240 THE VERMILION IRON-BEARING DISTRICT. 



paint rock dip to tlie north at an angle of about 70°. Figs. 10 and 11 are 

 respectively vertical E.-W. longitudinal and vertical N.-S. cross sections of 

 the Chandler mine showing the features here described. The ore is capped 

 by fractured iron-formation material, jasper, chert, and ore bands, which is 

 overlain by glacial drift. The ore body has been reached through five 

 shafts sunk in the greenstone. The greatest depth is attained Ijy No. 5 shaft, 

 which was down in 1902 to the eighteenth level, at a depth of 740 feet 

 vertically. All of the shafts were originally vertical, but shafts Nos. 2 and 

 4 Avere sunk so close to the ore body that the upper portion slid into the pit 

 as the result of the caving. Inclined shafts with openings farther back 

 from the pit were sunk to intercept the shafts at a point where the caving 

 has not injured them. Most of the work is now done from shafts Nos. 3 

 and 5. The method of mining is the caving system, slightly difFerent in 

 the newer workings — that is, in the lower levels — from what it is higher 

 up. The following concise description by Denton will give an idea of 

 the system:" 



Down to the eighth level the method of mining is as follows: Main levels are 

 driven 75 feet apart and generality there are two main drifts at the bottom of each 

 block, running approximate!}" parallel on opposite sides of the block of ore. From 

 these main drifts raises are put up at intervals of about 50 feet, and from these raises 

 four series of subdrifts are run. The sets in the main drifts are made of 9-foot caps 

 and 7-foot legs, and those in the "subs" of 6-foot caps, and 6-foot legs. This leaves 

 about 8 feet of ore between the sublevels. The sets are placed 3 to 4 feet apart. 

 As the raises are put up, sets are placed to start the first subdrifts; but these drifts 

 are not run at once, but are omitted to strengthen the main drifts until the fourth, 

 third, and second " subs" have been worked out. When the subdrifts are completed, 

 the block of ore between any two levels is hone^ycombed with drifts with vertical 

 intervals of 8 feet of ore. When mining above has been completed, the removal of the 

 ore pillars on the top "subs" begins. The pillars are sliced away, the back is caved, 

 and the caved ore is removed in wheelbarrows to the chutes leading to the main level 

 below. The chutes are 4 feet square and lined with 2-inch plank placed on edge. 

 When the sand or overlying timber appears, a new slice is taken ofl' the pillar and 

 the back of ore is caved, as before, until finally all of the subdrifts have been worked 

 out, when the operation of caving is continued in the block below, which in the 

 meantime will have been honeycombed hj the first or preparatory subdrifts. 



Below the eighth level the method of mining has been modified. What are 

 called intermediate main drifts are driven through the ore at intervals of 20 feet 



« Trans. Am. Inst. Min. Eng., Vol. XXI, 1892, p. 355. 



