Some 40 pods of segregated chromite occur over a distance of 50 km along a linear, alpine-type peridotite complex near Coolac, N.S.W. The composition and physical properties of the chromite differ widely from pod to pod.The Cr 2 O 3 :Al 2 O 3 ratio of the chromite ranges from about 62:6 to 33:35 wt% and the cell size varies sympathetically from about 8.32 Aa to 8.21 Aa. There is a bimodal frequency distribution of the pods with respect to the cell size of the chromite, with major and secondary maxima at 8.305 Aa ( approximately 58 wt% Cr 2 O 3 ) and 8.225 Aa ( approximately 38 wt% Cr 2 O 3 ). Cr 2 O 3 , FeO, reflectance and density vary directly, and Al 2 O 3 , MgO and hardness vary inversely, with the cell size.Pods of Cr-rich chromite (>50 wt% Cr 2 O 3 , <20 wt% Al 2 O 3 ) are randomly distributed along the strike of the complex. Pods of Al-rich chromite (> or =20 wt% Al 2 O 3 ) are interspersed with the others where mafic rocks are associated with the peridotite. The prior existence of the chromitites within a stratiform, abyssal protocomplex is postulated. A zone of mixed chromite autoliths may have developed above a zone of Cr-rich chromite autoliths during re-emplacement of the protocomplex. Structural highs and lows along the peridotite may account for the observed distribution of the chromitites and other rocks.

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