1916] Umpleby: Ore on the Limestone Side of Garnet Zones 



37 



ticular localization of the sulphide-bearing portions of the contact 

 zones seem to be more rationally explained by solutions of different 

 or gradually changing composition than by temperature control. 



Summary and Conclusions 



The preference of ore for the limestone side of seven important 

 contact zones has been shown by citations and diagrams, and a desire 

 has been expressed to ascertain through discussion how general this 

 relationship is. 



The phenomena may be interpreted as due either to heat control 

 or to a supply of solutions of changing composition such that lime- 

 silicates are predominantly formed during the earlier stages of depo- 

 sition and the sulphides during the later. The latter view is favored 

 by the writer. 



If the relationship should prove to be a constant one it will be 

 of considerable value in the exploitation of contact deposits, for other 

 things being equal, development work will follow the limestone rather 

 than the intrusive side of the garnet zone. Even at present enough 

 is known to recommend that the habit of the individual deposit in 

 this particular be carefully observed as a guide to later search for 

 ore. In the case of engulfed blocks of limestone the limestone-side 

 will in many places be the central part of the garnet mass. 



Transmitted May t, 1016. 



