Rare earth element movement during incipient alteration of pyroxenes in Guatemalan corestones

This study investigates the role of pyroxenes in the redistribution of rare earth elements (REE) in whole-rock geochemical data previously reported for a weathered corestone system in SE Guatemala. Previous work on spheroidal weathering has shown that variations in REE abundances can accompany minor changes in major elements.;Weathered augites within the corestone-interior are enriched in light REE (LREE), with abundances above fresh rock values. Several augites from the more weathered corestone-rind have passed the onset of weathering and have LREE similar to fresh rock values without a negative Ce anomaly. Products found within the augite dissolution features host the LREE during initial weathering. As alteration continues the products are subsequently depleted in LREE and lose the negative Ce anomaly. Identical behavior has been reported from intermediate degrees of weathering in whole-rock studies of spheroidal weathering.;Augite alteration creates an environment suitable for precipitation of LREE rich products, but the LREE abundances and patterns of the products are sufficiently unlike those of the primary augite that the augite itself is not the main source of the LREE in augite's weathering products. The source of the LREE must therefore be a phase other than augite, such as glass or microcrystalline groundmass. Formation of LREE rich secondary phases is associated with increased LREE and Ce anomaly in the whole-rock REE signature of the core and rind of the system.