The　Great　Xing＇an　Sn-polymetallic　metallogenic　belt　in　Inner　Mongolia　is　a　potential　district　for　indium　(In)　resources,　where　In　mineralization　has　been　discovered　in　the　Dajing　Sn-Cu　polymetallic　deposit,　but　the　occurrence　of　In　is　not　well　understood.　In　this　contribution,　detailed　mineralogical　investigations　of　In-bearing　minerals　in　the　Dajing　Sn-Cu　deposit　were　conducted,　based　on　fieldwork　and　ore　petrography,　combined　with　whole-rock　analysis,　EPMA,　and　LA-ICP-MS.　Three　ore-forming　stages　and　six　types　of　sphalerite　are　distinguished.　The　highest　In　content　(average　0.18　wt%)　is　observed　in　earlier　exsolved　sphalerite　(Ia)　in　the　Cu-Sn　stage,　other　types　of　sphalerite　contain　relatively　lower　In　concentration,　with　the　average　value　ranging　from　16　to　478　ppm.　Overall,　sphalerite　in　the　Cu-Sn　stage　is　more　enriching　in　In　than　that　in　the　Pb-Zn　stage.　Indium　mainly　occurs　as　solid　solution　in　sphalerite.　Other　minerals　such　as　stannite　and　chalcopyrite　(Ia)　exhibit　relatively　elevated　In　concentration　(average　＞202　ppm).　Cassiterite,　pyrite,　and　pyrrhotite　show　negligible　In　content　typically　below　10　ppm.　Combined　with　previous　studies　on　ore-forming　fluids,　indium　mineralization　in　the　Dajing　deposit　is　mainly　associated　with　early-stage　Cu-Sn　fluids.　The　enrichment　of　In　in　sphalerite　is　probably　attributed　to　the　migration　and　diffusion　of　In　in　the　Cu-Sn　fluid　during　high-temperature　conditions.　Local　dynamic　processes　(exsolution,　diffusion,　etc.)　possibly　have　facilitated　In　mineralization　in　sphalerite.　This　study　reveals　the　occurrence　and　distribution　patterns　of　In　in　the　Dajing　deposit,　promotes　the　recovery　and　utilization　of　In　resources,　and　proposes　new　insights　into　the　enrichment　mechanisms　and　potential　assessment　of　In.　©　2023