND RIDGE PROVINCE, CENTRAL PENNSYLVANIA

Paper number: 7-5
Program: Technical Sessions
Time: 8:00 AM – 12:00 PM

Authors

Abstract

Fluorite-calcite-quartz mineralization was collected from post-Alleghanian veins in limestones of the Silurian-Devonian boundary near Allenport, Pennsylvania. Microthermometric analysis focused on 2-phase (liquid + gas) fluid inclusions in fluorite, which are dominantly in primary fluid inclusion assemblages. Temperatures of homogenization (Th) (liquid + gas → liquid) were tightly constrained between 180 and 195°C. Ice melting temperature (Tm) showed a narrow range of -20.7 and -20.2°C. Collecting Tm was complicated by the formation of clathrates under freezing conditions, requiring that samples needed to be melted completely between observations of each Tm to allow the initial nucleation of the gas bubbles to be repeatable. A secondary fluid inclusion assemblage confined to a damaged corner of a euhedral fluorite crystal exhibited a much wider Th range (115.0˚C - 195.0˚C) than the inclusions in the primary FIA, but produced consistent Tm values at -21.0°C. The tight Th range from the primary FIA fits into the broad Th range reported by Howe (1988) of 160 ± 60°C for Mississippi Valley-type occurrences in central Pennsylvania. However, Evans and Battles (1999) reported lower and broader Th values (58 to 160°C) for vein minerals from Alleghanian veins in the same formation as our samples. Th data from vein quartz in other local formations are radically different as well: 100 to 106.1°C (Curry, 2013) and >130 to 190°C (Scudder, 2014).

Geological Society of America Abstracts with Programs. Vol. 48, No. 1

doi: 10.1130/abs/2016NE-272599

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