INTRODUCTION 



many of the workings. Bradley (1918, p. 154-168) 

 likewise was unable to get into many of the mine 

 workings in 1918, and as a result relied largely on 

 previous publications for descriptions of the local 

 geology. In 1929 C. N. Schuette (1931, p. 411-417), 

 on the basis of his familiarity with the parts of the 

 New Almaden mine accessible since 1916 and his study 

 of available company maps and records, included a 

 discussion of its geology and ores in a summary of 

 the salient features of quicksilver mines of the world. 

 More recently, Ransome and Kellogg (1939, p. 450- 

 457) briefly described the geology and ores of the 

 district in a summary account of the quicksilver mines 

 of California, but again because of the inaccessibility 

 of the mines, their principal contribution to geologic- 

 knowledge of the area consisted of the inclusion of a 

 reconnaissance geologic map of the district made by 

 John V. S. Tolman. 



In addition to these published articles we have had 

 the benefit of private reports to the mine owners pre- 

 pared by Luther Wagoner, 1 Samuel B. Christy (1889), 

 John A. Church (1892), Charles C. Derby (1908), 

 J. H. Farrell, 2 H. W. Gould, 8 and C. N. Schuette 

 (1935). The second of these, based on Dr. Christy's 

 16 years of intermittent study in the New Almaden 

 mine, was of particular value because it contained 

 some geologic maps of workings that have been in- 

 accessible for nearly half a century. 



PRESENT INVESTIGATION 



The U.S. Geological Survey investigation leading 

 to this report extended over a period of 6i/ 2 years 

 (1941-47), and many geologists contributed to the 

 resultant product. The authors, however, assume full 

 responsibility for the final maps and text. In 1939, 

 as a result of the urgent need to develop quicksilver 

 resources for wartime uses, the Survey began a co- 

 ordinated investigation of quicksilver districts in the 

 United States under the direction of Edwin B. Eckel. 

 Because of the shortage of geologists and the more 

 urgent requirements elsewhere, no specific study of the 

 New Almaden district was then made, but half a 

 dozen of the Survey geologists then studying other 

 quicksilver deposits began reconnaissance mapping of 

 the district during times when they could be spared 

 from other assignments. This preliminary mapping 

 served to delimit the potentially mineralized area, and 

 it also indicated that an exceptional amount of de- 

 tailed study would be required before the complex 



1 Wagoner, Luther, 1881, Unpublished report on the Gundnlupe mine. 



3 Farrell, J. H., 1923, Unpublished private report on the Senator 

 mine, October. 



3 Gould, H. W., 1925, Unpublished private report on the Guadalupe 

 mine, November. 



geologic features could be adequately understood. In 

 mid-1941 Lowell S. Hilpert and Paul Averitt were 

 assigned to study the district, and they were joined in 

 June 1942, by G. Donald Eberlein. Their work, be- 

 cause of its urgency and time limitations, was devoted 

 to deciphering the important structural control for the 

 ore deposits by rapid, but locally detailed, surface and 

 underground mapping. 



In September 1942, at the request of the U.S. Bu- 

 reau of Mines, a drilling and sampling project was 

 conducted jointly by the Bureau and the Survey at 

 the Guadalupe mine, and this was followed, late in 

 1943 and during the first half of 1944, by diamond 

 drilling at the New Almaden mine. The geologists 

 assigned to the project were kept so occupied by the 

 work it involved that they could make little headway 

 toward mapping either the district or the New Al- 

 maden mine. In the spring of 1944 nine Survey geolo- 

 gists, including the writers of this report, were as- 

 signed to prepare, under the direction of Aaron C. 

 Waters, detailed geologic maps of the extensive ac- 

 cessible workings of the New Almaden mine and to 

 complete a detailed map of the surface above the 

 mine workings. Shortly after the reassignment of 

 Waters to other work late in 1944, the project was 

 suspended for 3 months. Early in 1945 the writers 

 returned to the district to complete the underground 

 mapping, to prepare detailed maps of the areas over- 

 lying the New Almaden mine and the Guadalupe- 

 Senator mines, to make a geologic map of the district, 

 and to prepare this report. They carried on fieldwork 

 and the necessary office work continuously until Octo- 

 ber 1947, except that Everhart was assigned for 1 year 

 to another job; throughout the last year they were 

 very capably assisted in the geologic mapping by 

 Donald H. Kupfer. 



Many Survey geologists have thus contributed to 

 the final product. Where particular credit or respon- 

 sibility for a geologic idea, part of a map, or a carto- 

 graphic technique is due, their contributions are ac- 

 knowledged; but as so many ideas "just grow" from 

 informal discussions, the writers no doubt have failed 

 in some cases to give due credit. They are grateful, 

 however, to all their colleagues for their individual 

 and collective contributions. Preliminary mapping of 

 the district was done by Paul Averitt, Arthur E. 

 Bradbury, James B. Cathcart, Robert R. Compton, 

 G. Donald Eberlein, and W. Bradley Myers; aid in 

 the detailed mapping of the accessible underground 

 workings of the New Almaden mine was given by 

 Randall E. Brown, Juanita Crawford, G. Donald 

 Eberlein, Lowell S. Hilpert, David A. Phoenix, George 

 W. Walker, Aaron C. Waters, and Robert G. Yates. 



