520 GEOLOGY AND MINING INDUSTRY OF LEADVILLE. 



tribution of ore deposits in the area as a whole, which is sufficiently ac- 

 curate, although the details of ore occurrence, especially in some of the 

 larger mines, could not be ascertained, owing to their inaccessibility. Those 

 mines whose names are followed by an (L) were not seen by the writer, 

 but the information given has been obtained from the notes of Prof. Arthur 

 Lakes, who assisted in the examination. The same general order of topo- 

 graphical description that was followed in Part I, Chapter IV, is preserved 

 here. 



NORTHEASTERN REGION. 



Monte cristo mine. This mine is situated just beyond the northern limits 

 of the map, on the steeper slope of the spur running eastward from Quan- 

 dary Peak, just below timber line. Its ore is a low-grade argentiferous 

 galena, occurring in a bed of quartzite of Cambrian age, with little or no 

 accompaniment of vein material or of other minerals. The formation here 

 dips eastward at an angle of 35, which is approximately the slope of the 

 steeper eastern flank of the spur. The quartzite stratum which carries the 

 ore is the outcropping rock on this steeper part, so that it has only been 

 necessary to strip off the thin surface accumulations of soil and debris to 

 reach the mineral, which is thus exposed over an area of several acres. 

 The galena is rather coarse-grained and crystalline, and is irregularly in- 

 tergrown in the quartzite, occurring on its upper surface from a few inches 

 to a foot in thickness, but in one case extending eight feet below the surface 

 of the bed. It is evident at a glance that it could not have been deposited 

 contemporaneously with the quartzite, and no evidence was seen of any 

 pre-existing cavities ; whence it is assumed that its deposition was a meta- 

 somatic change by percolating water, like the limestone deposits of the 

 region. Although the ore, from its manner of occurrence, can be mined 

 very cheaply, its tenor in silver is so low and it is so intimately mixed with 

 the quartzite that it probably cannot be smelted profitably without previous 

 concentration in ore-dressing works. 



On North Peak ridge the North Star mine (L) is situated at the east- 

 ern end of its higher part, a short distance above and west of the saddle 

 marked by the Blue Limestone outcrop. Evidence afforded by the dump 

 shows that its shaft went through the Lower Quartzite cap of the ridge into 

 the Archean gneiss below. At the foot of the steep slope below this mine 



