Apatite　is　a　common　accessory　mineral　in　iron　oxide-apatite　(IOA),　magmatic　Fe-Ti　oxide,　and　metamorphosed　sedimentary　Fe　deposits.　Apatite　chronology　and　oxygen　isotopes　in　the　IOA　deposits　have　been　extensively　studied,　however,　such　information　in　the　metamorphosed　sedimentary　Fe　deposits　remains　poorly　understood.　Here,　we　report　detailed　trace　elements,　oxygen　isotopes,　and　U-Pb　chronology　of　apatite　from　the　Tianhu　metamorphosed　sedimentary　Fe　deposit　in　the　eastern　Tianshan,　NW　China.　To　our　knowledge,　this　is　the　first　report　on　the　in　situ　oxygen　isotopes　of　apatite　from　the　metamorphosed　sedimentary　Fe　deposits.　Cathodoluminescence　imaging　of　the　apatite　grains　from　the　Tianhu　massive　Fe　ores　show　a　homogeneous　texture,　suggesting　that　they　were　formed　by　a　single　event　rather　than　multiple　superimposed　events.　These　apatite　grains　contain　abundant　fluid　inclusions,　and　show　relatively　high　δ18O　values　of　7.9　‰-14.0　‰　and　low　Th　and　U　contents,　which　are　consistent　with　their　metamorphic　hydrothermal　origin.　Laser　ablation-inductively　coupled　plasma-mass　spectrometry　(LA-ICP-MS)　dating　of　the　studied　apatite　grains　yielded　a　U-Pb　age　of　348.5　±　18.5　Ma,　indicating　that　the　metamorphic　enrichment　of　the　Tianhu　metamorphosed　sedimentary　Fe　deposit　occurred　considerably　later　than　the　Ordovician　ore-hosting　rocks.　Combined　with　previous　studies,　we　suggest　that　the　metamorphic　massive　ores　of　the　Tianhu　metamorphosed　sedimentary　Fe　deposit　formed　in　an　orogenic　setting.　Our　study　highlights　that　a　combination　of　trace　elements,　oxygen　isotopes,　and　U-Pb　chronology　of　apatite　can　be　used　as　powerful　tools　to　constrain　the　genesis　of　metamorphosed　sedimentary　Fe　deposits.　©　2023　The　Authors