ON THE BARRIER RANGES SILVER FIELD. 191 



very irregular, oftentimes being only traceable by a thin compressed 

 layer of impure graphite on the smooth regular face of the hanging 

 wall. As a rule, where the latter bends to the west (or the 

 foot-wall side), generally resulting in a steeper dip, ore makes in 

 greater or less bodies, from a few inches to ten or twelve feet in 

 width, the length greatly depending on the dip of the walls. The 

 ores occurring in this vein may be roughly classed as galena, 

 zinc-blende, stephanite, and native silver, generally with more or 

 less antimony and bismuth, the matrix being chiefly siderite, in 

 which is often embedded large clearly defined crystals of galena, 

 zinc-blende, with sometimes iron and copper pyrites. In some 

 cases one or other of these are found penetrating crystals of 

 different kinds. From the inter-crystallization of these metallic 

 sulphides with siderite, we may assume their contemporaneous 

 formation from water holding the necessary elements in solution. 

 The occurrence of alternate layers of these several metallic 

 ores, on one or both sides of masses of such crystalline aggregates, 

 show that the later circulating waters must have been subject to 

 periodical variations in composition during the formation of these 

 different layers. Silver is generally confined to the lead ores or 

 associating with zinc or iron in their immediate vicinity. When 

 found in payable quantities with either of the latter ores, in the 

 absence of lead, there is often conclusive evidence of the replace- 

 ment of lead by zinc or iron, the lead, during its removal, having 

 left the silver behind, combined with the replacing material. 

 The lead ores, besides being highly argentiferous, carry con- 

 siderable quantities of native silver, either finely disseminated 

 through the mass, or lining crevices or vugs, the latter being 

 often filled with a friable mixture of native silver and iron, 

 arising from the decomposition of embedded crystals of siderite. 

 The zinc, when argentiferous, carries the silver chiefly as frosted 

 incrustations around and between its crystals, either in the forms 

 of native silver, or mixed with antimony and arsenic. In many 

 cases crystalline masses of galena and zinc-blende have had their 

 metallic salts removed and replaced, more or less completely, 

 by silver, iron, antimony, arsenic, copper, &c, giving rise to 

 antimonial silver and fahlerz ores (collectively designated by the 

 miners as grey ore) ; as a general rule the crystalline forms of 

 the lead and zinc ores are retained. By decomposition these 

 ores are often changed to impure friable native silver. Siderite 

 rarely carries sufficient silver to pay for extraction, unless it 

 occurs in close proximity to lead ores, or has replaced them. 

 Silver is also occasionally found associated with veins of earthy 

 graphite, especially in the near vicinity of ore bodies, such veins 

 being looked upon as a favourable indication when following an 

 otherwise blind lead. 



