The　Dulong　deposit　is　a　world-class　Sn-polymetallic　deposit　with　indium　mineralization,　which　is　associated　with　highly　evolved　Late　Cretaceous　S-type　granites,　indicating　the　magmatism　is　crucial　for　the　indium　enrichment.　Through　integrated　in-situ　geochemical　analyses　of　mica　and　apatite　across　variably　fractionated　granites　and　country　rocks,　this　study　reveals　a　systematic　evolution　of　redox　conditions,　halogen　chemistry,　and　metal　enrichment　during　magmatic　differentiation.　As　magmatic　evolution　progresses,　indium　and　tin　contentratons　in　mica　increase　progressively,　reaching　peak　vales　in　the　late　stage　of　evolution　at　Dulong　deposit.　Notably,　indium　concentration　in　muscovite　is　greater　than　that　in　biotite,　when　muscovite　converts　into　phengite.　Apatite　and　mica　compositions　indicate　low　oxygen　fugacity　(fO(2))　magmatism.　Fe-rich　biotite　in　Sn-In-bearing　granites　contrasts　with　Mg-biotite　in　Sn-poor　systems,　with　Fe3+/(Fe2++Fe3+)　ratios　＜　0.2　confirming　reduced　fO(2)　conditions　conducive　to　indium　melt　incorporation.　Apatite　geochemistry　reinforces　this:　low　SO3　(0.01-0.08　wt%),　As　depletion　(14.54-42.10　ppm),　and　marked　negative　Eu　anomalies　(Eu/Eu*　＜0.4).　Multi-proxy　evidence　collectively　confirms　a　reduced　magmatic　system.　Integrated　proxies　confirm　a　reduced　magmatic　system　where　progressive　redox　reduction　during　differentiation　fosters　indium　enrichment,　enhancing　metallogenic　potential.　Concurrently,　apatite　halogen　signatures　track　magmatic　evolution:　sustained　F　enrichment　with　late　Cl　spikes　aligns　with　mantle-derived　inputs　evidenced　by　mafic　enclaves.　Although　Cl　concentrations　remain　low　in　the　early　magmatic　stages,　their　subsequent　dramatic　increase　correlates　temporally　and　genetically　with　marked　enrichment　of　In　and　Sn　during　later　evolutionary　phases.　The　mixing　of　mantle-derived　magmas　may　bring　in　Cl-rich　fluids/melts　and　related　ore-forming　materials,　which　promotes　indium　mineralization.　The　concurrent　enrichment　of　halogen　elements,　F　and　Cl,　plays　a　crucial　role　in　the　extraordinary　accumulation　of　indium.