Rare earth element (REE) geochemistry and genetic implications of the Mortas bauxite deposit (Seydisehir/Konya - Southern Turkey)

The Mediterranean-type karst-bauxite deposit of Mortas, South Turkey, placed unconformably between Cenomanian and Senonian shallow marine limestones is built of massive (MB), oolithic (OB), breccia-bearing (BB) and earthy (EB) bauxite horizons, from top to bottom. The MB layer is enriched in Al and REE (except Cc) due to loss of Si, Na, K, Mg and P. REE are accumulated in the BB but depleted in the EB layers. The ferruginous OB lost LREE and gained in HREE probable due to scavenging by authigenic heavy minerals like rutile, anatase and titanite. Total REE contents in the bauxite profile display an increasing trend from bottom to top, while negative and maximum positive Ce anomalies characterize the upper and the lower parts of the profile, respectively. This unusual REE behavior is explicable by assuming mobilization of Ce(W) either under reducing condition or chemical complexation under alkaline conditions in the top layer and scavenging of Cc by Al-Mg hydrosilicates and Ti-oxides and/or precipitation with authigenic REE minerals, especially of the bastnasite group near the bedrock limestones. Similarity in chondrite normalized-REE patterns of the Seydisehir phyllites, bauxite and terra rossa samples and the presence of tridymite (?) in bauxites makes a felsic source rock most likely and reveal a close genetic relationship between the Seydisehir phyllites and the recent terra rossa occurrences. The REE patterns of the bauxites resemble those of the Katrangedigi limestone despite variations in Sigma REE. Field observations and geochemical data together with mass-balance calculations suggest that the Mortas deposit was derived from the Seydisehir phyllites and argillic phase within the Katrangedigi limestone which in turn have Precambrian (?) felsic, probably granitic precursors. (c) 2008 Elsevier GmbH. All rights reserved.