Abstract: Fluvial Heavy Mineral Variation Downstream from Magnet Cove, AR
E. B. Ledger, W. P. Roberts, M. C. Crocker
Heavy mineral analysis of clastic rocks is often used for correlation and provenance studies. Although the behavior during fluvial transport of most common minerals is well known, we investigated a contemporaneous source of heavy minerals that provides information not previously available. The source area is small enough (16 km2) to be considered a "point source", and it provides minerals not included in previous studies.
Quaternary fluvial sediment was analyzed for heavy mineral composition at and downstream from the alkalic igneous intrusion at Magnet Cove, AR. The 2 to 4-phi fraction was selected for point counting of grain mounts. Total heavy minerals constitute almost 50 percent by weight of the selected fraction of the sediment in the igneous outcrop area, but decrease to 0.01 percent 90 kilometers downstream. Pyrite, monticellite, and magnetite are present near the source, but quickly become undetectable downstream. Garnet, perovskite, ilmenite, pyroxene, apatite, titanite, and rutile are persistent in the sediment to 90 kilometers. Of these, only pyroxene is usually considered unstable. The presence of pyroxene in the sand fraction downstream can be accounted for by constant replenishment to th sand fraction by comminution of gravel size pyroxene-bearing rock fragments.
AAPG Search and Discovery Article #90955©1995 GCAGS 45th Annual Meeting and Gulf Section SEPM, Baton Rouge, Louisiana