Alteration zonation and mineralogy of the Dibaonamugang Lithocap: Implications for mineral exploration in the Duolong Ore District, NW Xizang (Tibet), China

• Lithocap is a landmark for locating potential deep porphyry mineralization. • Dibaonamugang Lithocap is formed in a high–sulfidation epithermal system. • The porphyry–type metallogenic system may be situated beneath and to the southeast of the Dibaonamugang lithocap. • The terrestrial volcanic rock–covered areas within the BNMB are the prospecting targets for porphyry–epithermal deposits. Lithocaps are usually formed at the top of porphyry–epithermal metallogenic systems, exhibiting distinctive mineral assemblages and white tones that render them a notable prospecting indicator for potential deep porphyry–type mineralization. The Dibaonamugang lithocap is the largest exposed hydrothermal alteration system in the Duolong Ore District of NW Xizang (Tibet), China; however, associated porphyry–epithermal mineralization has yet to be identified. In this study, detailed field work and microscopic examination, combined with 1:10,000 geological mapping, short–wave infrared spectroscopic testing, whole–rock geochemistry, and in situ LA–ICP–MS analysis, were conducted to examine the mineralogical and geochemical characteristics of the lithocap and its exploration indications. Our research revealed that the Dibaonamugang lithocap shows typical high–sulfidation epithermal alteration mineral assemblages and zonation patterns: Zone I, a typical residual silica core with massive and vuggy quartz–alunite; Zones II–IV show advanced argillic alteration with quartz–alunite–dickite–pyrophyllite–kaolinite–muscovite assemblages; Zone V, argillic alteration mainly comprises kaolinite–illite–montmorillonite and an outermost zone of propylitic (chlorite–epidote–kaolinite–montmorillonite–siderite) assemblages. The alteration assemblages and zonation patterns reflect decreasing acidity and temperature during the lateral flow of hydrothermal fluids from the central silicic cores to the exterior. The Dibaonamugang lithocap exhibits a hypogene origin superimposed by a later supergene environment, and its extension is controlled by structural (fracture and unconformity) and lithological (protolith composition and permeability) factors. Short–wave infrared spectral results, whole–rock and mineral chemistry strongly suggest the presence of a porphyry–high sulfidation epithermal metallogenic system situated beneath and to the southeast of the Dibaonamugang lithocap. These results imply great potential for discovering independent high–sulfidation epithermal Au (Cu) deposits within both the Duolong Ore District and the broader terrestrial volcanic–covered region of the Bangong–Nujiang Metallogenic Belt.