1978 



Limestone in the Coast Ranges 



67 



Photo 13. High-angle oblique oeriol viev. ;o uu.: of Notividod dolomite quarry and plant in Monterey County, 1968. Crystalline dolomite of the Sur Series 

 is obtained from multi-level quo'ry (top, center) , crushed, washed, screened, and beneficiated by heavy-media separation (center) ond finally crushed, screened, 

 and calcined at processing plant (bottom). Dolomite quarry is largest in California. Photo courtesy of Kaiser Refractories. 



further complicated by silica and silicate minerals im- 

 placed along shear planes and adjacent to dikes. Where 

 free from granitic and silicic impurities, the rock is 

 uniformly white, medium- to coarse-crystalline, rela- 

 tively pure dolomite. The company provided the fol- 

 lowing tvpical analyses for dolomite produced in 1962: 

 31.7.";% CaO, 20.30% MgO, 1.31% SiO;, 0.20% Fe^O,, 

 0.35% AI2O,, and 46.09% CO,. Except for the subordi- 

 nate production of exceptionally white material for 

 roofing and land.scaping granules, none of the dolo- 

 mite is selectively quarried. A relatively high-quality, 

 uniform product is maintained, however, by heavy- 

 media separation and other practices. It is estimated 

 that approximately half of the mined material is wast- 

 ed. 



Kaiser Aluminum and Chemical Corporation has 

 developed the Natividad quarry by two adjacent series 

 of benches (levels) cut into the western side of the 



hill. In the northern quarry area, the 700- and 77S-foot 

 levels are the most active. The 850-foot bench was 

 nearly worked out, and the 62 5-foot bench was inac- 

 tive when the quarry was last examined in September 

 1963. In the south part of the quarry, the 750- and 

 825-foot levels are worked to some extent, the others 

 being inactive. The highest level at 900 feet was 

 worked out. It was estimated that work on the lower 

 quarry levels would have to be resumed around 1970 

 at the 1963 rate of production. 



Benching is conducted at 75-foot intervals in each 

 quarry area. The faces are blasted using ammonium 

 nitrate in 9-inch diameter holes drilled vertically by 

 rotary methods to 85 feet. Generally, a total of 30 to 

 40 holes are drilled on 25-foot centers and arranged in 

 three parallel rows for each blast. Each blast common- 

 ly yields a 2- to 3-month supply of rock. Some second- 

 ary blasting is necessary to reduce the larger blocks. 



