ABSTRACT

Two marine concentrating processes operate to produce the heavy mineral deposits found on beaches in the vicinity of Apalachicola, Florida. The process operating in the more energetic Gulf of Mexico tends to remove the coarser grains from initial populations. This results in a relatively fine-grained black sand concentrate being delivered to the beach for deposition. The reverse occurs in the less energetic bays and sounds; the process tends to remove the finer grains and the deposits are coarser. The quartz associated with both types of deposits is in equilibrium, but not settling equivalence, with ilmenite, staurolite, and kyanite. Settling equivalence is present among the ilmenite, staurolite, and kyanite populations of the sheltered beach deposits only. Zircon and rutile ar too small in grain size to be in equilibrium with the other minerals. This `too small' nature most probably reflects smaller variances of the initial populations.

The dune deposits were concentrated by `gentler than normal' winds reworking beach sands containing areally limited heavy mineral deposits. Ilmenite, staurolite, kyanite, and quartz are in settling equivalence; the zircon and rutile are too small. Good evidence exists for a shape-based decrease in grain size for kyanite and rutile during wind transport.