Se. Kesler et al., NA-CL-BR SYSTEMATICS OF FLUID INCLUSIONS FROM MISSISSIPPI VALLEY-TYPEDEPOSITS, APPALACHIAN BASIN - CONSTRAINTS ON SOLUTE ORIGIN AND MIGRATION PATHS, Geochimica et cosmochimica acta, 60(2), 1996, pp. 225-233
This study evaluated Na-Cl-Br systematics of fluid inclusion-hosted br
ines in Mississippi Valley-type (MVT) deposits from the Appalachian Ba
sin. Unlike other geochemical tracers such as lead and strontium isoto
pes which constrain metal sources, Na-Cl-Br systematics identify sourc
es of brine salinity. Saline formation waters can vary systematically
within and between basins with regard to their Na-Cl-Br compositions d
epending on the importance of halite dissolution relative to retention
of subaerially evaporated seawater for the halogen budget. Oil field
brine compositions from the Illinois and Appalachian basins are quite
distinct in their Na-Cl-Br systematics. Compositions of saline fluid i
nclusions in MVT deposits generally are consistent with these regional
differences. These results shed new light on the extent of regional f
low systems and on the geochemical evolution of saline fluids responsi
ble for mineralization. Nearly all fluid inclusions analyzed from the
Appalachian MVT deposits have Na/Br and Cl/Br ratios less than modern
seawater, consistent with ratios observed in marine brines involved in
halite precipitation. The Na-Cl-Br systematics of the brines responsi
ble for Appalachian MVT deposits may be inherited from original marine
brines refluxed into the porous carbonate shelf sediments that host t
hese deposits. The Cl/Br and Na/Br ratios of most fluid inclusion-host
ed brines from Appalachian MVT sphalerites and fluorites fall into two
compositional groups, one from the Lower Cambrian paleoaquifer and an
other from the Lower Ordovician paleoaqaifer. Leachates from most MVT
barite deposits form a third compositional group having lower Na/Br an
d Cl/Br ratios than the other two. Appalachian MVT leachate compositio
ns differ significantly from those in MVT deposits in the Cincinnati a
rch-midcontinent region suggesting that these two MVT provinces formed
from brines of different origin or flow path.