392 



ZINC AND LEAD DEPOSITS OF BROKEN HILL. 



Zone 2a— the phosphate-vanadate zone, which occupies the 

 lower part of the oxidized portion, and consists of carbonates 

 and silicates, etc., mixed with phosphates and vanadates. It 

 is an irregular zone, in which the phosphates and vanadates are 

 locally much more abundant than tlie other oxidized minerals. 

 Presumably the pre-existent carbonates of zinc and lead have 

 reacted with phosphoric acid supplied by the extensive deposits 



Fig. 2. 

 Diagrammatic Section across " Kopje No. 1," 

 Shewing disposition of Mineral Groups. 

 2 = Carbonate-silicate zone ( 

 (2a =: Phosphate-vanadate zone) ' 

 1 =: Sulphide /.one 



Oxidized zone. 



of animal remains situated in this zone to produce the phosphates 

 of zinc and lead. The cave, which is situated in this zone, 

 contains a considerable thickness of mineralized bone-breccia. 

 Other accumulations of bone-breccia have been discovered in 

 various parts of this zone ; the positions of these are indicated 

 in Fig. 3 (a) and (&). 



The upper part of zone 2 consists mainly of carbonate of 

 lead, silicate of zinc, oxide of iron, and carbonate of zinc. No 

 phosphates or vanadates are present. 



The zones are fairly well marked, but a small amount of 

 galena was noted in the oxidized zone, and even on the surface 

 of the kopje. In one instance a very small amount of pyro- 

 morphite was found on the surface of the kopje at its summit, 



IV. Mode of Occurrence of the AIinerals. 



The details of the occurrence of the minerals are given 

 briefly hereunder : — 



Galena and Blende occur mainly below the water-level, 

 where exploited in Kopje No. i, in small but frequent dis- 

 semination and veinlets in the limestone. These veins are 

 generally not more than an inch or so wide. No sulphide 

 minerals have been exposed in Kopje No. 2, where work has 



