Types,temporal-spatial distribution and metallogenic lineage of ore deposits related to mantle-derived magma in northern Xinjiang

Mantle-derived magmatic ore deposits in northern Xinjiang are composed of chromite deposits,coppernickel sulfide deposits,platinumgroup elements(PGE)deposits,Cu-Ni～V-Ti-Fe composite deposits,cobaltbearing magnetite deposits,basalt-hosting native copper deposits,hydrothermal cobalt-polymetallic deposits and non-metallic deposits.Accordingtotypes of ore-bearing magmatic bodies,these ore deposits can be classifiedinto six types,i.e.,ophiolite type,layered intrusion type,minor intrusion type,Alaska type,hypabyssal type and extrusive rock type.These mantle-derived magmatic ore deposits can be divided into three series,namely,copper-nickel,vanadium-titaniumand ferrochrome series.Magmatic sources of these three series showsignificantly different features:the copper-nickel series with relatively abundant mafic tholeiitic basalts is significantly enrichedin Cu,Ni and Co;the vanadium-titaniumseries withiron-rich alkali basalts is enrichedin V,Ti and Fe;the ferrochrome series with magnesia-rich tholeiitic basalts is enriched in Cr.Therefore,the magmatic sources that had rich ore-forming elements andformed magmatic bodies constitutedthe main ore-forming conditions for these three series.The ore-forming mechanismof the three series can be dividedinto deep magmaticliquation and magmatic differentiation,in-situ liquation,ore magma injection and magmatic hydrothermal processes.Based onthe close relationships betweenthese series,we can construct theintegrated metallogenic model of the ore deposits related to mantle-derived magma.Mantle-derived magma fromdepleted mantle partial melting source might have experienced melt segregation and/or fractionation processes during their ascent,resulting in the association of these three series with different ore deposits.The external material that participated in the magmatic evoluationinthe deep crust couldformchromite,vanadium-titanium magnetite and copper-nickel sulfide deposits at different depths.When the evolved magma reached somewhere near the surface,they might combine with enriched fluid and ore-bearingfluid toformsubvolcanic magnetite and extrusive native copper deposits.The tectonic setting or tectonic stages of the ore deposits associated with mantle-derived magmain North Xinjiang can be classifiedinto three types as follows:i)the continental rift stage,which yielded copper-nickel deposits related to minor intrusions and iron-phosphate deposits associated with alkaline layered intrusions;ii)the plate subduction stage,which yielded ophiolite-associated chromite deposits and Alaska type copper-nickelPGE deposits;iii)collisionor post-collisionorogenicstage,whichcanbe dividedintothree sub-stages/processes:the post-collision stretching process yielded the basalt-associated native copper deposits,the mantle plume superi mpositon orogenic process yielded copper-nickel deposits relatedto minorintrusions and copper-nickel-vanadium-titanium-ironcomposite deposits relatedtolayeredintrusions,andthe collisiontermination or cratonization process yielded hypabyssal Co-bearing magnetite deposits and vanadium-titanium magnetite deposits associated with small layeredintrusions.