91 



the largest shoots was stoped for 590 feet (152 m.) vertically 

 and averaged 150 feet (32 m.) in length and 56 feet (17 m.) 

 in thickness. 



The higher grades of ore are often confined to certain 

 bands in the shoot parallel to the trend of the lode. They 

 either occur in the body of the shoot or on the hanging 

 or foot wall sides. These bands may also change their 

 relative positions suddenly and follow other though 

 parallel planes in the shoots. 



The pay ore is sometimes bounded by a fissure or fault 

 plane. More often, however, there is no sharply defined 

 wall, but a transition, usually rapid, from commercial 

 ore to "waste" or nearly barren rock. 



The positions of shoots are usually along contacts 

 between the lode and fault planes with impervious walls 

 or dykes. In the case of the dykes the shoots usually 

 form on the under side. When the mashing or shearing 

 of the rock is such that the metal bearing solutions are 

 restricted within zones of reasonable width, other things 

 being equal, the conditions are favorable for the formation 

 of productive ore shoots. The importance of the shoot 

 is ofttimes accentuated by the development of a system 

 of cross fractures emanating from the wall rock. 



In the LeRoi, shoots have been found along the contact 

 of the augite porphyrite series and the coarse monzonite 

 and diorite porphyry. 



Origin. 



Ore deposition began subsequent to the extensive 

 intrusions of alkali syenite and continued up to the 

 period of injection of the last system of dykes. It is 

 thought probable that the deposits are closely related to the 

 alkali syenite. 



The deposits were formed through the agency of ascend- 

 ing aqueous mineral-bearing solutions of high temperature 

 which gradually replaced the primary minerals of the 

 country rocks particularly the feldspar. 



Certain minerals in small quantities, such as garnet, 

 wollastonite, epidote, amphibole, pyroxene and magnetite 

 suggest an approach to the conditions under which contact 

 metamorphic deposits are formed. Other minerals are 

 characteristic of hydrothermal action such as tourmaline, 

 muscovite, chlorite and zeolites. The paragenesis of the 

 minerals has not been worked out, but pyrrhotite is cut 



