Microstructures and element geochemistry of anatase from the Laozuoshan gold skarn deposit, NE China

Abstract

Rutile, anatase, and brookite are polymorphs of titanium dioxide (TiO₂), and occur as accessory minerals in various lithologies. They provide important information for revealing magmatic–hydrothermal ore formation, yet the mineralogical characteristics and genesis of hydrothermal anatase is not well established. In this study, we focus on the texture and geochemical composition of anatase from the auriferous ore (quartz–ankerite–pyrrhotite–arsenopyrite vein) and barren rock (quartz–ankerite vein) from the Laozuoshan deposit. Five types of anatase were discovered, including (1) type-AI and −BI anatase in auriferous ore and barren rock, characterized by being homogeneous and isolated without mineral inclusions; (2) type-AII and −BII anatase in auriferous ore and barren rock, usually contains some biotite, ankerite, zircon or apatite inclusions. Some type-AII anatase grains in the auriferous ore show patchy zoning; (3) type-AIII anatase (only in auriferous ore) is characterized by well-developed sector or normal zoning. High W content is distributed in the patches and sector zones of type-AII and −AIII anatase, which could be attributed to the W substitution for Ti in the anatase. We suggest that F-rich ore fluids could facilitate the W incorporation into the anatase crystal, and W-rich anatase can serve as an indicator mineral for gold skarn exploration.