Relationship Between Orogenic Gold Mineralization and Crustal Shearing Along Ailaoshan‐Red River Belt, Southeastern Tibetan Plateau: New Constraint From Paleomagnetism

Abstract

AbstractA new perspective on the relationship between orogenic gold mineralization and crustal shearing is presented in this case study on the gold deposits along Ailaoshan‐Red River shear zone (ARSZ), southeastern Tibetan Plateau. The sinistral ductile shearing along the zone occurred from ca. 31 to 17 Ma resulting in a displacement of ~1,000 km. A series of orogenic gold deposits, represented by the Zhenyuan and Chang'an deposits, occur on western margin of the ARSZ. The timing of mineralization and its relationship to shearing continues to be debated despite extensive geological and geochemical studies. Here we try to clarify this issue by using paleomagnetism to constrain the paleolatitude of mineralized rocks. High temperature magnetization components were isolated from the mineralized rocks, and they record modification by ore‐forming fluid. Their magnetization yields a paleolatitude of 19.9° ± 3.6°N for the Zhenyuan deposit and 16.2° ± 2.9°N for the Chang'an deposit. The paleolatitudes from these deposits are similar to those of ca. 20 Ma strata (19.0° ± 3.6°N), deposited after the large‐scale shearing. By contrast, they differ significantly from the paleolatitude obtained from ca. 130 to 40 Ma strata (28.4° ± 1.1°N), which formed long before the onset of large‐scale shearing. These observations imply that the orogenic gold mineralization occurred after the main offset and associated ductile deformation of the ARSZ. Gold mineralization is thought to be related to ore‐forming fluids and metals derived from the subcrust, rather than from fluids released from shearing‐induced metamorphism of regional strata.