70 FLUORSPAR DEPOSITS OF SOUTHERN ILLINOIS, [bull. 255. 



There are no data at hand for predictions as to change in character 

 and richness of the ores with depth. Chani>-es in the country rock 

 may be expected to have an important influence, and so far the Ste. 

 (ienevieve and other Chester formations have proved most favor- 

 able. In the Illinois mines nothing suggesting rearrangement of the 

 ores and secondary enrichment coincident with degradation of the 

 surface was observed. At the Empire mine carbonates gave place 

 to sulphides within the first hundred feet, and below that level no 

 change was observed. 



In the Kentucky mines a number of deposits of first-grade fluorspar 

 are said to have given out or lost grade with depth. The significance 

 of this fact is uncertain. AVhether it is to be correlated with change 

 in wall rock, or indicates only the usual irregular distribution of ore 

 in depth as well as along a vein, is not clear. In no case was develop- 

 ment carried on to determine whether the ore would come in again at 

 lower levels. If it be true that the diminution in size of the ore bodies 

 was related to topography rather than stratigraphy, it can only be 

 stated that the best obtainable evidence in Illinois does not warrant 

 the belief that the rule is universal. The character and size of the 

 ore bodies certainly do not bear any constant relation to the present 

 land surface. 



In the light of these facts and the wide prospecting which has been 

 going on in the district, little encouragement is offered to the hope of 

 finding important bodies of lead and zinc on the northern side, at 

 least, of the river, but it is believed that the fluorspar deposits afford 

 the basis for an important and growing industry. 



GUIDES FOU PROSPECTING. 



Fluorite is such a distinctive and easily recognized mineral that it 

 is not often overlooked. Its presence, or that of galena or blende, is 

 usually sufficient to warrant careful prospecting for an ore body. 

 Calcite, on the other hand, is so conmion that its presence is not 

 often significant. The presence of faulting fissures may usually be 

 recognized by the fact that rocks of unlike character are brought into 

 contact along straight lines or by the presence of the quartzite reefs 

 already discussed. To a less extent any disturbance of the strata is 

 in this district probably connected with faulting. When a body of 

 spar has been formed along a fault contact it should first be pros- 

 pected by a few shallow shafts along the strike to determine its extent. 

 That proving favorable, regular sinking may be undertaken with 

 some confidence. In general it is to be remembered that the material 

 is of low value and expensive installations are not warranted. While 

 some lead and zinc may be saved in mining the spar, it is not thought 

 that they are generally of first importance. 



