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U-Pb DATING OF HYDROTHERMAL TITANITE RESOLVES MULTIPLE PHASES OF PROPYLITIC ALTERATION IN THE OYU TOLGOI PORPHYRY DISTRICT, MONGOLIA
Economic Geology ( IF 5.5 ) Pub Date : 2020-12-01 , DOI: 10.5382/econgeo.4780
Lisa Hart-Madigan 1, 2 , Jamie J. Wilkinson 1, 2 , Stephanie Lasalle 3 , Robin N. Armstrong 2
Affiliation  

Oyu Tolgoi is a world-class, Late Devonian porphyry district in southern Mongolia. Because of its age and geodynamic setting, it has undergone a complex geological history that includes major postmineralization magmatic-hydrothermal events in close proximity to the porphyry deposits. The propylitic alteration halos that surround the Cu-Au deposits contain widespread hydrothermal titanite, as do the younger altered volcanic and intrusive rocks.Here, we present a comprehensive laser ablation-inductively coupled plasma-mass spectrometry U-Pb study on in situ, propylitic titanite from the Oyu Tolgoi district. The results identify district-wide hydrothermal alteration episodes that coincide with known magmatic events: Devonian porphyry mineralization (~372 Ma); the intrusion of granodiorite plutons and andesite dikes in the Carboniferous (~320–310 Ma); and the emplacement of the Permian Khanbogd Granite alkaline batholith (~290 Ma). Both Carboniferous and Permian alteration events variably overprint the earlier porphyry alteration halo. Overdispersion in the U-Pb data from some samples, due to Pb and/or U mobility, makes interpretation of some titanite ages more difficult, but further exemplifies the complex alteration history of the district. We conclude that U-Pb dating of propylitic titanite is a viable means by which explorers can identify alteration within a prospect that is synchronous with potentially fertile intrusions of known age. The extent of the coeval propylitic alteration and its mineral chemistry can then be used to assess the likelihood of a major porphyry center being present.

中文翻译:

水热钛矿的U-Pb约会解决了蒙古奥尤·托尔戈伊斑岩区的多相质变

奥尤陶勒盖(Oyu Tolgoi)是蒙古南部世界一流的泥盆纪斑岩地区。由于它的年龄和地球动力学背景,它经历了一个复杂的地质历史,包括靠近斑岩矿床的主要矿化后岩浆热液事件。围绕Cu-Au矿床的质变蚀晕包括大量的热液钛矿,以及较年轻的变质火山岩和侵入性岩石。在此,我们对原位生质的丙炔化蚀变激光-电感耦合等离子体质谱U-Pb进行了全面的研究Oyu Tolgoi地区的钛矿。结果确定了与已知岩浆事件一致的全区热液蚀变事件:泥盆纪斑岩矿化(〜372 Ma);石炭纪(〜320-310 Ma)侵入花岗闪长岩岩体和安山岩堤;和二叠纪Khanbogd花岗岩碱性岩基(约290 Ma)的位置。石炭纪和二叠纪蚀变事件均覆盖了较早的斑岩蚀变晕。由于铅和/或铀的迁移,某些样品的铀-铅数据过度分散,使某些钛矿年龄的解释更加困难,但进一步例证了该地区复杂的蚀变历史。我们得出的结论是,丙炔钛矿的U-Pb测年法是一种可行的方法,勘探者可以通过该方法在与已知年龄的潜在可育入侵同步的前景中识别出变化。然后可以使用同年龄的丙炔变化及其矿物化学的程度来评估存在主要斑岩中心的可能性。石炭纪和二叠纪蚀变事件均覆盖了较早的斑岩蚀变晕。由于铅和/或铀的迁移,某些样品的铀-铅数据过度分散,使某些钛矿年龄的解释更加困难,但进一步例证了该地区复杂的蚀变历史。我们得出的结论是,丙炔钛矿的U-Pb测年法是一种可行的方法,勘探者可以通过该方法在与已知年龄的潜在可育入侵同步的前景中识别出变化。然后可以使用同年龄的丙炔变化及其矿物化学的程度来评估存在主要斑岩中心的可能性。石炭纪和二叠纪蚀变事件均覆盖了较早的斑岩蚀变晕。由于铅和/或铀的迁移,某些样品的铀-铅数据过度分散,使某些钛矿年龄的解释更加困难,但进一步例证了该地区复杂的蚀变历史。我们得出的结论是,丙炔钛矿的U-Pb测年法是一种可行的方法,勘探者可以通过该方法在与已知年龄的潜在可育入侵同步的前景中识别出变化。然后可以使用同年龄的丙炔变化及其矿物化学的程度来评估存在主要斑岩中心的可能性。使某些钛矿时代的解释更加困难,但进一步说明了该地区复杂的蚀变历史。我们得出的结论是,丙炔钛矿的U-Pb测年法是一种可行的方法,勘探者可以通过该方法在与已知年龄的潜在可育入侵同步的前景中识别出变化。然后可以使用同年龄的丙炔变化及其矿物化学的程度来评估存在主要斑岩中心的可能性。使某些钛矿时代的解释更加困难,但进一步说明了该地区复杂的蚀变历史。我们得出的结论是,丙炔钛矿的U-Pb测年法是一种可行的方法,勘探者可以通过该方法在与已知年龄的潜在可育入侵同步的前景中识别出变化。然后可以使用同年龄的丙炔变化及其矿物化学的程度来评估存在主要斑岩中心的可能性。
更新日期:2020-12-18
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