Geology and ore genesis of the carbonatite-associated Yangibana REE district, Gascoyne Province, Western Australia

Journal Publication ResearchOnline@JCU
Slezak, Paul;Spandler, Carl;Border, Andy;Whittock, Kieren
Abstract

The Yangibana rare earth element (REE) district consists of multiple mineral deposits/prospects hosted within the Mesoproterozoic Gifford Creek Carbonatite Complex (GCCC), Western Australia, which comprises a range of rock types including calcite carbonatite, dolomite carbonatite, ankerite-siderite carbonatite, magnetite-biotite dykes, silica-rich alkaline veins, fenite, glimmerites and what have historically been called "ironstones". The dykes/sills were emplaced during a period of extension and/or transtension, likely utilising existing structures. The Yangibana REE deposits/prospects are located along many of these structures, particularly along the prominent Bald Hill Lineament. The primary ore mineral at Yangibana is monazite, which is contained within ankerite-siderite carbonatite, magnetite-biotite dykes and ironstone units. The ironstones comprise boxwork-textured Fe oxides/hydroxides, quartz, chalcedony and minor monazite and subordinate rhabdophane. Carbonate mineral-shaped cavities in ironstone, fenite and glimmerite alteration mantling the ironstone units, and ankerite-siderite carbonatite dykes altering to ironstone-like assemblages in drill core indicate that the ironstones are derived from ankerite-siderite carbonatite. This premise is further supported by similar bulk-rock Nd isotope composition of ironstone and other alkaline igneous rocks of the GCCC. Mass balance evaluation shows that the ironstones can be derived from the ankerite-siderite carbonatites via significant mass removal, which has resulted in passive REE concentration by similar to 2 to similar to 10 times. This mass removal and ore tenor upgrade is attributed to extensive carbonate breakdown and weathering of ankerite-siderite carbonatite by near-surface meteoric water. Monazite from the ironstones has strong positive and negative correlations between Pr and Nd, and Nd and La, respectively. These relationships are reflected in the bulk-rock drill assays, which display substantial variation in the La/Nd throughout the GCCC. The changes in La/Nd are attributed to variations in primary magmatic composition, shifts in the magmatic-hydrothermal systems related to CO2 versus water-dominated fluid phases, and changes in temperature.

Journal

Mineralium Deposita

Publication Name

N/A

Volume

56

ISBN/ISSN

1432-1866

Edition

N/A

Issue

N/A

Pages Count

20

Location

N/A

Publisher

Springer

Publisher Url

N/A

Publisher Location

N/A

Publish Date

N/A

Url

N/A

Date

N/A

EISSN

N/A

DOI

10.1007/s00126-020-01026-z