The Nolans Bore rare-earth element-phosphorus-uranium mineral system: geology, origin and post-depositional modifications
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- 作者：David L. Huston ; Roland Maas ; Andrew Cross ; Kelvin J. Hussey…
- 刊名：Mineralium Deposita
- 出版年：2016
- 出版时间：August 2016
- 年：2016
- 卷：51
- 期：6
- 页码：797-822
- 全文大小：5,429 KB
- 刊物类别：Earth and Environmental Science
- 刊物主题：Earth sciences
Geology
Mineral Resources
Mineralogy - 出版者：Springer Berlin / Heidelberg
- ISSN：1432-1866
- 卷排序：51
文摘
Nolans Bore is a rare-earth element (REE)-U-P fluorapatite vein deposit hosted mostly by the ~1805 Ma Boothby Orthogneiss in the Aileron Province, Northern Territory, Australia. The fluorapatite veins are complex, with two stages: (1) massive to granular fluorapatite with inclusions of REE silicates, phosphates and (fluoro)carbonates, and (2) calcite-allanite with accessory REE-bearing phosphate and (fluoro)carbonate minerals that vein and brecciate the earlier stage. The veins are locally accompanied by narrow skarn-like (garnet-diopside-amphibole) wall rock alteration zones. SHRIMP Th-Pb analyses of allanite yielded an age of 1525 ± 18 Ma, interpreted as the minimum age of mineralisation. The maximum age is provided by a ~1550 Ma SHRIMP U-Pb age for a pegmatite that predates the fluorapatite veins. Other isotopic systems yielded ages from ~1443 to ~345 Ma, implying significant post-depositional isotopic disturbance. Calculation of initial εNd and 87Sr/86Sr at 1525 Ma and stable isotope data are consistent with an enriched mantle or lower crust source, although post-depositional disturbance is likely. Processes leading to formation of Nolans Bore began with north-dipping subduction along the south margin of the Aileron Province at 1820–1750 Ma, producing a metasomatised, volatile-rich, lithospheric mantle wedge. About 200 million years later, near the end of the Chewings Orogeny, this reservoir and/or the lower crust sourced alkaline low-degree partial melts which passed into the mid- and upper-crust. Fluids derived from these melts, which may have included phosphatic melts, eventually deposited the Nolans Bore fluorapatite veins due to fluid-rock interaction, cooling, depressurisation and/or fluid mixing. Owing to its size and high concentration of Th (2500 ppm), in situ radiogenic heating caused significant recrystallisation and isotopic resetting. The system finally cooled below 300 °C at ~370 Ma, possibly in response to unroofing during the Alice Springs Orogeny. Surface exposure and weathering of fluorapatite produced acidic fluids and intense, near-surface kaolinitised zones that include high-grade, supergene-enriched cheralite-rich ores.Editorial handling: M. FayekElectronic supplementary materialThe online version of this article (doi:10.1007/s00126-015-0631-y) contains supplementary material, which is available to authorized users.