i:ain-.] mode ok occurrence. 41 



In general the great width of the vein is probably clue to the facil- 

 ity with which tlie less soluble calciinn fluorite is formed in the place 

 of calcium carbonate wlienever fluorine is available. This has 

 resulted in extensive replacement of the limestone wall through 

 metasomatic processes, as Avas long since pointed out by Emmons." 

 The detailed microscopic e\adence of this is given in connection with 

 the description of the Lead Hill mine. This jirocess is not believed, 

 however, to have operated to the exclusion of normal vein filling in 

 open ca\'ities. since, for example, in the McClellan mine, later 

 described, there is a considerable l)ody of clear fluorspar where both 

 Avails are sandstone and where, accordingly, there is little opportunity 

 for simple replacement. The occasi(mal banding of the ore, while 

 not conclusive evidence, and often, indeed, the reverse, points, never- 

 theless, to the same conclusion. The cooperation of the two processes 

 of open fissure filling and metasomatism is, as Mr. Lindgren has 

 shown, '^ normal and quite in accord Avith Avhat should be expected. 



In connection Avith the A'eins, the AAall rock, Avhere composed of 

 sandstone, is commonly couA^erted to a quartzite. As this is a local 

 phenomenon, the quartzite occurring only along the A^eins, it points 

 apparently to the introduction of considerable amounts of silica at 

 the time the ore bodies Avere found — a conclusion apparently con- 

 firmed by the presence of crystals of quartz intimately intergroAvn 

 Avith the ore minerals. 



Ore .sJioots. — So far as is knoAvn, the ore does not occur in regular 

 ore shoots. In vicAV, hoAvcA-er, of the small amount of deA^elopment 

 work and the smaller amount of mining so far done, this appearance 

 may be deceptiA^e. The FairvieAV-Kosiclare ore body, if it l)e 

 regarded as a single ore shoot, is certainly one of unusual size. 



Strvctvral relation ff. — The A'eins are deA'eloped, as already indi- 

 cated, along fault planes, but tliese are neither necessarily nor fre- 

 quently planes of major faulting. The Ilamp mine, Avhich shoAvs 

 an excellent body of ore, is in a vein where there has been A^ery little 

 faulting. At the Empire mine, Avhile there has been considerable 

 faulting in the vicinity, the ore body is found along a plane AAhich 

 seemingly marks A^ery little displacement. This is, howeA^er, a com- 

 mon phenomenon. For some reason not Avell understood, the large 

 faults do not form the locus of ore bodies any more commonly than 

 smaller faults in their vicinitA^ 



The ore bodies so far developed are usually found where one Avail is 

 a sandstone and the other a limestone, generally the Ste. Genevieve. 

 The FairvieAV and Rosiclare may be cited as examples. They also 

 occur where both walls are limestones, as at the Hamp and Empire, 



" Loc. cit,. p. 51. 



'' Lindsren, Waldemar, Metasomntic processes in fissure veins : Trans. Am. Inst. Min. 

 Eng., vol. 30, 1901, pp. 578-002. 



