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首页> 外文期刊>Contributions to Mineralogy and Petrology >Crystal chemistry of titanite from the Roxby Downs Granite, South Australia: insights into petrogenesis, subsolidus evolution and hydrothermal alteration
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Crystal chemistry of titanite from the Roxby Downs Granite, South Australia: insights into petrogenesis, subsolidus evolution and hydrothermal alteration

机译：Titanite的水晶化学来自Roxby Downs Granite，南澳大利亚：洞察性洞察力，血上的进化和水热改变

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摘要

Titanite textures and chemistry have been investigated from the Roxby Downs Granite, host to the Olympic Dam Cu-U-Au-Ag deposit, South Australia. Three textural subtypes of titanite are documented: primary magmatic (cores and rims); deuteric; and hydrothermal (low T recrystallisation). Magmatic cores are defined by enrichment in LREE (similar to 3 wt%), Nb (up to 1 wt%) and Zr relative to rims, which typically contain<1 wt% LREE and Nb, as well as greater concentrations of Al, Ca, Fe and F. Deuteric titanite occurs as overgrowths on pre-existing titanite and other magmatic accessory minerals (magnetite and ilmenite), and is depleted in HFSE compared to magmatic rims, showing geochemical trends consistent with substitution of Ca2++Ti4+REE3++(Al, Fe)(3+). Hydrothermal titanite forms as a low-temperature hydrothermal overprint on primary titanite as well as an alteration product of chloritised phlogopite. Applying Zr-in-titanite geothermometry, three temperature ranges are obtained for titanite crystallisation: magmatic cores similar to 765 to 780 degrees C; rims similar to 705 to 740 degrees C; and deuteric similar to 680 to 690 degrees C. Titanite breakdown is a ubiquitous feature of the Roxby Downs Granite, and occurs through interaction with CO2- and F-rich fluids, forming pseudomorphs characterised by the presence of REE-fluorocarbonates, which are subsequently overprinted by REE-phosphates with increased proximity to the Olympic Dam Breccia Complex. This change is related to interaction with fluids containing appreciable PO42- liberated from local dissolution of fluorapatite. Such observations are consistent with and linked to later/retrograde stages in the formation of the Olympic Dam deposit.
机译：已经从Roxby Downs Granite调查了钛铁矿纹理和化学，宿主到南澳大利亚奥林匹克大坝Cu-U-Au-Ag押金。记录了三种纹理亚型亚型亚型：主要岩岩（核心和轮辋）; de和水热（低T重结晶）。岩浆芯通过富集（类似于3wt％），Nb（最多1wt％）和Zr相对于轮辋而定义，其通常含有<1wt％的lee和Nb，以及更大浓度的Al，Ca ，Fe和F.氘代钛矿作为预先存在的二氧化钛和其他岩浆附件矿物质（磁铁矿和ilmenite）的过度生长，并且与岩浆轮辋相比，HFSE耗尽，显示了与Ca2 ++ Ti4 + Ree3 ++的替代成一致的地球化学趋势（ Al，Fe）（3+）。水热量是初级二钛矿的低温水热套印形式，以及氯化磷酸盐的改变产物。施加Zr-In-Tianite地质测定法，获得三个温度范围，用于二钛矿结晶：类似于765至780摄氏度的岩浆芯;边缘类似于705至740摄氏度;与680至690摄氏度相似的纯钛矿次级是Roxby倒下花岗岩的无处不在的特征，并通过与CO 2和F的流体的相互作用，形成通过REE-氟碳化合物的存在，其特征在于，随后覆盖通过REE-磷酸盐增加到奥林匹克坝Breccia复合物的邻近。这种变化与与含有氟磷灰石局部溶解的含有可观的PO42的流体的相互作用有关。这种观察结果与奥林匹克坝床形成的后续/逆行阶段一致。

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