1978 



Limestone in the Coast Ranges 



89 



buff, hard, compact, high-calcium coquina. This is 

 composed almost entirely of shell fragments and cal- 

 cium carbonate cement with minor amounts of quartz 

 and rock grains. Small amounts of dove-gray, bitumi- 

 nous coquina also are present in the southwest part of 

 the quarry. I'he limestone is commonly brccciated 

 and fractured, the fissures being partly filled with 

 dripstone or aragonite crystals. The coarse-grained 

 limestone crops out as craggy, soil-free exposures that 

 weather gray. To the east of the quarry, much of the 

 limestone is pale-buff, moderately hard, fine- to me- 

 dium-grained material composed of sand-sized grains 

 of shell debris cemented with calcite. Quartz grains 

 and other impurities commonly constitute several 

 percent of the finer-grained limestone, which weath- 

 ers to more subdued exposures than the purer lime- 

 stone. Other rocks that are occasionally interbedded 

 with the limestone include pebbly, fossiliferous sand- 

 stone and gray shale. Between the main deposit and 

 satellite outcrops to the south and east, siltstone and 

 other non-carbonate rocks are sporadically exposed. 

 Chemical analyses of the more common types of lime- 

 stone are given in table 18. 



Table 18. Chemicol analyses of limestone from the 

 Lime Mountain deposit, San Luis Obispo County. 



Ign 



Simple C^O Mg() SiO. AI2O3 FeoOi PsOs loss 



LimeMtn-1 46.80% 0.63% 12.66% 1.18% 0.60% 0.03% 37.57% 



Lime Mm. 2 53.36 0.34 2.62 0.37 0.25 0.05 42.15 



LimeMtn. 3 54.50 0.0 0.97 0.17 O.I 0.02 43.60 



Lime Mtn. 4 54.70 0.0 0.76 0.12 0.09 0.02 43.73 



Lime Mtn. 5 54.50 0.0 1.03 0.18 0.09 0.05 43.56 



Samples collected Novcmt)cr 1962 by F.ari \S'- Hart No 1 i.s common sandy 

 limestone west of main quarry; no. 2 is dove-gray, bituminous coquina 

 from southwest part of main quarry; nos. 3 and 4 are typical high-grade 

 coquina from sugar-rock stockpile; no. 5 is composite from sugar-rock 

 stockpile. Analyzed by Lydia Lofgren, February 6, 1963. 



Development by the present owner has been con- 

 ducted in the main quarry and in a surrounding 

 stripped area and traces of all previous quarries, as 

 well as the original summit topography, have been 

 obliterated. The stripping program — initiated in 1958 

 to remove relatively low-grade (minus 95% CaCOa) 

 limestone, soil, and a 2-foot gray shale bed — was near- 

 ly complete in late November 1962. The stripped area 

 is roughly circular, measures about 1,000 feet in diam- 

 eter, and surrounds most of the main quarry. The 

 owner said that as much as 60 to 70 feet of overburden 

 had been removed in places. The main quarry is some- 

 what irregular in shape but is judged to be about 800 

 feet long by a maximum of 400 to 500 feet wide, with 

 the long axis trending west. The north and south faces 

 are estimated to be 60 to 70 feet high and 50 feet high, 

 respectively, and are developed by 20- to 25-foot 

 benches. It is planned that the main quarry, now 

 worked from the east, \*ill be devcloju'd from a quarry 

 being opened on the south flank of the mountain. 



Benches are currently blasted in air-drilled holes set 

 on 8- to lO-foot centers. Approximately half a pound 



of ammonium nitrate is used per cubic yard of rock 

 and .^000 to 10,000 cubic yards of rock is dislodged per 

 blast. Some secondary blasting also is necessary. The 

 rock is loaded by two power shovels (2'/,- and 1 '/<-yard 

 capacities) into end-dump trucks, hauled a short dis- 

 tance to the southeast side of the quarry, and dumped 

 into a hopper for processing. Some selective quarry- 

 ing is necessary to maintain a high-grade product. 



Another quarry, called the Sycamore Springs pit, 

 was opened recently and was yielding lime-qualit\' 

 rock averaging nearly 98% CaCC), ( VV. J. Smith, 1969, 

 personal communication). This quarry is believed to 

 be located in the satellite deposit just north of SW 

 corner sec. 15. 



Eaton and Smith's processing plant is located just 

 southeast of the main quarry. Here, raw rock dumped 

 in the hopper is fed over a vibrating grizzly with 8- 

 inch openings, and the oversize is crushed in a 30-inch- 

 by-42-inch jaw crusher. The crushed material joins the 

 minus 8-inch rock from the grizzly and all goes to a 

 double-deck vibrating screen with .^-inch and 8-inch 

 openings. Oversize and undersize fractions are con- 

 veyed to separate "waste" piles for possible future use. 

 The 3-inch-by-8-inch product is stored in a 225-ton 

 bunker and in open stockpiles for subsequent ship- 

 ment by truck 27 miles to the railroad loading facility 

 at San Miguel. The product is then shipped by rail to 

 sugar refineries at Spreckels and Tracy. The sugar 

 rock produced averages close to 97% CaCOa, fluctuat- 

 ing from 96 to 98.8%. 



In 1962, the owner was experimenting with an agri- 

 cultural limestone product which is obtained at the 

 fines "waste" pile. Here, minus '/-inch material is 

 screened and processed to obtain a minus 14-mesh 

 product. The product is trucked to the San Joaquin 

 X'allcy where it is sold as "Lime .Mountain Brand Ag- 

 ricultural Limestone." A minimum of 80% C^aC03 is 

 guaranteed, but the company reports that the product 

 generally contains 90% or more CaCO.i. The present 

 operator also occasionally sells minor amounts of or- 

 namental stone, riprap, crushed rock, and rubble to 

 local buyers. 



Recent production (sales) of limestone has aver- 

 aged about 100,000 tons per year, virtually all of which 

 was sugar rock. The company reports that this 

 amounts to about 65% of the material currently proc- 

 essed, the remainder being largely unsalable (\V. j. 

 Smith, 1962, oral communication). The operator em- 

 ploys 14 men at the quarry and plant and 18 to 20 truck 

 drivers and mechanics during much of the year. In the 

 winter, only a skeleton crew is retained to repair and 

 maintain roads and equipment and to strip overbur- 

 den and low-grade rock. 



Total limestone reserves at Lime Mountain are not 

 known, although Logan (1947, p. .H)4) states that 

 "drilling and examinations are reported to indicate 

 75,000,000 tons or more . . . ". Based on the areal 

 exposures shown in figure 8, estimated reserves of 

 limestone (exclusive of quality) are about 550,000 tons 



