This study investigates the paragenesis and ore mineral composition of xenotime [(Y,HREE)PO4] and florencite [LREEAl3(PO4)2(OH)6] from heavy rare earth element (HREE) deposits/prospects of the Tanami and Hall Creek regions of Western Australia. Two stages of xenotime-(Y) formation are recognized: (1) early xenotime-(Y) in breccias (breccia-hosted) and in quartz-xenotime-(Y) veins (vein-type); and (2) late xenotime-(Y) that occurs largely as dipyramidal-shaped overgrowths on the pre-existing early xenotime-(Y). Similarly, florencite-(Ce) formed in two stages including: (1) early florencite-(Ce) that coexists with and is enclosed by early xenotime-(Y) within mineralized veins; and (2) late florencite-(Ce) that replaces early xenotime-(Y), or appears as narrow rims on early florencite-(Ce). All xenotime-(Y) types from a number of examined HREE deposits/prospects are characterized by elevated U contents and marked negative Eu anomalies that we interpret to be inherited from the metasedimentary rocks from which REE and P required for the phosphate ore mineralization, were sourced. Compared to the early xenotime-(Y), the late xenotime-(Y) is richer in HREE and depleted in P, owing to the formation of the coexisting late florencite-(Ce). Moreover, early florencite-(Ce) has a near end-member florencite (s.s.) composition similar to those associated with unconformity-related U deposits, whereas late florencite-(Ce) sits on the florencite-svanbergite compositional spectrum. The high U content of xenotime-(Y) and composition of early florencite-(Ce) potentially support a genetic association between the HREE mineralization and the coeval unconformity-related U deposits of northern Australia. Nevertheless, we also urge for caution in using xenotime-(Y) composition in isolation as an indicator of geological setting.

中文翻译：

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西澳大利亚北部不整合相关重稀土元素矿化中磷钇矿-(Y)和萤石-(Ce)的共生和组成

本研究调查了来自 Tanami 和 Hall Creek 地区重稀土元素 (HREE) 矿床/前景的磷钇矿 [(Y,HREE)PO4] 和萤石 [LREEAl3(PO4)2(OH)6] 的共生作用和矿石矿物组成西澳大利亚州。公认的磷钇矿-(Y) 形成有两个阶段：(1) 角砾岩（角砾岩托管）和石英-磷钇矿-（Y）脉（脉型）中的早期磷钇矿-（Y）；(2) 晚期磷钇矿-(Y) 主要作为预先存在的早期磷钇矿-(Y) 上的双锥体状过度生长而发生。类似地，萤石-(Ce)形成两个阶段，包括：(1)早期萤石-(Ce)与矿化脉内的早期磷钇矿-(Y)共存并被其包围；(2)晚期萤石-(Ce)取代早期磷钇矿-(Y)，或在早期萤石-(Ce)上表现为窄边。来自许多检查的 HREE 矿床/前景的所有磷钇矿 (Y) 类型的特征是 U 含量升高和显着的 Eu 负异常，我们认为这些异常是从变质沉积岩继承的，其中 REE 和 P 是磷酸盐矿矿化所需的，是来源。与早期磷钇矿-(Y)相比，晚期磷钇矿-(Y)由于形成了共存的晚期萤石-(Ce)而富含HREE而贫P。此外，早期的萤石-(Ce) 的近端元萤石 (ss) 成分类似于与不整合相关的 U 矿床相关的成分，而晚期的萤石-(Ce) 位于萤石-钒钛矿的成分谱上。磷钇矿 (Y) 的高 U 含量和早期萤石 (Ce) 的组成可能支持 HREE 矿化与澳大利亚北部与同期不整合相关的 U 矿床之间的成因关联。尽管如此，我们也敦促在单独使用磷钇矿（Y）成分作为地质环境指标时要谨慎。