1978 



Limestone in the Coast Ranges 



51 



sills (Fitch, l'>3l,p. 3). Overlying the crystalline rocks 

 on both sides of San X'icente Oeek canyon and con- 

 cealing the southwest and northeast extent of the lime- 

 stone is a sequence of Miocene sedimentary rocks that 

 dips gently southwest. A maximum thickness of 350 

 feet of sedimentary overburden is exposed west of the 

 canyon and someu hat less is exposed to the northeast. 

 From bottom to top, the sedimentary strata are com- 

 posed of the following units, with estimated max- 

 imum thicknesses indicated: 1) hard calcareous 

 sandstone of the \'aqueros Formation (?), 20-100 feet; 

 2) transitional softer concretionary sandstone, 100 

 feet; and i) shale or mudstone of the Monterey Forma- 

 tion (?), 150 feet. 



The attitude and subsurface extent of the limestone 

 body is known only in places. Based on limited bed- 

 ding features and the fact that schist was encountered 

 in underground uorkings at a shallow depth below 

 limestone exposed in the west wall of the canyon, the 

 deposit appears to dip moderately northeast. If so, the 

 main limestone reserves would lie east of the canyon 

 beneath the sedimentary overburden. However, the 

 projected distribution of the deposit at depth may be 

 complicated by faulting as indicated by the broken 

 and crushed nature of the limestone and the presence 

 of minor faults. 



Most of the limestone is off white to light blue gray, 

 medium to very coarse crystalline, high in calcium, 

 and locally graphitic. Some magnesia is locally present 

 as silicates and dolomite but is considered a problem 

 only at the north end of the deposit. Limestone and 

 associated rocks (weathered schist and calc-silicate 

 rocks) are commonly broken and crushed, the inter- 

 mingling making it difficult to maintain good-quality 

 limestone in some parts of the quarry. Clay and other 

 noncarbonate fines tend to fill the interfragmental 

 spaces, thereby further diluting the limestone. Dis- 

 seminated pyrite is a common minor constituent in 

 some parts of the deposit. An average analysis of the 

 quarry-run limestone delivered to the mill is rep>orted 

 by the company (R. A. Kinzie, Jr., written communi- 

 cation, 1963) to be 43.6% CaO, 1.4% MgO, 14.5% 

 SiO,, 3.6% AKO„ 1.5% Fe^O,, 0.6% SO,, and 34.0% 

 ignition loss. 



Development of the deposit has been mainly south- 

 west of San \'icente Creek, although the northeast 

 wall of the canyon was worked to some extent in the 

 early years. By 1963, the quarry had been expanded to 

 an estimated maximum size of 2,700 feet by 1,600 feet. 

 Quarry operations are carried out in three more or 

 less distinct phases — stripping, quarrying, and under- 

 ground transfer. Stripping of the sedimentary over- 

 burden is done periodically under contract, the last 

 contract being completed in January 1963. 1 he strip- 

 ping bench uncovers a 1 50-foot-wide upper surface of 

 limestone at an average elevation of 870 feet; and the 

 sequence of sedimentary rock, 130 feet to more than 

 300 feet thick, is exposed in the bench face. Most of the 

 overburden is wasted, except for the hard sandstone of 



the \'aqueros Formation (?) which is utilized exten- 

 sively as riprap and breakwater stone. Recent strip- 

 ping should provide several years of limestone 

 reserves before further stripping is necessary. Dia- 

 mond drilling currently being conducted on the oppo- 

 site side of the canyon is designed to develop limestone 

 reserves in the northeast pan of the deposit. 



Quarrying is conducted along the southwest can- 

 yon wall where the developed limestone face rises 320 

 feet above the 550-foot elevation of the quarry floor. 

 The limestone is worked through several shallow 

 benches by blasting and bulldozing, the benches pro- 

 gressing down the face. Some selective quarrying is 

 necessary to maintain desirable grades of limestone. 

 Where schist is too prevalent, the material is wasted. 

 Broken rock collected at the toe of the face is moved 

 to glory holes on the quarry floor by end-dump trucks, 

 which are loaded by power shovel, and by a Michigan 

 loader. 



The limestone is drawn through an underground 

 transfer system which consists of three glory holes, 

 each connected to main haulage ways by a transfer 

 raise, bulldozing chamber, and loading chutes. Sec- 

 ondary blasting is used to reduce oversize blocks in the 

 bulldozing chambers and "hang-ups" in the transfer 

 system. The extensive underground transfer system 

 has been changed little since its installation in 1924, 

 although fewer glory holes are now employed. The 

 system is described in detail by Young (1925, p. 249; 

 1929, p. 954) . Open rail cars are filled at loading chutes 

 in the haulage ways and transported by battery-pow- 

 ered locomotives to the mine opening. Electrically 

 driven locomotives complete the 3-mile haul to the 

 plant near Davenport. 



At the plant, the material is reduced in gyratory 

 crushers and stored by grade. Two grades of raw lime- 

 stone are produced, based on the amount of contained 

 alkalies and other impurities. Raw limestone from the 

 storage piles is further processed by crushing, grind- 

 ing, and blending u ith shale and roasted pyrite ("iron 

 cinder"). The raw mix is then made into cement by 

 the dry process, partly by the Lepol system and partly 

 by conventional rotary kilns. The Lepol system con- 

 sists of three kilns, each uith four parts: 1) a drum- 

 pelletizcr uhere '/,- to J/^-inch pellets are formed from 

 the dry mix and added water; 2) a 47-foot traveling 

 grate where the pellets are partially calcined; 3) a 

 rotary kiln in which calcining of the pellets is com- 

 pleted; and 4) a moving-grate cooler. In addition to the 

 Lepol system, some cement is produced from the dry 

 mix in six rotary kilns in uhich conventional clinker 

 is made.'A seventh kiln is used to calcine shale for the 

 production of high-silica cement. 



Much of the alumina and silica used for cement 

 manufacture is derived from "shale" or mudstone of 



• It is reported by the company (Herb Gasltin, IV71. personal communica- 

 tion) that the rotary kilns will be shut down by the end of I97I because 

 of strmgent air-pollutton control standards recently established by the 

 Stale. 'I"he Ixpol kilns currently (June 1971) produce a major portion of 

 the total cement produced at the plant. 



