[Proc. Rot. Soc. Victoria, 25 (N.S.), Ft. I., 1912.] 



A III'. \.— Prelim imt/ry Notes on the Monchiquite Dykes of the 



Bendigo Goldjield. 



By F. L. STILLWELL, B.8c. 



(Carolina Kay Scholar and Government Research Scholar, 

 Melbourne University). 



(With Plate I.). 

 [Read 14th December, 1011]. 



Introduction. 



Tlie following: notes are the result of an unfinished study of the 

 dyke rocks occurring at Bendigo. 



References to the rocks are not very numerous among the literature 

 of this gold field, which is mostly contained in Professor Gregory's 

 Bibliography of the Economic Geology of Victoria (1). They are only 

 occasionally mentioned throughout the publications of the Victorian 

 Mines Dej^artment, excejDt in Mr. Dunn's monograph (2) where they are 

 treated at some considerable length, and in Dr. Howitt's petrographical 

 report (3). Elsewhere they have been referred to l)y Mugge{4) in a review 

 of Dr. Howitt's paper, and by T. A. Rickard in his descriptive papers 

 on the Bendigo field published in the Transactions of the American 

 Institute of Engineers. Kickard (5) has given special treatment to the 

 dykes in his paper on the Origin of the Gold-bearing Quartz of the 

 Bendigo Reefs. Australia. In this paper he gives a number of sketchies 

 illustrating the relations ot the dykes to the strata. One of these, 

 which is incorrect and deservedly critici^^ed by Argall (6) as being incon- 

 sistent with Rickard's stated facts, has recently been copied into 

 Malcolm Maclaren's book on Gold (6) as figure 127. The papers by Argall 

 resulted in the discussion on Rickard's work. 



Very little work has been done on these dykes within the last sixteen 

 years, and at the beginning of the present year it was thought that a 

 study of these rocks and their relation to the distribution of gold 

 could be profitably commenced. 



General Relations. 



The dykes, which are locally always termed " lavas,"' have been 

 injected into the folded ordovician sediments of the Bendigo field. Mr. 

 Dunn (2) has pointed out that the dykes are found along the course of 

 every anticline, and not in the synclines, and that they are not con- 



2 



