66 FLUORSPAR DEPOSITS OF SOUTHERN ILLINOIS, [blll. 255. 



fluorine, but the evidence that the material did actually come from 

 them is weak. If it is of any such origin, it presumably was not 

 segregated during the weathering of the rocks and, recalling the 

 field evidence, there seems little connection between particular dikes 

 and individual ore bodies. 



PROCESS OF CONCENTRATION. 



There are two broadly contrasted methods by which the present ore 

 l^odies may have been concentrated. The first is by the action of the 

 normal meteoric waters of the region, which may here, as in other 

 districts, have gathered the disseminated material from the country 

 rocks into the veins. The second is by the action of heated waters, 

 either originally meteoric or derived from the intruded igneous rock, 

 or in part from each source. It is believed that the evidence points 

 to heated waters having been the agency by which the ores were segre- 

 gated and that they obtained an essential portion of their load from 

 a large mass of lower-lying intruded rock, of which the dikes are the 

 offshoots. 



It has already been pointed out that the ore bodies show no sign 

 of secondary enrichment, and apparently the surface waters now in 

 the region can only operate to destroy rather than re-form the ore 

 bodies. As compared with limestone, fiuorite is relatively insoluble 

 in cold water, though still more soluble than barite, which is very 

 commonly concentrated by such waters. In the presence of an abun- 

 dance of calcium carbonate in the surface waters mass action would 

 demand that the waters largely exhaust their powers in working 

 upon the country rock rather than the vein minerals. This seems 

 to accord with the facts of the field, since the crystals of fluorspar in 

 druses, which might be considered to represent reconcentration, are 

 relatively rare, and, as has been seen, the sulphides, which are very 

 delicate indices of the process of reconcentration, show no clear 

 evidence of such action, but point rather to its absence. It is diffi- 

 cult to believe, therefore, that such waters have gathered minutely 

 disseminated quantities of fluorite from the surrounding limestone 

 and formed the veins as they now occur. It is also to be remembered 

 that in other districts of commercial importance in the Mississippi 

 Valley, where such waters have been shown to be effective, both the 

 ores and the gangue differ in the important particulars already 

 enmnerated. 



If it be held that the waters which formed the ores were heated 

 waters, but that they derived their load from the St. Louis, Ste. 

 Genevieve, and surrounding limestones, it may be pointed out that the 

 normal tendency of heated w^aters rising along faulting fissures would 

 undoubtedly be toward deposition and dissemination of material 

 rather than toward its segregation. This would seem to indicate 



