194 



C. W. MARSH. GEOLOGICAL NOTES 



occurring as pipes, which in some cases reach to considerable 

 depths. The sides of such openings are invariably more or less 

 decomposed and impregnated with metallic salts, which hare in 

 some instances penetrated to considerable distances as small 

 irregular pipe veins, often opening out to fairly sized chambers 

 filled with ores and earthy matters similar to the main body. By 

 the subsequent decomposition of these deposits near the surface, 

 their enclosing rocks have been further changed to what the 

 miners call kindly ground. 



The ore veins and deposits of the Barrier Ranges are not 

 strictly confined to any particular rock, being found alike in 

 gneiss, mica-schist, hornblende-schist, diorite, or granite, often 

 occurring along junction lines between any two of these rocks. 

 Grey gneiss appears to be the most favourable to large ore bodies, 

 while the more concentrated silver deposits accompany the car- 

 bonaceous schist and rocks mineralogically and lithologically 

 similar, except that graphite is not always visible, in which case 

 disseminated iron is generally more abundant. The removal of 

 this iron from terrestrial circulation has, no doubt, decomposed 

 a large amount of carbonaceous matter during its peroxidation ; 

 in fact, in all such ferruginous rocks we may reasonably look 

 upon their disseminated ferric oxide as the equivalent of oxygen 

 consumed and organic matter decomposed prior to the carbonate 

 of iron, which they invariably carry in their veins, being deposited. 

 Some of the contact deposits are very rich in silver, especially 

 when occurring between mica-schist or gneiss, and granitic or 

 dioritic rocks. Many of these are purely local, no fissure being 

 discernable passing beyond the deposit itself. The origin of these 

 deposits appear to be due to simple replacement of the rock's 

 material by ores. Several of these are sometimes found at greater 

 or less depths below each other, connected only by thin seams of 

 ferruginous clay adhering to the hanging wall, or otherwise 

 passing into it along some of its joints, where nice pockets of ore 

 have been sometimes found. The superior richness of the ore 

 generally found in these deposits have caused them to be much 

 sought after by prospectors, but beyond the more fortunate 

 discoveries made near the surface, the results so far have not 

 been encouraging. 



The following are the only statistics I have been able to 

 gather : — 



Mike. 



Deepest 



Shafts. 



553 Feet. 

 500 „ 

 600 „ 



Total Ore 

 Produced. 



2,500 tons 



387,300 tons 



Value — Ore. 



Levels Driven 



Umberumberka.. 



Broken Hill 



Bound Hill 



£250,000 

 £4,u00,000 



11,050 Feet. 



