USEFUL A//./ t/.S 211 



(2) in the basic igneous-limestone complex; (3) in the limestones 

 themselves. 



1. Ores in the Basic Igneous Rocks: The richer ores corwint 

 of aggregates of titaniferous magnetite and hunches of dark 

 brown mica. In such ores the pyroxenes are not abundant, but 

 the ores pass into leaner varieties in which the pyroxenes are abun- 

 dant and finally into a rock consisting almost exclusively of pyrox- 

 ene. There is little evidence of the occurrence of large ore bodies 

 but rather of the occurrence of a large number of small ore segre- 

 gations. The composition of the ores, their mineralogical asso- 

 ciation, and their manner of occurrence establishes beyond doubt 

 their genetic position. They are magmatic segregations of titanif- 

 erous magnetites in a basic igneous rock. 



2. Ores in the Basic Igneous-limestone Complex: The most 

 interesting feature of this complex is the occurrence of small de- 

 posits of contact metamorphic ore. The metamorphic rock is 

 made up of calcite, augite, garnet, and less abundantly, zoisite 

 and vesuvianite. Within the contact metamorphic rock are 

 numerous pockets and nests of magnet te. The ores consist of 

 ilmenite and magnetite. The most important and striking fea- 

 ture of the district is the occurrence of highly titaniferous mag- 

 netite of contact metamorphic origin. 



3. Ores in the Limestone: The limestone in this district, 

 wherever exposed, has been more or less replaced by iron. On 

 Iron Hill the ore is principally siderite and limonite. In the 

 small hill to the north the resulting product is chiefly a yellow 

 ferruginous jasper and a highly siliceous limonite. In some places 

 the siderite has been changed to hematite, but the structure and 

 cleavage of the siderite are still preserved. 



An analysis of the ore cited in the same paper gives the iron 

 protoxide as 8.46 per cent, and the iron peroxide as 69.04 per cent. 



Hematite deposits also occur in Carbon and Laramie Count ii -. 

 Wyoming, in the pre-Cambrian schists. Those in the Hartville 

 district in the latter county are of the greatest commercial sig- 

 nificance. The more important ore bodies occur as lenses in the 

 schists with a foot wall of limestone. In some instances it fills 

 the joint planes and breccia cavities. Two grades of ore are 

 found in this district. One a hard hematite with about 60 per 

 cent, iron content. The other is a soft, greasy, hydrated, reddish- 

 brown ore. This ore has been derived from the hard variety by 

 the action of waters. 



