中国地质大学（北京）邓军研究团队近日取得一项新成果。他们报道了成矿作用与岩石磁化作用的相互作用，即志留系—下泥盆统火山成因块状硫化物矿床的新约束。这一研究成果发表在2023年2月23日出版的国际学术期刊《JGR地球》上。

课题组人员通过对印度支那地块西北部大平掌火山成因块状硫化物矿床进行系统的古地磁、岩磁学、岩相学和x射线衍射研究来解决这一问题。磁铁矿是热液蚀变围岩和矿体的主要磁性载体。磁铁矿的消耗和次生磁铁矿的形成发生在不同的热液蚀变阶段和类型。磁铁矿浓度从绿泥石化、硅化到矿化的整体下降表明，磁铁矿主要是在热液蚀变过程中被消耗掉的。具有再磁化方向的次生单畴(SD)磁铁矿是在伊利石化过程中通过蒙脱石-伊利石转变形成的。次生超顺磁性(SP)磁铁矿不具有稳定的特征剩余磁化强度(ChRM)，极有可能形成于绿泥石化晚期。

高温和高矫顽力分量的位点均值方向为D_g/I_g = 324.5°/43.1°，k_g = 35.1，倾斜校正前α₉₅ = 6.8°，倾斜校正后D_s/ l_s = 316.2°/37.6°，k_s = 16.4， α₉₅ = 10.1°，经负折叠检验。然而，成矿后倾斜过程的不确定性和埋藏蚀变过程中再磁化的可能性限制了板块重建。因此，本研究为火山成因块状硫化物矿床的成矿过程中岩石磁性的变化和再磁化机制提供了依据。

据介绍，火山成因块状硫化物矿床的成矿作用、热液蚀变和岩石磁化之间的关系不明确，限制了对该类矿床磁异常和再磁化过程的全面认识。

附：英文原文

Title: Interaction between Mineralization and Rock Magnetization: New Constraints from a Silurian-Lower Devonian Volcanogenic Massive Sulfide (VMS) Deposit

Author: Xinwei Hu, Liang Gao, Qingfei Wang, Shihong Zhang, Xiang Sun, Shengchao Xue, Xin Tang, Zhenyu Yang, Jun Deng

Issue&Volume: 2023-02-23

Abstract: The unclear relationship between mineralization, hydrothermal alteration, and rock magnetization in volcanogenic massive sulfide (VMS) deposits limits us from fully understanding the magnetic anomalies and remagnetization process in this type of deposit. We address the issue by conducting systemic paleomagnetic, rock magnetic, petrographic, and X-Ray diffraction studies in the Dapingzhang VMS deposit on the northwestern Indochina Block. Magnetite is the dominant magnetic carrier of hydrothermally altered surrounding rocks and orebody. Magnetite consumption and secondary magnetite formation occurred at different stages and types of hydrothermal alteration. The overall decrease in magnetite concentration from chloritization via silicification to mineralization implies that the magnetite was mostly consumed during hydrothermal alterations. Secondary single domain (SD) magnetite, which can carry a remagnetization direction, is proposed to be formed during illitization via the smectite-to-illite transformation. Secondary superparamagnetic (SP) magnetite, which was most likely formed during the late stage of chloritization, is unable to carry the stable characteristic remanent magnetization (ChRM). The site-mean direction of high-temperature and high-coercivity components is D_g/I_g = 324.5°/43.1°, and k_g = 35.1, with α₉₅ = 6.8° before tilt correction, and D_s/I_s = 316.2°/37.6°, and k_s = 16.4, with α₉₅ = 10.1° after tilt correction, with a negative fold test. However, plate reconstruction is limited by the uncertainty of the tilting process following mineralization and the possibility of remagnetization during burial alteration. Therefore, this study provides a mechanism for rock magnetic variation and remagnetization during VMS mineralization.

DOI: 10.1029/2022JB025020

Source: https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2022JB025020