44S 



Report of the State Geologist, 



beds of magnetite, the Sterling and the Lake. They are evidently portions 

 of the same bed cut in two by a pinch. The direction of their longer axes 

 is about northwest and southeast, and this strike carries the Lake ore-body 

 beneath Sterling lake. The length of the Sterling ore-body at the surface is 

 500 feet, and 230 feet at the bottom of the workings. The length along the 

 slope, which runs obliquely dow n the dip, is 1,000 feet. The pinch is about 

 250 feet long and is succeeded by the Lake ore-bed, whose outcrop is of the 

 same length, but its depth is not know n, as it has never been fully exploited. 

 The slope is 1,100 feet long. 



The ore-bed varies in width from five to twelve feet and is sharply 

 defined. The ore formerly extended up the surface of the hill at whose base 

 the entrance to the present workings is situated, and quarrying methods were 

 therefore employed for operating this upper portion of the ore-bed. In a few 

 places on the face of the hill where the hanging wall remained, as in the 

 Clark mine, chamber-working was followed. The Clark ore-body dips to the 

 northeast, and swells and pinches in a remarkable manner. At one place 

 in the foot wall, two narrow anticlines have been produced, as shown in 

 Figure 15. 



The wall rock is a basic gneiss, with much hornblende, and the roof 

 of the chamber- working is a very coarse-grained mixture of plagioclase feld- 

 spar and hornblende. Just above the ore at the northwest end of the open 

 working is a feldspar vein, twelve inches thick, w hich extends for about 

 twelve feet and then suddenly pinches out. Veins of epidote and milky 

 quartz crystals occur in the wall rock and frequently cut across the strike. 

 The gneiss around the ore-body contains less hornblende than that farther 

 down the hill towards the Lake mine. 



The Lake mine has afforded quite a variety of minerals which occur on 

 the edge of the magnetite bed. The commonest are pyroxene and amphibole 

 either in distinct crystals or forming granular aggregates with the magnetite. 

 At other times there is present in these granular mixtures both white and red 

 feldspar, the former surrounding the latter. Clusters of small epidote crystals 

 are seen, usually in association with pyroxene. Some beautiful pegmatitic 

 intergrowths of quartz and tourmaline are found in the Lake mine, but in 

 just w hat part of it, the writer was unable to ascertain. Sometimes this 

 intergrow th is surrounded by red feldspar, and the latter encircled by mag- 

 netite. (>n the hill and along the highroad about 500 feet northeast of the 

 Lake mine, are several small lenses of magnetite in the gneiss. The stringer 

 is lens-shaped and near the outer margins contains some granular quartz. 



