Abstract

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.

First Page Preview

First page PDF preview
You do not currently have access to this article.