i 3 4 SCIENCE PROGRESS 



show that the lode is in the main a vertical lode, and it seems 

 to me to have been formed along a powerful fault plane. A 

 branch of the lode passes off to the south-east, but is not always 

 developed (as in fig. 5, c) ; the branch sometimes follows a folia- 

 tion plane, but elsewhere cuts directly across the foliation planes. 



Similar saddle-shaped offshoots are not uncommon in mines ; 

 the same branching is shown in the North Lyell Mine (fig. 6), 

 and another occurs at Kalgoorlie, where, in September 1904, I 

 had the opportunity of studying a similar saddle-shaped arch 

 in the telluride lode of the Oroya Brown Hill Mine. 



The use of the term saddle reef is, of course, only a matter 

 of definition ; and the term could be so defined as to include 

 lodes in igneous rocks and any lodes giving off saddle-shaped 

 flaps or pockets. But the term was proposed for isolated 

 arch-shaped lodes in folded sediments; and its extension to 

 branches off a vertical lode in foliated igneous rocks seems 

 to me inconvenient, as likely to encourage erroneous views as 

 to the distribution of the ores, and to lead to the laying out of 

 mines on unprofitable lines. 



(d) The Separation of the Broken Hill Zinc Ores 



The Broken Hill mines have a special interest at the present 

 time from the ingenious processes, which have at length con- 

 quered the difficulties, that have hitherto prevented the utilisation 

 of the zinc in the ores. The blende is associated with rhodonite, 

 a mineral which has almost the same specific gravity. Hence it 

 was impossible to separate these minerals by ordinary washing 

 processes, and the zinc ores have been thrown on to the waste 

 heaps. The tailings heap of the Broken Hill Proprietary Mine 

 alone is estimated to contain 2,500,000 tons of ore already 

 crushed and lying on the surface. Efforts were made to 

 separate the blende magnetically, with only partial success. In 

 one of the new processes the ore is treated in an acid solution, 

 whereby bubbles of gas are formed on the blende, and not on 

 the rhodonite. The gas keeps the blende floating on the 

 surface of the bath, whence it is skimmed off as a scum, while 

 the rhodonite falls at once to the bottom of the tank. This 

 process and others are now being discussed in the law courts ; 

 but to whomsoever the credit belongs, this method has 

 conquered the difficulties which have hitherto rendered it 

 impossible to utilise the zinc of the Broken Hill ores. 



