Heterogeneous incorporation of trace elements at the microscale and nanoscale during episodic epitaxial growth of pyrite.

Understanding the complex interplay between the processes of mineral crystallization and the incorporation of trace elements, particularly in economically significant deposits like Carlin-type gold systems, is essential for unraveling geological processes. This study investigates the microscale to nanoscale texture and composition of weakly deformed arsenian pyrite from the Shangmanggang Carlintype Au deposit in Southwest China, employing advanced techniques such as scanning transmission electron microscopy and atom probe tomography. Trace element-rich oscillatory zones in the pyrite are characterized by ~30-nm-thick bands enriched in As, Au, and Cu. Cu, As, Sb, Pb, Hg, and Tl are distributed heterogeneously and form clusters and discontinuous planar features on the outer edge of As-rich oscillatory bands. Discontinuous planar features, nucleating from trace element-enriched clusters, are oriented approximately in line with the direction of epitaxial growth. The nanoscale epitaxial growth zones are likely the result of the incorporation of impurity defects coupled with diffusion-limited self-organization and fluctuations in fluid composition. Arsenic-induced lattice distortion facilitates surface adsorption of dopant trace metals, which leads to "unstructured" impurities (Sb, Pb, Hg, and Tl) clustering locally in misfit crystal defects. The transition from homogeneous element distribution in As-rich bands to clustered trace elements suggests a Stranski-Krastanov growth process. Discontinuous planar features may represent the propagation of crystal defects locally and the further incorporation of trace elements. Our study provides insights into the factors governing the heterogeneous incorporation of trace elements, particularly Au, into pyrite during epitaxial growth. [ABSTRACT FROM AUTHOR]