The　Dulong　deposit　is　a　major　cassiterite-sulfide　skarn　deposit　in　Southwest　China,　hosting　significant　In　resources　(7,000t).　Although　the　occurrence　of　In　has　been　studied　in　detail,　its　spatiotemporal　distribution　and　controlling　factors　remain　poorly　understood.　This　study　therefore　systematically　analyzes　fluid　inclusions,　chlorite　geochemistry,　and　combined　with　published　In　contents　from　sphalerite　to　comprehensively　examine　ore-forming　fluid　evolution　and　its　impact　on　In　mineralization.　The　fluid　inclusions　data　show　that　S-type,　Ltype,　and　V-type　can　be　recognized　at　Dulong.　The　S-type　inclusions　predominantly　occur　in　pyroxene　from　prograde　stage　and　coexist　with　L-type　inclusions,　suggesting　that　fluid　boiling　occurred.　The　homogenization　temperature　and　salinity　of　fluids　show　a　significant　decrease　from　prograde　stage　(468-560　degrees　C,　44.7-49.6　%　NaCleqv)　to　retrograde　stage　(365-375　degrees　C,　3.1-3.7　%　NaCleqv),　indicating　potential　mixing　with　meteoric　waters.　From　retrograde　to　sulfide　stage,　both　temperature　and　salinity　decrease　slightly　(from　365-375　degrees　C　to　210-365　degrees　C,　and　3.1　%-3.7　%　NaCleqvto　0.3　%-2.6　%　NaCleqv,　respectively),　inferring　that　fluid　cooling　probably　was　the　key　factor　for　sulfide　precipitation　and　associated　In　enrichment.　The　chlorite　results　show　that,　from　bottom　to　top　of　the　open　pit,　this　variation　in　trace　element　concentrations　is　dominantly　related　to　the　decrease　in　temperature　that　occurs　during　the　migration　of　hydrothermal　fluid.　The　fluid　temperatures　correlate　with　increased　In　concentrations　in　sphalerite,　suggesting　temperature　controls　In　enrichment.　Additionally,　the　Ti/Sr　ratio　in　chlorite　indicate　the　possible　hydrothermal　center　at　the　bottom　of　the　Manjiazhai　ore　block　(approximately　1152　m-depth),　implying　that　the　Dulong　deposit　is　probably　a　distal　skarn　deposit.