Electronic supplementary material - Table 1. Field relationships and Petrography of Wadi Rajmi Chromitites

Locality Distance Sample GPS Field relationships Mineralogy Order of Petrography below nos (WGS84) crystallisatio Moho (m) n Rajmi 100-130 05-15 0425241 Several metres thick, dips Chromite, Chromite – Chromite forms large (5mm) subhedral grains, free north 03-16 2724404 steeply, concordant with the clinopyroxene, clinopyroxene of inclusions; core compositions cr# = 0.601-0.594, mantle layering and the Moho; magnesio- – magnesio- fe# = 0.443-0.384. Several grains zoned with interlayered with norite and in hornblende, hornblende decreasing cr# from core to rim. Chromite cores places contains irregular pods of plagioclase have the highest TiO2 concentrations recorded in olivine gabbro from a few this transect (0.32-0.60 wt %). Clinopyroxene centimeters to tens of (mg# 0.947-0.968) grains are up to 2mm in centimeters wide; whole mass is diameter and smaller grained, interstitial to enclosed within harzburgite. chromite, frequently rimmed by

magnesiohornblende. Plagioclase (ca An70), chlorite, epidote and sphene are accessory phases. Olivine is absent. Rajmi 200 03-18 0425245 Several metres thick and Chromite, Chromite – Chromite forms large (5mm) elliptical grains, with south 2724256 strongly serpentinised. magnesio- magnesio- irregular grain boundaries rimmed with hornblende, hornblende magnesiohornblende; cores vary from cr# 0.569- 523, fe# 0.427-0.382. Zoning, is from a low chrome core (cr# 0.525), to an enriched margin (cr# 0.545), to a low chrome rim (cr# 0.515). Ti concentrations in chromite cores are between 0.3 and 0.46 wt %

TiO2. Maharra 490-500 04-24 0426238 5m thick sill in harzburgite; dips Chromite, Chromite – Top of sill subhedral chromite grains, up to 4 mm south 04-25 2721975 at low angle; dunite sheath with Orthopyroxene (Olivine)- in diameter (cr#=0.519-0.516, fe#=0.309-0.330) in 04-26 a sharp upper contact and Clinopyroxene orthopyroxene a matrix of orthopyroxene (mg# 0.926) and gradational lower contact Olivine, + clinopyroxene (mg# 0.931-0.948). Small chromite comprising lenses and schlieren clinopyroxene grains in orthopyroxene. The pyroxenes are altered of chromitite in dunite – magnesio- to epidote, chlorite and uralite. hornblende Centre subhedral chromite up to abut 3 mm in diameter (cr#=0.537, fe#=0.339-0.342) interstitial olivine (Fo=0.944). The chromite is zoned (core to rim cr# 0.535 to 0.515) with olivine inclusions. Base more dunitic (75% chromite) - chromite grains (core compositions cr#=0.532-0.538, fe#=0.348-0.342) are up to 5 mm across and zoned (core cr#=0.538, rim cr#-0.509), with lower Fe(III) than the centre and top of the sill; contains olivine inclusions. Olivine grains (Fo 0.944-0.946) up to 4 mm, zoned with Mg-poor cores. Olivine altered to serpentine, calcite and tremolite.

Maharra 550 04-23 0426250 4.5m thick sill in harzburgite; Chromite Chromite – Centre of sill subhedral and irregular chromite, up north 04-22 2722026 dips at low angle; gradational Orthopyroxene orthopyroxene to 2 mm (cr# 0.543-0.527, fe# 0.304-0.330) matrix lower contact of chromitite Clinopyroxene + of orthopyroxene, clinopyroxene (mg# 0.936- veined with dunite Magnesio- clinopyroxene 0.938) and tremolite. Some chromites contain hornblende – tremolite inclusion-rich zones and others have a central grain with an inclusion-rich core surrounded by smaller grains nucleated on the margin. Complex zoning in chromite - cr# decreases from core to inclusion-rich zone, then increases again before falling at the rim. Base chromite 2-3 mm across (cr# 0.540-0.535, fe# 0.312-0.323) enclosed in orthopyroxene (mg# 0.931), clinopyroxene (mg# 0.937) and magnesiohornblende. Chromite zoned (core cr#=0.535, rim cr#-0.507) and contains silicate inclusions. NiS on chromite grain boundaries where chromite is altered to aluminous spinel.

Shamis 3500 04-05 0422817 Small chromitite pod, a few Chromite Chromite Chromite (up to 5mm) with interstitial olivine (up (small 2722147 metres in length, located a few Olivine rapidly to 2 mm). Olivine inclusions in the chromite cores. pit) hundred metres north of the followed by Chromite core cr# 0.585-0.581, fe# 0.310-0.314,

Shamis pit. olivine TiO2 0.220-0.230; zoned with low cr# rims. FeNiS and NiS at chromite grain boundaries. Olivine (Fo=0.948) zoned rims (up to Fo 0.959).

Shamis 3600 03-12 0423246 Main chromitite body Chromite Chromite Chromite - large angular grains up to 4mm. Core (working 2721511 subhorizontal, tabular, 1.5 m Olivine rapidly compositions cr# 0.639-0.632, fe# 0.334-0.353, pit) thick, enclosed in dunite sheath. followed by TiO2 0.217-0.235. Olivine inclusions and trails of Narrow dunitic veins cut the olivine, then melt inclusions in chromite and, small rounded chromitite - contacts show crystallize inclusions of chromite are present in the olivine. lobate, interpenetrating together Complex oscillatory zoning from core to rim cr# - relationships. 0.637 (core) to 0.633 to 0.639 to 0.630 to 0.634 03-13 (rim). Interstitial olivine zoned with magnesian rim (dunite) Olivine (Fo=0.959). Chromite Dunite - olivine with chromite, orthopyroxene (mg# Orthopyroxene Olivine – = 0.917), clinopyroxene (mg# = 0.949-0.940) and Clinopyroxene orthopyroxene magnesiohornblende. The olivines are less Magnesio- + magnesian than in the chromitite and show complex hornblende clinopyroxene oscillatory zoning with Fo- core to rim 0.916 (core) – chromite – to 0.913 to 0.917 to 0.912 to 0.918 (rim). Some magnesio- grains are rimmed with orthopyroxene. Chromite hornblende grains (< 1mm) are more aluminous than those in the chromitite (cr# 0.561-0.554) are Fe-rich - normal and reversed zoning; lower TiO2 than in the chromitite (0.11-0.13 wt %), are higher in Zn and Fe(III). Two types of magnesiohornblende - a low- Al variety on clinopyroxene and a high Al variety on chromite. Mining 4960 04-07 0420551 Float Chromite Chromite- Chromites up to 3 mm in diameter, cores cr# camp 2723913 amphibole amphibole 0.773-0.767, fe# 0.402-0.377, TiO2 0.15-0.14 wt %, normally zoned; abundant inclusions of an aluminous, Ca-free amphibole (mg# 0.97-0.98).

Mining 5050 04-11 0420738 Bands, lenses and dykes of Chromite Chromite Subhedral chromite up to 4 mm across, some camp 2723575 chromitite a few centimeters to olivine rapidly containing olivine inclusions; cores cr# 0.734- about a metre wide in dunite. followed by 0.730, fe# 0.412-0.326, TiO2 0.180-0.160 wt %; Discordant to structures in the olivine, then show complex zoning. Smaller chromite grains Fe- mantle. crystallize rich. Interstitial olivine (2-3 mm across); some together contain dense patches of rounded chromite grains; zoned core to rim Fo 0.955-0.965.

Mining 5120- 03-11a 0420746 As above. Chromite Chromite Chromite up to 6 mm intergrown with olivine. camp 5370 03-11b 2723060 Delicate structural features are Olivine - rapidly Chromite cores cr# 0.754-0.736, fe# 0.378-0.328, (aband- 05-13 preserved including a net-like amphibole followed by TiO2 0.196-0.168 wt %. Large grains are most oned pit) 05-10 veining and interfingering olivine - commonly normally zoned whereas small grains (< between chromitite and dunite. amphibole 1mm) show both normal and reverse zoning. Some bands have sharp tops Chromitites with a disseminated ore texture with dunite above, but irregular chromite intergrown with rounded grains of olivine bases where chromitite grades up to 2 mm; elsewhere they are intergrown with into dunite; some lenses appear smaller, more irregular olivine grains. Inclusions of to have been emplaced into olivine common in chromite. Olivines (cores Fo = sigmoidal tension gashes. Dunite 0.958-0.959) are zoned (core 0.958 – rim 0.967). In veins cut chromitite. dunitic patches the Fo content is slightly lower (Fo = 0.949).

Deepest 6500- 04-18 0419401 Narrow bands a few centimeters Chromite Chromite Chromitite bands: chromite - 1 mm subhedral chromiti- 6510 04-19 2722533 thick interlayered with dunite Olivine rapidly grains intergrown with rounded olivine grains up to te and irregular pods and veins of clinopyroxene followed by 2mm in diameter and interstitial olivine. Chromite chromitite in dunite. Chromitite olivine - contains olivine inclusions in core. Chromite core bands are cut by serpentinised clinopyroxene compositions cr# 0.713-0.717, fe# 0.447-0.336,

dunitic veins. TiO2 0.223-0.242 wt %. The grains show complex zoning. Olivine Fo= 0.958-0.959; NiO up to 0.83 wt %; zoned: core – Fo 0.959, rim Fo 0.963. Dunite bands contain serpentinised olivines (up to 4mm) and small elliptical chromite grains (< 1mm) and clinopyroxene (mg # 0.950-0.954). Small chromite grains more Cr-rich and Fe-rich compositions (cr# 0.726-0.714; fe# 0.481-0.345). Olivine less magnesian Fo 0.923-0.953 with a more Fe-rich rim.