GEOLOGY OF MOUNT MARCV 23 



45°. The pit is said to be between 250 and 300 feet deep (measured on the 

 bottom rock of the shoot). Crystalline limestone surrounded the ore on all 

 sides and was intimately mixed with it. From specimens seen limestone 

 appeared to foiTn the chief ganguc. 



The Hale mine was opened in the spring of 1S80. A shaft was sunk 50 

 feet through surface material and entered what appears to be a large body 

 of ore lying nearly horizontally in the limestone. A chamber 51 feet square 

 has been excavated. On the east the ore pinches out ; on the west it is cut 

 by a dike, which forms the west wall of the pit ; on the north there is a 

 breast of ore 8 to 10 feet high. In places the room is 16 feet high, with ore 

 still on the flioor. Ljdng in the ore, are, however, layers of limestone of 

 various thicknesses, so that this height does not represent the thickness of 

 good ore. Not enough work has yet heen done to determine definitely the 

 shape of the ore-body; but the probabilities are that the chamber is on the 

 top of a shoot of ore which pitches to the northward as in the Wood mine. 

 Samples of the ore as it comes from the mine and after concentration 

 contained : 



No. 1 199 No. 1200 



Metallic iron 49-37 59-92 



Phosphorus absent 0.002 



Titanic acid absent absent 



Phosphorus in 100 parts iron o.ooo 0.003 



Sample no. 1199 is from 50 tons "primitive ore." Sample no. 1200 is 

 from 100 tons of " separated " ore. The chief gangue is calcite. Pyrite 

 seems to be absent. 



A brief additional note was published on the mines in 1889 by 

 Prof. J. C. Smock, in Bulletin 7 of the State Museum, page 35, 

 and some geological details, with a small section at the mines by the 

 writer on the basis of observations made in 1893 (Report of the 

 State Geologist for 1893, page 468). Not one of the observers cited 

 was, however, impressed with the nature of the ore-bodies and their 

 associations as contact effects. The experience of the last 10 years 

 has been necessary to bring out these relations as they should be 

 understood. We now realize that the ores conform to the characters 

 lately established for many magnetite bodies and their associated 

 lime-silicates. 



The exposures extend for one-fourth of a mile or more in general 

 direction a little east of north. They are apparently surrounded on 

 all sides except the brook valley leading to the Ausable river, by 

 anorthosite. In the brook valley, syenites, or at least rocks believed 

 to be syenite appear. The anorthosite also penetrates the limestone 

 series as the geological section later given will show. Drift is heavy 

 and widespread, making some features a matter of inference rather 

 than observation. 



On the north the first exposures appear in an open cut, driven 

 across the measures in a westerly direction for 40 feet. The 

 details are shown in figure 2. About 50 feet of limestone have been 

 caught between two masses of anorthosite. The limestone has been 



