no 



Year. Tons. Value. 



1905 8,528 $104,585 



1906 8,750 92,100 



1907 7,196 72,901 



1908 7,225 82,008 



BLACK LAKE. 



At Black Lake the chief points of interest are: the 

 rock types of the peridotite series ; occurrence and relation 

 of asbestos veins; mining and milling of the asbestos- 

 bearing rock; occurrence, mining and milling of chromite 

 ore. 



Rock Types of the Peridotite Series. 



Of the rock types of the peridotite series, diabase, 

 porphyrite, peridotite, serpentine and granite are present 

 at Black Lake. 



The diabase and porphyrite occur as marginal phases 

 of the peridotite stock at the contact with the sediment, 

 in a few localities the contact being marked by a breccia 

 in which fragments of the sediments are cemented by a 

 paste of the diabase. In general both these rocks have 

 been so much altered that it is only by careful microscopic 

 work that they can be distinguished. Both are now 

 commonly represented by a fine grained chloritic or epidotic 

 rock. In some places typical pillow structure may be ob- 

 served ; at others, the rock has the appearance of a tuff or 

 breccia. 



It is difficult, and often impossible to distinguish 

 peridotite and serpentine in hand specimens. In the 

 field and in mining operations, they are collectively called 

 serpentine. The peridotite is composed of olivine, a 

 small amount of pyroxene, and a little chromite and mag- 

 netite. The serpentine is merely an altered phase of the 

 peridotite. The mineral serpentine is derived from olivine 

 by hydration accompanied by loss of the iron content. 

 Pyroxene may also alter to serpentine; but it changes 

 less readily than olivine, having originally more silica 

 in its composition, and more frequently it alters to soap- 

 stone or talc. The olivine is sometimes completely altered 

 to serpentine, in which case the pyroxene crystals when 



