108 PROCEEDINGS OF THE ROYAL SOCIETY OF QUEENSLAND. 



movement) in a south-east direction.* A similar feature is notice- 

 able in the southern portion of the Cordilleran belt, where the 

 area of plateau movement was extended from the south- 

 eastern massif north to embrace the South Coast and Sydney 

 districts prior to the deposition of the Hawkesbury sandstones. 



The true geosynclinal portion of the Cordillera extends^ 

 therefore, roughly from Port Stevens to Mackay. 



The true north-western massif (omitting the post- 

 Cambrian additions), including the Territory and West Aus- 

 tralian portions, has been an area of vertical movements only 

 since the Cambrian period. Consequently the fissures formed 

 by Archseozoic fracturing, which often constitute important 

 ore channels, are of large size and great continuity, and have 

 not been cut up, pinched out, partly obliterated and squeezed 

 into discontinuous lenses, as has been the case in the regions 

 Avliich have undergone great Carboniferous and Mesozoic earth- 

 fold movements. Thus, as far as Queensland is concerned, 

 the continuity of lode formations and the value of our ore 

 deposits increases from the Dawes Range northwards. 



Alternation of uplift and depression, the repetition of 

 plateau uplifts, may also have caused several zones of enrich- 

 ment in the lodes of the massif areas. It would not be sur- 

 prising here to fuid a second carbonate and oxide zone below 

 the sulphide zone (which is not necessarily primary in all 

 cases) in many lodes wliich have now been abandoned. Such 

 a zone was found at a depth of 500 feet in the Girofla Mine, 

 Mungana. 



General mining experience has proved that the auriferous 

 reefs of the East Australian Cordilleran region are principally 

 quartz lodes locally enriched where they intersect carbonaceous 

 beds, homblende-andesites, or other rocks which favour gold 

 deposition from magmatic solution. 



In the northern massif, however, the lodes comprise both 

 large fissures infilled with quartz, p3n:ites and sulphide ore, and 

 large shear zones consisting of a ferruginous matrix carrying 

 pay ores, and passing into sulphides below water level. An 

 abundance of graphite is a feature of these great shear zones. 

 In the sulphide levels graphite and pyrites are constant 

 associates, and bear a definite relation to one another. 



* Details of this zoning are given in a Queensland Geological 

 Survey Bulletin prepared by the writer in 1919 but not yet published. 



