South Australian Dolomites. 



451 



In the Hutchison area the same types of metamorphosed 

 sediments are to be found, but here the dolomites are more con- 

 spicuous, and calc-magnesian silicate rock do not form as 

 important a feature as in the southern outcrops. 



In the accompanying diagrammatic section (Fig. 1), the relations of 

 the dolomite and diopside rocks are shown for the Sleaford Bay area. 

 Only part of the Hutchison series exposed along the shore-line has 

 been represented in this section, nor are all the diopside rocks 

 revealed, there being a further development in a continuation of the 

 section eastward. 



Section along the shore at Sleaford Bay. 



^ 



Fig. 1. 

 500 yards 



tr 



gg 



= diopside rock with quartz veins. 

 = impure diopside rocks with 



micaceous bands. 

 = transition beds containing 



diopside, highly silicified, with 



fault breccia of siUcified quartz 



rock, 

 garnet-graphite gneiss. 



a = Flinders gneiss. d 



p = pegmatite. id 



gr = granite. 



f = ironstone band. 



fni = forsterite marble. 



gs = graphite schist. 



ggn = garnet gneiss. 



X = no exposure. 



dm = diopside-microcline rocks. ms = mica schists 



(Thickness of individual beds not to scale.) 



Some of the exposures are badly weathered, and in some cases 

 outcrops are missing, so that the succession cannot claim detailed 

 accuracy. 



Quartz veins from the neighbouring granites are often very 

 abundant in the diopside rocks, and pegmatite veins are present, 

 more especially in the graphite and garnet rocks. These rocks are, 

 however, outside the scope of the present inquiry. 



The Dolomites of the Hutchison Series. 



Dolomites form an important group of rocks of the Hutchison 

 series. They range from practically pure dolomites to calc- 

 magnesian silicate rocks, in which all traces of carbon dioxide have 

 been removed. The evidences of all these rocks show that the 

 pre-existing sediments were true dolomites or highly dolomitic 

 limestones. Dealing now with those less impure types in which 

 a carbonate mineral has been retained, we shall endeavour to describe 

 their characteristics under the grouping of those developed at 

 Sleaford Bay and those occurring in the Hutchison area. 



