66 



California Division of Mines and Geology 



Bull. 197 



October 1962, and the limestone probably is only of 

 local interest. 



Other references: Wilson, 1943, p. 193, plote 3; Bowen and Gray, 1959, 

 p. 39. 



Middle Dam deposit. Location: N'/ sec. 29 

 (proj.),T. 13 S., R. 5 E., M. D., 5 to 5/2 miles southwest 

 of Hollister; Hollister 15-minute quadrangle. Owner- 

 ship: Howard Harris, 7800 Cienega Road, Hollister 

 (1964). 



This deposit consists of mixed carbonate rock ex- 

 posed discontinuously for about a mile along the 

 north wall of North Canyon. Much of the rock is 

 white, very coarse-crystalline limestone and dolomitic 

 limestone. It occurs as thin, steeply dipping, discon- 

 tinuous lenses interbedded with schist and commonly 

 cut by granitic dikes. One of the largest lenses, at the 

 east end of the deposit, is reported to be an average of 

 30 feet thick by 300 feet long (Oliver E. Bowen, 1964, 

 personal communication). Analyses of three samples 

 collected by Bowen and Harris are given below. The 

 first one (GP-24) was analyzed by Abbot A. Hanks, 

 Incorporated, in 1954 (Bowen and Gray, 1959, p. 32). 

 The others were analyzed by the Division of Mines 

 and Geology laboratory in 1964. 



Ign. 

 Sample SiO, Fe,0, AW, CM MgO P,0, K.O loss 



GP-24.... 0.52% 0.08?i 



MD-1 1.60 0.06 



MD-2 5.40 0.58 



0.16% 43.17% 10.J2% tr n.d, n.d. 

 0.00 54.00 0.61 0.04% 0.00% 42.6% 

 0.90 42.80 11.10 1.00 0.10 36.8 



Carbonate rocks of the Middle Dam deposit appear 

 to be of mixed chemistry and limited reserves. Howev- 

 er, some of the material may be of economic interest 

 because of its whiteness and proximity to market. 



Other reference: Taliaferro, 1948, mop. 



Mount Harlan deposit. Location: Sec. 22, T. 14 S., 

 R. 5 E., M.D., 11 miles south of Hollister; Gonzales 

 15-minute quadrangle. Ownership: Not determined. 

 This deposit is referred to as the Hamilton deposit by 

 Bowen and Gray (1959, p. 38), apparently based on 

 interpretable data presented by Logan (1947, p. 275). 

 However, the location of the Hamilton deposit is 

 shown by Averill (1947, p. 51-52) to be near the lime 

 kiln in sec. 23 and is described that way herein. 



Data from U.S. Steel Corporation (in Jennings and 

 Strand, 1958) indicates that a northwest-trending, len- 

 ticular mass of crystalline limestone caps the 3,262- 

 foot-high Mount Harlan. The mass is shown to be 

 4,000 by 1,200 feet in maximum dimensions and is 

 bordered by granitic rocks. An average of 33 analyses 

 of samples collected by U.S. Steel at 5-foot intervals 

 across the strike of the main part of the mass is report- 

 ed to be 52.22% CaO, 2.60% MgO, 0.75% SiO^, and 

 0.64% AljO, and Fe^O, (Bowen and Gray, 1959, p. 

 38). The indicated size and quality of the deposit 

 would seem to warrant further examination. Howev- 



er, no limestone was observed during aerial reconnais- 

 sance of the Mount Harlan area (Oliver E. Bowen, 

 1967, oral communication). The mountain is accessi- 

 ble from the south via an unimproved dirt road and 

 trail from Thompson Valley. 



Natividad (Kaiser) deposit. Location: NW% sec. 

 1 and NE'X sec. 2, T. 14 S., and SE'X sec. 35 and SW'/, 

 sec. 36, T. 13 S., R. 3 E., M.D. (proj.), 6 miles northeast 

 of Salinas and 1 mile north of Natividad; Salinas and 

 San Juan Bautista 1 5-minute quadrangles. Ownership: 

 Kaiser Aluminum and Chemical Corporation, 300 

 Lakeside Drive, Oakland (1963). 



Early development of the Natividad deposit is not 

 clearly recorded in the literature, but it is probable 

 that some of the small dolomite producers listed by 

 Laizure (1925, p. 36) obtained dolomite here intermit- 

 tently from 1900 to 1925. By 1926, Pacific Coast Steel 

 Company (succeeded by Bethlehem Steel Company 

 m 1937) began quarrying dolomite for use as a refrac- 

 tory near the north end of the Natividad pendant, 

 near SE cor. sec. 35. The operation was more or less 

 continuous until 1944, when the company ceased pro- 

 duction. In 1942, Kaiser Aluminum and Chemical 

 Corporation (then known as Permanente Metals Cor- 

 poration) opened a dolomite quarry and processing 

 plant half a mile to the south in the same deposit. This 

 plant supplied calcined dolomite which was reacted 

 with seawater at Moss Landing in order to produce 

 magnesia. Magnesia was used for making magnesium 

 metal at their Permanente plant in Santa Clara 

 County until 1945. Calcined dolomite also was 

 shipped directly to a company plant in Manteca, San 

 Joaquin County, for the manufacture of magnesium 

 metal between 1942 and 1944. 



The demand for metallic magnesium was greatly 

 reduced by 1945, thereby critically decreasing the 

 need for Natividad dolomite. To offset the decrease, a 

 refractory brick plant was constructed next to the 

 Moss Landing seawater magnesia facility. This per- 

 mitted the company to utilize large amounts of mag- 

 nesia (and dolomite) and at the same time to provide 

 industry with a wide variety of refractory products. 

 Another operational change was made at the Nativi- 

 dad plant in 1952 when a heavy-media separation unit 

 was installed to beneficiate the dolomite. In addition, 

 the Moss Landing facilities have been expanded sev- 

 eral times. 



The Natividad deposit is a large irregular pendant 

 of crystalline dolomite within the Santa Lucia Gran- 

 ite. The pendant is exposed over nearly three-quarters 

 of a square mile of area (plate 2) and about 700 feet of 

 relief (Allen, 1946, plate 1). The internal geology of 

 the mass is complex, the dolomite body having been 

 penetrated by numerous irregular dikes and sills of 

 granitic rock that is now largely decomposed. Addi- 

 tional fracturing and shearing has made it virtually 

 impossible to selectively quarry high-grade dolomite 

 on a large scale. The composition of the dolomite is 



