Genesis of the central zone of the Nolans Bore rare earth element deposit, Northern Territory, Australia

Abstract

north and south-east zones. Breccia types BX2, BX3, and BX4 represent progressive stages of ore brecciation and development of calc-silicate mineral (amphibole, epidote, allanite, calcite) infill. Comparison of bulk ore sample geochemistry between breccia types indicates that REEs were not mobilised more than a few centimetres during hydrothermal alteration and brecciation. Instead, most of the REEs were partitioned from the original REE fluorapatite into newly formed allanite, REE-poor fluorapatite and minor REE carbonate in the breccias. Negative europium (Eu) anomalies in the breccia minerals are accounted for by a large positive Eu anomaly in epidote from the alteration zones surrounding the ore breccias. This observation provides a direct link between ore recrystallisation and brecciation, and the formation of the alteration halo in the surrounding host rocks. Where allanite and fluorapatite are texturally related, the fluorapatite is relatively depleted in the light rare earth elements (LREEs), whereas allanite is relatively LREE enriched, suggesting co-crystallisation. We tentatively date the BX1 ore stage to 1440 ± 80 Ma based on U-Pb dating of thorianite. Sm-Nd isotope isochrons derived from in situ isotope analysis of cognate apatite and allanite date the BX2 and BX3 events to ca. 400 Ma, while U-Pb dating of late-stage monazite from the BX4 ore stage returned an age of ca. 350 Ma. Therefore, formation of the central zone at Nolans Bore involved multiple alteration/brecciation events that collectively span over 1 billion years in duration. We suggest that the BX1-type veins and breccias were formed from REE-rich, saline (Fand Cl-bearing) fluids that infiltrated the granulite-grade host rocks in association with either shear activation events of the Redbank Shear Zone (1500-1400 Ma) or intrusion of late-stage pegmatites of the Mt Boothby area. BX2, BX3, and BX4 events record deformation and hydrothermal alteration associated with the Alice Springs Orogeny Abstract The Nolans Bore rare earth element (REE) deposit consists of a network of fluorapatite-bearing veins and breccias hosted within Proterozoic granulites of the Reynolds Range, Central Australia. Mineralisation is divided into three zones (north, central, and south-east), with the north and south-east zones consisting of massive REE-bearing fluorapatite veins, with minor brecciation and carbonate infill. The central zone is distinctively different in mineralogy and structure; it features extensive brecciation, a high allanite content, and a large, epidote-rich enveloping alteration zone. The central zone is a reworking of the original solid apatite veins that formed during the Chewings Orogeny at ca. 1525 Ma. These original apatite veins are thought to derive from phosphate-rich magmatic-hydrothermal fluid exsolved from as-yet unrecognised alkaline magmatic bodies at depth. We define four ore breccia types (BX1-4) in the central zone on the basis of detailed petrological and geochemical analysis of drillcore and thin sections. BX1 ore comprises fl...

REE Redistribution Textures in Altered Fluorapatite: Symplectites, Veins, and Phosphate-Silicate-Carbonate Assemblages from the Nolans Bore P-REE-Th Deposit, Northern Territory, Australia

“…The geological history of Nolans Bore has been described by Schoneveld et al (2015) and Huston et al (2016) and of the Aileron province, more…”

“…This alteration transformed the fluorapatite to REE-poor fluorapatite with abundant inclusions and veins of REE and Th phosphate, silicate, and carbonate minerals. The alteration mostly redistributed REE and Th between minerals within Nolans Bore itself, and did not transport any of these elements into the wall rocks (Schoneveld et al 2015).…”

“…Instead, it has recently been reconsidered as an igneous cumulate that crystallized directly from carbonatitic melt (Anenburg & Mavrogenes 2018). In this scenario, Nolans Bore was initially composed of REE-rich fluorapatite (via britholite substitution: Ca 2þ þ P 5þ REE 3þ þ Si 4þ ), which experienced several episodes of hydrothermal alteration (Schoneveld et al 2015, Huston et al 2016. This alteration transformed the fluorapatite to REE-poor fluorapatite with abundant inclusions and veins of REE and Th phosphate, silicate, and carbonate minerals.…”

Rare Earth and Phosphorus Leaching from a Flotation Tailings of Florida Phosphate Rock

“…Most of them are present in the form of isomorphous substitutions for Ca 2+ as REE-francolite, and a small amount of REEs is hosted in monazite ((Ce,La,Nd,Th)PO 4 ), xenotime (YPO 4 ), etc. [3,4]. In the wet-process, these REEs are also leached out with the decomposition of phosphate minerals and enter into the leaching product of phosphoric acid and residue of phosphogypsum (PG).…”

“…In the wet-process, these REEs are also leached out with the decomposition of phosphate minerals and enter into the leaching product of phosphoric acid and residue of phosphogypsum (PG). Similar to phosphate rock, monazite and xenotime react with sulfuric acid and can be expressed as: 2(Ce,La,Nd,Th)PO 4 + 3H 2 SO 4 = (Ce,La,Nd,Th) 2 (SO 4 ) 3 + 2H 3 PO 4 (2) 2YPO 4 + 3H 2 SO 4 = Y 2 (SO 4 ) 3 + 2H 3 PO 4…”