DistributionofCo-Niinmafic.ultramaficlayeredintrusion andimplicationsforformationofmagmaticdeposits:AcasestudyoftheStillwaterComplex

The Still water Complexis one oft he large layered intrusions on Earth and consists of Basal Series,Ultramafic Series,and Banded Series.This study aim store vealth efactors controlling the distribution of nickel (Ni) and cobalt (Co) contents in olivine, pyroxene,chromite,and whole.rocks from different rock series of the Still water Complex.In the Ultramafic Series,Ni and Cocontents in olivine range from 2070 x 10(-6) to 3019 x 10(-6) and 105 x 10(-6) to 205 x 10(-6),respectively,and chromite has Ni contents of 434 x 10(-6) similar to 1843 x 10(-6) and Co of 221 x 10(-6) similar to 737 x 10(-6), both higherth an orthopyroxene (Ni: 464 x 10(-6) similar to 678 x 10(-6);Co:31 x 10(-6) similar to 95 x 10(-6)),and clinopyroxene (Ni:237 x 10(-6)similar to 378 x 10(-6);Co:15 x 10(-6) similar to 45 x 10(-6)).Stratigraphic profile shows that olivine from the Lowest Cyclic Unithasthehighest Cocontent of 173x10(- 6) similar to 193 x 10(-6) on massivechromititeoftheG.HCyclicUnitscontainsthelowestCocontentsof125x10-6 similar to 141x10-6.Accordingly,themassive olivine cumulates contribute to the distinctly decreasing Ni contentsin hromite from chromitites in the other yclic Units (B Cyclic Unit: 700 x 10(-6)similar to 1843 x 10(-6);G.H Cyclic Units:641 x 10(-6) similar to 1206 x 10(-6);J.K Cyclic Units:1046 x 10(-6) similar to 1135 x 10(-6))to chromite from silicate cumulates in the Lowest Cyclic Unit having the lowest Ni contents of 434 x 10(-6) similar to 558 x 10(-6).In addition,themineral modal ratios of olivine and chromite avea distin ctlynegative correlation witht he Co/Nivalues of the whole.rocks,further suggesting the controlling effects of olivine on Ni and chromiteonCo.In the Banded Series,due to the limite damounts of olivine and chromitepresent, the Ni and Cocontents of orthopyroxene(Ni:375 x 10(-6)similar to 652 x 10(-6);Co:101 x 10(-6)similar to 112 x 10(-6)) and clinopyroxene(Ni:278x 10(-6) similar to 384 x 10(-6);Co:41 x 10(-6) similar to 56 x 10(-6))are slightly higher compared with those in the Ultramafic Series.None theless,the Ni and Cocontents of the whole rocks in the Banded Series(Ni:88 10(-6) similar to 947x10(-6);Co:21x10(-6) similar to 53x10(-6))are significantly lower than those in the Ultramafic Series(Ni:698 x 10(-6) similar to 1755 x 10(-6);Co:99 x 10(-6) similar to 207 x 10(-6)),sugges ting that the massivecumulates of olivine and chromite caused the depletion of Ni and Coin theme lts and baresulfidemineralizationinlargelayeredintrusions.The platinumgroupelements(PGEs) concentrated in liquid sreleased during chromitecry stallization may beessential for the formation of PGE deposits.The J.M ReefandPicketPinin OB.Iand OB.V indicate the sulfidesaturation andse gregation,as well as the precipitated PGEs from liquid stosulfides in the lower Banded Seriesand the Middle Banded Series

Automated summary

This study investigates the factors controlling the distribution of nickel (Ni) and cobalt (Co) contents in different rock series of the Stillwater Complex. It finds that in the Ultramafic Series, olivine has a Ni range of 2070 x 10(-6) to 3019 x 10(-6) and Co range of 105 x 10(-6) to 205 x 10(-6), while chromite has Ni contents of 434 x 10(-6) to 1843 x 10(-6) and Co contents of 221 x 10(-6) to 737 x 10(-6). The stratigraphic profile reveals that olivine from the Lowest Cyclic Unit has the highest Co content of 173x10(- 6) to 193 x 10(-6), while the G.H Cyclic Units have the lowest Co contents of 125x10(-6) to 141x10(-6).