ZINC AND LEAD DEPOSITS OF BROKEN HILL. 



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Fig. L 

 Rough Geological Sketch-Map ok Broken Hill. 



III. The Deposits. 



The distribution anc! association of the minerals are of 

 particular interest. Taking Kopje No. i as being the clearest 

 example and best exposed, the distribution may be diagrammati- 

 cally represented as follows (see Fig. 2): — 



Zone I. — The sulphide zone (occurring below water-level). 

 This consists of a hard crystalline limestone, fine-grained, 

 dolomitic and quartzose, usually considerably jointed, preva- 

 lently grey in colour, and containing scattered patches, particles 

 and small veins of zinc blende, galena and a little pyrite. The 

 water-level is very near the surface — some 17 feet below the 

 general level of the surrounding country. 



Zone 2. — The gossan or oxidized ore. A highly fer- 

 ruginized and silicified limestone, rotted and cavernous (see 

 Plate 4, lower ])hotograph ) and very strongly impregnated 

 with carbonate of lead (and to a lesser extent carbonate of 

 zinc), silicate of zinc, and the other oxidized zinc and lead 

 minerals. This zone extends from the water-level to the top 

 of the kopje, which is about 50 feet high. Small patches of 

 unaltered crystalline limestone remain in this pale brown rock. 

 This zone (2) comprises at its base — 



