Interaction Between Mineralization and Rock Magnetization: New Constraints From a Silurian‐Lower Devonian Volcanogenic Massive Sulfide (VMS) Deposit.

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 magnetite, which can carry a remagnetization direction, is proposed to be formed during illitization via the smectite‐to‐illite transformation. Secondary superparamagnetic magnetite, which was most likely formed during the late stage of chloritization, is unable to carry the stable characteristic remanent magnetization. The site‐mean direction of high‐temperature and high‐coercivity components is Dg/Ig = 324.5°/43.1°, and kg = 35.1, with α95 = 6.8° before tilt correction, and Ds/Is = 316.2°/37.6°, and ks = 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. Plain Language Summary: We conducted paleomagnetic, rock magnetic, petrographic, and X‐Ray diffraction studies on volcanogenic massive sulfide (VMS) deposit to better understand the interaction between mineralization, hydrothermal alteration, and magnetization in this kind of deposit. Magnetite is the main magnetic carrier of orebodies and surrounding rocks. The overall decrease in magnetite concentration from chloritized samples to orebodies, via silicified samples, explains the low magnetic anomalies in VMS deposits. However, in samples containing a high concentration of chlorite, a significant amount of secondary superparamagnetic magnetite was discovered. Secondary single domain magnetite is ascribed to be formed through the transformation of smectite to illite during hydrothermal alteration, providing an explanation for remagnetization in VMS deposits. Therefore, magnetite consumption and secondary magnetite formation occurred during different types and stages of hydrothermal alteration. The site‐mean paleomagnetic direction is calculated, but it cannot be used in plate reconstruction due to the unclear bedding attitudes prior to mineralization and the possibility of remagnetization during burial alteration. This research improves our understanding of the processes of magnetic mineral variation and remagnetization during VMS mineralization. Key Points: Magnetite is the major magnetic carrier of hydrothermally altered surrounding rocks and orebodiesMagnetite consumption occurred from chloritization via silicification to mineralizationRock magnetism reveals the neoformation of superparamagnetic and single domain magnetite during chloritization and illitization, respectively [ABSTRACT FROM AUTHOR]