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This CD contains the page images and searchable text from a 1940 United States Geological Survey report on the gold-bearing formations of the Grass Valley district, in western Nevada County, California. Between the 1850s and 1940, quartz mines of the district yielded over $150 million, with the Empire and North Star Mines producing $30 million each.
USGS Professional Paper 194 expanded upon two 1896 works by Waldemar Lindgren: Geologic Atlas of the United States, Folio #29 - Nevada City Special Folio (which is included on this CD), and an extract from the Seventeenth Annual Report of the U.S. Geological Survey, The Gold Quartz Veins of Nevada City and Grass Valley Districts, California.
Johnson's report describes the unusually favorable conditions facing miners: dry settings in moderate temperatures, with little timbering required, and little problem with rock bursts. Johnson also updates descriptions by Waldemar Lindgren of the two groups of quartz veins: those of the granodiorite area, with gentle dips averaging 35 degrees, and those of the serpentine area, which are much steeper. Since 1896, the principal mines had been deepened, many miles of underground workings had been opened, and new veins had been found.
The general discussion of area geology notes the important local group of quartz-free fractures ("crossings") perpendicular to the quartz veins, and differentiates the mineralogy of the two systems. The final thirty-five pages is a mine-by-mine assessment of vein yields and prospects. The 39 appended plates and 69 in-text figures include photographs of quartz and mineral samples, isometric block diagrams (in color) of the workings of the largest mines, and flat maps (in black and white) of the lesser mine workings.
Contents:
Abstract
Introduction
Location
Previous work
Present investigation
Acknowledgments
Topography
Climate and vegetation
Summary of the geologic history of the northern Sierra Nevada
Rock formations
Calaveras formation
Mariposa formation
Pre-Tertiary greenstones
Serpentine, gabbro, and diorite
Granodiorite
Dark-gray dikes intruding the granodiorite
Quartz-rich dike rocks
Tertiary rocks
Ore deposits
History and production
Mining conditions at depth
Mine waters
Magnetite-pyrrhotite vein
Gold quartz veins
Mineralogy
Paragenesis of the vein-forming minerals
Ore shoots
Hydrothermal alteration of the wall rocks
Origin of the deposits
Method of vein formation
Source of vein materials
Mines
Plan of treatment
Veins on the west side of the granodiorite area
Gold Hill, Massachusetts Hill, and neighboring veins
Gold Hill mine
Massachusetts Hill mine
Cincinnati Hill mine
Other eastward-dipping veins
Boundary mine
Peabody mine
Other westward-dipping veins
Golden Center mine
North Star mine
Mines on the Omaha vein system
Omaha, Lone Jack, and Homeward Bound mines
Hartery mine
Wisconsin mine
Allison Ranch mine
Phoenix mine
Veins on the east side of the granodiorite area
Pennsylvania mine
W. Y. O. D. mine
Kate Hayes vein
Parr, Cassidy, and Linden veins
Empire mine
Rich Hill mine
Mines south of Rich Hill
Daisy Hill mine
Orleans mine
Houston Hill mine
Prescott Hill and Betsy mines
Sebastopol mine
Sultana (Electric) mine
Osborne Hill mine
Centennial mine
Conlin mine
Ben Franklin Eureka mine
Diamond-Bullion-Alaska vein
St. John mine
Coe mine
Crown Point mine
Spring Hill mine
Eureka-Idaho-Maryland mine
Brunswick mine
Union Hill mine
Illustrations:
Plates
1. Geologic map of the Grass Valley quadrangle
2. Structure sections of the Grass Valley quadrangle
3. Photomicrographs of the Calaveras formation
4. Photomicrographs of diabase and porphyrite
5. Photomicrographs of granodiorite
6. Photomicrographs of postgranodiorite dike rocks of intermediate to basic composition
7. Vein walls and sheared quartz
8. Underground photographs of quartz veins
9. Underground photographs of quartz veins
10. Underground photographs of sheeted veins
11. Photographs of ore
12. Mineralogy of the veins
13. Mineralogy of the veins
14. Photomicrographs of polished ore
15. Vugs and comb quartz
16. Details of vug lining
17. Comb and sheared quartz
18. Comb quartz and carbonates
19. Photomicrographs of sheared quartz
20. Photomicrographs of brecciated quartz
21. Photomicrographs showing zoned enclosures and vacuoles
22. Vacuoles and phantom veinlets
23. Feather quartz
24. Underground photograph of the intersection of basic and aplite dikes that have been faulted by vein fracture
25. Development map of the Golden Center Mine, July 1934
26. Map showing workings on the North Star vein of the North Star mine in 1931
27. Isometric block diagram of the North Star vein of the North Star
28. Section through central North Star shaft and No. 1 winze
29. Map showing workings on the A vein, North Star mine
30. Map showing workings on the New York Hill vein of the North Star mine
31. Map showing workings on the X vein of the North Star, Empire, and Pennsylvania mines and the No. 3, Connecting, and No. 2 veins of the North Star mine in 1931
32. Isometric block diagram of the Pennsylvania, W. Y. O. D., and X veins and the No. 2 and No. 3 veins of the North Star mine
33. Isometric block diagram of the No. 2 vein of the North Star mine, showing detailed structural features
34. Section through No. 2 winze, North Star mine
35. Isometric block diagram of the Empire mine and part of the Empire-Osborne Hill vein system
36. Map showing workings in the Empire mine north of the Empire shaft
37. East-west section through the Empire shaft
38. Map showing workings in the Daisy Hill, Orleans, Houston Hill, Prescott Hill, Betsy, Sultana, Osborne Hill, Centennial, and Conlin mines
39. Map showing workings in the Brunswick mine, 1924
Figures
1. Map showing location of the Grass Valley quadrangle, Calif
2. Distribution of inclusions in the granodiorite, showing characteristic lack of orientation
3. Details of the contact between granodiorite and diabase, showing apophy8es of granodiorite in diabase
4. Horizontal projection of basic dike exposed in the roof of the 8,600-foot station of the No. 2 winze, North Star mine
5. Epidote segregation in small aplite dike, Chevanne shaft
6. Pregranodiorite aplite, 600-foot level, North Star mine
7. Gold production of Nevada County, Calif., 1880—1932, and of the principal Grass Valley mines
8. Depth-temperature curve of the Empire-Star mine, Grass Valley, Calif
9. Graph showing pumpage rate at various levels in the Empire and Pennsylvania mines
10. Graphic representation of analyses of mine
11. Outline map of the Grass Valley quadrangle showing vein outcrops and the strike of the crossings
12. Diagram illustrating Janin’s “rhombohedral theory”
13. Diagram illustrating Duggleby’s “rhombohedral
14. Geologic map of a part of the No. 2 vein, North Star mine, showing quartz vein confined between strong walls
15. Geologic map of a part of the 6,900-foot level, No. 2 vein, North Star
16. Diagrammatic plan illustrating the manner in which one vein weakens as a parallel vein strengthens
17. Sketch of small vug on the 6,300-foot level, No. 2 vein, North Star
18. Sketch of No. 1 vein, 6,600-foot level, North Star
19. Sketch of No. 1 vein, 7,200-foot level, North Star
20. Grade of ore mined in the Empire-Star mines between 1928 and 1934
21. Strike of crossings
22. Intersection of vein and crossing without displacement on either
23. Crossing offset by a vein
24. Vein offset by a crossing
25. Diagram illustrating how crossings permit vein segments to open or close independently of the neighboring segments
26. Diagram illustrating the steplike character of the Dromedary vein due to quartz following crossing fractures between vein segments
27. Sketch of part of the Dromedary vein showing chalcedony in
28. Drawing of pollshed sections of vein material showing euhedral quartz crystals occupying fractures in pyrite that were later filled with gold
29. Sketch of vein showing late pyrite and chlorite occupying seams in quartz
30. Distribution of gold in the south end of the No. 2 vein, 6,600- and 6,900-foot levels, North Star mine
31. Thickness and assay value of a part of the Phoenix vein on the 200-foot level north of the
32. Thickness and assay value of a part of the 500-foot level of the Church Hill vein, Golden Center mine
33. Distribution of gold, as determined by car samples, in some stopes in the North Star mine
34. Form of ore shoots
35. Diagram illustrating the fortuitous discovery of ore shoots 36. Sketch of drift face on 9,000-foot level of No. 3 vein, North Star mine
37. Diagram illustrating gains and losses of each chemical constituent in terms of percentage of mass of the fresh granodiorite
38. Isometric projection of the Grass Valley quadrangle cut parallel to the shaft of the Empire mine
39. Sketch of vein footwall on 7,200-foot level, North Star mine
40. Sketch of drift wall on 4,600-foot level, Empire mine
41. Sketch of drift wall on 5,600-foot level, North Star mine, showing crossing offset on vein fracture
42. Sketch of drift wall on 5,600-foot level, North Star mine, showing movement on the vein without offset of the crossing
43. Diagram to illustrate the building up of a thick quartz vein by successive reopening and filling
44. Development map of the Massachusetts Hill and Granite Hill mines
45. Development map of the Cincinnati Hill mine
46. Development map of the Boundary mine
47. Vertical section striking N. 40 W. through the 500-foot level crosscut of the Golden Center mine
48. Diagrammatic section through the North Star shaft with projection of principal raises and shafts on other veins.
49. Section parallel to No. 1 shaft, 230 feet southeast of collar of North Star inclined shaft
50. Section through the main A vein raise, North Star mine
51. Map showing workings on the Y and Z veins, North Star mine
52. Generalized section through the 600-foot station, central shaft, and the New York Hill raise of the North Star mine, with projections of the New York Hill and Chevanne shafts
53. Map showing workings on the New Rocky Bar and Chevanne-New York Hill veins
54. Sections through the New Rocky Bar and Chevanne veins
55. East-west section 240 feet north of the central shaft, North Star mine
56. Development map of the Omaha, Lone Jack, and Homeward Bound mines
57. Development map of the Wisconsin (Menlo) mine showing connecting workings
58. Development map of the Allison Ranch mine
59. Development map of the Phoenix mine, November 1934
60. Map showing workings on the Pennsylvania and W. Y. O. D. veins and the upper part of the X vein
61. Isometric block diagram showing the junction of the Pennsylvania and X veins between the 900- and 2,100-foot levels of the Pennsylvania mine
62. Section through the 3,400-foot crosscut, Pennsylvania mine
63. Development map of the Rich Hill mine, showing workings connecting with the Empire mine
64. Approximate outline of the Eureka-Idaho ore shoot
65. Section through the Maryland shaft, 1894
66. Generalized section through the inclined shaft of the Brunswick mine
67. Sketch section of the Brunswick vein on the 700-foot level 68. Map showing workings in the Union Hill mine, 1919
69. Generalized section through the Union Hill shaft
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