Apatite as a magma redox indicator and its application in metallogenic research
Apatite as a magma redox indicator and its application in metallogenic research
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磷灰石作为岩浆氧化还原指示剂及其在成矿研究中的应用
DOI：
10.1016/j.lithos.2022.106749
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发表时间：
2022
期刊：
影响因子：
3.5
通讯作者：
Zhiyong Zhang
中科院分区：
文献类型：
--
作者：
Hairuo Wang;Keda Cai;Min Sun;Xiao-Ping Xia;Chun-Kit Lai;Pengfei Li;Bo Wan;Zhiyong Zhang
磷灰石作为岩浆中的早期结晶相，可容纳多种多价阳离子，具有抗风化和热液蚀变的能力。这些特征使磷灰石能够记录前体岩浆的初级氧化还原状态。在这里，我们展示了图拉苏盆地（中亚西天山造山带）浅成热液金矿大哈拉君山组火山岩中磷灰石和锆石颗粒的新电子探针微分析（EPMA）和激光烧蚀-电感耦合等离子体质谱（LA-ICP-MS）地球化学数据。计算的锆石Ce-/Ti基氧压计结果和磷灰石硫含量表明火山岩母岩浆相对氧化。此外，我们编制了区域磷灰石化学数据集，以评估磷灰石中的其他元素（Mn、V、Eu、Ce、As 和 Ga）是否可以作为岩浆氧化还原代理。磷灰石Mn与全岩MgO呈明显的负相关关系，说明岩浆分异作用对磷灰石Mn含量的控制。此外，通过Mn-in-磷灰石氧压计计算的氧逸度（f O 2 ）与岩浆分馏密切相关，这表明分馏结晶（而不是f O 2 ）控制着磷灰石中Mn的吸收。磷灰石 As 预算对 f O 2 变化敏感，但与非桥接氧与四面体阳离子的比率 (NBO/T)、全岩 SiO 2 或铝饱和指数没有任何相关性。相反，磷灰石V和Ga含量与全岩SiO 2 和NBO/T有明显相关性，但与f O 2 没有相关性，磷灰石Eu和Ce异常与f O 2 没有相关性。因此，我们得出只有磷灰石As和S含量才能反映岩浆氧化还原状态的结论。大哈拉君山组火山岩计算的f O 2 为ΔFMQ+0.53±0.52（基于铁橄榄石+磁铁矿+石英缓冲剂），明显低于全球典型斑岩铜成矿岩浆的f O 2 。因此，从岩浆f O 2 角度来看，推测区域岩浆形成斑岩铜矿床的潜力不大。 • 通过S-in-磷灰石获得的准确f O 2 值显示出替代锆石氧压计的潜力。 • 磷灰石中的S、As可以代替Mn、V、Eu、Ce、Ga记录岩浆f O 2 值。 • 通过岩浆f O 2 分析构造环境和斑岩铜成矿潜力。
As an early crystallizing phase in the magma, apatite can accommodate a wide range of multivalent cations and has a capacity resistant to weathering and hydrothermal alteration. These features enable apatite to record the primary redox state of precursor magma. Here, we present new electron probe microanalysis (EPMA) and laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) geochemical data on apatite and zircon grains from the epithermal gold ore-hosting Dahalajunshan Formation volcanics in the Tulasu basin (Western Tianshan Orogen, Central Asia). Calculated zircon Ce-/Ti-based oxybarometric results and sulfur content of apatite suggest that the parental magma of the volcanics was relatively oxidized. Furthermore, we compiled a regional apatite chemical dataset to assess whether other elements (Mn, V, Eu, Ce, As and Ga) in apatite can serve as a magma redox proxy. Negative correlation between apatite Mn and whole-rock MgO is evident, implying the control of magma fractionation on apatite Mn contents. Also, oxygen fugacity ( f O 2 ) calculated by Mn-in-apatite oxybarometer correlates strongly with magma fractionation, which indicates that fractional crystallization (instead of f O 2 ) controlled the Mn-uptake in apatite. The apatite As budget is sensitive to f O 2 variation but does not show any correlation with the ratio of nonbridging oxygens to tetrahedral cations (NBO/T), whole-rock SiO 2 , or aluminum saturation index. In contrast, apatite V and Ga contents correlate obviously with whole-rock SiO 2 and NBO/T but not f O 2 , and apatite Eu and Ce anomalies show no correlation with f O 2 . Therefore, we conclude that only the apatite As and S contents can reflect the magma redox state. The calculated f O 2 of the Dahalajunshan Formation volcanic rocks is ΔFMQ+0.53 ± 0.52 (based on the fayalite+magnetite+quartz buffer), which is markedly lower than those of typical porphyry Cu ore-forming magmas worldwide. Thus, from the perspective of magma f O 2 , regional magma is inferred to have little potential to form the porphyry Cu deposit. • Accurate f O 2 values by S-in-apatite show the potential to replace zircon oxybarometer. • S and As in apatite can record the magma f O 2 value, instead of Mn, V, Eu, Ce, and Ga. • Tectonic setting and porphyry Cu ore-forming potential were analyzed by magmatic f O 2 .