Magmatic　Fe-Ti　oxide　deposits　are　one　of　the　most　important　iron　deposit　in　eastern　Tianshan,　NW　China,　and　their　ore-forming　mechanism　remains　obscure.　Here,　we　use　trace　elements　and　O-Sr　isotopes　of　apatite　from　two　representative　magmatic　Fe-Ti　oxide　deposits　(Niumaoquan　and　Weiya)　in　the　eastern　Tianshan　to　constrain　the　genesis　of　ore　formation.　The　apatites　from　the　Niumaoquan　Fe-Ti　oxide　ores　exhibit　higher　Eu/Eu*　values,　lower　Mn　contents,　and　larger　REE　variations　than　those　from　the　Weiya　Fe-Ti　oxide　ores,　indicating　a　protracted　evolution　process　of　the　Niumaoquan　ore-forming　magmas　under　a　relatively　reduced　condition.　Specifically,　the　apatites　from　the　Niumaoquan　Fe-Ti　oxide　ores　can　be　divided　into　two　groups:　Group　1　with　relatively　low　REE　contents,　low　87Sr/86Sr　ratios　(0.70574–0.70641)　and　high　δ18O　values　(5.1–5.6‰),　and　Group　2　with　relatively　high　REE　contents,　high　87Sr/86Sr　ratios　(0.70703–0.70792)　and　low　δ18O　values　(2.8–3.3‰).　The　Group　1　apatites　formed　by　early　crystallization　in　the　mantle,　while　the　Group　2　apatites　formed　by　assimilation　of　low　δ18O-high　87Sr/86Sr　altered　rocks　during　magmas　emplacement　en　route　to　the　continental　crust.　Unlike　the　Niumaoquan　apatites,　the　apatites　from　the　Weiya　Fe-Ti　oxide　ores　have　relatively　homogeneous,　high　δ18O　values　(8.3‰-9.1‰)　and　87Sr/86Sr　ratios　(0.70798–0.70848),　indicating　involvement　of　continental　crustal　materials　in　their　mantle　sources.　Combined　with　previous　studies,　we　suggest　that　the　Niumaoquan　and　the　Weiya　Fe-Ti　oxide　deposits　formed　in　a　non-plume　tectonic　setting　but　they　originated　from　different　magmatic　sources.　Our　study　highlights　that　trace　elements　and　O-Sr　isotopes　of　apatite　can　be　used　as　powerful　tools　to　constrain　the　source　characteristics　and　ore-forming　processes　of　magmatic　Fe-Ti　oxide　deposits.　©　2023　The　Author(s)