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Santa Cruz County History - Making a Living
Mineral Survey of Santa Cruz County - Cement
by C. McK. Laizure
Prepared by C. McK. Laizure,
Mining Engineer of the California State Mining Bureau
Cement is the most important single structural material in the mineral output of California. As a cement producer, the state ranks third in the United States, being surpassed only by Pennsylvania and Indiana.
California now has ten operating portland cement mills, one partly constructed mill upon which work has temporarily ceased, and another plant which is nearing completion and which will probably start production during 1926.
Of these, the largest single cement mill is in Santa Cruz County.
Santa Cruz Portland Cement Company
Home office, Crocker Building, San Francisco; plant at Davenport, Santa Cruz County; officers, George J. Cameron, president; W. K. Berry, secretary; George R. Gay, manager; Fred Davis, plant superintendent.
This company's mill site is at Davenport near the northern terminus of the marine terrace which borders the ocean northwesterly from Santa Cruz for 15 miles. The plant is within sound of the surf about one-half mile north of San Vicente Creek canyon and 13 miles from Santa Cruz. A branch line of the Southern Pacific Railroad from Santa Cruz serves it. A good paved highway closely parallels the railroad.
The first shipment of cement was made on May 17, 1907, since which time the company has been in continuous production, although not always at full capacity. The mill at present has a capacity of 10,000 barrels per day, and 350 men are on the pay roll. Electric power furnished by the Pacific Gas and Electric Company is used throughout, the connected load being 12,000 horsepower.
Limestone and a considerable portion of the clay used is obtained from the company quarry three miles up San Vicente Canyon. Additional clay is mined near Glendale and shipped to storage at the plant (see under Clay). The gypsum used comes from Nevada.
Additions to and changes in equipment and methods of operation, both at the mill and the quarry, have been adopted from time to time and some radical changes in the mill flow-sheet are now under way.
Additional equipment being installed will increase the mill capacity to 14,000 barrels per day. It will also permit an intimate and uniform mixture of the raw materials closely approaching or equalling that obtained in 'wet-process mills,' at the same time preserving the advantageous feature of the 'dry-process.' (U.S. Geological Survey Mineral Resources, 1905, p.1188)
The accompanying plan shows the general layout of the mill and equipment approximately as it will appear when alterations are completed, but it does not indicate the conveyor distributing system with its automatic weighing and mixture control arrangement and many other details. A low-pressure oil-burning system has replaced the high-pressure system formerly used. Hummer-screens, rolls and Hardinge mills have been added, in part replacing tube and ball mills.
The most important change at the quarry has been the abandonment of the original open quarry, worked by a single bench with steam-shovel loading, and the substitution of a new method of quarry operation designed and put in operation by Mr. Robert A. Kinzie, Mining Engineer, San Francisco.
The quarry and new method of working have been recently described in great detail in an illustrated article by George J. Young, (Young, George J., Mining Limestone by Glory Holes In California, Engineering and Mining Journal-Press, Vol. 120, No. 7, August 15, 1925) of which the following is a brief resume.
The plan of working is a combination of glory holes, transfer raises, bulldozing chambers, chute loading and adit transportation. Since it was put into operation, over 500,000 tons of limestone have been delivered to the mill at a greatly reduced cost.
Operations are divided into stripping and quarrying. Stripping is done by steam shovel mounted on caterpillar tractors. The overburden is loaded into dump cars which are hauled in trains by a 20-ton steam locomotive to the dump. Three trains are in operation. Stripping is carried on sufficiently in advance to provide four years' supply of limestone. About thirty men are employed on the stripping crew.
On the quarry loading-out level two haulage drifts 9 by 12 feet on 60-foot centers extend along the principal axis of the deposit. Between these drifts at an elevation of 30 feet above the haulage level are a series of bulldozing chambers. Each chamber is 80 feet in length, and 50 feet in width. Their bottom is hoppered out and connected to six chute raises, three on each side. The chute raises, 6 by 8 feet in section, are driven at an angle of 50 degrees with the bottom angle reduced to 37 degrees and are fitted with underswung arc-gates. Thirty-three chutes are now available for loading. The haulage cars have steel bodies of 253-cubic feet capacity and are loaded to 12 tons. Three storage battery locomotives are used for handling the cars in the drifts. They are handled in 8 to 10-car trains, both locomotives and cars being equipped with air brakes. The cars are made up in 200-ton trains in the yard at the quarry and ten trains per day are dispatched to the mill. Two 18-ton trolley-type electric locomotives are used for this work. Cars are dumped at the plant by a revolving tipple operated by compressed air.
From the top of each bulldozing chamber, referred to previously, a raise 10 by 11 feet square extends to the floor of the quarry. These raises establish the position of the surface glory holes, They are spaced 120 feet apart. Six raises have so far been extended to the quarry level. A glory hole is started by coning out the top of the raise to an angle of approximately 60 degrees. During the coning out the broken rock in the raises is drawn down to expose the benches that are cut. Bulldozing is done with 40% powder in the bulldozing chamber whenever necessary through man-way raises, intermediate and sub-drifts. The cones, transfer raises, bulldozing chambers and chute raises are kept full of rock, the subsidence being gradual as the chutes are drawn. The capacity of a bulldozing chamber, raise and cone is about 5000 tons of broken rock, so there is considerable storage in addition to the broken rock in the pit. No serious hang-ups in the system have occurred even though one raise is drawing from a portion of the quarry that contains a good deal of clay mixed with the limestone.
A total of 75 men are employed at the quarry, including 30 in the stripping crew, for the present output of 2000 tons per day, which is equivalent to 27 tons output per man-shift.
The deposit extends over a width of 1200 feet for approximately three-quarters of a mile. It is an homogeneous close-grained light gray to white limestone free from magnesium carbonate. The area was diamond-drilled prior to the adoption of the glory hole method and its extent found to be greater than anticipated, the tonnage being sufficient for a long period of operation.
|Bituminous Rock||Gold||Mineral Water|
|Black Sand||Granite||Moulding Sand & Peat|
|Cement||Iron||Petroleum & Potash|
The Mineral Survey of Santa Cruz County was printed in the Santa Cruz Chamber of Commerce Annual Report, 1926. Reproduced by permission of the Santa Cruz Area Chamber of Commerce.
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