40 FLUORSPAR DEPOSITS OP" SOUTHERN ILLINOIS. \i'.vi.l. 255. 



PAEVGENESIS AND ASSOCIATION. 



No definile order of deposition of the original hiinerals ca i be made 

 out. The various metallic sulphides and gangue minerals seem to 

 have crystallized at the same time, and beyond the general fact of the 

 replacement of calcite by fluorite there seems to be no system in their 

 deposition. All of the sulphides occur completely surrounded by the 

 fluorite. Tliere are none of the common evidences of secondary 

 enrichment, and in the veins the oxidation incident to the long period 

 of ei'osion siibse(|uent to the formation of the ore l)()dies has left few 

 traces. Ai)j)arently the sulphides, being j)ractically sealed u]) in fluor- 

 ite, are, so long as they remain in the vein, almost entirely unall'ected 

 by surface waters. Minor exceptions are noted in the descriptions of 

 the individual mines. In general the ore bodies are believed to be 

 practically umnoditied ores of primary deposition, or of first concen- 

 traction, as Professor Van Hise defines the term." 



MODE OF OCCURRENCE. 



Form and cliaracter of the ore hod'ies. — The deposits of this district 

 form typical fissure veins. The oi-e bodies are tabular; they occur 

 along planes that mark extensive faulting and that cut across the 

 strike aiul dip of the strata. Ore and gangue minerals in considera- 

 ble variety are present, and both fissure filling and metasomatic pro- 

 cesses have operated in their formation. The ore bodies are unusual 

 in respect to thickness — frequently 10 to I'i feet, and occasionally 25 

 feet or more — and in the great purity and abundance of the fluorite. 



The development work at Rosiclare gives some idea of the size of 

 at least one of the ore bodies. Mining has l)een carried on for [)rac- 

 tically tlie whole distance of three-fourths of a mile along the vein. 

 For the greater ])ortion of this length the sto})es have been 10 to 20 

 feet wide in very clean ore. In the Fairview shaft, at one end, levels 

 at a depth of 200 feet show the presence of a vein of undiminished 

 strength and an ore body of the full normal thickness. At the other 

 end the Rosiclare shaft shows the same thing to a depth of 300 feet. 

 Beyond these shafts very little work has been done, but even if the 

 vein or ore shoot — the two terms here seem almost synonymous — 

 goes no farther laterally, a very large body of spar is shown. 



This is the largest body of fluorspar yet developed in the two 

 coanties, but it is also the only place at which any considerable sink- 

 ing and drifting have been done. As the mine descriptions show, 

 there are a number of other points at which present indications point 

 to large ore bodies. 



" Van Hise, ('. II., Some principles controlling the disposition of ores : Trans. Am. Inst. 

 Min. Eng., vol. .".0, 1901, p. 173. 



