川西扎乌龙-青海草陇花岗伟晶岩型稀有金属矿床磷灰石地球化学特征及地质意义

扎乌龙-草陇锂矿床位于松潘-甘孜造山带中西部，为典型的花岗伟晶岩型稀有金属矿床。前人基于矿区花岗岩和伟晶岩紧密的时空及成因关系，认为伟晶岩与白云母花岗岩同源且成矿与花岗质岩浆的分异相关。然而，岩浆分异演化过程中熔体的信息记录及其何种地质过程对成矿起主导作用，仍缺乏有效制约。本文对矿区花岗质岩浆来源及其演化过程开展了研究，即对白云母花岗岩、14号成矿伟晶岩脉进行了精细的磷灰石微区原位分析测试。结果显示，磷灰石具有高的Sr同位素、高F低Cl及还原性质特征，指示了扎乌龙矿区初始岩浆源自于造山过程中深部三叠纪复理石沉积物的部分熔融作用。岩浆磷灰石记录了白云母花岗岩从中间相至边缘相，Th、U、Mn含量以及Th/U值升高，REEs、Y以及F含量降低；流体交代磷灰石则记录了伟晶岩阶段变化的但整体偏高的Th、U、Mn含量以及Th/U值，降低的REEs、Y以及F含量。这些地球化学的系统变化充分表明，白云母花岗岩为较原始的岩浆，伟晶岩为岩浆高度演化的产物。从白云母花岗岩到伟晶岩的岩浆演化过程中，经历了斜长石、钾长石、云母、锆石、独居石、榍石、石榴石和磷灰石的分离结晶作用。当岩浆演化到伟晶岩阶段时，熔体氧逸度升高并高度富集H₂O、F等挥发性组分，导致了熔体结构发生实质性变化并有利于Li、Be等稀有金属元素的富集。研究表明，花岗质岩浆的高度分异是花岗伟晶岩型稀有金属矿床成矿的关键控制因素。

The geochemical characteristics and their geological significance of apatite from the Zhawulong-Caolong granitic pegmatite-hosted rare metal deposit in Sichuan and Qinghai provinces, West China

The Zhawulong-Caolong lithium deposit is a typical granitic pegmatite-hosted rare metal deposit which explored in the mid-western Songpan-Ganze orogenic belt. Based on the close spatial-temporal and genetic relations between the muscovite granite and pegmatite in this region, previous studies have suggested that they were originated from the same magma source and the metallogeny is related to the magma fractionation. The information during the magma evolution process and whether the nature of the magmatic source or magmatic evolution process control lithium ore formation, however, are poorly constrained. This study focuses on the magmatic source and the evolution process by in-situ analyzing the apatite which produced from the muscovite granite and No.14 pegmatite. In combination of the evidence such as Sr isotope (0.7211~0.7333 for muscovite vs. 0.7134~0.7153 for No.14 pegmatite), high F but low Cl content, and the reduced magma nature source recorded by apatites, suggest that the primary magma was derived from the Triassic flysch sediments in the deep crust. From central phase of the muscovite granite to the marginal phase, Th, U, Mn contents and Th/U ratio of magmatic apatite increase; in contrast, REEs, Y and F contents decrease; similar variations are also recorded in the fluids altered apatite in the No.14 pegmatite. Such systematic variations imply that muscovite granite and pegmatite are cogenetic and muscovite granite represents the more primary melt, whereas pegmatite is a more evolved melt. During granitic magma evolution, mineral phase such as plagioclase, K-feldspar, muscovite, zircon, monazite, titanite, garnet, and apatite are crystallized and thus melt have fractionated. In the more evolved pegmatite, oxygen fugacity exchanged to the oxide state and the volatile contents (such as H₂O and F) are more enriched. Such changes might change the melt structure and composition, which may be benefit to the Li-Be metallogeny in the Zhawulong deposit. Accordingly, we conclude that the highly magma fractionation is the key controlling factors of granitic pegmatite-hosted rare metal deposit.