54 



GEOLOGY AND QUICKSILVER DEPOSITS, NEW ALMADEN DISTRICT, CALIFORNIA 



Chemical composition 



Chemical analyses of 3 serpentine rocks of the New 

 Almaden district are shown in table 9, along with 3 

 other analyses of serpentine rocks from elsewhere in 

 the Coast Ranges and a composite of 24 serpentines 

 from other regions for comparison. The 3 analyzed 

 rocks from the district are from the underground 

 workings of the New Almaden mine and are unweath- 

 ered. Two of them are from the central parts of large 

 massive blocks and contain no megascopic veinlets of 

 chrysotile; the third, which also contains no veinlets, 

 is a minutely sheared variety of serpentine from the 

 border of a large sill. The analyses show no signifi- 

 cant difference between the blocks and the sheared 

 matrix material, and thus confirm our belief that the 

 matrix is merely a sheared part of the rock rather 

 than a foreign material that has engulfed the blocks. 

 Also worthy of note is the high water content, which 

 indicates, as do also the thin sections, how complete 

 has been the serpentinization of the original rock. 

 Comparison of all the analyses suggests that the ser- 

 pentines of the New Almaden district are representa- 

 tive of those in the California Coast Ranges, and that 

 they are closely similar to the average of serpentines 

 from other parts of the world represented in column 7. 



Some partial chemical analyses of other serpentine 

 rocks from the New Almaden district and nearby 

 areas are shown in table 10. These would seem to 

 indicate that the fresh serpentine from the mine con- 

 tains a slightly greater amount of magnesium and less 

 silica than the other apparently fresh samples of ser- 

 pentine taken from the surface and shallow cuts. 



Origin 



The problem of the origin of such an unusually 

 hydrous rock as serpentine has been one of the more 



TABLE 9. Analyses of serpentine rocks from the New Almaden 

 district and from elsewhere in the California Coast Ranges, 

 together with a composite of H serpentines from other regions 

 for comparison 



Determinations made by J. J. Fahey, U.S. Geological Survey. 

 tDetermined spectroscopically by K. J. Murata, U.S. Geological Survey. 



NOTE. Description of sample and locality as follows: 



1. Unsheared fresh serpentine from the New Almaden mine, Santa Clara County. 



Calif. (Coordinates 1535 N .-5130 W., alt 1,183ft). F. A. Oonyer, analyst. 



2. Unsheared fresh serpentine from the New Almaden mine, Santa Clara County, 



Calif. (Coordinates 2427 N.-4703 W., alt 974 ft). F. A. Oonyer. analyst. 



3. Sheared but not veined fresh serpentine from the New Almaden mine, Santa Clara 



County, Calif. (Coordinates 1610 N.-5100 W., alt 1,183 ft). F. A. Gonyer, 

 analyst. 



4. Serpentine from the Mayacmas Ranee, near Missouri mine, Sonoma County, 



Calif. H. E. Kramm, analyst. From Kramm, 1910, p. 329. 



5. Serpentine described as "hastite with fine seamsof chrysotile" from Mount Diablo, 



Calif. \V II. Melville, analyst. From Turner, H. W.. 1891, p. 406. 

 6 Serpentine from Mount Diablo, Calif. \V. 11 Melville, analyst. From Turner, 



1891, p. 406. 

 7. Average of 24 serpentines of the "magma type." Average given is average of 



other average analyses from Massachusetts, Finland, Newfoundland, Southern 



Rhodesia, and Cuba, given by Hess, 1938, p. 330. 



elusive problems of igneous and metamorphic geology 

 for many years, and its solution is, of course, beyond 

 the scope of this report (see Benson, 1918; Hess. H. H., 

 1933). Some suggestions as to what seems to be the 

 most probable origin of the serpentine bodies in the 

 district, however, are justified, even if they serve only 

 to indicate that many features of these bodies as ex- 

 posed in the California Coast K:in<rcs are not yet en- 



TABLE 10. Partial analyses of serpentine rocks from the New Almaden district and adjacent area 

 [All analyses by Permanente Cement Co.; provided through courtesy of Messrs. E. A. Hassan, Jr., and W. R. Woodman. Analysts unknown) 



Total Fe reported as FeiOi, which results In totals being too high, 

 t Reported as "rest." 



N DTK. Description of sample and locality as follows: 



1. Fresh massive serpentine from large mass at mouth of Almaden Canyon. Con- 



tains some unaltered enstatlte. auglte, olivlne. and plcotlte. 



2. Highly sheared hut fresh-appearing serpentine from railroad cut on north side of 



Tulare Hill, In northeast corner of the New Almaden district. 



3. Sheared serpentine from 1 mile northwest of Coyote Peak, New Almaden 



district. 



4. Fresh massive bastltlc serpentine block embedded In sheared matrix: from hill 



north of Kdendale, 2 miles north of central part of New Almaden district. 



J, . Serpentine from Hlllsdale area, north of the New Almaden district. 



7 Highly sheared serpentine from margin of mass at mouth of Almaden Canyon 



8. Massive bastltlc block and sheared serpentine matrix from lllllsdale area, north 



of the New Almaden district. 

 . Sheared serpentine from one-half mile east of fluadalupe mine. 



10. Bulk analysis of serpentine quarried from north side of large Intrusive body at 



mouth of Almaden Canyon. 



11. Average of 1-10: HtO- omitted. 



