THE MINING AND QUARRY INDUSTRY 1912 IO3 



talc seams occurring nearly always on the southern or footwall 

 side of the latter. The association of the silicates and sulphides 

 is of considerable interest for the study of the derivation of the 

 ores. 



The zinc appears to have been introduced into its present place 

 by underground circulations and deposited mostly as a replacement 

 of the limestones, very little as a filling of open fissures. The view 

 as to the secondary nature of the deposits is supported by their 

 variable form, which ranges from narrow seams or bands to lenses 

 and again to very irregular shapes. The seams, in places, also break 

 across the bedding of the limestones. The horizon of the ore 

 varies considerably within the limits of a single locality as at 

 Edwards and in such a way as to be hardly explainable by struc- 

 tural disturbances of once continuous seams or beds. 



That the ores have replaced the limestones is indicated by the 

 lenticular or quite irregular forms assumed by the bodies, as above 

 noted, by the gradation along the borders from the rich sulphides 

 to leaner material and finally to barren limestone, and further by 

 the absence of banding in the arrangement and of drusy cavities 

 which characterize the fillings of open spaces. The ore body opened 

 by the southern shaft at Edwards, however, has quite well-defined 

 parallel walls as seen near the surface which may mark a fissured 

 zone or channel followed by the ore-bearing solutions. 



The specimens frequently exhibit nodules of talc and serpentine. 

 These range from very small size — a fraction of an inch in dia- 

 meter — up to nodules measuring a foot or more across. They 

 are practically barren of sulphides, except such as have been frac- 

 tured when the ore may be seen to extend into or across the nodules, 

 following the seams. The nodules more often than not consist of 

 a talc core with a surrounding shell of serpentine. The talc has a 

 massive appearance in the hand specimens, not fibrous like the usual 

 product of the talc mines in the vicinity; whether it has originated 

 from alteration of tremolite or has possibly been formed directly 

 from solutions in the period of metamorphism of the limestone can 

 not be stated at this time. At any rate, the mineral associations in- 

 dicate that the nodules, so far as represented by the talc cores, ex- 

 isted before the ores were deposited, though the serpentine is in 

 part of later formation. 



The serpentine which encrusts the nodules belongs to the massive 

 variety and shows no evidence of being pseudomorphic after an 

 anhydrous silicate. Its relations rather suggest a reaction product 



