212 ECONOMIC GEOLOGY 



According to Ball the ore was deposited by descending waters. 

 It occurs along zones of maximum downward circulation. Lenses 

 and veins are found along joints in the rock masses at a consider- 

 able distance from the main body. The associated minerals are 

 quartz, calcite and limonite which have been deposited from solu- 

 tion. In this case the magnetite and the pyrite of the overlying 

 schists would be the source from which the circulating solutions 

 derived the iron. 



In Iron Mountain, Wyoming, titaniferous magnetites are found 

 in dikes traversing anorthosites. The mountain itself is more 

 than a mile in length and the iron-bearing ridge is about 600 ft. 

 in width. The ore which is in the form of a dike extends the 

 length of the ridge and varies from 40 to 300 ft. in width. It is 

 flanked upon either side by the anorthosite and paralleled by 

 numerous smaller dikes. The presence of similar minerals in 

 both the anorthosite and the dikes, although the proportions vary 

 somewhat, suggests that they are differentiation products of the 

 same magma with the iron intruded after the complete solidifica- 

 tion of the anorthosite. The impurities in the dike material 

 are olivine, biotite and feldspar. The percentage of iron is 

 about 50. Lenticular masses of granite are also found asso- 

 ciated with the anorthosite. The granite is also traversed by a 

 pegmatite bearing magnetite and biotite. In order of age the 

 intrusives of the district may be given as anorthosite, iron ores, 

 granite, pegmatite. 



Hanover, New Mexico: A comparatively new field for the 

 production of iron ore is near Hanover, New Mexico. The 

 geological relations are fairly simple. A quartz diorite porphyry 

 has intruded Carboniferous limestones and other sedimentaries. 

 In a part of the area the intrusion has caused extensive met- 

 amorphism of the terranes, and, along the contact zone, ores of 

 iron, copper, and zinc have been deposited. The ore is primarily 

 magnetite but in part it is hematite. The ores are both hard and 

 soft. Of the former there are three large lenticular masses and 

 numerous outcrops that appear to have the same mode of occur- 

 rence. The soft ores occur at several places along the contact 

 between the igneous and sedimentary rocks. The ore content 

 is estimated by Paige as between 53 and 57 per cent. Solutions 

 from the heated magma, probably above the critical temperature, 

 impregnated certain strata of the surrounding rocks. Adjust- 

 ments due to cooling served to make the contact zone favorable 



