Model of an Arizona Gold Mine 11 



STULLS. The miners work on temporary wooden 

 platforms laid on the stulls. 



The drifts are made more secure by TIMBERING. 

 As the rock is firm and as these levels are so near the 

 surface that there is little pressure, not many timbers 

 are necessary. For a long- way from the shaft the 

 drifts have no timbers whatever. Towards the right, 

 where the rock is more broken, sets of timber designed 

 to hold the roof of the upper level consist of two 

 POSTS, one on each side supporting a CAP. 



The corresponding place on the lower level is 

 provided with full SETS of timber consisting of two 

 POSTS, a CAP and a SILL. 



Near the right of the model is a vein of another 

 kind which runs at right angles to the face of the 

 model. This vein carries silver and lead. In the 

 upper part the ore is an impure carbonate of lead 

 stained with iron oxides. In the lower part, it is 

 the dark-colored sulphide of lead, galena. The silver 

 content of the ore is disseminated in invisible form 

 through the lead-bearing minerals. This vein DIPS 

 to the left. The left wall overhangs the vein and is 

 the HANGING WALL. The wall to the right is the 

 FOOT WALL. This vein and its country rock are so 

 broken that the method of mining employed on the 

 gold-bearing vein cannot be used and exploitation 

 must be by more costly methods. 



On the upper level the stope runs upward from 

 the drift and will eventually break through at the 

 surface. The stope is left empty and is kept open by 

 numerous cross timbers (STULLS). At the lower 

 level the tendency to cave is too great to be resisted 

 by stulls and an elaborate system of timbering called 

 SQUARE SET is employed. This, which is often em- 

 ployed in deep mines and where the ground has much 



[11] 



