The ore deposits of Utah . roduction of the ore deposits as theynow exist. It is a striking fact that some ofthe deposits have been but little affected bysuch alteration, though the character of neigh-boring deposits has been completely changed. The secondary alteration has been dependenton several factors, among the more importantof which are the position of the ground-watertable, the rapidity of erosion, the physicalcharacter of the deposit, and the mineral com-position of the deposit. All these factors havedoubtless had some effect on each of the de-posits, but in several of the deposits so
The ore deposits of Utah . roduction of the ore deposits as theynow exist. It is a striking fact that some ofthe deposits have been but little affected bysuch alteration, though the character of neigh-boring deposits has been completely changed. The secondary alteration has been dependenton several factors, among the more importantof which are the position of the ground-watertable, the rapidity of erosion, the physicalcharacter of the deposit, and the mineral com-position of the deposit. All these factors havedoubtless had some effect on each of the de-posits, but in several of the deposits some onefactor seems to have been dominant. ADJACENT DISTRICTS. 521 WATER LEVEL. The position of the ground-water level haslargely determined the limit of secondaryalteration in the ore bodies, for alteration hasprobably not extended very far below this level,though if given sufficient time it would roachthis level regardless of other conditions. Other 6,750 6,500 6,250 6,000 •^ 5,750 > 3 % 5,500 5,250 5,000 4,750 4,500. Figure 57.—Diagram showing the relation of secondarj- alteration tooutcrop of ore body and to water level in San Francisco and adj;icentdistricts. factors have been of great importance, how-ever, in determining the rate of alteration. The water level has been determined in butfew mines of the district. Figure 57 shows theelevation above sea level of the outcrop ofseveral of the deposits, the lower limit of im-portant secondary alteration, and the upperlimit of the ground-water level (the actualposition may be considerably lower). It is not likely that the water level has re-mained constant for long periods in the past. 522 ORE DEPOSITS OF UTAH. In fact, there are good reasons for believingthat it has been both higher and lower thanit is now. The beaches of the old Lake Bonne-ville are about 750 feet above the present sur-face of Sevier Lake. On the other hand, thegreat alluvial cones at the mouths of the valleysupon which the Bonneville beaches were depos-
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Keywords: ., bookcentury1900, bookdecade1920, booksubjectminesandmineralresou
