L1N K D ANsoME ND ] RELATIONS OF ORE BODIES TO DEPTH. 27 



purposes of comparison, over thirty extended from the surface to a 

 depth of less than 500 feet. The maximum individual production of 

 these is less than $1,000,000. Near six of these ore bodies further 

 exploration developed new shoots below the old ones, but usually of 

 smaller extent. In practically all thirty cases the development work 

 hud been carried down a few hundred feet below the last ore of the 

 surface shoot. The form of these smaller shoots is often equidimen- 

 sional; in a few cases the horizontal extent is greater than the verti- 

 cal, or the shoot is wholly irregular; in many cases the shoot pitches 

 steeply northward on the plane of the vein and the ratio of vertical to 

 horizontal extent is 2:1 or 3:1. 



In eight of the sixty cases the shoot extended from the surface to a 

 depth of 1,000 feet, or a little more, and ended. Further development 

 to about 1,500 feet failed to find new shoots of any importance, though 

 small pockets were often discovered. In six of these eight cases the 

 ratio of vertical to horizontal extent varies from 3:1 to 5:1, and 

 the shoots usually pitch northward at angles of 60 to nearly 90 from 

 the horizontal. In the remaining two cases the shoots have about the 

 same horizontal as vertical extent. The maximum horizontal length 

 is 1,300 feet, while 400 is much more common. In two of the sixty 

 cases the pay shoot is 1,500 to 2,000 feet long, maximum depths of 

 600 and 1,000 feet having been attained and the bottom level being still 

 in ore. In thirteen of the sixty cases the shoot began over 200 feet 

 below the surface; in eight of these the bottom of the shoot has been 

 reached, while in five the lowest level is still in ore. Steeply dipping, 

 irregular elongated forms prevail. Many of this group of thirteen 

 represent veins parallel and close to those on which pay shoots out- 

 cropping at the surface were found. 



These statements will give an idea of the form of the shoots. Of 

 course, in the case of shoots reaching the surface, a certain part has 

 probably been removed by erosion. Judging from the shoots which 

 distinctly began below the surface, the normal form of the ore bodies 

 is elongated, vertical, or pitching sharply northward, the ratio of ver- 

 tical to horizontal extension varying from li : 1 to 5:1. Some of 

 these shoots are, however, of about equal dimensions, vertically and 

 horizontally, while in a few the horizontal dimension is the greater. 



Of the known ore bodies, as few exceed 1,000 feet in length, so 

 very few exceed 1,000 feet in depth or extend more than 1,000 feet 

 from the surface. Speaking broadly, explorations below that limit have 

 not proved very satisfactory. Drawing the lines a little closer, it may 

 be said that in proportion to the amount of exploration the upper 700 

 or 800 feet have yielded more than the interval frpm that limit to the 

 lowest levels reached about 1,500 feet. It must not be overlooked, 

 however, that four or five mines still have good ore bodies at a depth 



