Monte Orsello bauxite outcrop (Monte Orsello prospect), Lucoli, L'Aquila Province, Abruzzo, Italyi

Regional Level Types
Monte Orsello bauxite outcrop (Monte Orsello prospect)	Prospect
Lucoli	Commune
L'Aquila Province	Province
Abruzzo	Region
Italy	Country

Bauxite outcrop on the SW side of the Monte Orsello ridge, prospected in the period 1955-1975.

The dark red bauxitic lens has a maximum thickness of about 10 m and a length of 100 m. The texture is matrix-supported, but in comparison with the nearby Vecchia Miniera outcrop there is a greater abundance of both detrital and/or oolitic-pisolitic components, with a moderately homogeneous sorting. The footwall limestone is visible on the southeastern flank of the outcrop and shows evidence of karsting and of brittle deformation. A limestone layer follows on top of the bauxite body, showing a significant content in iron oxides. This calcareous layer passes laterally to ochraceous limestone (about 1 m thick) with a nodular appearance. On the top of this interval there is the milky-white hangingwall limestone.

Bauxite mainly consists of böhmite, hematite, anatase, and rutile. Another common phase is gibbsite. An ubiquitous clay mineral is kaolinite. Accessory minerals are calcite and illite. The texture of the ore is mainly matrix-supported, and only locally grain-supported. The structure is generally oolitic and seldom oolitic-conglomeratic with rare pisolites. The oolites have a moderate compositional heterogeneity: part of them (from 50 up to 70%) are hematitic, and reddish brown to black. In addition, in many cases bauxite pebbles occur as rounded clasts embedded in a whitish clayey matrix. The oolites have a high degree of textural complexity, and in many cases, they are characterised by concentric textures, with bands of Fe oxides alternated with layers of Al hydroxides or böhmite rims grown upon hematite-rich cores. The matrix of the bauxite samples is mainly kaolinitic, finely inter-mixed with böhmite and/or Fe oxy-hydroxides. Both the oolites and the matrix enclose a wide range of fine-grained (diameter < 30 μm) heavy minerals such as REE phosphates (monazite and xenotime), ilmenite, baddeleyite, rutile, and zircon. These phases exhibit smooth to angular surfaces and broken crystal forms, which highlight a certain degree of transport and thus their detrital origin. REEs authigenic minerals, such as fluoro-carbonate (parisite) and florencite-like phases, were also detected in cavities of the rocks. The florencite-like phases show high Ce (Ce₂O₃ average value = 25.72 wt.%, 1.07 a.p.f.u. Ce), and minor La (average La₂O₃ content = 12.20 wt.%, 0.51 a.p.f.u. La) and Nd amounts (Nd₂O₃ average value = 7.98 wt-%, 0.32 a.p.f.u. Nd). Concerning the chemistry of the florencite-like phases, it must be highlighted that a significant LREE (light rare earth elements) excess and a slight Al deficiency have been detected in the Abruzzo samples, in comparison with the classical florencite.

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